Thermodynamic stabilities of histidine related adducts of Rhodium(II) Carboxylates

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1976

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Abstract

The thermodynamic stabilities of the formation of 1:1 and 1:2 adducts of Rhlowered 2[lowered 4] where R = CH[lowered 3], CH[lowered 2]CH[lowered 3], and CH[lowered 2]OCH[lowered 3] and ligands, L-histidine, pyridine, imidazole, DL-histidyl — DL-histidine, L-histidylglycine and g-alanyl—L-histidine (carnosine) have been determined using a spectrophotometric method. For all ligands except imidazole the stabilities followed the order methoxyacetate > propionate > acetate. For imidazole the order was found to be propionate > acetate > methoxyacetate. This implies that several factors such as an inductive effect exhibited by the methoxyacetate, hydrophobic repulsion exhibited by the propionate, and the presence of charged groups within the neutral ligand must affect the stabilities. Also, stability constants obtained for different ligands are compared. The variation here depends upon basicity of the atom involved in complex formation, [pi] donor ability of the ligands, and steric hindrance in allowing bond formation.

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