Solvent-mediated isotope effects strongly influence the early stages of calcium carbonate formation: exploring D2O vs. H2O in a combined computational and experimental approach

In experimental studies, heavy water (D2O) is employed, e.g., so as to shift the spectroscopic solvent background, but any potential effects of this solvent exchange on reaction pathways are often neglected. While the important role of light water (H2O) during the early stages of calcium carbonate formation has been realized, studies into the actual effects of aqueous solvent exchanges are scarce. Here, we present a combined computational and experimental approach to start to fill this gap. We extended a suitable force field for molecular dynamics (MD) simulations. Experimentally, we utilised advanced titration assays and time-resolved attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. We find distinct effects in various mixtures of the two aqueous solvents, and in pure H2O or D2O. Disagreements between the computational results and experimental data regarding the stabilities of ion associates might be due to the unexplored role of HDO, or an unprobed complex phase behaviour of the solvent mixtures in the simulations. Altogether, however, our data suggest that calcium carbonate formation might proceed “more classically” in D2O. Also, there are indications for the formation of new structures in amorphous and crystalline calcium carbonates. There is huge potential towards further improving the understanding of mineralization mechanisms by studying solvent-mediated isotope effects, also beyond calcium carbonate. Last, it must be appreciated that H2O and D2O have significant, distinct effects on mineralization mechanisms, and that care has to be taken when experimental data from D2O studies are used, e.g., for the development of H2O-based computer models

Tailoring Fibre Structure Enabled by X-ray Analytics for Targeted Biomedical Applications

The rising interest in designing fibres via spinning techniques combining the properties of various polymeric materials into advanced functionalised materials is directed towards targeted biomedical applications such as drug delivery, wearable sensors or tissue engineering. Understanding how these functional polymers exhibit multiscale structures ranging from the molecular level to nano-, micro-and millimetre scale is a key prerequisite for their challenging applications that can be addressed by a non-destructive X-ray based analytical approach. X-ray multimodalities combining X-ray imaging, scattering and diffraction allow the study of morphology, molecular structure, and the analysis of nano-domain size and shape, crystallinity and preferential orientation in 3D arrangements. The incorporation of X-ray analytics in the design process of polymeric fibers via their nanostructure under non-ambient conditions (i.e. temperature, mechanical load, humidity…) allows for efficient optimization of the fabrication process as well as quality control along the product lifetime under operating environmental conditions. Here, we demonstrate the successful collaboration between the laboratory of Biomimetic Textiles and Membranes and the Center of X-ray Analytics at Empa for the design, characterisation and optimisation of advanced functionalised polymeric fibrous material systems

Stable Pre-nucleation Calcium Carbonate Clusters Define Liquid-Liquid Phase Separation

Liquid‐liquid phase separation (LLPS) is an intermediate step during the precipitation of calcium carbonate, and is assumed to play a key role in biomineralization processes. Here, we developed a model where homogeneous phase ion association thermodynamics determines the liquid‐liquid miscibility gap of the aqueous calcium carbonate system, verified experimentally using potentiometric titrations, and kinetic studies based on stopped‐flow ATR‐FTIR spectroscopy. The proposed mechanism explains varying solubilities of solid amorphous calcium carbonates, reconciling previously inconsistent literature values. Accounting for liquid‐liquid amorphous polymorphism, the model also provides clues to the mechanism of polymorph selection. It is general and should be tested for other systems than calcium carbonate, providing a new perspective on the physical chemistry of LLPS mechanisms—based on stable pre‐nucleation clusters rather than un‐/metastable fluctuations—in biomineralization, and beyond.publishe

Stabile Calciumcarbonat-Pränukleationscluster bestimmen die Flüssig-flüssig-Phasenseparation

Flüssig‐flüssig‐Phasenseparation (liquid‐liquid phase separation, LLPS) ist eine Zwischenstufe während der Fällung von Calciumcarbonat und man vermutet, dass sie eine entscheidende Rolle in Biomineralisationsprozessen spielt. In diesem Artikel stellen wir ein Modell vor, in dem die Flüssig‐flüssig‐Mischungslücke im wässrigen Calciumcarbonatsystem durch die Thermodynamik der Ionenassoziation in der homogenen Phase bestimmt wird, was experimentell durch potentiometrische Titrationen und kinetische Studien mittels ATR‐FTIR‐Spektroskopie bestätigt wird. Der vorgeschlagene Mechanismus erklärt die variable Löslichkeit von amorphen Calciumcarbonaten und räumt Widersprüche in Literaturdaten aus. Da flüssig‐flüssig amorphe Polymorphie berücksichtigt wird, liefert das Modell Hinweise zum Mechanismus der Polymorphselektion. Es ist allgemein und sollte für andere Systeme als Calciumcarbonat überprüft werden. Ausgehend von stabilen Pränukleationsclustern anstelle von in‐ oder metastabilen Fluktuationen ergibt sich ein neuer Blickwinkel auf die physikalische Chemie der Flüssig‐flüssig‐Phasenseparationen in Biomineralisationsprozessen und darüber hinaus.publishe