Spectroscopic studies on the interaction of nicotine and BSA

The interaction of nicotine and bovine serum albumin(BSA) was investigated by fluorescence spectra and U-V-vis spectra. The fluorescence spectrum showed that BSA fluorescence quench regularly with the addition of nicotine. The fluorescence quenching mechanisms were also studied in pH 5.0, pH 7.4 and pH 11.0 by Stern-Volmer equation, indicating dynamic quenching(pH 5.0) and static quenching(pH 7.4 and pH 11.0) respectively. Association constants W of nicotine and BSA at pH 7.4 and pH 11.0 at the temperatures of 20 and 37 degrees C were given by the Lineweaver-Buck equation, which are: k(20 degrees C) = 140.15 L(.)mol(-1) and k(37 degrees C) = 131.83 mol(.)L(-1) (pH 7.4), and k(20 degrees C) = 141.76 mol(.)L(-1), k(37 degrees C) = 27.79 mol(.)L(-1) (pH 11.0), suggesting that the association constant is effected by the temperature much more remarkably at pH 7.4 than that at PH 11.0 because of the different states of nicotine at different pHs. The UV-Vis spectra exhibit that the absorbance of BSA(210 nm) shifts to red and decreases gradually with the addition of nicotine, reflecting the transition of secondary structure of BSA, namely, the helix of BSA becomes looser. The UV-Vis second derivative spectra and synchronous spectra (Delta lambda = lambda em - lambda ex = 15 nm and Delta lambda = lambda em - lambda ex = 60 nm) imply the change of the microcircumstance of aromatic amino residues of BSA(Trp, Tyr and Phe) from hydrophobicity to hydrophilicity at high concentration of nicotine.