Abstract

The possible recognition interaction of R-/S-naproxen enantiomers with calf thymus DNA (ctDNA) is studied by UV absorption and fluorescence spectroscopy, KI fluorescence quenching and thermal denaturation experiments. The results indicate that ctDNA can act as host molecule to recognizing R- and S-naproxen enantiomers. As addition of ctDNA, the ρ (between 260-280 nm) and α (longer than 300 nm）absorption bands of R-/S-naproxen enantiomers show obvious hypochromic effect with bathochromic shift, indicating a typical intercalative binding mode. Importantly, the effect of ctDNA on hypochromic effect and bathochromic shift of S-naproxen is more noticeable than S-naproxen, ΔA_(S) 0.57 vs ΔA_(R) 0.35 at ρ band and Δλ_(S) 4 nm v.s. Δλ_(R) 3 nm at α band, respectively. Meanwhile, the existence of ctDNA makes the fluorescence behaviors of Rand S-naproxen enantiomers differentiable. The association constants (K_A) between R-/S-naproxen and ctDNA are estimated as 1.24×10⁴ and 1.55×10⁴ mol·L^-1, respectively, according to the Scatchard equation. Also the estimated binding sites are 0.98 and 1.0, respectively, indicating that both R- and S- naproxen could strongly and diacritically interact with ctDNA. Moreover, the Stern-Volmer fluorescence quenching constants (K_SV) of R-/S-naproxen by ctDNA are measured as K_S-SV 1.56×10⁴ and K_R-SV 1.41×10⁴ mol·L^-1 and their ratio, K_S-SV/K_R-SV, is 1.13. The fluorescence quenching by iodide anion and thermal denaturation experiments show further that the interaction mode of R-/S-naproxen and ctDNA should be an intercalative binding mode and intercalation of S-naproxen into ctDNA is stronger than R-Naproxen.

Keywords: ctDNA, fluorescence spectrometry, intercalative binding mode, molecular recognition, R-Naproxen, S-Naproxen.