Molecular Insights into the Protective Activity of Bioactive Purpurin against UV-Induced DNA Damage: Elucidation of the Binding Mechanism Using Spectroscopic and Computational Studies.

DNA, the fundamental genetic material in living organisms, is of great scientific interest due to its biological role and interactions with small molecules. Ultraviolet (UV) radiation poses a substantial environmental risk by inducing DNA damage, potentially leading to mutagenesis and skin cancers. The study investigated purpurin interaction with ct-DNA and its protective effect against UV-induced DNA damage. UV exposure caused significant DNA damage, indicated by 36% reduced absorbance; however, purpurin significantly lessened this damage to only 19%. In addition, Raman spectra showed no significant changes in purpurin-treated DNA, indicating that the DNA's native structure was preserved, suggesting that purpurin is able to protect the DNA against UV-induced DNA damage. UV-vis and cyclic voltammetry studies indicated purpurin-ct-DNA complex formation with a binding constant of 104 M-1. Thermodynamic analysis shows negative ΔH [-(39.91 ± 0.77) kJ mol-1] and ΔS [-(51.68 ± 2.70) J mol-1], indicating hydrogen bonding and van der Waals forces, with negative ΔG confirming spontaneity. Groove binding is the preferred binding mode as evaluated by various experimental techniques. Circular dichroism (CD) and Fourier-transform infrared (FT-IR) spectra suggested that purpurin binding does not alter DNA's structural integrity. Molecular dynamics (MD) simulation further supported the structural stability and flexibility of DNA. These findings provide mechanistic insight into the interaction of purpurin with DNA and its potential role in maintaining DNA structural integrity under UV irradiation.