Amorphes Kalziumcarbonat (ACC) ist ein wichtiger Vorläufer in der Biomineralisierung und von zentraler Bedeutung für die geologische und industrielle Kalzifizierung. Einige kleine organische Moleküle haben die Fähigkeit, die Bildung, Zusammensetzung und Stabilität von ACC stark zu beeinflussen. In ihrem Forschungsartikel (e202208475) entschlüsseln Asher Schmidt, Dirk Zahn, Stephan E. Wolf et al. die zugrundeliegenden molekularen Mechanismen, die sowohl die Pränukleation als auch die Zusammensetzung der Lösung regulieren. Amorphes Kalziumcarbonat (ACC) ist ein wichtiger Vorläufer in der Biomineralisierung und von zentraler Bedeutung für die geologische und industrielle Kalzifizierung. Einige kleine organische Moleküle haben die Fähigkeit, die Bildung, Zusammensetzung und Stabilität von ACC stark zu beeinflussen. In ihrem Forschungsartikel (e202208475) entschlüsseln Asher Schmidt, Dirk Zahn, Stephan E. Wolf et al. die zugrundeliegenden molekularen Mechanismen, die sowohl die Pränukleation als auch die Zusammensetzung der Lösung regulieren. Organische Halbleiter Photokatalyse Polymere Heterogene Katalyse

Understanding the underlying processes of biomineralization is crucial to a range of disciplines allowing us to quantify the effects of climate change on marine organisms, decipher the details of paleoclimate records and advance the development of biomimetic materials. Many biological minerals form via intermediate amorphous phases, which are hard to characterize due to their transient nature and a lack of long-range order. Here, using Monte Carlo simulations constrained by X-ray and neutron scattering data together with model building, we demonstrate a method for determining the structure of these intermediates with a study of amorphous calcium carbonate (ACC) which is a precursor in the bio-formation of crystalline calcium carbonates. We find that ACC consists of highly ordered anhydrous nano-domains of approx. 2 nm that can be described as nanocrystalline. These nano-domains are held together by an interstitial net-like matrix of water molecules which generate, on the mesoscale, a heterogeneous and gel-like structure of ACC. We probed the structural stability and dynamics of our model on the nanosecond timescale by molecular dynamics simulations. These simulations revealed a gel-like and glassy nature of ACC due to the water molecules and carbonate ions in the interstitial matrix featuring pronounced orientational and translational flexibility. This allows for viscous mobility with diffusion constants four to five orders of magnitude lower than those observed in solutions. Small and ultra-small angle neutron scattering indicates a hierarchically-ordered organization of ACC across length scales that allow us, based on our nano-domain model, to build a comprehensive picture of ACC formation by cluster assembly from solution. This contribution provides a new atomic-scale understanding of ACC and provides a framework for the general exploration of biomineralization and biomimetic processes.

Small-molecular-weight (MW) additives can strongly impact amorphous calcium carbonate (ACC), playing an elusive role in biogenic, geologic, and industrial calcification. Here, we present molecular mechanisms by which additives regulate stability and composition of both CaCO3 solutions and solid ACC. Potent antiscalants inhibit ACC precipitation by interacting with prenucleation clusters (PNC); they specifically trigger and integrate into PNCs or feed PNC growth. Only PNC-interacting additives are traceable in ACC, considerably stabilizing it against crystallization. The selective incorporation of potent additives in PNCs is a reliable chemical label that provides conclusive chemical evidence that ACC is a molecular precipitate derived PNCs. Our results reveal additive-cluster interactions beyond established mechanistic conceptions. They reassess the role of small-MW molecules in crystallization and biomineralization, while breaking grounds for new sustainable antiscalants.

Potentiometric titrations are a powerful tool to study the early stages of the precipitation of minerals such as calcium carbonate and were used among others for the discovery and characterisation of key precursors like prenucleation clusters. Here we present a modified procedure for conducting such titration experiments, in which the reactants (i.e. calcium and (bi)carbonate ions) are added simultaneously in stoichiometric amounts, while both the amount of free calcium and the optical transmission of the solution are monitored online. Complementarily, the species occurring at distinct stages of the crystallisation process were studied using cryogenic transmission electron microscopy. This novel routine was applied to investigate CaCO3 nucleation in the absence and presence of polymeric additives with different chemical functionalities. The obtained results provide new insights into the critical steps underlying nucleation and subsequent ripening, such as the role of liquid mineral-rich phases and their transformation into solid particles. The studied polymers proved to interfere at multiple stages along the complex mineralisation pathway of calcium carbonate, with both the degree and mode of interaction depending on the chosen polymer chemistry. In this way, the methodology developed in this work allows the mechanisms of antiscalants - or crystallisation modifiers in general - to be elucidated at an advanced level of detail.

To gain control over polymorph selection is a pivotal issue in the pharmaceutical, food, and fine chemical industry. However, the mechanisms which affect polymorph selectivity are still not fully chartered. In the present study, we demonstrated the complex crystallization behavior of L-glutamic acid under microfluidic conditions. Amorphous intermediates occur in the early stages of the experiment, which undergo a series of aging steps - such as aggregation/coalescence, growth, or shrinking - before the stable p-polymorph forms. Experiments indicated that the attachment of amorphous particles partly feds crystal growth. This complex mechanism, which was observed under laminar flow conditions, might lead to the preferential formation of a flower-like shape of p-L-glutamic acid. We accompanied these experiments, which were characterized by laminar flow-conditions, with experiments under acoustic levitation in which crystal formation takes place under constant but gentle convection in an evaporating droplet. In these experiments, a similar phenomenon was also observed. However, when crystallization was conducted in a conventional stirred-tank, a mixture of a-form and 13-form was formed, characterized by a prism, needle-and plate-like morphologies instead of the distinct flower-like in earlier experiments. This demonstrates that gentle flow conditions, such as a laminar flow in a microfluidic device, preferentially leads to a complex flower-like shape than conventional approaches in a stirred tank. (c) 2021 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Here, we approach the issue of ACC ultrastructure by applying a method for determining atomically resolved structures of amorphous materials using Monte Carlo simulations constrained by both X-ray and neutron scattering data. This structural analysis approach allows us to develop a detailed model for ACC at the atomic level. Our findings reveal that synthetic ACC, rapidly precipitated at high pH, consists of two-nanometer sized units containing a high degree of near range order similar to partially disordered nano-crystals. Small-angle scattering analyses show a multi-scale hierarchical organisation of the structure, supportive of a multi-step colloid self-assembly process. Computer simulations and high-resolution transmission electron microscopy show that the mesostructure of ACC resembles that of a glassy gel with crystalline material in domains. Our findings support the formation of ACC by a nanoparticle aggregation process that likely starts from prenucleation clusters in solution.

For bioactive biomaterials such as bioceramics and bioglass, it is generally accepted that, apart from acting as heterogeneous nucleators, it is their solubility and the resulting release of relevant ions such as calcium or basic anions which mainly governs the biomaterial's bioactivity. This contribution reveals that this bioactivity, as assessed by simulated body fluid (SBF), can also be considerably modified by the bioceramic's morphology, i.e., bioactivity is also governed by microstructure and surface morphology. When crystals are forced to adopt out‐of‐equilibrium crystal habit, this simple change in morphology converts an essentially bioinert material, here calcite, into a bioceramic which shows bioactivity in SBF. On larger length scales, already simple morphological changes, such as scratches, can have inverse effects. Limited mass transport into grooves and pits on a bioceramic surface can lead to local ion depletion which, in turn, causes reduced bioactivity of bioceramics which, otherwise, show distinct bioactivity in SBF. This contribution emblematically illustrates the unforeseen importance of even minor morphology changes on different length scales when assessing and designing a biomaterial's bioactivity through SBF assays.

Nature successfully employs inorganic solid-state materials (i.e., biominerals) and hierarchical composites as sensing elements, weapons, tools, and shelters. Optimized over hundreds of millions of years under evolutionary pressure, these materials are exceptionally well adapted to the specifications of the functions that they perform. As such, they serve today as an extensive library of engineering solutions. Key to their design is the interplay between components across length scales. This hierarchical design-a hallmark of biogenic materials-creates emergent functionality not present in the individual constituents and, moreover, confers a distinctly increased functional density, i.e., less material is needed to provide the same performance. The latter aspect is of special importance today, as climate change drives the need for the sustainable and energy-efficient production of materials. Made from mundane materials, these bioceramics act as blueprints for new concepts in the synthesis and morphosynthesis of multifunctional hierarchical materials under mild conditions. In this review, which also may serve as an introductory guide for those entering this field, we demonstrate how the pursuit of studying biomineralization transforms and enlarges our view on solid-state material design and synthesis, and how bioinspiration may allow us to overcome both conceptual and technical boundaries.