Anhydrous Amorphous Calcium Oxalate Nanoparticles from Ionic Liquids: Stable Crystallization Intermediates in the Formation of Whewellite

作者：Gehl Aaron; Dietzsch Michael; Mondeshki Mihail; Bach Sven; Haeger Tobias; Panthoefer Martin; Barton Bastian; Kolb Ute; Tremel Wolfgang^*

来源：Chemistry - A European Journal, 2015, 21(50): 18192-18201.

DOI：10.1002/chem.201502229

• amorphous materials
• anhydrous materials
• biomineralization
• calcium oxalates
• crystallization

The mechanisms by which amorphous intermediates transform into crystalline materials are not well understood. To test the viability and the limits of the classical crystallization, new model systems for crystallization are needed. With a view to elucidating the formation of an amorphous precursor and its subsequent crystallization, the crystallization of calcium oxalate, a biomineral widely occurring in plants, is investigated. Amorphous calcium oxalate (ACO) precipitated from an aqueous solution is described as a hydrated metastable phase, as often observed during low-temperature inorganic synthesis and biomineralization. In the presence of water, ACO rapidly transforms into hydrated whewellite (monohydrate, CaC2O4 center dot H2O, COM). The problem of fast crystallization kinetics is circumvented by synthesizing anhydrous ACO from a pure ionic liquid (IL-ACO) for the first time. IL-ACO is stable in the absence of water at ambient temperature. It is obtained as well-defined, non-agglomerated particles with diameters of 15-20 nm. When exposed to water, it crystallizes to give (hydrated) COM through a dissolution/recrystallization mechanism.

• 出版日期2015-12-7