The interactions of two organoplatinum complexes, [Pt(C^N)Cl(dppa)], 1, and [Pt(C^N)Cl(dppm)], 2 (C^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 (ΔG, ΔH, and ΔS) 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 IIA (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 Förster theory of nonradiation energy transfer.

The binuclear complex [Pt2Me2(ppy)2(mu-dppf)], 1, in which ppy = deprotonated 2-phenylpyridyl and dppf = 1,1'-bis(diphenylphosphino)ferrocene, was synthesized by the reaction of [PtMe(SMe2)(ppy)] with 0.5 equiv of dppf at room temperature. In this reaction when 1 equiv of dppf was used, the dppf chelating complex 2, [PtMe(dppf)(ppy-kappa1C)], was obtained. The reaction of Pt(II)-Pt(II) complex 1 with excess MeI gave the Pt(IV)-Pt(IV) complex [Pt2I2Me4(ppy)2(mu-dppf)], 3. When the reaction was performed with 1 equiv of MeI, a mixture containing unreacted complex 1, a mixed-valence Pt(II)-Pt(IV) complex [PtMe(ppy)(mu-dppf)PtIMe2(ppy)], 4, and complex 3 was obtained. In a comparative study, the reaction of [PtMe(SMe2)(ppy)] with 1 equiv of monodentate phosphine PPh3 gave [PtMe(ppy)(PPh3)], A. MeI was reacted with A to give the platinum(IV) complex [PtMe2I(ppy)(PPh3)], C. All the complexes were fully characterized using multinuclear (1H, 31P, 13C, and 195Pt) NMR spectroscopy, and complex 2 was further identified by single crystal X-ray structure determination. The reaction of binuclear Pt(II)-Pt(II) complex 1 with excess MeI was monitored by low temperature 31P NMR spectroscopy and further by 1H NMR spectroscopy, and the kinetics of the reaction was studied by UV-vis spectroscopy. On the basis of the data, a mechanism has been suggested for the reaction which overall involved stepwise oxidative addition of MeI to the two Pt(II) centers. In this suggested mechanism, the reaction proceeded through a number of Pt(II)-Pt(IV) and Pt(IV)-Pt(IV) intermediates. Although MeI in each step was trans oxidatively added to one of the Pt(II) centers, further trans to cis isomerizations of Me and I groups were also identified. A comparative kinetic study of the reaction of monomeric platinum(II) complex A with MeI was also performed. The rate of reaction of MeI with complex 1 was some 3.5 times faster than that with complex A, indicating that dppf in the complex 1, as compared with PPh 3 in the complex A, has significantly enhanced the electron richness of the platinum centers.

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The starting complexes [PtCl(C^N)(dmso)], in which C^N is either ppy = 2-phenylpyridinate, , or bhq = 7,8-benzo[h]quinolinate, , were prepared by a known method using the reaction of [PtCl2(dmso)2] with ppyH or bhqH, respectively, in toluene under reflux conditions. The reaction of [PtCl(C^N)(dmso)], or , with 1 equiv. of a number of biphosphine ligands, P^P, gave the cationic monomeric complexes [Pt(ppy)(P^P)]Cl, for which P^P is either 1,2-bis(diphenylphosphino)ethane (dppe), , 1,3-bis(diphenylphosphino)propane (dppp), , or bis(diphenylphosphino)methane (dppm), ; the bhq analogous complex [Pt(bhq)(dppe)]Cl, , was prepared similarly. However, the complex [Pt(ppy)(dfppe)]Cl, , in which dfppe is 1,2-bis(dipentafluorophenylphosphino)ethane, was prepared by the reaction of with excess amount of dfppe. When each of the starting complexes [PtCl(C^N)(dmso)], or , were reacted with 0.5 equiv. of any of the P^P ligands, the dimeric complexes [Pt2Cl2(ppy)2(μ-P^P)], , or [Pt2Cl2(bhq)2(μ-P^P)], , were formed. The complexes were fully characterized using multinuclear ((1)H and (31)P) NMR spectroscopy and elemental analysis. The structures of typical complexes , , , and were also confirmed by X-ray crystallography. The effect of ligands on the luminescent properties of the complexes was investigated and DFT calculations were performed to confirm the assignments.