Ante Miličević* and Nenad Raos

Institute for Medical Research and Occupational Health, Ksaverska c. 2, P.O. Box 291, HR-10000 Zagreb, Croatia
* Corresponding author: E-mail: antem@imi.hr

Abstract
Valence connectivity index ³χ^v was correlated to the log K¹(L) of copper(II) complexes with diethylenetriamines (CuL, N = 8), and to logarithm of the second, log K²(L) and log K²(A), and overall stability constant, log β², of copper(II) mixed complexes (CuLA, N = 18) with diethylenetriamines and amino acids. Regression on log K₁(L) strongly indicates that influence of alkylation at middle nitrogen atom differs from the influence of alkylation at terminal nitrogens. Thereby, in models for estimation of all stability constants we introduced an indicator variable, In; In = 1 for a complex with triamine alkylated at the middle nitrogen, otherwise In = 0. Also, we developed second set of models assuming there is no bonding between Cu(II) and middle N atom. Both approaches gave nearly the same standard error of estimate, i.e. 0.3 for log K₁(L) and log K₂(A), and 0.5 for log K₂(L) and log β2.

Keywords: Diethylenetriamines, amino acids, mixed complexes, indicator variable