title: Hydrogen-bonding Interactions between Apigenin and Ethanol/Water: A Theoretical Study.
abstract: In this work, hydrogen-bonding interactions between apigenin and water/ethanol were investigated from a theoretical perspective using quantum chemical calculations. Two conformations of apigenin molecule were considered in this work. The following results were found. (1) For apigenin monomer, the molecular structure is non-planar, and all of the hydrogen and oxygen atoms can be hydrogen-bonding sites. (2) Eight and seven optimized geometries are obtained for apigenin (I)-H2O/CH3CH2OH and apigenin (II)-H2O/CH3CH2OH complexes, respectively. In apigenin, excluding the aromatic hydrogen atoms in the phenyl substituent, all other hydrogen atoms and the oxygen atoms form hydrogen-bonds with H2O and CH3CH2OH. (3) In apigenin-H2O/CH3CH2OH complexes, the electron density and the E(2) in the related localized anti-bonding orbital are increased upon hydrogen-bond formation. These are the cause of the elongation and red-shift of the X-H bond. The sum of the charge change transfers from the hydrogen-bond acceptor to donor. The stronger interaction makes the charge change more intense than in the less stable structures. (4) Most of the hydrogen-bonds in the complexes are electrostatic in nature. However, the C4-O5···H, C9-O4···H and C13-O2···H hydrogen-bonds have some degree of covalent character. Furthermore, the hydroxyl groups of the apigenin molecule are the preferred hydrogen-bonding sites.
authors.affiliation: College of Bee Science, Fujian Agriculture and Forestry University, Fuzhou 350002, P. R. China.
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, P. R. China.
authors.forename: Yu
authors.initials: Y
authors.lastname: Zhou
authors.affiliation: College of Bee Science, Fujian Agriculture and Forestry University, Fuzhou 350002, P. R. China.
authors.forename: Qin
authors.initials: Q
authors.lastname: Liang
authors.affiliation: College of Bee Science, Fujian Agriculture and Forestry University, Fuzhou 350002, P. R. China.
authors.forename: Da-Fu
authors.initials: DF
authors.lastname: Chen
authors.affiliation: College of Bee Science, Fujian Agriculture and Forestry University, Fuzhou 350002, P. R. China.
authors.forename: Rui
authors.initials: R
authors.lastname: Guo
authors.affiliation: College of Bee Science, Fujian Agriculture and Forestry University, Fuzhou 350002, P. R. China.
authors.forename: Rong-Cai
authors.initials: RC
authors.lastname: Lai