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Original scientific paper

Estimation of Stability Constants of Copper(II) Chelates with Amino Acids by Overlapping Spheres Method

Nenad Raos

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page 175-180

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The method of overlapping spheres (OS) was applied to the estimation of stability constants of mono- (log β110) and bis-complexes (log β120) of α-amino acids and their N-alkyl and N,Ndialkyl 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, correlation coefficients (r) of 0.944 and 0.895 for log β110 and log β120, respectively. The best regressions (r = 0.977–0.998) were obtained by taking into account only the complexes of N-alkylated 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 estimate the measured stability constants with an error in the range 0.1–0.5 log β units.


N-alkylated amino acids, molecular volumes

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