QUENCHING OF SINGLET OXYGEN

Photoinduced Divergent Deaminative Borylation and Hydrodeamination of Primary Aromatic Amines

We have developed the divergent deaminative borylation and hydrodeamination of primary aromatic amines using bis(pinacolato)diboron. These transformations can be switched by the reaction conditions. Mechanistic and computational studies have suggested that the cleavage of the C-N bond and the formation of C-B bond are unlikely to involve free aryl radical intermediates. However, hydrodeamination is shown to proceed via hydrogen atom transfer between the corresponding aryl radical and an ethereal solvent.

Characterisation and Bioactivity Analysis of Peridinin-Chlorophyll a-Protein (PCP) Isolated from Symbiodinium tridacnidorum CS-73

Peridinin-Chlorophyll a-Proteins (PCP) are the major light harvesting proteins in photosynthetic dinoflagellates. PCP shows great variation in protein length, pigment ratio, sequence, and spectroscopic properties. PCP conjugates (PerCP) are widely used as fluorescent probes for cellular and tissue analysis in the biomedical field. PCP consists of a peridinin carotenoid; thereby, it can potentially be used as a bioactive compound in pharmaceutical applications. However, the biological activities of PCP are yet to be explored. In this study, we extracted, purified, and partially characterised the PCP from Symbiodinium tridacnidorum (CS-73) and explored its antioxidant, anti-cancer and anti-inflammation bioactivities. The PCP was purified using an ÄKTA™ PURE system and predicted to be of 17.3 kDa molecular weight (confirmed as a single band on SDS-PAGE) with an isoelectric point (pI) 5.6. LC-MS/MS and bioinformatic analysis of purified PCP digested with trypsin indicated it was 164 amino acids long with >90% sequence similarity to PCP of SymA3.s6014_g3 (belonging to clade A of Symbiodinium sp.) confirmed with 59 peptide combinations matched across its protein sequence. The spectroscopic properties of purified PCP showed a slight shift in absorption and emission spectra to previously documented analysis in Symbiodinium species possibly due to variation in amino acid sequences that interact with chl a and peridinin. Purified PCP consisted of a 19-amino-acid-long signal peptide at its N terminal and nine helixes in its secondary structure, with several protein binding sites and no DNA/RNA binding site. Furthermore, purified PCP exhibited antioxidant and in vitro anti-inflammation bioactivities, and anti-cancer activities against human metastatic breast adenocarcinoma (MDA-MB-231) and human colorectal (HTC-15) cancer cell lines. Together, all these findings present PCP as a promising candidate for continued investigations for pharmaceutical applications to cure chronic diseases, apart from its existing application as a fluorescent-probe.

Biomimetic Approach to Inhibition of Photooxidation in Organic Solar Cells Using Beta-Carotene as an Additive

Recent efficiency records of organic photovoltaics (OPV) highlight stability as a limiting weakness. Incorporation of stabilizers is a desirable approach for inhibiting degradation-it is inexpensive and readily up-scalable. However, to date, such additives have had limited success. We show that β-carotene (BC), an inexpensive and green, naturally occurring antioxidant, dramatically improves OPV stability. When compared to nonstabilized reference devices, the accumulated power generation of PTB7:[70]PCBM devices in the presence of BC increases by an impressive factor of 6, due to stabilization of both the burn-in and the lifetime, and by a factor of 21 for P3HT:[60]PCBM devices, owing to a longer lifetime. Using electron spin resonance and time-resolved near-IR emission spectroscopies, we probed radical and singlet oxygen concentrations. We demonstrate that singlet oxygen sensitized by [70]PCBM causes the "burn-in" of PTB7:[70]PCBM devices and that BC effectively mitigates it. Our results provide an effective solution to the problem that currently limits widespread use of OPV.

Reaction of phenol with singlet oxygen

Photo-degradation of organic pollutants plays an important role in their removal from the environment. This study provides an experimental and theoretical account of the reaction of singlet oxygen O2(1Δg) with the biodegradable-resistant species of phenol in an aqueous medium. The experiments combine customised LED-photoreactors, high-performance liquid chromatography (HPLC), and electron paramagnetic resonance (EPR) imaging, employing rose bengal as a sensitiser. Guided by density functional theory (DFT) calculations at the M062X level, we report the mechanism of the reaction and its kinetic model. Addition of O2(1Δg) to the phenol molecule branches into two competitive 1,4-cycloaddition and ortho ene-type routes, yielding 2,3-dioxabicyclo[2.2.2]octa-5,7-dien-1-ol (i.e., 1,4-endoperoxide 1-hydroxy-2,5-cyclohexadiene) and 2-hydroperoxycyclohexa-3,5-dien-1-one, respectively. Unimolecular rearrangements of the 1,4-endoperoxide proceed in a facile exothermic reaction to form the only experimentally detected product, para-benzoquinone. EPR revealed the nature of the oxidation intermediates and corroborated the appearance of O2(1Δg) as the only active radical participating in the photosensitised reaction. Additional experiments excluded the formation of hydroxyl (HO˙), hydroperoxyl (HO2˙), and phenoxy intermediates. We detected for the first time the para-semibenzoquinone anion (PSBQ), supporting the reaction pathway leading to the formation of para-benzoquinone. Our experiments and the water-solvation model result in the overall reaction rates of kr-solvation = 1.21 × 104 M-1 s-1 and kr = 1.14 × 104 M-1 s-1, respectively. These results have practical application to quantify the degradation of phenol in wastewater treatment.

Redox Conversion of Arsenite and Nitrate in the UV/Quinone Systems

Whether superoxide radical anion (O₂^•-) was a key reactive species in the oxidation of arsenite (As(III)) in photochemical processes has long been a controversial issue. With hydroquinone (BQH₂) and 1,4-benzoquinone (BQ) as redox mediators, the photochemical oxidation of As(III) and reduction of nitrate (NO₃^-) was carefully investigated. O₂^•-, singlet oxygen (¹O₂), H₂O₂, and semiquinone radical (BQH^•) were all possible reactive species in the irradiated system. However, since the formation of As(IV) is a necessary step in the oxidation of As(III), taking the standard reduction potentials into account, the reactions between the above species and As(III) were thermodynamically unfavorable. On the basis of radical scavenging experiments, hydroxyl radical (^•OH) was proved as the key species that led to the oxidation of As(III) in the UV/BQH₂ system. It should be noted that the ^•OH radicals were generated from the photolysis of H₂O₂, which came from the disproportionation of O₂^•- and the reaction of O₂^•- with BQH₂. Both the photoejected e_aq^- from ¹(BQH₂)* and the direct electron transfer with ³(BQH₂)* contributed to the reduction of NO₃^- in the UV/BQH₂ process. No synergistic effect was observed in the redox conversion of As(III) and NO₃^-, further demonstrating that the role of BQH^• was negligible in the studied systems. The results here are helpful for a better understanding of the photochemical behaviors of quinones in the aquatic environment.

Simple low cost porphyrinic photosensitizers for large scale chemoselective oxidation of sulfides to sulfoxides under green conditions: targeted protonation of porphyrins

Large scale chemoselective photooxidation of sulfides to sulfoxides in the presence of the diacids ofmeso-tetra(phenyl)porphyrin with different acids is reported.

Analysis of reactive oxygen and nitrogen species generated in three liquid media by low temperature helium plasma jet

In order to identify aqueous species formed in Plasma activated media (PAM), quantitative investigations of reactive oxygen and nitrogen species (ROS, RNS) were performed and compared to Milli-Q water and culture media without and with Fetal Calf Serum. Electron paramagnetic resonance, fluorometric and colorimetric analysis were used to identify and quantify free radicals generated by helium plasma jet in these liquids. Results clearly show the formation of ROS such as hydroxyl radical, superoxide anion radical and singlet oxygen in order of the micromolar range of concentrations. Nitric oxide, hydrogen peroxide and nitrite-nitrate anions (in range of several hundred micromolars) are the major species observed in PAM. The composition of the medium has a major impact on the pH of the solution during plasma treatment, on the stability of the different RONS that are produced and on their reactivity with biomolecules. To emphasize the interactions of plasma with a complex medium, amino acid degradation by means of mass spectrometry was also investigated using methionine, tyrosine, tryptophan and arginine. All of these components such as long lifetime RONS and oxidized biological compounds may contribute to the cytotoxic effect of PAM. This study provides mechanistic insights into the mechanisms involved in cell death after treatment with PAM.

Extraction, Identification and Photo-Physical Characterization of Persimmon (Diospyros kaki L.) Carotenoids

Carotenoid pigments were extracted and purified from persimmon fruits using accelerated solvent extraction (ASE). Eleven pigments were isolated and five of them were clearly identified as all-trans-violaxanthine, all-trans-lutein, all-trans-zeaxanthin all-trans-cryptoxanthin and all-trans-β-carotene. Absorption and fluorescence spectra were recorded. To evaluate the potential of ¹O₂ quenching of the purified carotenoids, we used a monocarboxylic porphyrin (P1COOH) as the photosensitizer to produce ¹O₂. The rate constants of singlet oxygen quenching (Kq) were determined by monitoring the near-infrared (1270 nm) luminescence of ¹O₂ produced by photosensitizer excitation. The lifetime of singlet oxygen was measured in the presence of increasing concentrations of carotenoids in hexane. Recorded Kq values show that all-trans-β-cryptoxanthin, all-trans-β-carotene, all-trans-lycopene and all-trans-zeaxanthin quench singlet oxygen in hexane efficiently (associated Kq values of 1.6 × 10⁸, 1.3 × 10⁸, 1.1 × 10⁸ and 1.1 × 10⁸ M^-1·s^-1, respectively). The efficiency of singlet oxygen quenching of β-cryptoxanthin can thus change the consideration that β-carotene and lycopene are the most efficient singlet oxygen quenchers acting as catalysts for deactivation of the harmful ¹O₂.

Reactive oxygen species in plant pathogenesis: the role of perylenequinone photosensitizers

SIGNIFICANCE

Reactive oxygen species (ROS) play multiple roles in interactions between plants and microbes, both as host defense mechanisms and as mediators of pathogenic and symbiotic associations. One source of ROS in these interactions are photoactivated, ROS-generating perylenequinone pigments produced via polyketide metabolic pathways in plant-associated fungi. These natural products, including cercosporin, elsinochromes, hypocrellins, and calphostin C, are being utilized as medicinal agents, enzyme inhibitors, and in tumor therapy, but in nature, they play a role in the establishment of pathogenic associations between fungi and their plant hosts.

RECENT ADVANCES

Photoactivated perylenequinones are photosensitizers that use light energy to form singlet oxygen (¹O₂) and free radical oxygen species which damage cellular components based on localization of the perylenequinone molecule. Production of perylenequinones during infection commonly results in lipid peroxidation and membrane damage, leading to leakage of nutrients from cells into the intercellular spaces colonized by the pathogen. Perylenequinones show almost universal toxicity against organisms, including plants, mice, bacteria, and most fungi. The producing fungi are resistant, however, and serve as models for understanding resistance mechanisms.

CRITICAL ISSUES

Studies of resistance mechanisms by perylenequinone-producing fungi such as Cercospora species are leading to an understanding of cellular resistance to ¹O₂ and oxidative stress. Recent studies show commonalities between resistance mechanisms in these fungi with extensive studies of ¹O₂ and oxidative stress responses in photosynthetic organisms.

FUTURE DIRECTIONS

Such studies hold promise both for improved medical use and for engineering crop plants for disease resistance.

Photodegradation of naproxen and its photoproducts in aqueous solution at 254 nm: a kinetic investigation

The kinetics of photodegradation of the non steroidal anti-inflammatory drug naproxen (+)-S-2-(6-methoxynaphthalen-2-yl)propanoic acid, an emerging organic pollutant, was studied in aqueous solutions under deaerated and aerated conditions. The photolysis experiments were carried out under monochromatic irradiation (λ = 254 nm) at pH = 7.0 and T = 25 °C. Simplified reaction schemes of photodegradation of naproxen are proposed in absence and in presence of oxygen respectively. The schemes take into account the photolysis of naproxen and its photoproducts and the reactions of the measured species with oxygen dissolved in the liquid bulk. According to these schemes, two kinetic models were developed which correlate the experimental data, for runs performed in absence and in presence of oxygen, with a fair accuracy and allowed to estimate the best values for the unknown kinetic parameters. The calculated quantum yield of direct photolysis of naproxen under deaerated media is in good agreement with the one previously reported. Under aerated conditions, the generation of singlet oxygen has also been taken into account. The obtained results, under the adopted conditions, indicated a marked influence of dissolved oxygen on the photodegradation rates of naproxen and the relative distribution of the major reaction intermediates.

Characterization of photoactivated singlet oxygen damage in single-molecule optical trap experiments

Optical traps or "tweezers" use high-power, near-infrared laser beams to manipulate and apply forces to biological systems, ranging from individual molecules to cells. Although previous studies have established that optical tweezers induce photodamage in live cells, the effects of trap irradiation have yet to be examined in vitro, at the single-molecule level. In this study, we investigate trap-induced damage in a simple system consisting of DNA molecules tethered between optically trapped polystyrene microspheres. We show that exposure to the trapping light affects the lifetime of the tethers, the efficiency with which they can be formed, and their structure. Moreover, we establish that these irreversible effects are caused by oxidative damage from singlet oxygen. This reactive state of molecular oxygen is generated locally by the optical traps in the presence of a sensitizer, which we identify as the trapped polystyrene microspheres. Trap-induced oxidative damage can be reduced greatly by working under anaerobic conditions, using additives that quench singlet oxygen, or trapping microspheres lacking the sensitizers necessary for singlet state photoexcitation. Our findings are relevant to a broad range of trap-based single-molecule experiments-the most common biological application of optical tweezers-and may guide the development of more robust experimental protocols.

The antioxidant effects of vitamin A, C, and E on aflatoxin B1-induced oxidative stress in human lymphocytes

The aim of this study was to investigate the possible protective role of vitamin A, C, and E on aflatoxin B1-induced in human lymphocytes using biochemical approaches. The control group received dimethyl sulfoxide, the second group of cultures were administered aflatoxin B1 (AFB1) at a dose of 5 μM. The other group of cultures were treated with AFB1+vitamin A (0.5 and 1.0 and 1.5 μM) and AFB1+vitamin C (25, 50, and 100 μM) and AFB1+vitamin E (40, 100, and 200 μM). The results of this experiment show that AFB1 significantly decreased the level of GSH and the activities of superoxide dismutase and GPx and increased level of malondialdehyde. Simultaneous supplementation with vitamin A, C, and E restored these parameters to that of normal range. In conclusion, vitamin A, C, and E exhibited protective effects in human lymphocytes by inhibiting AFB1-induced ROS generation.

Photochemical Instability of Thiol-Capped CdTe Quantum Dots in Aqueous Solution and Living Cells: Process and Mechanism

The process and mechanism of photochemical instability of thiol-capped CdTe quantum dots (QDs) in aqueous solution were experimentally studied. After laser irradiation, the corresponding Raman bands of the Cd-S bond decreased obviously, indicating bond breaking and thiol detachment from the QD surfaces. Meanwhile, a photoinduced aggregation of QDs occurred with the hydrodynamic diameter <Dh> increased to hundreds of nanometers from an initial 20 nm, as detected with dynamic light scattering measurements. The bleaching of the photoluminescence of QDs under laser irradiation could be attributed to the enhanced nonradiative transfer in excited QDs caused by increased surface defects due to the losing of thiol ligands. Singlet oxygen (1O2) was involved in the photooxidation of QDs, as revealed by the inhibiting effects of 1O2 quenchers of histidine or sodium azide (NaN3) on the photobleaching of QDs. The linear relationship in Stern-Volmer measurements between the terminal product and the concentration of NaN3 demonstrated that 1O2 was the main pathway of the photobleaching in QD solutions. By comparing the photostability of QDs in C2C12 cells with and without NaN3 treatment, the photooxidation effect of 1O2 on photobleaching of cellular QDs was confirmed.

Comparative cytoprotective activity of vitamin C, E and beta-carotene against chromium induced oxidative stress in murine macrophages

The present study reports the cytoprotective efficacy of vitamin C, E and beta-carotene against chromium (VI) induced oxidative stress in murine macrophages. Addition of chromium (VI) resulted in enhanced cytotoxicity as revealed by fall in neutral red uptake and increase in LDH release compared to control cells. Further there was an appreciable increase in apoptosis, ROS production and fall in reduced glutathione (GSH), glutathione peroxidase (GPx) and superoxide dismutase (SOD) activities. Chromium also inhibited macrophage proliferation and phagocytic activity. Addition of vitamin C but not vitamin E and beta-carotene inhibited chromium induced cytotoxicity, ROS generation and apoptosis. Vitamin C significantly inhibited NO production, enhanced macrophage proliferation and phagocytic activity while vitamin E and beta-carotene had marginal effect.

Possible involvement of singlet oxygen species as multiple oxidants in p450 catalytic reactions

Cytochrome P450 (P450) constitutes a superfamily of enzymes which activate dioxygen and carry out monooxygenation reactions of large numbers of endogenous and xenobiotic compounds. Drug metabolism is a particularly important P450 function, and, therefore, elucidating the metabolic products and pathways of drugs is essential for drug development. To explain the substrate selectivity of P450 reactions, it is necessary to understand the formation of multiple activated oxygen species to determine the type of catalyzed reactions, in addition to conducting structure analyses of P450s. Although an oxo-Fe(IV)-porphyrin-pi-cation radical is regarded as an activated oxygen species in P450 reactions, a nucleophilic Fe(III)-peroxo species has also been proposed as another oxidant. In the past decade, various studies indicated that P450-catalyzed oxygenations are complex, and that a single reaction pathway cannot explain all of the experimental results. In addition, the microsomal P450 system is known to generate reactive oxygen species (ROS). However, the contribution of ROS to P450 reactions remains unclear. We recently found that singlet oxygen (1O2) was involved in both several rat liver microsomal P450 reactions and four human CYP subfamily activities, as confirmed by the ESR spin-trapping method. In this review, we describe the studies that have been conducted on the detection and characterization of ROS in P450 reactions related to drug metabolism that involve the possibility of 1O2 in the P450 catalytic cycle. Gaining an understanding of the activated oxygen species that determine the type of drug metabolism will help us to predict the important metabolites formed.

Effect of nutrient depletion on beta-carotene and glycerol accumulation in two strains of Dunaliella sp

The response of two strains of Dunaliella, a beta-carotene accumulating halotolerant alga, was evaluated under sulphate, nitrate and phosphate limitation. All these factors decreased the growth rate and chlorophyll content but, increased the beta-carotene content of the two isolates of Dunaliella, D1, obtained from GTCC and D2 an indigenous strain isolated from Sambhar salt lake, India. Both the strains exhibited accumulation of beta-carotene and glycerol under the different nutrient limiting conditions. A maximum accumulation of 3.99 pg/cell of beta-carotene was observed under phosphate depletion. However, nutrient depletion did not significantly affect the glycerol accumulation in these cells. D2, the indigenous isolate, was found to be a better accumulator of beta-carotene than D1.

Preparation and physical characterization of pure beta-carotene

Pure all-trans beta-carotene has been prepared on the 10's of grams scale by isothermal Fractional Dissolution (FD) of commercial laboratory samples in tetrahydrofuran (THF). beta-Carotene purified in this way is black, with a faint brownish tinge. The electronic spectra of black samples extend into the near infrared, with end-absorption past 750 nm. Black samples react directly with dioxygen under mild conditions to yield the familiar orange or red powders. Pure beta-carotene rigorously obeys Beer's Law in octane over the entire UV-Vis spectral range, while commercial laboratory samples and recrystallized samples do not. NMR self-diffusion coefficient data demonstrate that beta-carotene exists as simple molecular solutions in octane and toluene. The anomalously high crystallinity of beta-carotene can be attributed (from analysis using molecular mechanics) to the facts that: (1) the number of theoretically possible conformers of beta-carotene is extremely small, and (2) only a small fraction of these (ca. 12%, or 127) may actually exist in fluid phases.

Antioxidant effect of beta-carotene on hypoxia induced oxidative stress in male albino rats

Hypoxia is known to induce oxidative stress in organisms leading to tissue injury. In the present study beta-carotene (BC) given at 10 mg/kg body weight (BW) in reducing the oxidative stress induced by hypoxia was evaluated on male albino rats. Hypoxia exposure caused an increase in malondialdehyde (MDA) levels in plasma and tissues, a concurrent decrease in blood glutathione (GSH), glutathione peroxidase (GPx), plasma protein and plasma BC content. Hemoglobin concentration, Red blood corpuscles (RBC) and White blood corpuscles (WBC) count were also increased under hypoxia. BC supplementation reversed the trend, inducing a significant decrease (P<0.05) in MDA and subsequent increase in plasma and tissue GSH levels in animals exposed to hypoxia. Blood GPx and plasma protein also increased significantly in BC supplemented animals. BC supplementation did not alter the changes in Hb concentration, RBC and WBC count. BC has potent antioxidant activities in reducing the oxidative stress induced by hypobaric hypoxia.

Evidence for Singlet Oxygen Involvement in Rat and Human Cytochrome P450-dependent Substrate Oxidations

Recently, we proposed that singlet oxygen ((1)O(2)) plays an essential role in microsomal cytochrome P450 (P450)-dependent p-hydroxylation of aniline and O-deethylation of 7-ethoxycoumarin. We then examined whether the role of (1)O(2) is general in the P450-dependent substrate oxidations. In the present study, we examined omega- and (omega-1)-hydroxylations of lauric acid, O-demethylation of p-nitroanisole, and N-demethylation of aminopyrine in rat liver microsomes. The addition of beta-carotene and NaN(3) significantly suppressed these reactions in a concentration-dependent manner, and (1)O(2) during the reactions was detected by ESR spin-trapping using 2,2,6,6-tetramethyl-4-piperidone (TMPD) as a (1)O(2)-spin trapping reagent, where the addition of (1)O(2) quenchers, SKF-525A as a P450 inhibitor, or p-nitroanisole decreased ESR signal intensities due to TMPD-(1)O(2) adduct. Next, we examined the effect of (1)O(2) quenchers on P450-dependent reactions in the human liver microsomes, and (1)O(2) was also indicated to be an active species in substrate hydroxylations and dealkylations such as nifedipine oxidation by CYP3A4. On the basis of the results, we concluded that (1)O(2) is an essentially important active oxygen species in both rat and human P450-dependent substrate oxidations.

Girard's reagent P derivative of beta-Apo-8'-carotenal: a potent photoprotective agent

A cationic carotenoid derivative (GRP-carotenal) was synthesized by the reaction of Girard's reagent P and beta-apo-8'-carotenal. The singlet-oxygen quenching constants for GRP-carotenal were 1.3 +/- 0.1 x 10(10) and 1.0 +/- 0.1 x 10(10) M-1 s-1 in acetonitrile and in detergent micelles, respectively. Photosensitized damage to K562 leukemia cells from cis-di(4-sulfonatophenyl)diphenylporphine, hypericin and protoporphyrin IX was inhibited by GRP-carotenal under conditions where beta-apo-8'-carotenal, beta-carotene and crocetin were ineffective. The unique cytoprotective properties of GRP-carotenal, relative to the other carotenoids studied, could not be explained by the differences in the cell content of the various carotenoids or by the changes in the cell content of the photosensitizers used. Photosensitizer fluorescence from labeled K562 cells was reduced by GRP-carotenal but not by the other carotenoids studied. The novel photoprotective properties of GRP-carotenal may be due to its subcellular distribution. In photosensitizer-containing detergent micelles, novel properties of GRP-carotenal were not apparent. None of the carotenoids studied reduced photosensitizer fluorescence or singlet-oxygen generation. Singlet-oxygen quenching by GRP-carotenal and by beta-apo-8'-carotenal were roughly the same. Crocetin has a singlet-oxygen quenching constant that is about a factor of five lower. Singlet-oxygen quenching by beta-carotene was limited by its aggregation.

Peridinin as the major biological carotenoid quencher of singlet oxygen in marine algae Gonyaulax polyedra

Carotenoids in light-harvesting proteins and reaction centers increase the overall efficiency of photosynthesis by transferring absorbed light energy to chlorophylls. Peridinin and beta-carotene were isolated from Gonyaulax polyedra in a one-step purification protocol using the preparative circular chromatography (Chromatotron), performed on silica gel under N(2) atmosphere and n-hexane/acetone 8:2 as mobile phase and characterized by extensive (1)H NMR, infrared, and electrospray ionization mass spectrometry analyses. The quenching of singlet molecular oxygen [O(2) ((1)Delta(g))] was evaluated by NIR-emission assays using singlet oxygen generated by sensitization of either perinaphthenone or methylene blue. The NIR-emission assay showed that peridinin quench as singlet oxygen (k(q) = 9.5 x 10(8) M(-1) s(-1)) 5-fold less efficiently than beta-carotene (52 x 10(8) M(-1) s(-1)). A method, based on the use of high-performance liquid chromatography with UV-VIS detection, was then developed for the sensitive quantification of peridinin (55% of total carotenoids) and beta-carotene (4.1% of total carotenoids). Thus, since peridinin is 10-fold more abundant than beta-carotene, it is expected to be the major protector against the deleterious effects of O(2) ((1)Delta(g)) in Gonyaulax polyedra.

ESR study on the structure-antioxidant activity relationship of tea catechins and their epimers

The purpose of this study is to examine the relationship between the free radical scavenging activities and the chemical structures of tea catechins ((-)-epigallocatechin gallate (EGCG), (-)-epigallocatechin (EGC) and (-)-epicatechin (EC)) and their corresponding epimers ((-)-gallocatechin gallate (GCG), (-)-gallocatechin (GC) and (+)-catechin ((+)-C)). With electron spin resonance (ESR) we investigated their scavenging effects on superoxide anions (O-.2) generated in the irradiated riboflavin system, singlet oxygen(1O2) generated in the photoradiation-hemoporphyrin system, the free radicals generated from 2,2'-azobis(2-amidinopropane)hydrochloride (AAPH) and 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical. The results showed that the scavenging effects of galloylated catechins (EGCG and GCG) on the four free radicals were stronger than those of nongalloylated catechins (EGC, GC, EC, (+)-C), and the scavenging effects of EGC and GC were stronger than those of EC and (+)-C. Thus, it is suggested that the presence of the gallate group at the 3 position plays the most important role in their free radical-scavenging abilities and an additional insertion of the hydroxyl group at the 5' position in the B ring also contributes to their scavenging activities. Moreover, the corresponding phenoxyl radicals formed after the reaction with O-.2 were trapped by DMPO and the ESR spectra of DMPO/phenoxyl radical adducts were observed (aN=15.6 G and aHbeta=21.5 G). No significant differences were found between the scavenging effects of the catechins and their epimers when their concentrations were high. However, significant differences were observed at relatively low concentrations, and the lower their concentrations, the higher the differences. The scavenging abilities of GCG, GC and (+)-C were stronger than those of their corresponding epimers (EGCG, EGC and EC). The differences between their sterical structures played a more important role in their abilities to scavenge large free radicals, such as the free radicals generated from AAPH and the DPPH radical, than to scavenge small free radicals, such as O-.2 and 1O2, especially in the case with EGCG and GCG with more bulky steric hindrance.

Proposed mechanism for the photodynamic generation of 8-oxo-7,8-dihydro-2'-deoxyguanosine produced in cultured cells by exposure to lomefloxacin

In this study, lomefloxacin (LMX), a widely used quinolone antibiotic with a high frequency of clinical phototoxicity, was investigated by measuring the effects of several antioxidants on its ability to form of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG) in cultured adult rat liver cells after exposure to UVA. In the current study the observed DNA damage, reflected by the formation of 8-oxo-dG, was almost completely inhibited by co-incubation of LMX and cultured cells with sodium azide (NaN3) that specifically quenches singlet oxygen. Vitamin E (alpha-tocopherol), known to quench both superoxide and singlet oxygen, inhibited 8-oxo-dG formation by approximately 54%. Mannitol, a hydroxyl radical scavenger, inhibited 8-oxo-dG formation by 64%. Butylated hydroxyanisole (BHA), a scavenger of hydroxyl, peroxy and alkoxy radicals, showed no inhibition of 8-oxo-dG formation but in fact enhanced levels of 8-oxo-dG by 169%. The results of this study suggest that the mechanism for the photodynamic generation of 8-oxo-dG by LMX is mediated, at least in part, by both singlet oxygen and hydroxyl radical and involves both type I and type II photosensitization.