Chemiluminescence associated with singlet oxygen reactions with amino acids, peptides and proteins

Low level chemiluminescence (CL) is observed after protein oxidation mediated by singlet oxygen produced in Rose Bengal (RB) irradiation. This CL lasts for several minutes after the end of the photolysis. In this work, the mechanism of the process was assessed from the spectral characteristics of the CL and the effect of antioxidants (Trolox or ascorbate), Ebselen (a compound with peroxidase-like activity), azide (a singlet oxygen scavenger) and D2O, added prior to or after RB irradiation. It is concluded that most of the light emission is due to formation of excited states generated in the decomposition of peroxides and/or hydroperoxides accumulated during the photolysis. Experiments carried out in the presence of several amino acids (Cys, Met, His, Tyr and Trp) and di- and tripeptides suggest that peroxides (and/or hydroperoxides) of Trp residues are mainly responsible for the CL observed after singlet oxygen-mediated protein oxidation. The much weaker CL observed after the oxidation of proteins without Trp residues supports this conclusion. A comparison of the results obtained employing free Trp, Ala-Trp and Trp-Ala dipeptides, Ala-Trp-Ala tripeptide and Trp-containing proteins supports the conclusion that blocking the amino group of the Trp moiety strongly increases the efficiency of the chemiluminescent process, producing approximately 2.5x10(-8) photons per oxidized Trp group in Ala-Trp. A mechanism comprising two chemiluminescent oxidation pathways of Trp residues is proposed to explain the results.     

Chemiluminescence from singlet oxygen under laminar flow condition in a micro-channel

Singlet oxygen was generated by reaction of sodium hypochlorite and hydrogen peroxide in a micro-channel. The two reagent solutions were delivered into the micro-channel by syringe pumps, providing a laminar flow. Such a laminar flow forms a liquid–liquid interface instantly in a micro-channel, and then the interface collapses gradually through molecular diffusion with the residence times. The chemiluminescence from the singlet oxygen was emitted in the course of the collapse of the interface under laminar flow condition. The chemiluminescence intensity was observed continuously and stably in the micro-channel as long as the reagents were fed into the channel. We examined the features of the chemiluminescence emitted in the micro-channel by changing the flow rates of reagents and the detection points in the micro-channel. The data obtained were considered along with the residence times and diffusion lengths. We also examined the effects of antioxidants, such as sodium azide, histidine, nitroblue tetrazolium, and 2-propanol on the chemiluminescence intensity.     

Synthesis and application of alkenylstannanes derived from base-sensitive cyclopropenes

In the presence of stoichiometric potassium fluoride, a range of base-sensitive cyclopropenes undergo direct stannylation using (pentafluoroethyl)tributylstannane. The resulting stannylcyclopropenes serve as precursors to a variety of tetrasubstituted cyclopropenes that might otherwise be difficult to access using alternative methods.     

Chemiluminescence from singlet oxygen that was detected at two wavelengths and effects of biomolecules on it

We developed the detection apparatus that equipped with the two-photomultiplier tubes for chemiluminescence from singlet oxygen. Singlet oxygen was generated with reaction between sodium hypochlorite and hydrogen peroxide. The chemiluminescence from singlet oxygen, the dimol light emission (ca. 634 nm) and the monomol light emission (ca. 1270 nm), was observed simultaneously for the same reaction cell. The effects of sodium azide as an antioxidant, human serum albumin, and α-amino acids on the chemiluminescence based on the both emissions were examined; the observed chemiluminescence could provide direct information with regard to the reaction between singlet oxygen and antioxidant/biomolecules. The apparent rate constants for quenching singlet oxygen in the presence of human serum albumin were calculated to be ca. 3.3 × 10⁹ and ca. 8.8 × 10⁸ M⁻¹ s⁻¹ for the dimol and monomol light emissions, respectively, under the present conditions. The chemiluminescence intensities of the dimol emission decreased in the presence of His, Asp, Phe, Ser, and Tyr, and that of the monomol decreased in the presence of Cys and Trp. The chemiluminescence observed in the presence of biomolcules was discussed together with the reactivities of sodium hypochlorite and hydrogen peroxide to biomolecules.     

Biological consequences associated with DNA oxidation mediated by singlet oxygen.

Singlet oxygen is a major oxidative species that can be generated by numerous biological processes such as photosensitization. This oxidant can react with deoxyguanosine and with guanine in deoxyribonucleic acid (DNA) leading to the induction of at least four different reaction products such as 4,8-dihydro-4-hydroxy-8-oxodeoxyguanosine and 7,8-dihydro-8-oxodeoxyguanosine. The induction of true single-stranded breaks in the oxidated DNA is still a matter of controversy and is not yet clearly established. This paper focuses mainly on several biological consequences which can be associated with the induction of DNA lesions by singlet oxygen. Oxidated DNA loses its transformation efficiency probably because unrepaired lesions can partially inhibit DNA replication. Mutagenesis is one of the main effects induced by guanine oxidation products. Molecular analysis of mutated genes reveals that G to T transversions are the most frequent mutations; these are probably introduced in DNA by misincorporation of deoxyadenosine monophosphate (dAMP) opposite to the lesion. Efficient repair of these oxidated guanine residues can take place via specific glycosylase, endonuclease or the SOS network. However, the data concerning the toxicity of singlet oxygen for eukaryotic cells are not frequent enough in the literature to draw a clear picture of the effects of this activated species in several biologically revelant phenomena.     

Chemistry of singlet oxygen with arylphosphines

The chemistry of singlet oxygen with a variety of arylphosphines has been studied. Rates of singlet oxygen removal by para-substituted arylphosphines show good correlation with the Hammett σ parameter (ρ=−1.53 in CDCl₃), and with the Tolman electronic parameter. The only products for the reactions of these phosphines with singlet oxygen are the corresponding phosphine oxides. Conversely, for ortho-substituted phosphines with electron-donating substituents, there are two products, namely a phosphinate formed by intramolecular insertion and phosphine oxide. Kinetic analyses demonstrate that both products are formed from the same intermediate, and this allows determination of the rate ratios for the competing pathways. Increasing the steric bulk of the phosphine leads to an increase in the amount of insertion product. VT NMR experiments show that peroxidic intermediates can only be detected for very hindered and very electron-rich arylphosphines.     

Reactions of singlet oxygen with biomolecules

Rate constants of singlet oxygen quenching by glycyrrhetic acid, glycyrrhizic acid, isoliquiritigenin, licurazide,d-glucose, andl-arabinose were determined. An increase in the quenching rate constants by more than an order of magnitude is observed on going from aglycone to the corresponding glycoside.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 57–59, January, 1996.     

Optical detection of singlet oxygen from single cells

The lowest excited electronic state of molecular oxygen, singlet molecular oxygen, O(2)(a (1)Delta(g)), is a reactive species involved in many chemical and biological processes. To better understand the roles played by singlet oxygen in biological systems, particularly at the sub-cellular level, optical tools have been developed to create and directly detect this transient state in time- and spatially-resolved experiments from single cells. Data obtained indicate that, contrary to common perception, this reactive species can be quite long-lived in a cell and, as such, can diffuse over appreciable distances including across the cell membrane into the extracellular environment. On one hand, these results demonstrate that the behavior of singlet oxygen in an intact cell can be significantly different from that inferred from model bulk studies. More generally, these results provide a new perspective for mechanistic studies of intra- and inter-cellular signaling and events that ultimately lead to photo-induced cell death.     

Quantum‐chemical study of the singlet oxygen emission

Intensity distribution in rotational lines of the 0–0 band of the a¹Δ_g → X³Σ transition in the oxygen molecule at λ = 1270 nm is studied by quadratic response (QR) method in a framework of multiconfiguration self‐consisted field (MCSCF) theory. The distance dependence of the transition magnetic moment and the (0–0)/(0–1) bands intensity ratio are calculated. A short review of previous theory of the red and infrared atmospheric oxygen bands and of their enhancement by collisions is presented to analyze and compare the new results. Enhancement of these bands in O₂ collisions with Li₂ and N₂ molecules is calculated by QR method. Diamagnetic species simulate solvent molecules of different optical polarizability. Specific influence of collisions on vibronic bands is stressed. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Synthesis of endoperoxides derived from cyclooctatetraenes via singlet oxygenation

Cyclooctatetraene (1) reacted with photo-generated singlet oxygen to give the endoperoxide 7,8-dioxabicyclo[4.2.2]deca-2,4,9-triene (1a), which was further transformed to the cis-diepoxide 1b by catalytic rearrangement with Co-TTP to the unsaturated cis-diol 1c and the saturated cis-diol 1d by catalytic hydrogenation, to the saturated endoperoxide 1e by reaction with diimide, and to the epoxycyclooclatetraene If by deoxygenation with dimethylphosphine. Similarly, the methoxy-, phenyl- and methyl-substituted cyclooctatetraenes 3-5, respectively, gave the corresponding endoperoxides with the substituents located at the 1-position (3a, 5a), the 2-position (5b) and the 9-position (3b, 4a). Their structures were determined on the basis of their ¹H- and ¹³C-NMR data and by means of chemical transformation to the corresponding syn-diepoxides, i.e. 5,10-dioxatricyclo[7.1.0.0^4,6]deca-2,7-dienes. The formation of the endoperoxides is postulated to involve an electron transfer mechanism to give the radical cation of cyclooctatetraene and the superoxide ion. The latter couples into the homotropylium-type zwitterionic intermediate and subsequent cyclization leads to the endoperoxides.     

Reactions of singlet oxygen with polyisoprene and model compounds

Results from the study of singlet oxygen reaction with cis-1,4-polyisoprene and with various models are compared. The nature of the products and their reactivity are discussed for two kinds of models, namely oligodienes and trisubstituted mono-olefins with various substituent length. The reactivity of the double bond decreases with lengthening of the alkyl substituents but the reactivity of 4-methyl-4-octene is close to that of the polymer. The hydroperoxidation of a unit in an oligodiene does not deactivate significantly the adjacent units towards singlet oxygen addition. The reactivity of the allylic hydrogen a, b, and c in the olefin

depends on both the position and the length of the substituents and follows the sequences K _c > k _b > k _a. The principle of syn-ene addition can be extrapolated to polyisoprene. The rate constant determined for the cis-1,4-polyisoprene ¹O₂ reaction allows the conclusion that the probability of reaction of ¹O₂ with the solid polymer may be high. Similarity in the behaviour of polymer and models in this reaction allows for the estimation of the reactivity of other unsaturated or reactive polymers towards ¹O₂.     

Photogeneration of the free radicals and singlet oxygen by chrysophanol from rheum

Chrysophanol (3-methyl-1,8-dihydroxyanthraqui-none) belongs to a family of anthraquinone pigmentsthat naturally exist in many kinds of plants, such asrheum, a Chinese herbal medicine growing abundantlyin China. Besides their biological activities, thesepigments are also well known as photosensitizers[1,2].Photosensitizers are able to photochemically producehighly reactive species, such as O2, O2 , ?OH, and 1 ??induce a series of damage to biologic…     

New and stable endoperoxide from the pteridin-2,4,7-trione and singlet oxygen

1,3,8-Trimethyl-6-phenylpteridin-2,4,7-trione (1) reacted with singlet oxygen to give the pteridin-2,4,7-trione 6,8′-endoperoxide (2), which on warming generates singlet oxygen. Generation of singlet oxygen from thermolysis of the endoperoxide (2) was confirmed by trapping experiments using typical singlet oxygen acceptors.     

Intermediates in the reaction of singlet oxygen with trisubstituted oxazoles

Trisubstituted oxazoles I react at ?15° with singlet oxygen to give dioxazoles III and iminoanhydrides V which rearrange at room temperature to triamides VI. The intermediate ratio (III/V) is sensitive to the reaction temperature. It is likely that at room temperature triamides VI are essentially formed via imino-anhydrides V.     

Reaction of singlet oxygen with some benzylic sulfides

Product distribution, total quenching rate (k_T), and rate of chemical reaction (k_r) with singlet oxygen have been determined for some alkyl, benzyl, α-methylbenzyl, and cumyl sulfides. Their contributions depend on the steric hindering around the sulfur atom. In protic solvents, the sulfoxide is the main product via a hydrogen-bonded persulfoxide. In apolar solvents, intramolecular α-H abstraction leads to oxidative C-S bond cleavage, with varying efficiency. The behavior of sulfides is compared to that of alkenes and amines.