Nature has evolved efficient strategies to synthesize complex mineralized structures that exhibit exceptional damage tolerance. One such example is found in the hypermineralized hammer-like dactyl clubs of the stomatopods, a group of highly aggressive marine crustaceans. The dactyl clubs from one species, Odontodactylus scyllarus, exhibit an impressive set of characteristics adapted for surviving high-velocity impacts on the heavily mineralized prey on which they feed. Consisting of a multiphase composite of oriented crystalline hydroxyapatite and amorphous calcium phosphate and carbonate, in conjunction with a highly expanded helicoidal organization of the fibrillar chitinous organic matrix, these structures display several effective lines of defense against catastrophic failure during repetitive high-energy loading events.

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Nature's use of proteins to direct and control the synthesis of inorganic solids represents an important paradigm for bioinspired materials synthesis. However, the mechanism by which polypeptides direct inorganic synthesis, particularly with regard to selective formation of crystals polymorphs, remains unknown. An important step in understanding polypeptide-directed inorganic synthesis is the identification of sequence regions in biomineralization proteins that can affect crystal growth. In this report, we identify that the 30 AA N-and C-terminal sequence regions (n16-N and n16-C, respectively) of the oyster shell aragonite-associated protein, n16, exhibit control over the morphology of calcium carbonate crystals grown in geologic calcite overgrowth assays and polyimide (Kevlar)-based assays. Here, we find that calcium carbonate crystals, which grow in the presence of model peptides representing the n16-N and n16-C sequences, adopt dendritic or circular overgrowth in geological calcite overgrowth assays and "staircase" structures in Kevlar-based assays, as compared to negative controls and to parallel assays conducted in the presence of AP24-1, the 30 AA N-terminal sequence region of the nacre-associated protein, AP24, which interrupts step edge growth. Synchrotron X-ray diffraction studies reveal that the crystals grown in the presence of n16-N are calcite. Circular dichroism spectrometry studies of n16-N and n16-C model peptides reveal qualitatively similar solution state conformations that consist of either random coil in equilibrium with other secondary structures (e.g., -strand, turn, loop, polyproline type II) or, at higher concentrations, a -strand secondary structure in equilibrium with random coil. We conclude that the N-and C-terminal sequence regions of the nacre-associated n16 protein most likely play a role in n16-mediated effects on calcium carbonate crystal growth in the nacre layer.Nature's use of proteins to regulate the growth of inorganic solids is one of the major hallmarks of the biomineralization process and represents one possible pathway for the construction of unique and useful inorganic materials. A great deal of interest has centered on calcium carbonate-based mineralization processes, where several crystalline polymorphs (calcite, aragonite, and vaterite) and amorphous calcium carbonates are preferentially created within certain organisms. 1 An interesting model system of polymorph selection exists in the mollusk shell, where two polymorphs, calcite (prismatic layer) and aragonite (nacre layer), coexist side by side. 2-7 Recent protein studies have identified a number of unique polypeptides associated with the nacre layer, 5,6,9 and it is believed that these proteins participate in the stabilization of the aragonite polymorph during shell synthesis. 3-8 Thus, if one is interested in exploiting the principles of bioinspired inorganic synthesis and protein-mediated phase stabilization for material science, 10 we need to obtain a better understanding of how these proteins affect mineral f...

We report x-ray reflectivity (XR) and small angle off-specular diffuse scattering (DS) measurements from the surface of liquid Indium close to its melting point of 156 • C. From the XR measurements we extract the surface structure factor convolved with fluctuations in the height of the liquid surface. We present a model to describe DS that takes into account the surface structure factor, thermally excited capillary waves and the experimental resolution. The experimentally determined DS follows this model with no adjustable parameters, allowing the surface structure factor to be deconvolved from the thermally excited height fluctuations. The resulting local electron density profile displays exponentially decaying surface induced layering similar to that previously reported for Ga and Hg. We compare the details of the local electron density profiles of liquid In, which is a nearly free electron metal, and liquid Ga, which is considerably more covalent and shows directional bonding in the melt. The oscillatory density profiles have comparable amplitudes in both metals, but surface layering decays over a length scale of 3.5 ± 0.6Å for In and 5.5 ± 0.4Å for Ga. Upon controlled exposure to oxygen, no oxide monolayer is formed on the liquid In surface, unlike the passivating film formed on liquid Gallium.