Synthesis, Characterization, and Biomolecular Interactions of a novel Copper(II) Complex: DNA and BSA Binding Studies

This study synthesizes and characterizes the mononuclear complex [Cu(phen)₂(NO₃)]NO₃·H₂O using analytical techniques such as infrared spectroscopy (FT-IR), elemental analysis, molar conductivity measurements, and single-crystal X-ray crystallography. The complex exhibited 1:1 electrolyte behavior. X-ray crystallography revealed a distorted trigonal bipyramidal geometry around Cu(II), stabilized by two 1,10 phenanthroline ligands and a nitrate ion. Crystallographic data were further analyzed using Hirshfeld surface analysis to quantify intermolecular interactions. The analysis revealed the following percentages: O…H (30.3%) and H…H (25.6%). DNA binding studies using UV-vis absorption spectroscopy demonstrated a hypochromic effect, suggesting a partial intercalative or groove-binding mode due to steric hindrance. The binding constant (K_b) was determined to be 3.74 × 10⁴ M⁻¹, indicating a relatively high affinity for DNA. The interaction of the complex with BSA was investigated using UV-vis absorption and fluorescence spectroscopy. Hyperchromism in UV-vis spectra and fluorescence quenching of BSA tryptophan residues were observed, indicating complex binding and conformational changes in BSA. Stern-Volmer analysis revealed a binding-dominated quenching mechanism. Thermodynamic parameters calculated from fluorescence data suggested that van der Waals forces and hydrogen bonding are the dominant interactions in the complex-BSA binding, which was found to be spontaneous and enthalpy-driven. Cyclic voltammetry confirmed the complex's interaction with DNA, showing a decrease in peak currents and negative shifts in peak potentials, further supporting the proposed binding mode.