Metal Complexes of Some Model Peptides. Part-I : Complex Formation of Cu(II) with N-Salicyloyl Glycine

Department of Chemistry, University College of Science, Calcutta-700 009 Manuscript received 9 March 1981, revised 7 April 1982, accepted 21 July 1982 pH-Metric study of the interaction of Cu(II) with N-salicyloyl glycine, o-(OH)- C6H4CONHCH2COOH, LH3, indicated the stepwise formation of 1 : 1 and 1 : 2 metal ligand complexes. The phenolic -OH group was not involved in coordination to Cu(II), as its deprotonation occurred only after the completion of formation of the 1 : 2 complex. Coordination from the N-(peptide) atom occurred only through depro­tonation. The stepwise equilibrium constants (K'1 and K'2) of complex formation, stepwise deprotonatfon constants (k2OH and k1OH) of the 1:2 complex, \(Cu(LH)_2^{2-}\) ion and successive acid dissociation constants (kCOOH, kOH and kNH) of the ligand LH3 have been determined. The overall stability constants, βpqr of the complexes [CupHqLr +2p+q-3r]have been calculated. The pK'1, pK'2, pk2OH, pk1OH , pkCOOH, pkOH, pkNH, log β 111, log β 122, log β 112, log β 102 values have been found to be 6.54+0.04, 6.76±0.04, 8.68±0.0, 9.46±0.04, 4.26±0.02, 9.12±0.04, 12.88± 0.01, 6.81+0.01, 13.46±0.0-1, 17.66 ±0.0.4 and 21.08±0.04, respectively at 30±0.5° in 50% (v/v) water-ethanol at a constant iconic strength µ=0.2 M (NaClO4). Trends in the pkOH values of the free and of the complexed ligand and the equilibrium distribution of the complex species have been discussed