Symposium Organizers
John H. Harding University of Sheffield
James A. Elliott University of Cambridge
John S. Evans New York University
Y1: The Organic/Mineral Interface
Session Chairs
James Elliott
John Harding
Monday PM, December 01, 2008
Berkeley A/B (Sheraton)
9:30 AM - **Y1.1
Biomineral Formation: Spectromicroscopy Experiments and Theoretical Simulations.
Pupa Gilbert 1 , Rebecca Metzler 1 , Susan Coppersmith 1 , John Evans 2 , Fred Wilt 3 , Elia Beniash 4 , Peter Rez 5 , Yael Politi 6 , Yurong Ma 6 , Steve Weiner 6 , Lia Addadi 6
1 Physics, University of Wisconsin, Madison, Wisconsin, United States, 2 , NYU, New York, New York, United States, 3 , UC, Berkeley, California, United States, 4 , UPitt, Pittsburg, Pennsylvania, United States, 5 , ASU, Tempe, Arizona, United States, 6 , Weizmann Institute of Science, Rehovot Israel
Show AbstractSynchrotron spectromicroscopy is an experimental method only recently introduced into the study of biominerals. As it detects both the organic and mineral components, the bonds at their interface, as well as crystal orientation at the nano-scale, it has great potential for revealing biomineralization mechanisms. We will discuss the interplay of theoretical modeling and spectromicroscopy results in amorphous-to-crystalline transitions in sea urchin spicules and forming enamel, nano-crystal assembly in nacre and sea urchin tooth, and bonding at the organic-mineral templating interface.
10:00 AM - Y1.2
Formation of Calcium Carbonate Crystal on DPPC Monolayer.
Tapanendu Kamilya 1 , Prabir Pal 1 , Mrityunjoy Mahato 1 , Gautam Talapatra 1
1 Spectroscopy, Indian Association for the Cultivation of Science, Kolkata India
Show Abstract10:15 AM - Y1.3
Molecular Dynamics Simulations of Organic-Acid Adsorption on Calcite.
Donald Mkhonto 1 , Nita Sahai 1 2
1 Geology and Geophysics, University of Wisconsin, Madison, Wisconsin, United States, 2 Department of Chemistry, University of Wisconsin, Madison, Wisconsin, United States
Show Abstract10:30 AM - Y1.4
Possible Fuction of the Pinctada Fucata Nacre Protein n16.
Rebecca Metzler 1 , John Evans 2 , Christopher Killian 3 , Mike Abrecht 4 , Susan Coppersmith 1 , Pupa Gilbert 1
1 Physics, University of Wisconsin at Madison, Madison, Wisconsin, United States, 2 Center for Biomolecular Materials Spectroscopy, Laboratory for Chemical Physics, New York University, New York, New York, United States, 3 Molecular and Cell Biology, University of California- Berkeley, Berkeley, California, United States, 4 , Synchrotron Radiation Center, Stoughton, Wisconsin, United States
Show AbstractWe analyzed the morphology and chemical composition of CaCO3 crystals grown from solution in the presence of n16N, a 30-amino acid synthetic peptide sequenced after the mineral binding portion of the nacre protein n16 from Pinctada fucata.Using X-ray absorption near edge (XANES) spectromicroscopy, x-ray photoelectron emission spectromicroscopy (X-PEEM), and scanning electron microscopy (SEM), we revealed that n16N induces the nucleation of aragonite as well as calcite.We also revealed that the peptides self-assemble into regularly spaced parallel layers.The crystals grow between and across these layers, and exhibit multiple orientations. The crystal habit obtained in the presence of n16N is also dramatically different from the rhombohedra of control crystals.
10:45 AM - Y1.5
Ab Initio Studies of Calcite-water Interactions.
Dorothy Duffy 1 , Jennifer Lardge 1 , Mike Gillan 1
1 London Centre for Nanotechnology, UCL , London United Kingdom
Show AbstractLiving organisms exhibit remarkable control over the structure and shape of inorganic crystals and this biomineralisation process is controlled by interactions between organic molecules and mineral surfaces. However, water must be displaced before molecules can be adsorbed on mineral surfaces, therefore understanding water-mineral interactions is fundamental to understanding biomineralisation processes. In this study we focus on calcite, which is a common biomineral. Experimental studies have detected hydroxide and bicarbonate ions on wet calcite surfaces [1], leading to the conclusion that water molecules dissociate on calcite. Previous ab initio calculations have, however, indicated that dissociated water is unstable [2]. We have carried out a comprehensive series of density functional theory (DFT) calculations of water molecules on (10.4) calcite surfaces, for a range of coverage. We have calculated a binding energy for isolated water molecules of 0.9 eV and we have found a metastable dissociated water configuration which is 1.8 eV higher in energy than the corresponding associated water configuration. Increasing the water coverage did not stabilize the dissociated configuration. Molecular dynamics simulations at a range of temperatures demonstrated that water molecules desorbed from the surface within 2 ps at temperatures of 1200K and above. DFT calculations were also performed for defective (10.4) calcite surfaces. Water molecules were found to spontaneously dissociate at carbonate vacancies and the binding energy of the dissociated molecule was found to be 2.9 eV. Water molecules were found to bind much more strongly to acute steps (binding energy 2.3 eV) than obtuse steps (binding energy 1.0 eV). MD simulations revealed spontaneous water dissociation at acute steps, but not at obtuse steps. Thus we assert that the observed experimental effects are due to defects, such as carbonate vacancies and acute surface steps.1.S L S Stipp, Mol. Sim., 28, 497 (2002)2.S Kerisit, S C Parker and J H Harding, J. Phys. Chem. B 107, 7676 (2003)
11:30 AM - **Y1.6
Density Functional Theory Calculations and Molecular Dynamics Simulations of the Interaction of Bio-molecules with Surfaces of Hydroxyapatite in an Aqueous Environment.
Nora de Leeuw 1 2 , Neyvis Almora Barrios 1
1 Chemistry, University College London, London United Kingdom, 2 Institute of Orthopaedics & Musculoskeletal Science, University College London, London United Kingdom
Show AbstractHydroxyapatite is the mineral phase of mammalian bone and tooth enamel which is an organic/inorganic composite, comprising the collagen I protein as the organic phase. Due to its importance in the natural bone tissue, hydroxyapatite is also used as a synthetic biomaterial, for example in hydroxyapatite/glass and hydroxyapatite/polymer composites, and insight at the molecular level into the processes occurring at the interface between hydroxyapatite and bio-molecules is important to gain understanding of the nucleation and growth of the composite material, as well as its interaction with proteins and other soft tissue molecules. The knowledge gained will aid the better design of composite materials for bio-medical applications. We first present Molecular Dynamics simulations of the adsorption of citric acid molecule to the (0001) and (01-10) surfaces of hydroxyapatite, which is known to both inhibit the growth of hydroxyapatite crystal as well as assist the dissolution of tooth enamel. We compare adsorption both in vacuo and in an aqueous environment, which is added through the explicit introduction of water molecules in the simulation cell. The calculated average adsorption energies in aqueous solution are +291.4 kJ/mol and -17.4 kJ/mol for the (0001) and (01-10) surfaces respectively. Citric acid thus adsorbs to the (01-10) surface and hence would inhibit growth of this surface more effectively than growth of the (0001) plane with which it does not interact strongly in an aqueous environment, where the water competes with the citric acid for adsorption. The implication is that in the presence of citric acid the hydroxyapatite crystal grows more rapidly in the [0001] direction than in the [01-10] direction, leading to elongation in the c-direction and more pronounced expression of the (01-10) surface in the hydroxyapatite morphology.In view of the composite nature of the natural bone material, we next present the results of a series of DFT calculations of the interaction of the same hydroxyapatite surfaces with the constituent amino acids of the collagen matrix, namely glycine, proline and hydroxy-proline. The calculations show that the amino acids are capable of forming multiple interactions with surface species, particularly if they can bridge between two surface calcium ions. All three amino acids should be good sites for the nucleation and growth of the hydroxyapatite surface at the collagen matrix. The results of the DFT calculations are used to obtain relevant interatomic potential parameters for the organic/mineral interface, and we finally present preliminary MD simulations of the interaction of a complete collagen strand with the (0001) and (01-10) surfaces of hydroxyapatite in an aqueous environment.
12:00 PM - Y1.7
Probing the Organic-Mineral Interface at the Molecular Level in Model Biominerals.
Rebecca Metzler 1 , Il Won Kim 2 , Katya Delak 2 , John Evans 2 , Dong Zhou 1 , Elia Beniash 3 , Fred Wilt 4 , Christopher Killian 4 , Mike Abrecht 5 , Jinghua Guo 6 , Susan Coppersmith 1 , Pupa Gilbert 1
1 Physics, University of Wisconsin at Madison, Madison, Wisconsin, United States, 2 Center for Biomolecular Materials Spectroscopy, Laboratory for Chemical Physics, New York University, New York, New York, United States, 3 Biomineralization, The Forsyth Institute, Boston, Massachusetts, United States, 4 Molecular and Cell Biology, University of California- Berkeley, Berkeley, California, United States, 5 , Synchrotron Radiation Center, Stoughton, Wisconsin, United States, 6 , Advanced Light Source, Berkeley, California, United States
Show AbstractProteins control nucleation and growth of inorganic materials during the process of biomineralization. Many proteins from the nacre and prismatic layers of mollusk shells have been identified and sequenced. However, the molecular interaction, organization, and rearrangements of proteins upon interaction with inorganic solids during biomineralization and the effect of this interaction on crystal formation, deformation, and orientation are poorly understood. The organic-mineral interface (OMI) is expected to be the site for these phenomena, and is therefore extremely interesting to investigate. To examine the OMI in biominerals, we prepared model systems consisting of calcium carbonate crystals grown in the presence of model biomineral polypeptides. We probe the OMI within these model systems with a combination of X-ray absorption near edge (XANES) spectromicroscopy, x-ray photoelectron emission spectromicroscopy (X-PEEM), and scanning electron microscopy (SEM). XANES was used to investigate the electronic structure of both the calcium carbonate mineral crystals and the polypeptides, and was found to detect changing bonds at the OMI in crystals grown in the presence of polypeptides. We acquired XANES spectra from calcium carbonate crystals grown in the presence of synthetic polypeptides sequenced after mollusk nacre proteins, or a biomineral protein. The polypeptides are: AP7N, AP24N, and n16N, the protein is LSM34 from sea urchin spicule matrix. All these model biominerals gave similar results, including the disruption of CO bonds in calcite and enhancement of the peaks associated with C-H bonds bonds in peptides, indicating ordering of the amino acid side chains upon mineral binding. We also show that these changes do not occur when Asp and Glu are replaced in the n16N sequence with Asn and Gln, respectively, demonstrating that carboxyl groups in Asp and Glu do participate in organic-mineral interaction at the molecular level (1).1. Metzler et al. Langmuir 24, 2680-2687 (2008).
12:15 PM - Y1.8
Energetics of Vacancies and Protons in Hydroxyapatite from First Principles.
Katsuyuki Matsunaga 1
1 Dept. of Materials Science and Engineering, Kyoto University, Kyoto Japan
Show AbstractHydroxyapatite (HAp) tends to have a Ca-deficient nonstoichiometric chemical composition, depending on the surrounding chemical environments. The nonstoichiometry is closely related to chemical stability and bioactivity of HAp minerals in human bodies. In order to address the origin of the nonstoichiometry, first-principles plane wave based calculations are performed for intrinsic ionic vacancies and protons in HAp. From total energies of HAp supercells, defect formation energies and equilibrium concentrations are evaluated, under assumption of chemical equilibrium between HAp and aqueous solution saturated with respect to HAp. It is found that protons at interstitial sites and substituting for Ca are stably formed, as compared to calcium and phosphate vacancies. In addition, defect association decreases the defect formation energies, and an associated defect of interstitial and substitutional protons, which is located around the c-axis of the HAp lattice, is found to exhibit a considerably small formation energy. Owing to abundant formation of the proton-related defects, Ca contents in HAp decrease with lowering pH, which explains experimental pH dependence of Ca/P molar ratios of HAp.
12:30 PM - Y1.9
Nanoscopic Observation of the Effect of NaCl and NaF on Hydroxyapatite Dissolution Studied by Atomic Force Microscopy.
Ki-Young Kwon 1 , Eddie Wang 2 , Seung-Wuk Lee 1 2
1 Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 Bioengineering, UC Berkeley, 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. Here, we addressed these issues by using single crystal hydroxyapatite (HAP) as a well-defined bone surface model, and directly observing its surface using in situ atomic force microscopy. Specifically, we investigated the effects of NaCl and NaF concentration on the dissolution of HAP (100) surfaces and found that both NaCl and NaF strongly suppressed HAP dissolution kinetics, but inhibition mechanism is different. Inhibition of HAP dissolution by the presence of NaCl may originate from the high degree of saturation in the solution phase which lessens the thermodynamic driving force 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 the specific molecular steps, which result in the shape change of etch pits. 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.
12:45 PM - Y1.10
Ab Initio Calculations on Substituted Hydroxyapatite Systems: The Combined Role of Advanced Solid State NMR Techniques and DFT.
Christian Bonhomme 1 , Christel Gervais 1 , Florence Babonneau 1 , Satoshi Hayakawa 2 , Akiyoshi Osaka 2
1 , universite P et M Curie, Paris France, 2 Biomaterials laboratory, Graduate school of national science and technology, Okayama Japan
Show Abstract The biological role of substituted hydroxyapatite (SHap) structures (by silicates, carbonates…) is of paramount importance [1]. Most investigations of such structures were performed by using X-ray diffraction techniques and vibrational spectroscopies. Nevertheless, some controversial statements remain, including the space group of pure HAp! Recently, major breakthroughs were obtained in: a) the detailed description of complex structures by using advanced Solid State NMR techniques [2]. b) the description of substitution sites in HAp structures by using extensive modelling [3].The aim of this Communication is devoted to the combination of the latest developments in Solid State Nuclear Magnetic Resonance, the ab initio calculation of NMR parameters by the GIPAW method (based on DFT) [4], and the use of models for SHAp [3].For pure HAp, 1H, 17O, 31P and 43Ca CSA (chemical shift anisotropy) and quadrupolar parameters (for 17O and 43Ca) were successfully calculated, allowing for the clear distinction between the monoclinic and hexagonal structures. As Solid State NMR is sensitive to the asymmetric unit of a given structure (through the number of isotropic lines), it offers a powerful tool of investigation for HAp polymorphism (in combination with ab initio calculations based on DFT). We have shown recently [5] that silicate substitution of HAp could be completely described by combining 29Si, 1H and 1H/29Si double resonance experiments. It has been shown without any ambiguity that the silicate anions could be classified as intra- and extra- HAp groups. This result contradicts partially previous assumptions already published in the literature.The A, B, and A/B site distributions in carbonated HAp structures were fully characterized by combining: i) 13C double and triple resonance experiments (1H/13C/31P) using fully enriched carbonate groups. ii) models of A, B, and A/B substitutions recently proposed by de Leeuw and coworkers [3]. iii) systematic calculation of 13C CSA parameters by GIPAW.It is claimed that the combination of i), ii) and iii) allows for the safe deconvolution of any 13C Solid State NMR spectrum related to carbonated SHAp.In particular, the fine study of the 1H/13C double resonance spin dynamics proved that (CO3)2-/OH- associations should be taken into account, but not HCO3- species (as proposed in the literature).We strongly believe that Solid State NMR combined to ab initio calculations should solve many questions related to SHAp. This approach can be easily extended to amorphous phases (including biologically relevant amorphous calcium phosphates), biominerals and biomaterials. [1] E. Fujii, C. Bonhomme et al., Acta Biomaterialia, 2, 69 (2006). [2] C. Bonhomme et al., Accounts Chem. Res., 40, 738 (2007).[3] S. Peroos, N. de Leeuw, Biomaterials, 27 (2006), 2150.[4] C. Gervais, C. Bonhomme et al., J. Phys. Chem. A, 109, 6960 (2005). [5] G. Gasquères, C. Bonhomme et al., Magn. Reson. Chem., 46, 342 (2007).
Y2: Biomolecules on surfaces
Session Chairs
Mehmet Sarikaya
Tiffany Walsh
Monday PM, December 01, 2008
Berkeley A/B (Sheraton)
2:30 PM - **Y2.1
Genetically-Selected Solid-Binding Peptides: Molecular-Structure, -Recognition, -Binding, -Assembly, and -Function
Mehmet Sarikaya 1 , John Evans 1 , Ram Samudrala 1 , Beth Traxler 1 , Candan Tamerler 1
1 GEMSEC, Materials Science and Engineering, University of Washington, Seattle, Washington, United States
Show AbstractPhysical and chemical functions of organisms are carried out by a very large number of proteins and peptides through robust and self-sustaining molecular recognition. In Nature, biomolecule-material interaction is accomplished via molecular specificity and high efficiency leading to the formation and self-assembly of controlled functional constructs, structures, tissues, and systems at all scales of dimensional hierarchy. Through evolution, Mother Nature developed molecular recognition via successive cycles of mutation and selection. With the recent developments of nanoscale engineering in physical sciences and the advances in molecular biology, we are combining genetic molecular tools with synthetic nanoscale constructs in creating a hybrid methodology, molecular biomimetics. In this approach, we use biology as a guide and adapt bioschemes including combinatorial biology, post-selection engineering, bioinformatics, and computational modeling to select and tailor short peptides (7-60 amino acids) with specific binding to and self- and targeted-assembly on functional solid materials, including metals, ceramics and semiconductors. Based on the fundamental principles of genome-based design, molecular recognition, and binding, we can now engineer peptides for solids and synthetic functional molecules as nucleators, catalyzers, growth modifiers, molecular linkers, scaffolds, and erector sets, i.e., simply as fundamental molecular utilities for nano- and nanobio-technology. We will review the latest developments from our collaborative research groups in this rapidly developing polydisciplinary field, focusing on: i. Fundamental issues in genetic design, molecular recognition, binding, and assembly of peptides on solids, ii. Practical implementation in bio-enabled nano-photonics, -magnetics, and –electronics in technology, and iii. In inorganic biosynthesis, fabrication, and functionalization towards molecular and nano-imaging, sensing (diagnostics), and tissue regeneration in medicine. Research is supported by NSF-MRSEC and BioMat programs.
3:00 PM - Y2.2
Peptide Binding to Metal, Bimetal, and Sheet Silicate Even Surfaces.
Hendrik Heinz 1 , Pratyush Dayal 1 , Ras Pandey 2 , Jian-jie Liang 3 , Joseph Slocik 4 , Lawrence Drummy 4 , Peter Mirau 4 , Ruth Pachter 4 , Rajesh Naik 4 , Barry Farmer 4
1 Department of Polymer Engineering, University of Akron, Akron, Ohio, United States, 2 Department of Physics and Astronomy, University of Southern Mississippi, Hattiesburg, Mississippi, United States, 3 , Accelrys, Inc., San Diego, California, United States, 4 Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, Ohio, United States
Show AbstractShort peptides (7 to 12 amino acids, excluding Cys) bind selectively to nanoparticles composed of Au, Pd, or montmorillonite depending on the sequence of amino acids, as evidenced by screening of several billion distinct peptide sequences using phage-display techniques [1]. The molecular reasons for binding versus non-binding and the specificity toward a certain surface are analyzed by molecular dynamics simulation at pH ~7 using extended biomolecular force fields with accurate force field parameters for the inorganic components [2]. The force field parameters reproduce surface and interface energies with <10% deviations from experiment. The analysis of the adsorption energies of the peptides, changes in chain conformation relative to solution, Ramachandran plots, orientational parameters, and computed NMR chemical shifts provide first suggestions on the mechanism of binding. On the metal {111} and {100} surfaces, binding versus nonbinding amino acid residues can be distinguished, of which the binding residues are directly in touch with the metal surfaces and the non-binding (or less-binding) residues are separated from the surface by one or two water layers. The binding energy can reach up to 80 kcal per mol peptide. On bimetallic surfaces such as Pd-Au, the polarity at the interfacial junction increases the binding energy by ~10 kcal per mol peptide. On the montmorillonite {001} surface, the ion exchange of Lys side groups against alkali ions has been directly observed in the simulation and identified as the primary factor for binding of one peptide. The data are in good agreement with binding constants, binding data for single amino acids on metal surfaces, TEM observations, NMR chemical shifts, and quantum-mechanical data for small molecules. The present work focuses on even surfaces, and further results on curved and shaped surfaces will follow soon.[1] Slocik, J. M; Naik, R. R Adv. Mat. 2006, 18, 1988−1992.[2] Heinz, H.; Koerner, H.; Vaia, R. A.; Anderson, K. L.; Farmer, B. L. Chem. Mater. 2005, 17, 5658–5669; Heinz, H.; Vaia, R. A.; Naik, R. R.; Farmer, B. L. (submitted).
3:15 PM - Y2.3
Molecular Simulations of the Interactions between Strong-Binding Peptides and Quartz Surfaces.
Rebecca Notman 1 , Tiffany Walsh 1
1 Department of Chemistry and Centre for Scientific Computing, University of Warwick, Coventry United Kingdom
Show AbstractThe specific binding of peptide sequences to inorganic surfaces is of considerable interest for its applications in biotechnology and materials science. Whilst there has been rapid experimental growth in this area, a fundamental understanding of the interactions that regulate binding is still lacking. A number of peptides that bind with a high affinity and specificity to quartz surfaces have been identified by phage display experiments followed by optimisation using a bioinformatics approach [1]. Our goal is to characterise the interactions of these peptides with various quartz surfaces and elucidate the key mechanisms of binding. An increased understanding of peptide-inorganic interactions would be a significant step towards the control of molecular recognition and self assembly processes.We are currently using molecular dynamics (MD) simulations to build up a molecular-level picture of the peptide-quartz interface system. We have carried out simulations of the hydroxylated quartz (100), (001) and (011) surfaces in order to investigate the water structure at these surfaces and the role that this may play in the peptide-surface interactions. In addition, Replica exchange MD simulations are used to explore the solution structures of strong and weak binding peptides with the purpose of identifying key structural properties of the peptides that may be important for binding. Furthermore, we will present ongoing simulations of the peptides in the presence of the surfaces, in which we aim to determine the roles of the residue sequence, and secondary structure in binding.Our results indicate that there is at least one layer of loosely-adsorbed water on the surface of hydroxylated quartz. The interfacial water molecules may be displaced upon peptide binding or they may play a direct role, for example mediate the binding with a hydrogen bond network. We find that, in solution, the weak binding peptides adopt conformations which are stabilised by the formation of intramolecular hydrogen bonds. On the other hand, the strong binding sequences do not tend to form intramolecular hydrogen bonds and therefore lack this intrinsic stability. It follows that a possible driving force for binding may be peptide stabilisation via interactions with the surface. The simulations of the peptides on the quartz surface suggest that the peptides bind in a number of different configurations. The proline residues appear to play a key role in binding as they interact directly with the surface and also strongly influence the conformations of the peptides by reducing the flexibility of the backbone. At this stage, our results support the idea that peptides which have a high binding affinity have many local minima on the binding energy landscape. 1. Oren et al. (2007) Bioinformatics, 23,2816
3:30 PM - Y2.4
A Knowledge-based Quest for Amelogenin Function in Enamel Biomineralization.
Ersin Emre Oren 1 2 , Mustafa Gungormus 1 , Ram Samudrala 2 , Jeremy A Horst 2 , Hanson Fong 1 , Marketa Hnilova 1 , John S. Evans 3 , Malcolm L. Snead 4 , Martha Somerman 5 , Candan Tamerler 1 6 , Mehmet Sarikaya 1
1 GEMSEC, Materials Science and Engineering Department, University of Washington, Seattle, Washington, United States, 2 Computational Biology Research 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 School of Dentistry, University of Southern California, Los Angeles, California, United States, 5 School of Dentistry, University of Washington, Seattle, Washington, United States, 6 Molecular Biology and Genetics, Istanbul Technical University, Istanbul Turkey
Show AbstractIn nature, proteins control nucleation, growth morphology, crystallography, and spatial organization of minerals and provide molecular scaffolds in the formation of hard tissues with complex and highly functional architectures. Silica based skeletal units of single-celled organisms (e.g. radiolarian and spicules of sponges), calcium carbonate-based composites in mollusk shell and sea-urchin skeletal units, and hydroxyapatite biominerals in bone and dental tissues of mammalians are just a few examples. Mammalian tooth enamel is the hardest and most highly mineralized material of the human body and along with dentin, cementum, pulp, PDL, and bone is one of the six tissues which make up the tooth organ. The high mineral content of enamel makes it vulnerable to demineralization process resulting in cavities. There has been considerable investigation in the literature to understand enamel formation, in particular the control amelogenin has over hydroxyapatite (HAp) formation towards regeneration of enamel or understand the basis for genetic diseases such as Amelogenin imperfecta. To understand the function of amelogenin (180 aa) in HAp formation, we performed a homology analysis using HAp-binding peptides selected using biocombinatorics, in particular, using 7-aa constrained and 12-aa linear phage display libraries. We developed a method that combines experimental knowledge from bioinformatics that enables to identify sequence similarities within any given peptide/protein groups using the selected and molecularly characterized strong and weak HAp-binding peptides as the input data. Here, the generated novel scoring matrices allow aligning a selected polypeptide and a natural protein sequence, e.g., selected HAp-binding peptides and amelogenin. Using the scoring matrices, we identified similarity sequences and determined the potentially functional domains on amelogenin. Using the identified domains, supplemented by the knowledge of Ca2+ ion binding domains, we identified two putative functional domains that may primarily be involved in enamel biomineralization. We will present recent results where we isolate these homology domains, synthesize the corresponding peptides, find key secondary structural signatures via circular dichroism spectral analysis, and finally use these peptides in HAp binding and mineralization experiments. Supported by mainly NSF-MRSEC, and also by NSF-BioMat, and NSF CAREER Award (RS).
3:45 PM - Y2.5
Directed Laboratory Evolution of Biomineralizing Enzymes.
Lukmaan Bawazer 1 2 3 , Michi Izumi 2 , Dmitriy Kolodin 4 , Birgit Schwenzer 5 , Daniel Morse 2 3 4
1 Biomolecular Science and Engineering Interdepartmental Program, University of California, Santa Barbara, California, United States, 2 Institute for Collaborative Biotechnologies, University of California, Santa Barbara, California, United States, 3 Materials Research Laboratory, University of California, Santa Barbara, California, United States, 4 Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, California, United States, 5 California NanoSystems Institute, University of California, Santa Barbara, California, United States
Show AbstractPurposefully manipulating generative conditions of inorganic material synthesis to tailor corresponding material structure, properties and function is the essential challenge for materials engineering. Biological systems have successfully addressed this challenge via evolution to generate sophisticated mineral components under ambient conditions. Investigations of biosilica skeletal elements from a marine sponge led to identification of the silicateins, enzymes that exhibit unique catalytic and templating activities in silica biogenesis. Here, a method has been developed to recapitulate, in a laboratory setting, the essential evolutionary processes responsible for the development of these biological glass-forming systems, and to direct this evolution to engineer novel mineral forming enzymes with specifically tailored activities. Millions of unique silicatein mutants are generated and reacted in parallel in artificial biomineralization vesicles formed in multi-phasic emulsions. High-throughput screening for mineralizing activity is conducted using fluorescence-activated cell sorting, permitting vesicles containing functional mutants to be identified and isolated either on the basis of photoluminescent signals from the target mineral, or from light-scattering signals indicating mineral growth. Using this strategy, we have isolated mutant mineralizing genes associated with characteristic CdS nanoparticle photoluminescence. In screening for oxide formation, we have produced mutant genes encoding enzymes that we show catalyze the room-temperature synthesis of cristobalite, a crystalline polymorph of silicon dioxide that has not before been synthesized below 400 degrees C. The strategy we have developed should be generally applicable for generating novel mineral forming enzymes from a wide range of recombinant parent enzymes. The results of these investigations will help elucidate native biological mechanisms of mineralization, provide new pseudo-synthetic models for extending biomimetic materials engineering strategies, and establish substantial groundwork towards the future development of gene-based synthetic materials.
4:30 PM - **Y2.6
Modelling Binding Affinity at Peptide-surface Interfaces: the Role of Mutations.
Tiff Walsh 1 , Adam Skelton 1 , Rebecca Notman 1 , Susana Tomasio 1 , Taining Liang 1
1 Chemistry and Centre for Scientific Computing, University of Warwick, Coventry United Kingdom
Show AbstractConsiderable experimental advances are being made in the study of organisation of peptides on inorganic surfaces. In contrast, comparable advances in the modelling of these interfaces lags behind substantially. In this contribution, the information that can be gathered from molecular simulation of these interfaces will be outlined, with particular attention paid to how targeted mutations can reveal the importance of the interplay between sequence, 3D structure, and ultimately, the binding properties of peptides at these interfaces. We will outline our recent work in predicting binding behaviour for mutations of a titania-binding peptide, which has led to unexpected results. We will also discuss how mutations that do not lead to huge changes in binding also lead to useful information; our example in this case is the peptide-nanotube interface[1]. Finally, we will discuss our current work in exploring target residues for mutation in quartz-binding peptides[2].References[1] S. D. Tomasio and T. R. Walsh, Molec. Phys. 105, 221 (2007)[2] E. E. Oren, C. Tamerler, D. Sahin, M. Hnilova, U. O. Seker, M. Sarikaya and R. Samudrala, Bioinformatics 23, 2797 (2007).
5:00 PM - Y2.7
Genetically Tailored Peptides for Bionanotechnology.
Candan Tamerler 1 2 , Mehmet Sarikaya 2
1 Molecular Biology and Genetics, Istanbul Technical University, Istanbul Turkey, 2 Materials Science and Engineering, University of Washington, Seattle, Washington, United States
Show AbstractThe genetically engineered peptides for inorganics (i.e., GEPI) when originally selected, using biocombinatoral procedures such as phage display and cell surface display, may present a specific degree of evolved sequences. After this initial step, genetic engineering approaches can further be utilized to evolve these peptides towards a desired functionality. The simple inorganic-binding characteristics of a GEPI appear as a result of the first evolutionary cycle during the selection process where the weak binder or no binders are eliminated from the pool. The selected strong-binding peptides, however, could be improved by introducing mutations through cycles of new generations similarly to the natural selection and evolution processes. Here, we apply variety of design strategies, including multimerization, introduction of functional domains, or insertion of spacers for improved functions. Desired peptides or multifunctional molecular constructs, for example including a GEPI genetically fused to a functional protein or an enzyme, could also be developed under in vivo environment, such as using bacterial or viral expression systems, for example, with additional modifications such as introduction of cleavable hexahistidine tails to simplify fusion peptide purification. The GEPIs can then be produced in desired amounts following the removal of purification tags for use as molecular tools for wide ranging applications In this presentation, we will explain how genetic engineering tools can be employed to tailor the functionality, and then present examples in wide ranging applications in nanobiotechnology, including, e.g., in: i. Synthesis of inorganics with controlled morphology (hydroxyapatite formation), ii. Production of molecular linkers in developing functional constructs, e.g., multifunctional proteins to control spacing and orientation. (oriented enzyme immobilization & fusion products of inorganic binding peptides with disease related domains to investigate the repair mechanism), iii. Developing molecular erectors to join synthetic entities including nanostructures on molecular templates, iv. As molecular films and scaffolds in developing biocompatible materials, including testing engineered peptide effects on cell proliferation, adhesion and toxicity.This collaborative research is supported by State Planning Organization of Turkey, NSF/USA via MRSEC and BioMat programs, and NIDCR/USA
5:15 PM - Y2.8
Adsorption of Peptide Chains (CR31, S2) on a Clay Surface by a Coarse-grained Monte Carlo Simulation.
Ras Pandey 1 , Hendrik Heinz 2 , Lawrence Drummy 3 , Richard Vaia 3 , Rajesh Naik 3 , Barry Farmer 3
1 Physics and Astronomy, University of Southern Mississippi, Hattiesburg, Mississippi, United States, 2 Polymer Engineering, University of Akron, Akron, Ohio, United States, 3 Materials and Manufacturing Directorate, Air Force Research Laboratory, Dayton, Ohio, United States
Show AbstractA Monte Carlo simulation is performed on a cubic lattice to study the adsorption of peptide chains, CR31: Trp-Pro-Ser-Ser-Tyr-Leu-Ser-Pro-Ile-Pro-Tyr-Ser and S2: His-Gly-Ile-Asn-Thr-Thr-Lys-Pro-Phe-Lys-Ser-Val on a clay surface in presence of explicit solvent. Peptides are described by bond-fluctuating chains with specific sequence of their amino acids, solvent by particles and clay substrate by an impenetrable immobile surface. Structural details of these components (amino acids, solvent, and clay platelets) are ignored but their specific characteristics are considered via appropriate interactions e.g., hydrophobic, polar, electrostatic. The phenomenological interaction matrix among the constituents (residues, solvent, and clay) is based on off-lattice atomistic simulations. 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 with specific anchor residues is predicted.
5:30 PM - Y2.9
Single Wall Carbon Nanotube-Peptide Hybrid for theDetection of TNT: Simulation and Experiments.
Zhifeng Kuang 1 , Sang Nyon Kim 1 , Wendy Crookes-Goodson 1 , Barry Farmer 1 , Rajesh Naik 1
1 Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, Ohio, United States
Show AbstractThe high sensitivity of single wall carbon nanotubes (SWCNTs) to their physicochemical environment has opened new possibilities for creating sensitive, lightweight sensors for the detection of chemical and biological agents. However, their low selectivity towards specified targets needs to be improved for such high-end sensors. Here we present the functionalization of SWCNTs with engineered peptides to enhance the selectivity for the detection of chemical agents, while maintaining or improving sensitivity. We have designed a multifunctional peptide that is capable of non-covalently adhering to the SWCNT surface as well as binding to 2,4,6-trinitrotoluene (TNT). The peptide consists of two domains – the first domain contains the SWCNT binding sequence (identified from a phage peptide library), while the second domain is based on a peptide sequence from the odorant binding protein (Asp1) from honeybees. This peptide sequence is predicted to bind to odorant molecules, including TNT. Molecular dynamic simulations were performed to investigate the secondary structure changes of the peptide in the presence of SWCNT in water. Circular dichroism from this peptide-SWCNT hybrid is compared to the simulation as a bench-mark. The self-assembly mechanism of the peptide on SWCNT is revealed from the equilibrated structure. TNT molecules are docked into active sites of this equilibrated structure and the binding free energy is estimated based on the combination of molecular dynamics simulation and Poisson-Boltzmann method. The calculated number of bound TNT per unit length of 1nm diameter SWCNT is compared with the experimental TNT/Peptide ratio estimated from SEM, AFM and SWCNT-field effect transistor chemosensor analysis.
5:45 PM - Y2.10
Self-Assembled Oligopeptides on the Au(111) Surface: a Molecular Dynamics Study of the Peptide-Surface Adhesion and Detachment Mechanisms in Water.
Stefano Corni 1 , Susanna Monti 2
1 , INFM-CNR National Research Center S3, Modena Italy, 2 , IPCF-CNR, Pisa Italy
Show AbstractIonic self-complementary oligopeptides [1] are an interesting class of biomaterials, which present spontaneous self-assembling to form various macroscopic structures. RAD16II is a 16-mer self-complementary oligopeptide (sequence: RARADADARARADADA), composed of a structural motif involving arginine (R), alanine (A) and aspartic acid (D), that self-assembles in long β-sheet fibers. The deposition of RAD16II (or similar peptides) on inorganic surfaces (notably Ti/TiO2) has been proposed as a way to enhance the bio-compatibility of the surface itself, since RAD16 peptides are known to produce good substrates for various cell cultures [2]. The stability of the self-assembled peptides, together with its anti-parallel β-sheet structure, also makes it an interesting case study to understand the basic interaction mechanisms between proteins and inorganic surfaces in water. In the present study, we have performed long (tens of ns) classical atomistic molecular dynamics simulations of a portion (composed of 16 peptide chains) of a self-assembled β-sheet of RAD16II [4,5] on Au(111). Gold has been chosen both for its importance in practical applications (e.g., gold nanoparticles for the iperthermia therapy of cancer [3], gold contacts in nanobioelectronics) and for its suitability for fundamental studies of the problem (well-defined surfaces, availability of different experimental techniques to characterize protein absorption such as spectroscopy, electrochemistry, scanning probe microscopy). The simulations have been performed in explicit water; the interaction between the peptide and the surface has been described by a recently developed protein-Au(111) force field [6], which also includes gold-polarization effects. In particular, simulations addressed the mechanisms of peptide filament adhesion and detachment on the Au surface in water, based on unbiased dynamics and on pulling techniques. The results show that the β-sheet filament detaches or adheres to the surface by a quasi-continuous process composed of small discrete steps, always conserving its secondary structure. The physical origin of this behavior, related to the interplay between intra-molecular and water/surface interactions of the charged amino-acid side chains will be also discussed. [1] S. Zhang, T.C. Holmes, C. Lockshin, A. Rich, Proc. Natl. Acad. Sci. U.S.A. 90, 3334 (1993).[2] T.C. Holmes, S. de Lacalle, X. Su, G. Liu, A. Rich, S. Zhang, Proc. Natl. Acad. Sci. USA. 97, 6728 (2000).[3] D. O’Neal , L. Hirsch , N. Halas , J. Payne , J. West, Cancer Letters 209, 171 (2004). [4] J. Park, B. Kahng, R.D. Kamm, W. Hwang, Biophys. J. 90, 2510 (2006).[5] S.Monti, J. Phys. Chem. C 111, 16962 (2007).[6] F. Iori, S. Corni, J. Comp. Chem. 29, 1656 (2008); F. Iori, S. Corni, R. Di Felice, E. Molinari, submitted.
Y3: Poster Session
Session Chairs
Tuesday AM, December 02, 2008
Exhibition Hall D (Hynes)
9:00 PM - Y3.1
Coexistence of Calcite and Amorphous Calcium Carbonate(ACC)in Acid Polysaccharide-mediated Biomimetic CaCO3 Spherulites.
Chao Zhong 1 , C. Chu 1 2
1 Fiber science program, Cornell University , Ithaca, New York, United States, 2 Biomedical Engineering Program, Cornell University, Ithaca, New York, United States
Show AbstractUsing a synthesis strategy inspired by biominerals, we have produced novel CaCO3 superstructures from a biomimetic mineralizing system in which maleic chitosan,an acid polysaccharide,was used as a novel organic template to control calcium carbonate formation in aqueous solution. The resulting crystals possess features of two independent types of biominerals: the radially ordered structure of spherulitic biominerals and the coexistence of crystalline calcite and stable amorphous calcium carbonate (ACC) of composite skeletal minerals. We demonstrate that the crystallization begins with the formation of amorphous thin films, probably in transient ACC form. Next, amorphous nanoparticles are deposited and stabilized by acid polysaccharide onto a pre-defined center area of the film to form a stable ACC core. This ACC core then acts as nucleus to initiate radial growth of needle-like calcite subunits, a role that goes beyond the known functions of ACC in both biogenic and synthetic forms. After approximately an hour, the spherulitic superstructures appear in which the ACC and calcite phase form at the core and outer layer, respectively. In short, we suggest that a 2-D transformation is followed by a 3-D transformation to produce the superstructures. Moreover, we believe that acid polysaccharide plays important roles in mediating both transformations. These findings may provide insights into spherulitic crystallization and the formation of spherulitic biominerals in nature.
9:00 PM - Y3.2
Molecular Dynamics Simulations of Peptides on Calcite Surfaces.
Mingjun Yang 1 , Mark Rodger 2 , John Harding 3
1 NanoScience Center, 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 AbstractA series of MD simulations have been carried out to investigate the interaction between peptides and a calcite surfaces in water solution. Two peptides (R2E2W2D2-16 and R2E2W2D2P-17) have been built, and three different configurations for each peptide are used as starting configurations. The dynamics behavior of these peptides has been studied by calculating their radius gyration and dihedral angles. For comparison, the simulations of peptides in vacuum and water have also been carried out. The simulations indicate that these peptides generally have strong interactions with the calcite surface, and the configurations of the peptides have also been changed to favor the interfacial interaction. Continuum electrostatic calculations based on Poisson-Boltzmann equation (PBE) have also confirmed strong electrostatic interactions between peptides and the calcite surface. The results suggest that peptides may play an important role during calcite crystallization such as biomineralisation of eggshell.
9:00 PM - Y3.3
Models for the Nucleation and Growth of Calcium Carbonate.
John Harding 1 , Colin Freeman 1 , Mingjun Yang 2 , James Elliott 3 , Dorothy Duffy 5 , Jennifer Lardge 5 , David Cooke 4 , David Quigley 6 , P. Rodger 6
1 Engineering Materials , Univ. of Sheffield , Sheffield United Kingdom, 2 Nano-Science Center, University of Copenhagen, Copenhagen Denmark, 3 Dept. of Materials, University of Cambridge, Cambridge United Kingdom, 5 Dept. of Physics and Astronomy, University College London, London United Kingdom, 4 School of Applied Sciences, University of Huddersfield, Huddersfield United Kingdom, 6 Dept. of Chemistry, University of Warwick, Coventry United Kingdom
Show AbstractThe nucleation and growth of calcium carbonate is important in fields from biomineralization through geology to industrial processing. Much work has been published in the area (a summary can be found in [1]), but there remains much to be understood. Simulation is a major tool in obtaining this understanding. We have developed a consistent set of potentials for carbonates (including a range of species in solution), organic functional groups and water based on well-known models for the carbonates, the AMBER forcefield for organic molecules and the TIP3P model for water[2]. This potential set has been used to investigate a range of nucleation and growth phenomena in calcium carbonate. We have shown how the growth and morphology of calcite can be controlled by organic molecules such as polysaccharides, peptides and proteins or by molecular arrays by calculating absorption energies (for molecules) and interfacial energies (for the arrays). In all cases, we have demonstrated the importance of the local structure of water close to the interface in determining the behaviour. We have also considered the nucleation of calcite using mechanisms other that those based on classical nucleation theory. Simulation of nano-particles is important because it allows size and shape-dependent properties to be studied directly. We have shown the importance of size, the presence and structure of surface water and the effects of organic molecules and arrays in determining the structure of nanoparticles. Simulations using metadynamics [3] have shown both that amorphous calcium carbonate is the stable form for small particles and that it is stabilised by proteins. We shall also present initial results on the interactions of nanoparticles and proteins and their relevance to the structure of egg-shells.1. J.H. Harding and D.M. Duffy; J. Mater. Chem. 16 (2006) 1105-11122. C.L. Freeman, J.H. Harding, D.J. Cooke, J.A. Elliott, J. Lardge and D.M. Duffy; J Phys Chem C 111 (2007) 119433. D. Quigley and P. M. Rodger J. Chem. Phys. 128, (2008) 221101
9:00 PM - Y3.6
The Role of Molecular Monolayers in Biomineralisation.
Colin Freeman 1 , John Harding 1 , David Cooke 2
1 Engineering Materials, University of Sheffield, Sheffield United Kingdom, 2 School of Applied Sciences, University of Huddersfield, Huddersfield United Kingdom
Show AbstractMolecular involvement in biomineralisation is often cited e.g. [1] for controlling the crystal morphology.These molecules can bind to surfaces and inhibit their growth thus controlling the final shape of the crystal.Experiment has successfully demonstrated the ability of these molecules to adsorb onto surfaces and simulations have managed to emulate some of these results [2].However these theoretical studies have so far only tended to consider single molecules on surfaces.These molecules must compete with organised structured water layers at the surface so it is perhaps not surprising that the adsorption energies are often small.In the biomineralisation process it is likely that the molecules exist in high enough concentrations to adsorb as a monolayer on the surface which creates new opportunities as the molecules can stabilise the interface via inter-molecular interactions.We have performed a range of simulations on molecules of varying sizes adsorbing at calcite and magnesite surfaces for a range of concentrations.We have selected several molecules with different functional groups and sizes to study how these can aggregate at surfaces and how their adsorption characteristics vary with their surface concentration.We have considered this behaviour with several different surface types to explore the effects of different water structures that can occur at these surfaces.Our results demonstrate that the adsorption energy is highly dependent on the molecular density at the surface and that the nature of the surface is also vital in determining the strength of interaction.[1] F. Manoli, J. Kanakis, P. Malkaj, E. Dala, Journal of Crystal Growth, 236 (2002) 363[2] S. Elhadj, E.A. Salter, A. Wierzbicki, J.J. De Yoreo, N. Han, P.M. Dove, Crystal Growth and Design, 6 (2006) 6197
9:00 PM - Y3.7
Development of Nano- and Micro-structured Calcium Phosphate Composites.
Deng (Debra) Lin 1 , Hiroaki Sai 1 , Kunjal Patel 1 , Chris Sarra 1 , Ulrich Wiesner 1 , Lara Estroff 1
1 Materials Science & Engineering, Cornell University, Ithaca, New York, United States
Show AbstractCalcium phosphate-organic composites with a continuous inorganic phase have potential applications as materials for hard tissue repair with superior mechanical properties to dental composites and bone cements. We present two approaches for forming such composites: microstructured composites via colloidal templating and nanostructured composites using block copolymers as structure-directing agents. For both approaches, we use calcium phosphate nanoparticles with controlled surface chemistry, which is achieved through the use of organic additives. The morphology, size, and surface chemistry of these calcium phosphate nanoparticles facilitate their incorporation into collodial crystals and block copolymer. By varying the chemical composition of the crystallization solutions, particles ranging in size from 4 nm to 100 nm with morphologies from spherical to needle-like plates were obtained. Structured composites are then synthesized either by coassembly of polystyrene beads and the calcium phosphate nanoparticles, or by selectively swelling one block of the amphiphilic block copolymer mesophases with appropriately functionalized calcium phosphate nanoparticles. The size, shape, and phase of the calcium phosphate particles, as well as the resulting composites were characterized via TEM, AFM, and XRD.
9:00 PM - Y3.8
Morphological and Kinetic Transformation of Calcium Carbonate Crystal Growth by Water-Soluble Synthetic Polymers.
Raehyun Kim 1 , Sang-soo Lee 1 , Il Won Kim 2 , Junkyung Kim 1
1 Hybrid Materials Research Center, Korea Institute of Science and Technology, Seoul Korea (the Republic of), 2 Chemical & Environmental Engineering, Soongsil University, Seoul Korea (the Republic of)
Show Abstract9:00 PM - Y3.9
Monomer Adsorption, Cluster Mobility, and Self-Assembly of Inorganic Binding Peptides on Solid Surfaces.
Christopher So 1 , Hakim Meskine 3 , Candan Tamerler 2 , Paul Mulheran 3 , Mehmet Sarikaya 1
1 Materials Science and Engineering, GEMSEC, University of Washington, Seattle, Washington, United States, 3 Chemical Engineering, University of Strathclyde, Glasgow United Kingdom, 2 Molecular Biology, Istanbul Technical University, Istanbul Turkey
Show AbstractBased upon prevalently non-covalent interactions, peptides and proteins exhibit mechanisms of sequence-dependent physisorption onto solid surfaces of interest. These interactions often involve complex binding, surface diffusion, and aggregation phenomena unexplained by one single adsorption phenomenon, e.g., chemi- or physio-sorption. While a wide ranging applications of genetically engineered peptides for inorganics (GEPIs) have grown significantly in recent times, little is known about the functional mechanism of these material selective peptide-solid systems. Here, we combine ex situ time-lapsed AFM results with ad hoc Kinetic Monte Carlo (KMC) modeling to investigate the observed spatial nucleation and growth mechanisms of Gold Binding Peptide-1 (3rGBP1) onto an Au(111) surface. The various states of peptide morphology observed on AFM are explained and correlated to KMC modeling with considerations for both monomer and size-dependent cluster mobilities. ‘Branched’ percolation states of peptide observed by AFM can be modeled close to those of the monomers themselves, leading to morphologies of high fractal dimension. These properties of peptide surface dynamics and diffusivity offer new insight into the function of GEPIs and their molecular recognition and self-assembly mechanism(s) on specific solid systems.
Symposium Organizers
John H. Harding University of Sheffield
James A. Elliott University of Cambridge
John S. Evans New York University
Y4: Mesocrystals and Aggregation
Session Chairs
Amanda Barnard
Kiyotaka Shiba
Tuesday AM, December 02, 2008
Berkeley A/B (Sheraton)
9:30 AM - **Y4.1
Biomineralization Studies Using Motif-Programmed Artificial Proteins.
Kiyotaka Shiba 1
1 Protein Engineering, Cancer Institute, Tokyo Japan
Show AbstractMotif-programming is a method for constructing artificial proteins by embedding peptide motif(s) within artificial protein sequences. To embed motifs, we are using our MolCraft system (J Mol Catal B 28:215). I will now describe our efforts of understanding the mechanisms of biomineralization and to utilize the biomineralization phenomena in nanotechnology or the medical area using this motif-programming approach. In the first example, we created artificial proteins by programming the Asn-Gly-Asx motif that is repeated within pearl shell proteins as an idiosyncratic domain. This domain has been shown to have an inhibitory effect on calcification. The purpose of this experiment was to determine how readily functional mineralization-related proteins can arise from repeats of such a short motif. The results demonstrated that some of the created artificial proteins carrying the motif had a robust suppression of calcification, suggesting that the mineralization activity likely evolved from reiteration of a short motif with relative ease (Biomacromolecules 8:2659). The second example of our studies using motif-programmed proteins focused on motifs related to the mineralization of bone. The two motifs, which are parts of the sequences of the Dentin Matrix Protein 1 (DMP1) and were previously shown to enhance hydroxyapatite (HAP) formation when immobilized on a glass substrate, were programmed to create artificial proteins. From the motif-programmed artificial proteins, we selected clones that have an accelerated formation of HAP without immobilization. The good solubility of the selected proteins allowed us to perform time-resolved light scattering photometry analyses. The result suggested that the proteins facilitated the direct transformation of amorphous calcium phosphate to HAP, thereby acting as a trigger for precipitation of the crystalline calcium phosphate. In the last example, I show the creation of artificial proteins by programming artificial peptide motifs. As for the artificial motifs, we are using the minTBP-1 and NHBP-1 motifs. The minTBP-1 motif is a hexapeptide sequence corresponding to the core region of the 12-aa peptide TBP-1, which was originally isolated as a Ti-binding peptide (J Am Chem Soc 125:14234). The NHBP-1motif is also a peptide aptamer that binds to the surface of carbonaceous nanomaterials (Langmuir 20:8939). Interestingly, these material-binding peptides, among others, have been shown to also possess biomineralization activities (MRS Bulletin 33:524). The minTBP-1 peptide enhances the formation of titania and silica (Langmuir 21:3090; Nano Letters 7:3200), while NHBP-1 accelerates gold particle formation. The NHBP-1 motif has also been shown to act as a structural motif in motif-programming experiments (Protein Eng Des Sel 20:109). By combining these artificial proteins, we are studying the effect of the protein structures on mineralization.
10:00 AM - Y4.2
Dynamics of Peptide Self-assembly at Interfaces.
Lorraine Leon 1 , Phillip Logrippo 2 , Raymond Tu 1
1 Chemical Engineering, The City College of New York - CUNY, New York, New York, United States, 2 Chemical engineering, Manhattan College, New York, New York, United States
Show AbstractNaturally occurring biological interfaces assemble nano-scale patterns of chemical functionality with exceptional precision. Moreover, the role of dynamics during the assembly of the organic phase appears to be important for mineralization processes. Our work applies model sheet-forming peptides at interfaces to explore the dynamics of assembly. Rationally designed amphiphilic peptides are deposited at the air-water interface with a propensity for sheet-like secondary structure. We then explore the dynamics of self-assembly by controlling the surface pressure of a langmuir film, and we measure the development of 2D order with circular dichroism, Brewster angle microscopy and attenuated total reflectance-FTIR. Thermodynamic analysis of structure formation with increasing pressure allows us to understand the nature of self-assembly with iterative changes in the peptide sequence. Additionally, we look at the dynamics of the self-assembled state, where the organic phase switches between short- and long-range order. This model system allows us to explore our underlying hypothesis that the time-scale of the phase-transitions of the peptide at the interface defines the length-scale of the mineral phase. This is in contrast to a system that starts with a well-ordered preformed template that defines the epitaxial growth of the mineral phase.
10:15 AM - Y4.3
Phase Behavior of Surface-adsorbed Polymers Studied by Lattice Chain Modeling: Implications for Biomineralization.
James Elliott 1 , Dmytro Antypov 1
1 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, CB2 3QZ, United Kingdom
Show AbstractThe coarse-graining of molecular interactions provides an effective way of exploring the conformational space of long polymer molecules, such as proteins and polysaccharides, which plays an important role in determining their adsorption behavior on biomineral surfaces. The competition of entropic and enthalpic effects involved in polymer adsorption near a flat surface, near a cylinder or in the suspension of large number of interacting nanoparticles have been studied here using an FCC lattice model, which allows efficient calculation of the total thermodynamic properties of the system. In each case, the complete partition function of the system was calculated numerically and a corresponding phase diagram built. While these phase diagrams can in principle be mapped quantitatively onto real systems using experimental data or output from molecular simulations, in this paper we focus on describing qualitative differences in behavior between each type of surface considered.For a chain adsorbed on a planar surface, a 2D chain collapse similar to the 3D isolated chain coil-globule transition was observed, together with a series of layering transitions in the third dimension perpendicular to surface. When the same chain was adsorbed on a cylinder, representing a nanotube, the stability of these multilayered phases significantly decreased. In addition to the above transitions, which are mainly driven by the competition between the interaction with the surface and the solvent properties, the influence of further parameters such as polymer concentration, chain stiffness, tethering and the surface specific effects have also been studied. Under similar conditions, stiffer chains were found to adsorb more strong than flexible ones. The pattern of adsorption sites on the surface was found to strongly affect adsorption energies, while tethering of the chain caused very little change in its behavior.For a free chain in a dilute solution of small interacting particles we found that a strong polymer-particle interaction inevitably caused the chain to collapse. Depending on the solvent properties, the particles could be found either inside the polymer coil or attached only to its surface. We report on a new transition between weak and strong adsorption regimes, characterized by a peak in specific heat and non-monotonic behavior of the chain dimensions.
10:30 AM - Y4.4
SP1, A Switchable Silicon Oxide Binding Protein Scaffold for Nano-Fabrication.
Arnon Heyman 1 , Izhar Medalsy 2 , Oron Bet Or 1 , Or Dgany 1 , Danny Porath 2 , Oded Shoseyov 1
1 The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture Faculty of Agricultural, Food and Environmental Quality Sciences, The Hebrew University of Jerusalem, Rehovot Israel, 2 Physical Chemistry Department, The Hebrew University of Jerusalem, Jerusalem Israel
Show AbstractSelf-assembly is a prerequisite for the fabrication of nanoscale structures. Biomolecules in general and proteins in particular are capable of self-assembling into a wide variety of structures that can be readily manipulated and functionalized. An ideal protein scaffold provides a rigid folding unit, which spatially brings together different functional domains. SP1 is an extremely stable homo-oligomeric protein. This ring-shaped homododecamer protein is utilized to display both inorganic nano-particles and protein domains in a pre-defined manner. In this study we present selective and controlled attachment of the SP1 protein scaffold monolayer, to metal and semi-conducting surfaces. Using genetic engineering, the protein was designed to bind various molecules and nano particles such as gold, silicon oxide and titanium oxide, assemble two and three dimensional arrays and structures, and display various protein domains. We demonstrate the position effect of a single cysteine point mutation on the protein specificity to gold surfaces and the display of 12 silicon oxide binding peptides in the protein inner-protected pore. Moreover, the silica binding ability can be switched on and off by exposing its affinity peptides only in response to high concentration of GuHCl while significantly reducing non-specific binding. Upon binding of a silica nano-particle to the SP1 inner pore we have succeeded to selectively charge the nano-particle, thus creating a single nano-metric memory unit. Here we present a switchable silicon oxide binding protein scaffold, useful for various applications ranging from bioelectronics to materials engineering.
10:45 AM - Y4.5
Comparative Effects of Self-assembled Noncollageneous Extracellular Proteins on Biomineralization in Vitro.
Xiaolan Ba 1 , Yizhi Meng 2 , Elaine DiMasi 3 , Helga Fueredi-Milhofer 4 , Yi-Xian Qin 2 , Nadine Pernodet 1 , Miriam Rafailovich 1
1 Materials Sciences and Engineering, SUNY-Stony Brook, Stony Brook, New York, United States, 2 Biomedical Engineering, SUNY-Stony Brook, Stony Brook, New York, United States, 3 National Synchrotron Light Source, Brookhaven National Laboratory, Upton, New York, United States, 4 , The Hebrew University, Jerusalem Israel
Show Abstract11:30 AM - **Y4.6
Modeling the Shape of Nanoscale Iron Sulphides Formed During Biomineralization.
Amanda Barnard 1 , Salvy Russo 2
1 School of Chemistry, University of Melbourne, Melbourne, Victoria, Australia, 2 Applied Physics, School of Applied Sciences, RMIT University, Melbourne, Victoria, Australia
Show AbstractThe intracellular biomineralization of single nanocrystals of the non-magnetic mineral iron pyrite (FeS2) in multicellular magnetotactic bacterium is usually observed in sulphide-rich water and sediment (associated with ferrimagnetic greigite, Fe3S4). The morphology of the individual nanocrystals is related to the species of the micro-organism and the local environmental conditions. However, characterizing these nanocrystals and understanding biomineralization processes in micro-organisms inhabiting sulphidic environments is challenging, as anisotropic surface growth, alteration and dissolution are linked to the crystallographic orientation of surface facets, as well as microbial activity. In the present study we outline a multi-scale thermodynamic model capable or describing the stability (formation) of nanocrystals as a function of size, shape, temperature and chemical environment, and use it to examine the phase, shape and orientation of nanoscale iron sulphides formed during biomineralization. Abiotic components such as the coverage of water on the surface, and the super-saturation of sulphur are investigated, based on parameters obtained from first principles calculations. We will show that an advantage of this approach is the facilitation of a more systematic and comprehensive analysis than is possible using traditional (purely) computational approaches.
12:00 PM - Y4.7
Doping Magnetosomes with Mn, Co and Ru: Effects on Morphology, Chemical Composition, and Magnetic Properties.
Tanya Prozorov 1 , Ruslan Prozorov 1 2 , Surya K. Mallapragada 1 3 , Teresa Perez-Gonzalez 4 , Concepcion Jimenez-Lopez 4 , Dennis Bazylinski 5
1 Materials Chemistry and Biomolecular Materials, Ames Laboratory, Ames, Iowa, United States, 2 Physics and Astronomy, Iowa State University, Ames, Iowa, United States, 3 Chemical and Biological Engineering, Iowa State University, Ames, Iowa, United States, 4 Microbiology, University of Granada, Granada Spain, 5 School of Life Sciences, University of Nevada, Las Vegas, Nevada, United States
Show AbstractIn nature, magnetotactic bacteria produce exquisitely ordered chains of uniform magnetite nanocrystals. These bacterial magnetite nanoparticles have become topic of intense research due to their ordered crystal structure, narrow size- and shape distribution and, as a consequence, well-defined magnetic properties. It was long argued that it should be possible to influence the biomineralization of magnetite via controlled culturing in the presence of a variety of metal ions, in order to produce nanocrystals of complex stoichiometry. Not only may this result in materials that are difficult or impossible to produce otherwise, but it is also potentially useful in learning how to tune magnetic properties. Here we report on controlled in-vivo feeding studies of Magnetospirillum gryphiswaldense, strain MSR-1 with ruthenium, cobalt, and manganese. “Doped” in such a way magnetosomes exhibit changes in particle size, chemical composition and shape that correlates with the observed changes in their magnetic properties. These results provide important clues for establishing not-yet-understood biochemical mechanism of a controlled magnetite biomineralization in magnetotactic bacteria. In addition, we present a novel way of rational altering of the magnetic properties of bacterial magnetite.
12:15 PM - Y4.8
Understanding the Plate-Shaped Morphology of Hydroxyapatite Crystals and Implications to the Structure of the Bone.
B. Viswanath 1 , Ravishankar Narayanan 1
1 Materials Research Centre, Indian Institute of Science, Bangalore India
Show AbstractUnderstating the morphology of crystals formed from solution phase, vapor phase, naturally occurring crystals, crystals formed during biomineralization are of great interest for several decades. Especially hydroxyapatite, one of the widely studied bio-mineral that exist in human bone with plate shaped morphology is far from the clear understanding. Here morphology diagram has been developed for the growth of hydroxyapatite by combining the driving forces of chemical reaction with the two-dimensional nucleation considering the interfacial energy. The validity of the morphology diagram has been tested by critical experiments carried out at different conditions coupled with microstructural analysis. Different morphologies ranging from single crystalline sheets, rods to equiaxed particles of hydroxyapatite are achieved by tuning the driving force of the chemical reactions by varying the parameters such as pH and temperature in the absence of capping/surfactant agents. The synthesis and analysis presented here has important consequences with the plate shaped morphology of hydroxyapatite crystals that are exist in the human bone. The generality of the method is tested for several systems such as CaCO3, ZnO and CuO.
12:30 PM - Y4.9
Molecular-scale Model for Predicting Crystal Growth Morphology: A First Principles Approach.
Manoj Singh 1 , Arup Banerjee 2
1 Laser Materials Development and Devices Division, Raja Ramanna Centre For Advanced Technology, Indore, M.P., India, 2 Laser Physics Applications Division, Raja Ramanna Centre for Advanced Technology, Indore, India, Indore, M.P., India
Show Abstract12:45 PM - Y4.10
Formation of CaCO3 Microspheres from Urease-Immobilized Substrates.
Bongjun Yeom 1 , Kookheon Char 1
1 , Seoul National University, Seoul Korea (the Republic of)
Show AbstractNatural biominerals with exquisite and hierarchical architectures provide us with a source of inspiration and concepts for the noble design of artificial crystalline materials and/or hybrid composites. Particularly, the preparation of calcium carbonate (CaCO3) nano and micron-sized particles has been the subject of active research due to its great potentials in biotechnology, materials science and many other applications in industry. In this presentation, CaCO3 microspheres were prepared on the substrates by the catalyzed reaction of urease (Ur). (Ur/poly(diallydimethylammonium chloride)(PDAC))n multilayered films were assembled on substrates by the layer-by-layer deposition method with immobilized Ur used as a source of carbonate ions. As the urease decomposes urea in solution containing supersaturated calcium ions, CaCO3 crystals with micron-sized structure with different morphology were grown from the (Ur/PDAC)n film. Various morphological and polymorphic forms of the calcium carbonate crystals were examined by scanning electron microscopy and X-ray diffraction.
Y5: Biomimetics and Biomineralization
Session Chairs
Tuesday PM, December 02, 2008
Berkeley A/B (Sheraton)
2:30 PM - **Y5.1
New Functional Ceramic Composits through Biomineralization?
Monika Fritz 1
1 Pure and Applied Biomineralisation, Biophysics Institute, University Bremen, Bremen Germany
Show AbstractThe biogenic polymer/mineral composite nacre is grown by a self-organisation process, where a few weight percent of organic material governs the specific crystallization of the calcium carbonate polymorph aragonite. The thus developed material shows a dense packing of thin layers (500nm) of mineral interdispersed by a few nanometer of organics, acting like a glue to improve the mechanical properties of this biogenic ceramic by making it non-brittle. Several proteins influence the crystallization of calcium carbonate. Some of them are attached to chitin, while others are water soluble. The organic components in conjunction with the mineral platelets are responsible for the outstanding mechanical properties of nacre. Thus the organic material first guides the self-organisation process of nacre and than acts as few nanometer thick layers between the mineral plates as the critical component for the excellent properties of the composite.Forming new material on the basis of nacre chitin is used as a matrix for calcium carbonate mineralisation to manifest the effect of selected templates on the crystallization of calcium carbonate (Fig.) In order to be able to make use of this process for future purposes and applications we have to understand this self-organised structure formation, which results in the microstructure with mineralized platelets embedded in bioorganic nanolayers. We employ SEM (scanning electron microscopy), AFM (atomic force microscopy), precipitation assays, XRD (x-ray diffraction), contact angle measurements and theoretical simulations to investigate the interaction processes between organic and inorganic material in the natural and synthetic composites.
3:00 PM - Y5.2
Biomineralisation of Calcite with Ovocledin-17: The Chicken and the Egg.
Colin Freeman 1 , John Harding 1 , David Quigley 2 , Mark Rodger 2
1 Engineering Materials, University of Sheffield, Sheffield United Kingdom, 2 Chemistry, University of Warwick, Coventry United Kingdom
Show AbstractThe avian eggshells is a perfect example of bimimetics.It is one of the fastest hard tissue mineralisation processes found in biological systems [1].Control of the structure and therefore functionality of the shell is vital or the embryo maydie. Recent experiments have identifued a number of proteins associtated with the eggshell,particularly the C-type lectin proteins which appear to be important in controlling calcitedeposition [2]. In vitro studies with ovocledin-17 (chicken) [3] have shown that the proteinwill promote and have a strong effect on calcite morphology. Understanding the role of thisprotein and others in the biomineralisation of the eggshell is still poor.We present the first atomistic simulations of a biomineralisation protein at a mineralinterface. Our calculations analyse the interactions between the whole ovocledin-17 proteinand various calcite surfaces and nanoparticles in an explicit water environment. We haveidentified both the residues of the protein that interact with the calcite and thesignificant features of the amino acid sequence. The simulations have looked at theinteraction energy between the protein and the (10.4), (31.8), (31.16) and amorphous calcitesurfaces. By using long-timescale methods we are also able to crystallise an amorphousnanoparticle in contact with the protein. These results allow us to comment on theinvolvement of the protein during much of the crystallisation process. We have shown thatthe water structure is a major component of the interfacial energy and strong proteinbinding relies on causing the minimum disruption to this water. This factor is crucialwhen we consider the pre-crystallised state. Using these data we are able to comment onthe role of the protein in controlling calcite biomineralisation.[1] Lavelin I.; Meiri N.; Pines M. Poultry Science 2000, 79, 1014[2].Mann, K.; Siedler, F. Comp. Biochem. & Physiol. B, 2006, 143, 160; Mann, K. British Poultry Sci. 2004, 45, 483[3] Lakshminarayanan, R.; Joseph, J. S.; Kini, R. M.; Valiyaveettil, S. Biomacromolecules 2005 6, 741
3:15 PM - Y5.3
Micro-beam SAXS/WAXS Study of the Nano-Structure in Biogenic Calcite.
Christoph Gilow 1 , Barbara Aichmayer 1 , Oskar Paris 1 , Frédéric Marin 2 , Emil Zolotoyabko 3 , Peter Fratzl 1
1 Department of Biomaterials, Max-Planck Institute of Colloids and Interfaces, Potsdam Germany, 2 Laboratoire de Biogéosciences, UMR 5561, Université de Bourgogne, Dijon France, 3 Department of Materials Engineering, Technion – Israel Institute of Technology, Haifa Israel
Show AbstractBiogenic crystals, i.e., crystals produced by living organisms, often exhibit superior mechanical and other properties which originate in the hierarchically arranged microstructures. Organisms fabricate these complex material systems at room temperature (or close to it) with a fascinating degree of control on the orientation, polymorphism and morphology of the resulting crystals, which contain some amount of intra-crystalline organic macromolecules. A deeper understanding of the structure of biominerals and the processes involved in biomineralization is of great importance to the development of the bio-inspired composite materials.In this work we investigate the atomic and nano-structure of biogenic crystals influenced by the presence of the intra-crystalline macromolecules. For this purpose, the simultaneous Small- and Wide-Angle X-Ray Scattering (SAXS/WAXS) technique is applied to individual single-crystalline calcitic prisms extracted from the mollusk shells of Pinna nobilis. Experiments are carried out at the µ-Spot beam line of the synchrotron radiation source BESSY II (Berlin, Germany).We find that the SAXS intensity distribution is strongly anisotropic in the reciprocal space and well correlated with the WAXS angular pattern. This finding indicates the existence of firm orientation relations between the nanometer-sized structural features, apparently induced by intra-crystalline macromolecules, and the atomic lattice of calcite. Upon annealing at a moderate temperature of 300 °C, which is expected to affect mainly the organic macromolecules within the prisms, the correlation between the SAXS and WAXS intensity distributions becomes significantly less pronounced. The experimental data are used in order to determine the preferential binding sites of organic macromolecules within the calcite lattice.
3:30 PM - Y5.4
Effect of Self-Assembled Porcine Amelogenins on Calcium Phosphate Formation in Vitro.
Seo-Young Kwak 1 , Felicitas Wiedemann-Bidlack 1 , Elia Beniash 3 , Yasuo Yamakoshi 2 , James Simmer 2 , Henry Margolis 1
1 Biomineralization, The Forsyth Institute, Boston, Massachusetts, United States, 3 Department of Oral Biology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2 Dental Research Laboratory, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractDental enamel is the hardest tissue in the human body and comprised primarily of parallel arrays of carbonated hydroxyapatite (HA) crystals packed in an intricate interwoven structure. This is a major factor that contributes to enamel’s unique mechanical properties. The formation of the highly organized enamel tissue is regulated in part by the extracellular matrix protein amelogenin. Although amelogenin is processed by proteinases soon after secretion, our previous findings suggest that the self-assembly of full-length mouse amelogenin can provide an organized microstructure that regulates the formation of parallel arrays of apatitic crystals. However, the role of prominent amelogenin cleavage products is not well understood. Hence, we have now carried out studies to assess the effect of recombinant porcine amelogenins rP161 and rP147, which lack the hydrophilic C-terminus found in full-length amelogenin (rP172), on the spontaneous formation of calcium phosphates was assessed in comparison to rP172. We also examined the effect of the native (phosphorylated) amelogenin (P148). Calcium and phosphate were sequentially added to ice-cold protein solutions (2mg/ml in water, pH<4) to yield concentrations of 2.5mM Ca and 1.5mM P in 60μL. The pH of solution was quickly adjusted (KOH) to 7.4±0.1 and incubated at 37oC. The change in pH was monitored continuously, as an indication of mineralization progress. Formed minerals were analyzed using TEM and electron diffraction. In the absence of protein, following a short induction period (~20min), a sharp drop in pH was observed that corresponded to the formation of randomly oriented plate-like apatite crystals. In the presence of rP172, a longer induction period (60-90min) was observed along with a smaller decrease in pH that corresponded to the formation of needle-like apatite crystals with preferred orientation. In the presence of rP161 and rP147, relatively shorter induction periods (10-20min) were observed, prior to the onset of the formation of randomly arranged apatite crystals. Using P148 (1 and 2mg/mL), however, relatively little pH change was observed for up to 24h and TEM analyses showed the presence of nanoparticles of amorphous calcium phosphate(ACP). In the presence of lower P148 concentrations (200-400μg/mL), apatitic mineral was found to form after a 300-500min. induction period. These results demonstrate that P148 stabilizes ACP phase and inhibits its transformation to apatitic crystals in a concentration-dependent fashion. This function was found to depend on the single covalently bound phosphate group present in the native P148, while the hydrophilic C-terminus found in rP172 was shown to a play a role in the formation of organized bundles of crystals. In conclusion, the present results show that full-length amelogenin and specific amelogenin cleavage products have distinct functional capabilities in controlling calcium phosphate mineralization. Supported by NIDCR grant DE-16376.
3:45 PM - Y5.5
Analysis of the Microstructure of the Coral Skeleton of Porites Lutea with Respect to the Coral Growth Mechanism.
Roland Kroeger 1 , Tim Rixen 2 , Christian Kuebel 3 , Eunah Lee 4
1 Department of Physics, University of York, York United Kingdom, 2 , Center for Tropical Marine Ecology, Bremen Germany, 3 , Fraunhofer Institute for Manufacturing Technology and Applied Materials Research, Bremen Germany, 4 , Horiba Jobin-Yvon Inc, Edison, New Jersey, United States
Show Abstract4:30 PM - **Y5.6
Directed Assembly in Charged Systems.
Murugappan Muthukumar 1
1 , University of Massachusetts, Amherst, Massachusetts, United States
Show Abstract5:00 PM - Y5.7
Room-temperature Synthesis of Highly Crystalline Oxide Semiconductors on Enzymatic Templates: Urease as a Biocatalytic Nanoreactor for the Growth of ZnO Nanoshells.
Roberto de la Rica 1 , Hiroshi Matsui 1
1 Chemistry and Biochemistry, City University of New York-Hunter College, New York, New York, United States
Show AbstractOxide semiconductors are expected to have important impact on oncoming optics, electronics and catalysis. It is desirable to develop the room-temperature synthetic process for oxide semiconductor materials that ensures low costs and compatibility with other fabrication processes. In the past, it was demonstrated that certain proteins could be used as biocatalitic templates for obtaining a variety of nanomaterials which do not grow at room temperature in conventional synthetic methods. Recently we also demonstrated that peptide nanotubes could catalyze the growth of ZnO on their surface to form ZnO nanowires. However, the mechanism of this room temperature biomineralization process is not well understood and thus it is difficult to control the reaction parameters to tether precise morphology of ZnO by this biomimetic method. We hypothesize that the peptide interface has a distinguished character in local pH and charge distribution as compared to bulk properties of those and this characteristic biomolecular interface should contribute the catalytic activity of biomineralization. To evaluate this hypothesis, we examined the enzyme urease as a model biocatalytic template for the room-temperature synthesis of highly crystalline zinc oxide nanoshells because we can control local pH at the interface of urease with the assistance of urea. Urease is inexpensive enzyme that catalyzes the hydrolysis of urea into ammonia and carbonic acid with a concomitant increase in the local pH around the biomolecule. Furthermore, the enzyme can concentrate the precursors of the reaction at its surface through electrostatic interactions. There, the basic condition created by the ammonia production at the enzyme interface was able to condense the concentration of Zn precursor and catalyze the sol-gel process for the synthesis of zinc oxide around the urease nanoparticle. The entropy gain by replacing well-ordered solvation layer with these cations on urease could further stimulate the dehydration of the hydroxide intermediates and yield ZnO. As a consequence, single-crystalline ZnO nanoshells in the diameter of 18 nm were obtained on the enzyme core in a simple one-step room-temperature process. The procedure could be easily applied to the synthesis of other relevant oxide semiconductors that can be obtained through the sol-gel route.
5:15 PM - Y5.8
The Formation of a Thin Uniform Calcium-phosphate Layer on Alumina and Zirconia Ceramics by Biomimetic Method.
Irena Pribosic 1 , Tomaz Kosmac 1 , Sabina Beranic-Klopcic 1
1 Engineering Ceramics, Jozef Stefan Institute, Ljubljana Slovenia
Show Abstract