Estimation of stability constants of copper(II) chelates with triamines and their mixed complexes with amino acids by using topological indices and the overlapping spheres method. Polyhedron 2007

The method of overlapping spheres (OS) was applied to the estimation of stability constants of mono- (log 110) and bis-complexes (log 120) of -amino acids and their N-alkyl and N,N-dialkyl derivatives with copper(II). The central sphere, with a 0.3 or 0.4 nm radius, was placed at the central (Cu), equatorial (N) or apical (X) position of the coordination polyhedron. The overlapping volume of the central sphere and the van der Waals spheres of neighbouring atoms was calculated and correlated with the measured stability constants. The training set (N = 11) consisted of four naturally occurring amino acids and seven N-alkylated and N,N-dialkylated glycines. It gave, upon linear regression of stability constants on the overlapping volume, cor-relation coefficients (r) of 0.944 and 0.895 for log 110 and log 120, respectively. The best re-gressions (r = 0.977–0.998) were obtained by taking into account only the complexes of N-al-kylated glycine (N = 5) and placing the central sphere at the position of equatorial nitrogen atom(s). Using the regression functions derived from the training set, it was possible to esti-mate the measured stability constants with an error in the range 0.1–0.5 log units. Keywords N-alkylated amino acids molecular volumes * Dedicated to Dr. Edward C. Kirby on the ocassion of his 70th birthday