Calcium-43 NMR studies of polymorphic transition of calcite to aragonite
| Autor: | Yun Mou, Yu-Chieh Huang, Jerry C. C. Chan, Hsin-Kuan Lee, Shing-Jong Huang, Yu-Ju Wu, Tim W. T. Tsai |
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| Rok vydání: | 2012 |
| Předmět: |
Calcite
Calcium Isotopes Magnetic Resonance Spectroscopy Surface Properties Aragonite Nuclear magnetic resonance spectroscopy engineering.material Phase Transition Surfaces Coatings and Films Calcium Carbonate Crystallinity Crystallography chemistry.chemical_compound Calcium carbonate chemistry Materials Chemistry engineering Crystallite Physical and Theoretical Chemistry Particle Size Magnesium ion Biomineralization |
| Zdroj: | The journal of physical chemistry. B. 116(49) |
| ISSN: | 1520-5207 |
| Popis: | Phase transformation between calcite and aragonite is an important issue in biomineralization. To shed more light on the mechanism of this process at the molecular level, we employ solid-state (43)Ca NMR to study the phase transformation from calcite to aragonite as regulated by magnesium ions, with (43)Ca enrichment at a level of 6%. Using the gas diffusion approach, the phase of Mg-calcite is formed initially and the system subsequently transforms to aragonite as the reaction time proceeds. Our (43)Ca solid-state NMR data support the dissolution-recrystallization mechanism for the calcite to aragonite transition. We find that the (43)Ca NMR parameters of Mg-calcite are very similar to those of pure calcite. Under the high-resolution condition provided by magic-angle spinning at 4 kHz, we can monitor the variation of the (43)Ca NMR parameters of the aragonite signals for the samples obtained at different reaction times. Our data suggest that in the presence of a significant amount of Mg(2+) ions, aragonite is the most stable polymorph of calcium carbonate. The initial precipitated crystallites of aragonite have spine-like morphology, for which the (43)Ca spin-lattice relaxation data indicate that the ions in the lattice have considerable motional dynamics. As the crystallinity of aragonite improves further, the (43)Ca T(1) parameter of the aragonite phase changes considerably and becomes very similar to that obtained for pure aragonite. For the first time, the difference in crystal morphologies and crystallinity of the aragonite phase has been traced down to the subtle difference in the motional dynamics at the molecular level. |
| Databáze: | OpenAIRE |
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