COMPETITIVE INTERACTIONS OF RUTHENIUM COMPLEXES CONTAINING DIMETHYLSULFOXIDE AND N-HETEROCYCLIC LIGANDS WITH HUMAN SERUM ALBUMIN

Two ruthenium complexes of the type [RuCl(dmso)(L)2]Cl {L = 4,4’-dimethyl-2,2’-bipyridine (dmbpy); 4,4’-dinonyl-2,2’-bipyridine (dnbpy)} have been synthesized and characterized by elemental analysis, 1H NMR, FTIR, electronic spectra, and molar conductivity. The IR spectral studies revealed that the DMSO molecule is S-bound ( νSO= 1100 cm-1; 1079 cm-1). For complexes, MLCT bands were observed around 390 nm and 440 nm. The measurements of conductivity revealed the presence of 1:1 electrolyte. Interactions of ruthenium complexes with human serum albumin were examined by fluorescence spectroscopy. The results revealed a combined quenching mechanism of HSA fluorescence by [RuCl(dmso)(dmbpy)2]Cl, with binding constant of 5.82 ± 0.08 x 105 mol-1 L (297 K), 5.29 ± 0.06 x 105 mol-1 L (303 K), and 4.68 ± 0.06 x 105 mol-1 L (313 K), whereas the [RuCl(dmso)(dnbpy)2]Cl caused static quenching predominantly, with binding constant of 9.87 ± 0.05 x 105 mol-1 L (297 K), 3.41 ± 0.04 x 105 mol-1 L (303 K), and 0.89 ± 0.05 x 105 mol-1 L (313 K). The binding process occurred spontaneously and was mainly driven by enthalpy, as evidenced by thermodynamic parameters. Site marker competitive experiment showed that ruthenium complexes bind to the warfarin binding site in subdomain IIA of HSA.