Estimation of stablity constants of mixed amino acid complexes with copper(II) from topological indices

Stability constants of binary and ternary complexes of five naturally occurring amino acids (Gly, Ala, Val, Phe, Tyr) with copper(II) were correlated with the Wiener (W) and the valence-connectivity indices (chi) of their ML2 complexes, yielding the correlation coefficient r = 0.931-0.997 and the root-mean-square (rms) deviation of the measured and estimated values in the range of 0.013 to 0.065 log K units. Multiple regression of 27 second ligation constants of binary and ternary complexes of 10 amino acids (Gly, Ala, Val, Leu, Ser, Thr, Met, Phe, Tyr, Trp) on topological indices of various molecular species (L, ML, ML2) yielded R = 0.696-0.756 and rms = 0.17-0.19 log K-2 units. The result is essentially better than the results obtained by the mechanistic method of M. Tabata and M. Tanaka (see Ref. 8) on the same set of data (rms = 0.39 log K-2 units). The method appeared to be sensitive to the amino acid ability of additional (apical) coordination, but not very sensitive to other structural properties (aromaticity, polarity). Among the models used, the best results were obtained with the third-order valence-connectivity index (3 chi (v)) calculated from the formula of complex compounds (ML and ML2)