Symposium Organizers
John Harding University of Sheffield
John Evans New York University
James Elliott University of Cambridge
Robert Latour Clemson University
UU1: Biomimetic Materials Design
Session Chairs
James Elliott
John Harding
Tuesday PM, December 01, 2009
Room 205 (Hynes)
9:30 AM - **UU1.1
Crystallization of Bifunctional Organic Molecules on Self-Assembled Monolayers.
Boaz Pokroy 1 , Victoria Chernow 1 , Joanna Aizenberg 1
1 , Harvard University, Cambridge, Massachusetts, United States
Show AbstractThe formation of a variety of crystalline materials in organisms is templated by bioorganic substrates that exert very high control over crystal nucleation and growth. In the materials community, there is a growing appreciation of the potential of the biomimetic approach to crystallization, when organic surfaces are used to template the formation of both organic and inorganic materials. We have previously proposed that the orientation of growing crystals in these systems is not governed by the epitaxial match between the lattices of the SAM and the crystal nucleation plane, as observed in the traditional inorganic substrates, but rather by their stereochemical registry – a spatial match between the orientation of the SAM’s functional groups and that of the certain moiety or ion in the nucleated crystal. Here we demonstrate the generality of the proposed mechanism of oriented nucleation at organic surfaces, by presenting a more complex case of crystallization of bifunctional organic molecules. The knowledge of the mechanisms of oriented crystallization and polymorph selectivity in such systems has essential implications for pharmaceutical industry, where controlled crystallization of complex, multifunctional organic molecules often presents a critical difficulty.
10:00 AM - UU1.2
Molecular Biomimetics: Genetically-Controlled Synthesis, Assembly and Formation of Functional Materials Using Solid Binding Peptides.
Candan Tamerler 1 2 3 , Mehmet Sarikaya 1 2
1 Genetically Engineered Materials Science and Engineering Center, University of Washington, Seattle, Washington, United States, 2 Materials Science and Engineering Department, University of Washington, Seattle, Washington, United States, 3 Molecular Biology-Biotechnology and Genetics Research Center, Istanbul Technical University, Istanbul Turkey
Show AbstractWith the recent developments of nanoscale engineering in physical and chemical sciences and the advances in molecular biology, molecular biomimetics is combining genetic tools and evolutionary approaches with synthetic nanoscale constructs to create a new hybrid methodology, genetically designed peptide-based molecular materials. Following the fundamental principles of genome-based design, molecular recognition, and self-assembly in nature, we can now use recombinant DNA technologies to design single or multifunctional peptides and peptide-based molecular constructs that can interact with solids and synthetic systems. These GEPIs, genetically engineered peptides for inorganics, have been making significant impact as inorganic material synthesizers, nano-particle linkers, and molecular assemblers, simply as molecular building blocks, in a wide range of fields from chemistry to materials science to medicine. As part of our broad-based collaborative polydisciplinary approach, for the last decade, we have been biocombinatorially selecting and bioinformatically tailoring solid binding peptides, developing the protocols to investigate quantitative molecular binding, kinetics and recognition, and using these peptides in practical nanotechnology and regenerative medicine, from hard tissue engineering to biosensing and cancer probing. This review presents a synopsis of the developments, current challenges, and future prospects. The research supported by NSF-MRSEC, -BioMat, and -IRES and TUBITAK-NSF programs. 1. M. Sarikaya, C. Tamerler et al., Molecular Biomimetics – Nanotechnology through Biology, Nature Materials, 2(9), 577-585 (2003). 2. C. Tamerler and M. Sarikaya, MRS Bulletin Guest Editors on “Molecular Biomimetics”, May Issue (2008).
10:15 AM - UU1.3
Constrained Synthesis and Organization of Catalytically-Active Metal Nanoparticles by Using a Highly Stable Protein as Template.
Silke Behrens 1 , Arnon Heyman 4 , Wolfgang Wenzel 2 , Jochen Buerck 3 , Oded Shoseyov 4
1 Institute of Technical Chemistry, Research Center Karlsrue, Karlsruhe Germany, 4 The Robert H. Smith Institute of Plant Science and Genetics, The Hebrew University, Rehovot Israel, 2 Institute of Nanotechnology, Research Center Karlsruhe, Karlsruhe Germany, 3 Institute for Biological Interface, Research Center Karlsruhe, Karlsruhe Germany
Show AbstractWe report the size-constrained synthesis and organization of highly monodisperse metal nanoparticles using a genetically modified stable protein (SP1) expressed during stress in aspen plants. The protein is a ring-shaped homododecamer with a central, 2 – 3 nm inner-pore and has an extremely high thermal and chemical stability (e.g., resistance to boiling, proteases and detergents). For material synthesis we have genetically fused histidine tags to the N-termini of SP1 (6hisSP1) thus obtaining a mutant with 72 additional His residues facing the inner-pore of the ring structure. We then grow monodisperse Pd nanoparticles by in situ reduction of metal salts inside the inner pore of the mutant. Our studies demonstrate that the 6hisSP1 mutant not only initiates material nucleation at the histidine sites but also restricts particle growth. The formed nanoparticle – protein hybrids further self-assemble spontaneously in solution, thus forming well-defined, chain-like particle – protein structures. As shown by CD spectroscopy the protein structure remains intact after the metallization procedure and particle binding. To elucidate the experimental results, we employed a recently developed atomistic protocol for theoretically simulating nanoscale structure formation in this system. The nanoparticles is initially “grown” in molecular-mechanics simulations and then the generated nanoparticle/protein complex is used to analyze the fluctuations of the protein with and without nanoparticle in molecular dynamics simulations. We further investigated the catalytic properties of the Pd–6hisSP1 composites in a model reaction and show that the as-synthesized metal particle – protein hybrids represent active biofunctional nanocatalysts. After functionalization with affinity reagents by genetic engineering, such site-specific nanocatalysts would potentially allow to enhance sensitivity in diagnostic assays by catalytic signal amplification. Hybrid structures formed by coupling nanoparticles of various nature and proteins are promising for divers applications, e.g., in electronics, imaging, sensing, catalysis, and cell targeting.
10:30 AM - UU1.4
Three Dimensional Biomimetic Mineralization of Dense Hydrogel Templates.
Gao Liu 1 , Dacheng Zhao 1 , Antoni Tomsia 2 , Andrew Minor 2 3 4 , Eduardo Saiz 2
1 Environmental Energy Technologies Division, Lawrence Berkeley National Lab, Berkeley, California, United States, 2 Materials Sciences Division, Lawrence Berkeley National Lab, Berkeley, California, United States, 3 National Center for Electron Microscopy, Lawrence Berkeley National Lab, Berkeley, California, United States, 4 Department of Materials Science and Engineering, University of California Berkeley, Berkeley, California, United States
Show AbstractIn biological materials, form and function are intimately related. From nacre to bone, nature achieves unique structural and functional properties through the combination of organic and inorganic phases in complex hierarchical structures.These natural composites are often created through carefully orchestrated biomineralization processes that result in an extremely accurate control of the shape, size and distribution of the inorganic crystals. Recreating natural mineralization in the laboratory to build new bio-inspired composites is a very attractive prospect but has been extremely difficult. Promoting ion transport into the organic matrix is one of the key issues in the mineralization of dense polymer networks. In this work, we use a direct electric current-assisted diffusion approach to promote the transportation of essential ions into the hydrogel matrix to achieve three dimensional biomimetic mineralization of dense hydrogel templates. The mineralization technique and the chemistry of the organic matrix control the microstructure of the final material, whose organic and inorganic phases are integrated at the nanoscale while the mineral particles assemble into well-defined microscopic structures leading to high mineral concentrations.
11:30 AM - **UU1.6
From Biominerals to Biomaterials: the Role of Biomolecule-mineral Interactions.
Carole Perry 1 , Siddharth Patwardhan 1 , Mei-Keat Liang 1 , Olivier Deschaume 1
1 School of Science and Technology, Nottingham Trent University, Nottingham United Kingdom
Show AbstractInteractions between inorganic materials and biomolecules at the molecular level, although complex, are common occurrences. Examples include biominerals, implanted biomaterials and the processing and passage of food and drugs through an organism. The effectiveness of these functional materials is to a large extent dependent on the interfacial properties, i.e. the extent of molecular level ‘association’ with biomolecules. A wide range of experimental techniques (microscopic, spectroscopic, particle sizing, thermal methods and solution methods) are used by the research group to study interactions between (bio)molecules and molecular and colloidal species that are coupled with computational simulation studies to gain as much information as possible on the molecular-scale interactions. Examples that will be used to illustrate our current level of understanding include (i) peptide mediated crystal formation, (ii) peptide binding to amorphous particles and (iii) protein binding to surfaces with defined chemistry and topography. Our goal is to uncover the mechanisms underpinning any interactions and to identify ‘rules’ or ‘guiding principles’ that could be used to explain and hence predict behaviour for a wide range of (bio)molecule-mineral systems. An understanding of these interactions would be highly fruitful not only to understand biological mineralization processes per se but also to design novel materials and processing technologies for applications in fields as diverse as biological imaging and biosensors, implant integration, food and drug processing and delivery, and electronic materials.
12:00 PM - UU1.7
A Scaffold of Biological Molecules to Manufacture Glass Nanotubes.
Emilie Pouget 1 , Christophe Tarabout 1 , Celine Valery 1 , Maite Paternostre 3 , Erik Dujardin 2 , Franck Artzner 1
1 IPR, UMR 62 51, CNRS, Rennes France, 3 URA CNRS 2096, IBiTechS, CEA, Saclay France, 2 NanoSciences Group, CEMES UPR 8011, CEMES, Toulouse France
Show AbstractDiatoms, shells, bones and teeth are exquisite examples of well-defined structures, arranged from nanometre to macroscopic length scale, produced by natural biomineralization using organic templates to control the growth of the inorganic phase. Although strategies mimicking Nature have partially succeeded in synthesizing humandesigned bio-inorganic composite materials, our limited understanding of fundamental mechanisms has so far kept the level of hierarchical complexity found in biological organism out of the chemists’ reach.We used a therapeutic peptide [1], lanreotide that could serve as a scaffold for the spontaneous formation of silica nanotubes by simple mixing with a silica precursor in water. These hybrid tubes consist in a perfect assembly of molecules of the drug in a 24 nm diameter tube, the internal and external surfaces of which are covered with two thin and uniform layers of 2 nm silica. The tubes are several micrometers long and aligned in fibers of a few millimeters. Their organization is thus controlled hierarchically over more than 6 orders of magnitude [2].To achieve this detailed study, we developed a slow technique which enabled the coating with silica of nanotubes of biological molecules forming in water. We observed that the silica deposit favored the gradual lengthening of the organic nanotube, the new tip of which could then serve again as a scaffold for further silica deposits. This recurrent process ensured both control of the organization at a molecular scale and the growth of an organic scaffold as the mineral was deposited. This process is astonishingly similar to the construction of a sky-scraper, during which assembly of the metallic framework and the application of concrete are alternated with precision. This work opens two new perspectives. Firstly, based on a simplified system, it provides a clearer understanding of some of the astute, but still mysterious, mechanisms developed by nature to produce skeletons and spicules. Secondly, it opens the way to novel materials with nanometric dimensions, whose organization in space can be controlled up to macroscopic scales, thus endowing them with unique properties. REFERENCES : 1] Biomimetic organization : octapeptide self assembly into nanotubes of viral capsid like dimension, C. Valéry, M. Paternostre, B.Robert, T. Gulik-Krzywicki, T. Narayanan, J.-C. Dedieu, G. Keller, M.-L. Torres, R. Cherif-Cheikh, P. Calvo & F. Artzner, Proc. Natl. Acad. Sci. USA, 2003,100(18), 10258-10262. 2] Hierarchical architectures by synergy between dynamical template self-assembly and biomineralization, E. Pouget, E. Dujardin, A. Cavalier, A. Moreac, C. Valéry, V. Marchi-Artzner, T. Weiss, A. Renault, M. Paternostre, F. Artzner, Nature Materials, 2007, 6, 434-439.
12:15 PM - UU1.8
Biomimetic Growth of Non-biogenic Semiconductor Materials.
Mikala Shremshock 1 , R. Lloyd Carroll 1 , Rachel Wallner 2
1 Chemistry, West Virginia University, Morgantown, West Virginia, United States, 2 , New Jersey Institute of Technology, Newark, New Jersey, United States
Show AbstractSemiconductor nanomaterials are of great interest for a wide variety of applications. Nanorods and nanowires composed of semiconducting materials are particularly interesting because of their potential applications in communications, optical technologies, and integration with computational, sensing, and lab-on-a-chip devices. Existing synthetic strategies for semiconductor nanomaterials have required the use of potentially hazardous reactants, elevated temperatures, and complex synthetic schemes. These negative aspects have created significant challenges for further development and integration. New synthetic and assembly approaches are often necessary to facilitate novel materials and applications.We have demonstrated a novel synthesis for templated growth of nanomaterials at a liquid:solid interface under ambient conditions with low hazard reactants. We have successfully produced rods of various inorganic semiconductor materials (CdS, PbS, ZnS) in sizes ranging from nano- to microscale. The composition, crystalline structure, and spectroscopic properties of these materials have been extensively characterized. Of particular interest is the suitability of these rods for device applications such as biosensors and coherent light emitters. We present the characterization of the electronic properties of the semiconductor rods, as well as changes in apparent conductivity following surface binding events with small biological molecules. Our ongoing efforts to use microfluidic techniques to produce multifunctional nanorods composed of multiple serially grown semiconductor materials will be described. We will also show results from patterning, controlled assembly, and chemical modification of the semiconductor nanorods. Further testing of the electronic and optical capabilities of these materials is underway with a long-term goal of device development and other potential high-impact applications.
12:30 PM - UU1.9
Peptide-Nanowire Hybrid Materials for Selective Sensing of Small Molecules.
Michael McAlpine 1
1 Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey, United States
Show AbstractThe development of a miniaturized sensing platform for the selective detection of chemical odorants could stimulate exciting scientific and technological opportunities. Biomimicking smart materials which integrate chemical recognition moieties with sensitive transducers could provide a general system for highly specific smell sensors. Oligopeptides are robust substrates for the selective recognition of a variety of chemical and biological species. Likewise, semiconducting nanowires are extremely sensitive gas sensors. Here we explore a bio-inspired approach to mimicking olfaction by linking peptides to silicon nanowire sensors for the selective detection of small molecules. The silica surface of the nanowires is passivated with peptides using amide coupling chemistry. The peptide/nanowire sensors can be designed, through the peptide sequence, to exhibit orthogonal responses to acetic acid and ammonia vapors, and can detect traces of these gases from "chemically camouflaged" mixtures. Through both theory and experiment, we find that this sensing selectivity arises from both acid/base reactivity and from molecular structure. These results provide a model platform for what can be achieved in terms of selective and sensitive "electronic noses," and suggest application as implantable breath sensors for molecular disease indicators.
12:45 PM - UU1.10
Biofunctionalized Carbon Nanotube Transistor for Chemical Sensors.
Steve Kim 1 , Zhifeng Kuang 1 2 , Barry Farmer 1 , Rajesh Naik 1
1 , Air Force Research Labs, Wpafb, Ohio, United States, 2 , Universal Technology Corporation, Dayton, Ohio, United States
Show AbstractHigh strength, large flexibility and superb chemical stability are well-known properties of carbon nanotubes (CNTs). Moreover, their excellent electronic properties have driven significant interests among scientific communities in developing CNT-based hybrid for enhanced physicochemical properties. With diameters similar to individual DNA and peptide, CNTs are expected to be ideal conduits for interfacing electronics with biomolecules. By introducing biomolecules onto CNTs, selectivity towards specific targets could be achieved. In this study, CNT field effect transistor (CNT-FET) is functionalized with designer biomolecules that exhibit receptor-like function. We demonstrate that biofunctionalization of the CNT-FET device enhances the sensitivity and selectivity. In addition, we will present surface characterization of the biofunctionalized CNT-FET hybrid device.
UU2: Mechanisms of Biomineralization
Session Chairs
Tuesday PM, December 01, 2009
Room 205 (Hynes)
2:30 PM - **UU2.1
Understanding the Growth Mechanisms of Minerals Through Dynamical Simulation: The Role of Water and Amino Acids.
Julian Gale 1 , Paolo Raiteri 1 , Stefano Piana 1 , Franca Jones 1 , David Quigley 2 , Mark Rodger 2
1 Chemistry, Curtin University of Technology, Perth , Western Australia, Australia, 2 Chemistry, University of Warwick, Coventry United Kingdom
Show AbstractDetermining the atomic level details of biomineralization represents a significant scientific challenge that requires the complementary use of experiment and computer simulation. In this work, the use of dynamical simulation methods will be highlighted as a method for gaining valuable insights as to how the surface growth of minerals occurs under aqueous conditions. Barite (BaSO4) represents a simple compound that can be biomineralized. Simulations have already demonstrated that surface specific solvation can significantly alter the kinetics of growth leading to accelerated nucleation [1]. Furthermore, the presence of amino acids is found to catalyse the growth of surfaces at low concentrations in contrast to the standard model of inhibition by organic additives [2]. This observation is in agreement with recent experimental studies of the influence of polyaspartates on step propagation on calcite [3].While simulation of barite has already revealed considerable insights, the real challenge is to understand the biomineralization of calcium carbonate polymorphs. Although there have been numerous studies of the surfaces and solvation of CaCO3, most simulation models fail to correctly describe the free energy for the dissolution/growth process and/or the relative stability of the key polymorphs, both of which are fundamental requirements. A new model will be presented that is able to correctly describe the properties of CaCO3 in equilibrium with aqueous solution. Based on this, accelerated dynamics and umbrella sampling are used to obtain free energy profiles for key steps in the surface growth processes, with implications for the role of steps on calcite growth. Finally, possible approaches to the incorporation of speciation effects into the simulations will be discussed, as well as preliminary results regarding the influence of amino acids.[1] S. Piana, F. Jones and J.D. Gale, J. Am. Chem. Soc., 128, 13568 (2006)[2] S. Piana, F. Jones and J.D. Gale, CrystEngComm, 9, 1187 (2007)[3] S. Elhadj, P.M. Dove, A. Wierzbicki, J.R. Hoyer and J.J. de Yoreo, Proc. Natl. Acad. Sci., 51, 19237 (2006)
3:00 PM - UU2.2
Bio-Mineralization of Calcium Carbonate: Case Study of Terminal Sequences in Polymorph Crystal Formation.
Irit Katash 1 , John Evans 1
1 Chemistry, New York University, New York, New York, United States
Show AbstractIn an effort to elucidate bio-mineralization mechanism in pearl oyster Pinctada fucata we looked at 30AA C- and N-terminals of two proteins: PFMG1 (mantle) and N19 (nacre).Using in-vitro calcium carbonate mineralization assays, we demonstrate that unfolded random-coil in apo-state peptides (N19-N, PFMG1) affect the morphology of forming CaCO3 crystals, leading to irregular growth. The folded alpha-helix peptide (N19-C) showed no effect on crystal growth. Ca(II) binding-tests showed no to very slight folding of the peptides.Results indicate that presence of Ca(II) binding residues (Asp, Glu) is required to exhibit a change in the nucleation, morphology, and growth of Calcite crystals, as seen with PFMG1-C and N19-N. Absence of these groups may play a negative regulatory role, as displayed with N19-C. Results may also suggest that abundant presence of carbonate interaction residues (Ser, Arg, Lys, Tyr), may lead to the formation of Vaterite polymorph, as displayed with PFMG1-N.
3:15 PM - UU2.3
Simulating Orientational Specificity in the Growth of Calcite on Self-Assembled Monolayers.
Colin Freeman 1 , John Harding 1 , David Quigley 2 , Mark Rodger 2 , Dorothy Duffy 3
1 Engineering Materials, University of Sheffield, Sheffield United Kingdom, 2 Department of Chemistry, University of Warwick, Coventry United Kingdom, 3 Department of Physics and Astronomy, University College London, London United Kingdom
Show AbstractCrystalline mineral phases appear in nature as a major component of biocomposite materials such as shells, coral, teeth and bone. The organisms which exploit these phases exert a remarkable degree of control over the morphology and orientation of the growing crystal, sometimes employing multiple polymorphs within a single structure. There is considerable interest in understanding and reproducing the mechanisms behind this control, with the aim of developing biomimetic processes for materials engineering.One such biomimetic process is the crystallisation of calcite on a monolayer of self-assembled carboxylic acid molecules[1]. This has been studied in a range of experiments, demonstrating orientational specificity with a preference for nucleation at the (01.2) plane. In contrast, purely epitaxial arguments suggest the (0001) plane as preferable. Furthermore, the specificity is sensitive to the length of the chain, exhibiting an odd-even effect [2]. Simulation of the amorphous to crystalline transition can play a valuable role in understanding this phenomenon at the nucleation stage. Previous simulations have been hampered by use of elevated temperatures to overcome the timescale problem associated with simulating crystallisation [3]. This precludes the possibility of treating the monolayer dynamically, and the inclusion of explicit water. In contrast, the metadynamics method [4] has proven useful in the context of freezing from the melt without the need to impose unrealistic thermal conditions [5]. We have adapted our implementation of this method to the crystallisation of amorphous calcium carbonate and applied to heterogeneous nucleation on self-assembled monolayers. By including the dynamics of the organic chains, we are able to simulate the orientational selectivity in this system without imposing any structural defects. Furthermore, we are able to investigate the role of head-group ionisation, chain flexibility and chain length in the selection process, generating a number of crystal orientations which agree directly with experiment. As a result of this investigation we propose a "complimentary nucleation" process in which both the organic and mineral phases adapt to achieve a local charge epitaxy and trigger a nucleation event.[1] AM Travaille, L Kaptijn, P Verwer, B Hulsken, JAAW Elemans, RJM Nolte, H van Kempen J. Am. Chem. Soc. 125 (2003) 11571-11577[2] YJ Han, J Aizenberg Angew. Chem. Int. Edit. 42 (2003) 3668-3670[3] CL Freeman, JH Harding, DM Duffy Langmuir 24 (2008) 9607-9615[4] A Laio, M Parrinello Proc. Nat. Acad. Sci. 99 (2002) 12562-12566[5] D Quigley, PM Rodger J. Chem. Phys. 128 (2008) 221101
3:30 PM - UU2.4
Artificial Nacres Composed of CaCO3/Polymer Hybrid Nanolaminates.
Bongjun Yeom 1 , Kookheon Char 1
1 Chemical & Biological Engineering, Seoul National University, Seoul Korea (the Republic of)
Show Abstract Nacres, known as the Mother of Pearl, have been spotlighted in recent years due to their exceptional mechanical toughness, originating from the sandwiched structure consisting of 300 ~ 900 nm thick CaCO3 platelets in between 10 ~ 30 nm thick organic mortar layers. To mimic such noble structure of the nacres, there have been many efforts to prepare the organic/inorganic hybrid structure in the artificial way for various potential applications such as nanocomposites and synthetic hard tissues for biomedical applications. In this presentation, CaCO3/polymer hybrid nanolaminates were prepared by the sequential deposition of polymer and CaCO3 layers in different film thickness on the ‘seed’ CaCO3 crystalline layer. First, thin polymeric multilayers, consisting of (poly(allylamine)(PAM)/poly(acrylic acid)(PAA))n, were deposited at the top of the ‘seed’ CaCO3 crystalline by the layer-by-layer (LbL) deposition. A CaCO3 layer was then allowed to grow on the ‘polymer-coated seed crystalline layer’. It is important to note that the thickness of the organic layers dramatically influences the overgrowth of the CaCO3 layers in terms of coverage and crystal orientation. Based on the understanding of the CaCO3 overgrowth mechanism, CaCO3/polymer hybrid nanolaminates were fabricated by the alternative deposition of polymer and CaCO3 layers, mimicking the naturally occurring nacres.
3:45 PM - UU2.5
Silica Coated Peptide Fibril Networks with Tunable Shear Modulus.
Aysegul Altunbas 1 , Nikhil Sharma 1 , Radhika Nagarkar 1 , Joel Schneider 1 , Darrin Pochan 1
1 , University of Delaware, Newark, Delaware, United States
Show AbstractIn this study, a 3D hybrid network that displays hierarchical organization of an inorganic layer around an organic self-assembled peptide fibril template was fabricated. The 20 amino acid peptide used in this study consisted of alternating hydrophilic (lysine) and hydrophobic (valine) residues flanking a four amino acid turn sequence in the center (VKVKVKVKVDPLPTKVEVKVKV-NH2). After intramolecular folding into a beta-hairpin conformation on addition of a desired solution stimulus, this peptide self-assembles into a 3D network of entangled and branched fibrils rich in beta-sheet with a high density of lysine groups exposed on the fibril-surfaces. The lysine-rich surface chemistry was utilized to create a silica shell around the fibrils. The mineralization process of the fibrils was initiated under physiological conditions by adding a silica precursor to the pre-assembled hydrogel,that resulted in a porous silica network that retains the nanoscale and mesoscale structure of the peptide fibril network. The structures of the networks were examined with Small Angle Neutron and X-Ray Scattering as well as Electron Microscopy. Various peptide:silica precursor ratios have proven to proceed with a high fidelity of the precursor towards the peptide fibrils resulting in controllable silica shell thicknesses. This effect was utilized for the fabrication of a number of scaffolds with a variety of stiffnesses with the same network structure.
4:30 PM - **UU2.6
Amorphous Calcium Carbonate Is Stabilised with Respect to Calcite in a Thin Wedge.
Christopher Stephens 1 , Sophie Ladden 1 , Fiona Meldrum 2 , Hugo Christenson 1
1 School of Physics and Astronomy, University of Leeds, Leeds United Kingdom, 2 School of Chemistry, University of Leeds, Leeds United Kingdom
Show AbstractCalcium carbonate has been precipitated in the annular wedge-pore formed around the contact of two crossed cylinders. The glass cylinders have a radius of curvature of 1/2” and were in most experiments coated with carboxylic-acid terminated thiols on an evaporated gold film, a surface known to promote the oriented growth of calcite. Precipitation was carried out either from a metastable mixture of calcium chloride and sodium carbonate (1-100 mM), or by diffusion into a calcium chloride solution (1- 10mM) of carbon dioxide formed by decomposing ammonium carbonate. Far from the contact zone the two surfaces are effectively isolated and SEM showed that the calcium carbonate precipitated on the thiols predominantly as well-oriented, micron-size calcite crystals. On the bare glass surface non-oriented calcite and vaterite formed, and at 1 and 2 mM calcium chloride no crystals were found on either surface. As the separation between the two surfaces decreases on moving towards the vertex of the wedge the orientation and characteristic habit of the calcite on the thiol surfaces were lost, with grossly distorted crystals becoming dominant. Very close to the vertex, at submicron surface separations, flattened, irregular structures were found, both on thiols and on glass, down to calcium chloride concentrations at which no calcite was evident on the “isolated” surfaces. The number and size of these irregular structures increased with the calcium chloride concentration, and Raman microscopy showed that it consisted mostly of amorphous calcium carbonate (ACC). We suggest that ACC is stabilised in the thin end of the wedge, preventing its conversion into calcite. The phenomenon is thus analogous to capillary condensation from vapour below the bulk melting point of the condensing substance, where supercooled liquid is stabilised both with respect to vapour and with respect to the crystal.
5:00 PM - UU2.7
The Calcium Phosphate binding Properties of the Serum Protein Fetuin-A explored with SANS Contrast Variation Technique.
Dietmar Schwahn 1 , Alexander Heiss 2 , Vitaliy Pipich 3 , Willi Jahnen-Dechent 2
1 IFF, FZ-Juelich, Juelich Germany, 2 Biomedical Engineering, RWTH University, Aachen Germany, 3 JCNS at FRM II , FZ-Juelich, Garching Germany
Show AbstractThe patho-physiologic relevance of the serum protein fetuin-A/alpha2 HS-glycoprotein as a systemic inhibitor of uncontrolled mineral deposition in the soft tissue has been demonstrated in fetuin-A knockout mice [1]. Moreover, clinical studies showed that patients with a low fetuin-A serum level are exposed to an increased calcification risk [2]. To elucidate the inhibition mechanism of calcification by the protein fetuin-A, we explored several in vitro model systems with SANS contrast variation technique [3]. The principle outcome was a two stage formation process of transiently stable nanometer sized colloidal composites of fetuin-A and calcium phosphate, which we denoted as calciprotein particles (CPPs); the initial form is spherical with a diameter in the 500Å range which, after several hours at room temperature, transform to elongated particles of about twice the initial size. The CPPs consist of fetuin of about 25% volume fraction and of the octacalcium phosphate (OCP) polymorph representing the mineral phase [3]. The secondary CPPs are stable for at least 24 hours, which can be explained by a dense fetuin monolayer covering the mineral as determined from SANS contrast variation experiments [3]. However, a detailed analysis suggested that the buffering of calcium and phosphate ion super saturation by the CPPs is not the whole story of the inhibition mechanism. The analysis of the SANS scattering patterns revealed that 3-5% of the total fetuin-A and about half of the total mineral can only be attributed to the CPPs. As SANS reflects the presence of fetuin monomers at large momentum transfer, we speculated that the other half of the mineral is attached to the monomers. Recent contrast variation experiments indeed identified these particles as calciprotein monomers (CPM) with varying amount of the mineral when changing the fetuin concentration. So, the inhibition mechanism of mineralization in the presence of the protein fetuin-A proceeds on two pathways, namely by CPP and CPM formation. [1] C. Schäfer et al., J. Clin. Invest. 112, 357 (2003).[2] M. Ketteler et al., Lancet 361, 827 (2003).[3] A. Heiss, W. Jahnen-Dechent, H. Endo, D. Schwahn, Biointerphases 2, 16 (2007).
5:15 PM - UU2.8
Exploring Templated Nucleation and Growth in Biomimetic Systems through In Situ, Fluid Cell TEM.
Michael Nielsen 1 , Jonathan Lee 2 , Yong Han 2 , Jim De Yoreo 1
1 , Lawrence Berkeley Lab, Berkeley, California, United States, 2 , Lawrence Livermore National Lab, Livermore, California, United States
Show AbstractOne of the challenges in understanding templated growth of biominerals is probing the early events that determine the nucleation pathway and final mineral structure. We report the development of an in situ transmission electron microscopy (TEM) technique suitable for imaging dynamic processes in liquid environments at high temporal resolution. The capability for in situ measurements is enabled by the combination of a custom designed TEM stage and cell. Significantly, the design of the cell and holder ensures temperature and electrochemical control over the reaction environment, which can be used to initiate processes of interest, such as the onset of crystal nucleation and nanoparticle growth. Moreover, the system allows for direct investigation of templated nucleation because the working electrode sits in the path of the electron beam. Time-resolved imaging permits the observation of changes in the structural morphology of growing crystals. In conjunction with the solution parameters, these observations allow for determination of kinetic and thermodynamic factors that drive crystal nucleation and growth. Furthermore, dynamic diffraction provides the capability for direct investigation into the pathways of crystal growth, thereby enabling the determination of the underlying mechanisms that take a species from its solvated state to final crystalline form. Using the same experimental setup to image with atomic force microscopy (AFM) reveals complementary surface information for the nucleating species, albeit at a much lower temporal resolution. Herein we report the observation of electrochemically driven calcium carbonate nucleation on self-assembled monolayers and surfactant-directed, oriented growth of gold nanoparticles. We present data on the dependence of nucleation rates on driving force, and on the morphological and structural evolution of the incipient nuclei and growing nanoparticles. We show how this approach can be extended to observation of mineralization on biological structures such as protein cages and fibers.
5:30 PM - UU2.9
The Effect of Organic and Inorganic Modifiers on Hydroxyapatite Dissolution Studied by Atomic Force. Microscopy
Seung-Wuk Lee 1 2 , Ki-Young Kwon 2 1 , Eddie Wang 1 2
1 Bioengineering , University of California, Berkeley, Berkeley, California, United States, 2 Physical Bioscience Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractThe complexity of bone tissue and the lack of techniques for directly probing bone surfaces in vivo have hindered studies on the fundamental mechanisms of bone mineral remodeling. We are addressing these issues by using single crystal hydroxyapatite (HAP) as a well-defined bone surface model, and directly observing its surface under various aqueous solution environments using in situ atomic force microscopy. Specifically, we investigated the effects of 1) inorganic ions (NaCl and NaF) and 2) organic molecules (amino acids, and short peptide motifs) on the dissolution of HAP (100) surfaces. We have found that both NaCl and NaF strongly suppress HAP dissolution kinetics, but their inhibition mechanisms are different. We proposed that inhibition by NaCl is the result of competition for surface protonation sites between Na+ and H+ ions rather than the interaction of chloride ions with specific molecular steps. However, inhibition of HAP by NaF can be attributed to the interaction between fluoride ions and specific molecular steps, which results in the shape change of etch pits. Second, we found that HAP binding short peptides selected by phage display dramatically retards HAP dissolution and this inhibition is sensitive to pH. Our molecular level, real-time observations of HAP dissolution are significant for understanding bone resorption and dental carries and provide useful insights for the design of novel therapies for treating bone and teeth related diseases.
UU3: Poster Session
Session Chairs
Wednesday AM, December 02, 2009
Exhibit Hall D (Hynes)
9:00 PM - UU3.1
Theory and Simulation of Texture Transformations during Plant Cell Wall Morphogenesis.
Yogesh Kumar Murugesan 1 , Alejandro Rey 2
1 Department of Chemical Engineering, McGill University, Montreal, Quebec, Canada, 2 Department of Chemical Engineering, McGill University, Montreal, Quebec, Canada
Show AbstractSecondary cell walls of different plant species possess highly ordered twisted plywood architecture giving them enhanced mechanical properties. Understanding the principles that govern this micro-structural development of plant cell wall is essential in design and fabrication of light weight materials with similar properties. Owing to the striking similarities between the defect patterns observed in plant cell walls and chiral nematic liquid crystals, it has been hypothesed that liquid crystalline self-assembly is present during the cell wall morphogenesis[1]. A continuum model, based on Landau-de Gennes theory of liquid crystals, simulating the process of chiral fibrous molecules forming twisted plywood architecture in biological composites has been developed in the past[2]. In the current work, the model is modified by incorporating higher order gradient terms allowing variable helicoidal pitch. Temporal evolution of microstructure in plant cell wall, driven by free energy minimization, is simulated by solving this model using finite element methods with strong molecular anchoring over circular geometry representing plant cell. The model can predict pitch dilation and chiral melting, owing to surface constraints induced by the presence of cells in the domain of self assembly. It can also demonstrate formation of disclinations, dislocations and textures similar to those observed in plant cell wall.References:1.Neville, A.C.: Biology of fibrous composites. Cambridge University Press, New York (1993)2.G. De Luca, A.D. Rey, Physical Review E 69 (2004) pp. 011706.1-011706.13
9:00 PM - UU3.10
Synthesis of Ordered Mesoporous Silica Nanoparticles Incorporating Magnetic Nanoparticles.
Teeraporn Suteewong 1 , Hiroaki Sai 1 , Jinwoo Lee 2 , Ulrich Wiesner 1
1 Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 2 Engineering, Pohang University of Science and Technology, Kyungbuk Korea (the Republic of)
Show AbstractHexagonally ordered-mesoporous silica nanoparticles provide a large functionalizable surface area, which is desired in many applications e.g. separation, catalysis and adsorption1. By incorporating magnetic nanoparticles inside the siliceous matrix, the composite will offer magnetic properties which could be used in biomedical applications such as MRI2. There have been many attempts to incorporate inorganic materials into the matrix of silica particles; common problems include the destruction of the ordered structure and size control. In this work, we present the one-pot formation of ordered mesoporous silica nanoparticles embedding magnetic particles. 8 nm magnetic nanoparticles are separately synthesized using a thermal decomposition method, and their surfaces are modified with hexadecyltrimethylammonium bromide before being introduced to the synthetic system for fabricating the nanocomposites. From dynamic light scattering and transmission electron microscopy (TEM), the particle size of resulting materials is smaller than 100 nm. TEM images shows that magnetic particles are embedded in the siliceous matrix without disrupting the ordered structure of silica. Small-angle x-ray scattering as well as TEM elucidate the structural evolution of the magnetic nanoparticle-encapsulated MCM-41 type silica nanoparticles, transitioning from a disordered to an ordered structure. N2 sorption measurement of these particles show high surface area and uniform pore size distribution.
9:00 PM - UU3.14
Preparation of Magnetic Polymer from Chitosan Chelates.
Marco Garza-Navarro 1 2 , Virgilio Gonzalez 1 2 , Moises Hinojosa 1 2 , Martin Reyes-Melo 1 2 , Alejandro Torres-Castro 1 2
1 Facultad de Ingeniería Mecánica y Eléctrica, Universidad Autónoma de Nuevo León, San Nicolas de los Garza, Nuevo León, Mexico, 2 Centro de Innovación, Investigación y Desarrollo en Ingeniería y Tecnología , Universidad Autónoma de Nuevo León, Apodaca, Nuevo León, Mexico
Show AbstractThe preparation and characterization of magnetic polymer composed by cobalt-ferrite nanoparticles (CFN) within a chitosan matrix (CHN) is reported. The magnetic polymers were synthesized from chelates films of coordinated Co(II) and Fe(III) cations within the chitosan matrix, which were prepared at the necessary proportions to obtain, under NaOH addition, CHN/CFN ratios of 25/75 and 50/50 w/w. The crystalline and morphological studies of the magnetic phase were performed by high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and selected area electron diffraction (SAED), resulting in cuasi-spherical cobalt-ferrite nanoparticles with a narrow particle size distribution of 2 nm to 5 nm. The study of the CHN-CFN interactions was conduced by infrared spectroscopy, and suggests that the stabilization of the magnetic phase occurs due to the coordination of cations at the CFN surface with amino and hydroxyl groups of the CHN chains. The magnetic properties of the magnetic polymer was evaluated by static magnetization field dependent, M(H), and magnetization temperature dependent, M(T), measures, which depict that the spin magnetic moment response of the magnetic phase strongly depends of both intra and interparticle interactions. The dynamic isochronal magnetic measures also show this dependence, which resembles the glassy magnetic behavior of spin glasses materials.
9:00 PM - UU3.15
Bioinspired Hierarchical Structures for Applications in Thermal Management and Energy Harvesting.
Zhiping Xu 1 , Markus Buehler 1
1 Civil and Environmental Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractThe miniaturization and higher integration of components in nano-devices lead to high density, point-load singular heat sources that often induce device failure, thereby significantly reducing their operational reliability. Conventional thermal management strategies to mitigate heat sources by using heat fins, fluids, heat pastes or metal wiring fail in nano-devices because of the limited area of heat dissipation, the high energy densities and the dynamically changing or a priori unknown locations of heat sources. To solve these problems, a high-performance heat transfer path must be designed with two features: (1) comprising of high thermal conductivity components and (2) being capable to migrate heat from a small, confined space to larger-scale heat sinks. Here we show that hierarchical structures based on one-dimensional filaments such as carbon nanotubes lead to superior thermal management networks, capable of effectively mitigating high-density ultra-small nanoscale heat sources through volumetric heat sinks at micrometer and larger scales. The figure of merit of heat transfer is quantified through the effective thermal conductance as well as the steady-state temperature distribution in the network. In addition to providing an overall increased thermal conductance, we find that hierarchical structures drastically change the temperature distribution in the immediate vicinity of a heat source, significantly lowering the temperature at shorter distances. From a practical point of view, the hierarchical network can be synthesized through molecular assembling of nanofilaments. Functionalization at their ends with adaptive agents can help to activate the self-assembly process, which is confirmed by coarse grained simulations. The topology of the network can be tuned through interactions between filaments, i.e. from bundles to branched networks with hierarchy. Moreover, the interfacial thermal conductivity is calculated for carbon nanotubes as thermal conducting fibers. The conductivity across graphene layers interacted through the van der Waals forces is found to be very low and restricts the performance of whole network. Approaches such as polymer wrapping and metal layer coating are proposed and found to be able to significantly improve the thermal transfer through these interfaces. As in the photosynthesis system in algae and plants where photon energy absorbed by pigments is transferred through light harvesting complex to the reaction center, several energy harvesting solutions such as photovoltaic materials involve spatially localized energy conversion as the first step and subsequently energy collection process. An efficient network for energy collection can also be achieved by utilizing hierarchical networks. Our work brings about a synergistic viewpoint that combines advances in materials synthesis and insight gained from hierarchical biological structures, utilized to create novel functional materials with exceptional thermal properties.
9:00 PM - UU3.16
Atomic-scale Modelling of the Interaction Between Synthetic Peptides and Carbon Surfaces.
Giulio Gianese 1 , Vittorio Rosato 1 2 , Fabrizio Cleri 3 , Massimo Celino 2 , Piero Morales 2
1 , YLICHRON Srl, Roma Italy, 2 Dipartimento Tecnologie Fisiche e Nuovi Materiali, ENEA Centro Ricerche Casaccia, Santa Maria di Galeria (Roma) Italy, 3 Institut d'Electronique, Microelectronique et Nanotechnologie (IEMN), University of Lille I, Lille France
Show AbstractWe report the comparative study of the adsorption of an artificial peptide on two different carbon surfaces: a flat graphene and a curved (0,15) nanotube. The peptide sequence was selected from recent experiments (Wang et al., Nature Mat. 2003) as the one giving the highest carbon affinity for carbon nanotubes. Rigid docking of the molecule on the two surfaces by a genetic algorithm was followed by molecular dynamics with empirical force fields (OPLS-AA) in water at finite temperature. Total free energies of folding and adhesion, and the quality of surface binding were determined, based on a combination of solvation energy, formation of hydrogen bonds, amount of the apolar (hydrophobic) contact surface between peptide and carbon surface. In both cases we find a strong adhesion energy and large non-polar contact surface. Isoleucines and triptophans are the most strongly bound residues to the two carbon surfaces, the latter one largely dominating. Despite the fact that the adsorption free energy is slightly larger on the flat surface, in the case of the carbon nanotube, however, the peptide shows several competing stable structures, corresponding to different possible molecular foldings, and propensity to enhance the intramolecular stability by forming new hydrogen bonds. In both systems, different arrangements of the histidine and triptophan residues are observed enabling a better adaptation to the carbon surfaces. Such findings suggest that the experimentally observed surface-specificity of the peptide on nanotubes could have an entropic origin, depending on the ability to support multiple strongly bound configurations.
9:00 PM - UU3.17
Adsorption of Peptides CR3-1, S2 on Clay and A3, Flg, Pd2, and Pd4 on Au and Pd Surfaces by Computer Simulations.
Hendrik Heinz 2 , Ras Pandey 1 , Barry Farmer 3
2 Polymer Engineering, University of Akron, Akron, Ohio, United States, 1 Physics and Astronomy, University of Southern Mississippi, Hattiesburg, Mississippi, United States, 3 Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright Patterson Air Force Base, Dayton, Ohio, United States
Show AbstractComputer simulations are performed to study adsorption of CR3-1 and S2 on a clay surface and A3, Flg, Pd2, and Pd4 on gold and palladium surfaces by all atomic Molecular Dynamics and coarse-grained Monte Carlo methods in presence of explicit solvent. All atomic description entails structural details of each residue, solvent, and substrate involving accurate force field between each element. Adsorption probabilities of each peptide on appropriate surfaces are predicted from a detailed analysis of energy and structural profiling. Using the interaction energy of residues as an input, a coarse-grained model is developed. Monte Carlo simulations are performed on a cubic lattice to study the adsorption of these peptide chains on corresponding clay and gold and palladium surfaces in presence of explicit solvent. In the coarse-grained description, peptides are described by bond-fluctuating chains with specific sequence of their amino acid nodes; although the atomistic details of each amino acid are ignored, their specificity is incorporated via a phenomenological interaction matrix. Solvent is represented by mobile particles and surfaces by impenetrable immobile substrates. Peptide chains (and solvent constituents) execute their stochastic motion starting at the substrate. Mobility of each amino acid (node), its energy, and correlations to their neighboring constituents are analyzed in detail. Relative probability of adsorption of these peptides on the substrate is predicted including the identification of specific residues that anchor them to appropriate surfaces. Results of both atomistic and coarse-grained simulations are consistent with some of the experimental observations.
9:00 PM - UU3.18
Artificial Silicatein Active Sites: Employing Bicephalic Peptide Amphiphiles.
Dan Krogstad 1 , Brian Lin 2 , James Nielson 4 , Daniel Morse 5 , Matthew Tirrell 3
1 Materials, University of California at Santa Barbara, Santa Barbara, California, United States, 2 Chemistry, University of California at Santa Barbara, Santa Barbara, California, United States, 4 Biomolecular Science and Engineering, University of California at Santa Barbara, Santa Barbara, California, United States, 5 Molecular Cellular and Developmental Biology, University of California at Santa Barbara, Santa Barbara, California, United States, 3 Chemical Engineering, University of California at Santa Barbara, Santa Barbara, California, United States
Show AbstractBicephalic peptide amphiphiles have been synthesized that mimic the catalytic and templating capabilities of the silica producing protein, silicatein α, of the marine sponge Tethya aurantia. The active site of silicatein α consists of a hydrogen bonded serine and histidine residue; this is readily mimicked by the bicephalic nature of the peptide amphiphiles. These novel molecules consist of a lipid tail attached to two head groups through azide-alkyne cycloadition in which one head group is a triserine peptide and the other head group is a trihistidine peptide. The peptide amphiphiles self-assemble into extended cylindrical micelles up to 25 microns long and 7 nm in diameter. We have shown that tetraethoxysilane (TEOS) can be catalytically hydrolyzed and condensed on the peptide amphiphile micelles at room temperature and near neutral pH, creating silica nanowires. The micelles have been imaged by atomic force microscopy and cryo-transmission electron microscopy and the catalytic ability of the molecules to produce silica was determined by a molybdic acid assay, optical microscopy and energy dispersive X-ray spectroscopy. The highly tunable nature of peptide amphiphile micelles makes them a promising biomimetic silicatein system.
9:00 PM - UU3.19
Synthesis and Application of Metal-siloxane Hybrid Nanostructures.
Anubha Goyal 1 , Ashavani Kumar 1 , P. Ajayan 1
1 Mechanical Engineering and Materials Science, Rice University, Houston , Texas, United States
Show AbstractSiloxane based materials are well known for their applications as implants, biosensors and optical devices. Embedding nanoparticles in such materials could lead to novel advanced materials wherein unique properties of the nanomaterial can be exploited for a range of applications. Development of simple, scalable synthesis protocols for such materials would be of great interest. We demonstrate simple one-step methods for synthesizing metal-siloxane based hybrid nanomaterials. The synthesis was carried out by metal ion induced polymerization of silane polymers or by curing of the mixture of metal salt and elastomer at an elevated temperature. A range of nanostructures like nanowires, core-shell structures and nanomaterial based flexible membranes were achieved by tailoring reaction parameters. The hybrid materials were characterized using UV-Vis spectroscopy, transmission electron microscopy and X-ray photoemission spectroscopy. These hybrid materials could be used for catalytic activity, enzyme immobilization and optical applications.
9:00 PM - UU3.2
Metallized Porous Microframes via Biofunctionalization.
Srikanth Singamaneni 1 , Eugenia Kharlampieva 1 , Ji-Hyun Jang 2 , Michael McConney 1 , Hao Jiang 3 , Timothy Bunning 3 , Edwin Thomas 2 , Vladimir Tsukruk 1
1 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Institute for Soldier Nanotechnologies, Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Materials Directorate, Airforce research laboratories, Wright Patterson, Dayton, Ohio, United States
Show AbstractWe demonstrate metallized 3D periodic, porous polymer microstructures decorated with metal nanoparticles by their direct growth on outer and inner surfaces, enabled by SU8 biofunctionalization with nanoscale polyaminoacid coating. Conventional approaches such as electroless deposition, or synthetic polymer mediated growth of nanoparticles involves in either tedious multi-step process or use of harsh reducing agents, which can perturb the 3D topology of soft polymer structure. By applying either solution (spin coating) or vapor (plasma enhanced chemical vapor deposition) based biofunctionalization, we achieved the nanoparticle coverage ranging between 10 NP/µm2 and 220 NP/µm. The diameter of gold nanoparticles can controlled from 10 to 90 nm by the variation of parameters of biofunctionalization. The highest surface coverage achieved in the case of the poly-L-tyrosine deposited from water/alcohol. The reported results on biomolecular-based formation of 3D metalized porous templates can be readily expanded to wide variety of inorganic microstructures, providing a simple, robust, and environmentally-friendly method of fabrication of robust metal-polymer organized microcomposites.
9:00 PM - UU3.3
Probing the components of nacre by contact angle measurements
Malte Launspach 1 , Fabian Heinemann 1 , Monika Fritz 1
1 Institute of Biophysics, University of Bremen, Bremen Germany
Show AbstractNacre is a highly structured polymer/mineral composite, which has been brought to perfection by evolution over millions of years. It is part of the shell of some marine organisms.A dense packing of thin layers of mineral platelets is interdispersed by a few nanometer of organics. The order and the dimension of the platelets, which are embedded in an organic matrix, lead to astonishing mechanical properties like high tensile strength, ductility and fracture resistance. The process of shell formation is biologically controlled. Proteins are involved in the formation of the aragonite platelets. These proteins are either soluble or insoluble attached to a chitin core. Last-mentioned combination of protein and chitin forms the organic matrix.The process of crystallisation of the mineral platelets is still under investigation.In this study the surface energy properties of the insoluble organic matrix are probed by contact angle measurements. The aim is to quantify the adhesive strength between the mineral and organic phase and to investigate the relevance of the organic matrix with respect to platelet formation.Measurements were conducted with a home-built device. Pieces of the demineralised and slightly dehydrated insoluble organic matrix in a native state and after enzymatic treatment were probed as well as the (001) surface of geological aragonite. The (001) surface of aragonite is not a cleavage plane. Therefore the tested mineral surfaces had to be processed in a special way.The surface free energy of the organic matrix was calculated using semi-empirical approaches (e.g. van Oss et al. [1]). It turns out that three different models yield a total surface free energy between 40 and 44 mJ/m^2 for the native matrix and a value between 51 and 59 mJ/m^2 after enzymatic treatment.The Lifschitz-van der Waals surface energy component is almost constant in both cases whereas the Lewis acid-base component of the surface free energy increases after protein digestion. This is in accordance with values obtained for chitin.The applied liquid droplet was soaked up by the dehydrated matrix with different rates depending on the liquid. This provides additional information of differences between surface and bulk properties of the processed organic matrix.In the case of the minerals the method of Schultz et al. [2] was applied. The obtained values could not be used for further calculations since the influence of the preparation process was to dominant.[1] van Oss, C. et al. (1986). The role of van der Waals forces and hydrogen bonds in "hydrophobic interactions" between biopolymers and low energy surfaces. Journal of Colloid and Interface Science, 111:378–390[2] Schultz, J. et al. (1977). Surface properties of high-energy solids 1. Journal of Colloid and Interface Science, 59:272–276
9:00 PM - UU3.5
Study on the Effects of Type I Collagen Combined with Noncollagenous Proteins on Hydroxyapatite Formation in vitro.
Xiaolan Ba 1 , Elaine DiMasi 2 , Yizhi Meng 1 , Miriam Rafailovich 1
1 ESM, SUNY-Stony Brook, Stony Brook, New York, United States, 2 National Synchrotron Light Source, Brookhaven National Laboratory, Upton, New York, United States
Show AbstractIn this paper, we present an approach to mimic the ECM in vitro. Using a charged polymer substrate we show that the pure Type I collagen and collagen binding with two NCPs, Fibronectin (FN) and Elastin (EL), self assemble into a common fiber network. Our previous work has demonstrated that those two NCPs have opposite functions during biomineralization. To improve the understanding of the interaction mechanism of organic molecular and biominerals during the initial stage of biomineralization, we demonstrate complementary surface sensitive techniques to study the process of biomimetic mineralization from the earliest stages. By exposing the fibers to calcium phosphate solution at physiological pH and ionic concentration, we are able to track the mineralization process, starting from incorporation of the ions into the proteins, through nucleation of HAP crystals. Synchrotron-based STXM, in combination with grazing incidence X-ray diffraction (GIXD), is used to differentiate between calcium ions bound to the fibers versus nucleation of crystalline mineral. These crystals appear to form from ions contained within the fibers. We found that the ability to absorb ions varied between the three different protein matrices.
9:00 PM - UU3.6
Modelling the Nucleation and Growth of Calcium Carbonate.
Colin Freeman 1 , John Harding 1 , David Quigley 3 , Mark Rodger 3 , Mingjun Yang 4 , Susan Stipp 4 , Dorothy Duffy 2
1 Engineering Materials, University of Sheffield, Sheffield United Kingdom, 3 Chemistry, University of Warwick , Coventry United Kingdom, 4 Nano-Science Center, University of Copenhagen, Copenhagen Denmark, 2 London Centre for Nanotechnology, University College London, London United Kingdom
Show AbstractThe nucleation and growth of biominerals is controlled by organic molecules or molecular arrays. This control can determine the mineral phase, orientation of growth and shape of the resulting crystal. We show how atomistic simulation can demonstrate these effects by considering the example of calcium carbonate. Simulations of nanoparticles of various sizes in water, both alone [1] and in the presence of proteins [2] shows the importance of surface interactions in determining the behaviour. Metadynamics simulation methods [3] are used to overcome the problem of reaching the timescales that are typical for nucleation. We also use these methods to investigate the mechanism of templating in the growth of oriented calcite crystals on self-assembled monolayers [4]. The results show that the control of the crystal orientation is not simply a matter of epitaxial matching; the flexibility of the chains in the monolayer is also of fundamental importance.Individual molecules (peptides and polysaccharides) can also affect crystal morphology through their binding to various surfaces and steps. We calculate absorption energies of these molecules for a number of cases [5] and demonstrate the importance of the water structure in determining whether or not binding will occur. Estimates of the entropy of binding show that it is significant but not large enough to modify the conclusions arrived at based on the energy alone. While this is true for the cases considered here, it may not be true in general and we consider the likely consequences for the binding configuration of molecules if the absorption is dominated by the entropy. [1] D. Quigley and P.M. Rodger, J. Chem. Phys. 128 (2008) 221101.[2] C.L. Freeman, J.H. Harding, D. Quigley and P.M. Rodger, submitted to Nat Mater.[3] A. Laio and M. Parrinello, Proc. Nat.Acad. Sci. 99 (2002) 12562.[4] D.Quigley, C.L. Freeman, P.M. Rodger, J.H. Harding and D.M. Duffy, submitted to J. Am. Chem. Soc.[5] M. Yang, S.L.S. Stipp, and J.H. Harding Cryst. Growth Des., 8 (2008) 4066.
9:00 PM - UU3.7
Enzymatic Modification of Hemicellulose to Introduce Functionalities to Cellulose.
Sofia Hiort af Ornaes 1
1 , SweTree Technologies, Uppsala Sweden
Show AbstractSweTree Technologies is a plant and forest biotechnology company providing products and technologies to improve the productivity and performance properties of seedlings, wood and fiber for forestry, pulp & paper, packaging, hygiene, textile and other fiber related industries.SweTree Technologies develops and commercializes new biotechnological methods to improve cellulose-based fibers and products. One of the technology platforms used for this is based upon innovations from research at the Royal Institute of Technology (KTH) in Stockholm, Sweden, which has shown that the plant polysaccharide xyloglucan (XG) can be used to positively affect fiber properties, either in its native form or following chemo-enzymatic modification using the “XET technology”. Briefly, the XET technology relies upon the use of a carbohydrate-active enzyme, xyloglucan endotransglycosylase (XET), to introduce comparatively small, chemically-modified xylo¬glucan oligosaccharides (XGO-R) into high molar mass xyloglucan (XG). This catalytic reaction thus produces a modified xyloglucan (XG-R), which bears the functional group (R). Importantly, the backbone of the xyloglucan molecule remains unmodified and retains its intrinsic high affinity for paracrystalline cellulose. XG-R is therefore readily adsorbed to e.g. wood or cotton fibers. With the use of this technology a multitude of different properties can be introduced to cellulose fibers without loss of fiber integrity or strength. Novel properties can thereby be introduced to renewable materials.1,2References:1.Brumer, H., Zhou, Q., Baumann, M J, Piispanen, P, Carlsson, K, Teeri, T, J. Am. Chem. Soc., 2004, 126, 5715-57212.Zhou Q, Baumann MJ, Piispanen PS, Teeri TT, Brumer H, Biocatal Biotransform, 2006, 24, 107–120
9:00 PM - UU3.8
DNA Hydrogel Fibers Prepared through Ionic Liquid.
Chang Kee Lee 1 , Su Ryon Shin 1 , Sun Hee Lee 1 , Seon Jeong Kim 1
1 , Hanyang University, Seoul Korea (the Republic of)
Show AbstractDNA hydrogels have a wide range of biomedical applications in tissue engineering and drug-delivery systems. There are two ways to create hydrogel structures: one is enzyme catalyzed assembly of synthetic DNA and the other is by crosslinking natural DNA chemically. For natural DNA, formaldehyde and metal compounds such as arsenic, chromate, and nickel are widely used as crosslinkers. However, these modified DNA hydrogels are unsafe to apply in biological systems because the crosslinkers have potentially adverse side effects, with some being carcinogens. Besides this, these DNA hydrogels are difficult to form into hydrogel fibers by using conventional spinning methods in the absence of chemical crosslinking. In this work, DNA hydrogel fibers were developed without the need for crosslinking agents by using ionic liquid. The DNA hydrogel consisted of native DNA that formed random entanglements to provide physically crosslinked networks. Circular dichroism (CD) spectroscopy was employed to elucidate the molecular state of DNA and Polarized Raman spectroscopy was used to confirm the state of structure of DNA hydrogel fiber. DSC and XPS were also used to characterize the DNA hydrogel fiber. The DNA fibers maintained their hydrogel form for about 3 months after soaking in deionized water. Such DNA hydrogel fibers showed resistance to digestion by DNases and may be exploited in a variety of biomedical applications.
9:00 PM - UU3.9
Improved Mechanical Properties of Macroscopic Synthetic Polymers through Metal Ion Complexation.
Matthew Howard 1 , Juliana Bernal Ostos 2 , Gregory Gause 1 , Galen Stucky 2
1 Department of Chemistry and Life Sciences, United States Military Academy, West Point, New York, United States, 2 Materials Science, University of California Santa Barbara, Santa Barbara, California, United States
Show AbstractMetal ion complexation in marine biomaterials leads to increased hardness and stiffness, giving these biomaterials mechanical properties superior by weight to engineering polymers. Studies of the jaws of Nereis and Glycera marine worms indicate complexation of histidine with Zn2+ and Cu2+ respectively, increasing the hardness and stiffness of their jaws. Here we investigate the complexation of Poly (N-vinylimidazole) (PVIm) with Cu2+ and Zn2+ ions, and study the mechanical advantages resulting from complexation. We have developed a technique for creating macroscopic PVIm samples and introducing zinc/copper complexation. These samples have undergone tensile testing and complexation has been shown to lead to markedly improved tensile strengths. Thus, we elucidate a bio-inspired procedure for improving the mechanical properties of polymeric materials with negligible increase in weight. This methodology is general so it is easily extendible in other systems with similar functionalities. This tough molecular-level composite material offers a novel paradigm for energy absorbing applications such as personnel protective systems.
Symposium Organizers
John Harding University of Sheffield
John Evans New York University
James Elliott University of Cambridge
Robert Latour Clemson University
UU4: Molecular Interactions with Surfaces
Session Chairs
Wednesday AM, December 02, 2009
Room 205 (Hynes)
9:30 AM - **UU4.1
Dynamics of Proteins and Peptides on Lipid and Mineral Surfaces.
Jim DeYoreo 1 , Sungwook Chung 1 , Seong-Ho Shin 1 , Stephen Whitelam 1 , Raymond Friddle 1 2 , Roger Qiu 2 , Andrzej Wierzbicki 3 , Carolyn Bertozzi 1
1 Molecular Foundry, Lawrence Berkeley Lab, Berkeley, California, United States, 2 Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Berkeley, California, United States, 3 Department of Chemistry, University of South Alabama, Mobile, Alabama, United States
Show AbstractLiving organisms achieve a high density of functionality through hierarchical organization of proteins and create materials with unique properties via protein-directed mineralization. Developing an understanding of the structural, thermodynamic and kinetic controls on these processes has the potential to define new approaches to materials synthesis. Here we report the results from investigations of 2D assembly by S-layer proteins on lipid bi-layers as well as peptide adsorption dynamics on single crystal surfaces obtained via in situ AFM, dynamic Monte Carlo (DMC) simulations, and molecular modeling.Results on S-layer self-assembly show that the monomers adsorb onto lipid bi-layers to form a mobile unstructured film that condenses into liquid-like or amorphous clusters. These clusters slowly relax into a more compact and well-ordered lattice consisting of folded tetrameric units. Further growth of these crystalline clusters is limited by the rate at which the unstructured monomers undergo a cooperative transformation into tetramers, which occurs only at the edge-sites of existing 2D crystals. A simple model of domain growth through tetramer formation at edge sites predicts growth curves that give an excellent fit to experimental data, identifies surface coverage and the energy barrier to tetramer formation as the rate-determining parameters, and provides a rough estimate of that barrier. Dynamic Monte Carlo simulations of a simple model of associating S-layer proteins on a substrate show that a combination of strong, asymmetric binding and weak, uniform attractions can induce crystallization via amorphous intermediates. Our results suggest that non-specific attractions between S-layer monomers combined with site-specific binding are the key factors in the two-step crystallization we observe.Results on peptide and protein interactions with calcium oxalate monohydrate (COM) show that the mechanism through which crystal growth is altered depends strongly on the charge state of the crystal surface. When the interaction is strongly attractive, the overlap in timescales for step advancement and peptide adsorption leads to a sudden jump in growth rate accompanied by growth hysteresis. On surfaces where peptide binding should be unfavorable, the repulsion is apparently overcome by cluster formation. At high peptide concentrations, cluster density is high and growth is inhibited. But at low concentrations, peptides accelerate growth kinetics on these surfaces. A model in which the activation barrier for step propagation decreases with increasing peptide concentration but the clusters serve to block the steps provides a good fit to the data.
10:00 AM - UU4.2
Material Selectivity of Genetically Engineered Peptides for Inorganics.
Brandon R. Wilson 1 , Urartu O. S. Seker 1 , Candan Tamerler 1 , Mehmet Sarikaya 1
1 Materials Science and Engineering Department, University of Washington, Seattle, Washington, United States
Show AbstractThe GEPIs, genetically engineered peptides for inorganics, identified through combinatorial biology approaches, have the capability to bind to a wide variety of solid surfaces specifically and tightly. Material selectivity is the major and the critical trait of these peptides, especially for biosynthesis of inorganics, targeted immobilization of nanoparticles and self-assembly on multi-material micro-patterned surfaces. To quantitatively assess material-specificity of GEPIs, we investigated the binding kinetics of platinum-binding septapeptides, silica-binding dodecapeptides, and gold-binding 14 amino acid peptides using a modified surface plasmon resonance spectroscopy (SPR) on gold, platinum and silica surfaces. These peptides were selected by, either, cell surface-, phage- or flagellar-display approaches. All of the peptides were synthesized singly to investigate their binding kinetics and specific quantitative specific affinity of each of the substrate materials. The SPR spectroscopy, normally using gold surfaces, was modified to contain a thin (a few nm thick) film of the material of interest (silica or platinum) onto gold to allow SPR signal. The SPR experiments, carried out at different concentrations, resulted in Langmuir behavior allowing determination of the kinetic parameters, including adsorption, desorption, and equilibrium binding constants, for each of the solids, as well as free energy of adsorption. In general, peptides showed high affinity to the surface for which they were originally selected while displaying low affinity for other two materials. This included substantial material selectivity between the two noble metal surfaces by the platinum-binding and gold-binding peptides. The peptides were also post-selection engineered to contain multiple copies of the same original sequences to quantify the effects of repeating units, specifically 3-tandem repeats. In general, 3-repeat peptides displayed significantly different traits than the single-repeat peptides in their material selectivity. We attribute materials affinity of each of the tandem-repeat peptides versus single repeats to the molecular architectural changes between these two sets of peptides. The implications of the amino acid contents versus amino acid sequences of these GEPIs will be discussed versus their material affinity characteristics. These results, the first report on the quantitative material specificity of solid binding peptides, will form the basis of their future practical utility in a wide range of bionanotechnology applications. This project is supported by GEMSEC, an NSF-MRSEC at the University of Washington.
10:15 AM - UU4.3
Peptides on a Calcite Surface: A Molecular Dynamics Study.
Mingjun Yang 1 , Mark Rodger 2 , Harding John 3 , Susan Stipp 1
1 Nano-Science Center, Department of Chemistry, University of Copenhagen, Copenhagen Denmark, 2 Department of Chemistry, University of Warwick, Coventry United Kingdom, 3 Department of Engineering Materials, University of Sheffield, Sheffield United Kingdom
Show AbstractThe control of calcite biomineralization by peptides and proteins has attracted a lot of interest. Recent experiments have found that egg protein (ovocleidin-17) and some charged peptides are able to regulate the crystal growth of calcite. Charged amino acid groups strongly prefer to be on the exterior of peptides because of the high dielectric constant of water. Such groups play an important role in interactions with the calcite surface. Therefore the underlying mechanism is critical for the study of control of calcite biomineralization. In this study, a series of molecular dynamics simulations have been carried out to investigate interactions between peptides and the calcite surface in water. A 5 ns MD simulation was carried out for each model. During the MD simulation, the peptides were gradually adsorbed onto the calcite surface and the system reached equilibrium. The radial distribution function (RDF) gives the probability of finding an atom at a distance r from another atom. The RDF of pairs of atoms were calculated to compare the distance between peptides/water and the calcite surface. The results indicate that acidic amino acids can bind stronger with the calcite surface than either neutral or basic units, and acidic peptides are able to transport Ca2+ ions and facilitate calcite crystal growth.
10:30 AM - UU4.4
Designing Peptides for Chemsensing Using a Varied Gridcenter Docking Approach.
Zhifeng Kuang 1 , Rajesh Naik 1 , Barry Farmer 1
1 AFRL/RXBN, Air Force Research Laboratory, Wright-Patterson AFB, Ohio, United States
Show AbstractDocking methods have been used for screening libraries to identify peptides for specific binding to target analytes. However, existing docking methods often suffer from trapping in local energy minimum states. Here we describe a global searching approach called varied gridcenter docking to overcome this disadvantage. It is demonstrated that using this varied gridcenter docking approach may significantly improve the native binding prediction by taking statistical distribution into account. Using this approach, we studied the binding affinity of the honeybee antennal pheromone-binding protein (ASP1) and demonstrate that a peptide excised from the C-terminal end of ASP1 may bind to trinitrotoluene (TNT) by comparing with the binding affinity of phage displayed peptides.
10:45 AM - UU4.5
Surfaces and Biomaterials: A New Solid State NMR Approach.
Christian Bonhomme 1 , Florence Babonneau 1 , Dimitris Sakellariou 2 , Pedro Aguiar 2
1 , universite P et M Curie, Paris France, 2 , CEA Iramis, Saclay France
Show AbstractSolid state Nuclear Magnetic Resonance (NMR) – and its latest experimental, instrumental and theoretical developments – appears as a remarkable tool of investigation for hybrid materials and interfaces [1-2]. The characterization of interfaces involving minerals and organic / bioorganic molecules remains a huge technical challenge in terms of both selectivity and sensitivity. In this communication, the synthesis of bio-inspired materials will be presented, as well as new spectroscopic methods to attain the ultimate description of H-bond networks within the final hybrid materials [3]. The key characterization of the H-bond networks was based on advanced 1H double quantum dipolar recoupling techniques allowing for the detailed description of proton connectivities in the crystalline precursors, as well as in the amorphous final materials. The approach was successfully extended to Adenine (A) and Thymine (T) silylated derivatives. Homo-associations (A/A and T/T), as well as hetero-association (A/T), were clearly evidenced by high resolution 1H NMR [4]. As a matter of fact, the main drawback of NMR remains sensitivity, excluding the study of small amounts of matter (one hundred of micrograms). Recently, Sakellariou and coworkers [5] proposed the so-called MACS (Magic Angle Coil Spinning) technique, combining the fast rotation at the magic angle of the sample and of a micro-coil (located inside the main rotor). A gain of 10 in sensitivity (and 100 in time) was expected. In this communication, we show the first 1D and 2D 1H MACS NMR spectra of hybrid derivatives related to a single nanostructured film (TEOS/CTAB/PhenylSi(OEt)3), corresponding to roughly 100 micrograms of matter. The sensitivity is high, as "noiseless" spectra were obtained in less than 2 min. In our opinion, the NanoMACS approach should offer new perspectives for the description of biological moieties adsorbed on mineral surfaces.[1] C. Bonhomme et al. Accounts Chem. Res., 40 (2007) 738 [2] N. Baccile et al. Chem. Mater., 19 (2007) 1343 [3] G. Arrachart et al., Chem. Eur. J., 15 (2009) 5002 [4] G. Arrachart et al., J. Mater. Chem., 18 (2008) 392 [5] D. Sakellariou et al., Nature, 447 (2007) 694.
11:30 AM - **UU4.6
Employing Computational and Experimental Techniques to Study Adsorption at Liquid – Crystal Interfaces.
Andrzej Wierzbicki 1 , S. Qiu 2 , J. De Yoreo 3
1 Department of Chemistry, University of South Alabama, Mobile, Alabama, United States, 2 , Lawrence Livermore National Laboratory, Livermore, California, United States, 3 , Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show Abstract The recent rapid progress in experimental techniques has greatly increased our ability to study crystal growth at interfaces. At the same time, however, it has opened a vast array of new questions related to the molecular-level mechanisms governing interfacial phenomena. Consequently, computational chemistry methods have been employed to provide molecular-level insights into these mechanisms. Due to great complexity of interfacial systems, computational methods must be closely complemented by experiment to aid the molecular-level interfacial studies. We will discuss the application of combined computational and experimental techniques, which were successfully employed to study the interfacial crystal growth in several important biomineralization systems involving crystallization of: calcite, hydroxyapatite, calcium oxalate monohydrate, and calcium pyrophosphate dihydrate. A similar approach, which was employed to study subtle structure-function relationships in the molecular-level mechanism of interfacial adsorption of antifreeze proteins will also be presented.
12:00 PM - UU4.7
Binding, Molecular Recognition, and Supramolecular Assembly of Solid Binding Peptides on Solid Substrates: a Multi-Scale Perspective.
Christopher So 1 , John Kulp 2 3 , Hakim Meskine 4 , Paul Mulheran 4 , Ersin Oren 1 , Candan Tamerler 1 5 , John Evans 3 , Mehmet Sarikaya 1
1 Genetically Engineered Materials Science and Engineering Center, MSE, University of Washington, Seattle, Washington, United States, 2 , Naval Research Laboratory, Washington, District of Columbia, United States, 3 Laboratory for Chemical Physics, New York University, New York, New York, United States, 4 Chemical Engineering, University of Strathclyde, Glasgow United Kingdom, 5 Molecular Biology and Genetics, Istanbul Technical University, Istanbul Turkey
Show AbstractThe understanding of biomineralization and realization of biology-inspired materials technologies depends on understanding the nature of the chemical and physical interactions between proteins and biominerals or synthetically made inorganic materials. Recently, combinatorial genetic techniques permit the isolation of peptides recognizing specific inorganic materials that are used as molecular building blocks for novel applications. Little is known about the molecular structure of these peptides and the specific recognition mechanisms onto their counterpart inorganic surfaces. Here, we combine high-resolution atomic force microscopy (AFM) and nuclear magnetic resonance (NMR) experiments with both atomistic and molecular-scale simulation methods to understand the binding, molecular recognition and supramolecular self-assembly of a genetically engineered gold binding peptide, 3rGBP1 ([MHGKTQATSGTIQS]3), and its correlation with the symmetry of the Au{111} surface lattice. Using simulated annealing molecular dynamics (SA/MD) studies based on nuclear magnetic resonance (NMR), we confirmed the intrinsic disorder of 3rGBP1 and identified putative Au docking sites where surface-exposed side chains align with both the <110> and <211> Miller indices of the Au lattice. Further, we combine ex situ time-lapsed AFM results with an ad hoc Kinetic Monte Carlo (KMC) coarse-grained modeling approach to describe the observed spatial nucleation and growth mechanisms of a Gold Binding Peptide-1 (3rGBP1) onto an Au(111) surface. The evolution of structures observed on AFM are explained and correlated to KMC modeling based on molecular epitaxy theory with considerations for both monomer and size-dependent cluster mobilities. Our results provide fundamental insight for a multi-scale understanding of peptide/solid interfaces and the intrinsic disorder that is inherent in some of these peptide sequences. Analogous to the well-established atomically controlled thin-film heterostructure formation on semiconductor substrates, the basis of today’s microelectronics, the fundamental observations of peptide-solid interactions here may well form the basis of peptide-based hybrid molecular technologies of the future. The research was supported by Genetically Engineered Materials Science and Engineering Center (GEMSEC), an NSF-MRSEC, and an NSF-BioMat grant at the UW.
12:15 PM - UU4.8
Modelling Binding Affinity at Peptide-surface Interfaces: the Role of Intra-peptide Interactions.
Tiff Walsh 1
1 , University of Warwick, Coventry United Kingdom
Show AbstractConsiderable experimental advances are being made in the study of the binding of peptides to inorganic surfaces, both in terms of binding affinity and specificity. Modelling and simulation are useful tools that are complementary to several experimental characterization techniques for such peptide-inorganic systems. Many challenges in molecular simulation must be overcome in order for progress in this area to match the advances made by experiment. In this contribution, we discuss some of these challenges, with particular reference to our work on titania, quartz, and carbon nanotube systems. Specifically, we will outline how targeted mutations and/or sequence scrambling can disrupt intra-peptide interactions, to reveal the importance of the interplay between sequence, 3D structure, and ultimately, the binding properties of peptides at these interfaces. We will also flag up the importance (or not) of the role that water structuring plays in mediating peptide-surface binding, with reference to our calculations of the free energy of binding for selected amino-acid analogs.
12:30 PM - UU4.9
Bioinformatics-Based Design of Multifunctional Solid-Binding Peptides.
Ersin Emre Oren 1 2 , Ram Samudrala 2 , John Spencer Evans 3 , Candan Tamerler 1 4 , Mehmet Sarikaya 1
1 Genetically Engineered Materials Science and Engineering Center, Materials Science and Engineering Department, University of Washington, Seattle, Washington, United States, 2 Computational Genomics Group, Department of Microbiology, University of Washington, Seattle, Washington, United States, 3 Laboratory for Chemical Physics, New York University, New York, New York, United States, 4 Molecular Biology and Genetics, Istanbul Technical University, Istanbul Turkey
Show AbstractProteins control nucleation, growth, morphology, crystallography, and spatial organization of inorganic materials and provide molecular scaffolds in the formation of hard tissues with complex and highly functional architectures. In an emerging field we call molecular biomimetics, recent adaptation of combinatorial biological techniques provides ways to genetically select peptides (GEPI: genetically engineered proteins for inorganics) with affinities to a variety of materials leading to their utility as molecular building blocks in synthesis, nanostructural organization, and directed assembly. The understanding of the relationships between the solid-binding peptide sequences and their binding affinities or specificities enables further design of novel peptides with selected properties of interest both in engineering and medicine. We developed a bioinformatics approach that permits us to generate novel material-specific scoring matrices by optimizing the similarities within the strong-binding peptide sequences and the differences between the strong- and weak-binding peptides. With the scoring matrices thus generated, we design novel peptides with specific affinities and multiple functionalities (e.g., peptides capable of binding to material A or B, both or neither). The multifunctional peptides have utility in developing surface engineering of solids including metals (e.g., Au) and oxides (e.g., silica), combining several nanomaterials, nanoparticles or nanowires, or molecular erectors when conjugated to other proteins, enzymes, DNA or to each other via a linker, as we demonstrate in this presentation. To control the spatial organization between attached nanoentities, we also design unique linkers. These computationally-designed linkers between two GEPIs have different lengths and no binding affinity to either of the material on each side, e.g., gold and silica. We predict, first, the structure of the bifunctional construct to show that the solid binding peptides are intact and spaced correctly; and then we synthesize and experimentally validate their bi-functionality by assembling, e.g., Au and silica, nanoparticles on alternate substrates. The approach has a great potential as heterofunctional material-specific molecular building blocks. This project is supported by GEMSEC (all), and NSF-MRSEC at the University of Washington, NSF-BioMat (EEO, JSE, CT, MS), NSF CAREER Award (RS), and SPO/Turkey (CT).
UU5: Nucleation, Growth and Aggregation
Session Chairs
John Harding
Robert Latour
Wednesday PM, December 02, 2009
Room 205 (Hynes)
2:30 PM - **UU5.1
Methods for Simulating Crystal Nucleation and Biomineralization.
P.Mark Rodger 1 2 , David Quigley 2 3 , John Harding 4 , Colin Freeman 4
1 Chemistry, University of Warwick, Coventry United Kingdom, 2 Centre for Scientific Computing, University of Warwick, Coventry United Kingdom, 3 Physics, University of Warwick, Coventry United Kingdom, 4 Materials Engineering, University of Sheffield, Sheffield United Kingdom
Show AbstractThe use of biomolecules in nature to direct the path of crystal growth leads to a degree of polymorph and morphology control that far surpasses anything that can currently be effected in a laboratory. Important and topical examples include the intricate nano- and micro-crystalline structures found in mollusc shells, coccoliths and avian eggshells. An ability to model the onset of crystal formation at a molecular level would considerably enhance our ability to understand, and potentially to mimic, how such exquisite control of crystal form is brought about; unfortunately, the timescales on which crystal nucleation occurs is much longer than the timescales accessible to standard molecular simulation methods. However, a number of recent developments in molecular simulation methods have begun to change this, so that routine, direct molecular simulations of the critical stages of crystal nucleation are becoming feasible for many systems. In this talk we will show how the “metadynamics” method can be adapted to simulate the onset of crystal formation with statistical reliability, to extract rigorous thermodynamic information about the nucleation process and to characterise how chemical additives can modify the nucleation and subsequent growth. Several examples of applications of the method will be given, including spontaneous formation of ice in constant pressure simulations, crystal formation from amorphous calcium carbonate, and the role of ovocleidin-17 (a protein found in the chicken eggshell) in the eggshell formation.
3:00 PM - UU5.2
A New Perspective on the Concentration Dependence of Ice-binding Proteins.
Yeliz Celik 1 , Natalya Pertaya 1 , Yangzhong Qin 1 , Peter Davies 2 , Ido Braslavsky 1
1 Physics and Astronomy, Ohio University, Athens, Ohio, United States, 2 Biochemistry, Queen's University, Kingston, Ontario, Canada
Show AbstractIce-binding proteins, IBPs, include those that have the ability to stop ice crystal growth and inhibit ice recrystallization. IBPs can be low, moderate or hyperactive according to their thermal hysteresis activity, which is defined as the amount of non-colligative freezing point depression. Inhibition of recrystallization and ice growth by IBPs suggest potential applications of these proteins in preventing frost damage to plants and in cryo-preservation of food and organs. We have developed microfluidic devices in which the solution around small ice crystals can be exchanged in a temperature-controlled environment. The experiments we performed with the novel microfluidic devices clearly showed that ice crystals were highly stabilized by bound hyperactive IBP even if the solution IBP concentration was reduced. Thus we found that thermal hysteresis is not a direct function of the concentration in the solution at the time of the measurement. Additionally, we used fluorescently tagged IBPs to demonstrate that IBPs stay on ice crystals even after the protein concentration in the solution is reduced. These results imply that adsorption to the ice surface of these proteins is irreversible and the concentration dependence of the activity is time dependent. The techniques we have developed to investigate IBPs such as fluorescently tagged IBPs combined with microfluidics can improve the understanding of how IBPs influence ice growth. We suggest that hyperactive IBPs hold great promise for cryobiology and an understanding of their function is essential for their effective usage. --------------------------------- Supported by the National Science Foundation (NSF) under Grant No. CHE-0848081 (co-funded by the MPS/CHE and the Molecular and Cellular Biosciences Divisions, and by the Office of International Science and Engineering and the Office of Polar Programs) and by Canadian Institutes for Health Research (CIHR) and by the Biomemetic Nanosciences and Nanosacle Technology (BNNT) at Ohio University.
3:15 PM - UU5.3
Molecular Simulation as a Tool to Study Interfacial Interactions at the Atomic Level.
Robert Latour 1
1 , Clemson University, Clemson, South Carolina, United States
Show AbstractAs biotechnology continues to transition from the nano- to the atomic-scale of resolution for materials design, there is increasing need for all-atom molecular simulation methods that are specifically developed for the accurate simulation of the interactions between biomolecules and synthetic materials surfaces. The uniqueness of these types of molecular interactions requires that existing methods that have been developed for other applications cannot simply be borrowed and applied, but rather methods must be specifically developed, evaluated, and validated for this application. In this talk I will present our combined experimental and computational efforts for the development of all-atom molecular simulation methods to accurately represent protein-surface interactions for a broad range of surface chemistries. In particular, we are working to develop methods for force field evaluation and validation for protein-surface interactions, program development to enable multiple force fields to be used in the same simulation to accurately control the behavior of the solution phase, solid phase, and interphase in a multiphase system, and the development of efficient accelerated sampling methods for large molecular systems. Once developed, these types of methods have the potential to serve as a valuable tool to study, understand, and control interfacial processes at the atomic level.
3:30 PM - UU5.4
Synthesis and Characterization of Peptidomimetic Self-Assembled Biodegradable Nanoparticles.
Angel Mercado 1 , Esmaiel Jabbari 1
1 Chemical Engineering, University of South Carolina, Columbia, South Carolina, United States
Show AbstractShort sequences of amino acids are especially attractive for self-assembly because nanostructures with varying size, shape, morphology, and surface functional groups can be assembled by arranging the naturally accruing amino acids in different sequences or by changing the sequence length. Peptidomimetic self-assembled structures can potentially possess biological recognition motifs as well as desired engineering properties such as degradability and sustained release characteristics. The objective of this work was to investigate self-assembly, degradation, and Paclitaxel release characteristics of poly(lactide fumarate) (PLAF) conjugated to CV6K2 peptide. PLAF was synthesized by condensation polymerization of ULMW PLA with fumaryl chloride (FC). Amphiphilic poly(lactide-co-ethylene oxide fumarate) (PLEOF) was synthesized by condensation polymerization of ULMW PLA and polyethylene glycol (PEG) with FC. The CV6K2 peptide was synthesized manually on Rink Amide NovaGel resin in the solid phase. CV6K2 peptide was conjugated to PLAF macromer by the reaction between the sulfhydryl group of cystine with fumarate group of PLAF. PLAF-CV6K2 (with or without Paclitaxel) in DMF/DMSO solvent mixture was self-assembled into NPs by dialysis against PBS buffer. Degradation of the NPs was followed by measuring their particle size and mass loss as a function of incubation time. For determination of release characteristics, at each time point, NPs suspension was centrifuged, supernatant was removed, and Paclitaxel content was analyzed by HPLC.The size distribution of CV6K2, PLAF-PLEOF, CV6K2-PLAF, and mutant C(V2K)2V2-PLAF NPs was compared. CV6K2 peptides self-assembled into NPs with 70 nm average size and narrow distribution of 30-110 nm. PLAF macromer alone did not produce particles but blends of PLAF and PLEOF macromers produced NPs with 300 nm average size and relatively wide distribution of 160-430 nm. Interestingly, when CV6K2 was conjugated to PLAF and self-assembled in the absence of PLEOF, NPs with 110 nm average size and relatively narrow distribution of 50-170 nm were produced. Furthermore, When a mutant C(V2K)2V2 peptide (a peptide sequence with the same composition as CV6K2 that does not self-assemble into NPs) was conjugated to PLAF, the conjugate self-assembled into NPs with average and distribution similar to PLAF-PLEOF blend. These results demonstrate that the CV6K2 peptide induced self-assembly when conjugated to a non self-assembling PLAF macromer. The release characteristic of Paclitaxel from PLAF-CV6K2 NPs was measured. There was approximately 20% burst release in the first 2 h followed by a sustained linear release for up to 4 weeks, concurrent with erosion/degradation of NPs. Paclitaxel was linearly released from the self-assembled PLAF-CV6K2 conjugate concurrent with the erosion of the NPs. Peptidomimetic PLAF-CV6K2 conjugate is potentially useful for targeted delivery of chemotherapeutic agents in cancer therapy.
3:45 PM - UU5.5
Hierarchical Pattern of Microfibrils in a 3D Fluorapatite–gelatine Nanocomposite: Simulation of a Bio-related Structure Building Process.
Juergen Brickmann 1 , Raffaella Paparcone 1 , Simon Kokolakis 1 , Ruediger Kniep 2 , Paul Simon 2 , Patrick Duchstein 2 , Dirk Zahn 2
1 Department of Chemistry, Darmstadt University of Technology, Darmstadt Germany, 2 , Max-Plack-Instutute for Chemical Physics of Solids, Dresden Germany
Show AbstractThe shape development of a biomimetic fluorapatite–gelatine nanocomposite on the micrometer scale is characterised by a fractal mechanism with the origin being intrinsically coded in a (central) elongated hexagonal-prismatic seed. The 3D superstructure of the seed is distinctively overlaid by a pattern consisting of gelatine microfibrils. The orientation of the microfibrils is assumed to be controlled by an intrinsic electrical field generated by the nanocomposite during development and growth of the seed [1,2]. In order to confirm this assumption and to get more detailed information on orientational relations of the complex nanocomposite we simulated the pattern formation process up to the micrometer scale. The results from experimental studies and simulation results on an atomistic level support a model scenario [3] wherein the elementary building blocks for the aggregation are represented by elongated hexagonal-prismatic objects (A-units), with the embedded collagen triple-helices in their centers. The interactions of the A-units are consequently modelled by three contributions: the crystal energy part (originating from the pair-wise interactions of the ‘‘apatite shells’’ of the prismatic units), the electrostatic interaction (originating from the unit charges located at the ends of the collagen triple helices), and the interaction energy of the A-units mediated by the solvent. The next level of complexity is related to the fact that micro fibrils are additionally present in the fluorapatite–gelatine nanocomposites. They consist of bundles of triple helical protein molecules, which are embedded within the 3D-hexagonal prismatic arrangement of the A-units. In our approach we consider the microfibrils as chains of flexible dipoles with effective dipole moments. The hierarchical growth processes are modelled as an energetically controlled stepwise association of elementary building blocks of different kind on a 3D-grid. The remarkable and excellent qualitative agreement between the simulated fibril patterns and the experimental observations made by SEM and TEM support the concept of an intrinsic electric field driven morphogenesis of the fluorapatite–gelatine nanocomposite. The simulated fibril pattern also bears the chance to make fresh attempts in order to find explanations for a number of experimental observations which are not fully understood up to now. References[1] P. Simon, D. Zahn, H. Lichte and R. Kniep, Angew. Chem. Int. Ed., 2006, 45, 1911–1915.[2] A. Kawska, O. Hochrein, J. Brickmann, R. Kniep and D. Zahn, Angew. Chem. Int. Ed., 2008, 47, 4982–4985.[3] R. Paparcone, R. Kniep and J.Brickmann, Phys.Chem.Chem.Phys., 2009, 11, 2186-2194
4:30 PM - **UU5.6
De novo Computational Design of Peptide-calcite Biomineralization Systems.
David Masica 2 , Elizabeth Specht 1 , Sarah Schrier 1 , Jeffrey Gray 1 2 3
2 Program in Molecular Biophysics, Johns Hopkins University, Baltimore, Maryland, United States, 1 Chemical & Biomolecular Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 3 Institute for NanoBioTechnology, Johns Hopkins University, Baltimore, Maryland, United States
Show AbstractMany organisms produce complex, hierarchically structured, inorganic materials via protein-influenced crystal growth—a process known as biomineralization. Understanding this process would shed light on hard-tissue formation and guide efforts to develop biomaterials. We created and tested a computational method to design protein-biomineralization systems. The algorithm folds a protein from a fully extended structure and simultaneously optimizes the fold, orientation, and sequence of the protein adsorbed to a crystal surface. We used the algorithm to design peptides (16 residues) to modify calcite (CaC03) crystallization. We chemically synthesized six peptides that were predicted to bind different states of the {001} growth plane of calcite. All six peptides dramatically affected calcite crystal growth (as observed by scanning electron microscopy), and the effects were dependent on the targeted state of the {001} growth plane. Additionally, we synthesized and assayed scrambled variants of all six designer peptides to distinguish cases where sequence composition determines the interactions versus cases where sequence order (and presumably structure) plays a role. Scrambled variants of negatively charged peptides also had dramatic effects on calcite crystallization; conversely, scrambled variants of positively charged peptides had a variable effect on crystallization, ranging from dramatic to mild. Special emphasis is often placed on acidic protein residues in calcified tissue mineralization; the work presented here suggests an important role for basic residues as well. In particular, this work implicates a potential role for basic residues in sequence-order specificity in peptide-mineral interactions.
5:00 PM - UU5.7
Synthesis and Application of Biomimetic Bridged-Nanocrystals as a Mesocrystal.
Yuya Oaki 1 , Hiroaki Imai 1
1 Department of Applied Chemistry, Keio University, Yokohama Japan
Show AbstractBiominerals have inspired researchers to develop new functional materials through mild condition routes. We can obtain ideas from the structures and formation processes of biological architectures. Recently, mesoscale structures consisting of nanocrystals with organic molecules have attracted much attention in both biominerals and biomimetic materials. Our next target is to develop a functional material based on the nature of mesocrystals. In this presentation, we report our recent findings of the bridged nanocrystals, as a mesocrystal. We have studied the mesoscale structures and their applications in biominerals and the mimetic materials.The mesocrystal of the bridged nanocrystals has been found in the hierarchical structures of carbonate-based biominerals, such as nacreous layer and sea urchin spine. The layered and porous morphologies consist of aragonite and calcite nanocrystals 20–100 nm in size, respectively. Our observations implied that the nanocrystals form the oriented structures with biological macromolecules through the sequential crystal growth including inhibition and restart. The bridges between each nanocrystal play an important role for the formation of the oriented nanocrystals. We have prepared the hierarchical architectures based on the bridged-type mesocrystals. As observed in biomineralization, the presence of organic polymers facilitates the generation of hierarchically organized materials consisting of the bridged nanocrystals. We have applied the methods to synthesize functional metal oxide nanostructures. The mesocrystal structures of manganese oxides and cobalt hydroxides were formed through the crystal growth in the presence of the organic polymers. The approach can be widely applied to prepare other functional materials through biomimetic approaches. In another application, the nanospace in the mesocrystal structures can be used for a host material of small organic molecules. The dye molecules were homogeneously introduced in the bridged nanocrystals in biominerals and their mimetic structures. The photochromic and photochemical reactions also proceeded in the nanoscopic space with the irradiation of UV light. The nanoscopic space in the mesocrystals can be regarded as a new type of host material.
5:15 PM - UU5.8
Nanostructured Calcium Phosphate/organic Composites for Dental Restorative Applications.
Hiroaki Sai 1 , Christopher Sarra-Kopowski 2 , Priyam Sarma 1 , Miki Kunitake 1 , Deng Wen (Debra) Lin 1 , Shefford Baker 1 , Ulrich Wiesner 1 , Lara Estroff 1
1 Department of Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 2 Macromolecular Science and Engineering Center, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractCalcium phosphate-organic composites with a 3D-continuous inorganic nanostructure can provide improvements to the current dental composite fillers by reducing the volume shrinkage upon the curing of the organic phase and by enhancing the mechanical properties. Here we provide a route to continuous nanoporous hydroxyapatite scaffolds prepared by vacuum-assisted infiltration of calcium phosphate nanoparticles into colloidal assemblies of polystyrene microspheres, which can be backfilled with photocrosslinkable monomers. We show that the surface functionalities on the polystyrene nanospheres affect the crystallinity of the resulting scaffold, and investigate the mechanical properties of such materials by nanoindentation experiments.
5:30 PM - UU5.9
Synthesis of Hydroxyapatite on Block Co-polypeptide and Peptide Conjugated Copolymers.
Mufit Akinc 1 4 , Yusuf Yusufoglu 1 4 , Yanyan Hu 2 4 , Mathumai Kanapathipillai 3 4 , Klaus Schmidt-Rohr 2 4 , Surya Mallapragada 3 4
1 Materials Sci. & Eng., Iowa State University, Ames, Iowa, United States, 4 Ames Laboratory, Iowa State University, Ames, Iowa, United States, 2 Chemistry, Iowa State University, Ames, Iowa, United States, 3 Chemical and Biological Engineering, Iowa State University, Ames, Iowa, United States
Show AbstractTemplated growth of hydroxyapatite (HAp) was investigated on Pluronic® based pentablock peptide-conjugated polymer and diblock co-polypeptide polymer gels from aqueous solutions. The polymers used in this study thermoreversibly gel at or above room temperature. Hydroxyapatite nanoparticles were formed at the polymer-aqueous interface presumably nucleated by the ionic interactions. Nanocomposites were characterized by TGA, FTIR, NMR, TEM, and X-ray scattering techniques. Inorganic content of the nanocomposite depends on the critical gelling concentration of the template polymer and the nature of the interaction between polymer and calcium ions. FTIR spectra of calcium phosphate nanocomposite showed characteristic features of organic matrix, phosphate. Hydroxyapatite was shown to grow in the form of thin, elongated crystallites as evidenced by electron microscopy and small angle X-ray scattering techniques. This work offers routes for bioinspired bottom-up approach for the development of novel nanocomposites.Acknowledgment: This work was supported by the U.S. Department of Energy through Ames Laboratory. Ames Laboratory is operated through the U.S. Department of Energy by Iowa State University under contract number DE-AC02-07CH11358.
5:45 PM - UU5.10
Sequence-Dependent Shape Control of Gold Nanoparticles Using DNA.
Zidong Wang 1 3 , Yi Lu 1 2 3
1 Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 3 Beckman Institute for Advanced Science and Technology , University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractShape control of nanomaterials is an active and important area of research as nanomaterials of different shapes, such as nanorods, prisms and cubes, exhibit unique properties for selective catalysis, sensitive sensing and enhanced imaging. To control the shapes, molecular capping agents play a critical role and among them, organic surfactants and polymers are the most commonly used so far. Despite tremendous progresses made, the mechanism of the shape control is not well understood, in part due to the difficulty in defining structures and conformations of these surfactants and polymers in solution and in systematic variation of functional groups. DNA is a well known biopolymer with more defined structure and conformation in solution and unique programmable nature to tune its functional properties. We demonstrate for the first time that DNA can be used to tune metal nanoparticle morphology in a sequence dependent manner. Poly A or poly C induced the formation the flower shaped gold nanoparticle, while poly T gave spherical nanoparticle. Mechanism of sequence dependent shape control from spherical to flower-like nanoparticle is also elucidated. Furthermore, DNA functionalization was realized in-situ during the one-step synthesis while retaining their bio-recognition ability, allowing programmable assembly of new nanostructures. These particles could find wide applications in fields such as bio-inspired nano-assembly, biosensing, and imaging.