Complexation reactions, electronic properties, and reactivity descriptors of cysteamine-based ligands in aqueous solution: a PCM/DFT study

Computational approaches based on density functional theory (DFT) combined with polarizable continuum model (PCM) of solvation have been used to probe the likelihood of complexation in water between oxo-vanadium(IV) and various medicinal cysteamine-based ligands. The experimental electronic spectra of a complex formed by oxo-vanadium(IV) and penicillamine in water agree well with the theoretical spectra based on the time-dependent density functional theory (TD-DFT) calculations. Among all density functionals adopted, CAM-B3LYP outperforms the others in predicting both structural and spectroscopic properties of oxo-transition metal complexes of cysteamine-based ligands. A variety of chelation behaviors have been found for the ligands tested, depending on the choice of substituent added to the cysteamine backbone. Solvation has a great impact on the thermodynamic driving force for cysteine and its derivatives to undergo complexation. In all cases, the thiolate sulfur atom forms stronger coordination bond than either the amine nitrogen or carboxylate oxygen atoms. Based on the thermodynamic and nucleophilicity index calculations, penicillamine has the highest potential to form complex with oxo-vanadium(IV).