The stability constants of 1:1 complexes formed between M2+ : Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+ , Cd2+ and the thymidine-5’-diphosphate (dTDP3-) were determined by potentiometric pH titration in aqueous solution (I= 0.1 M, NaNO3 25°C). For comparison, the same values were used the simple diphosphates monoesters (R-DP3-). The acidity constants for dTDP3- i.e. و و were measured also via potentiometric pH titration and various comparisons with related constants were made. By constraction of log versus p plots for the complexes of the diphosphates and by a carful evaluation of the various data pairs from the straight-line correlation, the results show that in the M(dTDP)-- complexes the points lie on the line and the metal ion is only diphosphate-coordinated. This means that there is no interaction between suger and nucleoside base with metal ion. The straight line equations, which result from the mentioned correlations, together with the pKa value of a given monoprotonated diphosphate monoester allow now to predict the stability constants of M(R-DP)--complexes.

Keywords: nucleotides, diphosphate monoesters, acidity constants, stability constants

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