| Project/Area Number |
12640469
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Petrology/Mineralogy/Science of ore deposit
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| Research Institution | Yamaguchi University |
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Principal Investigator |
KAI Ayako Yamaguchi University, Faculty of Engineering, Lecturer, 工学部, 講師 (50253167)
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| Project Period (FY) |
2000 – 2001
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| Project Status |
Completed (Fiscal Year 2001)
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| Budget Amount *help |
¥3,100,000 (Direct Cost: ¥3,100,000)
Fiscal Year 2001: ¥1,300,000 (Direct Cost: ¥1,300,000)
Fiscal Year 2000: ¥1,800,000 (Direct Cost: ¥1,800,000)
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| Keywords | calcium carbonate / calcite / vaterite / amino acid / crystal growth / hybridization / radiation / electron spin resonance / ESR |
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| Research Abstract |
Vaterite with a thermally unstable phase is crystallized dominantly under the coexistence of noncharged-polar and acidic amino acids. Basic amino acids slightly affected the vaterite formation, while nonpolar amino acids had no effect on it. SEM photographs indicated that vaterite was prevented from growing in the initial stage of precipitation. Among the factors investigated, it was determined that pH of the solution and the molecular weight of the amino acids did not affect the formation of vaterite but the incorporation of amino acids was necessary. The content of vaterite was correlated to the concentration of amino acids in CaCO_3.
Differential scanning calorimetry showed an exothermic peak around 450℃ attributable to the phase transition from vaterite and an exothermic peak around 410℃ due to the phase transition from aragonite to calcite. The phase-transition temperature is related with the decomposition temperature of amino acid in the precipitates. The vaterite phase in amino-acid-doped CaCO_3 seemed to be stabilized at ambient temperature by the change of crystal energy.
Semi-empirical quantum-mechanical techniques using ZINDO : INDO1 indicated the possibility that amino acids are covalently bonded to CaCO_3, and the assumption that the reactivity of the acidic amino acids is the highest, and that of the basic ones is the lowest of the four types of amino acids. This assumption is consistent with the experimental results.
Radiation induced organic radicals in amino-acid -doped CaCO_3. However, the radicals have a -C(NH)CH_3 component which is absent from those in irradiated amino acid crystals. Thus, the radicals with amino group in amino-acid-doped CzCO_3 appear to play an important role in the synthesis of peptide with -CO-NH- bonds between two amino acid molecules. It is considered that the hybrid carbonate formed on the primitive earth might have provided a reaction field for the pre-biomolecule synthesis.
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