DNA Binding of a Nitro-Substituted Schiff Base Cu (II) Complex: a Combined Spectroscopic, Viscometric, and Molecular...

An integrated experimental and computational approach, including UV-Vis absorption, fluorescence quenching, circular dichroism (CD) spectroscopy, viscosity measurements, agarose gel electrophoresis, thermodynamic analysis, molecular docking, and Molecular Electrostatic Potential (MEP) mapping, was used to study the DNA-binding behavior of a nitro-substituted Schiff base Cu (II) complex. With a binding constant of approximately 1.7 × 10⁵ M^-1, spectroscopic analyses verified an efficient interaction with fish salmon DNA (FS-DNA). Thermodynamic characteristics revealed a spontaneous process supported mainly by hydrogen bonding and van der Waals interactions, while fluorescence data suggested a static quenching mechanism and approximately 1:1 binding stoichiometry. The molecular docking results, together with the absence of any significant change in DNA viscosity and the negligible DNA-cleavage activity, suggest that groove binding is more likely than classical intercalation. The electron withdrawing nitro substituent really changes how the complex's electrons are spread out, creating clear electrophilic and nucleophilic zones. These regions facilitate interaction through the groove, while also reducing the electron density that would be required for the classical π-π stacking, as indicated by the MEP analysis. Overall, these findings suggest the nitro group governs the DNA binding preference, providing valuable insights for the design of metal complexes aimed at nucleic acids in future applications.