As one of the most abundant materials in the world, calcium carbonate, CaCO
, is the main constituent of the skeletons and shells of various marine organisms. It is used in the cement industry and ...plays a crucial role in the global carbon cycle and formation of sedimentary rocks. For more than a century, only three polymorphs of pure CaCO
-calcite, aragonite, and vaterite-were known to exist at ambient conditions, as well as two hydrated crystal phases, monohydrocalcite (CaCO
·1H
O) and ikaite (CaCO
·6H
O). While investigating the role of magnesium ions in crystallization pathways of amorphous calcium carbonate, we unexpectedly discovered an unknown crystalline phase, hemihydrate CaCO
·½H
O, with monoclinic structure. This discovery may have important implications in biomineralization, geology, and industrial processes based on hydration of CaCO
.
Most of the world's bacteria exist in robust, sessile communities known as biofilms, ubiquitously adherent to environmental surfaces from ocean floors to human teeth and notoriously resistant to ...antimicrobial agents. We report the surprising observation that Bacillus subtilis biofilm colonies and pellicles are extremely non-wetting, greatly surpassing the repellency of Teflon toward water and lower surface tension liquids. The biofilm surface remains nonwetting against up to 80% ethanol as well as other organic solvents and commerical biocides across a large and clinically important concentration range. We show that this property limits the penetration of antimicrobial liquids into the biofilm, severely compromising their efficacy. To highlight the mechanisms of this phenomenon, we performed experiments with mutant biofilms lacking ECM components and with functionalized polymeric replicas of biofilm microstructure. We show that the nonwetting properties are a synergistic result of ECM composition, multiscale roughness, reentrant topography, and possibly yet other factors related to the dynamic nature of the biofilm surface. Finally, we report the impenetrability of the biofilm surface by gases, implying defense capability against vapor-phase antimicrobials as well. These remarkable properties of B. subtilis biofilm, which may have evolved as a protection mechanism against native environmental threats, provide a new direction in both antimicrobial research and bioinspired liquid-repellent surface paradigms.
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Bandgap engineering of zinc oxide semiconductors can be achieved using a bio‐inspired method. During a bioInspired crystallization process, incorporation of amino acids into the crystal structure of ...ZnO induces lattice strain that leads to linear bandgap shifts. This allows for fine tuning of the bandgap in a bio‐inspired route.
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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 Ophiocoma wendtii. 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.
A novel, single‐step and single‐component bio‐inspired fabrication method of hierarchical superoleophobic surfaces is presented. The method consists in thermal deposition of self‐assembling ...ultra‐low‐surface‐energy fluorinated wax on diverse surfaces. The thermal deposition results in crystalline, oriented, three‐dimensional hierarchical structures with high surface roughness and re‐entrant curvature, which in combination with the low surface energy of the fluorinated wax results in high contact angles of low‐surface‐tension liquids and low contact‐angle hysteresis (CAH) values (Δθ). The values achieved for Δθ are below 10° even for ethanol, which exhibits a surface tension as low as 22.4 mN·m−1. In addition to their superoleophobic properties our substrates exhibit extreme superhydrophobic qualities (CAH as low as 2° and contact angle >170°) with exceptional surface stability over many months. The proposed fabrication method may be utilized for a variety of applications where non‐wetting of low‐surface‐tension liquids is required, for example non‐staining surfaces and antifouling. The ease of fabrication and the variety of substrates that can be modified will undoubtedly widen its use.
Single step production of bio‐inspired hierarchical fluorinated wax crystalline surfaces, which exhibit superoleophobic characteristics, is reported. The marked surface roughness and re‐entrant curvature, in combination with the low surface energy of the fluorinated wax, results in high contact angles of low‐surface‐tension liquids and low contact‐angle hysteresis values.
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Coumarin, a simple, commodity chemical isolated from beans in 1820, has, to date, only yielded one solid state structure. Here, we report a rich polymorphism of coumarin grown from the melt. Four new ...metastable forms were identified and their crystal structures were solved using a combination of computational crystal structure prediction algorithms and X-ray powder diffraction. With five crystal structures, coumarin has become one of the few rigid molecules showing extensive polymorphism at ambient conditions. We demonstrate the crucial role of advanced electronic structure calculations including many-body dispersion effects for accurate ranking of the stability of coumarin polymorphs and the need to account for anharmonic vibrational contributions to their free energy. As such, coumarin is a model system for studying weak intermolecular interactions, crystallization mechanisms, and kinetic effects.
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Arsenic and barium are ubiquitous environmental toxins that accumulate in higher trophic-level organisms. Whereas metazoans have detoxifying organs to cope with toxic metals, sponges lack organs but ...harbour a symbiotic microbiome performing various functions. Here we examine the potential roles of microorganisms in arsenic and barium cycles in the sponge Theonella swinhoei, known to accumulate high levels of these metals. We show that a single sponge symbiotic bacterium, Entotheonella sp., constitutes the arsenic- and barium-accumulating entity within the host. These bacteria mineralize both arsenic and barium on intracellular vesicles. Our results indicate that Entotheonella sp. may act as a detoxifying organ for its host.
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