Crystallization of Calcium Carbonate Beneath Insoluble Monolayers: Suitable Models of Mineral–Matrix Interactions in Biomineralization?

Composition inversion to form calcium carbonate mixtures

A solid mixture of reactants undergoes composition inversion to form calcium carbonate.

Surface Tension Drives the Orientation of Crystals at the Air-Water Interface

The fabrication of oriented crystalline thin films is essential for a range of applications ranging from semiconductors to optical components, sensors, and catalysis. Here we show by depositing micrometric crystal particles on a liquid interface from an aerosol phase that the surface tension of the liquid alone can drive the crystallographic orientation of initially randomly oriented particles. The X-ray diffraction patterns of the particles at the interface are identical to those of a monocrystalline sample cleaved along the {104} (CaCO3) or {111} (CaF2) face. We show how this orientation effect can be used to produce thin coatings of oriented crystals on a solid substrate. These results also have important implications for our understanding of heterogeneous crystal growth beneath amphiphile monolayers and for 2D self-assembly processes at the air-liquid interface.

Selective growth of MFU-4l single crystals on microstructured plasma polymer coatings

Crystals of the metal–organic framework Ulm-4l(arge) grow site selectively and with 〈1 0 0〉 orientation on microtextured plasma polymer coatings.

Induced transformation of amorphous silica to cristobalite on bacterial surfaces

Phase transformation of amorphous silica to cristobalite at a relatively low temperature of 800 °C has been achieved on bacterial surfaces.

Calcium carbonate crystal growth beneath Langmuir monolayers of acidic β-hairpin peptides

Four amphiphilic peptides with designed hairpin structure were synthesized and their monolayers were employed as model systems to study biologically inspired calcium carbonate crystallization. Langmuir monolayers of hairpin peptides were investigated by surface pressure area isotherms, surface potential isotherms, Brewster angle microscopy (BAM), atomic force microscopy (AFM) and Fourier transform infrared (FTIR) spectroscopy. A β-hairpin conformation was found for all peptides at the air-water interface although their packing arrangements seem to be different. Crystallization of calcium carbonate under these peptide monolayers was investigated at different surface pressures and growth times both by in situ optical microscopy, BAM and ex situ investigations such as scanning electron microscopy (SEM) and transmission electron microscopy (TEM). An amorphous calcium carbonate precursor was found at the initial crystallization stage. The crystallization process occurred in three stages. It starts from the nucleation of amorphous particles being a kinetically controlled process. Crystal nuclei subsequently aggregate to large particles and vaterite crystals start to form inside the amorphous layer, with the monolayer fluidity exerting an important role. The third process includes the re-crystallization of vaterite to calcite, which is thermodynamically controlled by monolayer structural factors including the monolayer flexibility and packing arrangement of the polar headgroups. Thus, the kinetic factors, monolayer fluidity and flexibility as well as structure factors govern the crystal morphology and polymorph distribution simultaneously and synergistically.

Biomineralization as an inspiration for materials chemistry

Living organisms are well known for building a wide range of specially designed organic-inorganic hybrid materials such as bone, teeth, and shells, which are highly sophisticated in terms of their adaptation to function. This has inspired physicists, chemists, and materials scientists to mimic such structures and their properties. In this Review we describe how strategies used by nature to build and tune the properties of biominerals have been applied to the synthesis of materials for biomedical, industrial, and technological purposes. Bio-inspired approaches such as molecular templating, supramolecular templating, organized surfaces, and phage display as well as methods to replicate the structure and function of biominerals are discussed. We also show that the application of in situ techniques to study and visualize the bio-inspired materials is of paramount importance to understand, control, and optimize their preparation. Biominerals are synthesized in aqueous media under ambient conditions, and these approaches can lead to materials with a reduced ecological footprint than can traditional methods.

Bio-inspired synthesis: understanding and exploitation of the crystallization process from amorphous precursors

Many biominerals, such as mollusk nacre, sea urchin, bone and teeth, are found to form by an amorphous precursor pathway, and these biominerals have remarkable properties, which are better than their artificial material counterparts that are formed at high temperatures and high pressures. More than ever, synthesizing technologically relevant materials following nature's way with a specific size, shape, orientation, organization, and complex form has been a focus of ongoing interest due to the increasing need for low cost and environmentally friendly approaches to processing advanced materials. Herein, we present recent developments in the crystallization process from amorphous precursors by primarily drawing on results from our own laboratory, and discuss some unique characteristics from the transformation process that can be exploited for the design and synthesis of artificial functional materials.

Biomimetic fabrication of pseudohexagonal aragonite tablets through a temperature-varying approach

Pseudohexagonal and single-crystal-like aragonite tablets, found in nacre, could be uniformly fabricated through a temperature-varying approach for the first time, indicating the triplet twinning nature and implying a potential significance in biomineralization.

On self-organized shell formation by bovine carbonic anhydrase II, and soluble protein extracted from regenerated shell

The soluble protein of hemocytes from diseased shell (HDS) of oyster, Crassostrea gigas, was shown to play a key role in the rapid growth of calcium carbonate crystals. In this study, we compared HDS extracted from regenerated (or diseased) shell with bovine carbonic anhydrase II in terms of their ability to promote the growth of calcium carbonate crystals. On the basis of scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) analysis, a high growth rate of calcium carbonate crystals was identified under artificial seawater and atmospheric temperature. The function and role of HDS extracted from regenerated shell are discussed at the molecular point as compared to aragonite-specific soluble proteins. Our findings suggest that hemocytes function as a soluble protein, with repeated GX (G: Gly, X: Asp, Asn or Glu) or negative charged amino acid domains binding calcium and specific surface features for catalyzing rapid shell regeneration.

Crystal structure analysis of [Ca(O3SC18H37)2(DMSO)2], a lamellar coordination polymer and its relevance for model studies in biomineralization

Single crystals of a one-dimensional Ca coordination polymer of the surfactant octadecyl sulfonate (C(18)H(37)SO(3)(-)) have been grown from hot DMSO solution. The X-ray structure analysis of the compound [Ca(O(3)SC(18)H(37))(2)(DMSO)(2)] (1) shows a lamellar interdigitated arrangement of hydrophobic tails of the amphiphilic ligands. Each Ca ion is coordinated by four different sulfonate groups, and its nearly octahedral coordination environment is completed by two dimethyl sulfoxide (DMSO) ligands. The octadecyl sulfonate ligand coordinates to Ca ions in a micro(2)-bridging mode, which contrasts to information from literature suggesting a micro(3)-bridging coordination mode. Since the growth of highly oriented calcite single crystals underneath Langmuir monolayers of this particular surfactant is often regarded as textbook example of a heteroepitaxy ("template") mechanism in biomineralization, we present a critical discussion of the crystal structure of the title compound in this context.