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PubMedDate not supplied

Singlet oxygen in plants--its significance and possible detection with double (fluorescent and spin) indicator reagents.

Direct detection of reactive oxygen species (ROS), especially singlet oxygen, in plants under stress conditions is of special importance, not only to identify primary events of oxidative damage, but also in studies exploring the potential role of ROS as signal molecules. Due to short life-times and diffusion distances of ROS, these tasks require highly reactive and selective indicator reagents, localized at the presumed site of production. In the present study, we compared four double sensors: ROS indicator reagents in which partial fluorescence quenching of a dansyl moiety occurs as a result of nitroxide radical formation from a sterically hindered amine constituent. Our experiments support the idea that shorter donor-acceptor distances within these molecules result in higher reactivity to ROS. The presence of a diethylaminoethyl side chain resulted in better selectivity to singlet oxygen: reagents lacking such substituent had an additional reactivity to superoxide anions, probably as a result of the formation of zwitterionic structures. Fluorescence localization studies of the indicator reagents in tobacco leaves and in Chlamydomonas cells show promising perspectives of their applications to plant stress studies.

Biology↗
PubMedDate not supplied

Singlet oxygen luminescence dosimetry (SOLD) for photodynamic therapy: current status, challenges and future prospects.

As photodynamic therapy (PDT) continues to develop and find new clinical indications, robust individualized dosimetry is warranted to achieve effective treatments. We posit that the most direct PDT dosimetry is achieved by monitoring singlet oxygen (1O2), the major cytotoxic species generated photochemically during PDT. Its detection and quantification during PDT have been long-term goals for PDT dosimetry and the development of techniques for this, based on detection of its near-infrared luminescence emission (1270 nm), is at a noteworthy stage of development. We begin by discussing the theory behind singlet-oxygen luminescence dosimetry (SOLD) and the seminal contributions that have brought SOLD to its current status. Subsequently, technology developments that could potentially improve SOLD are discussed, together with future areas of research, as well as the potential limitations of this method. We conclude by examining the major thrusts for future SOLD applications: as a tool for quantitative photobiological studies, a point of reference to evaluate other PDT dosimetry techniques, the optimal means to evaluate new photosensitizers and delivery methods and, potentially, a direct and robust clinical dosimetry system.

Animals↗
PubMed2004

Direct optical detection of singlet oxygen from a single cell.

Singlet oxygen has been detected in single nerve cells by its weak 1270 nm phosphorescence (a1deltag --> X3sigmag-) upon irradiation of a photosensitizer incorporated in the cell. Thus, one can now consider the application of direct optical imaging techniques to mechanistic studies of singlet oxygen at the single-cell level.

Animals↗
PubMed1991

[Chemiluminescence decrease of singlet oxygen in NaClO+H2O2 reaction in the presence of different anti-cataract drugs].

Singlet oxygen was produced in chemical reaction NaClO+ H2O2. Action of different well-known anti-cataract drugs on this reaction was studied. There is no doubt that the singlet oxygen chemiluminescence decreases in the presence of Catalin and Baineiting. Finnish Catachrom Ophthan, Vita iodurol (France) and Quinax (USA) have no such effect at all which may be a result of the interaction of these remedies with H2O2 and/or with NaClO.

Acridines↗
PubMed1991

Singlet oxygen induced cerebral vasospasm: an experimental study in rats.

A new experimental model is described which can be used as an alternative to study the effects of subarachnoid hemorrhage (SAH) in rats. Vasospasm of the basilar artery is induced photochemically after transpalatal illumination of intracisternally injected rose bengal in two different rat strains. Singlet oxygen, generated in the subarachnoid space, elicits vasospasm which has been demonstrated angiographically at 90 min and 24 h after photosensitisation. Sprague Dawley rats responded better than Wistar rats. Dilution of rose bengal in water was more vasospastic than dilution of rose bengal in artificial CSF. Since the action of singlet oxygen is similar to that of free radicals, this experiment gives an argument for the hypothesis that free radicals play a leading role in the pathogenesis of cerebral vasospasm after subarachnoid hemorrhage.

Animals↗
PubMed1990

[Decrease of singlet oxygen chemiluminescence by the presence of carnosine].

To test antiradical medicines effect the chemical production of singlet oxygen (NaClO + H2O2) was investigated. The quantity singlet oxygen chemiluminescence was decreased in the presence of Japanese Catalin and Chine Baineiting, antirheumatic Voltaren and less strong Finish Catachrome and Carnosine. American Quinax does not possess such an effect. One of the possible starting mechanisms causing different diseases (atherosclerosis, cataract etc.) is destruction of biomembranes by active forms of oxygen.

Acridines↗
PubMed1988

[Correlation of the rates of singlet oxygen inactivation by phenols and their efficacy in the inhibition of neoplasms induced by benzo(a)pyrene].

Prooxidant states, characterised by an increase in the intracellular concentration of activated forms of oxygen, are able to promote tumors. The inhibitory effects of synthetic phenolic compounds added to the diet of mice on benzo(a)pyrene-induced neoplasia of the forestomach have been determined by Wattenberg et al. The efficiency of this inhibition has been estimated quantitatively for each phenol, using the ratio R of the number of tumors per mouse in the treated group over the number of tumors per mouse in the control group. We have observed a linear correlation between the antitumoral efficiency (1-R) and the logarithm of the rate of quenching of singlet oxygen, k, y, by this family of phenols, log k being itself correlated with the half-wave oxidation potential of the phenols. These correlations suggest a charge transfer mechanism for the inhibition of neoplasia induced by benzo(a)pyrene, B(a)P. It should be pointed out that singlet oxygen can be generated via enzymatic reactions in the dark and thus might play a role in the formation of the ultimate carcinogenic metabolite B(a)P-7, 8-dihydroxy-9, 10-epoxide. The correlations described emphasize the interest in scaling the inhibitors of mutagenicity induced by polycyclic aromatic hydrocarbons with respect to their oxidation potentials. Our result is a first step towards a better understanding of the molecular reactions involved in chemically-induced neoplasia and in its prevention.

Animals↗
PubMedDate not supplied

[Sensibilized dimer luminescence of singlet molecular oxygen in solutions].

With the use of mechanical phosphoroscope the "universal" delayed emission has been found in aerobic solutions of different sensitizers in CCl4. The spectrum of this emission has the main maximum at 703 nm. The luminescence intensity is proportional to the square of the intensity of the exciting light. Removal of oxygen or addition of 10% of acetone led to disappearance of the luminescence. At equal intensities of singlet oxygen generation relative intensities of the 1272 and 703 nm bands differed by several orders of magnitude in solutions of different sensitizers. The energy migration from the molecules responsible for the luminescence to bacteriopheophytin and phtalocyanine has been observed. The luminescence is interpreted as dimol emission of solvated singlet molecular oxygen activated by sensitizer molecules.

Luminescence↗
PubMed1994

A sensitive detection of neutrophil activation by fluorescence quenching of membrane inserted singlet oxygen probe.

Fluorescence emission intensity of 1,3-diphenylisobenzofuran incorporated in polymorphonuclear granulocytes plasma membranes was investigated in basal conditions and during stimulation with different activators. Phorbol myristate acetate, known as the most effective "oxygen burst" inducer, produced a larger decrease in 1,3-diphenylisobenzofuran fluorescence intensity than 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine (platelet activating factor) and N-formyl-methionyl-leucyl-phenylalanine, known as weak stimulants of oxygen uptake. Diphenyl iodonium an inhibitor of leukocyte NADPH oxidase, and the singlet oxygen selective trap alpha-terpinene inhibited the quenching effect of phorbol myristate acetate on 1,3-diphenylisobenzofuran fluorescence. These data suggest formation of singlet oxygen in activated leukocytes and demonstrate that measurement of 1,3-diphenylisobenzofuran fluorescence intensity provides a new sensitive method of detection of neutrophils activation.

Benzofurans↗
PubMed1997

Predictions of mathematical models of tissue oxygenation and generation of singlet oxygen during photodynamic therapy.

Photodynamic therapy (PDT) is a relatively new protocol for cancer treatment which has recently been approved for limited clinical use. Traditionally, the success of treatment with PDT has been compared on the basis of total light delivery. Using the mathematical model of Henning et al. (Radiat. Res. 142, 221-226, 1995), we have determined that when oxygen is not depleted from the tissue, the concentration of singlet oxygen that is generated is directly proportional to the product of the light fluence rate (phi) and the concentration of the photosensitizer (Cs). Therefore, phiCs is an appropriate parameter for comparing the potential success of PDT protocols under these conditions. For a treatment of time t, the observed photodynamic effect resulting from singlet oxygen exposure should be directly related to phiCst. For high phiCs, the model predicts that oxygen depletion occurs within the tumor tissue. As a result, the photodynamic effect is no longer proportional to phiCst. We have expanded the model of Henning et al. to include the changes in oxygen concentration which occur within the capillary as blood flows through the tissue. Our new predictions with the mathematical model for optimal PDT treatment conditions are significantly different from those predicted by the previous models. Predictions of the model are given using parameters relevant for treatment of solid tumors with Photofrin.

Dihematoporphyrin Ether↗
PubMed1997

Hypochlorite reacts with an organic hydroperoxide forming free radicals, but not singlet oxygen, and thus initiates lipid peroxidation.

The mechanism of the reaction of hypochlorite with t-butyl hydroperoxide as a model organic hydroperoxide was studied. The reaction produces chemiluminescence with rate constant 13 +/- 2 mM-1.sec-1. The chemiluminescence of this reaction was compared with that of the hypochlorite reaction with H2O2 where singlet oxygen (1O2) is formed. In the hypochlorite reaction with H2O2, the effect of hypochlorite concentration on the integrated chemiluminescence intensity is quadratic: a red filter with transmission > 600 nm did not significantly decrease the chemiluminescence intensity: substitution of D2O for H2O increased the luminescence intensity 10-fold; infrared monomol emission was observed at 1270 nm. These results confirm the formation of 1O2 during the hypochlorite reaction with H2O2. However, when t-butyl hydroperoxide was used instead of H2O2, the concentration effect significantly differed from quadratic, and the red filter decreased the luminescence intensity by approximately 99%; D2O slightly decreased the luminescence intensity. Finally, addition of t-butyl hydroperoxide to hypochlorite was not associated with monomol emission of 1O2 in the infrared region. The data exclude the possibility of singlet oxygen formation in the hypochlorite reaction with the organic hydroperoxide. According to 1H-NMR spectroscopy, di-t-butyl peroxide is the main product of the hypochlorite reaction with t-butyl hydroperoxide; its production can be explained by radical formation, i.e., by generation of t-butyloxy radical. t-Butyl hydroperoxide and cumene hydroperoxide promoted hypochlorite-induced lipid peroxidation of phospholipid liposomes. The free radical scavenger butylated hydroxytoluene completely inhibited this effect. The data suggest that organic hydroperoxides, always present in certain amounts in vivo, may be the intermediates that interact with hypochlorite-forming free radicals which are initiators of lipid peroxidation.

Free Radicals↗
PubMed1998

Fluoroquinolone antimicrobials: singlet oxygen, superoxide and phototoxicity.

The fluoroquinolone antibacterial agents possess photosensitizing properties that lead to phototoxic responses in both human and animal subjects. The phototoxicity order reported in humans is: fleroxacin > lomefloxacin, pefloxacin >> ciprofloxacin > enoxacin, norfloxacin and ofloxacin. Studies both in vivo and in vitro have related this phototoxicity to the generation of reactive oxygen species including hydrogen peroxide and the hydroxyl radical. We determined the quantum yields of singlet oxygen generation (phi delta) by detection of the singlet oxygen (1O2) luminescence at 1270 nm for several fluoroquinolones, naphthyridines and other structurally related compounds. All the fluoroquinolones examined have low phi delta values ranging from 0.06 to 0.09 in phosphate buffer at pD 7.5. We also determined the 1O2 quenching constants for these compounds and their values were on the order of 10(6) M-1 s-1, except for lomefloxacin whose rate constant was 1.8 x 10(7) M-1 s-1. The phi delta values were significantly decreased in a solvent of lower polarity such as methanol (0.007 < or = phi delta < or = 0.02). The production of 1O2 by these antibiotics did not correlate with the order reported for their phototoxicity. We also measured the photogeneration (lambda > 300 nm) of superoxide by these antibacterials in dimethylsulfoxide using electron paramagnetic resonance and the spin trap 5,5-dimethyl-1-pyrroline N-oxide. Although there is not a one-to-one correspondence between the relative rates of superoxide generation and the phototoxicity ranking of the fluoroquinolones, the more phototoxic compounds tended to produce superoxide at a faster rate. Nevertheless, the magnitudes of the observed differences do not appear sufficient to explain the range of fluoroquinolone phototoxicity potencies in human and animal subjects in general and the high activity of fleroxacin and lomefloxacin in particular. For these latter drugs the photoinduced loss of the F8 atom as fluoride and the concomitant generation of a highly reactive carbene at C-8 provide a more plausible mechanism for their potent phototoxic and photocarcinogenic properties.

Animals↗
PubMed1998

Singlet oxygen- versus nonsinglet oxygen-mediated mechanisms of sensitizer photobleaching and their effects on photodynamic dosimetry.

We report the effects of singlet oxygen (1O2) and non-1O2-mediated sensitizer photobleaching on oxygen consumption and dosimetry during photodynamic therapy (PDT) of sensitized multicell tumor spheroids. We develop a theoretical model for the description of non-1O2-mediated photobleaching resulting from irreversible reactions of the excited singlet or triplet sensitizer populations with cell substrate. We show that the fluence-dependent simple exponential decay expression of sensitizer degradation is not consistent with these mechanisms and, therefore, with any reasonable mechanism that we consider, because we have shown previously that 1O2-mediated photobleaching cannot be described by a simple exponential with a constant photobleaching coefficient (I. Georgakoudi et al., Photochem. Photobiol. 65, 135-144, 1997). Analysis of oxygen microelectrode measurements performed at the edge of Nile blue selenium (EtNBSe)- and protoporphyrin IX (PpIX)-sensitized spheroids during PDT demonstrates that the former drug photobleaches via a non-1O2-mediated mechanism, while the latter is degraded via a 1O2-mediated mechanism. Comparisons of the cytotoxic effects of EtNBSe with those of Photofrin (a drug that is degraded via a 1O2-mediated mechanism) indicate that the lower threshold 1O2 dose and the higher extinction coefficient and 1O2 yield for EtNBSe do not necessarily result in improved photodynamic effects, thus emphasizing the importance of the sensitizer photobleaching mechanism for dosimetry.

Animals↗
PubMed1998

Photoproduction and direct spectral detection of singlet molecular oxygen (1O2) in keratinocytes stained with rose bengal.

In vivo, keratinocyte skin cells are exposed to photooxidative processes, some of which can be mediated by singlet molecular oxygen (1O2), a species that is very difficult to detect spectrally in cells. We photosensitized 1O2 in cultured HaCaT keratinocytes stained with rose bengal (RB) that localizes exclusively inside the keratinocyte hydrophobic regions, as evidenced by strongly red-shifted absorbance and intense fluorescence. We used keratinocytes grown in a monolayer on a plastic coverslip and in suspension. The phosphorescence spectrum (1200-1350 nm) from 1O2 was strongest when the coverslip containing RB-stained keratinocytes was irradiated in air. The spectral intensity decreased when the coverslip was immersed in D2O during irradiation and was almost completely quenched when it was irradiated while immersed in water. Water not only shortens the 1O2 lifetime but also reabsorbs part of the 1O2 phosphorescence, processes that do not occur when 1O2 is produced in a keratinocyte layer exposed to air. Because the RB was inside keratinocytes, singlet oxygen must also be produced inside the keratinocytes. However, the sensitivity to the extracellular environment suggests that most of the detectable 1O2 phosphorescence originates from those 1O2 molecules that escaped from the cell through its membrane into D2O or into the air, where 1O2 has longer lifetimes. Our results confirm directly that 1O2 is indeed photosensitized in living cells by RB. They also suggest that keratinocyte monolayers may be a good cell model to examine in vitro the production of 1O2 by other photosensitizers of environmental and photomedical interest.

Cell Line, Transformed↗
PubMed2001

Theoretical characterization of photoisomerization channels of dimethylpyridines on the singlet and triplet potential energy surfaces.

Photoexcitations and photoisomerizations due to low-lying n pi* and pi pi* excited states of dimethylpyridines are investigated by density functional theory, CASSCF, CASPT2 and MRCI methodologies. Mechanistic details for the formation of Dewar dimethylpyridines and the interconversions of dimethylpyridines are rationalized through the characterization of minima and transition states on the singlet and triplet potential energy surfaces of relevant intermediates. Our present theoretical schemes suggest that Mobius dimethylpyridine intermediate 14 and azabenzvalene intermediate 10 can serve as possible precursors to Dewar dimethylpyridines and singlet phototransposition products, respectively. The calculations suggest that an S1(pi pi*)/S0 conical intersection in dimethylpyridines 2 is involved in the formation of 14. An azabenzvalene 10 might be formed through S2(pi pi*)/S1(n pi*) interaction followed by an S1/S0 decay in dimethylpyridine 6. Calculated barriers of isomerizations from 14 to Dewar dimethylpyridine 7 and from 10 to 4 are 8.4 and 28.5 kcal mol(-1) at the B3LYP/6-311 G** level, respectively. In the suggested triplet multistage transposition mechanism, an out-of-plane distorted geometry 19 due to vibrational relaxation of the T1(3B1) excited state of 3,5-dimethylpyridine 6 is a precursor of the interconversion of 6 to 2.4-dimethylpyridine 4. The formation of a triplet azaprefulvene 21 with a barrier of 20.7 kcal mol(-1) is a key step during the triplet migration process leading to another out-of-plane distorted structure 27. Subsequent rearomatization of 27 completes the interconversion of 6 with 4. Present calculations provide some insight into the photochemistry of dimethylpyridines at 254 nm.

Journal Article↗
PubMed2003

Bonding of multiple noble-gas atoms to CUO in solid neon: CUO(Ng)n (Ng=Ar, Kr, Xe; n=1, 2, 3, 4) complexes and the singlet-triplet crossover point.

Laser-ablated U atoms co-deposited with CO in excess neon produce the novel CUO molecule, which forms distinct Ng complexes (Ng=Ar, Kr, Xe) with the heavier noble gases. The CUO(Ng) complexes are identified through CO isotopic and Ng reagent substitution and comparison to results of DFT frequency calculations. The U[bond]C and U[bond]O stretching frequencies of CUO(Ng) complexes are slightly red-shifted from neon matrix (1)Sigma(+) CUO values, which indicates a (1)A' ground state for the CUO(Ng) complexes. The CUO(Ng)(2) complexes in excess neon are likewise singlet molecules. However, the CUO(Ng)(3) and CUO(Ng)(4) complexes exhibit very different stretching frequencies and isotopic behaviors that are similar to those of CUO(Ar)(n) in a pure argon matrix, which has a (3)A" ground state based on DFT vibrational frequency calculations. This work suggests a coordination sphere model in which CUO in solid neon is initially solvated by four or more Ne atoms. Up to four heavier Ng atoms successively displace the Ne atoms leading ultimately to CUO(Ng)(4) complexes. The major changes in the CUO stretching frequencies from CUO(Ng)(2) to CUO(Ng)(3) provides evidence for the crossover from a singlet ground state to a triplet ground state.

Journal Article↗
PubMed2003

Lanthanum(III)-catalyzed disproportionation of hydrogen peroxide: a heterogeneous generator of singlet molecular oxygen-1O2 (1Deltag)-in near-neutral aqueous and organic media for peroxidation of electron-rich substrates.

The decomposition of hydrogen peroxide into singlet molecular oxygen-(1)O(2) ((1)Delta(g))-in the presence of lanthanum(iii) salts was studied by monitoring its characteristic IR luminescence at 1270 nm. The process was found to be heterogeneously catalyzed by La(III), provided that the heterogeneous catalyst is generated in situ. The yield of (1)O(2) generation was assessed as 45+/-5 % both in water and in methanol. The pH-dependence on the rate of (1)O(2) generation corresponds to a bell-shaped curve from pH 4.5 to 13 with a maximum around pH 8. The study of the influence of H(2)O(2) showed that the formation of (1)O(2) begins as soon as one equivalent of H(2)O(2) is introduced. It then increases drastically up to two equivalents and more smoothly above. Unlike all other metal salt catalyst systems known to date for H(2)O(2) disproportionation, this chemical source of (1)O(2) is able to generate (1)O(2) not only in basic media, but also under neutral and slightly acidic conditions. In addition, this La-based catalyst system has a very low tendency to induce unwanted oxygenating side reactions, such as epoxidation of alkenes. These two characteristics of the heterogeneous lanthanum catalyst system allow non-photochemical (i.e., "dark") singlet oxygenation of substrate classes that cannot be peroxidized successfully with conventional molybdate catalysts, such as allylic alcohols and alkenyl amines.

Journal Article↗
PubMed2002

Singlet energy transfer as the main pathway in the sensitization of near-infrared Nd3+ luminescence by dansyl and lissamine dyes.

In general, sensitization of lanthanide(III) ions by organic sensitizers is regarded to take place via the triplet state of the sensitizers. Herein, we show that in dansyl- and lissamine-functionalized Nd3+ complexes energy transfer occurs from the singlet state of the sensitizers to the Nd3+ center. No sensitized emission was observed in the corresponding complexes with Er3+, Yb3+, and Gd3+ ions. Furthermore, the fluorescence of the sensitizers was quenched only in the Nd3+ complex and not in the complexes with the other ions. Only Nd3+ centers can accept energy from the singlet state of the dyes, because the excited states of Nd3+ have a high spectral overlap with the fluorescence of the dansyl and lissamine sensitizers, and because the selection rules allow a fast energy transfer, which apparently is competitive with the fluorescence.

Journal Article↗