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采用荧光光谱、紫外光谱、CD光谱法研究了K_2Cr_2O_7与牛血清白蛋白(BSA)的相互作用.实验结果表明, 铬(Ⅵ)使BSA的紫外吸收降低,峰位红移,表明铬(Ⅵ)与BSA发生较强的相互作用;铬(Ⅵ)酸根离子与BSA形成基态复合物导致BSA内源荧光猝灭,猝灭机理主要为静态猝灭.测定了不同温度下该反应的热力学参数,ΔG~θ＜0,ΔH~θ和ΔS~θ分别为-12.60 kJ/mol和56.60 J/(mol·k),表明上述作用过程是一个熵增加、自由能降低的自发分子间作用过程,铬(Ⅵ)酸根离子与BSA之间以静电作用力为主;非辐射能量转移机理确定了铬(Ⅵ)与牛血清白蛋白中色氨酸残基之间的距离r=2.85 nm;同步荧光和CD光谱研究表明,铬(Ⅵ)使BSA的二级结构发生改变,α-螺旋含量降低,色氨酸残基所处微环境的极性减小.

The interaction between chromium( Ⅵ ) and bovine serum albumin(BSA) was investigated via fluorescence, UV/Vis and CD spectroscopies. It is shown that Cr( Ⅵ ) decreased the intensity of UV absorption peak of BSA, accompanied by red-shift. The fluorescence experimental results show that the fluorescence quenching of BSA by chromium( Ⅵ ) is a result of the formation of Cr( Ⅵ )-BSA complex; static quenching was confirmed to result in the fluorescence quenching. The thermodynamic parameters were calculated(ΔG~θ＜0, ΔH~θ=-12.60 kJ/mol, ΔS~θ=56.60 J/(mol·k)), the process of binding Cr( Ⅵ ) molecule on BSA was a spontaneous molecular interaction procedure, during which the entropy increased and the Gibbs free energy decreased. The electrostatic force interaction plays a major role in stabilizing the complex. The distance between the tryptophane residue of BSA and Cr_2O_7~(2-) anion(2.85 nm) was determined by the mechanism of the energy transfer of dipole-dipole interaction. The results of synchronous fluorescence spectroscopy and CD spectroscopy indicate that Cr( Ⅵ ) had a strong impact on BSA conformation, resulting in the change of the tryptophane residues environments and the decrease of the α-helical content of the protein.