Flavonoids provide potential health benefits due to their antioxidant properties. The antioxidant activity of natural flavonoids is primarily exerted by phenolic hydroxyl groups; however, C–H bonds also contribute to these properties. In this study, the contributions of phenolic groups and C–H bonds to the antioxidant properties of 13 flavonoids were investigated by using the (RO)B3LYP/6-311++G(2df,2p)//B3LYP/6-311G(d,p) model chemistry in the gas phase and water and ethanol solvents. It was found that the C–H bonds have lower bond dissociation energies than O–H bonds in the 4-carbonyl and/or 3-hydroxyl group containing flavonoids and hence define antioxidant activity. The HOO · radical scavenging of the selected flavonoids is also investigated in detail through the potential energy surface, natural bond orbitals, and kinetic calculations. It was found that the favored radical scavenging mechanism of the flavonoids is hydrogen atom transfer, with the gas phase rate constants in the range of 7.23 × 10 3 –2.07 × 10 9 L·mol –1 ·s –1 . The results suggest that the flavonoids, isomelacacidin, isoteracacidin, melacacidin, and teracacidin, have antioxidant properties as high as typical phenolic compounds such as quercetin, trans -resveratrol, trolox, and ascorbic acid.

Interactions of dimethyl sulfoxide with carbon dioxide and water molecules which induce 18 significantly stable complexes are thoroughly investigated. An addition of CO 2 or H 2 O molecules into the DMSOÁ Á Á1CO 2 and DMSOÁ Á Á1H 2 O systems leads to an increase in the stability of the resulting complexes, in which it is larger for a H 2 O addition than a CO 2 . The overall stabilization energy of the DMSOÁ Á Á1,2CO 2 is mainly contributed by the S=OÁ Á ÁC Lewis acid-base interaction, whereas the O − HÁ Á ÁO hydrogen bond plays a significant role in stabilizing complexes of DMSOÁ Á Á1,2H 2 O and DMSOÁ Á Á1CO 2 Á Á Á1H 2 O. Remarkably, the complexes of DMSOÁ Á Á2H 2 O are found to be more stable than DMSOÁ Á Á1CO 2 Á Á Á1H 2 O and DMSOÁ Á Á2CO 2 . The level of the cooperativity of multiple interactions in ternary complexes tends to decrease in going from DMSOÁ Á Á2H 2 O to DMSOÁ Á Á1CO 2 Á Á Á1H 2 O and finally to DMSOÁ Á Á2CO 2 . It is generally found that the red shift of the O − H bond involved in an O − HÁ Á ÁO hydrogen bond increases while the blue shift of a C − H bond in a C − HÁ Á ÁO hydrogen bond decreases when a cooperative effect occurs in ternary complexes as compared to those of the corresponding binary complexes.

Two new lindenane sesquiterpenes were obtained from the roots of Lindera myrrha. These compounds were structurally elucidated by HRMS data, extensive NMR analyses, and comparison between experimental and theoretical 13C-NMR data. Myrrhalindenane A is the first monomeric seco-d lindenane displaying a non-rearranged, cyclohexanic C-ring. Myrrhalindenane B is the second occurrence of an angular lindenane-sesquiterpene related to a C6-C7 lactonization.

Hydrogen bonds (H-bonds) in the complexes between aldehydes and hydrogen chalcogenides, XCHO...nH 2 Z with X = H, F, Cl, Br, and CH 3 , Z = O, S, Se, and Te, and n = 1,2, were investigated using high-level ab initio calculations. The C sp2 − H...O H-bonds are found to be about twice as strong as the C sp2 − H...S/Se/Te counterparts. Remarkably, the S/Se/Te−H...S/Se/Te H-bonds are 4.5 times as weak as the O−H...O ones. The addition of the second H 2 Z molecule into binary systems induces stronger complexes and causes a positive cooperative effect in ternary complexes. The blue shift of C sp2 −H stretching frequency involving the C sp2 −H...Z H-bond sharply increases when replacing one H atom in HCHO by a CH 3 group. In contrast, when one H atom in HCHO is substituted with a halogen, the magnitude of blueshifting of the C sp2 −H...Z H-bond becomes smaller. The largest blue shift up to 92 cm −1 of C sp2 −H stretching frequency in C sp2 −H...O H-bond in CH 3 CHO...2H 2 O has rarely been observed and is much greater than that in the cases of the C sp2 −H...S/Se/Te ones. The C sp2 −H blue shift of C sp2 −H...Z bonds in the halogenated aldehydes is converted into a red shift when H 2 O is replaced by a heavier analogue, such as H 2 S, H 2 Se, or H 2 Te. The stability and classification of nonconventional H-bonds including C sp2 −H...Se/Te, Te−H...Te, and Se/Te−H...O have been established for the first time.

Structural transformation is a unique characteristic of atomic clusters, but it turns out very different from cluster to cluster. This theoretical study proves that the isomeric transformation between hexagonal prism and hexagonal antiprism is found for the doubly doped Cr2Ge12 cluster but not for singly doped CrGe12 cluster. We confirm that the ground state of CrGe12 is the distorted hexagonal prism C 2h at the 3Bg triplet state instead of various shapes predicted in the previous studies. Upon comparison between the estimation at the B3P86/6-311+G­(d) level of theory and the detachment energies measured by photoelectron spectroscopy, hexagonal antiprismatic shape is identified as the most stable isomer of the Cr2Ge12 cluster and it is easy to transform to the hexagonal prisma less stable isomer by the rotation of the hexagonal rings. That is the first evidence for the structural transformation between a hexagonal prism and an antiprism of the germanium clusters, referring to the ability of Ge-based clusters in the formation of tubular geometry by doping Cr atoms. All the low-energy isomers of both Cr-doped germanium clusters have high magnetic moments. Interestingly, there is a tuning in magnetic properties of Cr2Ge12 from the ferromagnetism of the lowest-lying hexagonal antiprism to the ferrimagnetism of the higher-energy hexagonal prism. The stronger Cr–Cr bond and stronger interaction between the Cr2 moiety and the antiprism cage are accounted for by the higher stability of the hexagonal antiprismatic isomer.