Resveratrol (RSV) analogues have attracted much attention because of the expected health functions including antioxidant activities. We have carried out a quantitative determination of the scavenging abilities of six trans-RSV analogues against various reactive oxygen species and methyl radical (hydroxyl radical, superoxide, alkoxyl radical, peroxyl radical, methyl radical, and singlet oxygen). RSV analogues are in general more potent scavenger than the parent RSV. Furthermore, piceatannol (PIC) having two OH groups in the ortho position of resveratrol was found to show 11 times higher scavenging ability against peroxyl radical than parent resveratrol. With the aid of previous theoretical studies, the enhanced antioxidant ability was interpreted based on the effects of substituent that modifies the original resveratrol structure and function.Antioxidant abilities of resveratrol (RSV) analogues. High scavenging ability of piceatannol (PIC) for active species. Trolox equivalent unit (TEU).Download high-res image (121KB)Download full-size image

The inclusion complexation of aromatic amines with cucurbit[6]uril (CB[6]) capped with alkali metal cations was studied spectrophotometrically. We showed that CB[6] capped with alkali metal cations forms a 1:1 inclusion complex with the aromatic amine guests (neutral organic molecules), independent of the length of guest molecules. The effects of salts on the inclusion constants of CB[6] in the presence of different alkali salts were examined and it was found that the inclusion constants increased in the order of alkali cation Cs+ < Na+ < K+, suggesting the interaction of amine guests with the capped alkali metal cation. Further, the structures of the inclusion complexation of aromatic amines with CB[6] were characterized by 1H NMR measurements. Based on the results, the inclusion abilities of CB[6] capped with alkali metal cations are discussed.

Using the inclusion complexation of methylene blue as a chemical indicator, the inclusion constants of imidazolium and pyrrolidinium chlorides (ionic liquids (IL)) with p-sulfonatocalix[6]arene (Calix-S6) were determined in a water–methanol mixture. In the inclusion of imidazolium chlorides, we found the characteristic inclusion constants, dependent on the length of the alkyl side chain. From the temperature effect on the inclusion, the differences in the inclusion interactions of imidazolium and pyrrolidinium ring moiety with the sulfonate groups of the Calix-S6’s portal were observed. Further, from high-pressure studies on the inclusion complexation, the volume changes caused by the conformational changes of Calix-S6 and desolvation around the guest and host molecules upon inclusion were evaluated. Based on the results, we demonstrated that the volume change related to desolvation upon inclusion plays an important role in the reaction volume for the inclusion equilibrium of IL with Calix-S6. The structures of the inclusion complexes were established from 2D ROESY NMR measurements and a volumetric study of the inclusion complexation with p-sulfonated Calix-S6 having a flexible cavity was performed.

The scavenging rates of DOPA (dl- and l-3-(3,4-dihydroxyphenyl)alanine) and Tyr (tyrosine (dl- and l-3-(4-hydroxyphenyl)alanine)) against five reactive oxygen species (ROS) and methyl radical were measured with the use of electron spin resonance (ESR) spin-trapping method and the scavenging rate constants of DOPA and Tyr were determined. The scavenging rate constants for multiple active species increased in the order of O2− < RO < 1O2 < H3C < HO for Tyr and RO ≈ O2− < 1O2 ≈ H3C < HO for DOPA, and the differences in the radical scavenging abilities for l-enantiomers and dl-mixtures of DOPA and Tyr were shown. Further, based on the redox potentials, we have suggested that the primary chemical process of antioxidant reactions with O2− and 1O2 can be characterized with the electron transfer of antioxidants (DOPA and Tyr).

Edaravone (3-methyl-1-phenyl-2-pyrazoline-5-one) is a neuroprotective drug that has been used for brain ischemia injury treatment. Because its activity is speculated to be due to free radical scavenging activity, we carried out a quantitative determination of edaravone’s free radical scavenging activity against multiple free radical species. Electron spin resonance (ESR) spin trapping-based multiple free-radical scavenging (MULTIS) method was employed, where target free radicals were hydroxyl radical, superoxide anion, alkoxyl radical, alkylperoxyl radical, methyl radical, and singlet oxygen. Edaravone showed relatively high scavenging abilities against hydroxyl radical (scavenging rate constant k = 2.98 × 1011 M−1 s−1), singlet oxygen (k = 2.75 × 107 M−1 s−1), and methyl radical (k = 3.00 × 107 M−1 s−1). Overall, edaravone’s scavenging activity against multiple free radical species is as robust as other known potent antioxidant such as uric acid, glutathione, and trolox. A radar chart illustration of the MULTIS activity relative to uric acid, glutathione, and trolox indicates that edaravone has a high and balanced antioxidant activity with low specificity.

•The fluorescence quantum yields for the inclusion complexes of ANSs were determined.•Based on emission mechanism, we discussed on the enhanced quantum yields of ANS.•By using 2,6-ANS, the microenvironmental polarity inside CD and CB[7] was evaluated.The association constants (K) for the inclusion complexation of four kinds of cyclodextrins (CDs (β- and γ-), 2,6-di-O-methylated β-CD, and 2,3,6-tri-O-methylated β-CD) and cucurbit[7]uril (CB[7]) with 1,8- and 2,6-anilinonaphthalene sulfonic acids (ANSs) were determined from fluorescence spectra enhanced by inclusion. Various CDs and CB[7] form stable 1:1 inclusion complexes with 1,8- and 2,6-ANSs: K = 80–11 700 M−1 for 2,6-ANS and 50–195 M−1 for 1,8-ANS. The high stability of the inclusion complexes of 2,6-ANS with CB[7] and 2,6-di-O-methylated β-CD is shown. Further, we determined the fluorescence quantum yields (Φ values) for the inclusion complexes of ANSs by using a fluorescence spectrophotometer equipped with a half-moon unit. The Φ values of 1,8- and 2,6-ANSs were largely enhanced by the inclusion of methylated β-CDs and did not correlate with the degree of stability (K) of the inclusion complexes. We characterized the structures of the inclusion complexes by 2D ROESY-NMR measurements. In addition, the microenvironmental polarity inside the hydrophobic CD and CB[7] cavities was evaluated using the fluorescence probe 2,6-ANS. Based on the emission mechanism and the aspect of inclusion in a hydrophobic cavity, we have suggested that the microenvironmental polarity and viscosity for the excited state of ANS plays an important role for the Φ values of inclusion complexes.

The effect of high static pressure on the microscopic properties of triglyceride (HCO-10) and phosphatidylcholine (DLPC) membranes was investigated by ESR (electron spin resonance). The external pressure was varied to ascertain the distribution equilibrium constant between the aqueous and vesicle phases, depending on the molecular sizes of various nitroxide probes relative to that of the interstitial space of the HCO-10 and DLPC membranes. The distribution equilibrium of any probe for the HCO-10 membrane was shifted to the aqueous phase side with increasing the external pressure. However, the distribution equilibrium of di-tert-butyl nitroxide (DTBN) for the DLPC membrane was shifted to the vesicle phase side with increasing external pressure. Furthermore, information on the rotational motion of the nitroxide probes in the HCO-10 and DLPC vesicle was obtained from the anisotropic ESR signals. Rotational correlation times (τR) of the nitroxide probes in the vesicle phases increased with increasing external pressure. The magnitude of the activation volume (ΔV‡) obtained using τR in both vesicles is TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) > DTBN > DMDEN (2,2-dimethyl-5,5-diethylpyrroline N-oxide), which might be attributed to the interaction between the probes and the membrane chains.Graphical abstractHighlights► The pressure effect on the microscopic property of two membranes was investigated. ► We found the characteristic pressure dependence inside the DLPC membrane. ► The pressure-induced viscosity change inside the membranes have been evaluated. ► The differences in the microscopic properties of the two membranes were discussed.

Relative nitric oxide scavenging rates of water-insoluble lipophilic antioxidants, such as resveratrol and flavonoids were determined using a β-cyclodextrin analog, DM-β-CD (heptakis(2,6-di-O-methyl)-β-cyclodextrin) as a solubilizer. Antioxidant-mediated decrease of NO concentration was measured with the electron spin resonance-based PTIO (2-phenyl-4,4,5,5-methylimidazoline-1-oxyl 3-oxide) method, from which scavenging rates were calculated. Because both the antioxidant and PTIO form inclusion complex with DM-β-CD, a kinetic treatment was necessary to calculate the scavenging rates. Resveratrol showed the highest NO scavenging rate among the tested antioxidants. The magnitudes of scavenging rates were in the order of: resveratrol > catechin ≈ myricetin > epicatechin > epigallocatechin gallate > kaempferol. This order is not in agreement with the oxygen radical scavenging rates: i.e., myricetin > epigallocatechin gallate > catechin ≈ epicatechin > resveratrol > kaempferol. The tested antioxidants showed lower scavenging rates than hydrophilic antioxidants such as uric acid and caffeic acids. Previous redox potential measurement of antioxidants revealed that NO scavenging occurs through non-free radical mechanism, indicating that the scavenging capacity is dependent on the nature of the scavenging reaction.Graphical abstractDownload full-size imageHighlights► Using the ESR competitive method, the relative NO-scavenging rates were determined. ► The six lipophilic antioxidants solubilized with a β-cyclodextrin analog were used. ► The NO-scavenging capacities of lipophilic antioxidants were relatively small. ► Resveratrol showed the highest NO scavenging rate among the tested antioxidants.