Temperature and methyl substitution effect on copper(II) complexes with biorelevant ligands and species distribution in aqueous solution.

In the present work, the stability constants of copper(II) complexes with 1,10-phenanthroline (phen), its methyl derivatives [4-methyl-1,10-phenanthroline (4-mphen) and 4,7-dimethyl-1,10-phenanthroline (dmphen)] and L-tryptophan (trp) were investigated using potentiometric method in 0.1 mol⋅L−1 KCl aqueous ionic media at 298.15 K, 308.15 K and 318.15 K. 'BEST' software package was applied to the potentiometric data for the calculation of the protonation constants of the ligands and the stability constants of the copper(II) binary and ternary complexes. The concentration distributions of the various complex species formed in solution were also evaluated as a function of pH using the 'SPE' software package. The thermodynamic parameters, enthalpy change (ΔH°), entropy change (ΔS°) and Gibbs energy change (ΔG°) were determined from the stability constants using Gibbs and van't Hoff equations. The complexation of copper(II) with the ligands in this work is spontaneous, exothermic and favourable at lower temperatures. [ABSTRACT FROM AUTHOR]