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1. Multi‐Step Nucleation of a Crystalline Silicate Framework via a Structurally Precise Prenucleation Cluster

   https://doi.org/10.1002/anie.202303770  

   Jin, Biao; Chen, Ying; Tao, Jinhui; Lachowski, Kacper J.; Bowden, Mark E.; Zhang, Zihao; Pozzo, Lilo D.; Washton, Nancy M.; Mueller, Karl T.; De Yoreo, James J. (July 2023, Angewandte Chemie International Edition)

   Abstract Hierarchical nucleation pathways are ubiquitous in the synthesis of minerals and materials. In the case of zeolites and metal–organic frameworks, pre‐organized multi‐ion “secondary building units” (SBUs) have been proposed as fundamental building blocks. However, detailing the progress of multi‐step reaction mechanisms from monomeric species to stable crystals and defining the structures of the SBUs remains an unmet challenge. Combining in situ nuclear magnetic resonance, small‐angle X‐ray scattering, and atomic force microscopy, we show that crystallization of the framework silicate, cyclosilicate hydrate, occurs through an assembly of cubic octameric Q 3 8 polyanions formed through cross‐linking and polymerization of smaller silicate monomers and other oligomers. These Q 3 8 are stabilized by hydrogen bonds with surrounding H 2 O and tetramethylammonium ions (TMA + ). When Q 3 8 levels reach a threshold of ≈32 % of the total silicate species, nucleation occurs. Further growth proceeds through the incorporation of [(TMA) x (Q 3 8 )⋅ n  H 2 O] ( x −8) clathrate complexes into step edges on the crystals. 

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2. Pre-nucleation Clusters and Complex Nucleation in Soft Matter and the Potential Roles of Space Experiments

   Katamreddy, S.; Cho, Y. C.; Lee, S.; Lee, G. W.; Lee, J. (July 2022, IJMSA)

   N/A (Ed.)

   For more than a century, Classical Nucleation Theory (CNT) has been used to explain the process of crystallization in supersaturated solutions. According to CNT, nucleation is a single-step process that occurs via monomer-by-monomer addition. However, recent findings from experiments and numerical simulations have shown that nucleation is a multi-step process that occurs via more complex pathways that involve intermediate species such as ion complexes, dense liquid precursors, or even nanocrystals. Such non-classical pathways observed in protein solutions, colloidal suspensions and electrolytes are reviewed in this paper. The formation of stable Pre-nucleation Clusters (PNCs) in the crystallization of biominerals is also discussed. In spite of the mounting evidence for non-classical nucleation behaviors, the knowledge about the structural evolution of the intermediate phases and their role in polymorph selection is still limited. It has also been observed that gravitational force interferes with the crystallization behavior of materials thereby posing limitation to ground-based experiments. Microgravity conditions, coupled with containerless processing techniques provide a suitable alternative to overcome these limitations. 

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3. Significant contributions of trimethylamine to sulfuric acid nucleation in polluted environments

   https://doi.org/10.1038/s41612-023-00405-3  

   Cai, Runlong; Yin, Rujing; Li, Xue; Xie, Hong-Bin; Yang, Dongsen; Kerminen, Veli-Matti; Smith, James N.; Ma, Yan; Hao, Jiming; Chen, Jingwen; et al (June 2023, npj Climate and Atmospheric Science)

   Abstract As one of the least understood aerosol processes, nucleation can be a dominant source of atmospheric aerosols. Sulfuric acid (SA)-amine binary nucleation with dimethylamine (DMA) has been recognized as a governing mechanism in the polluted continental boundary layer. Here we demonstrate the importance of trimethylamine (TMA) for nucleation in the complex atmosphere and propose a molecular-level SA-DMA-TMA ternary nucleation mechanism as an improvement upon the conventional binary mechanism. Using the proposed mechanism, we could connect the gaseous amines to the SA-amine cluster signals measured in the atmosphere of urban Beijing. Results show that TMA can accelerate the SA-DMA-based new particle formation in Beijing by 50–100%. Considering the global abundance of TMA and DMA, our findings imply comparable importance of TMA and DMA to nucleation in the polluted continental boundary layer, with probably higher contributions from TMA in polluted rural environments and future urban environments with controlled DMA emissions. 

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4. Molecular H2 in silicate melts

   https://doi.org/10.1016/j.gca.2024.10.020  

   Foustoukos, Dionysis I (January 2025, Geochimica et Cosmochimica Acta)

   A series of hydrothermal diamond anvil cell experiments was conducted to constrain the equilibrium distribution of molecular H2 between H2O-saturated sodium aluminosilicate melts and H2O at elevated temperatures (600 – 800 °C) and pressures (317 – 1265 MPa). The distribution of H2 between the silicate liquid and the aqueous fluid was achieved through real-time monitoring of the H-H stretching vibration under in situ conditions using Raman vibrational spectroscopy. Results show that the solubility of H2 in silicate melts saturated with H2O decreases as the temperature increases, with control exerted by the mole fraction of H2O in the melt. The dissolution of H2 in the hydrous silicate melts appears to follow Henrian behavior, resembling that of an inert, neutral non-polar species. The implications are extended into developing an understanding of the H partitioning between H2-rich atmospheres blanketing magma oceans in the early history of planetary bodies. For example, transferring H from primordial atmospheric envelopes to the interior of rocky exoplanets may be less efficient than previously believed, which should be considered in models of volatile retention. Experimental data also suggest that minimal amounts of solar nebula H2 are likely to dissolve in the molten surface of primitive objects in the protoplanetary disk (~10-5 to 10-9 mole faction H2 in melt), contradicting the highly reducing conditions observed in chondrule mineral compositions. 

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5. Phase and Morphology Control of Hexagonal MoO ₃ Crystals via Na ⁺ Interactions: A Raman Spectroscopy Study

   https://doi.org/10.1021/acs.jpcc.3c02821  

   Vargas-Consuelos, C Ingram; Camacho-López, Marco A; Ramos-Sanchez, Victor H; Graeve, Olivia A (July 2023, The Journal of Physical Chemistry C)

   We present the effect of sodium ions (Na+) on the nucleation process and phase selectivity for the formation of hexagonal molybdenum trioxide crystals (h-MoO3). The phase selectivity during the reaction is attributed to the interaction of Na+ with the molecules in our precursor solution formed by metallic molybdenum dissolved in a mix of hydrochloric and nitric acids. The vibrational characteristics of the precursor solutions were studied by Raman spectroscopy in combination with density functional theory modeling, showing the presence of [MoO2Cl3(H2O)] ions within the solutions. The symmetric stretching vibration of the Mo-O bonds found at 962 cm-1 in [MoO2Cl3(H2O)]- proved that the addition of Na+ (in the form of dissolved NaCl) to the precursor solutions resulted only in an electrostatic interaction with the aquo (H2O) and chloro (Cl-) ligands in the complex. After heating the precursor solutions, X-ray diffraction, Raman spectroscopy, and scanning electron microscopy of the obtained powders showed that adding NaCl contributed to the phase selectivity of the reaction, with the Na+ ions playing a vital role in the formation of h-MoO3 over other crystalline phases. Based on the nature of the molybdenum complexes found in the precursor solutions and the structural characteristics of the powders, a formation mechanism to obtain h-MoO3 is proposed. Additionally, the phase stability of the h-MoO3 crystals was studied by calorimetry techniques showing that h-MoO3 transforms to a-MoO3 at ~649 K. These results provide important insights into phase control to selectively form hexagonal MoO3. 

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