Affinity of Two Novel Five-Coordinated Anticancer Pt(II) Complexes to Human and Bovine Serum Albumins: A Spectroscopic Approach

The interactions of two organoplatinum complexes, [Pt(C boolean AND N)Cl(dppa)], 1, and [Pt(C boolean AND N)Cl(dppm)], 2 (C boolean AND N = N(1), C(2')-chelated, deprotonated 2-phenylpyridine, dppa = bis(diphenylphosphino)amine, dppm = bis(diphenylphosphino)methane), as antitumor agents, with bovine serum albumin (BSA) and human serum albumin (HSA) have been studied by fluorescence and UV-vis absorption spectroscopic techniques at pH 7.40. The quenching constants and binding parameters (binding constants and number of binding sites) were determined by fluorescence quenching method. The obtained results revealed that there is a strong binding interaction between the ligands and proteins. The calculated thermodynamic parameters (Delta G, Delta H, and Delta S) confirmed that the binding reaction is mainly entropy-driven, and hydrophobic forces played a major role in the reaction. The displacement experiment shows that these Pt complexes can bind to the subdomain HA (site I) of albumin. Moreover, synchronous fluorescence spectroscopy studies revealed some changes in the local polarity around the tryptophan residues. Finally, the distance, r, between donor (serum albumin) and acceptor (Pt complexes) was obtained according to Forster theory of nonradiation energy transfer.