Recognition of the R- and S-Naproxen Enantiomers by an Intercalative Binding Mode with Calf Thymus DNA

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. (between 260-280 nm) and alpha (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 Delta A((S)) 0.57 vs Delta A((R)) 0.35 at rho band and Delta lambda((S)) 4 nm v.s. Delta lambda((R)) 3 nm at alpha band, respectively. Meanwhile, the existence of ctDNA makes the fluorescence behaviors of R- and S-naproxen enantiomers differentiable. The association constants (K-A) between R-/S-naproxen and ctDNA are estimated as 1.24x10(4) and 1.55x10(4) 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 KS-SV 1.56x10(4) and KR-SV 1.41x10(4) mol.L-1 and their ratio, KS-SV/KR-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.