Study On The Interactions Of Ascorbic Acid With Several Bioactive Substances

Intermolecular interactions has an important significance in biochemical,chemical and mainly pharmacological.The combination of theory and experiment could help us understand deeply the interaction type and sites with the experimental and theoretical increased,and have more comprehensive understanding on it.Ascorbic acid(AA),namely vitamin C,is one of the most essential nutrients in our body.AA is often found in vegetables and fruits,and it is also as a drug for treating scurvy and disease caused by free radicals.As a necessary substance to our body,it is inevitable that AA can interact with some active small molecules in vivo.The research on the interactions between AA and bioactive substances can provide a theoretical basis for the study and application of AA,and for the clinical medicine.In this thesis,basing on the study of AA and water system,we studied the interactions of AA with several biological active substances(Glycine,Proline,Adenine,Cytosine,Uracil,D-Glucose,Inositol and Urea)by ultraviolet-visible(UV-Vis)absorption spectroscopy,electrochemical cyclic voltammetry(CV),nuclear magnetic resonance(NMR)spectroscopy,and density functional theory(DFT).The results are summarized as follows:1.The interactions of AA with water were investigated using UV-Vis and CV methods.The results indicated that the hydrogen bonding formed between the hydrogen atoms on enediol,oxygen atoms on carbonyl group of ascorbic acid molecule and the oxygen and hydrogen atoms of water molecule,which results in a more difficult electrochemistry oxidation process of ascorbic acid and a hypsochromic shift in the UV-vis absorption spectra.In addition,the pH value of the solution has significant influence on the electrooxidation behavior of ascorbic acid.2.The interaction of AA with glycine and proline were studied by CV,DFT or NMR.The CV results that of in aqueous solutions and PBS buffered solutions indicated that hydrogen bonding formed between the hydrogen atoms on enediol,oxygen atoms on carbonyl group of AA and the oxygen atoms,hydrogen atoms on carboxyl of glycine in the AA/glycine system;and the hydrogen atoms on enediol of AA and the oxygen atoms on carboxyl of proline can form hydrogen bonding in the AA/proline system,which leading to the difficult oxidation of AA.The chemical shifts of the protons on methylene of glycine move to downfield,which indicate hydrogen bonding formed in AA/glycine system.Geometry optimizations of all complexes were performed using DFT.The existence of hydrogen bonding was confirmed by analysing the structural parameters.3.The interaction of AA with adenine,cytosine and uracil were studied by CV,DFT or NMR.The CV results that of in aqueous solutions and PBS buffered solutions indicated that hydrogen bonding formed between the hydrogen atoms on enediol,oxygen atoms on carbonyl group of AA and the nitrogen atoms,hydrogen atoms on purine ring and amine of adenine in the AA/adenine system;the hydrogen atoms on enediol of AA and the oxygen atoms on carbonyl of cytosine can form hydrogen bonding in the AA/cytosine system;the hydrogen atoms on enediol,oxygen atoms on carbonyl group of AA and the oxygen atoms on carbonyl,hydrogen atoms on pyrimidine ring of uracil molecule can form hydrogen bonding in the AA/uracil system,which leading to the difficult oxidation of AA.The chemical shifts of the protons on carbon of cytosine move to downfield,which indicate hydrogen bonds formed in AA/cytosine system.The DFT results further confirmed the existence of hydrogen bonding in above systems.4.The interaction of AA with glucose and inositol were studied by CV and DFT.The CV results that of in aqueous solutions and PBS buffered solutions indicated that hydrogen bonding formed between the hydrogen atoms on enediol,oxygen atoms on carbonyl group of AA and the oxygen atoms,hydrogen atoms on hydroxyl of glucose and inositol molecules in above two systems,which leading to the difficult oxidation of AA.The DFT results further confirmed the existence of hydrogen bonding in above systems.5.The interaction of AA with urea was studied by CV and DFT.The CV results that of in aqueous solutions and PBS buffered solutions indicated that hydrogen bonding formed between the hydrogen atoms on enediol,oxygen atoms on carbonyl group of AA and the oxygen atoms on carbonyl,hydrogen atoms on amino of urea,which leading to the difficult oxidation of AA.The DFT results further confirmed the existence of hydrogen bonding in this system.