New insights into the nucleation of magnesium hydroxide and the influence of poly(acrylic acid) during the early stages of Mg(OH)2 crystallisation
2022-11-17, Scheck, Johanna, Berg, John K., Drechsler, Markus, Kempter, Andreas, Van Driessche, Alexander E. S., Cölfen, Helmut, Gebauer, Denis, Kellermeier, Matthias
Nucleation is a unique process with broad relevance across a wide range of scientific disciplines and applications. While considerable progress in the understanding of the mechanisms underlying the nucleation of minerals from solution has been made for popular model systems such as calcium carbonate, corresponding detailed insights are still missing for other, less prominent minerals. Here, we present a potentiometric titration-based method that allows the early stages of the crystallisation of brucite, Mg(OH)2, to be monitored and quantified. Together with complementary characterisation provided by (cryogenic) transmission electron microscopy, the collected data shed novel light on the species occurring prior to, during, and after nucleation of brucite. In the second part of the work, the newly developed approach was applied to investigate the effects of added poly(acrylic acid) on the different stages of the crystallisation process. The polymer is found to stabilise brucite nanoplatelets and co-precipitate with the inorganic phase, yielding a composite material. The methodology established in this study can readily be used to screen other chemistries for their ability to prevent magnesium hydroxide scaling and/or afford brucite nanomaterials with tailored properties.
Role of Water in CaCO3 Biomineralization
2021-02-03, Lu, Hao, Huang, Yu-Chieh, Hunger, Johannes, Gebauer, Denis, Cölfen, Helmut, Bonn, Mischa
Biomineralization occurs in aqueous environments. Despite the ubiquity and relevance of CaCO3 biomineralization, the role of water in the biomineralization process has remained elusive. Here, we demonstrate that water reorganization accompanies CaCO3 biomineralization for sea urchin spine generation in a model system. Using surface-specific vibrational spectroscopy, we probe the water at the interface of the spine-associated protein during CaCO3 mineralization. Our results show that, while the protein structure remains unchanged, the structure of interfacial water is perturbed differently in the presence of both Ca2+ and CO32– compared to the addition of only Ca2+. This difference is attributed to the condensation of prenucleation mineral species. Our findings are consistent with a nonclassical mineralization pathway for sea urchin spine generation and highlight the importance of protein hydration in biomineralization.
Highly hydrated paramagnetic amorphous calcium carbonate nanoclusters as an MRI contrast agent
2022-08-29, Dong, Liang, Xu, Yun-Jun, Sui, Cong, Zhao, Yang, Gebauer, Denis, Rosenberg, Rose, Avaro, Jonathan Thomas, Lu, Yang, Cölfen, Helmut, Yu, Shu-Hong
Amorphous calcium carbonate plays a key role as transient precursor in the early stages of biogenic calcium carbonate formation in nature. However, due to its instability in aqueous solution, there is still rare success to utilize amorphous calcium carbonate in biomedicine. Here, we report the mutual effect between paramagnetic gadolinium ions and amorphous calcium carbonate, resulting in ultrafine paramagnetic amorphous carbonate nanoclusters in the presence of both gadolinium occluded highly hydrated carbonate-like environment and poly(acrylic acid). Gadolinium is confirmed to enhance the water content in amorphous calcium carbonate, and the high water content of amorphous carbonate nanoclusters contributes to the much enhanced magnetic resonance imaging contrast efficiency compared with commercially available gadolinium-based contrast agents. Furthermore, the enhanced T1 weighted magnetic resonance imaging performance and biocompatibility of amorphous carbonate nanoclusters are further evaluated in various animals including rat, rabbit and beagle dog, in combination with promising safety in vivo. Overall, exceptionally facile mass-productive amorphous carbonate nanoclusters exhibit superb imaging performance and impressive stability, which provides a promising strategy to design magnetic resonance contrast agent.
Potentiometric Titration Method for the Determination of Solubility Limits and pKa Values of Weak Organic Acids in Water
2020-07-21, Wiedenbeck, Eduard, Gebauer, Denis, Cölfen, Helmut
The determination of solubility limits of compounds in water is unprecise and relies on certain prerequisites such as UV-Vis absorption activity. In this study we designed an experimental approach based on potentiometric titrations to determine solubility limits of various organic compounds by exploiting their pH-active carboxylic acid groups. By applying the law of mass action, utilizing a double-dosing method ensuring a constant compound concentration, it is possible to determine the intrinsic solubility limits, which are independent of the pH value. The derived equations enable the precise and fast determination of intrinsic solubility limits of organic compounds in aqueous solutions within 2 - 4 hours. Moreover, it is shown how the pKa value can be determined based on titrations carried out at two different compound concentrations.
Crystal Nucleation and Growth of Inorganic Ionic Materials from Aqueous Solution : Selected Recent Developments, and Implications
2022-07, Gebauer, Denis, Gale, Julian D., Cölfen, Helmut
In this review article, selected, latest theoretical, and experimental developments in the field of nucleation and crystal growth of inorganic materials from aqueous solution are highlighted, with a focus on literature after 2015 and on non-classical pathways. A key point is to emphasize the so far underappreciated role of water and solvent entropy in crystallization at all stages from solution speciation through to the final crystal. While drawing on examples from current inorganic materials where non-classical behavior has been proposed, the potential of these approaches to be adapted to a wide-range of systems is also discussed, while considering the broader implications of the current re-assessment of pathways for crystallization. Various techniques that are suitable for the exploration of crystallization pathways in aqueous solution, from nucleation to crystal growth are summarized, and a flow chart for the assignment of specific theories based on experimental observations is proposed.