Comparative study on the interaction of three cationic cycloplatinated(II) complexes with DNA and HSA

The biomolecular interactions of three previously reported cationic cycloplatinated complexes, [Pt(dfppy)(dppm)]Cl, C1, [Pt(dfppy)(dppe)]Cl, C2, and [Pt(dfppy)(dppbz)]Cl, C3, (dfppy = 2-(2,4-difluorophenyl)pyridine; dppm = bis(diphenylphosphino)methane; dppe = 1,2-bis(diphenylphosphino)ethane; dppbz = 1,2-bis(diphenylphosphino)benzene) with calf thymus DNA (ctDNA) and human serum albumin (HSA) have been investigated. The competitive behavior of the Pt complexes with four different fluorescent probes displayed multiple DNA binding mechanisms, including both intercalation and minor groove binding. The negative values of ΔH° and ΔS° suggested that van der Waals and hydrogen bonding are the predominant forces in the interactions of C1 and C2 with DNA. The sign of ΔH° and ΔS° changes at 298 K for interaction of C3 with DNA from negative to positive. Also, the binding of C3 to DNA occurs with the highest affinity compared to C1 and C2. The positive values of ΔH° and ΔS° revealed that hydrophobic interactions were the main force in the binding of the Pt complexes to HSA. Experimental results and docking investigations showed that the binding sites of HSA for C1, C2, and C3 are mainly located in the subdomain IIA (site I). The results of molecular docking investigations demonstrated that π-π-stacking and hydrophobic interactions are involved upon HSA binding of these complexes.