title: A theoretical study on the hydrogen-bonding interactions between flavonoids and ethanol/water.
abstract: Ethanol and water are the solvents most commonly used to extract flavonoids from propolis. Do hydrogen-bonding interactions exist between flavonoids and ethanol/water? In this work, this question was addressed by using density functional theory (DFT) to provide information on the hydrogen-bonding interactions between flavonoids and ethanol/water. Chrysin and Galangin were chosen as the representative flavonoids. The investigated complexes included chrysin-H2O, chrysin-CH3CH2OH, galangin-H2O and galangin-CH3CH2OH dyads. Molecular geometries, hydrogen-bond binding energies, charges of monomers and dyads, and topological analysis were studied at the B3LYP/M062X level of theory with the 6-31++G(d,p) basis set. The main conclusions were: (1) nine and ten optimized hydrogen-bond geometries were obtained for chrysin-H2O/CH3CH2OH and galangin-H2O/CH3CH2OH complexes, respectively. (2) The hydrogen atoms except aromatic H1 and H5 and all of the oxygen atoms can form hydrogen-bonds with H2O and CH3CH2OH. Ethanol and water form strong hydrogen-bonds with the hydroxyl, carbonyl and ether groups in chrysin/galangin and form weak hydrogen-bonds with aromatic hydrogen atoms. Except in structures labeled A and B, chrysin and galangin interact more strongly with H2O than CH3CH2OH. (3) When chrysin and galangin form hydrogen-bonds with H2O and CH3CH2OH, charge transfers from the hydrogen-bond acceptor (H2O and CH3CH2OH in structures A, B, G, H, I, J) to the hydrogen-bond donor (chrysin and galangin in structure A, B, G, H, I, J). The stronger hydrogen-bond makes the hydrogen-bond donor lose more charge (A> B> G> H> I> J). (4) Most of the hydrogen-bonds in chrysin/galangin-H2O/CH3CH2OH complexes may be considered as electrostatic dominant, while C-O2···H in structures labeled E and C-O5···H in structures labeled J are hydrogen-bonds combined of electrostatic and covalent characters. H9, H7, and O4 are the preferred hydrogen-bonding sites.
authors.affiliation: College of Bee Science, Fujian Agriculture and Forestry University, Fuzhou, 350002, People's Republic of China. zhengyz15@gmail.com.
authors.forename: Yan-Zhen
authors.initials: YZ
authors.lastname: Zheng
authors.affiliation: Key Laboratory of Bioorganic Phosphorous Chemistry and Chemical Biology (Ministry of Education), Department of Chemistry, Tsinghua University, Beijing, 100084, People's Republic of China.
authors.forename: Yu
authors.initials: Y
authors.lastname: Zhou
authors.affiliation: College of Bee Science, Fujian Agriculture and Forestry University, Fuzhou, 350002, People's Republic of China.
authors.forename: Qin
authors.initials: Q
authors.lastname: Liang
authors.affiliation: College of Bee Science, Fujian Agriculture and Forestry University, Fuzhou, 350002, People's Republic of China. dfchen826@163.com.
authors.forename: Da-Fu
authors.initials: DF
authors.lastname: Chen
authors.affiliation: College of Bee Science, Fujian Agriculture and Forestry University, Fuzhou, 350002, People's Republic of China.
authors.forename: Rui
authors.initials: R
authors.lastname: Guo
mesh_terms: D000431:Ethanol / Q000737:chemistry*; D005419:Flavonoids / Q000737:chemistry*; D006860:Hydrogen Bonding; D059625:Liquid-Liquid Extraction; D008958:Models, Molecular; D011429:Propolis / Q000737:chemistry; D011789:Quantum Theory; D055672:Static Electricity; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
chemical_list: D005419:Flavonoids; D014867:Water; C037032:galangin; C043561:chrysin; D000431:Ethanol; D011429:Propolis
keywords: Density functional theory; Extraction; Flavonoids; Hydrogen-bond; Propolis