New advances in the study on the interaction of [Cr(phen)2(dppz)]3+ complex with biological models; association to transporting proteins

The present study reports a detailed investigation with the interaction of [Cr( phen)(2)(dppz)](3+) with serum albumins, the key protein for the transport of drugs in the blood plasma, which allows us to understand further the role of [Cr(phen)(2)(dppz)](3+) as sensitizer in Photodynamic Therapy (PDT). Chromium(III) complex [Cr(phen)(2)(dppz)](3+), (dppz = dipyridophenazine and phen = 1,10-phenanthroline), where dppz is a planar bidentate ligand with an extended pi system, has been found to bind strongly with bovine and human serum albumins (BSA and HSA) with an intrinsic binding constants, K-b, of (1.7 +/- 0.3) x 10(5) M-1 and (2.2 +/- 0.3) x 10(5) M-1 at 295 K, respectively. The interactions of serum albumins with [Cr(phen)(2)(dppz)](3+) were assessed employing fluorescence spectroscopy, circular dichroism and UV-vis absorption spectroscopy. The serum albumins-[Cr(phen)(2)(dPPz)](3+) interactions caused conformational changes with the loss of helical stability of the protein and local perturbation in the domain IIA binding pocket. The relative fluorescence intensity of the albumin (BSA or HSA) bound to the Cr(III) complex decreased, suggesting that perturbation around the Trp 214 residue took place. The analysis of the thermodynamic parameters Delta G, Delta H, Delta S indicated that the hydrophobic interactions played a major role in both BSA-Cr(III) and HSA-Cr(III) association processes. The binding distances and transfer efficiencies for BSA-Cr(III) and HSA-Cr(III) binding reactions were calculated according to the Foster theory of non-radiation energy transfer. All these experimental results suggests that [Cr( phen)(2)(dppz)](3+) binds to serum albumins, by which these proteins could act as carriers of this complex for further applications in PDT. (C) 2011 Elsevier Inc. All rights reserved.