Investigation on the physicochemical properties of trans-4-stilbenecarboxaldehyde-derived hydrazones and their copper(II) complexes

Abstract

[Cu(HL)2Cl2] complexes (1–6) were prepared with trans-4-stilbenecarboxaldehyde-para-tolyl-hydrazone HStpT (HL1), trans-4-stilbenecarboxaldehyde-para-chloro-phenylhydrazone HStpClPh (HL2), trans-4-stilbenecarboxaldehyde-para-hydroxy-phenylhydrazone HStpOHPh (HL3), trans-4-stilbenecarboxaldehyde-para-nitro-phenylhydrazone HStpNO2Ph (HL4), trans-4-stilbenecarboxaldehyde-acetylhydrazone HStAc (HL5), and trans-4-stilbenecarboxaldehyde-benzoylhydrazone HStBz (HL6). Infrared spectra suggested that the hydrazones act as bidentate ligands which bind to the copper(II) center through the Nimine-O chelating system. EPR spectra of complexes (1–6) were recorded at room temperature for powder samples and at 77K for DMSO solution. The EPR parameters were compatible with the presence of copper(II). Since the spectroscopic data for complexes (1–6) did not allow the unambiguous determination of the exact geometry of the complexes in the solid state or in solution, theoretical studies were carried out considering five possible isomers, in order to get information on the predominant species. However, although one of the isomers revealed to be the most thermodynamically favorable, free energy differences were not larger than 3kcal·mol−1. Hence, differences in lattice energy or packing forces could influence the geometry adopted in the solid. The thermodynamic analysis of the five isomers indicated that all of them are in equilibrium in solution. EPR studies suggested that complexes (1–6) interact with bovine (BSA) and human (HSA) serum albumin, with displacement of the hydrazone ligands and coordination of copper(II) to site 1, together with formation of hydrazone-cysteine mixed-ligand copper(II) complexes at site 2 of the albumins.