Fluorescence Spectral Studies On Interactions Of Quercetin With Several Biological Molecules And Effects Of Coexisting Nanomaterials

The fluorescence spectral method has many advantages for wide applications,such as high sensitivity,good specificity,small-quantity sampling and simple manipulation.In recent years,the nanobiotechnology has developed rapidly and evolved as a strong discipline-growth point for both nanomaterials science and biology.In this thesis,on the basis of a brief literature review about the principles and applications of fluorescence spectral method for biochemical studies, fluorescence spectral and UV-Vis spectrophotometric methods were used to study the interactions of quercetin with several biological molecules. The main contents are as follows:1.Fluorescence quenching and synchronous fluorescence methods were used to study the interactions of fluorescence-active quercetin(Qct) with casein(Cas) and bovine serum albumin(BSA) in phosphate buffer solution(PBS,pH 7.4) with and without coexisting carbon nanotubes (CNTs).Formulae for binding constant(K) and molar binding ratio(n) were established for methods 1(fixing protein concentration,changing Qct concentration,and monitoring the fluorescence of protein) and 2 (fixing Qct concentration,changing protein concentration,and monitoring the fluorescence of Qct),to which values of K and n were calculated via nonlinear least-squares fitting of the experimental data,and the "optical inner filtering induced fluorescence quenching" effect was thus quantitatively evaluated.The quenching effects of coexisting CNTs on the fluorescence of Qct,BSA,and Cas,as well as the effects of coexisting CNTs on Qct-BSA and Qct-Cas interactions,were examined. Synchronous fluorescence was also used to examine the effects of coexisting CNTs and Qct on the conformations of BSA and Cas,with relevant K and n values for tyrosine(Tyr) and tryptophan(Trp) residues estimated.It is concluded that the CNTs mainly interacted with the Trp residues locating near the protein surfaces,but small-sized Qct molecules can further interact with the Tyr residues locating inside the protein molecules.2.The interaction between Qct and bovine hemoglobin(BHb) was studied in 0.1 mol L^-1 PBS with and without coexisting Au nanoparticles (AuNP) by fluorescence spectroscopy,and the effects of AuNP on the fluorescence of BHb and Qct as well as the BHb-Qct interaction were evaluated.The apparent binding constants(K) and molar binding ratio(n) for Qct-BHb interactions in the PBS were measured versus the solution temperature via nonlinear fitting of the experimental data. Thermodynamic constants for the Qct-BHb interaction were measured, and the interaction forces are discussed.The binding distance and energy transfer efficiency were obtained by F(o|¨)rsters non-radiation energy transfer mechanism.3.The interactions of Qct with tryptophan(Try),Tyrosine(Yyr),and phenylalanine(Phe) were studied by fluorescence spectroscopy.In 0.1 mol L^-1 phosphate buffer solution(PBS,pH 7.4),the binding constants K and binding site n at different temperatures were determined,The interactions between:Qct and the three amino acids are strong,This work is helpful for the understanding of Qct-protein interactions.