Density functional theory study on hydrogen bonding interaction of luteolin–(H2O)n

Theoretical investigation of the chiral transition of serine and the roles of water, hydroxyl radical and hydroxide ion

The serine chiral transition and the roles of water, hydroxyl radical and hydroxide ion as catalysts were theoretically investigated.

Theoretical studies on the hydrogen-bonding interactions between luteolin and water: a DFT approach

Flavonoids are among the most important bioactive compounds responsible for the medical properties of honey and propolis. Water is the solvent most commonly used to extract flavonoids from honey and propolis. Hydrogen-bonding interactions are of great importance in the extraction process. In this work, hydrogen-bonding interactions between a representative flavonoid, luteolin, and water were investigated by density functional theory (DFT) from a theoretical viewpoint. The following conclusions were drawn: first, the molecular structure of luteolin is non-planar. Second, nine optimized geometries for the luteolin-H₂O complex were obtained. With the exception of the aromatic hydrogen atoms in the phenyl substituent, the other hydrogen and oxygen atoms formed hydrogen-bonds with H₂O. Third, luteolin-H₂O complexation is accompanied by charge rearrangement. The electron density and the second-order perturbation stabilization energy [E(2)] in the related anti-bonding orbital of the hydrogen-bond donors were increased, causing elongation and a red-shift of the X-H bond in X-H···Y. The stronger interaction makes the electron density and the E(2) increase more in the more stable geometries. The sum of the electron density is transferred from hydrogen-bond acceptors to donors. Fourth, the hydrogen-bonds in the luteolin-H₂O complex are weak and basically electrostatic in nature. In addition, O-H···O hydrogen-bonds are stronger than C-H···O hydrogen-bonds in the luteolin-H₂O complex.

Enantiomerization mechanism of thalidomide and the role of water and hydroxide ions

The significance of the molecular chirality of drugs has been widely recognized due to the thalidomide tragedy. Most of the new drugs reaching the market today are single enantiomers, rather than racemic mixtures. However, many optically pure drugs, including thalidomide, undergo enantiomerization in vivo, thus negating the single enantiomers' benefits or inducing unexpected effects. A detailed atomic level understanding of chiral conversion, which is still largely lacking, is thus critical for drug development. Herein, we use first-principle density function theory (DFT) to explore the mechanism of enantiomerization of thalidomide. We have identified the two most plausible interconversion pathways for isolated thalidomide: 1) proton transfer from the chiral carbon center to an adjacent carbonyl oxygen atom, followed by isomerization and rotation of the glutarimide ring (before the proton hops back to the chiral carbon atom); and 2) a pathway that is the same as "1", but with the isomerization of the glutarimide ring occurring ahead of the initial proton transfer reaction. There are two remarkable energy barriers, 73.29 and 23.59 kcal mol(-1), corresponding to the proton transfer and the rotation of the glutarimide ring, respectively. Furthermore, we found that water effectively catalyzes the interconversion by facilitating the proton transfer with the highest energy barrier falling to approximately 30 kcal mol(-1), which, to our knowledge, is the first time that this important role of water in chiral conversion has been demonstrated. Finally, we show that the hydroxide ion can further lower the enantiomerization energy barrier to approximately 24 kcal mol(-1) by facilitating proton abstraction, which agrees well with recent experimental data under basic conditions. Our current findings highlight the importance of water and hydroxide ions in the enantiomerization of thalidomide and also provide new insights into the mechanism of enantiomerization at an atomic level.