Multispectroscopic studies of paeoniflorin binding to calf thymus DNA in vitro

The mechanism of paeoniflorin binding to calf thymus DNA in physiological buffer (pH 7.4) was investigated by multispectroscopic methods including UV–vis absorption, fluorescence, circular dichroism (CD) and Fourier transform infrared (FT-IR) spectroscopy, coupled with viscosity measurements and DNA melting techniques. The results suggested that paeoniflorin molecules could bind to DNA via groove binding mode as evidenced by no significant change in iodide quenching effect, increase in single-stranded DNA (ssDNA) quenching effect, and almost unchanged relative viscosity and melting temperature of DNA. The observed changes in CD signals revealed that DNA remains in the B-conformation. Further, the displacement experiments with Hoechst 33258 probe and the results of FT-IR spectra indicated that paeoniflorin mainly binds in the region of rich A–T base pairs of DNA. The thermodynamic parameters, enthalpy change (ΔH°) and entropy change (ΔS°) were calculated to be –30.09±0.18 kJ mol−1 and –14.07±0.61 J mol−1 K−1 by the vanʹt Hoff equation, suggesting that hydrogen bond and van der Waals forces play a predominant role in the binding of paeoniflorin to DNA.