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The Study of Antioxidant Mechanism of some Flavonoids without and in Presence of Cyclodextrins: Theoretical Point of View

Gerayeli, Narges | 2018

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 51513 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry Science
  6. Advisor(s): Tafazzoli, Mohsen; Ghiasi, Mina
  7. Abstract:
  8. Antioxidants are compounds with anti-cancer, anti-bacterial, anti-viral, anti-aging and anti-allergic properties. In the present study, a quantum mechanical approach has been used to shed light on the presence effect of glycoside group on the antioxidant ability of chrysin as one of the most important consumable flavonoids and two glycoside derivatives, chrysin-6-C-fucopyranoside and chrysin-3-malonyl-6-C-fucopyranoside which has electron-withdrawing group (EWG) in its C3 of glycoside group. Density functional theory (DFT) using B3LYP and UB3LYP functional and split-valance 6-311++G ** basis set were used to optimize chrysin, its different derivatives, and their radicals. Analysis of theoretical parameters including bond dissociation enthalpy (BDE), energy gap (∆E) and spin density for three above mentioned flavonoids for all OH sites in gas and solution phase clearly shows that presence glycoside group does not have significant effect on the antioxidant ability of flavonoids.
    In the second step to examine glycoside group effects on thermodynamic parameters of the separate steps of antioxidant mechanisms, O–H bond dissociation enthalpies (BDE), ionization potentials (IP), proton dissociation enthalpies (PDE), proton affinities (PA) and electron transfer enthalpies (ETE) as antioxidant mechanism parameters were computed using B3LYP/311++G** method. The solvent effect has been considered in water, DMSO and benzene using PCM model. The results demonstrate:1- the presence of glycosyl group has no significant effect on antioxidant mechanism thermodynamic parameters in polar and non-polar solvents. 2-Formation of intra molecular hydrogen bonding between glycosyl group site and flavonoid structure and space hindrance because of glycosyl group presence impresses on antioxidant mechanism parameters.
    In the third step, chrysin as a lipophilic compound has a low solubility in water and β-cyclodextrin is one of the major drug carriers for lipophilic drugs to increase solubility. Therefore inclusion complex between chrysin and β-cyclodextrin has been studied. Complex creation of host-guest was carried out between chrysin and cyclodextrin in three different methods including HF, B3LYP and M05-2X by 3-21G and 6-31G basis sets and the single point calculation at B3LYP/6-311++G** level in gas and water. Result confirms that the A ring of chrysin tend to big mouth of β-cyclodextrin. Comparing the AIM analysis, the structural details, HOMO energies, Mulliken atomic charges, BDEs and vibrational frequencies between Chrysin and Chrysin/ β-CD (AB) in water at M05-2x /6-31G level is carried out
  9. Keywords:
  10. Hydrogen Atom Transfer ; Antioxidant ; Chrysin ; Beta-Cyclodextrin ; Inclusion Complex ; Computational Chemistry ; Antioxidant Activity ; Flavonoids

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