Spectroscopic Studies On Binding Of Several Simple Organic Molecules Or Rare Earth Complexes To Bovine Serum Albumin

Serum albumin,the most abundant protein in blood plasma,has many important physiological functions.The most remarkable property of albumin is that it serves as a depot and transport protein for numerous endogenous and exogenous compounds. Investigating the binding mechanism of drugs with serum albumin has importance in pharmacokinetics.It has been an interesting research field of life science,chemistry and clinical medicine.In this dissertation,on the basis of previous research,the interactions of bovine serum albumin(BSA)with 1-phenyl-3-(coumarin-6-yl)sulfonyl -urea(SU22),3-acetylacetyl-4-hydroxycoumarin(H₂aac)and its La(â…¢) complex(La(Haac)₃),N²-(2"-hydroxybenzoyl)-N-(4'-tolylsulfonamido)carboxhydrazine (M)and its Sm(â…¢)complex(SmL₃),and N-salicylidene-3-aminocoumarin(SAC), respectively,have been studied by using spectroscopy under simulative physiological conditions.The thesis contains four parts:1.Through studying the interaction of SU22 with BSA,the quenching mechanism of BSA fluorescence by SU22 was proved to be a static quenching and the number of binding sites was about 1;the association constant at 298K was 1.569×10⁵L·mol^-1, which,indicated it can be deposited and transported by albumin;the thermodynamic parameters explained that hydrogen bond and Van der Waals interaction were the main binding force stabilizing the complex.The binding average distance between SU22 and tryptophan(Trp)of BSA was 3.20 nm on the basis of the Forster's theory. In addition,The CD spectra and FTIR spectra have proved that BSA has some conformational changes in the presence of SU22 in aqueous solution.2.Using similar methods,the quenching mechanism of BSA fluorescence by H₂aac or La(Haac)₃ was a static quenching process and both of the number of binding sites were about 1;the association constants at 298K were 2.236×10⁵L·mol^-1and 4.085×10⁵L·mol^-1,respectively,which indicated they can be deposited and transported by albumin and La(Haac)₃ had higher affinity;hydrophobic interaction was the main binding force stabilizing H₂aac-BSA complex,and electrostatic and hydrophobic force for La(Haac)₃-BSA complex.The binding average distance between them and Trp was 3.48nm and 3.35nm,respectively;the binding location of H₂aac in BSA was in siteâ…¡,and La(Haac)₃ in siteâ… ;In addition,The CD and FTIR spectra have proved that BSA conformation changed in the presence of them. 3.The binding of M or SmL₃ to BSA was studied under simulative physiological conditions.The quenching mechanism of BSA fluorescence by M or SmL₃ was a static quenching process and both of the number of binding sites were about 1;the association constants at 298K were 1.294×10⁵L·mol^-1and 1.465×10⁵L·mol^-1, respectively,Which indicated they can be deposited and transported by albumin; hydrogen bond and Van der Waals force was the main affinity for M-BSA system,but electrostatic and hydrophobic interaction for SmL₃-BSA system.The binding average distance between them and Trp was 3.83nm and 3.71nm,respectively;the binding average location of M in BSA was in siteâ… ;and SmL₃ in siteâ…¡;In addition,the Synchronous fluorescence spectra of BSA indicated that the tryptophan residues were place in a less hydrophobic microenvironment after binding to them;The CD spectra proved that BSA conformation changed in the presence of them.4.Fluorescence and UV-absorption spectra suggested that the quenching mechanism of BSA fluorescence by SAC was a static quenching and the number of binding sites was about 1;the association constant at 298K was 1.632×10⁵L·mol^-1, which indicated SAC can be deposited and transported by albumin;hydrogen bond and Van der Waals force was the main affinity for SAC-BSA complex.The binding average distance between SAC and Trp was 3.61 nm,and the binding location of SAC in BSA was in site I.In addition,the synchronous fluorescence spectra of BSA indicated that the tyrosine residues were place in a more hydrophobic microenvironment after binding to SAC;The CD spectra proved that BSA secondary structure changed in the presence of it.Based on above results,various compounds had different affinities,strength and binding location to BSA.To various degrees,they also changed BSA conformation. Binding to BSA,the complex had stronger binding force,more various affinities than the ligand,and had different binding location to it.These results are important to understand the role of these molecules in biological process,and the knowledge of the binding capacity of the compounds and BSA may prompt us to design the most suitable derivatives existed in thenew therapeutic drugs,which will be important in modern medical research.