Kinetic studies on the formation of ternary complexes in the reaction of diaquonitrilotriacetatonickelate(II) with amino acids in aqueous solution |
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Authors: | Asim Das Soma Gangopadhyay Debabrata Banerjea |
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Institution: | (1) Department of Chemistry, Inorganic Chemistry Division, University College of Science, 92 Acharya P.C. Road, 700009 Calcutta, India |
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Abstract: | Summary Kinetics of formation of ternary complexes in the reaction of Ni(NTA)(H2O)
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with several amino acids, LH± (glycine, -alanine, -alanine, L-valine and L-phenylalanine) have been studied by a pH indicator method using stopped-flow spectrophotometry. The results conform to 1/kobs = 1/k + H+]/ kKTL where K is the equilibrium constant for formation of Ni(NTA)(–L)(H2O)2–, and k is the specific rate constant for the subsequent rate-determining ring-closure step leading to Ni(NTA)(=L)2–. For the different amino acids studied, the k values decrease in the sequence: glycine > -alanine > L-phenylalanine > L-valine > -alanine. These k values areca. 1000 times lower than the values for complexation of Ni(NTA)(H2O)
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with NH3 and imidazole and the spread in k values is much less than the pKa values of the amino acids. The relative rates are enthalpy controlled and the S values are highly negative in conformity with ring closure as the rate determining step. |
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