Tunneling in the Hydrogen-Transfer Reaction from a Vitamin E Analog to an Inclusion Complex of 2,2-Diphenyl-1-picrylhydrazyl Radical with β-Cyclodextrin in an Aqueous Buffer Solution at Ambient Temperature

Recently, increasing attention has been paid to quantum mechanical behavior in biology. In this study, we investigated the involvement of quantum mechanical tunneling in the hydrogen-transfer reaction from Trolox, a water-soluble analog of vitamin E (α-tocopherol), to 2,2-diphenyl-1-picrylhydrazyl radical (DPPH•) in a phosphate buffer solution (0.05 M, pH 7.0). DPPH• was used as a reactivity model of reactive oxygen species and solubilized in water using β-cyclodextrin (β-CD). The second-order rate constants, kH and kD, in 0.05 M phosphate buffer solutions prepared with H2O (pH 7.0) and D2O (pD 7.0), respectively, were determined for the reaction between Trolox and DPPH•, using a stopped-flow technique at various temperatures (283-303 K). Large kinetic isotope effects (KIE, kH/kD) were observed for the hydrogen-transfer reaction from Trolox to the β-CD-solubilized DPPH• in the whole temperature range. The isotopic ratio of the Arrhenius prefactor (AH/AD = 0.003), as well as the isotopic difference in the activation energies (19 kJ mol-1), indicated that quantum mechanical tunneling plays a role in the reaction.

Chebulic acid derivatives from Balakata baccata and their antineuroinflammatory and antioxidant activities

Sixteen chebulic acid derivatives, including nine new (1-9) and seven known (10-16) ones, were isolated from an ethanol extract of the branches and leaves of Balakata baccata. The structures of the new compounds were elucidated by their UV, IR, HRESIMS, NMR, electronic circular dichroism (ECD) and single-crystal X-ray diffraction data. The effects of all the isolates on antineuroinflammatory and antioxidant activities were evaluated. Compared with the positive control minocycline (IC₅₀ = 1.21 ± 0.71 μM), compounds 1-16 with IC₅₀ values being greater than 50 μM, displayed almost no effects on the inhibition of NO production in LPS-induced BV-2 microglial cells, however, the results of antioxidant activity for compounds 1-16 showed significant DPPH-radical scavenging abilities with EC₅₀ value ranging from 3.98 to 14.24 μM, while the EC₅₀ value of positive control vitamin C was 14.31 μM. At last, the results of PCR (qRT-PCR) analysis showed that compound 1 could enhance the expression of antioxidases (HO-1, GCLC, and NQO1) at the mRNA levels.