John Harding, University of Sheffield
Derk Joester, Northwestern University
Roland Krouml;ger, University of York
Paolo Raiteri, Curtin University
Symposium Support ACS Biomaterials Science amp; Engineering
Biomaterials Science, RSC
University of Sheffield
E2: New Approaches to Hard/Soft Interfaces
Monday PM, December 01, 2014
Sheraton, 2nd Floor, Back Bay B
2:30 AM - *E2.01
Linking Theory and Experiment in Biomineralisation
Susan Stipp 1 D. J. Tobler 1 K. N. Dalby 1 T. Hassenkam 1 N. Bovet 1 M. P Andersson 1 D. Mueter 1
1University of Copenhagen Kamp;#248;benhavn amp;#216; DenmarkShow Abstract
Biomineralisation relies on the ability of an organism to control the structure and form of a solid phase that it can use for a specific purpose. This control takes place at the boundary between fluid and solid, nearly always mediated by some organic compound. Traditional analytical methods give information about the properties of the bulk solid or the bulk fluid that can be used to make interpretations about what goes on at the interface between the two, which is often only a few molecular layers thick. Computational methods have added considerably to understanding the relationships between components on both sides of the boundary but by combining experiment and theory, we can advance much further in our understanding. Analyses made with nanotechniques, that can "see" at the molecular level, provide data that can be used directly for calibrating simulations. Likewise, theory can provide information that makes it possible to more fully interpret experimental data. By combining the two approaches, we can begin to understand some of the processes that organisms use to tailor their environment.
Atomic force microscopy (AFM) allows us to map the topography and other physical parameters at the nanometre scale. By functionalising the AFM tip with organic compounds, one can map adhesion or elasticity over surfaces in contact with fluids and one can monitor their response as the fluids are changed. X-ray photoelectron spectroscopy (XPS) provides information about the composition and bonding environment in the top 10 nm of a solid and ultrarapid cooling of a wet sample vitrifies the adsorbed water, allowing the solid-fluid interface to be characterised. Field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDXS) provide images with chemical mapping and using a focussed ion beam (FIB) to sequentially mill through a sample, one can create 3D images that show the internal structure and composition at submicrometer scale. X-ray nanotomography (XNT) also provides 3D images without destroying the sample, allowing us to determine physical properties and how they change with time or exposure to solutions, temperature or pressure. Several other synchrotron radiation methods provide a range of other types of information such as atomic structure, particle size and crystal size. Applying these techniques on calcite and chalk, with complementary modelling using density functional theory (DFT) and molecular dynamics (MD), has provided interesting new insight into the processes that affect coccoliths, the hard parts formed by some species of algae. For example, combining nanoscale observations with computational results has proven that organic molecules bind to calcite through -OH functional groups and this bond is much stronger than water, allowing organisms to block some crystal sites, thus favouring growth in a desired direction. Other work has shown that only a few percent of Mg2+ adsorption can change calcite surface tension dramatically.
3:00 AM - E2.02
Low Voltage Electron Microscopy for Imaging the Soft/Hard Materials Interface
David C Bell 1 Natasha Erdman 2
1Harvard University Cambridge USA2JEOL Peabody USAShow Abstract
The interface between soft and hard materials is currently underexplored territory which is critical to underrated structure relationships with the hard/soft materials interface domain. You want high resolution of the hard material, but good contrast (and resolution) of the corresponding soft materials. Low-voltage Electron Microscopy has several advantages: increased cross-sections for inelastic and elastic scattering and hence higher contrast efficiency from each atom and reduced radiation knock-on damage to samples insensitive to other damage mechanisms, which includes most metals, semiconductors and other solid state materials.
Historically, the use of higher TEM voltages were favored since they reduce the spherical and chromatic aberration effects, but the development of spherical aberration correctors has allowed atomic resolution at lower voltages. Although the TEM samples must be significantly thinner for low keV observation, the improvement in contrast for inorganic materials, biological samples and especially nano-biological samples in low-voltage TEM while retaining atomic resolution cannot be understated.
The fundamental aspects of electron microscopy all relate directly to the physics of the interactions between the electron beam and sample. Energetic electrons are described as “ionizing radiation” - the general term used to describe radiation that is able to ionize or remove the tightly bound inner shell electrons from a material. This is obviously an advantage for electron microscopy in that it produces a wide range of secondary signals such as secondary electrons and X-rays, but is also a disadvantage from the perspective that the sample is “ionized” by the electron beam and possibly structurally damaged, which depending on the accelerating voltage happens in a number of different ways.
Low-Voltage High-Resolution Electron Microscopy has several advantages (and of course disadvantages), including increased cross-sections for inelastic and elastic scattering, increased contrast per electron and improved spectroscopy efficiency, decreased delocalization effects and reduced radiation knock-on damage. Together, these often improve the contrast to damage ratio obtained on a large class of samples. 3rd order aberration correction now allows us to operate the TEM at low energies while retaining atomic resolution, which was previously impossible. Using the spherical aberration corrector in conjunction with electron monochromator for example at 40 keV takes the user surprisingly close to the lower bound imposed by fifth-order spherical aberration, and enables imaging with an information limit better than 1Å, and a workable resolution of better than 1.4Å.
3:15 AM - E2.03
Molecular Bridge Enables Anomalous Enhancement in Thermal Transport across Hard-Soft Material Interfaces
Teng Zhang 1 Tengfei Luo 1 2
1University of Notre Dame Notre Dame USA2Center for Sustainable Energy at Notre Dame Notre Dame USAShow Abstract
Thermal resistance at hard-soft material interfaces has been one of the most important bottlenecks for the improvement of thermal transport properties of nanocomposites which are critical for a wide range of applications like thermal interface materials, nanofluids and nanoparticle-assisted therapeutics. Conventional strategies have focused on improving adhesion of the interface to increase thermal conductance. Here we demonstrate a significant enhancement of thermal transport across the hard-soft material interfaces consisting of gold and amorphous polyethylene (PE) by functionalizing the gold surfaces with self-assembled monolayers (SAM). Our transient thermoreflectance (TTR) measurements show remarkable increases by as much as 7 times in the thermal conductance of gold-hexadecane (HD) and gold-paraffin wax (PW) interfaces. Surprisingly, such significant increases are realized despite the observed decrease in the interface adhesion energy when the gold surface is functionalized. Our molecular dynamics (MD) simulations reveal that the SAMs chemically absorbed on the gold surface act as media to bridge the vibrational mismatch (acoustic mismatch) between gold and polymer and thus enable efficient resonance-like thermal transport. Such a strategy can be generalized to any hard-soft material interfaces to provide a design principle that can be used to synthesize nanocomposites for heat transfer applications.
3:30 AM - E2.04
Controlled Morphology of Thin Film Silicon Integrated with Soft Environmentally Responsive Hydrogels
Prithwish Chatterjee 1 Teng Ma 2 Hanqing Jiang 1 2 Lenore Dai 1
1Arizona State University Tempe USA2Arizona State University Tempe USAShow Abstract
Novel materials based on various environmentally responsive polymers hold multiple important applications. However, the functionality of these materials alone is often limited, and thus the integration of these, with other functional materials like Silicon, is strongly desired. Here we demonstrate the capability of integrating thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) hydrogels with Silicon nanoribbons. This will enable the stiff silicon ribbons to become adaptive and drivable by the soft environmentally sensitive substrate, such as becoming mechanically stretched and compressed when inducing a temperature change. Furthermore, we investigate how advanced lithographic techniques can be used to generate patterned deformation on the above integrated structures. We also explore bi-layer hydrogel structures formed by the integration of different types of polymers of PNIPAAm. These structures have been determined to achieve tunable curvature under the influence of different stimuli. The integration of soft materials with traditional hard semiconductor materials could have interesting implications for the development of novel “smart” devices especially in bio-medical aplications.
3:45 AM - E2.05
Integrated Experimental and Computational Studies of Energy-Relevant Hard-Soft Interfaces
Peter Cummings 1 2
1Vanderbilt University Nashville USA2Vanderbilt University Nashville USAShow Abstract
Hard-soft interfaces are ubiquitous in energy-relevant systems. Examples include the subterranean mineral-fluid interfaces that govern carbon sequestration, the electrode-fluid interfaces in batteries and supercapacitors, and the fluid-solid interfaces at which heterogeneous catalysis takes place. For many years, we have studied mineral-fluid interfaces with a combination of molecular (e.g., X-ray reflectivity, quasi-elastic neutron scattering and neutron spin echo) and bulk (e.g., titration) experimental probes closely integrated with molecular dynamics simulations using fluid-solid forcefields derived from ab initio calculations. Recently, as part of the activities of the Fluid Interface Reactions Structure and Transport (FIRST) Engineering Frontier Research Center (EFRC), we have extended this approach to the study of interfaces encountered in batteries, supercapacitors, and heterogeneous catalysis. The FIRST Center performs fundamental research on fluid-solid interfaces based on the premise that the next generation of electrical storage devices with superior performance will require a fundamental knowledge of the nanoscale architecture of the interface, the effect of nanotexture on interfacial properties, and the structural and dynamic changes that occur during charge and discharge cycles. In this presentation, we will provide an overview of our research on the molecular-level modeling and experimental characterization of energy-relevant hard-soft interfaces.
4:30 AM - *E2.06
Particle Mediated Crystal Formation
Jennifer A. Soltis 1 Kairat Sabyrov 1 Virany M. Yuwono 1 Nathan D. Burrows 1 R. Lee Penn 1
1University of Minnesota Minneapolis USAShow Abstract
An on-going challenge in materials synthesis is purposeful control over crystallite size, shape, and microstructure. Our research focuses on the mechanisms by which crystals form, grow, crystallize, and transform, with particular focus on particle mediated crystal formation, crystal growth, and phase transformations. Oriented attachment is a non-classical crystal growth mechanism that can result in twinning as well as the incorporation of defects like dislocations and stacking faults. This mechanism can be exploited to produce nanocrystals with unique and symmetry-defying shapes. Generally speaking, crystal growth typically occurs by a combination of mechanisms. For example, oriented attachment is a particle mediated crystal growth mechanism, but experimental data consistently demonstrate that crystals concomitantly grow by dissolution and reprecipitation. We employ cryogenic transmission electron microscopy (TEM) and in situ TEM, in combination with conventional TEM, dynamic light scattering, X-ray diffraction and scattering, UV-visible spectroscopy, as well as kinetic modeling, to elucidate the fundamental processes that govern the kinetics of crystal growth. Each of these techniques has advantages and limitations, and a combination of methods is crucial to push our understanding of nonclassical crystal growth forward.
5:00 AM - E2.07
Biomolecule Adsorption at Aqueous Graphene Interfaces: Predictions from Advanced Molecular Simulations
Zak E. Hughes 1 Tiffany R Walsh 1
1Deakin University Geelong AustraliaShow Abstract
The non-covalent interaction of biomolecules with materials interfaces and/or nanoparticles is of great interest due to potential applications such as material synthesis, biosensing and nano-medicine.1 These applications have prompted significant interest in the field, however, to fully realize these applications, a deeper understanding of the interfacial interactions occurring at the molecular level is required. Molecular dynamics (MD) simulations, with the ability to predict and reveal interactions at the atomic level, can play a contributing role in elucidating the structure/property relationships of such systems.2
Here, we investigate the interaction of both individual amino acids and peptides at the aqueous graphene interface using a polarizable force-field specifically developed to model the interaction of biomolecules with graphitic nanostructures.3 The free-energy of adsorption of all twenty naturally-occurring amino acids has been determined from meta-dynamics simulations.4 Furthermore, we model the adsorption of peptides known to bind to the basal plane of graphene,5,6 and mutant analogues. Traditionally, MD simulations of peptides at interfaces have struggled to ensure adequate sampling of the conformational space. We address this challenge via use of the replica exchange with solute tempering (REST) technique.7,8 Our results allow the binding propensity of the individual amino acids to be compared against the binding propensity of residues within peptides. This provides valuable information regarding how the peptide sequence influences the interfacial binding properties, moving us closer to the ultimate goal of de novo design of materials-selective peptides.
 Grey, J.J., The interaction of proteins with solid surfaces, Curr. Opin. Struct. Biol., 2004, 14, 110-115.
 Tang, Z., et al., Biomolecular recognition principles for bionanocombinatorics: an integrated approach to elucidate enthalpic and entropic factors, ACS Nano, 2013, 7, 9632-9646.
 Hughes, Z.E., Tomásio, S.M. and Walsh, T.R., Efficient simulations of the aqueous bio-interface of graphitic nanostructures with a polarisable model, Nanoscale, 2014, 6, 5438-5448.
 Laio, A. and Parrinello, M., Escaping free-nergy minima, Proc. Natl. Acad. Sci. USA, 2002, 99, 12562-12566.
 Kim, S.N., et al., Preferential Binding of Peptides to Graphene Edges and Planes, J. Am. Chem. Soc., 2011, 133, 14480-14483.
 So, C.R., et al., Controlling Self-Assembly of Engineered Peptides on Graphite by Rational Mutation,ACS Nano, 2012, 5, 1648-1656.
 Terakawa, T., et al., On easy implementation of a vairent of the replica exchange with solute tempering in GROMACS, J. Comput. Chem., 2010, 32, 1228-1234.
 Wright, L.B. and Walsh, T.R., Efficient conformational sampling of peptides adsorbed onto inorganic surfaves: insights from a quartz binding peptide, Phys. Chem. Chem. Phys.,2013, 15, 4715-4726.
5:15 AM - E2.08
Understanding the Structure and Dynamics of Peptide-Based Switchable Metamaterials: A Molecular Dynamics Study
Kurt Laurence Murray Drew 1 J. P. Palafox-Hernandez 1 Tiffany R. Walsh 1
1Deakin University Geelong AustraliaShow Abstract
An area of growing interest is the development of noble-metal metamaterials because of their unique properties[1,2]. Development of versatile generation strategies for production of these metamaterials remains challenging; these materials comprise assemblies of nanoparticles of different compositions, arranged in 3-D arrays; fine control over the interparticle spacings in these arrays is essential. It is also highly desirable that these arrays can be dynamically reconfigured. As the first steps towards realizing these goals, we investigate Au- and Ag-binding peptide sequences conjugated with light-switchable azobenzene moieites, for the purpose of designing stimuli-responsive biomolecule linkers that can ultimately facilitate assembly of different types of nanoparticles into 3D arrays. Here, we use advanced sampling molecular dynamics simulations to investigate the molecular conformations and materials-binding properties of these molecules. These peptide sequences have a light sensitive thiol-maleimide azobenzene thiol-maleimide (MAM) unit conjugated onto either the N- or the C-terminus of the peptide. We have also carried out well-tempered meta-dynamics simulations to estimate the free energy of binding, of the MAM unit alone, at the Au and Ag aqueous interfaces. Our results indicate that the MAM unit binds more strongly at Au compared with Ag, with the trans conformation of the MAM binding more strongly than the cis for both metals. Our simulations of the N- and C-conjugated peptides reveal that the presence of the MAM unit can significantly affect the adsorbed structures and conformational dynamics of the surface adsorbed peptide. Our findings provide guidance in the design and development of a stimuli-responsive biomolecule linker for nanoparticle assembly purposes.
 P.-Y. Chen, J. Soric and A. Alu, Adv. Mater., 2012, 24, OP281-304.
 K. L. Young, M. B. Ross, M. G. Blaber, M. Rycenga, M. R. Jones, C. Zhang, A. J. Senesi, B. Lee, G. C. Schatz and C. A. Mirkin, Adv. Mater., 2014, 26, 653-9.
 T. Terakawa, T. Kameda and S. Takada, J. Comput. Chem., 2011, 32, 1228-34.
 A. Barducci, G. Bussi and M. Parrinello, Phys. Rev. Lett., 2008, 100, 020603.
 K. L. M. Drew, Z. Tang, J. P. Palafox-Hernandez, Y. Li, M. T. Swihart, C. -K. Lim, P. N. Prasad, M. R. Knecht and T. R. Walsh, in preparation.
5:30 AM - E2.09
A Silica Surface Model Database and Computational Prediction of Specific Peptide Binding as a Function of pH and Particle Size
Fateme S Emami 1 Rajiv J Berry 2 Rajesh R Naik 2 Valeria Puddu 3 Siddarth V Patwardhan 4 Carole C Perry 3 Hendrik Heinz 1
1University of Akron Akron USA2Air Force Research Laboratory Dayton USA3Nottingham Trent University Nottingham United Kingdom4University of Strathclyde Glasgow United KingdomShow Abstract
Silica nanostructures are biologically available and find wide applications for drug delivery, catalysts, separation processes, and composites. However, specific recognition of biomolecules on silica surfaces and control in biomimetic synthesis remain largely unpredictable. A silica force field is introduced that resolves numerous shortcomings of prior silica force fields over the last 30 years and reduces uncertainties in computed interfacial properties relative to experiment
from several 100% to less than 5%. In addition, a silica surface model database is introduced for the full range of variable surface chemistry and pH (Q2, Q3, Q4 environments with adjustable degree of ionization) that have shown to determine selective molecular recognition. The force field enables accurate computational predictions of aqueous interfacial properties of all types of silica, which is substantiated by extensive comparisons to experimental measurements. The parameters are integrated into multiple force fields for broad applicability to biomolecules, polymers, and inorganic materials (AMBER, CHARMM, COMPASS, CVFF, PCFF, INTERFACE force fields). We also explain mechanistic details of molecular adsorption of water vapor, as well as significant variations in the amount and dissociation depth of superficial cations at silicaminus;water interfaces that correlate with zeta;-potential measurements and create a wide range of aqueous environments for adsorption and self-assembly of complex molecules.
The systematic analysis of adsorption free energies and binding conformations of distinct peptides to silica surfaces as a function of pH and particle size will be specifically reported as a prime example for validation and specific predictions. Example peptides were positively charged, neutral, and negatively charged, and a variety of silica surfaces were employed. The computed binding affinities agree remarkably with adsorption isotherms and zeta potential measurements for the same systems, and underline the significance of the surface chemistry, pH, and topography for specific binding outcomes. Adsorption free energies and binding residues were quantitatively analyzed, and tunable contributions to binding identified, including ion pairing, hydrogen bonds, hydrophobic interactions, and conformation effects. The resulst show that molecular dynamics simulation with the CHARMM-INTERFACE force field and synthesis can be employed to optimize interactions of all types of silica surfaces with organic and biological molecules under realistic solution conditions at the scale of 1 to 100 nm. Applications include the controlled binding and release of drugs, cell receptors, polymers, surfactants, and gases.
5:45 AM - E2.10
Conformational Effects of Histidine Protonation on Gold-Peptide Adsorption
J. Pablo Palafox-Hernandez 1 Tiffany R. Walsh 1
1Institute for Frontier Materials, Deakin University Waurn Ponds AustraliaShow Abstract
Controlled peptide adsorption at aqueous metallic interfaces is relevant to many bio-inspired applications including self-assembled materials, biosensors, and nano-catalytic materials. To realize these applications, a greater depth of understanding of the underlying principles governing peptide adsorption is required. Recently, a comprehensive study of peptide binding affinity at aqueous gold interfaces identified certain residues as behaving as strong-binding ‘anchor&’ points (1). This study also suggested that the local environment of these anchoring residues could modulate the binding propensity of these residues. Here, we use the known peptide sequence Z1, KHKHWHW (2), to systematically investigate how a small change to the sequence environment, namely the position of the histidine protonation site, impacts on adsorption at the aqueous Au (111) interface, employing state-of-the-art replica-exchange simulation approaches (3). The sequence characteristics of Z1 allow us to methodically probe these positional and environmental effects (4). We find that the position of the protonated histidine drastically modifies the modes of adsorption of this peptide at the aqueous Au interface, producing non-local effects that can modulate the behavior of non-neighboring residues. We also find that the location of the protonated histidine could either promote or disrupt co-operative binding of the peptide as a whole. These findings contribute to the on-going generation of systematic rules that will ultimately facilitate greater control over peptide-materials binding.
(1) Tang Z.; Palafox-Hernandez J. P.; Law C. W.; Hughes Z. E.; Swihart M. T.; Prasad P. N.; Knecht M. R.; Walsh T. R. ACS Nano 2013, 7, 9632
(2) Peelle B. R.; Krauland E. M.; Wittrup K. D.; Belcher A. M. Langmuir, 2005, 21, 6929.
(3) Terakawa, T.; Kameda, T.; Takada, S. J. Comput. Chem.2011, 32, 1228.
(4) Palafox-Hernandez J. P.; Walsh T. R. in submmition, 2014.
E1: Nucleation and Self-Assembly
Monday AM, December 01, 2014
Sheraton, 2nd Floor, Back Bay B
9:30 AM - *E1.01
Do We Understand Crystallization?
Jens Rieger 1 Matthias Kellermeier 1
1BASF SE Ludwigshafen GermanyShow Abstract
Crystallization of inorganic (and organic) matter often proceeds via intermediate stages, rather than by simple nucleation and growth mechanisms.These precursor stages not only comprise crystal modifications that are less stable than the final one, but also amorphous, hydrated (nano-) particles and emulsion-like precursors have been observed. These precursors tend to aggregate or restructure before being dissolved and entering the next structural stage.[1,2]
Structural information on all these intermediates - and by which mechanisms they form - is essential for the development of additives to control crystallization processes - either to achieve particles with a certain size distribution, with certain functionalities or to impede crystallization in water treatment processes.
Data on the structural evolution of precipitating calcium carbonate and other systems obtained by means of X-ray microscopy and quench cryo-transmission electron microscopy will be presented, emphasizing that the respective particle formation processes do not follow classical nucleation and growth mechanisms.
The role of polymers in nucleating, templating, stabilizing and/or preventing these structures is outlined, together with possible applications. Since charged polymers, like polycarboxylates, not only interact with the inorganic precursors and crystals but also with the cations right from the beginning of the crystallization it is essential to understand the details of this interaction. Time-resolved molecular modelling experiments on the complexation mechanisms of calcium to polycarboxylates unravel an unexpected richness in the binding process.
 Rieger, J.; Kellermeier, M.; Nicoleau, L.; Angew. Chem. Int. Ed. 2014 in press.
 Gebauer, D.; Kellermeier, M.; Gale, J.D.; Bergström, H.; Cölfen, H.; Chem. Soc. Rev. 43, 2014, 2348.
10:00 AM - E1.02
Regulating Ice Nucleation via Modifying Solid Surfaces with Anti-Freezing Proteins
Jianjun Wang 1
1Institute of Chemistry Chinese Academy of Sciences Beijing ChinaShow Abstract
Regulating the ice nucleation has broad implications in a variety of areas such as cryopreservation of cells and tissues, prevention of the freezing of crops, cloud seeding and snow making etc. Although it is well recognized that ice nucleation usually initiates at the liquid-solid interfaces, current fundamental understanding of nucleation in general and ice nucleation in particular is insufficient. Thus it remains a great challenge to tune the ice nucleation.This talk discusses the tuning of ice nucleation via modifying the solid surfaces with antifreeze proteins (AFP), which play an irreplaceable role for the survival of many living organisms in subzero environments. Moreover we found in our experiments that the structure of the interfacial water is crucial in tuning the ice nucleation. Our results not only complements the widely accepted mechanism of AFPs, that is, AFPs inhibit the growth of microscopic ice crystals at subzero temperatures via absorption-inhibition. Also the results shed a new light on the fundamentals of the ice nucleation, which is critical for the promotion or suppression of the ice nucleation.
10:15 AM - E1.03
Polymorph Control via Surface-Selective Peptide Adsorption: Insights from the Intrinsically Disordered Peptide n16N
Aaron H. Brown 1 2 Tiffany R Walsh 1
1Deakin University Geelong Australia2Warwick University Coventry United KingdomShow Abstract
Bio-composites provide inspiration for the design and generation of new synthetic high-performance composites. For example, in nacre, proteins play an important role in exerting polymorph control of CaCO3, stabilizing the aragonite polymorph1 over the more favorable calcite. How this stabilization works at the molecular level is unknown, due to our lack of understanding of how the protein structure(s) relate to the function in this context. Determination of these protein structures particularly when adsorbed at the mineral interface, is now possible, but challenging to accomplish in practice2.
A derivative of one such protein known as n16N, an intrinsically disordered peptide, has been experimentally shown to stabilize aragonite at a model tri-layer interface comprising chitin, an n16N overlayer and the mineral3; all of which approximate the interfaces found in nacre. Chitin is chiefly found in two polymorphs, α- and β-chitin. Experiments show that only β-chitin, in the presence of the adsorbed n16N overlayer, is capable of conferring polymorph control (i.e. aragonite formation)3. Experiments also suggest that n16N preferentially binds to β- over α-chitin3. Having previously successfully predicted the ensemble of structures of n16N in solution4, here we build on these insights to investigate the structures of n16N adsorbed at the aqueous α- and β-chitin interfaces, to determine the origins of this selectivity and reveal the exposed sites on the peptide potentially responsible for aragonite stabilization.
Using molecular dynamics simulations, namely Replica Exchange with Solute Tempering (REST)5, we provide insight into the chitin polymorph binding selectivity of n16N. The interplay between the n16N sequence, structure and function at the chitin interface is further investigated via umbrella sampling simulations of 9 representative amino acids adsorbed at both the (100) and (010) facets of the α- and β-chitin aqueous interfaces. Our findings are not only key to understanding the mechanism by which n16N can facilitate the formation of aragonite, but are also applicable to the potential use of chitin nanoparticles as a drug delivery vehicle.
1. S. Collino and J. S. Evans, Biomacromol., (2008), 9, 1909-1918
2. P. A. Mirau, R. R Naik and P. Gehring, J. Amer. Chem. Soc., (2011), 133, 18243-18248
3. E. C. Keene, et al., Cryst. Growth Des. (2010), 10, 5169-5175.
4. A. H. Brown, P. M. Rodger, J. S. Evans , T. R. Walsh, (2014), In preparation
5. T. Terakawa, et al., J. Comput. Chem., (2011), 32, 1228-1234
10:30 AM - E1.04
Precise Control of Polymorphism in CaSO4 Mineralization at Room Temperature
Matthias Kellermeier 1 Ulrich Tritschler 2 Alexander E. S. Van Driessche 3 Helmut Coelfen 2
1BASF SE Ludwigshafen Germany2University of Konstanz Konstanz Germany3Free University of Brussels Elsene BelgiumShow Abstract
Calcium sulfate is a highly abundant natural mineral that finds extensive application as raw material in construction processes. It can exist in three major crystalline polymorphs, or rather hydrates, which differ essentially in their respective water content: gypsum (the dihydrate, CaSO4#8729;2H2O), bassanite (the hemihydrate, CaSO4#8729;0.5H2O), and anhydrite (the anhydrous form, CaSO4). All of these three phases are used as key components in products like mortars, plasters, binders or adhesives. Thus, it is desirable to get access to either of the different polymorphs and control their formation in, ideally, straightforward reactions at low temperatures. Under ambient conditions, precipitation of calcium sulfate from aqueous solutions readily affords gypsum, the thermodynamically stable form, while bassanite and in particular anhydrite can only be obtained at significantly higher temperatures. Therefore, the current practice to produce these phases is (partial) dehydration of gypsum by heating at 100-150°C, an energy- and cost-intensive process.
In the present contribution, we show that both bassanite and anhydrite can also be obtained at room temperature by means of a simple precipitation step in organic media. To that end, aqueous solutions of calcium sulfate were reacted with an excess of an organic solvent like ethanol, giving well-defined bassanite nanoparticles. Both the yield and kinetic stability of these particles can be tuned by adjusting certain experimental parameters, such as the final water content in the reaction medium. In this way, either phase-pure bassanite or defined mixtures with gypsum can be prepared. Furthermore, below a certain threshold in the water content, a gradual transition in the product composition from bassanite to anhydrite is observed so that, again, either phase-pure materials or binary mixtures of the two polymorphs are formed. Taken together, the collected data allow for a precise control of calcium sulfate polymorphism under ambient conditions and even enable the formulation of phase diagrams for predicting product composition as a function of distinct process parameters. Our results thus provide an alternative low-temperature route for the synthesis of bassanite and anhydrite, and furthermore highlight that organic solvents - which are often used to quench crystallization reactions - can actually induce the formation of metastable phases rather than freezing any ongoing processes.
10:45 AM - E1.05
Soft Matter under Hard Confinement
George A Floudas 1 Yasuhito Suzuki 2 Stelios Alexandris 1 Agathaggelos Iosifidis 1 Hatice Duran 3 Martin Steinhart 4 Hans Juergen Butt 2
1University of Ioannina Ioannina Greece2Max Planck Institute for Polymer Research Mainz Germany3TOBB University of Economics and Technology Ankara Turkey4University of Osnabrueck Osnabrueck GermanyShow Abstract
Soft matter organization under hard confinement can be fundamentally different from that obtained in thin films or in the bulk. Nanoporous hard templates provide a two-dimensionally confined space in which self-organization processes such as crystallization, protein secondary structure formation, mesophase formation and phase separation can be altered. Herein we employ self-ordered nanoporous aluminum oxide (AAO) made by the electrochemical anodization of aluminum substrates as the inorganic model matrix that provides the required uniformity in diameter/length, thermal stability and resistance to organic solvents. Understanding the self-assembly, thermodynamics and dynamics of soft materials under confinement will allow for their rational design as functional devices with tunable mechanical strength, processability, electronic and optical properties.
A principal focus of this work is finding the basic underlying principles that give rise to directed self-assembly and controlled phase state in a range of soft materials under confinement. This includes the synthesis of hard templates, subsequent infiltration, surface functionalization and surface characterization as well as structural, thermodynamic and dynamical characterization in a number of soft materials with different type of interactions. These encompass crystallizable polymers [1-4], amorphous polymers , amphiphilic molecules, liquid crystals [6,7] and biopolymers  with important potential applications. These studies addressed the effect of confinement on: (a) the type of nucleation (homogeneous vs. heterogeneous), the size of critical nucleus, crystal orientation and the possibility to control the overall crystallinity; (b) the segmental and global polymer dynamics; (c) the nematic-to-isotropic, crystal-to-nematic and columnar liquid crystal-to-crystal phase transitions in rod- and disk-like liquid crystals, respectively and (d) the self-assembly and dynamics on α-helical polypeptides.
 H. Duran, M. Steinhart, H.-J. Butt, G. Floudas, Nano Letters 11,1671, 2011.
 Y. Suzuki, H. Duran, M. Steinhart, H.-J. Butt, and G. Floudas, Soft Matter 9, 2769, 2013.
 Y. Suzuki, H. Duran, W. Akram, M. Steinhart, G. Floudas and H.-J. Butt, Soft Matter, 9, 9189, 2013.
 Y. Suzuki, H. Duran, M. Steinhart, H.-J. Butt and G. Floudas, Macromolecules 47, 1793, 2014.
 S. Alexandris, G. Sakellariou, M. Steinhart, G. Floudas, Macromolecules (DOI: 10.1021/ma5006638) 2014.
 H. Duran, M. Steinhart, H.-J. Butt, G. Floudas, Nano Letters 11,1671, 2011.
 C. Grigoriadis, H. Duran, M. Steinhart, M. Kappl, H.-J. Butt, G. Floudas ACS Nano 11, 9208, 2011.
 H. Duran, A. Gitsas, G. Floudas, M. Mondeshki, M. Steinhart, W. Knoll, Macromolecules (Commun.) 42, 2881, 2009.
11:30 AM - *E1.06
Exploring the Physical Basis of Dense Liquid Formation in the CaCO3-H2O System
Adam Wallace 1
1University of Delaware Newark USAShow Abstract
Interest in the molecular scale processes underlying the onset of mineral formation is on the rise due to the detection of nanoscale ion aggregates in concentrated aqueous solutions. As the archetypal system for “pre-nucleation” clusters, the early stages of calcium carbonate have been intensely scrutinized from both theoretical and experimental perspectives. The definition of a pre-nucleation cluster, initially described as being relatively constrained in size and thermodynamically stable with respect to both dissolution and growth , is currently evolving and is now identified with a rather broad distribution of aqueous species whose continued growth is restricted by diffusion limitation . This reinterpretation is due in part to the results of molecular dynamics simulations that suggest an exponentially decaying cluster size distribution rather than monodisperse cluster species . The simulated size distribution is also consistent with the results of cryo-TEM  and the predictions of classical nucleation theory (CNT). This work  uses atomistic and coarse-grained simulation techniques to explore the formation of clusters from supersaturated solutions. The results of molecular dynamics simulations indicate the accessibility of a metastable liquid-liquid binodal/spinodal. Coalescence and partial dehydration of the dense liquid droplets results in the formation of a solid phase whose structure is consistent with amorphous calcium carbonate. Coarse-grained simulations of fluid-fluid separation in the spinodal regime produce cluster size distributions that are qualitatively similar to those produced from molecular dynamics simulations of spontaneous phase separation in the CaCO3 system . The presence of a dense liquid phase of CaCO3 is also supported by recent experimental efforts , which suggest an entropy driven phase transition may precede solid CaCO3 formation under certain conditions.
 Gebauer et al. (2008) Science322 1819-1822.  (2012) Faraday Discuss.155, 139-180.  Demichelis et al. (2011) Nat. Commun. 2, 590.  Pouget et al. (2009) Science323 1455-1458.  Wallace et al. (2013) Science341 885-889.  Bewernitz et al. (2012) Faraday Discuss.159 291-312.
12:00 PM - E1.07
Functionalized Carbon Nanomaterials as Nucleants for Crystallization
Hannah S Leese 2 Lata Govada 1 Emmanuel Saridakis 1 3 Sahir Khurshid 1 Robert Menzel 2 Sheng Hu 2 Takuya Morishita 4 Adam Clancy 2 Naomi Chayen 1 Milo S. P. Shaffer 2
1Imperial College London London United Kingdom2Imperial College London London United Kingdom3National Centre of Scientific Research amp;#8220;Demokritos,amp;#8221; Aghia Paraskevi Athens Greece4Toyota Central Ramp;D Labs Nagakute JapanShow Abstract
Protein crystallisation is a vital process towards the success of rational drug design for treatment of diseases.1 However, obtaining protein crystals of high quality to determine their complex structure is non-trivial. Therefore, the design of nucleant materials to positively direct protein crystallisation is sought. Here, by tailoring properties through the functionalisation of several nanocarbons including commercial and in house MWNTs and SWNTs, we have systematically assessed how these materials direct and promote protein crystallisation.
Two complementary techniques have been utilised for nanocarbon functionalisation resulting in a library of anionic, cationic, hydrophilic and hydrophobic nucleants. The versatile nature of nanocarbons has enabled us to tailor the nucleant chemistry and as a result several proteins were crystallised including five model proteins: lysozyme, thaumatin, trypsin, haemoglobin and catalase. The crystallisation of target proteins has also been investigated.
1. E. Saridakis and N. E. Chayen Trends in Biotechnology, 2009, 27, 99.
12:15 PM - E1.08
Atomistic Modeling of Colloidal Nanoparticles with Active Ligands: Solvation, Electroactivity, pH-Activity, and Bio-Activity
Petr Kral 1
1University of Illinois at Chicago Chicago USAShow Abstract
We present our recent collaborative studies of colloidal nanoparticles with active ligands that can control the nanoparticle behavior. In particular, we show that 1) nanoparticles of different sizes can have different solvation properties, 2) self-assembly and positioning of nanoparticles at the interfaces of different ionic solvents can be controlled by electric fields, 3) pH can control the self-assembly of nanoparticles into exotic superstructures, and 4) ligands can determine the biological responses or nanoparticles. We use atomistic molecular dynamics simulations to capture the unique characteristics of these novel systems and explain their properties through the physical, chemical, and biological processes taking part at their ligands.
12:30 PM - E1.09
Soft, Stretchable Surface-Chemical Patterns for the Controlled Synthesis and Manipulation of Hard Materials
John J. Bowen 1 Jay Taylor 1 Stephen A. Morin 1 2
1University of Nebraska - Lincoln Lincoln USA2University of Nebraska - Lincoln Lincoln USAShow Abstract
We describe the synthesis of micron-scale patterns of surface-chemical functional groups on thin films of elastomeric polymers and illustrate the use of these soft structures in hard material crystallization. Using elastic deformations, such as those caused by tensile strain, we reconfigure critical features (e.g., geometry and molecular density) of these “soft” surface-chemical patterns enabling dynamic control of surface energy and the arrangement of functional groups. We use this capability to direct the surface nucleation and growth of hard, crystalline materials that possess functional (e.g., electronic or optical) properties. We further modify the morphology and structure-property relationships of these crystals by rationally manipulating their spatial arrangement through reversible deformations of the elastomeric films. Specifically, we report the surface-chemical patterning of silicones, such as polydimethylsiloxane, and the use of these materials as dynamic substrates for the mineralization of metal chalcogenides and oxides. We are inspired by the soft, active materials (e.g., cellular machinery) that produce sophisticated hard-soft composites in biomineralization processes; however, we do not attempt to replicate the mechanistic complexity found in these systems. Instead, our approach focuses on simple analogs—chemically patterned two-dimensional soft surfaces in this case—that mimic important characteristics (e.g., dynamic surface chemistry) found in biology. This approach eliminates many of the constraints presented by biology and simplifies experimental design and interpretation. The hybrid hard-soft materials we report are difficult to fabricate directly using other approaches and their physical properties are potentially applicable to soft sensors and electronics.
12:45 PM - E1.10
Nucleation and Growth of Mineral Salts on Liquid-Impregnated Surfaces
Srinivas Bengaluru Subramanyam 1 Gisele Azimi 2 Kripa Varanasi 2
1Massachusetts Institute of Technology Cambridge USA2Massachusetts Institute of Technology Cambridge USAShow Abstract
Crystallization plays a vital role in many fields like biomineralization, production of pharmaceuticals, scale and gas hydrate formation in oil and gas pipelines etc. Controlling the nucleation and growth aspects of crystallization is of utmost importance to achieve a better understanding of the processes and to improve the efficiency of the systems. Here we suggest a novel way of achieving this by designing a solid-liquid hybrid surface - a solid textured surface imbibed with a liquid. The properties of the impregnating liquid can be modified to alter the nucleation and growth rates of the crystals on the surface. We use gypsum as a model system to demonstrate the advantages of these impregnated surfaces. The use of a lower surface tension liquid that completely spreads on the solid surface results in a lower nucleation rate of the gypsum crystals. The growth of the salt crystals is also dependent on the crystal orientation, which in turn can be controlled by suitably modifying the liquid. The flexibility offered by these surfaces in terms of the solid texture and the impregnating liquid can be used to tune the different aspects of crystallization with high precision.
John Harding, University of Sheffield
Derk Joester, Northwestern University
Roland Krouml;ger, University of York
Paolo Raiteri, Curtin University
Symposium Support ACS Biomaterials Science amp; Engineering
Biomaterials Science, RSC
University of Sheffield
E4: Carbonate-Based Systems
Tuesday PM, December 02, 2014
Sheraton, 2nd Floor, Back Bay B
2:30 AM - *E4.01
Precipitation of CaCO3 in Microemulsions
Liane G. Benning 2 Tomasz M Stawski 2 Adriana Matamoros Veloza 2 Teresa Roncal-Herrero 1 Roland Kroeger 1
1Department of Physics, University of York York United Kingdom2University of Leeds Leeds United KingdomShow Abstract
Calcium carbonates are the most ubiquitous functional biomineral in nature. Microscopic living organisms direct CaCO3 precipitation from aqueous ions with an unprecedented level of control and this underpins a vast array of Earth system processes, including the global carbon cycle. For example, cocolithophores internally mineralize CaCO3 into single crystal calcite frustule plates that are structurally highly complex suggesting a complicated, but controlled chemical route between dissolved ions and final calcite morphology. Being able to elucidate and mimic, such biomineralization mechanisms, would not only increase our knowledge about important processes supporting a vast array of marine planktonic life forms, but would also provide us with a powerful tool to nanoengineer complex (bio)inorganic materials.
Here we report on a study that mimiced such processes through the use of water-in-oil microemulsions. Microemulsions increasingly gain interested in colloid chemistry because they offer a confined reaction environment ideal for synthesis of nanoparticles of low polydispersity and well-defined shapes. Water-based micelles stabilised by an interface surfactant are typically 1-10 nm in diameters and each carries dissolved ions and upon mixing and collision the individual micelles exchange their contents. Thus, they are well-suited for mimicking the nanoscale mineral precipitation at the polar/non-polar interface. We used such microemulsions as bioinspired nanoreactor systems and mimiced CaCO3 mineralization. We followed the reaction upon mixing of two initally clear microemulsions (containing either [Ca2+] or [CO32-]) and quantified the gradual development of a white precipitate using ex situ and in situ methods.
Our ex situ data showed stabile nanoparticles (Oslash; ~10 nm) of low-polydispersity that eventually formed large aggregates (Oslash; ~250 nm). Time-resolved, in situ small angle X-ray scattering demonstrated a slow but progressive agglomeration of liquid-like, ion-carrying micelles to larger mass-fractals (Oslash; ~ 100 nm ) of high fractal dimension (Df >2.8). Our liquid-cell TEM results confirmed that these liquid phase aggregates remain stable and only upon destabilization did a transformation to crystalline phases take place.
By combining these results with the fact that an individual micelle can accommodate in its water core only a limited number of reacting ions, we hypothesize that these micellar mass-fractal-like aggregates likely contain only liquid-like CaCO3 complexes stabilised by the confinement and interfaces and not CaCO3 solid particles per se. Only once the micellar large aggregates are destabilized is crystallization induced.
3:00 AM - E4.02
On the Existence of Prenucleation Clusters of Alkaline Earth Carbonates
Paolo Raiteri 1 Raffaella Demichelis 1 Julian D Gale 1 Matthias Kellermeier 2 Denis Gebauer 2
1Curtin University Perth Australia2University of Konstanz Konstanz GermanyShow Abstract
Carbonates are ubiquitous materials that can either have a positive or negative impact on life and the economy. Biomineralisation and carbon sequestration are examples of areas where the formation of carbonate minerals have a positive effect, while the formation of scale in pipes is a global industrial problem, which causes down times and major losses to chemical and oil extraction companies.
In recent years the appearance of calcium carbonate stable clusters and of a dense liquid phase before the onset of nucleation has been proposed and verified, both experimentally and computationally [1-3]. This has led to a new picture of the formation pathway of carbonate minerals emerging. Initially, the ions aggregate to form dynamic chain like structures [1,2] (DOLLOP) that, upon increase in the ion activities, undergo a liquid-liquid phase separation to form a dense liquid phase . This dense liquid phase progressively looses water and precipitates in the form of amorphous calcium carbonate, which eventually transforms into one of the commonly found anhydrous polymorphs.
This phenomenon is believed not to be limited to calcium carbonate, but to be a general growth mechanism for the formation of many minerals , such as the other alkaline earth carbonates, sulphates and phosphates. Here large-scale computer simulations can provide a unique opportunity to test this hypothesis . A carefully parameterised force field, which was calibrated against the thermodynamics of the species in solution and in the crystalline phases [2,5], has indeed been already used to study this very phenomenon for the calcium carbonate system . Here we will present our results on the development of new force fields for the study of alkaline earth metal carbonates in aqueous solution and their application to investigate the existence of prenucleation clusters in these systems.
 Gebauer et. al. (2008) Science. 322, 1819-1822.
 Demichelis et. al. (2011) Nat. Commun. 2, 590.
 Wallace et. al. (2013) Science, 341, 885-889.
 Gebauer et. al. (2014) Chem. Soc. Rev., DOI: 10.1039/C3CS60451A.
 Raiteri, et al. (2010) J. Phys. Chem. C, 114, 5997- 6010.
3:15 AM - E4.03
Interfacial Chemistry and Stability of Membrane-Confined Mineral Precursors
Michael L. Whittaker 1 Chantel C. Tester 1 Derk Joester 1
1Northwestern University Evanston USAShow Abstract
Many biological minerals are synthesized from metastable precursor nanophases, which are concentrated at the site of mineral deposition and subsequently converted to a stable biomineral composite. These transient precursors are first synthesized within lipid membrane vesicles, which facilitate the formation, stabilization, transport, and deposition of the metastable material. Organisms&’ use of metastable precursors within liposomes is well documented, but the mechanism(s) of stability and the role of the lipid membrane chemistry on the mineralization process remain poorly understood. Using dioleoylphosphotidylcholine (DOPC) liposomes as a model system for intravesicular mineral precursor formation, we have previously shown that membrane confinement alone can stabilize single amorphous calcium carbonate (ACC) nanoparticles for over 24 hours. Recently, we have extended this model to giant liposomes 10-100 mu;m in diameter. These liposomes enclose over six orders of magnitude more volume than biological vesicles, yet ACC particles formed in the absence of any additives do not crystallize for over one week. We attribute the (meta)stability afforded by liposomal confinement to the exclusion of strong heterogeneous nucleators and the resulting high nucleation barriers for crystalline polymorphs.
In nanoscale biological vesicles, the high surface-to-volume ratio of a liposome permits extensive interaction with a mineral phase contained within. Membrane surface chemistry is therefore an important consideration in the pathway from precursor to stable biomineral. In both small and giant liposomes, ACC was distributed throughout the liposome lumen just after formation and was not intimately associated with the DOPC membrane. However, altering the methylation of lipid headgroups, or introducing biologically important lipids like phosphatidylethanolamine and phosphotidylserine drastically alters the degree of membrane interaction, morphology, and stability of ACC. Large populations of thousands of giant liposomes, isolated from highly concentrated suspensions, were observed with polarized light microscopy and characterized with confocal Raman spectroscopy to study the rates of ACC crystallization within liposomes of different lipid compositions. From these rates, kinetic barriers for crystallization and the relevant interfacial energies were determined. These data will help guide experimental and computational investigations of ACC in complex, but biologically relevant conditions.
1. Tester, Chantel C. et al. Faraday Discussions 159 (2012): 345-356.
2. Tester, Chantel C. et al. Chemical Communications 50.42 (2014): 5619-5622.
3:30 AM - E4.04
Shell Mineralization of the Acorn Barnacle Balanus Amphitrite
Richard K Everett 2 Daniel K Burden 1 Daniel E Barlow 1 Kenan P Fears 1 Bradley de Gregorio 2 3 Rhonda M Stroud 2 Beatriz Orihuela 4 Daniel Rittschof 4 Kathryn J. Wahl 1
1U.S. Naval Research Laboratory Washington USA2Naval Research Laboratory Washington USA3Nova Research Alexandria USA4Duke University Beaufort USAShow Abstract
Acorn barnacles like Balanus amphitrite develop complex, protective shells surrounding their soft tissues. On the sides, the shells are comprised of multiple, interlocking plates enabling vertical and circumferential expansion throughout the life of the organism; on the top, there are two movable plates enabling feeding when open and protecting the barnacle from predation and from dehydration during intertidal cycles when closed. Many acorn barnacles also have a mineralized base plate underneath. The shells are composed primarily of calcium carbonate, and unlike mollusks, in the form of calcite rather than aragonite. We have examined the initial formation of calcified structures in juvenile and adult barnacle base plates using a variety of optical and x-ray spectroscopies including x-ray tomography, high resolution transmission electron microscopy (HR-TEM), atomic force microscopy-based Fourier transform infrared spectroscopy (AFM-IR), micro-Raman spectroscopy, and scanning electron microscopy (SEM). Samples were examined in plan view, both in vivo and ex situ, as well as with focused ion beam milled cross sections ex situ. We find that the mineralized regions of the base plates are comprised of highly oriented, hierarchically structured calcite with nanometer to micron-sized grains. Underneath the calcified structures are cuticular tissues enriched in Ca and Mg, and proteinaceous material. The initial mineralization of barnacle shell begins on the upper shell, while the base plate underneath begins to calcify about two weeks after metamorphosis from cypris larvae. Mineralization proceeds inwards in a thin prismatic layer, as well as outwards from the periphery as the barnacle grows. We will describe the heirarchy, structure and composition of the base plate as it develops, including evidence for amorphous calcium carbonate within the mineralized regions.
3:45 AM - E4.05
Incorporation, Structure and Properties of Calcite Crystals Occluding Amino Acids
Yi-Yeoun Kim 1 Beatrice Demarchi 2 Miki E. Kunitake 4 David Sparks 5 Boaz Pokroy 6 Chiu C. Tang 7 David Christopher Green 1 Kirsty Penkman 3 Lara A. Estroff 4 John Harding 5 Fiona C. Meldrum 1
1University of Leeds Leeds United Kingdom2University of York York United Kingdom3University of York York United Kingdom4Cornell University Ithaca USA5University of Sheffield Sheffield United Kingdom6Technion Haifa Israel7Diamond Didcot United KingdomShow Abstract
The introduction of occluded biomacromolecules in biogenic calcite has been shown to physical properties such as hardness. Inspired by this, synthetic ‘large&’ molecules such as micelles, when incorporated, can also increase hardness with comparable structural effects. Further still, unprecedentedly high incorporation of amino acids has been reported, however the physical ramifications were not investigated. Here, the incorporation of Asp and Gly in calcite is studied extensively by HPLC, high-resolution pXRD and nanoindentation. Initially, quantification of occluded amino acid in calcite single crystals is determined, revealing a quasi-linear dependence on initial [amino acid]/[Ca] ratio. Secondly, a strong relationship between pXRD/Rietveld-derived microstrain and concentration of occluded amino acid; and anisotropic lattice distortion, confirms direct incorporation. Finally, nanoindentation studies revealed hardness measurements comparable to biogenic calcite, commensurate with imposed inhomogeneous microstrain. We propose, therefore, that structural biomacromolecules may have roles beyond that of increasing mineral hardness.
4:30 AM - *E4.06
Strong Stabilization of Amorphous Calcium Carbonate by Proteins, Polymers and Solvents
Filipe Natalio 2 Michael Dietzsch 1 Franziska Emmerling 3 Ute Kolb 4 Wolfgang Tremel 1
1Johannes Gutenberg-Universitamp;#228;t Mainz Germany2Martin Luther Universitamp;#228;t Halle Germany3Bundesanstalt famp;#252;r Materialpramp;#252;fung Berlin Germany4Johannes Gutenberg Universitamp;#228;t Mainz GermanyShow Abstract
The formation of CaCO3 has been studied for many years. Much attention has been devoted to amorphous CaCO3 (ACC) as a singular material, because there is increasing evidence that this phase plays a crucial role in biomineralization. ACC is the least stable form of CaCO3, and under ambient conditions it transforms quickly into more stable crystalline forms, such as vaterite and calcite. Many mineralization processes are now believed to occur through the transformation of a transient amorphous precursor, which has been shown to act a reactive in intermediate in generating complex functional materials.
We have studied the effect of proteins on the homogeneous formation of the liquid-amorphous CaCO3 (LACC) precursor, by a combination of complementary methods like in situ WAXS, light scattering, TEM and cryo-TEM. Lysozyme destabilizes the LACC emulsion, whereas the glycoprotein ovalbumin extends the lifetime of the emulsified state. We demonstrate ovalbumin to act as a stabilizer for a polymer-induced liquid precursor (PILP) process. Emulsified LACC carries a negative surface charge and is stabilized electrostatically. We propose that the liquid amorphous CaCO3 is affected by polymers by depletion stabilization and de-emulsification rather than by acidic proteins and polymers during a polymer-induced liquid precursor process. Thus, the original PILP coating effect appears to be a result of a de-emulsification process of a stabilized LACC phase. Silicatein-a, a protein from marine sponges, guides the self-assembly of calcite “spicules” similar to the spicules of the calcareous sponge Sycon. The spicules, 10-300 µm in length and 5-10 µm in diameter, are composed of aligned calcite nanocrystals. They are initially amorphous but transform into calcite within months, exhibiting unusual growth along . They scatter X-rays like twinned calcite crystals. While natural spicules evidence brittle failure, the synthetic spicules show an elastic response, which greatly enhances bending strength. This feature is linked to a protein content of approx. 10%.
Later stages of nucleation have been studied by “trapping” nuclei from solution. This yields snapshots of the structure formation process at given point. In a first step the full determination of the structure of vaterite, one of the common CaCO3 polymorphs, was solved on nanometer-sized crystallites by electron crystallography. These results demonstrate that crystals that are too small for single-crystal X-ray diffraction and too difficult to solve by powder diffraction may nevertheless be amenable to accurate structure determination by electron crystallography.
5:00 AM - E4.07
Fluid Cell TEM Observation of CaCO3 Formation Pathways: Inorganic System vs. Alkanethiol SAMs
Michael H Nielsen 1 2 Shaul Aloni 2 James J De Yoreo 3
1UC Berkeley Berkeley USA2Lawrence Berkeley National Lab Berkeley USA3Pacific Northwest National Lab Richland USAShow Abstract
The study of nucleation is of paramount importance because it represents the seminal event in the growth of a solid phase from solution. Organothiol self-assembled monolayers (SAMs) have been utilized as a model system to mimic biological templates, with which to investigate the underlying mechanisms by which organic matrices control nucleation. There exist many long-standing questions surrounding templated nucleation due to a lack of experimental approaches suitable for probing this seminal event in mineral formation. Of particular interest is the formation pathway that takes the mineral from its solvated state to the final, oriented calcite crystal. Whether mineralization pathways on organic templates differ from pathways in purely inorganic calcite formation is currently unknown. Resolving this question is of great importance to understanding the mechanisms by which organic matrices exert control over the organization of minerals.
In recent years developments in transmission electron microscopy (TEM) have produced platforms allowing observation of fluid environments. Here we use fluid cell TEM to investigate calcium carbonate (CaCO3) nucleation. During nucleation in the absence of organic templates, we observe direct formation of amorphous calcium carbonate (ACC), as well as the three predominant crystalline phases: calcite, vaterite, and aragonite. The direct formation of the crystalline phases is observed under conditions in which ACC readily forms. These observations provide direct evidence that multiple phases of calcium carbonate can form without the intermediate stage of ACC. For all phases measured, radial/edge growth rates following nucleation are constant, showing growth is limit by reaction kinetics.
In addition to direct formation pathways, in a purely inorganic system we observe transformation from ACC to