Singlet Oxygen Scavenger Research Articles

An Antioxidant Extract of Tropical Lichen,Parmotrema reticulatum, Induces Cell Cycle Arrest and Apoptosis in Breast Carcinoma Cell Line MCF-7

This report highlights the phytochemical analysis, antioxidant potential and anticancer activity against breast carcinoma of 70% methanolic extract of lichen, Parmotrema reticulatum (PRME). Phytochemical analysis of PRME confirms the presence of various phytoconstituents like alkaloids, carbohydrates, flavonoids, glycosides, phenols, saponins, tannins, anthraquinones, and ascorbic acid; among which alkaloids, phenols and flavonoids are found in abundant amount. High performance liquid chromatography (HPLC) analysis of PRME revealed the presence of catechin, purpurin, tannic acid and reserpine. Antioxidant activity was evaluated by nine separate methods. PRME showed excellent hydroxyl and hypochlorous radical scavenging as well as moderate DPPH, superoxide, singlet oxygen, nitric oxide and peroxynitrite scavenging activity. Cytotoxicity of PRME was tested against breast carcinoma (MCF-7), lung carcinoma (A549) and normal lung fibroblast (WI-38) using WST-1 method. PRME was found cytotoxic against MCF-7 cells with an IC50 value 130.03±3.11 µg/ml while negligible cytotoxicity was observed on A549 and WI-38 cells. Further flow cytometric study showed that PRME halted the MCF-7 cells in S and G2/M phases and induces apoptosis in dose as well as time dependent manner. Cell cycle arrest was associated with downregulation of cyclin B1, Cdk-2 and Cdc25C as well as slight decrease in the expression of Cdk-1 and cyclin A1 with subsequent upregulation of p53 and p21. Moreover PRME induced Bax and inhibited Bcl-2 expression, which results in increasing Bax/Bcl-2 ratio and activation of caspase cascade. This ultimately leads to PARP degradation and induces apoptosis in MCF-7 cells. It can be hypothesised from the current study that the antioxidant and anticancer potential of the PRME may reside in the phytoconstitutents present in it and therefore, PRME may be used as a possible source of natural antioxidant that may be developed to an anticancer agent.

The inter-monomer interface of the major light-harvesting chlorophyll a/b complexes of photosystem II (LHCII) influences the chlorophyll triplet distribution

Under strong light conditions, long-lived chlorophyll triplets (3Chls) are formed, which can sensitize singlet oxygen, a species harmful to the photosynthetic apparatus of plants. Plants have developed multiple photoprotective mechanisms to quench 3Chl and scavenge singlet oxygen in order to sustain the photosynthetic activities. The lumenal loop of light-harvesting chlorophyll a/b complex of photosystem II (LHCII) plays important roles in regulating the pigment conformation and energy dissipation. In this study, site-directed mutagenesis analysis was applied to investigate triplet–triplet energy transfer and quenching of 3Chl in LHCII. We mutated the amino acid at site 123 located in this region to Gly, Pro, Gln, Thr and Tyr, respectively, and recorded fluorescence excitation spectra, triplet-minus-singlet (TmS) spectra and kinetics of carotenoid triplet decay for wild type and all the mutants. A red-shift was evident in the TmS spectra of the mutants S123T and S123P, and all of the mutants except S123Y showed a decrease in the triplet energy transfer efficiency. We propose, on the basis of the available structural information, that these phenomena are related to the involvement, due to conformational changes in the lumenal region, of a long-wavelength lutein (Lut2) involved in quenching 3Chl.

Singlet oxygen scavenging by leaf flavonoids contributes to sunlight acclimation in Tilia platyphyllos

Both high photosynthetically active radiation (PAR) and ultraviolet radiation (UV) are capable of causing photooxidative stress, but leaves are equipped with an array of protective mechanisms making life under full sunlight possible. Comparing acclimation strategies of Tilia platyphyllos leaves we found that sun leaves were better protected against stress than shade leaves by having (i) more efficient regulated non-photochemical quenching, (ii) a higher capacity to neutralize singlet oxygen, a reactive oxygen species known to be capable of promoting oxidative damage by excess PAR and (iii) containing more UV absorbing pigments. HPLC–MSn analysis showed both quantitative and qualitative differences in higher flavonoid contents: sun leaves contained 4.2-times more flavonoids than shade leaves and the quercetin:kaempferol ratio was also higher in the former. In addition, sun leaves also contained significant amounts of myricetin, which was detectable only in traces in shade leaves. Flavonols were mainly present as rhamnosides and in vitro tests of these compounds showed that quercetin and myricetin glycosides were much better singlet oxygen antioxidants than kaempferol glycosides. Thus a shift from monohydroxylated flavonols (kaempferol derivatives) towards dihydroxylated quercetin or trihydroxylated myricetin improves the singlet oxygen targeted antioxidant potential of leaves and potentially improves protection against photoinhibition by high PAR. On the other hand, experiments with pure test compounds also showed that multihydroxylated flavonol rhamnosides do not have better UV-B absorption than monohydroxylated ones. Thus the observed difference in flavonoid composition is not expected to contribute to the observed better UV-B absorbing capacity of sun leaves. Our data suggest that responses to high intensity PAR and to solar UV-B are closely connected and that UV-inducible flavonols play a key role in the successful acclimation of sun leaves to high PAR as efficient singlet oxygen antioxidants.

Isolation of antioxidative and ACE inhibitory peptides from protein hydrolysate of skipjack (Katsuwana pelamis) roe

Bioactive peptides from protein hydrolysate of defatted skipjack (Katsuwonus pelamis) roe with 5% degree of hydrolysis (DH) prepared by Alcalase digestion were isolated and characterised. Two active fractions with ABTS radical scavenging activity (973.01–1497.53μmol TE/mg sample) and chelating activity (0.05–0.07μmol EE/mg sample) from consecutive purification steps including ultrafiltration, cation exchange column chromatography and reverse phase high performance liquid chromatography (RP-HPLC), were subjected to analysis of amino acid sequence by LC–MS/MS. Seven dominant peptides with 6–11 amino acid residues were identified as DWMKGQ, MLVFAV, MCYPAST, FVSACSVAG, LADGVAAPA, YVNDAATLLPR and DLDLRKDLYAN. These peptides were synthesised and analysed for ACE-inhibitory activity and antioxidative activities. MLVFAV exhibited the highest ACE inhibitory activity (IC50=3.07μM) (p<0.05) with no antioxidative property, whilst DLDLRKDLYAN showed the highest metal chelating activity, ABTS radical and singlet oxygen scavenging activities. Therefore, peptides prepared from skipjack roe could be further employed as a functional food ingredient.

Singlet oxygen scavenging activity of tocopherol and plastochromanol in Arabidopsis thaliana: relevance to photooxidative stress

In the present study, singlet oxygen (¹O₂) scavenging activity of tocopherol and plastochromanol was examined in tocopherol cyclase-deficient mutant (vte1) of Arabidopsis thaliana lacking both tocopherol and plastochromanol. It is demonstrated here that suppression of tocopherol and plastochromanol synthesis in chloroplasts isolated from vte1 Arabidopsis plants enhanced ¹O₂ formation under high light illumination as monitored by electron paramagnetic resonance spin-trapping spectroscopy. The exposure of vte1 Arabidopsis plants to high light resulted in the formation of secondary lipid peroxidation product malondialdehyde as determined by high-pressure liquid chromatography. Furthermore, it is shown here that the imaging of ultra-weak photon emission known to reflect oxidation of lipids was unambiguously higher in vte1 Arabidopsis plants. Our results indicate that tocopherol and plastochromanol act as efficient ¹O₂ scavengers and protect effectively lipids against photooxidative damage in Arabidopsis plants.

Mesopolymer modified with palladium phthalocyaninesulfonate as a versatile photocatalyst for phenol and bisphenol A degradation under visible light irradiation

A novel versatile photocatalyst, FDU-PdPcS, was prepared by immobilizing palladium phthalocyaninesulfonate (PdPcS) onto the FDU-15 mesopolymer via multi-step chemical modification processes involving chloromethylation of the FDU-15 mesopolymer first with chloromethyl methyl ether, a subsequent amination reaction with ethylenediamine, and finally modification with palladium phthalocyaninesulfonate via ionic interaction. The obtained FDU-PdPcS photocatalyst was characterized by the X-ray diffraction (XRD), UV-Vis spectrosopy and inductively coupled plasma (ICP) techniques. This photocatalyst not only affords a high dispersion of monomeric PdPcS molecules, which may further be stabilized by the π-electron of benzene rings of FDU-15, but also provides a number of diamino groups inside the mesopores, which could be advantageous for the photodegradation of phenolic pollutants. In photodegradation studies of phenolic pollutants, the FDU-PdPcS catalyst exhibited excellent visible light photocatalytic activity and reusability. The photodegradation products of phenol and bisphenol A were investigated by the gas chromatoghraphy-mass spectrometry (GC-MS) technique. The results showed that the photodegradation products were composed of carboxylic acids and CO2. Isopropanol, sodium azide and benzoquinone were used as hydroxyl radical (OH•), singlet oxygen (1O2) and superoxide radical (O2•–) scavengers, respectively. The results suggested that 1O2 and O2•– were the prominent active species during the photodegradation process. A possible mechanism for the photodegradation of phenol was also discussed.

Folate in human skin: its correlation with serum levels, and the unusual abundance in the epidermis of 5‐methyltetrahydrofolate

Understanding the biology of folates in human skin is of considerable interest not only because they may be at risk for degradation by ultraviolet light, but they may also have photoprotective properties. We have previously measured 5‐methyltetrahydrofolate (5‐MTHF) in fresh ex vivo skin samples by a recovery validated extraction method, and found that epidermis contains an order of magnitude higher concentration than the dermis. Skin samples from black and white subjects not exposed to light were not different from each other (FASEB J. 2011, 25:608.2). We now show that the abundance of 5‐MTHF in both layers of skin in relation to total folate (TFOL) as determined by microbiological assay are highly and linearly correlated with the serum folate status. Surprisingly, while the percentage of TFOL present as 5‐MTHF in the dermis was typical of other organs, it constituted an unusually high percentage in the epidermis, increasing (to over 70%) as serum folate (and thus skin total folate) decreased. The high percentage of 5‐MTHF in the epidermis, and its maintenance in mildly folate deficient subjects, points to a special role for this form of folate in skin, perhaps as a scavenger of singlet oxygen produced in UV induced photosensitization reactions (FASEB J. 2007, 21:2101–7).Supported by NSF 009185353; LZH is recipient of a predoctoral fellowship from the Graduate Research Scholars Program of Alabama.

Efficient induction of apoptosis in HeLa cells by a novel cationic porphycene photosensitizer

In the present study we analyze the photobiological properties of 2,7,12-tris(α-pyridinio-p-tolyl)–17-(p-(methoxymethyl)phenyl) porphycene (Py3MeO-TBPo) in Hela cells, in order to assess its potential as a new photosensitizer for photodynamic therapy of cultured tumor cells. Using 0.5 μM Py3MeO-TBPo, flow cytometry studies demonstrated an increase of intracellular drug levels related to the incubation time, reaching a maximum at 18 h. LysoTracker® Green (LTG) and MitoTracker® Green (MTG) probes were used to identify the subcellular localization. Upon exposure to ultraviolet excitation, red porphycene fluorescence was detected as red granules in the cytoplasm that colocalized with LTG. No significant toxic effects were detected for Py3MeO-TBPo in the dark at concentrations below 1 μM. In contrast, Py3MeO-TBPo combined with red-light irradiation induced concentration- and fluence-dependent HeLa cells inactivation. Besides, all photodynamic protocols assayed induced a clear effect of cell detachment inhibition after trypsin treatment. Both apoptotic and necrotic cell death mechanisms can occur in HeLa cells depending on the experimental protocol. After 18 h incubation with 0.5 μM Py3MeO-TBPo and subsequent red light irradiation (3.6 J/cm2), a high number of cells die by apoptosis, as evaluated by morphological alterations, immunofluorescent relocalization of Bax from cytosol to mitochondria, and TUNEL assay. Likewise, immunofluorescence techniques showed that cytochrome c is released from mitochondria into cytosol in cells undergoing apoptosis, which occurs immediately after relocation of Bax in mitochondria. The highest amount of apoptosis appeared 24 h after treatment (70%) and this cell death occurred without cell detachment to the substrate. In contrast, with 0.75 μM Py3MeO-TBPo and 3.6 J/cm2 irradiation, morphological changes showed a preferential necrotic cell death.Singlet oxygen was identified as the cytotoxic agent involved in cell photoinactivation. Moreover, cell cultures pre-exposed to the singlet oxygen scavenger sodium azide showed pronounced protection against the loss of viability induced by Py3MeO-TBPo and light.Different changes in distribution and organization of cytoskeletal elements (microtubules and actin microfilaments) as well as the protein vinculin, after apoptotic and necrotic photodynamic treatments have been analyzed. Neither of these two cell death mechanisms (apoptosis or necrosis) induced cell detachment.In summary, Py3MeO-TBPo appears to meet the requirements for further scrutiny as a very good photosensitizer for photodynamic therapy: it is water soluble, has a high absorption in the red spectral region (where light penetration in tissue is higher), and is able to induce effective high apoptotic rate (70%) related to the more widely studied photosensitizers.

Involvement of type I and type II mechanisms on the photoinactivation of non-enveloped DNA and RNA bacteriophages

Microbial photodynamic inactivation (PDI), involving the use of a photosensitizer (PS), light and molecular oxygen, with the subsequent production of reactive oxygen species (ROS), has been considered a promising and effective technology for viral inactivation. Although singlet oxygen is generally accepted as the main damaging species in PDI, ROS like free radicals may also be involved in the process, inducing damages to proteins, lipids, nucleic acids and other molecular structures. In this study, the relative importance of each mechanism (type I and type II) on the photoinactivation of non-enveloped DNA (T4-like phage) and RNA (Qβ phage) viruses was evaluated. For this purpose, two cationic porphyrins (Tri-Py+-Me-PF and Tetra-Py+-Me) and four different ROS scavengers were used. The scavenging effect of sodium azide and L-histidine (singlet oxygen quenchers) and of D-mannitol and L-cysteine (free radical scavengers) was assessed by exposure of both phages (T4-like and Qβ) to each cationic porphyrin (5.0μM for T4-like phage and 0.5μM for Qβ phage) and white light (40Wm−2) in the presence of different concentrations of the scavengers (5, 10, 50 and 100mM). Sodium azide and L-histidine gave the best protection, reducing the phototoxic effect of Tri-Py+-Me-PF on T4-like phage respectively by 80% and 72% and in the presence of Tetra-Py+-Me by 90% and 78%. Free radical scavengers D-mannitol and L-cysteine did not significantly reduce the rate of T4-like phage photoinactivation (around 20% protection, for both PS). The sodium azide protection on Qβ phage photoinactivation, in the presence of Tri-Py+-Me-PF, was lower (39%) when compared with T4-like phage. D-mannitol did not exert on Qβ phage any protective effect after 90min of irradiation. The effect of the simultaneous presence of singlet oxygen and free radicals scavengers at 100mM confirmed that singlet oxygen (type II mechanism) is clearly the main ROS involved in T4-like and Qβ phages photoinactivation by these two cationic PS. As RNA-type phages are more easily photoinactivated when compared with DNA-type ones, the protection conferred by the scavengers during the PDI process is lower and this should be taken into account when the main mechanism involved in PDI of different viruses is to be studied.

Zinc Coproporphyrin I Derived from Meconium Has an Antitumor Effect Associated with Singlet Oxygen Generation

Introduction: Zinc coproporphyrin I (ZnCP-I) is a photosensitive molecule and a major component of meconium. Here, we examined the effects of ZnCP-I as a potential photosensitizer in photodynamic therapy for tumors. Materials and Methods: (1) Aqueous ZnCP-I was irradiated with a pulsed YAG-SHG laser (wavelength: 532 nm)/YAG-SHG dye laser (wavelength: 566 nm). (2) HeLa cells were incubated in 200 m<smlcap>M</smlcap> ZnCP-I, and accumulation of ZnCP-I in HeLa cells was evaluated with ZnCP-I-specific fluorescence over 500 nm. (3) Aqueous ZnCP-I was administered intravenously to HeLa tumor-bearing mice at a dose of 10.2 mg/kg body weight. The tumors were irradiated with a filtered halogen lamp (wavelength: 580 nm) at 100 J/cm² 20 min after administration. Results: (1) An intense near-infrared emission spectrum was observed at around 1,270 nm after irradiation. The emission intensity was proportional to the laser power between 10 and 80 mW and was completely inhibited by addition of NaN₃, a singlet oxygen scavenger. (2) ZnCP-I-specific fluorescence was detected in the HeLa cell cytoplasm. (3) Irradiated tumors treated with ZnCP-I were mostly necrotized. Conclusion: ZnCP-I accumulated in tumor cells, produced singlet oxygen upon irradiation, and necrotized the tumor cells. These results suggest that ZnCP-I may be an effective photosensitizer.

Hepatoprotective Effect of Vitamin C (Ascorbic Acid)

Human and animal studies have shown that some drugs and chemical agents have potential hepatotoxic effects. The hepatotoxic effect of drugs and some chemical agents is reported to be associated with the generation of reactive oxygen species (ROS). These ROS are reported to be associated with lipid peroxidation in the liver. This mechanism has led to continuous evaluation of the hepatoprotective effect of antioxidants in humans and animals. Among the antioxidants been evaluated is vitamin C which is a water soluble antioxidant. Reports have linked vitamin C with hepatoprotective property in animals and humans. It synergistic hepatoprotective effect with other antioxidants was also reported. Due to these reports a comprehensive literature review on the hepatoprotective property of vitamin C in humans and animals was performed. It was observed that vitamin C exhibited a reputable hepatoprotective effect in humans and animals. Research showed that vitamin C inhibited hepatotoxicity induced by drugs, heavy metals, organophosphate insecticides and some chemical agents. Vitamin C was reported to normalized levels of serum alanine aminotransferase, aspartate aminotransferase, gamma glutamine, alkaline phosphatase, lactate dehydrogenase and malondialdehyde and serum bilirubin in intoxicated animals. It potentiates the activities of free radical scavengers, superoxide dimutase, and catalase glutathione peroxidase thereby preventing microsomal lipid peroxidation, liver fibrosis, liver necrosis and hepatic inflammation. In humans vitamin C was reported to be beneficial in non alcoholic steatohepatitis and in patients with fatty liver disease. Hepatoprotective property of vitamin C is attributed to it antioxidant property. Vitamin C (ascorbic acid) which is a major water-soluble antioxidant is believed to decrease lipid peroxidation either directly or indirectly by regenerating vitamin E. Vitamin C is an important free radical scavenger in extracellular fluids, trapping radicals and protecting biomembranes from peroxide damage. Vitamin C effectively scavenges singlet oxygen, superoxide, hydroxyl, water soluble peroxyl radical and hypochlorous acid. It is also reported to be an excellent source of electrons and therefore can donate electrons to free radicals such as hydroxyl and super oxide radicals and quench their activity. Vitamin C is an essential co-factor involved in many biochemical functions and acts as an electron donor or reducing agent. In this review it is observe that vitamin C has hepatoprotective effect which increases when co administered with other agents precisely antioxidants.

Carotenoids and Cardiovascular Risk

Fruits and vegetables (typically associated with the Mediterranean diet) are very rich in carotenoids, i.e. fat-soluble pigments really important in human life. Structurally, carotenoids consists of eleven (beta-carotene, zeaxanthin, lycopene) or ten (alpha-carotene, lutein) conjugated double bonds, responsible for their antioxidant capability in agreement with their substituents. Low-Density Lipoprotein (LDL) particles oxidation process is the one of the most important first steps of atherosclerotic disease and, consequentially, the first pathogenetical step of cerebro- and cardiovascular events like myocardial infarction and stroke, which are the first cause of death in industrialized countries. Reactive oxygen species (ROS) also seem to be the target of Carotenoids main action, by scavenging singlet oxygen (1O2) and free radicals. Literature data showed that ROS increase atherosclerotic individual burden. The carotenoids scavenging action could reduce atherosclerosis progression partly due to such a decrease in ROS concentrations. Many studied demonstrated such a reduction by analyzing the relationship between carotenoids and Intima-Media Thickness of common carotid artery wall (CCA-IMT), [a well established marker of atherosclerosis evolution] reduction. Aim of this review is to evaluate actual knowledge about the importance of carotenoids molecules in slowing down the starting and the progression of atherosclerotic plaque, and to consider their implementation in everyone's diet as a tool to obtain a sharp decrease of LDL oxidation and their possible effect on endothelial function.

Photodegradation of trimeprazine triggered by self-photogenerated singlet molecular oxygen

The antihistaminic drug trimeprazine (1, also known as alimemazine) is photolabile under UV-A light in aerobic conditions. Irradiation of a methanol solution of trimeprazine produces two photoproducts which were isolated as N,N2-trimethyl-3-(10H-phenothiazin-10-yl sulfoxide) propan-1-amine (2) and N,2-dimethyl-3-(10H-phenothiazin-10-yl) propan-1-amine (4). The formation of products was explained by the oxidative photodegradation of trimeprazine in an irreversible trapping of the self-photogenerated 1O2 by the type II photodynamic action of the drug. The generation of singlet oxygen during photolysis of trimeprazine was confirmed by singlet oxygen scavenger 2,5-dimethylfuran (2,5-DMF).

Carotenoid Lutein: A Promising Candidate for Pharmaceutical and Nutraceutical Applications

ABSTRACTCarotenoids play a major role in scavenging singlet oxygen and peroxyl radicals in human. Several studies have shown that lutein and zeaxanthin help to protect the skin and eyes from photodamage and offer several other health benefits. The potential benefits of using lutein as nutritional or cosmetic ingredient are reviewed in this paper. Recent advances in health and cosmetic care provided by lutein are also discussed. This review also mentions various drug carrier systems that have been studied for the delivery of lutein.

LHCBM1 and LHCBM2/7 Polypeptides, Components of Major LHCII Complex, Have Distinct Functional Roles in Photosynthetic Antenna System of Chlamydomonas reinhardtii

The photosystem II antenna of Chlamydomonas reinhardtii is composed of monomeric and trimeric complexes, the latter encoded by LHCBM genes. We employed artificial microRNA technology to specifically silence the LHCBM2 and LHCBM7 genes, encoding identical mature polypeptides, and the LHCBM1 gene. As a control, we studied the npq5 mutant, deficient in the LHCBM1 protein. The organization of LHCII complexes, functional antenna size, capacity for photoprotection, thermal energy dissipation and state transitions, and resistance to reactive oxygen species was studied in the various genotypes. Silencing of the LHCBM2/7 genes resulted in a decrease of an LHCII protein with an apparent molecular mass of 22 kDa, whereas silencing/lack of LHCBM1 caused the decrease/disappearance of a 23-kDa protein. A decrease in the abundance of trimeric LHCII complexes and in functional antenna size was observed in both LHCBM2/7 and LHCBM1 knockouts. In agreement with previous data, depletion of LHCBM1 decreased the capacity for excess energy dissipation but not the ability to perform state transitions. The opposite was true for LHCBM2/7, implying that this polypeptide has a different functional role from LHCBM1. The abundance of LHCBM1 and LHCBM2/7 is in both cases correlated with resistance to superoxide anion, whereas only LHCBM1 is also involved in singlet oxygen scavenging. These results suggest that different LHCBM components have well defined, non-redundant functions despite their high homology, implying that engineering of LHCBM proteins can be an effective strategy for manipulating the light harvesting system of Chlamydomonas reinhardtii.

Singlet oxygen and non-photochemical quenching contribute to oxidation of the plastoquinone-pool under high light stress in Arabidopsis

The redox state of plastoquinone-pool in chloroplasts is crucial for driving many responses to variable environment, from short-term effects to those at the gene expression level. In the present studies, we showed for the first time that the plastoquinone-pool undergoes relatively fast oxidation during high light stress of low light-grown Arabidopsis plants. This oxidation was not caused by photoinhibition of photosystem II, but mainly by singlet oxygen generated in photosystem II and non-photochemical quenching in light harvesting complex antenna of the photosystem, as revealed in experiments with a singlet oxygen scavenger and with Arabidopsis npq4 mutant. The latter mechanism suppresses the influx of electrons to the plastoquinone-pool preventing its excessive reduction. The obtained results are of crucial importance in light of the function of the redox state of the plastoquinone-pool in triggering many high light-stimulated physiological responses of plants.

Enhancing the Emissive Properties of Poly(p-phenylenevinylene)-Conjugated Polyelectrolyte-Coated SiO2 Nanoparticles

Here we describe single-particle imaging studies conducted on the conjugated polyelecrolyte poly[5-methoxy-2-(3-sulfopropoxy)-1,4-phenylenevinylene] (MPS-PPV) supported on SiO(2) nanoparticles. The particles are subjected to a time-programmed sequence involving addition and removal of different additives, including excited-triplet-state quenchers and scavengers of singlet oxygen as well as ground-state oxygen. Our studies show that these additives enhance the emission intensity and photostability of the nanoparticles and may further repair photodamaged conjugated polymer. The ability to monitor the emission from individual particles along multiple cycles under a range of conditions provides a mechanistic insight into the action of these additives.

Singlet Oxygen Formation and Scavenging in Cytochromeb6fComplex from Spinach

Electron spin resonance spectroscopy was used to study the mechanism of the singlet oxygen(1O2*) production and scavenging in cytochrome b6f complex(Cyt b6f) of spinach.The results showed that under white-light illumination and aerobic conditions,1O2* was detected in isolated Rieske-depleted Cyt b6f and isolated Rieske Fe-S protein,indicating that both Chl a cofactor and Rieske Fe-S protein were responsible for 1O2* formation,with Chl a being the major source.This conclusion was further corroborated by 1O2* formation under selective excitation of Chl a by using monocolor red light at 675 nm.Furthermore,1O2* was scavenged by adding antioxidative substance such as L-histidine,ascorbate,β-carotene or glutathione.This offered protection against singlet oxygen oxidation of Cyt b6f complex.

Synthesis, physical–chemical properties and in vitro photodynamic activity against oral cancer cells of novel porphyrazines possessing fluoroalkylthio and dietherthio substituents

Novel porphyrazines possessing fluoroalkylthio and dietherthio peripheral substituents were synthesized and tested from the peripheral substituent effects on their physical–chemical properties, including metal binding abilities and solvatochromic effects. Two porphyrazines were subjected to singlet oxygen generation measurements using 1,3-diphenylisobenzofuran as a singlet oxygen scavenger and examined in vitro towards oral cancer cells. Biological investigation performed on two human squamous carcinoma cell lines derived from the tongue (HSC-3) and from the buccal mucosa (H413) revealed moderate activity and selectivity of novel magnesium(II) porphyrazine possessing peripheral 4-fluorobutylthio substituents.

Plastoquinol is more active than α-tocopherol in singlet oxygen scavenging during high light stress of Chlamydomonas reinhardtii

In the present study, we have performed comparative analysis of different prenyllipids in Chlamydomonas reinhardtii cultures during high light stress under variety of conditions (presence of inhibitors, an uncoupler, heavy water). The obtained results indicate that plastoquinol is more active than α-tocopherol in scavenging of singlet oxygen generated in photosystem II. Besides plastoquinol, also its oxidized form, plastoquinone shows antioxidant action during the stress conditions, resulting in formation of plastoquinone-C, whose level can be regarded as an indicator of singlet oxygen oxidative stress in vivo. The pronounced stimulation of α-tocopherol consumption and α-tocopherolquinone formation by an uncoupler, FCCP, together with the results of additional model system studies, led to the suggestion that α-tocopherol can be recycled in thylakoid membranes under high light conditions from 8a-hydroperoxy-α-tocopherone, the primary oxidation product of α-tocopherol by singlet oxygen.