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

Protonation (pK(1) and pK(2)) and copper(II) binding stability constants (l og beta(110) and log beta(120)) of glycine and five N-alkylated glycines (m ethyl, dimethyl, diethyl, tert-butyl and tert-butylmethyl) were determined by potentiometric titration. These constants and the constants of eight N-a lkylated glycinates, measured previously, were correlated with four topolog ical indices (Wiener index, W, and the first-, second- and third-order vale nce-connectivity indices, (1)chi(v), (2)chi(v) and (3)chi(v)) calculated fo r the ligand. The first protonation constants (ascribed to the dissociation of COOH group ) do not correlate with any of the chosen topological indices (r(2) < 0.3), but significant correlation was obtained for pK2 (dissociation of amino gr oup) with r(2) values up to 0.920. "Corrected stability constants (obtained by subtracting pK(2) value) yielded a generally better fit than the uncorr ected ones. Our stability constants are better correlated with topological indices (max. r(2) = 0.993) than the constants measured previously (max. r( 2) = 0.836). From the regression analysis it is possible to predict the val ues of pK(2), log beta(110) and log beta(120) with an error less than 0.1, 0.3 and 0.3 log units, respectively.