Generation Of Singlet Molecular Oxygen Research Articles

Singlet oxygen generation using PDMS occluded dyes

Several dyes that generate singlet molecular oxygen (1O2) were occluded in polydimethylsiloxane (PDMS). For the homogeneous dyes, this occlusion forms an easy way of heterogenization, whereas it improves the performance of dyes that are heterogenized already in molecular sieves. These systems were investigated for the singlet oxygenation of test substrates, such as 2,3-dimethyl-2-butene and 1-methyl-1-cyclohexene. The PDMS elastomer was selected for its transparent, hydrophobic and permeability characteristics. The elastomer is ‘wrapped’ around the sensitizing system and hence shields the dyes from polar components, such as water, and balances the sorption of solvents and reagents. This results in an enhanced oxygenate yield for water sensitive dyes. Finally, a new porphyrin, 5,15-(2,6-dichlorophenyl)-10,20-(4-allyloxyphenyl)porphyrin, was synthesized and chemically anchored to PDMS, resulting in a highly active heterogeneous singlet oxygen generating system.

Antioxidant properties of natural flavonoids: quenching and generation of singlet molecular oxygen

Summary This paper describes the interaction between photochemically generated singlet molecular oxygen [O2(1Δg)] and a series of naturally occurring flavonoids (FL) (2′,4′‐dihydroxychalcone (I), 2′,4′‐dihydroxy, 3′‐methoxy chalcone (II), 7‐hydroxyflavanone (III) and 7‐hydroxy‐8‐methoxyflavanone (IV) all obtained from Zuccagnia punctata Cav. The properties of these compounds as generators and quenchers of the known oxidative species O2(1Δg), upon direct and dye‐sensitized photoirradiation, were investigated. Time‐resolved phosphorescence detection, and conventional spectroscopic measurements demonstrate that compounds I‐IV are fairly good O2(1Δg) deactivators with overall rate constant for the process of quenching in the range of 3.7 x 106 (IV) to 2.8 × 108 M−1s−1 (I). Because the O2(1Δg) quenching possesses an exclusively physical component, O2(1Δg) scavenging is not accompanied by consumption of the flavonoid. Compounds I, III and IV are poor O2(1Δg) generators upon direct (near UV) photoirradiation, whereas compound II does not generate any of the oxidative species. Experiments measuring inhibition by flavonoids I‐IV of the photosensitized lipid peroxidation employed linoleic acid as a photoxidizable substrate and Rose Bengal and Methylene Blue as photosenstizers. Results demonstrate that the interesting properties of flavonoids I‐IV as O2(1Δg) scavengers cannot be straightforwardly extrapolated to their potential activity as photoprotectors for lipid peroxidation.

Antioxidant properties of natural flavonoids: quenching and generation of singlet molecular oxygen

Antioxidant properties of natural flavonoids: quenching and generation of singlet molecular oxygen

Generation of Singlet Molecular Oxygen from H2O2 with Molybdate-Exchanged Layered Double Hydroxides: Effects of Catalyst Composition and Reaction Conditions

(Mg, Al)-layered double hydroxides (LDHs) with different Mg/Al ratios in the octahedral layer were prepared via the coprecipitation method and were exchanged with varying amounts of molybdate. The composition of the LDH supports and the state of the molybdate in these materials were studied with X-ray diffractometry, X-ray photoelectron spectroscopy and Raman. As was proven by NIR luminescence, aqueous H2O2 is converted at the surface of these catalysts into excited, singlet molecular dioxygen (1O2). The singlet dioxygen diffuses away from the 1O2 generating centers and can perform selective oxygenations, such as endoperoxidations of dienes, or hydroperoxidations of olefins. Catalyst composition and reaction conditions (temperature, solvent) have major effects on the catalyzed 1O2 generation and the subsequent substrate oxygenation. In order to maximize the efficiency of the H2O2 use and to limit the epoxidation side reaction, it is advisable to limit the amount of exchanged molybdate to ∼0.2 mmol per g and to use an LDH with Mg0.9Al0.1 composition in the octahedral layer. The latter material provides the optimum basicity for the catalytic activity of the exchanged molybdate.

Photophysical properties of corrphycenes

The photophysical properties of the Zn salt of octaethylcorrphycene (compound 1) and the doubly protonated octaethylcorrphycene (compound 2) were determined in benzene solutions. Fluorescence spectra and fluorescence quantum yields of ΦF ( 1)=0.03±0.02 and ΦF ( 2)=0.06±0.02 were measured. The triplet–triplet absorption spectra were obtained by means of flash-photolysis experiments. The triplet quantum yield values ΦT ( 1)=0.79±0.08 and ΦT ( 2)=0.82±0.08 were obtained by using laser-induced optoacoustic spectroscopy. The quantum yield of singlet molecular oxygen generation in air-saturated solutions, Φ Δ ( 1)=0.55±0.07 and Φ Δ ( 2)=0.38±0.05, were also measured using time resolved NIR luminescence.

Post-column photochemical reaction detection in liquid chromatography based on photosensitized generation of singlet molecular oxygen: Study of reaction parameters and application to the determination of polychlorinated biphenyls

The parameters effecting the sensitivity and selectivity of a photochemical reaction detection scheme based on the reaction of 3-substituted pyrroles with singlet molecular oxygen (1O2) in HPLC are reported. Polychlorinated biphenyls (PCBs) were chosen as model compounds for the detection scheme. Following separation by reverse-phase chromatography, PCBs are excited by a Hg pen-ray lamp in a crocheted PTFE photochemical reactor. PCBs that are efficient1O2-sensitizers promote ground state O2 (3Σ-3) to an excited state (1Σg+ or1Δg) which rapidly oxidizes 3-substituted pyrroles which are added to the mobile phase. 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 of1O2. Detection limits for 4,4′-dichlorobiphenyl and Aroclors 1242, 1248 and 1254 were improved by 1–2 orders of magnitude over optimized UV-absorbance detection. Configuration of the photochemical reactor and judicious choice of the wavelength used to follow the loss of pyrrole were determined to be the most important factors in terms of sensitivity of the detection scheme. Comparison of three reagents (i.e. 3-substituted-pyrroles) used for trapping1O2 demonstrates the effect of substitution on sensitivity and to some extent selectivity of PCB determination.

Interaction of UV photostabilizers with singlet molecular oxygen ([O 2( 1Δ g)]). The case of 1′-hydroxy-2′-acetonaphthone

The interaction between photochemically generated singlet molecular oxygen [O 2( 1Δ g)] and the relatively recently reported photostable compound, 1′-hydroxy-2′-acetonaphthone (1OH2AN) has been studied. The behavior of the isomer 2′-hydroxy-l-acetonaphthone (2OH1AN) was also investigated for comparative purposes. The former belongs to the family of extremely photostable intramolecular hydrogen bonded systems, much used in polymer photoprotection. Our study analyses the properties of these compounds as generators, by direct photoirradiation, and quenchers of the known oxidative species O 2 ( 1Δ g) upon indirect, dye-sensitized photoirradiation. Time resolved phosphorescence detection of O 2 ( 1Δ g) and polarographic and spectrophotometric measurements demonstrate that both 1OH2AN and 2OH1AN are excellent O 2 ( 1Δ g) quenchers in alkaline media (ionized-phenolic form). Nevertheless the process of quenching has a mainly chemical component, producing photodegradation of both isomers with photooxidation quantum efficiencies of 0.33 and 0.16 for 1OH and 2OH derivatives, respectively. These compounds are poor O 2 ( 1Δ g) quenchers when the molecular (non-ionized) phenolic form predominates through an exclusive O 2 ( 1Δ g)-physical quenching process. The failure of O 2 ( 1Δ g) generation upon direct photoirradiation of 1OH2AN constitutes a desirable condition for a polymer photoprotector against photooxidative damage.

Cholate-interspersed porphyrin–anthraquinone conjugates: Photonuclease activity of large sized, ‘tweezer-like’ molecules

In a new approach towards the development of a ‘dual-wavelength dual-mechanism’ type of photosensitizer for use in photodynamic therapy (PDT), covalently linked bichromophoric systems comprising of porphyrin (P) and anthraquinone (AnQ) subunits have been synthesized and fully characterized by FAB-MS, IR, UV–Visible and 1H NMR methods. The porphyrin donor and the anthraquinone acceptor subunits of these mono- or bis-intercalating hybrid molecules are interspersed with either cholate or polymethylene spacers. There exists minimal ground- and singlet-state interaction between the porphyrin and anthraquinone subunits in the giant-sized, cholate-interspersed P–AnQ systems as revealed by a comparison of their spectroscopic and electrochemical properties with those of the corresponding individual reference compounds. On the other hand, quenching of fluorescence observed for the P–AnQ systems endowed with polymethylene spacers has been interpreted in terms of a possible intramolecular electron transfer between the singlet porphyrin and the anthraquinone acceptor. When excited into their porphyrin absorption band maxima, each new P–AnQ system could generate singlet molecular oxygen in good-to-moderate yield. Wavelength-dependent photonuclease activity of these new bis-intercalating species has been examined.

Heterogeneous molybdate catalysts for the generation of singlet molecular oxygen (1Δg) from H2O2

The immobilisation of molybdate on Mg,Al-LDH leads to an active, heterogeneous catalyst that generates singlet molecular oxygen from hydrogen peroxide in the absence of soluble base.

Identification of the precursor of singlet oxygen (1O2, 1Δg) involved in the disproportionation of hydrogen peroxide catalyzed by calcium hydroxide

Catalytic disproportionation of hydrogen peroxide by calcium hydroxide generates singlet molecular oxygen 1O2 (1Δg) through the diperoxohydrate peroxide CaO2·2H2O2 with a 50% yield based on the calcium peroxide.

Spin–orbital coupling effects on the photophysical properties and photocytotoxicity of merocyanine dyes

A series of merocyanine dyes possessing different heteroatoms in the terminal aromatic and barbiturate units has been synthesized. The nature of the heteroatom does not affect the all-trans alignment of the central polyenic bridge, as demonstrated by 1 H NMR spectroscopy. There are pronounced changes, however, in the photophysical properties of the individual molecules due to structural, electronic and spin–orbital coupling effects induced by the heteroatoms. In particular, it has been possible to vary the quantum yield for formation of the lowest-energy triplet excited state by more than two orders of magnitude. Quantum yields and lifetimes for fluourescence and photoisomerization are also affected by the choice of heteroatom. Despite the major changes in triplet yield that take place upon insertion of heteroatoms displaying strong spin–orbital coupling effects (e.g., Se) the efficacy for light-induced cytotoxicity towards cancer cells shows but a modest dependence on the structure of the dye. There is a reasonably good correlation between triplet yield and the rate of light-induced cell killing as might be expected for a mechanism based on intermediate generation of singlet molecular oxygen. However, equally good correlations exist between cell-killing performance and both relative lipophilicity and the rate at which the dye penetrates into intact biological cells.

Singlet Oxygen Production in Water: Aggregation and Charge-Transfer Effects

Precise quantum yields for generation of singlet molecular oxygen, O2(1Δg), have been measured for tetrakis(4-sulfonatophenyl)porphyrin (TSPP), closely-related water-soluble porphyrin derivatives, and tris(2,2‘-bipyridyl)ruthenium(II) (bpy3Ru2+) in O2-saturated water. Under the experimental conditions, TSPP is present in an aggregated state, but the measured quantum yield for formation of O2(1Δg), ΦΔ = 0.51, remains on the same order as that of the corresponding monomer in methanol, ΦΔ = 0.70. Comparison with the quantum yield for formation of the triplet state indicates that quenching of the triplet by O2 gives O2(1Δg) with an efficiency of ca. 80%. There is a small but significant increase in ΦΔ when D2O is used in place of H2O. For the other porphyrin derivatives, the ability of the aggregate to sensitize formation of O2(1Δg) appears to depend on the total electronic charge resident on the molecule, decreasing with decreasing negative charge. A strong solvent dependence noted for O2(1Δg) production with (bpy3Ru2+) is explained in terms of competition between triplet energy transfer and photoinduced electron (or partial charge) transfer. Similar behavior could be responsible for the relatively low ΦΔ value observed for TSPP.

Comparison of photosensitized plasma membrane damage caused by singlet oxygen and free radicals

The efficiency and selectivity of photosensitized damage to membrane functions may be influenced strongly by the identity of the initial reactive species formed by the photosensitizer. To test this possibility, a photosensitizer, rose bengal (RB), was used that resides in the plasma membrane and which generates singlet molecular oxygen ( 1O 2 ∗) upon excitation with visible light, and radicals plus 1O 2 ∗ upon excitation with UV radiation. With this approach, 1O 2 ∗ and radicals are formed at the same locations in the plasma membrane. The response of three plasma membrane functions, namely, proline transport, membrane potential, and membrane impermeability to charged dye molecules, was assessed. The efficiencies of the responses in the presence and absence of oxygen were compared per photon absorbed by RB at two wavelengths, 355 nm (UV excitation) and 532 nm (visible excitation). The efficiency of oxygen removal before irradiation was assessed by measuring the RB triplet lifetime. The three membrane functions were inhibited more efficiently at 355 nm than at 532 nm in the presence of oxygen indicating that the radicals are more effective at initiating damage to membrane components than 1O 2 ∗. The ratio of photosensitized effects at the two wavelengths in the presence of oxygen was the same for two membrane functions but not for the third suggesting that 1O 2 ∗ and radicals initiate a common mechanistic pathway for damage to some membrane functions but not to others. Removing oxygen reduced the efficiency of 355 nm-induced photosensitization by factors of 1.4 to 7. The sensitivity of the three membrane functions to 1O 2 ∗-initiated damage varied over a factor of 50 whereas radical initiated damage only varied by a factor of 15. In summary, these results indicate that radicals and 1O 2 ∗ formed at the same locations in the plasma membrane vary in their efficiency and specificity for membrane damage but may, in some cases, operate by a common secondary damage mechanism in the presence of oxygen.

Porphocyanines: Expanded Aromatic Tetrapyrrolic Macrocycles

Porphocyanines are tetrapyrrolic macrocycles containing two dipyrromethene units linked together by two CN−C bridges. The syntheses of 2,3,7,8,14,15,19,20-octaethylporphocyanine, 5,17-diphenylporphocyanine, 2,3,7,8-tetraethyl-17-phenylporphocyanine, and other meso-aryl and β-alkyl, including a tetra-β-propionate, derivatives and metal complexes are described. The physical and chemical properties of porphocyanines show them to be aromatic. The aromaticity is reflected in the large deshielding of the outer β-protons and shielding of the inner pyrrolic protons in their NMR spectra. The optical spectra of these compounds exhibit Soret and Q bands similar to porphyrins but all significantly bathochromically shifted. The ability of porphocyanines to act as catalysts for the generation of singlet molecular oxygen was investigated using a cholesterol oxidation assay.

37] Reaction of peroxynitrite and hydrogen peroxide to produce singlet molecular oxygen (1Δg)

This chapter discusses the reaction of peroxynitrite and hydrogen peroxide to produce singlet molecular oxygen ( 1 Δ g ). Peroxynitrite (ONOO – ) is a biologically active species produced by the reaction of the superoxide anion radical (O 2 – ) with nitric oxide (NO . ). The decomposition of ONOO– generates the hydroxyl radical, a strong oxidant. Nitric oxide, identified as the endothelium-derived relaxing factor (EDRF), is formed by conversion of L -arginine to L -citrulline by NO synthase. The production of singlet molecular oxygen [O 2 ( 1 Δ g )] in the reaction of ONOO – with H 2 O 2 , uses (1) chemiluminescence (CL) measurement of dimol or monomol light emission in the visible and infrared spectral regions, and (2) water-soluble chemical trap, the sodium salt of anthracene 9,10-diyldiethyl disulfate (EAS), to provide evidence for the formation of O 2 ( l Δ g ) in this system. Peroxynitrite is synthesized in a quenched-flow reactor. The singlet molecular oxygen generation in the peroxynitrite-H 2 O 2 reaction is monitored by chemical trapping with EAS.

Inactivation of viruses by chemically and photochemically generated singlet molecular oxygen

Inactivation of viruses in blood plasma can be achieved by photodynamic procedures using methylene blue (MB) or other photoactive dyes. Singlet molecular oxygen ( 1O 2) probably contributes to the virucidal effects of photosensitization. We report the inactivation of herpes simplex virus type 1 (HSV-1) and suid herpes virus type 1 (SHV-1) by chemically generated singlet oxygen, produced by thermal decomposition of the endoperoxide of 3,3′-(1,4-naphthylidene)dipropionate (NDPO 2). We demonstrate that viruses can be inactivated by 1O 2 generated by chemiexcitation in a reaction in the dark, even in the presence of human plasma. Virus inactivation in phosphate-buffered saline (PBS) was enhanced when water was replaced by deuterium oxide (D 2O) and diminished when human plasma or quenchers (imidazole or histidine) were added. The singlet oxygen quenching activities of plasma, imidazole and histidine correlated with their inhibitory effects on virus inactivation. The production of 1O 2 was assessed by an indicator reaction: the bleaching of p-nitrosodimethylaniline (RNO) with imidazole as 1O 2 acceptor. Virus inactivation and singlet oxygen generation of NDPO 2 were compared with those of MB/light-mediated photosensitization. Based on similar amounts of 1O 2 generated by either procedure, virus inactivation by MB/light was more effective. Virus inactivation by MB/light was not affected by type I quenchers (e.g. mannitol), but was inhibited by human plasma or singlet oxygen quenchers. Furthermore, in D 2O-based PBS, virus inactivation was more effective than that in H 2O. These observations confirm that singlet oxygen is involved in virus inactivation by MB/light. Taken together, the results demonstrate that singlet oxygen produced by either procedure is virucidal. The enhanced effect of the photochemical procedure suggests that, in addition to type II, type I reactions and/or the binding affinity of the dye for the virus contribute to virus killing by MB/light.

Porphyrin-Sensitized Generation of Singlet Molecular Oxygen: Comparison of Steady-State and Time-Resolved Methods

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPorphyrin-Sensitized Generation of Singlet Molecular Oxygen: Comparison of Steady-State and Time-Resolved MethodsCharles Tanielian and Christian WolffCite this: J. Phys. Chem. 1995, 99, 24, 9825–9830Publication Date (Print):June 1, 1995Publication History Published online1 May 2002Published inissue 1 June 1995https://doi.org/10.1021/j100024a025RIGHTS & PERMISSIONSArticle Views982Altmetric-Citations69LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (689 KB) Get e-Alerts

Dioxetane chemiluminescence detection in liquid chromatography based on photosensitized on-line generation of singlet molecular oxygen; a thorough examination of experimental parameters and application to polychlorinated biphenyls

Experimental parameters influencing sensitivity and selectivity in chemiluminescence detection based on photoinduced production of singlet molecular oxygen in liquid chromatography, an approach introduced in earlier papers, are extensively studied. Normal-phase liquid chromatography is applied in addition to reversed-phase chromatogra phy, using polychlorinated biphenyls (PCBs) as analytes. The photochemical reactor parameters play the most important role. The chemiluminescence detector parameters are generally restrained by the required photochemical reactor conditions. An alternative, commercially available, reagent for addition of singlet molecular oxygen (i.e., ethyl vinyl ether) and a new photochemical reactor construction are introduced and compared to the former ones. The experiments show that the optimum conditions are strongly determined by the individual PCB concerned. Planar PCBs known for their high toxiciry, such as the PCBs 77, 126 and 169 can be detected far more sensitively than the non-planar ones. The inherent selectivity of the method is shown for a herring oil sample, spiked with the above PCBs, utilizing normal-phase liquid chromatography with a pyrenyl column.

Synthesis and Photoproperties of Silicon Phthalocyanines and Silicon Naphthalocyanines

AbstractSilicon phthalocyanines and silicon naphthalocyanines, which are two derivatives in the family of hematoporphyrin, have been synthesized to assess their potential as photosensitizers for photodynamic therapy. For these complexes the red shift of their Q‐band maximum absorption tends to depend on the nature of the axial substituent. The bimolecular rate coefficients for the interacting between photosensitizer, either SiNC or SiPC, and generated singlet molecular oxygen were determined from the time‐resolved emission spectrum of singlet oxygen at 1.27 μm. On the basis of these data the electron‐transfer quenching mechanism is discussed in relation to the Marcus model.

Singlet molecular oxygen generation from the decomposition of sodium peroxotungstate and sodium peroxomolybdate

Singlet oxygen is formed by thermal decomposition of peroxomolybdates and peroxotungstates in basic aqueous solution. As shown by both infrared chemiluminescence and chemical trapping, the yield of 1 O 2 released by this system is a total of about 160% (80% based on O 2 released). The infrared chemiluminescence technique is particularly useful for studying reaction kinetics in this system