Molecular Spectroscopic Studies On The Reaction Mechanism Between Some Synthetic Food Colorants And Drugs With Protein

The interactions between small molecules and protein are important for chemistry biology investigation. Serum albumin, the most abundant carrier protein in blood plasma, can bind many exogenous and endogenous compounds extensively, and realize transport and distribution of many molecules and metabolites. Investigating the binding mechanism of drugs and toxic materials with serum albumin is important in pharmacokinetics and toxicology. Thus, it has been an interesting research field of life sciences, chemistry and clinical medicine. This paper has carried on the study about the mechanism between synthetic food colorants, drugs and serum albumin by spectroscopy. It divided into five chapters:Chapter one: The contents of interaction between small molecules and serum albumin by fluorescence spectroscopy were reviewed. The requirement and progress of competitive interaction of two kinds of small ligands with protein were briefly introduced. Based on this, the research route and contents for study of the reaction mechanism between small molecules and protein were established, with 52 literatures quoted.Chapter two: The interaction between synthetic food colorants and bovine serum albumin (BSA) was investigated by fluorescence spectroscopy. Tartrazine (TTZ), sunset yellow (SY) and erythrosine (ETS) could form non-covalent compounds with BSA in Tris–HCl buffer medium of pH 7.40, which led to the static quenching of endogenous fluorescence of BSA. The binding ability followed the pattern: ETS > TTZ > SY. The values of Hill's coefficients were slightly more than 1 in all systems. Thermodynamic parameters indicated that hydrogen bond and van der Waals played a major role in the binding of food colorants to BSA. Besides, the competitive experiments suggested that the primary binding site for three synthetic food colorants was located at siteⅠin sub-domainⅡA of BSA. According to F?rster's non-radiative energy transfer theory, the binding distances (r) between synthetic food colorants and BSA were much smaller than 7 nm.Chapter three: The effects of synthetic food colorants on the combination between norfloxacin (NFLX) and BSA were investigated by fluorescence spectroscopy. The fluorescence of BSA could be quenched by TTZ, SY, ETS and NFLX. NFLX bound to BSA mainly by electrostatic interaction. The primary binding site for NFLX was also located at subdomainⅡA of BSA (siteⅠ). In addition, the food colorants could compete with NFLX for the binding sites from BSA. As a result, the free concentration of NFLX in blood increased, and the efficacy of the drugs changed. According to F?rster's theory, the effects of synthetic food colorants on the binding distances (r) between drug and BSA were evaluated. Results suggested that the values of r increased due to existent of synthetic food colorants.Chapter four: The effects of synthetic food colorants on the binding reaction between ciprofloxacin hydrochloride (CPFX) and BSA were investigated by fluorescence spectroscopy. CPFX bound to BSA by electrostatic interaction. The primary binding site for CPFX was also located at subdomainⅡA of BSA. The presence of synthetic food colorants could alter the binding constants and distances between BSA and CPFX. The effects of colorants were dependent on their concentrations and binding affinity to BSA. The interaction could result in the change of the free, biological active fraction of CPFX in blood.Chapter five: The binding reaction between cefotaxime sodium (CTX) and chloramphenicol (CHL) with BSA at different temperatures was studied by fluorescence spectroscopy. In Tris–HCl buffer medium of pH 7.40, the quenching mechanism of the combination for BSA and drugs was a static procedure. In addition, the competitive experiments suggested that the primary binding site for both CTX and CHL was located at siteⅠin sub-domainⅡA of BSA. The fluorescence would quench to a larger degree when CTX (or CHL) was added to the system of BSA–CHL (or BSA–CTX). Binding constants of one drug with BSA decreased when the other drug was added. Hill's coefficients of the ternary systems were less than 1. It showed that the negative cooperativity was found when CTX and CHL bound to BSA simultaneously. Thermodynamic parameters indicated that the electrostatic interaction played a major role in the binding of drugs with BSA.