Estimation of Stability Constants of Copper(II) Bis-chelates by the Overlapping Spheres Method
Ante Miličević, Nenad Raos · University of Zagreb University Computing Centre (SRCE) · 2006
The method of overlapping spheres (OS) was applied for the estimation of stability constants (b 2 ) of sets of (binary) copper(II) bis-complexes with 1,2-diaminoethanes (N = 14), aliphatic amino acids and their N-alkylated derivatives (N = 11), and naturally occurring amino acids (N = 9), along with a set of 16 mixed (ternary) copper(II) bis-complexes with naturally occurring amino acids.The central sphere, with the radius, R v , 300 or 400 pm, was situated at the copper atom.The OS volumes (V*) of the central sphere and the van der Waals spheres of the surrounding atoms were calculated from the structures of bis-or corresponding mono-complexes and correlated with the log b 2 values.Both approaches yielded similar results, differing in the reproduction of stability constants by less than 20 %.Bivariate linear regression was performed for mixed complexes, using (V* 1 + V* 2 ) and (V* 1 -V* 2 ) as independent variables (V* 1 and V* 2 correspond to the OS values for the two constituting chelate rings).The bivariate linear regression gave r = 0.961 and the reproduction of experimental data from 0.00 to 0.16 log b units (S.E.cv = 0.08 log b units).