Kinetics and Mechanism of Aquation and Anation of Some Amino Acid Pentamminecobalt(III) Complexes in Acid Aqueous Solutions
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概要
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Kinetics of aquation has been studied with pentamminecobalt(III) complexes containing aliphatic amino acids (γ-aminobutyric acid, ε-aminocaproic acid, α-amino-isobutyric acid, ornithine, and proline), aromatic acids (benzoate, anthranilic, and <I>p</I>-aminobenzoic acid), and α-substituted acetates (monochloroacetate and glycolate). Anation rate constants were obtained for glycine, β-alanine, and ε-aminocaproic acid, and equilibrium constants between [CoH<SUB>2</SUB>O(NH<SUB>3</SUB>)<SUB>5</SUB>]<SUP>3+</SUP> and [Co(NH<SUB>3</SUB>)<SUB>5</SUB>amH]<SUP>3+</SUP> (amH=amino acid), <I>K<SUB>eq</SUB></I> were calculated. The free energy plot log<I>k<SUB>aq</SUB></I> <I>vs.</I> log<I>K<SUB>eq</SUB></I> gave a straight line with a gradient 0.6. This value has been discussed in terms of two possible mechanisms. The dependence of acid catalysed aquation rate constant, <I>k</I><SUB>H</SUB><SUP>+</SUP> on p<I>K<SUB>a</SUB></I> of carboxylate group of the amino acid is written as log<I>k</I><SUB>H</SUB><SUP>+</SUP>=0.5 p<I>K<SUB>a</SUB></I>+ const., while that for α-substituted acetates log <I>k</I><SUB>H</SUB><SUP>+</SUP>=p<I>K<SUB>a</SUB></I>+ const. Such a difference in the slope is interpreted as due to the electrostatic influence of–NH<SUB>3</SUB><SUP>+</SUP> group of coordinated amino acid.
- 公益社団法人 日本化学会の論文
著者
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MURAKAMI TASUKU
Chemical Research Institute of Non-aqueous Solutions, Tohoku University
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Saito Kazuo
Chemistry Department, Faculty of Science, Tohoku University
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Kobayashi Hiromi
Chemistry Department, Faculty of Science, Tohoku University
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Murakami Tasuku
Chemistry Department, Faculty of Science, Tohoku University
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Ogino Kazuko
Chemistry Department, Faculty of Science, Tohoku University
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Yamazaki Hiroshi
Chemistry Department, Faculty of Science, Tohoku University
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