Estimation of Stability Constants of Copper(II) Chelates with N-alkylated Amino Acids using Topological Indices
Branka Grgas, Sonja Nikolić, Nevenka Paulić, Nenad Raos · Institutional Repository of the Ruđer Bošković Institute (Ruđer Bošković Institute) · 1999
Protonation (pK 1 and pK 2 ) and copper(II) binding stability constants (log b 110 and log b 120 ) of glycine and five N-alkylated glycines (methyl, dimethyl, diethyl, tert-butyl and tert-butylmethyl) 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 third-order valence-connectivity indices, 1 c v , 2 c v and 3 c v ) calculated for 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 pK 2 (dissociation of amino group) with r 2 values up to 0.920.»Corrected« stability constants (obtained by subtracting pK 2 value) yielded a generally better fit than the uncorrected 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 values of pK 2 , log b 110 and log b 120 with an error less than 0.1, 0.3 and 0.3 log units, respectively.