Type of complex–BSA binding forces affected by different coordination modes of alliin in novel water-soluble ruthenium complexes†
Three novel water-soluble ruthenium complexes having differently bound alliin ligands were prepared by solution synthesis and characterized by chemical analysis, and infrared, mass, nuclear magnetic resonance and electron paramagnetic resonance spectroscopies. The reaction of (de)protonated alliin with cis,fac-[RuCl2(dmso-S)3(dmso-O)] in the presence of silver triflate afforded cationic [RuII(dmso-S)2(alliin-NS)2]2+ (1) and neutral [RuII(dmso-S)(OH2)(alliin-NO)2] (2), while [RuIII(NH3)5(alliin-O)]2+ (3) was prepared starting from [RuCl(NH3)5]Cl2. The interaction of the complexes with bovine serum albumin and apo-transferrin was investigated by spectrofluorimetry. The complexes showed higher affinity toward BSA compared to apo-transferrin. Deeper insight into the nature of the binding forces between the complexes and BSA was provided from the thermodynamic measurements, and synchronous and 3D emission spectra. Different coordination modes of alliin in complexes (1)–(3) affect the type of binding forces between the complexes and BSA. Complexes having O-bound alliin, (2) and (3), predominantly interact with the BSA through hydrogen bonding and van der Waals interactions, while hydrophobic forces govern the interaction of (1) with BSA. In vitro antiproliferative and antimicrobial activity of the complexes and alliin was also tested.