Effect of 2, 5-substituents on the stability of cyclic nitrone superoxide spin adducts: A density functional theory approach.

In the present study, five cyclic nitrone superoxide spin adducts, i.e. DMPO-OOH, M(3)PO-OOH, EMPO-OOH, DEPMPO-OOH and DEPDMPO-OOH, were chosen as model compounds to investigate the effect of 2,5-subsitituents on their stability, through structural analysis and decay thermodynamics using density functional theory (DFT) calculations. Analysis of the optimized geometries reveals that none of the previously proposed stabilizing factors, including intramolecular H-bonds, intramolecular non-bonding interactions, bulky steric protection nor the C(2)-N(1) bond distance can be used to clearly explain the effect of 2,5-substituents on the stability of the spin adducts. Subsequent study found that spin densities on the nitroxyl nitrogen and oxygen are well correlated with the half-lives of the spin adducts and consequently are the proper parameters to characterize the effect of 2,5-substituents on their stability. Examination of the decomposition thermodynamics further supports the effect of the substituents on the persistence of cyclic nitrone superoxide spin adducts.

Enhanced radical scavenging activity by antioxidant-functionalized gold nanoparticles: a novel inspiration for development of new artificial antioxidants.

Because of its potent antioxidant function and important role in clinical treatment, alpha-tocopherol (vitamin E) is a good starting point in the development of new synthetic antioxidants with improved properties. In this paper the first example of antioxidant-functionalized gold nanoparticles, Au@Trolox, was synthesized by self-assembly of thiol ligands derived from Trolox, a vitamin E analogue, on gold nanoparticles. DPPH* (2,2-diphenyl-1-picrylhydrazyl) radical scavenging experiments revealed that the rate constant for the reaction of Au@Trolox with DPPH* was about eight times greater than that for Trolox. The product analysis showed that both the quinonoid and the diepoxide forms were possible oxidized products of the chromanol group of Au@Trolox treated with DPPH* radical. No remarkable influence was found on the antioxidant activity of Au@Trolox when the coverage rate of the antioxidant group on the surface of the gold was varied. All our results proved that the assembly of chromanol groups on gold nanoparticles could efficiently enhance the activity of the vitamin E-derived antioxidant, which presents a potential new strategy for antioxidant design with novel perspectives in potential applications.

A novel flavonoid from Lespedeza virgata (Thunb.) DC.: structural elucidation and antioxidative activity.

Bioactivity guided fractionation of the ethanolic extract of the whole plants of Lespedeza virgata (Thunb.) DC. resulted in the isolation of a novel flavonoid (1) along with five known compounds 2-6. The molecular and structural formula as well as the stereochemistry of compound 1 were determined using data obtained from (1)H and (13)C NMR spectra, DEPT135 and by 2D HSQC, HMBC, (1)H-(1)H correlated spectroscopy ((1)H-(1)H COSY), and nuclear overhauser effect spectroscopy (NOESY) experiments. The superoxide anion scavenging activities of all isolated compounds were evaluated by the hypoxanthine nitro blue tetrazolium and ESR methods and the new compound 1 showed the strongest antioxidative activity 95.79% (IC(50)=0.14 mg/ml).

Immuno-stimulating properties of diosgenyl saponins isolated from Paris polyphylla.

The effects of three diosgenyl saponins isolated from Paris polyphylla on the immuno-stimulating activity in relation to phagocytosis, respiratory burst, and nitric oxide production in mouse macrophage cells RAW 264.7 have been investigated. Our results showed that all three diosgenyl saponins significantly enhanced phagocytic activity that increased with the concentration of saponins to reach a maximum, and then tended to decrease with higher concentrations. Saponins with sugar moiety directly induced respiratory burst response in RAW 264.7 cells that increased with the concentrations and reached a maximum, then decreased with higher concentrations after 2-h incubations, however, diosgenin had no PMA-triggered respiratory burst response. Treatment of RAW 264.7 cells with saponins with sugar moiety for 24-h caused a significant increase in the production of nitric oxide, while diosgenin had no effect at all. Consequently, relationship between molecular structures of three diosgenyl saponins and their immunomodulatory activities was discussed, and a possible mechanism of immuno-stimulating function of diosgenyl saponins was accordingly explored.

Damage to the oxygen-evolving complex by superoxide anion, hydrogen peroxide, and hydroxyl radical in photoinhibition of photosystem II.

Under strong illumination of a photosystem II (PSII) membrane, endogenous superoxide anion, hydrogen peroxide, and hydroxyl radical were successively produced. These compounds then cooperatively resulted in a release of manganese from the oxygen-evolving complex (OEC) and an inhibition of oxygen evolution activity. The OEC inactivation was initiated by an acceptor-side generated superoxide anion, and hydrogen peroxide was most probably responsible for the transportation of reactive oxygen species (ROS) across the PSII membrane from the acceptor-side to the donor-side. Besides ROS being generated in the acceptor-side induced manganese loss; there may also be a ROS-independent manganese loss in the OEC of PSII. Both superoxide anion and hydroxyl radical located inside the PSII membrane were directly identified by a spin trapping-electron spin resonance (ESR) method in combination with a lipophilic spin trap, 5-(diethoxyphosphoryl)-5-phenethyl-1-pyrroline N-oxide (DEPPEPO). The endogenous hydrogen peroxide production was examined by oxidation of thiobenzamide.

Effect of the phosphoryl substituent in the linear nitrone on the spin trapping of superoxide radical and the stability of the superoxide adduct: combined experimental and theoretical studies.

A new phosphorylated linear nitrone N-(4-hydroxybenzyliene)-1-diethoxyphosphoryl-1-methylethylamine N-oxide (4-HOPPN) was synthesized, and its X-ray structure was determined. The spin trapping ability of various kinds of free radicals by 4-HOPPN was evaluated. Kinetic study of decay of the superoxide spin adduct (4-HOPPN-OOH) shows the half-life time of 8.8 min. On the basis of the X-ray structural coordinates, theoretical analyses using density functional theory (DFT) calculations at the B3LYP/6-31+G(d,p)//B3LYP/6-31G(d) level were performed on spin-trapping reactions of superoxide radical with 4-HOPPN and PBN and three possible decay routes for their corresponding superoxide adducts. The comparative calculations on the spin-trapping reactions with superoxide radical predicted that both spin traps share an identical reaction type and have comparable potency when spin trapping superoxide radical. Analysis of the optimized geometries of 4-HOPPN-OOH and PBN-OOH reveals that an introduction of the phosphoryl group can efficiently stabilize the spin adduct through the intramolecular H-bonds, the intramolecular nonbonding attractive interactions, as well as the bulky steric protection. Examination of the decomposition thermodynamics of 4-HOPPN-OOH and PBN-OOH further supports the stabilizing role of the phosphoryl group to a linear phosphorylated spin adduct.

An exploratory theoretical elucidation on the peroxyl-radical-scavenging mechanism and structure-activity relationship of nonsteroidal anti-inflammatory drugs.

The peroxyl-radical-scavenging mechanism of some nonsteroidal anti-inflammatory drugs (NSAIDs), namely tolmetin, ketorolac, indomethacin, acemetacin, and oxaprozin, is clarified by combined density functional theory (DFT) calculations. It is revealed that H-atom-abstraction rather than electron transfer reaction is involved in the radical-scavenging process of these NSAIDs in polar aqueous solution. This seems contrary to the common viewpoint that the latter is predominant in polar media. The calculated results also show that H-atom at C(beta) or C(gamma) position is readily to be abstracted, and the lowest C-H bond dissociation enthalpy (BDE) can qualitatively account for the activity difference for the five NSAIDs.

Isolation, structure elucidation, antioxidative and immunomodulatory properties of two novel dihydrocoumarins from Aloe vera.

Two new dihydrocoumarin derivatives, compounds 1 and 2, were isolated from Aloe vera. Their structures were determined by X-ray crystallographic diffraction analysis and extensive 1D, 2D NMR spectroscopic data. Both of them evidently showed antioxidant activity against superoxide and hydroxyl radicals. Only 1 obviously exhibited immunomodulatory activity in relation to increasing the phagocytic activity and stimulating the production of superoxide anions in the oxygen respiratory burst of rat peritoneal macrophages.

A theoretical study of the different radical-scavenging activities of catechin, quercetin, and a rationally designed planar catechin.

To improve the radical-scavenging activity of catechin, a planar catechin analogue was designed and synthesized by Fukuhara [J. Am. Chem. Soc. 124 (2002) 5952]. Although the planar catechin is less active than quercetin, it is much more active than catechin in its ability to scavenge galvinoxyl radical, suggesting that the rational design was successful. However, an interesting question remains: what is the basis for the enhanced radical-scavenging activity of the planar catechin? By DFT calculations, we determined that the galvinoxyl radical is scavenged through an electron-transfer mechanism rather than a hydrogen-atom-transfer mechanism. Moreover, the antioxidant anion, derived from proton dissociation, plays a key role in the radical-scavenging process. Hence, the different radical-scavenging activities of the three antioxidants may result from the different ionization potentials of their anions.

Radical scavenging potential of phenolic compounds encountered in O. europaea products as indicated by calculation of bond dissociation enthalpy and ionization potential values.

The radical scavenging potential of phenolic compounds occurring in Olea europaea and of recently identified hydroxytyrosol metabolites was evaluated by means of quantum chemical calculations. The bond dissociation enthalpy (BDE) of phenolic hydroxyl groups and the ionization potential (IP) were calculated as descriptors to predict the H-atom-donating and electron-donating abilities of antioxidants, respectively. Catechol derivatives had the lowest BDE values (77.7-80.1 kcal/mol) whereas the lignans, pinoresinol and 1-acetoxypinoresinol, and other monophenols had much higher BDE values (85.1-88.0 kcal/mol), which suggested a lower potential for radical scavenging. Side chain characteristics were not found to affect the size of BDE values although differences in lipophilicity (on the basis of calculated Log P values) indicate variability in the activity in real systems. Conclusions for the antioxidant potential could not be drawn based on the IP values. Lack of experimental data for most of the studied compounds due to oxidative instability and difficulties in synthesis or isolation supports the usefulness of a computational approach for those interested in the antioxidant potential of phenolics encountered in O. europaea products.

Solvent effects are important in elucidating radical-scavenging mechanisms of antioxidants. A case study on genistein.

In two recent researches on antioxidant mechanisms of flavonoids and isoflavonoids, quantum chemical method was employed to calculate the proton dissociation energies, the bond dissociation energies and the ionization potentials for the phenols and derived radicals to help determine the radical-scavenging mechanisms. As the solvent effect was left out of consideration, the conclusion drawn from the calculation incurred some controversies. In the current study, we re-calculated the parameters for genistein and its anion by employing a B3LYP/6-311+G(d,p)//6-31G(d,p) method with solvent effect. Accordingly, a more reasonable explanation on the experimentally observed behavior of genistein as a radical scavenger was obtained. Therefore, solvent effect should be considered in the investigation of radical-scavenging mechanisms of antioxidants in polar solvents.

Estimation of scavenging activity of phenolic compounds using the ABTS(*+) assay.

Observations on the applicability of the ABTS(*+) assay to define structure-activity relationships (SARs) among phenols (AH) were based on experimental data and theoretical calculations. All AH examined (hydroxycinnamic derivatives, simple polyphenols, polyhydroxybenzoates, and flavonoids) were found to be active toward ABTS(*+). Moreover, known weak radical scavengers (i.e., coumaric and isoferulic acids) were found to be efficient or comparatively active to caffeic or rosmarinic acids in contradiction to the AH classification based on 1,1-diphenyl-2-picrylhydrazyl (DPPH) data or the bond dissociation enthalpy values. This behavior was observed both in ethanol and in buffered (pH 7.4) environment. Resorcinol and phloroglucin were found to be more active than catechol and hydroquinone, whereas, among polyhydroxybenzoates, 2,4-dihydroxybenzoic acid was the least active, in line with the DPPH and theoretical data. Therefore, it can be argued that the ABTS(*+) assay may give an indication for the presence of antioxidants in a certain system but SARs cannot be readily inferred.

Unexpected role of 5-OH in DPPH radical-scavenging activity of 4-thiaflavans. Revealed by theoretical calculations.

The O-H bond dissociation enthalpies (BDEs) of 4-thiaflavans were calculated by a combined density functional theory method (RO)B3LYP/6-311 + G(2d,2p)//AM1/AM1. The calculated BDEs not only gave a reasonable explanation on the DPPH radical-scavenging activity difference of 4-thiaflavans, but also revealed the unexpected role of 5-OH in enhancing the antioxidant activity of A-ring.

A theoretical investigation on DPPH radical-scavenging mechanism of edaravone.

The mechanism of edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one) to scavenge DPPH radical is clarified by density functional theory (DFT) calculations. It is revealed that H-atom-abstraction rather than electron-transfer reaction is involved in the radical-scavenging process of edaravone, and H-atom at position 4 is readily to be abstracted. The C-H bond dissociation enthalpy (BDE) of edaravone is higher than the O-H BDE of alpha-tocopherol, accounting for the activity difference between the two antioxidants. As substituents have little influence on the C-H BDE, 2-pyrazolin-5-one is recognized as the active center for edaravone.

Why B-ring is the active center for genistein to scavenge peroxyl radical: a DFT study.

The structure-activity relationship for genistein to scavenge peroxyl radical was clarified by density functional theory (DFT) calculations using the B3LYP/6-31G(d,p) method. It was revealed that the conjugation of an electron-withdrawing 1,4-pyrone group with A-ring of genistein was not beneficial to enhance the radical-scavenging activities. Thus, hydroxyl in B-ring became the active center of genistein to scavenge peroxyl radical.

[Prognostic significance of cellular DNA content and AgNOR count in ovarian cystadenoma].

BACKGROUND & OBJECTIVE: It has been showed that cellular DNA content and silver-staining nucleolar organizer region (AgNOR) count were significantly associated with the prognosis of some tumors; however, it is not yet clear whether these two parameters be helpful in predicting the prognosis of ovarian cystadenoma. This study was designed to evaluate the prognostic significance of these two parameters in ovarian cystadenoma. METHODS: Cellular DNA content and AgNOR count of the tumor cells for the samples from 42 patients with ovarian cystadenoma were measured by using computerized image analysis. The relationship between clinical as well as histomorphologic factors and the overall survival was evaluated by multivariable analysis. RESULTS: Univariate analysis showed that AgNOR count, DNA index, FIGO stage, degree of differentiation, presence of distant metastasis, residual tumor, lymph node metastasis, and age were the clinical variates with significant difference (P < 0.05). Multivariate analysis showed that DNA index > 1.4, FIGO stage, degree of differentiation, and residual tumor were prognostic predictors of ovarian cystadenoma. CONCLUSION: The DNA index may be a useful independent factor for predicting the diagnosis of ovarian cystadenoma.

Theoretical elucidation on structure-antioxidant activity relationships for indolinonic hydroxylamines.

Indolinonic hydroxylamines (IH), representing a new type of antioxidants, are comparative to alpha-tocopherol to protect lipids from oxidation. To elucidate the structure-activity relationship for IH, B3LYP/6-31G(d, p) method was employed to calculate the O-H bond dissociation enthalpy (BDE), a theoretical parameter to characterize the free radical scavenging activity. By constructing several model molecules, it was revealed that hydroxylamine was the key structural factor for this type of antioxidants, and substituents had little effect on the O-H BDE. If the =NR of IH was substituted by =O, its activity got lower.