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PubMed1989

Singlet oxygen formation in monomeric and aggregated porphyrin c.

The absorption and fluorescence spectra of monomeric and aggregated species present in aqueous solutions of porphyrin c have been resolved by steady-state and time-resolved spectroscopy. The dependence of the singlet oxygen formation yield (phi delta) on excitation wavelength has also been determined. In the Q-band spectral region, the aggregate absorption and emission spectra are shifted to longer wavelengths with respect to the monomer spectrum with phi delta (monomer) = 0.59 and phi delta (aggregate) = 0.33. The relevance of these findings to the optimization of irradiation conditions in tumour phototherapy using porphyrin c are discussed.

Chemical Phenomena↗

PubMed1991

Chemically induced Parkinson's disease. III: A study of a possible role of singlet molecular oxygen in Parkinson's disease.

The near IR emission at 1270 nm following pulsed laser excitation of methylene blue in deuterium oxide, was used to study the interaction of a singlet molecular oxygen (1O2) with (i) 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and its oxidation products, and (ii) biosubstrates of relevance in Parkinson's disease. Steady state irradiation of methylene blue and MPTP led to a product with an absorption profile consistent with that of 1-methyl-4-phenyl-2,3-dihydropyridinium ion. This may suggest that even if monoamine oxidase enzyme activity is inhibited by the use of drugs such as Deprenyl and Paragyline the underlying conversion of MPTP to its neurotoxic oxidation product via 1O2 may still take place.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMed2006

Limited sensitivity of pigment photo-oxidation in isolated thylakoids to singlet excited state quenching in photosystem II antenna.

Light-induced pigment oxidation and its relation to excited state quenching in photosystems antennae have been investigated in isolated thylakoids. The results indicate that (i) chlorophyll oxidation takes place in two sequential steps. A slow initial phase is followed by a steep increase in the bleaching rate when more than one quarter of the chromophores are oxidised. (ii) During the initial slow phase, the carotenoid pool is bleached with an apparent rate which is about three times faster than that found for chlorophyll a and more than six times faster than that of chlorophyll b. (iii) Pigment bleaching has been observed both in photosystem I and photosystem II, and it has been possible to estimate a similar carotenoid bleaching rate in the two photosystems. (iv) The protection conferred by singlet state quenchers in the initial slow phase of pigment oxidation is modest. Taking into consideration that both the photosystems are subjected to the oxidative treatment, a somewhat larger protective effect than those estimated for photo-inhibition in thylakoids [S. Santabarbara, F.M. Garlaschi, G. Zucchelli, R.C. Jennings, Biochim. Biophys. Acta 1409 (1999) 165-170] can be computed, although it is less than 50% of the expected level on the basis of the observed reciprocity to the number of incident photons. (v) Pigment oxidation is associated with the loss of membrane ultra-structure, which is interpreted as originating from a decrease in grana stacking. The dynamics of loss of membrane ultra-structure parallel the phases observed for chlorophyll photo-bleaching.

Carotenoids↗

PubMed2005

Towards elucidating the energy of the first excited singlet state of xanthophyll cycle pigments by X-ray absorption spectroscopy.

The first excited singlet state (S(1)) of carotenoids (also termed 2A(g)(-)) plays a key role in photosynthetic excitation energy transfer due to its close proximity to the S(1) (Q(y)) level of chlorophylls. The determination of carotenoid 2A(g)(-) energies by optical techniques is difficult; transitions from the ground state (S(0), 1A(g)(-)) to the 2A(g)(-) state are forbidden ("optically dark") due to parity (g <-- //--> g) as well as pseudo-parity selection rules (- <-- //--> -). Of particular interest are S(1) energies of the so-called xanthophyll-cycle pigments (violaxanthin, antheraxanthin and zeaxanthin) due to their involvement in photoprotection in plants. Previous determinations of S(1) energies of violaxanthin and zeaxanthin by different spectroscopic techniques vary considerably. Here we present an alternative approach towards elucidation of the optically dark states of xanthophylls by near-edge X-ray absorption fine structure spectroscopy (NEXAFS). The indication of at least one pi* energy level (about 0.5 eV below the lowest 1B(u)(+) vibronic sublevel) has been found for zeaxanthin. Present limitations and future improvements of NEXAFS to study optically dark states of carotenoids are discussed. NEXAFS combined with simultaneous optical pumping will further aid the investigation of these otherwise hardly accessible states.

Spectrophotometry, Ultraviolet↗

PubMed2004

Quantum-chemical study of the structure of the acetyl fluoride molecule in the ground and lowest excited singlet and triplet electronic states.

The structure of the conformationally flexible acetyl fluoride molecule (CH3CFO and CD3CFO) in the ground (S0) and lowest excited triplet (T1) and singlet (S1) electronic states was calculated by different quantum-chemical methods (RHF, UHF, MP2, CASSCF). The equilibrium geometric parameters and harmonic vibrational frequencies of the molecules in these electronic states were estimated. The calculations demonstrated that the electronic excitation causes considerable conformational changes involving the rotation of the CH3(CD3) top and a substantial deviation of the CCFO carbonyl fragment from planarity. For large-amplitude vibrations, namely, for the torsional vibration in the S0 state and the torsional and inversion (nonplanar carbonyl fragment) vibrations in the T1 and S1 states, the quantum-mechanical problems were solved in one-dimensional (1D) and two-dimensional (2D) approximations. The results of calculations are in good agreement with experimental data.

Acetaldehyde↗

PubMed2005

Calculation of the fine structure and intensity of the singlet-triplet transitions in the imidogen radical.

The singlet-triplet transition moments are calculated for the NH radical by multiconfiguration self-consistent field (MCSCF) method with a quadratic response (QR) technique. The band systems in the visible region (b(1)Sigma(+)-->X(3)Sigma(-) and a(1)Delta-->X(3)Sigma(-)) of the NH radical are analyzed in comparison with previous ab initio treatments and with the recent experimental data in attempt to solve some discrepancies. The b(1)Sigma(+)-->X(3)Sigma(Omega)(-) transition moments ratio for the two spin sublevels Omega = 1 and Omega=0 of the ground state is well reproduced and the radiative lifetime of the b(1)Sigma(+) state (tau(b)=58 ms) is obtained in a good agreement with the experimental value tau(b)=53((-13)(+17)) ms. The A(3)Pi<--a(1)Delta transition probability is calculated for the first time and found to be in an excellent agreement with the recent optical pumping measurements of the NH radical in a molecular beam, where population transfer from the metastable a(1)Delta state to the ground X(3)Sigma(-) state is achieved. For the a(1)Delta-->X(3)Sigma(-) transition some improvement is achieved in comparison with the previous ab initio results, but the calculated radiative lifetime (tau(a)=3.9 s) is still much lower than the recent measurement provides (tau(a)=12.5 s). The zero field splitting and spin-rotation coupling constants are calculated for the ground state by different methods and advantage of the density functional theory is stressed.

Free Radicals↗

PubMed2006

Photo-irradiation of Aloe vera by UVA--formation of free radicals, singlet oxygen, superoxide, and induction of lipid peroxidation.

Aloe vera whole leaf extracts are incorporated into a wide variety of topically applied commercial products. Aloe vera whole leaf extracts may contain anthraquinones, which have been shown to generate reactive oxygen species in the presence of ultraviolet A (UVA) light. Exposure to UVA light alone can also generate reactive oxygen species and is associated with photo-damaged and photo-aged skin in humans. This paper examines the photochemical properties of two Aloe vera whole leaf extracts that differed in their anthraquinone content. In the presence of methyl linoleate, the UVA irradiation of Aloe vera leaf extracts induced lipid peroxidation. The amounts of lipid peroxides formed were higher in the Aloe vera leaf extract that contained lower amounts of anthraquinones. Superoxide dismutase and sodium azide inhibited and deuterium oxide enhanced the formation of lipid peroxides, suggesting that singlet oxygen and superoxide were involved in the mechanism. Spin trapping electron spin resonance (ESR) spectroscopy was used to investigate the generation of free radicals by the UVA photo-irradiated Aloe vera plant extracts. ESR measurements indicated that the UVA photo-irradiation of Aloe vera plant extracts produced carbon-centered free radicals. These results suggest that humans exposed to products that contain Aloe vera whole leaf extracts may have enhanced sensitivity to ultraviolet light.

Aloe↗

PubMed2001

Evaluation of the energetic position of the lowest excited singlet state of beta-carotene by NEXAFS and photoemission spectroscopy.

In carotenoids the lowest energetic optical transition belonging to the pi-electron system is forbidden by symmetry, therefore the energetic position of the S(1) (2(1)A(g)) level can hardly be assessed by optical spectroscopy. We introduce a novel experimental approach: For molecules with pi-electron systems the transition C1s-->2p(pi*) from inner-atomic to the lowest unoccupied molecular orbital (LUMO) appears in X-ray absorption near edge spectra (NEXAFS) as an intense, sharp peak a few eV below the carbon K-edge. Whereas the peak position reflects the energy of the first excited singlet state in relation to the ionization potential of the molecule, intensity and width of the transition depend on hybridization and bonding partners of the selected atom. Complementary information can be obtained from ultraviolet photoelectron spectroscopy (UPS): At the low binding energy site of the spectrum a peak related to the highest occupied molecular orbital (HOMO) appears. We have measured NEXAFS and UPS of beta-carotene. Based on these measurements and quantum chemical calculations the HOMO and LUMO energies can be derived.

Electron Probe Microanalysis↗

PubMed2003

The CRG1 gene required for resistance to the singlet oxygen-generating cercosporin toxin in Cercospora nicotianae encodes a putative fungal transcription factor.

The Cercospora nicotianae CRG1 gene is involved in cellular resistance to the perylenequinone toxin, cercosporin, that generates highly toxic singlet oxygen upon exposure to light. The entire open reading frame (ORF) of CRG1 was isolated and sequenced. The gene contains an ORF of 1950bp including a 65-bp intron. The predicted 650 amino acid CRG1 protein contains a Cys(6)Zn(2) binuclear cluster DNA-binding motif with homology to various fungal regulatory proteins, indicating that CRG1 may act functionally as a transcription activator. Targeted gene disruption of CRG1 resulted in mutants that are partially sensitive to cercosporin and reduced in cercosporin production. Genetic complementation revealed that CRG1 fully restored cercosporin resistance, but only slightly restored cercosporin production in a UV-derived mutant (CS10) containing a single nucleotide substitution in crg1. Complementation of a crg1-null mutant, however, yielded strains that are similar to the wild-type in both phenotypes. These results indicate that the transcription regulator CRG1 is involved in the activation of genes associated with cercosporin resistance and production in the fungus Cercospora nicotianae.

Amino Acid Sequence↗

PubMed1983

Further study discounts role for singlet oxygen in fungal degradation of lignin model compounds.

This study reexamined our contention that singlet oxygen (1O2) plays a role in the fungal degradation of lignin (BBRC 102(1981)484). Cultures of Phanerochaete chrysosporium and a photochemical 1O2-generating system (riboflavin/light/O2) cleaved a lignin substructure model compound, 1,2-bis(4-methoxyphenyl)propane-1,3-diol (I), by indistinguishable mechanisms. However, the rate of cleavage of I in D2O was the same as in H2O in the photochemical 1O2-generating system, indicating that 1O2 was not involved. Furthermore, products formed from I in a chemical system for generating 1O2 (H2O2 + NaOCl) differed from those produced by cultures or the photochemical system. It is concluded that 1O2 is not responsible for cleavage of I or related compounds in the fungal cultures or in the photochemical system.

Chemical Phenomena↗

PubMed2001

Singlet oxygen generation from phosphatidylcholine hydroperoxide in the presence of copper.

This study pursued whether singlet oxygen ((1)O2) is generated from phosphatidylcholine hydroperoxide (PCOOH), the oxidized modification product of a major constituent of biomembranes and serum lipoproteins. The (1)O2 formation was detected, by utilizing the oxidation of 2,2,6,6-tetramethyl-4-piperidone (TMPD) by (1)O2 to yield 2,2,6,6-tetramethyl-4-piperidone-1-oxyl (TEMPONE), which generates electron spin resonance (ESR) signals. The TEMPONE signal was detected in human plasma with addition of PCOOH by ESR determination after introducing copper(II). The TEMPONE formation was proportional to the amounts of PCOOH added according to moles of active oxygen. The TEMPONE signal intensity was weakened significantly in the presence of beta-carotene and histidine in a concentration-dependent manner, but was not at all decreased by mannitol, Mn-superoxide dismutase and catalase. In addition, HPLC-chemiluminescence analysis demonstrated that incubation with the PCOOH/Cu(II) combination oxidized cholesterol, a relatively oxidation-resistant component, to the cholesterol hydroperoxide. These results reveal that (1)O2 is generated from PCOOH in contact with copper(II). In conclusion, this in-vitro study provides directly the (1)O2 formation in living organisms following the advancement of peroxidation of constitutive lipids.

Catalase↗

PubMed2003

Aqueous photodegradation of fenthion by ultraviolet B irradiation: contribution of singlet oxygen in photodegradation and photochemical hydrolysis.

The objective of this study was to evaluate the photodegradation of the organophosphorus pesticide fenthion in the environment from a human health effect viewpoint. The major photodegradation products of fenthion in an aqueous solution under UVB irradiation (280-320nm radiation) were identified as fenthion sulfoxide, 3-methyl-4-methylthiophenol (MMTP), dimethyl phosphorothioate and 3-methyl-4-methylsulfinylphenol (MMSP). MMTP, dimethyl phosphorothioate and MMSP were discovered as novel photodegradation products of fenthion. Kinetic analysis of these products showed the formation of MMTP and dimethyl phosphorothioate by the photochemical hydrolysis of fenthion, which was accelerated under alkaline conditions. The former was further oxidized to MMSP. Fenthion sulfoxide was directly produced by the oxidative reaction of fenthion. Contribution of dissolved oxygen in this photooxidation was observed by replacing the air with nitrogen gas in the reaction system, which prevented oxidative formation of fenthion sulfoxide from fenthion and MMSP from MMTP. These oxidative compounds were also formed from fenthion in the presence of singlet oxygen (1O2) generated by the visible light irradiation of rose bengal solution, while 1O2 scavengers, L-histidine and sodium azide (NaN3) inhibited this reaction. The aqueous photolysis mechanisms of fenthion were proposed from a kinetic photolysis experiment study as follows: there were two kinds of UVB photodegradation pathways of fenthion, one being photochemical hydrolysis of the phosphorus-O-phenyl ester to form MMTP and dimethyl phosphorothioate, and the other oxygenation triggered by 1O2 and producing fenthion sulfoxide and MMSP. Therefore, the steady photodegradation products of fenthion in the water environment may be fenthion sulfoxide and MMSP.

Fenthion↗

PubMed2001

Formation of singlet oxygen during farmorubicin oxidation.

The enhanced generation of singlet oxygen (1O2) during oxidation of farmorubicin in the Co(II) + H2O2 system was studied using chemiluminescent, fluorescent and spectrophotometic techniques. The influence of 1O2-quenchers, catalase, superoxide anion radical (O2*-) and hydroxyl radical (HO*) scavengers on the light emission was studied. The spectrophotometric determination of 1O2 was based on bleaching of p-nitrosodimethylaniline caused by an intermediate product of the reaction of 1O2 with imidazole, and was followed by monitoring the decrease in optical density at 440 nm.

Antibiotics, Antineoplastic↗

PubMed2000

Effect of singlet oxygen generating substances on the ascorbic acid and glutathione content in pea leaves.

Ascorbate and glutathione levels were investigated in pea leaf discs exposed to various singlet oxygen generating compounds: eosin, rose bengal, monuron, acifluorfen and 5-amino-levulinic acid (ALA). The cellular level of the major antioxidant ascorbate was markedly decreased by the herbicides monuron, acifluorfen and ALA (in light-dependent reactions), as well as by the xanthene dyes eosin and rose bengal (independently of light). No significant accumulation of dehydroascorbate could be observed in any treatments. In contrast to ascorbate, the foliar glutathione levels were considerably increased by subtoxic or slightly toxic concentrations of eosin, rose bengal, acifluorfen and ALA in a light-dependent manner. Monuron treatments led to unchanged or decreasing glutathione contents. The activities of three antioxidative enzymes (ascorbate peroxidase, glutathione reductase and glutathione S-transferase) were also induced by eosin in light-dependent reactions.

Journal Article↗

PubMed1996

Receptor inactivation by dye-neuropeptide conjugates: 2. Characterization of the quantum yield of singlet oxygen generated by irradiation of dye-neuropeptide conjugates.

Different neuropeptide analogues of the neurotransmitter FMRFamide were covalently attached to a tethered dye, forming dye-neuropeptide conjugates capable of stably binding to the FMRFamide receptors. Singlet oxygen (1 delta O2) generated by laser irradiation of the conjugates bound to this receptor should inactivate it if (a) the distance 1 delta O2 must diffuse to reach the photo-sensitized receptor is less than 1000 A, (b) the conjugate binds the receptor with the same affinity as the indigenous neurotransmitter, and (c) the quantum yield (phi) of 1 delta O2 is sufficient. Previous studies determined that the first two constraints are satisfied. The results of the present study confirm that the third constraint is also satisfied, as the phi of 1 delta O2 resulting from the laser irradiation of the conjugates were uniformly large, exceeding those for the dye itself, ranging from 0.25 at pD 6.0 to 0.93 at pD 9.0.

Animals↗

PubMedDate not supplied

Time-resolved detection of singlet oxygen luminescence in red-cell ghost suspensions: concerning a signal component that can be attributed to 1O2 luminescence from the inside of a native membrane.

For about ten years, it has been debated whether in principle it is possible to detect 1O2 located within the cell membrane by performing experiments with cell suspensions or even in tissue. In this paper we present our investigations on photosensitized red-cell ghost suspensions (RCGSs) and our strategy for the detection of luminescence of singlet oxygen (1O2) from the inside of the cell membrane. Using a very sensitive apparatus for time-resolved 1O2 detection, a very promising sensitizer and an adequate experimental strategy, a very small amount of the detected luminescence indeed can be attributed to 1O2 from the inside of the ghost membrane.

Erythrocyte Membrane↗

PubMed2000

Reinvestigation of the triplet-minus-singlet spectrum of chloroplasts.

A comparison of the triplet-minus-singlet (TmS) absorption spectrum of spinach chloroplasts, recorded some thirty years ago, with the more recently published TmS spectrum of isolated Chla/b LHCII (light-harvesting complexes associated with photosystem II of higher plants) shows that the two spectra are very similar, which is to be expected, since only the carotenoid pigments contribute to each spectrum. Be that as it may, the comparison also reveals a dissimilarity: photoexcitation of the sample does, or does not, affect the absorbance in the Qy region (650-700 nm), depending on whether the sample is a suspension of chloroplasts or of isolated LHCII. The Qy-signal in the TmS spectrum of LHCII decays, it should be noted, at the same rate as the rest of the difference spectrum, and its most prominent feature is a negative peak. As the carotenoids do not absorb in the Qy region, the presence of a signal in this region calls for an explanation: van der Vos, Carbonera and Hoff, the first to find as well as fathom the phenomenon, attributed the Qy-signal to a change, in the absorption spectrum of a chlorophyll a (Chla) molecule, brought about by the presence of triplet excitation on a neighbouring carotenoid (Car). The difference in the behaviours of chloroplasts and LHCII, if reproducible, would imply that the Car triplets which give rise to the TmS spectrum of chloroplasts do not influence the absorption spectra of their Chla neighbours. With a view to reaching a firm conclusion about this vexed issue, spinach chloroplasts and thylakoids have been examined with the aid of the same kinetic spectrometer as that used for investigating LHCII; the TmS spectra of both chloroplasts and thylakoids contain prominent bleaching signals centred at 680 nm, and the triplet decay time in each case is comparable to that of the Chla/b LHCII triplets. Results pertaining to other closely related systems are recalled, and it is concluded that, so far as the overall appearance of the TmS spectrum is concerned, spinach chloroplasts are by no means abnormal.

Carotenoids↗

PubMed2000

Coupling photochemical reaction detection based on singlet oxygen sensitization to capillary electrochromatography

Despite the impressive separation efficiency afforded by capillary electrochromatography (CEC), the detection of UV-absorbing compounds following separation in capillary dimensions remains limited by the short path length (5-75 microm) through the column. Moreover, analytes that are poor chromophores present an additional challenge with respect to sensitive detection in CEC. This paper illustrates a new photochemical reaction detection scheme for CEC that takes advantage of the catalytic nature of type II photooxidation reactions. The sensitive detection scheme is selective toward molecules capable of photosensitizing the formation of singlet molecular oxygen (1O2). Following separation by CEC, UV-absorbing analytes promote groundstate 3O2 to an excited state (1O2) which reacts rapidly with tert-butyl-3,4,5-trimethylpyrrolecarboxylate, which is added to the running buffer. Detection is based on the loss of pyrrole. The reaction is catalytic in nature since one analyte molecule may absorb light many times, producing large amounts of 1O2. The detection limit for 9-acetylanthracene, following separation by CEC, is approximately 6 x 10(-9) M (S/N = 3). Optimization of the factors effecting the S/N for four model compounds is discussed.

Journal Article↗