Organisms have the ability to produce structures with superior characteristics as in the course of biomineralization. One of the most intriguing characteristics of biominerals is the existence of intracrystalline macromolecules.Despite several studies over the last two decades and efforts to mimic the incoporation of macromolecules synthetically, a fundamental understanding of the mechanism of incorporation is as yet lacking. For example, which of the common 20 amino acids are really responsible for the interaction with the mineral phase? Here a reductionist approach, based on high-resolution synchrotron powder diffraction and analytical chemistry, is utilized to screen all of these amino acids in terms of their incorporation into calcite. We showed that the important factors are amino-acid charge, size, rigidity and the relative pKa of the carboxyl and amino functional groups. It is also demonstrated that cysteine, surprisingly, interacts very strongly with the mineral phase and therefore, like acidic amino acids, becomes richly incorporated. The insights gained from this study shed new light on the incorporation of organic molecules into an inorganic host in general, and in particular on the biomineralization process.

Calcite, aragonite, and vaterite are the three anhydrous polymorphs of calcium carbonate, in order of decreasing thermodynamic stability. Although vaterite is not commonly found in geological settings, it is an important precursor in several carbonate-forming systems and can be found in biological settings. Because of difficulties in obtaining large, pure, single crystals, the crystal structure of vaterite has been elusive for almost a century. Using aberration-corrected high-resolution transmission electron microscopy, we found that vaterite is actually composed of at least two different crystallographic structures that coexist within a pseudo-single crystal. The major structure exhibits hexagonal symmetry; the minor structure, existing as nanodomains within the major matrix, is still unknown.

In contrast to synthetic materials, materials produced by organisms are formed in ambient conditions and with a limited selection of elements. Nevertheless, living organisms reveal elegant strategies for achieving specific functions, ranging from skeletal support to mastication, from sensors and defensive tools to optical function. Using state-of-the-art characterization techniques, we present a biostrategy for strengthening and toughening the otherwise brittle calcite optical lenses found in the brittlestar This intriguing process uses coherent nanoprecipitates to induce compressive stresses on the host matrix, functionally resembling the Guinier-Preston zones known in classical metallurgy. We believe that these calcitic nanoparticles, being rich in magnesium, segregate during or just after transformation from amorphous to crystalline phase, similarly to segregation behavior from a supersaturated quenched alloy.

We present experimental evidence of inhomogeneous distribution of organic inclusions within individual aragonitic lamellae forming the nacre layer of mollusk shells. This nanoscale-inhomogeneity is visualized in the Perna canaliculus (green mussel) shells by the aid of high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) in the tomography mode. Electron tomography reconstructions of the three-dimensional distribution of intracrystalline organic inclusions, ranging in size between 2 to 25 nm, clearly reveal 50 nm wide depletion zones adjacent to the organic sheets between lamellae. The interrelation between the observed fine-scale inhomogeneity of nacre layer and its improved mechanical properties is discussed.

No abstract

High-resolution synchrotron X-ray powder diffraction (XRD) combined with the Rietveld refinement method and confocal laser scanning microscopy (CLSM) were utilized in this study to elucidate the interaction between a recombinant biomineralization protein (perlucin) fused to green fluorescent protein (GFP) and synthetic calcite. Although recombinant perlucin is insoluble, its solubility was increased via fusion to the highly soluble GFP. We demonstrate that GFP-perlucin derivatives become incorporated into the calcite structure and induce concentration-dependent anisotropic lattice distortions along the host’s c-axis. In contrast, GFP alone is hardly incorporated at all. The observed lattice distortions and peculiar microstructure of the crystals are comparable to those previously observed in biogenic calcite. Taking advantage of biotechnology to optimize individual protein properties, such as the solubility of an otherwise insoluble protein derivative, is a promising route toward the synthesis of new and improved biocomposite materials.

Single crystals in nature often demonstrate fascinating intricate porous morphologies rather than classical faceted surfaces. We attempt to grow such crystals, drawing inspiration from biogenic porous single crystals. Here we show that nanoporous single crystals of gold can be grown with no need for any elaborate fabrication steps. These crystals are found to grow following solidification of a eutectic composition melt that forms as a result of the dewetting of nanometric thin films. We also present a kinetic model that shows how this nano-porous single-crystalline structure can be obtained, and which allows the potential size of the porous single crystal to be predicted. Retaining their single-crystalline nature is due to the fact that the full crystallization process is faster than the average period between two subsequent nucleation events. Our findings clearly demonstrate that it is possible to form single-crystalline nano porous metal crystals in a controlled manner.

Various molecules are known to form self-assembled monolayers (SAMs) on the surface of liquids. We present a simple method of investigating the kinetics of such SAM formation on sessile drops of various liquids such as mercury, water and fluorocarbon. To measure the surface tension of the drops we used an optical tensiometer that calculates the surface tension from the axisymmetric drop shape and the Young-Laplace relation. In addition, we estimated the SAM surface coverage fraction from the surface tension measured by other techniques. With this methodology we were able to optically detect concentrations as low as tenths of ppb increments of SAM molecules in solution and to compare the kinetics of SAM formation measured as a function of molecule concentration or chain length. The analysis is performed in detail for the case of alkanethiols on mercury and then shown to be more general by investigating the case of SAM formation of stearic acid on a water droplet in hexadecane and of perfluorooctanol on a Fluorinert FC-40 droplet in ethanol.