Synthesis, structural determination and HSA interaction studies of a new water-soluble Cu(II) complex derived from 1,10-phenanthroline and ranitidine drug

A new water-soluble Cu(II) complex containing ranitidine drug and 1,10-phenanthroline was synthesized and characterized by elemental analysis, molar conductivity, spectroscopic and computational methods. In vitro human serum albumin (HSA)-interaction studies of Cu(II) complex were performed by employing fluorescence spectroscopy in combination with UV–vis absorption and circular dichroism (CD) spectroscopies. The results of fluorescence titration showed that Cu(II) complex strongly quenched the intrinsic fluorescence of HSA through a static quenching mechanism with an intrinsic binding constant (6.05 × 10⁴ M⁻¹) at 286 K. The thermodynamic parameters ΔG, ΔH, and ΔS at different temperatures were calculated and suggested that the hydrophobic and hydrogen bonding interactions play major roles in Cu(II) complex-HSA association. The displacement experiments using warfarin and ibuprofen as site I and II probes proved that the Cu(II) complex could bind to site I (subdomain IIA) of HSA. Finally, CD spectra indicated that the interaction of the Cu(II) complex with HSA leads to an increase in the α-helical content. The main result of this study was the finding that the binding affinity of the Cu(II) complex to HSA is three orders of magnitude stronger than that of ranitidine drug.