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Estimation of stability constants of copper(II) chelates with N-alkylated amino acids using topological indices

Protonation (pK1 and pK2) and copper(II) binding stability constants (log beta110 and log beta120) of glycine and five N-alkylated glycines (methyl, dimethyl, diethyl, tert-butyl and tert-butyl-methyl) were determined by potentiometric titration. These constants and the constants of eight N-alkylated glycinates, measured previously, were correlated with four topological indices (Wiener index, W, and the first-, second- and the third-order valence-connectivity indices) calculated for the ligand. The first protonation constants (ascribed to the dissociation of the COOH group) do not correlate with any of the chosen topological indices, but significant correlation was obtained for pK2 (dissociation of amino group). Correlated stability constants (obtained by substracting pK2 value) yielded a general better fit than the uncorrected ones. Our stability constants are better correlated with topological indices than the constants measured previously. From the regression analysis it is possible to predict the values of pK2, log beta 110 and log beta 120 with en error less than 0.1, 0.3 and 0.3 log units, respectively.

Stability constants; Copper(II) chelates; N-alkylated glycinates; topological indices

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