engleski

The use of graph-theoretical models to evaluate two electroanalytical methods for determination of stability constants

Stability constants K1 and β 2 of copper(II) complexes with alanine and its five N-alkylated and N, N-dialkylated derivatives, as measured by glass electrode potentiometry (GEP) and square wave voltammetry (SWV), were evaluated by graph-theoretical models. The correlations with the connectivity index of the 3rd order, 3χ v, shows that values of log K1(GEP) constants were better reproduced than that of the log K1(SWV) ; S.E. = 0.18 and 0.16 vs. 0.29 and 0.35, respectively. The oppostite is true for log β 2 (S.E. = 0.51 – 0.56 vs. 0.39 – 0.47 for GEP and SWV, respectively). This conclusion is also in accordance with estimates of copper(II) alaninates from regression models done on 11 copper(II) chelates with glycine and its N-alkylated derivatives. By applying three criteria – (1) difference between GEP and SWV values, (2) difference between SWV and theoretical values, and (3) correlation of experimental error (S.E.) to the difference between experimental and theoretical values - it was possible to mark three experimental logK1(SWV) values as problematic. This report demonstrates the value of recently developed graph-theoretical models in discussing the results and planning the experiments.

glass electrode potentiometry (GEP); square wave voltammetry (SWV); copper(II) chelates; amino acid; stability constant; topological indices

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