Singlet oxygen and polymer photooxidations. II. Photodegradation of an olefinically unsaturated polymer

A method based on infrared spectral changes in thin films was devised and used to evaluate the relative effectiveness of various types of additives on photodegradative processes in an olefinically unsaturated polymer. Nickel chelates of the thiobisphenol-amine complex type are shown to be quantitatively more effective in retarding the photodegradation of these polymers than other additives having greater singlet oxygen quenching efficiencies, ultraviolet absorption, or radical antioxidant properties. Photosensitization with a singlet oxygen sensitizer (fluoranthene) rapidly produces degradative effects in the polymer which are identical with those of its direct degradation by light. The sensitized effects are also retarded by the nickel chelates. Photosensitization by a hydrogen atom-abstracting sensitizer (a benzophenone) proved considerably less effective. The effectiveness of the nickel complexes appears to be due to a combination of their ability to quench singlet oxygen and precusor excited states and their relative stability under photoexposure conditions.     

Photo-stabilising action of metal chelate stabilisers in polypropylene—Part VI: Importance of singlet (1Δg) oxygen quenching and UV screening,and flash photolysis studies

The importance of singlet (¹Δ_g) oxygen quenching in the stabilisation mechanism of polypropylene by metal chelates has been investigated. Methylene blue was used as the sensitiser and 9,10-dimethyl anthracene was used as a singlet oxygen chemical trap. The results show that singlet oxygen quenching has no important rôle in the stabilising mechanism of metal chelates, in a polypropylene matrix.The importance of ultraviolet screening by the chelates as a stabilising mechanism is also considered. Various concentration levels, ranging from 0·001% to 1·0% w/w, were used. The results show that, as in the case of singlet oxygen quenching, ultraviolet screening is unimportant as an effective photo-stabilising mechanism.The photo-stability of four nickel chelates in both polar and non-polar solvents has been examined using conventional flash photolysis. It is found that their activity correlates with their ability to protect the polymer at concentrations below 0·2% w/w. The radicals formed during flash photolysis are tentatively assigned to be phenoxy radicals.     

Recent developments in the detection of singlet oxygen with molecular spectroscopic methods

Singlet oxygen is a unique reactive oxygen species, as its chemical reactivity derives from its characteristic electronically-excited state. The involvement of singlet oxygen in many important atmospheric, physical, chemical, biological, and therapeutic processes has attracted intense research interest in recent years. The detection and the quantification of singlet oxygen are very important for understanding its mechanism of action in various processes.Due to its highly reactive nature, singlet oxygen has very few direct methods of determination. Only molecular phosphorescence at 1270 nm has been utilized. Indirect methods using spectrophotometric, fluorescent or chemiluminescent probes have therefore been extensively studied.This review reflects recent developments in singlet-oxygen detection with molecular spectroscopic methods. We begin with a brief introduction of the basic properties, the production and the applications of singlet oxygen. With this background information, we review the four molecular spectroscopic methods (i.e., emission, spectrophotometry, fluorescence and chemiluminescence). We pay special attention to attractive chemical probes with high selectivity and sensitivity in quantifying singlet oxygen.     

Energy transfer processes involving ultraviolet stabilizers. Quenching of singlet oxygen

The role of electronically excited singlet (¹Δ_g) oxygen molecules in the photooxidation of polymers has received increased attention in recent years. Little information regarding the interaction of ultraviolet stabilizers with singlet oxygen is known, however. In this study, singlet oxygen was produced by a microwave discharge in a flow system and rate constants were obtained for quenching by ultraviolet stabilizers. It was found that some nickel chelate stabilizers are effective quenchers of singlet oxygen and their quenching behaviors can be correlated with ultraviolet stabilization effectiveness in thin polypropylene and polyethylene films. The best oxygen quenchers of those examined are nickel chelates with sulfur donor ligands.     

Electrochemical Monitoring of Singlet Oxygen Production

The exploitation of singlet oxygen generating compounds as a means of targeted therapies drives the need to develop methods for assessing the efficacy of such compounds and their capacity for generating the reactive oxygen species. Degradation of diphenylisobenzofuran by singlet oxygen is widely used as a spectroscopic probe but its application can be problematic. An alternative detection strategy exploiting the electrochemical monitoring of the quencher concentration, by square wave voltammetry, has been shown to provide a more sensitive and flexible option that could be used to address the increasing interest in photosensitizing materials.     

Studies of the photo-oxidation of polydienes: Part 1—Photo-stabilising effect of some derivatives of diacetyl-monooxime benzoylhydrazone nickel(II) chelates on cis-1,4-polybutadiene

Three derivatives of diamagnetic diacetyl-monooxime benzoylhydrazone nickel(II) chelates were evaluated as uv stabilisers for cis-1,4-polybutadiene (BR) in solution and in films. In the presence of methylene blue (MB) as singlet oxygen sensitiser, such chelates inhibit the effect of singlet oxygen formed during irradiation by visible light. The photo-stabilising mechanism of the chelates is discussed in terms of their action as singlet oxygen quencher as well as their action as uv absorbers. Further, a stabilising mechanism which involves the trapping of alkyloxy and/or alkylperoxy radicals has also been suggested for two of the chelates. Combination of the most effective chelate and β-carotene as singlet oxygen quencher exhibits synergistic behaviour. The polymer samples which were irradiated in its presence were examined using the Differential Scanning Calorimeter (DSC) technique. The results obtained also demonstrate the photo-stabilising effect of the chelate.     

THE QUENCHING OF SINGLET OXYGEN BY AMINO ACIDS AND PROTEINS

Abstract— The physical quenching of singlet molecular oxygen (¹Δ_g) by amino acids and proteins in D₂O solution has been measured by their inhibition of the rate of singlet oxygen oxidation of the bilirubin anion. Steady-state singlet oxygen concentrations are produced by irradiating the oxygenated solution with the 1–06 μm output of a Nd-YAG laser, which absorbs directly in the electronic transition ¹Δ_g+ 1 v →³Σ_g^-. The rate of quenching by most of the proteins studied is approximated by the sum of the quenching rates of their amino acids histidine, tryptophan and methionine, which implies that these amino acids in the protein structure are all about equally accessible to the singlet oxygen. The quenching constants differ from those obtained by the ruby-laser methylene-blue-photosensitized method of generating singlet oxygen, or from the results of steady-state methylene-blue-photosensitized oxidation, where singlet oxygen is assumed to be the main reactive species. The singlet oxygen quenching rates in D₂O, pD 8, are (10⁷ℒ mol^-1 s^-1): alanine 0–2, methionine 3, tryptophan 9, histidine 17, carbonic anhydrase 85, lysozyme 150, superoxide dismutase 260, aposuperoxide dismutase 250.     

Functionalized derivatives of 1,4-dimethylnaphthalene as precursors for biomedical applications: synthesis, structures, spectroscopy and photochemical activation in the presence of dioxygen

Decomposition of endoperoxide containing molecules is an attractive approach for the delayed release of singlet oxygen under mild reaction conditions. Here we describe a new method for the adaptation of the corresponding decay times by controlling the supramolecular functional structure of the surrounding matrix in the immediate vicinity of embedded singlet oxygen precursors. Thus, a significant prolongation of the lifetime of the endoperoxide species is possible by raising the energy barrier of the thermal (1)O(2)-releasing step via a restriction of the free volume of the applied carrier material. Enabling such a prolonged decomposition period is crucial for potential biomedical applications of endoperoxide containing molecules, since sufficient time for appropriate cell uptake and transport to the desired target region must be available under physiological conditions before the tissue damaging-power of the reactive oxygen species formed is completely exhausted. Two novel polyaromatic systems for the intermediate storage and transport of endoperoxides and the controlled release of singlet oxygen in the context of anticancer and antibiotic activity have been prepared and characterized. These compounds are based on functionalized derivatives of the 1,4-dimethylnaphthalene family which are readily forming metastable endoperoxide species in the presence of dioxygen, a photosensitizer molecule such as methylene blue and visible light. In contrast to previously known systems of similar photoreactivity, the endoperoxide carrying molecules have been designed with optimized molecular properties in terms of potential chemotherapeutic applications. These include modifications of polarity to improve their incorporation into various biocompatible carrier materials, the introduction of hydrogen bonding motifs to additionally influence the endoperoxide decay kinetics, and the synthesis of bifunctional derivatives to enable synergistic effects of multiple singlet oxygen binding sites with an enhanced local concentration of reactive species. With these compounds, a promising degree of endoperoxide stability adjustment within the carrier matrix has been achieved (polymer films or nanoparticles), which now opens the stage for appropriate targeting of the corresponding pro-drugs into live cells. First results on cytocidal and cytostatic properties of these compounds embedded in ethylcellulose nanoparticles are presented. Furthermore, an efficient low-cost method for the photochemical production of reactive endoperoxides based on high-power 660 nm LED excitation at room temperature and ambient conditions in ethanol solution is reported.     

Generation of Singlet Molecular Oxygen by Lipid Hydroperoxides and Nitronium Ion†

Singlet molecular oxygen is a reactive species involved in biological oxidative processes. The major cellular targets of singlet molecular oxygen are unsaturated fatty acids in the membrane, as well as nucleic acids and proteins. The aim of this study was to investigate whether lipids and commercial hydroperoxides generate singlet molecular oxygen, in presence of nitronium and activated nitronium ion. For this purpose, monomol light emitted in the near-infrared region (λ = 1270 nm) was used to monitor singlet molecular oxygen decay in different solvents, with different hydroperoxides and in the presence of azide. Direct measurements of the singlet molecular oxygen spectrum at 1270 nm recorded during the reaction between lipids and commercial hydroperoxides and nitronium ions unequivocally demonstrated the formation of this excited species.     

Potential photosensitizers for photodynamic therapy. III. Photophysical properties of a lipophilic chlorin and its zinc and tin chelates.

Photophysical properties of a lipophilic chlorin derivative and its zinc and tin chelates were investigated in chloroform. The quantum yields of the fluorescence phi F, of the S1----T1 intersystem crossing phi T and of singlet oxygen (1 delta g) formation phi delta, as well as the Stern-Volmer constants for the quenching of the S1 states by oxygen and the rate constants of quenching of O2(1 delta g) by the chlorins were measured. In comparison to the metal-free chlorin an increase of phi T and a decrease of phi F have been observed for the metal-containing derivatives, whereas the phi delta values remain constant.     

Singlet Oxygen-Mediated Inactivation of Acetylcholinesterase: A Comparison of Purified Enzyme in Solution and Enzyme Bound to K562 Leukemia Cells

Abstract— We have compared the singlet oxygen-mediated inactivation of acetylcholinesterase (ACE) in solution with the inactivation of ACE on the surface of K562 leukemia cells. In solution, the actions of the singlet-oxygen quenchers, methionine, azide, disodium [ N,N '-ethylene-bis(5-sulfosalicylideneinuninato)]nickelate(II) (Ni-chelate 1) and disodium [( N,N '-2,3-propionic acid)bis(5-sulfosal-icylideneimminato)]nickelate(II) (Ni-chelate 2) could be explained quantitatively by assuming their only mechanism of action was to quench singlet oxygen. The singlet oxygen quenchers, azide, Ni-chelate 1 and Ni-chelate 2, caused smaller inhibitions in the rate of singlet oxygenmediated inactivation of ACE on K562 cells than ACE in solution. The effects of these quenchers and of deuterium oxide were interpreted using a mathematical model of singlet-oxygen quenching and diffusion to estimate the lifetime of singlet oxygen near the cell surface. The azide quenching data and the deuterium-oxide data gave lifetimes of 0.9 ± 0.2 μs and 0.45 ± 0.15 μs, respectively. The increases in ACE inactivation lifetime caused by the nickel chelates were anomalously large. The unexpectedly large quenching due to the nickel chelates may have been due to a nonuniform distribution of the chelates in the cytoplasm with a large concentration of the chelate near the cell membrane.     

The extra-weak chemiluminescence generated during oxidation of some tetracycline antibiotics. II. Peroxidation.

This study was undertaken to establish the mechanism of chemiluminescence during the oxidation reaction of tetracycline antibiotics in the presence of molecular oxygen and H2O2. The spectral distribution of chemiluminescence and fluorescence and the quantum yields of chemiluminescence were measured. The chemiluminescence spectrum measured with cut-off filters revealed one broad blue-green band and bands with maxima at 580, 640 and 700 nm. The bands at 580, 640 and 700 nm were similar to those observed for singlet molecular oxygen. The effect of superoxide radical, hydroxyl radical inhibitors, singlet oxygen quenchers and D2O as solvent on the light emission was also studied. The formation of singlet oxygen during the oxidation of the investigated tetracyclines was also checked using the spectrophotometric method based on the bleaching of p-nitrosodimethylaniline. A mechanism for the reactions generating electronically excited compounds is proposed.     

Benzo[A]Pyrene and Benzo[E]Pyrene: Photoreactivity and Phototoxicity toward Human Keratinocytes

Polycyclic aromatic hydrocarbons (PAHs) are a group of organic compounds derived mostly from the incomplete combustion of fossil fuels and biomass. Human skin can absorb PAHs and the uptake increases with their molar mass and lipophilicity. Benzopyrene is high molecular weight PAH frequently appearing in ambient pollution. It exists in two isomeric forms: benzo[a]pyrene (BaP) and benzo[e]pyrene (BeP), which exhibit different biological activity. Although certain properties of benzopyrenes suggested photoreactivity of the compounds, no direct measurements were previously conducted to characterize their photochemical activity. In this study, quantum yield and action spectra of singlet oxygen photogeneration by BaP and BeP were measured by time-resolved near-infrared phosphorescence, and the ability of both compounds to photogenerate superoxide anion was assessed by electron paramagnetic resonance (EPR) spin-trapping. The measurements revealed high efficiency of benzopyrenes to photogenerate singlet oxygen and their ability to photogenerate superoxide anion. Using HaCaT cells as single-layer skin model, we demonstrated concentration-dependent and light-dependent cytotoxicity of BaP and BeP. The compounds induced damage to the cell mitochondria and elevated the levels of intracellular reactive oxygen species.     

Enabling Photo-Crosslinking and Photo-Sensitizing Properties for Synthetic Fluorescent Protein Chromophores

Synthetic fluorescent protein chromophores have been reported for their singlet state fluorescence properties and applications in bioimaging, but rarely for the triplet state chemistries. Herein, we enabled their photo-sensitizing and photo-crosslinking properties through rational modulations. Extension of molecular conjugation and introduction of heavy atoms promoted the generation of reactive oxygen species. Unlike other photosensitizers, these chromophores selectively photo-crosslinked aggregated proteins and uncovered the interactome profiles. We also exemplified their general applications in chromophore-assisted light inactivation, photodynamic therapy and photo induced polymerization. Theoretical calculation, pathway analysis and transient absorption spectroscopy provided mechanistic insights for this triplet state chemistry. Overall, this work expands the function and application of synthetic fluorescent protein chromophores by enabling their triplet excited state properties.     

Photogeneration of reactive oxygen species and photoinduced plasmid DNA cleavage by novel synthetic chalcones

This paper describes the synthesis and photodynamic properties of six different chalcone derivatives. Using N,N-dimethyl-4-nitrosoaniline (RNO) bleaching assay, the singlet oxygen generating efficiencies of these chalcones are determined relative to rose bengal (RB). Superoxide dismutase (SOD) inhibitable cytochrome c reduction assay and electron magnetic resonance (EMR) spin trapping techniques are used to determine the superoxide anion radical (O?·?) yield upon photoirradiation. Photoinduced DNA scission studies show that O?·? is involved in the DNA strand break. In addition, antimicrobial activity of these chalcones is also investigated. Structure activity relationship accounts for the difference in the photogeneration of reactive oxygen species (ROS) by these sensitizers. Presence of electron releasing -OCH? groups enhances the photogeneration of ROS. Cyclic voltammetry studies indicate a correlation between enzymatic O?·? generation efficiency and redox potential of chalcones. Both O?·? (Type I) and 1O? (Type II) paths are involved in the photosensitization of chalcones. The LUMO energies obtained by molecular modeling correlate with the one-electron reduction potentials.     

Kinetics of the reactions of singlet molecular oxygen (O21Δg) with organic compounds in the gas phase

The reactions of singlet molecular oxygen (O₂¹Δ_g) with a series of organic compounds have been studied in the gas phase at 298°K. The concentration of singlet molecular oxygen was determined by titration with 2,5-dimethylfuran. The titration technique was checked using a photoionization technique. Absolute rate constants were measured on the basis of the loss of organic reactant and, in some cases, of singlet molecular oxygen. It was found that the usual method of producing singlet molecular oxygen in the gas phase can also, under some conditions, allow reactive species other than singlet molecular oxygen to enter the reactor, leading to serious errors in the determination of rate constants. This problem was eliminated by carrying out the rate measurements in the presence of a small amount of nitrogen dioxide a radical scavenger.     

不对称五氮齿镉和铟大环配合物的激发态性能研究

本文研究了不对称五氮齿镉和铟大环配合物的激发态性能及其光稳定性。结果表明:它们的三重态能量在120kJ/mol左右,最低激发三重态敏化产生单重态氧的量子产率在0.6～0.9,它们的分子一阶超极化率在～10^-28esu,在光照的条件下,配合物Ⅰ相当稳定,而配合Ⅱ则形成不稳定化合物导致光褪色。     

BIOLOGICAL ACTIVITIES OF PHTHALOCYANINES—IV. TYPE II SENSITIZED PHOTOOXIDATION OF L-TRYPTOPHAN AND CHOLESTEROL BY SULFONATED METALLO PHTHALOCYANINES

Abstract— Sulfonated phthalocyanine and a series of its metal chelates in combination with red light irradiation led to the degradation of L-tryptophan in oxygenated aqueous solution. The photoproducts and the rate of transformation of L-tryptophan are compared with hematoporphyrin and rose bengal sensitized photooxidation. In all cases the primary photoproducts are characterized as cis and trans -3a-hydroperoxy-l,2,3,3a,8,8a-hexahydropyrrolo[2,3-b]indole-2-carboxylic acid. Support for the involvement of singlet excited oxygen is obtained from azide inhibition and the formation of the specific singlet oxygen product with cholesterol. We observed the contribution of another pathway in the case of the manganese complex.     

Resacetophenone oxime–formaldehyde resin and its metal chelates. III

In this paper the synthesis and properties of resacetophenone oxime–formaldehyde resin are described. The number-average molecular weights of the resin determined by vapor-pressure osmometry and nonaqueous conductometric titration are 2200 ± 10% and 2500 g/mol, respectively. Cu(II), Ni(II), and Co(II) chelates of the resin were prepared. Elemental analysis of the chelates indicates a metal to ligand ratio of 1:2. The diffuse reflectance spectra and magnetic moments of Ni(II) and Co(II) chelates show tetrahedral structure, whereas Cu(II) chelate shows a square planar structure. Infrared spectral studies show that the metals are coordinated through the nitrogen of the oximino group and oxygen of the phenolic group. The presence of methylene bridges is also indicated by IR spectral studies. The thermal behavior of the resin and its metal chelates are also discussed.     

Subcellular, time-resolved studies of singlet oxygen in single cells

In time-resolved and spatially resolved experiments, singlet molecular oxygen, O2(a1Deltag), was created in a single nerve cell upon irradiation of a sensitizer incorporated in the cell using a focused laser beam. The singlet oxygen thus produced was detected by its infrared phosphorescence. Data obtained indicate that in both the cytoplasm and the nucleus of the cell, this reactive species is approximately 1-2 orders of magnitude longer-lived than previously believed. The data demonstrate that deactivation of singlet oxygen in the cell is dominated by interactions with the solvent not cellular constituents such as proteins. These results provide a new perspective for mechanistic studies of the role of O2(a1Deltag) in photoinduced cell death and intracellular signaling.