Study On Antioxidant Activity For Flavonoid And Chalcone Compounds, And Structural Stability For B-amylose By Molecular Simulations

Molecular simulation technology has developed to be a powerful research tools for fields of chemistry, physics, life science, material science and so on. Nowdays, molecular simulation is widely used in food research. Molecular simulation method is divided into quantum chemistry and molecular mechanics. The quantum chemistry method based on the electronic level has high calculation accuracy, which is only applicable for small molecule systems with simple structure; while molecular mechanics method based on the molecular modeling has fast calculation speed, which is suitable for large molecules and aggregating systems.It is very important to choose rational theoretical method in accuracy of research. After comparing calculated results with experimental data, the rationality can be verified by their accordance degree. Only when theoretical results are in good accordance with the experimental data, the simulated results are acceptable and this method may be used in providing more predictive data to guide further experiments.This paper firstly investigated the antioxidant activity for such natural compositions as flavonoids and chalcones by density functional method in quantum chemistry, and then studied their structural stabilities of B-amylose in different polar solvents by molecular dynamics method in molecular mechanics. 1. Study on antioxidant and electronic spectroscopic properties of flavonoids with the same B ring structures(1) Two isoflavones with different A ring structuresTwo isoflavone compounds such as genistein and daidzein were investigated by using density functional level of theory at B3LYP/ 6-311++G** basis set. Two thermodynamic parameters such as the frontier molecular orbital energy gap and enthalpy of radical formation were calculated to predict their antioxidant capacities, the main mechanism of antioxidant action was explored at the molecular level. The potentiality of antioxidant activity was highly related to oxygen free radical scavenging capability. Because the easier the electron transfer and the hydrogen abstraction reaction were, the stronger the antioxidant ability would be. Results showed that the order of antioxidant efficacies predicted by frontier molecular orbital energy gap was genistein > daidzein, in good agreement with that predicted by enthalpy of radical formation.(2) Three flavonoids with different C ring structuresThe antioxidant capacities of three flavonoids quercetin, luteolin and taxifolin have been investigated at density functional level of theory with the aim of verifying the cellular antioxidant activity(CAA) values representative of experimental findings. The selected flavonoids were believed to act through the H-atom transfer mechanism. Their potentiality of hydrogen abstraction was evaluated by computing the O-H bond dissociation enthalpy(BDE) in gas-phase and in dimethylsulfoxide solution. Results indicated that the order of antioxidant efficacies calculated in this work was quercetin > luteolin > taxifolin, in agreement with that reported by experimental results of CAA. Time-dependent density functional theory(TDDFT) calculations were also performed both in gas-phase and in dimethylsulfoxide to reproduce the electronic UV-vis spectra of the three flavonoids. 2. A DFT study on the structural, electronic and antioxidant properties of three flavonols with different B ring structuresThe structural and antioxidant activity properties of three flavonols kaempferol, galangin and morin have been investigated at density functional level of theory. The potentialities of antioxidant activity were highly related to their capabilities to scavenge free radicals. Since two potential working mechanisms of the hydrogen-atom transfer and single-electron transfer, two parameters of the O-H bond dissociation enthalpy(BDE) and ionization potential(IP) in the presence of water medium are computed to estimate the antioxidant capacities. Results indicated that the order of antioxidant efficacies predicted by both BDE and IP was kaempferol > morin > galangin, which was in agreement with that reported by experimental results of oxygen radical-scavenging capacity(ORAC) assay. This demonstrated the importance of the hydrogen-atom and single-electron transfer mechanisms to explain their capacities to scavenge peroxyl radical. 3. DFT-based quantum chemical studies on conformational, electronic and antioxidant properties of isobavachalcone and 4-hydroxyderricinIsobavachalcone and 4-hydroxyderricin which exhibited numerous biological activities were two major chalcone constituents isolated from the roots of Angelica keiskei KOIDZUMI. The conformational and antioxidant activity properties have been investigated by quantum chemical calculations based on the density functional level of theory, with the aim of verifying dominant antioxidant mechanism. Three parameters of the O-H bond dissociation enthalpy(BDE), ionization potential(IP) and acidity in the presence of an implicit solvent for methanol were computed to estimate the antioxidant capacities. Results revealed that the order of antioxidant efficacies predicted by BDE and IP, different from that predicted by acidity, is in agreement with that obtained by experimental data. This demonstrated to some extent that the importance of the hydrogen atom and single electron transfer mechanisms to explain their capacities to scavenge 2, 2-diphenyl-1-pycril-hydrazyl(DPPH) free radical. 4. Study on structural and spectral properties of isobavachalcone and 4-hydroxyderricin by computational methodQuantum chemical methods have been employed to investigate the structural and spectral properties of isobavachalcone and 4-hydroxyderricin. The ground state structures were optimized using density functional B3 LYP method with 6-311G(d, p) basis set in both gas and solvent phases. Based on the optimized geometries, the harmonic vibrational frequency, the 1H and 13 C nuclear magnetic resonance(NMR) chemical shift using the GIAO method were calculated at the same level of theory, with the aim of verifying the experimental values. Results revealed that B3 LYP was a good method to study their vibrational spectroscopic and NMR spectral properties of the two chalcones. The electronic absorption spectra were calculated using the time-dependent density functional theory(TDDFT) method. The solvent polarity effects were considered and calculated using the polarizable continuum model(PCM). Results also showed that substitutions of different electron donating groups could alter the absorption properties and shift the spectra to a higher wavelength region. 5. Study on structural stability of B-amylose in different polar solvents and inclusion with lipidThe conformational behavior of a short B-amylose fragment in solution has been studied by molecular dynamics. The first part concerned the stability of B-amylose without a lipid in different polar solvents. It was observed that the double strand helix unfolded rapidly to a more extended conformation in a strong polar solvent like water, which could be due principally to the disruption of inter-residual hydrogen bonds. The double strand of amylose chains preserved its well-defined helical structure in non-polar solvent like n-butane, in contrast to that observed in aqueous solution. The second part described the characteristics of amylose chains in apolar solvent when inclusion with monostearin. In contrast, the amylose chains preserved its well-defined helical structure on the whole after the formation of complex. This could be attributed principally to the interaction of aliphatic lipid tail with the hydrophobic core formed among the glucoses.