Metal complexes of some peptide derivatives. Part-XIV. Complex formation of copper(II) with N-benzenesulfonamides of some dipeptides

Department of Chemistry, University of Calcutta, University College of Science,

92 Acharya Prafulla Chandra Road, Kolkata-700 009, India

E-mail: gurunath@cucc.ernet.in           Fax: 91-033-3519755/2413222

Bengal Chemical and Pharmaceutical Works, Kolkata-700 009, India

Manuscript received 11 August 2000, revised 13 July 2001, accepted 14 July 2001

Combined potentiometric and spectrophotometric investigation on the complex formation equilibria of Cu^ll with N-benzenesulfonyl derivatives of some dipeptides, viz. glycylglycine, glycyl-dl-α-alanine, glycyl-dl-methionine, glycyl-β-alanine, β-alanylglycine (AH₂) in aqueous solution provides evidence of complexes of the types : Cu(AH)⁺, Cu(H_-1AH), Cu(H_-1 Ai, Cu(H_-1 A)(OH)^2- , Cu(AH)2, Cu(H_₁AH)(AH)^-, Cu(H-₁ AH)\(_2^2\)^-, Cu(H_-1A)(H_-1AH)³ and Cu(H_₁A)\(_2^4\)^- .Deprotonation constants (pK^HCOOH  and pK^HSO₂NH) of the ligands and formation constants of the complexes at 25 ± 1⁰ in aqueous solution, I = 0.2 M (NaNO₃), are correlated with the modes of coordination of the amide and sulfonamide groups, size of the chelate rings, and metal-ligand and ligand-ligand it-interactions. Deprotonation constants of coordinated H₂O molecules in the square-planar, or distorted octahedral Cu(H_-1A)(H₂0)^- complexes indicate their equatorial disposition. The tendency of the ternary hydroxo complexes, Cu(H_₁A)(OH)^2- to transform into to Cu(H_₁A)\(_2^4\)^- with precipitation of Cu(OH)₂ at pH >9 is found to be in the inverse order of stability constants of these complexes.