Abstract
Seven-coordinate Fe(EDTA)-L complexes, where L represents a DNA constituent (uracil, uridine, thymine, thymidine and inosine), methylamine, ammonium chloride or imidazole, were investigated to resolve the solution chemistry of this system. The results show formation of 1:1 complexes with DNA constituents and the other ligands, supporting the hepta-coordination mode of Fe(III) ion. Stability constants of the complexes were measured by potentiometric titration at 25 A degrees C and ionic strength 0.1 mola <...L-1 NaNO3. The hydrolysis constant of [Fe(EDTA)(H2O)](-) and the formation constants of the complexes formed in solution were calculated using the non-linear least-squares program MINIQUAD-75. The concentration distributions of the various complex species were evaluated as a function of pH. The thermodynamic parameters Delta H (0) and Delta S (0), calculated from the temperature dependence of the equilibrium constants, were determined for the Fe(EDTA)-uracil complex. The effect of dioxane as a solvent on the protonation constant of uracil, hydrolysis constants of [Fe(EDTA)(H2O)](-), and the formation constants of the Fe(EDTA)-uracil complex are discussed.