Physical Quenchers Of Singlet Oxygen Research Articles

Photogeneration and quenching of singlet molecular oxygen by bacterial C40 carotenoids with long chain of conjugated double bonds.

Measurement of photosensitized luminescence of singlet oxygen has been applied to studies of singlet oxygen generation and quenching by C40 carotenoids (neurosporene, lycopene, rhodopin, and spirilloxanthin) with long chain of conjugated double bonds (CDB) using hexafluorobenzene as a solvent. It has been found that neurosporene, lycopene, and rhodopin are capable of the low efficient singlet oxygen generation in aerated solutions upon photoexcitation in the spectral region of their main absorption maxima. The quantum yield of this process was estimated to be (1.5-3.0) × 10-2. This value is near the singlet oxygen yields in solutions of ζ-carotene (7 CDB) and phytoene (3 CDB) and many-fold smaller than in solutions of phytofluene (5 CDB) (Ashikhmin et al. Biochemistry (Mosc) 85:773-780, https://doi.org/10.1134/S0006297920070056 , 2020, Biochemistry (Mosc) 87:1169-1178, 2022, https://doi.org/10.1134/S00062979221001082022 ). Photogeneration of singlet oxygen was not observed in spirilloxanthin solutions. A correlation was found between the singlet oxygen yields and the quantum yields and lifetimes of the fluorescence of the carotenoid molecules. All carotenoids were shown to be strong physical quenchers of singlet oxygen. The rate constants of 1O2 quenching by the carotenoids with long chain of CDB (9-13) were close to the rate constant of the diffusion-limited reactions ≈1010M-1s-1, being many-fold greater than the rate constants of 1O2 quenching by the carotenoids with the short chain of CDB (3-7) phytoene, phytofluene, and ζ-carotene studied in prior papers of our group (Ashikhmin et al. 2020, 2022). To our knowledge, the quenching rate constants of rhodopin and spirilloxanthin have been obtained in this paper for the first time. The mechanisms of 1O2 photogeneration by carotenoids in solution and in the LH2 complexes of photosynthetic cells, as well as the efficiencies of their protective action are discussed.

Taming of Singlet Oxygen: Towards Artificial Oxygen Carriers Based on 1,4-Dialkylnaphthalenes.

Naphthalene endoperoxides are known as convenient sources of singlet oxygen (O2 , 1 Δg ), which is the major product of endoperoxide cycloreversion reaction. However, their potential as carriers of ground-state molecular oxygen (O2 , 3 Σg ) similar to artificial oxygen carriers remains largely unexplored. This is due to the extreme reactivity and cytotoxic effects of the released singlet oxygen. We now report that a compound with a bimodular design, which incorporates an endoperoxide and an efficient physical quencher of singlet oxygen, 1,4-diazabicyclo[2.2.2]octane (DABCO), produces exclusively ground-state molecular oxygen. This result, coupled with the fact that oxygen release rates from endoperoxides are highly amenable to fine-tuning in a very broad range, and open to targeting by ligand attachment, raises the potential of these compounds far above any comparable chemical, or even biochemical sources. In cell culture experiments, we showed that the addition of the endoperoxide-quencher conjugate can enhance and sustain cell proliferation.

Singlet oxygen formation in Na[sbnd]O2 battery cathodes catalyzed by ammonium Brönsted acid

The presence of singlet oxygen in metal-O2 batteries is one of the major factors responsible for the degradation of the electrolyte. The formation of singlet oxygen, 1O2, at NaO2 cathodes in sodium trifluoromethane sulfonate (NaOTf)-diglyme electrolyte has been detected in-operando by fluorescence quenching of 9,10-dimethylanthracene, DMA, a specific chemical monitor of singlet oxygen. Furthermore, ammonium Brönsted acid protonates superoxide and the further disproportionation of HO2 results in a catalytic EC' mechanism that recycles oxygen, a fraction of which has been found to be 1O2. Unlike, ammonium trifluoromethane sulfonate (NH4OTf), in tetrabutylammonium trifluoromethane sulfonate (TBAOTf), which lacks acidic protons, superoxide is stabilized by the large cation and no 1O2 could be detected. The addition of sodium azide to the electrolyte, an efficient specific physical quencher of singlet oxygen, results in negligible detection of this harmful oxygen reduction intermediate and proves the nature of 1O2.

Tetrakis(N-methyl-p-pyridinio)porphyrin and its zinc complex can photosensitize damage of human serum albumin through electron transfer and singlet oxygen generation

The photosensitized protein-damaging activity of water-soluble freebase tetrakis([Formula: see text]-methyl-[Formula: see text]-pyridinio)porphyrin (H2TMPyP), and its zinc complex (ZnTMPyP) was investigated using human serum albumin (HSA) as a target protein. These porphyrins bound to HSA and caused photosensitized oxidation of the tryptophan residue. The protein damage was enhanced in deuterium oxide and inhibited by sodium azide, a physical quencher of singlet oxygen, suggesting the contribution of singlet oxygen. However, an excess amount of sodium azide could not completely inhibit protein damage. These findings suggest the partial contribution of another mechanism to the protein damage, possibly the electron transfer mechanism. The Gibbs free energy of the electron transfer mechanism showed that electron transfer-mediated tryptophan oxidation by photoexcited H2TMPyP is more advantageous than that by ZnTMPyP. Actually, the quantum yield of protein damage through electron transfer by H2TMPyP was larger than that by ZnTMPyP. In addition, this study demonstrated that the association between porphyrin and protein plays an important role in photosensitized protein damage.

Potential Role of Carotenoids as Antioxidants in Human Health and Disease

Carotenoids constitute a ubiquitous group of isoprenoid pigments. They are very efficient physical quenchers of singlet oxygen and scavengers of other reactive oxygen species. Carotenoids can also act as chemical quenchers undergoing irreversible oxygenation. The molecular mechanisms underlying these reactions are still not fully understood, especially in the context of the anti- and pro-oxidant activity of carotenoids, which, although not synthesized by humans and animals, are also present in their blood and tissues, contributing to a number of biochemical processes. The antioxidant potential of carotenoids is of particular significance to human health, due to the fact that losing antioxidant-reactive oxygen species balance results in “oxidative stress”, a critical factor of the pathogenic processes of various chronic disorders. Data coming from epidemiological studies and clinical trials strongly support the observation that adequate carotenoid supplementation may significantly reduce the risk of several disorders mediated by reactive oxygen species. Here, we would like to highlight the beneficial (protective) effects of dietary carotenoid intake in exemplary widespread modern civilization diseases, i.e., cancer, cardiovascular or photosensitivity disorders, in the context of carotenoids’ unique antioxidative properties.

Singlet Oxygen-Induced Photodegradation of the Polymers and Dyes in Optical Sensing Materials and the Effect of Stabilizers on These Processes

A comprehensive study of photodegradation processes in optical sensing materials caused by photosensitized singlet oxygen in different polymers is presented. The stabilities of the polymers are accessed in the oxygen consumption measurements performed with help of optical oxygen sensors. Polystyrene and poly(phenylsilesquioxane) are found to be the most stable among the polymers investigated, whereas poly(2,6-dimethyl-p-phenylene oxide) and particularly poly(methyl methacrylate) and their derivatives show the fastest oxygen consumption. The effect of the stabilizers (singlet oxygen quenchers) on the oxygen consumption rates, the photostability of the sensitizer, and the total photon emission (TPE) by singlet oxygen is studied. 1,4-Diazabicyclo[2.2.2]octane (DABCO) was found to significantly reduce both the TPE and the oxygen consumption rates, indicating its role as a physical quencher of singlet oxygen. The addition of DABCO also significantly improved the photostability of the sensitizer. The N-alkylated derivative of DABCO and DABCO covalently grafted to the polystyrene backbone are prepared in an attempt to overcome the volatility and water solubility of the quencher. These derivatives as well as other tertiary amines investigated were found to be inefficient as stabilizing agents, and some of them even negatively affected the oxygen consumption rates.

Azide Quenching of Singlet Oxygen in Suspensions of Microenvironments of Neutral and Surface Charged Liposomes and Micelles

The azide anion is often used as a physical quencher of singlet oxygen, the important active intermediate in photosensitized oxidation. An observed effect of azide on the rate of a reaction is considered an indication to the involvement of singlet oxygen. In most biological photosensitizations, the light-absorbing sensitizer is located in a membrane or in an intracellular organelle, whereas azide is water soluble. The quenching it causes relies on a physical encounter with singlet oxygen during the latter's short lifetime. This can happen either if azide penetrates into the membrane's lipid phase or if singlet oxygen is intercepted when diffusing in the aqueous phase. We demonstrate in this article the difference, in liposomes' suspension, between the effect of azide when using a water-soluble and membrane-bound chemical targets of singlet oxygen, whereas this difference does not exist when micelles are used. We explain the difference on the population of sensitizer and target in the liposome vs micelle. We also show the effect that exists on azide quenching of singlet oxygen by electrically charged lipids in liposomes. This is a result of the accumulation or dilution of azide in the debye layer near the membranes' surface, due to the surface Gouy-Chapman potential.

Interaction of Phosphatidylcholine and α‐Tocopherol on the Oxidation of Sunflower Oil and Content Changes of Phosphatidylcholine and Tocopherol in the Emulsion under Singlet Oxygen

Interaction of phosphatidylcholine (PC) and α-tocopherol (α-Toc) on the oxidation of oil in the emulsion consisting of sunflower oil and water under singlet oxygen at 25 °C was studied by determining peroxide value (PV) and conjugated dienoic acid (CDA) contents. Singlet oxygen was produced by chlorophyll b under 1700 lux. Single addition of PC or α-Toc decreased the values of peroxides and CDAs of oil in the emulsion via singlet oxygen quenching. PC and α-Toc showed simply additive interaction in decreasing the singlet oxygen oxidation of oil in the emulsion. α-Toc was a physical quencher of singlet oxygen in the emulsion, but PC involved chemical quenching in the antioxidant action. Chlorophyll and PC contents were decreased in the emulsion under singlet oxygen, while α-Toc was not. α-Toc protected chlorophyll and PC from degradation, and was a more important component than PC in the oil oxidation under singlet oxygen in the emulsion.

On the photochemical behaviour of some diarylpyrazolines

The excited state behaviour of 1-phenyl-3(2,4,6-trimethylphenyl)-4,5-dihydropyrazole ( 1) and of the corresponding 1-(4-diethylaminophenyl) ( 2) and 1-(4-morpholinophenyl) ( 3) derivatives has been explored. All of these compounds fluoresce efficiently and the Stokes shift (11.6 × 10 −3 cm −1 with 1) increases by (2–3) × 10 3 cm −1 with the introduction of the electron-donating groups. They are unaffected both by direct irradiation in deoxygenated solution or by photosensitization with benzophenone. Compounds 1 and 2, but not 3 are dehydrogenated to the corresponding pyrazoles by irradiation in deoxygenated acetone. In air-equilibrated toluene, acetonitrile or ethanol, direct irradiation (λ > 300 nm) of these pyrazolines causes only a slow reaction. However, 2 and 3 are dehydrogenated by irradiation at 254 nm in toluene. 1 is dehydrogenated by singlet oxygen in a dye-sensitized reaction, but this is not the case with 2 and 3, and these compounds act as physical quencher of singlet oxygen with no measurable reaction. The key factor for rationalizing these reaction is the low oxidation potential of the substrates.

Quenching of singlet molecular oxygen by phthalocyanines and naphthalocyanines.

Using the direct measurement of the photosensitized luminescence of singlet molecular oxygen (1O2) the rate constants (kq) have been determined for 1O2 quenching by the monomeric molecules of the following phthalocyanines and naphthalocyanines in chloroform: tetra-(4-tert-butyl) phthalocyanine (I); octa-(3,6-butoxy) phthalocyanine (II), tetra-(6-tert-butyl)-2,3 naphthalocyanine (III), aluminium tetra-(1-tert-phenyl)-2,3 naphthalocyanine (IV), tri-(n-hexyl-siloxy) derivatives of silicon- (V), tin- (VI), aluminium- (VII) and gallium- (VIII) 2,3 naphthalocyanine. The following kq values were obtained (kq x 10(-8) M-1 s-1): 2.9 (I), 59 (II), 100 (III), 20 (IV), 3.9 (V), 53 (VI), 33 (VII), 110 (VIII). As most of the quenchers have the low-lying triplet levels, a contribution of the quenching mechanism based on the energy transfer from 1O2 to these levels has been analysed. A formula is proposed describing the relation between kq values caused by this mechanism, and photophysical constants of the quencher triplet state. This formula was applied to phthalocyanines, naphthalocyanines, beta-carotene and bacterochlorophyll a. The data suggest that the energy transfer can fully explain the activity of V and strongly contributes into the activities of II, III and VI-VIII. A charge transfer interaction might be an additional mechanism involved in 1O2 quenching by compounds studied. As some phthalocyanines and naphthalocyanines are strong physical quenchers of singlet oxygen they can be used as efficient inhibitors for photodestructive processes in photochemical systems.

Hydrazines: new charge-transfer physical quenchers of singlet oxygen

Hydrazines: new charge-transfer physical quenchers of singlet oxygen

Oxygen consumption in two aqueous systems: excited nitrite ions-oxygen and nitrite ions-singlet oxygen

Abstract It was found molecular oxygen is consumed during the photolysis of aerated aqueous solutions of nitrite ions. The photoprocess dominates in alkaline solutions (pH 8.3) while in acidic media (pH 5.3) thermal reactions overshadow photochemically induced changes. The absolute quantum yield of oxygen depletion was established. We also found that nitrite ions are more easily oxygenated by singlet oxygen. The process is profoundly affected by pH and depends on the ionic strength of the solutions. Steady state experiments with eosin Y as a sensitizer, and with continuous monitoring of oxygen concentration, allowed us to elucidate the absolute yield of 1 O 2 chemical consumption as a function of NO 2 − concentration and the ionic strength of the solutions. Since we tried to use the azide ions as physical quenchers of singlet oxygen, some supplementary remarks concerning their oxygen consumption are also presented in the Appendix.

Is self-sensitized photo-oxidation a significant pathway in the photofading of azo dyes?

The photofading in aerated solution of 4-diethylaminoazobenzene (1) and of the corresponding 4′-methoxy (2) and 4′-nitro derivatives (3) under various conditions has been examined and compared with naphthol derivatives which are subject to azo–hydrazone tautomerism. Dyes (1)–(3) are efficient physical quenchers of singlet oxygen but show very little chemical reactivity with oxygen. Their ability to sensitize oxygen is low. More efficient photo-oxidative fading is observed upon short-wavelenght irradiation, which results from the reaction of oxygen with hydrazyl radicals, formed by initial hydrogen abstraction from the solvent.

The photosensitised oxidation of amines. Part I. The use of benzophenone as a sensitiser

Product studies are reported on the benzophenone-sensitised photo-oxidation of primary, secondary, and tertiary aliphatic amines and N-alkylanilines. Aliphatic amines gave aldehydes and imines, whereas N-alkylanilines were dealkylated but did not give imines. Amines which are known physical quenchers of singlet oxygen were efficiently oxidised. The reactivity of these compounds, and the type of products formed in the reaction, are explainable in terms of a mechanism in which hydrogen atom abstraction from the amine by triplet ketone is the primary chemical reaction. The results are not in accord with the participation of singlet oxygen. Quantum yield measurements of oxygen uptake, amine disappearance, and product formation are consistent with the proposed mechanism.