Excited State Of Molecular Oxygen Research Articles

Singlet oxygen is produced from brown carbon-containing cooking organic aerosols (BrCOA) under indoor lighting

Indoor BrC-containing cooking organic aerosols (BrCOA) can act as sensitizers generating the first excited state of molecular oxygen, singlet oxygen, under indoor lighting conditions. Sustained singlet oxygen steady-state levels lead to prolonged oxidation of indoor aerosols impacting air quality.

Singlet Molecular Oxygen: from COIL Lasers to Photodynamic Cancer Therapy.

Translation of experimental techniques from one scientific discipline to another is often difficult but rewarding. Knowledge gained from the new area can lead to long lasting and fruitful collaborations with concomitant development of new ideas and studies. In this Review Article, we describe how early work on the chemically pumped atomic iodine laser (COIL) led to the development of a key diagnostic for a promising cancer treatment known as photodynamic therapy (PDT). The highly metastable excited state of molecular oxygen, a1Δg, also known as singlet oxygen, is the link between these disparate fields. It powers the COIL laser and is the active species that kills cancer cells during PDT. We describe the fundamentals of both COIL and PDT and trace the development path of an ultrasensitive dosimeter for singlet oxygen. The path from COIL lasers to cancer research was relatively long and required medical and engineering expertise from numerous collaborations. As we show below, the knowledge gained in the COIL research, combined with these extensive collaborations, has resulted in our being able to show a strong correlation between cancer cell death and the singlet oxygen measured during PDT treatments of mice. This progress is a key step in the eventual development of a singlet oxygen dosimeter that could be used to guide PDT treatments and improve outcomes.

Singlet Oxygen Seasonality in Aqueous PM10 is Driven by Biomass Burning and Anthropogenic Secondary Organic Aerosol.

The first excited state of molecular oxygen is singlet-state oxygen (1O2), formed by indirect photochemistry of chromophoric organic matter. To determine whether 1O2 can be a competitive atmospheric oxidant, we must first quantify its production in organic aerosols (OA). Here, we report the spatiotemporal distribution of 1O2 over a 1-year dataset of PM10 extracts at two locations in Switzerland, representing a rural and suburban site. Using a chemical probe technique, we measured 1O2 steady-state concentrations with a seasonality over an order of magnitude peaking in wintertime at 4.59 ± 0.01 × 10-13 M and with a quantum yield of up to 2%. Next, we identified biomass burning and anthropogenic secondary OA (SOA) as the drivers for 1O2 formation in the PM10 aqueous extracts using source apportionment data. Importantly, the quantity, the amount of brown carbon present in PM10, and the quality, the chemical composition of the brown carbon present, influence the concentration of 1O2 sensitized in each extract. Anthropogenic SOA in the extracts were 4 times more efficient in sensitizing 1O2 than primary biomass burning aerosols. Last, we developed an empirical fit to estimate 1O2 concentrations based on PM10 components, unlocking the ability to estimate 1O2 from existing source apportionment data. Overall, 1O2 is likely a competitive photo-oxidant in PM10 since 1O2 is sensitized by ubiquitous biomass burning OA and anthropogenic SOA.

Singlet oxygen quenching as a probe for cytochrome c molten globule state formation.

Singlet oxygen refers to the nonradical metastable excited state of molecular oxygen that readily oxidizes various cellular components. Its behavior in different biological systems has been studied for many years. Recently, we analyzed the effect of singlet oxygen quenching by heme cofactor in cytochrome c (cyt c). Here, we have exploited this effect in the investigation of conformational differences in the molten globule states of cyt c induced by different sodium anions, namely sulfate, chloride and perchlorate. The high efficiency of heme toward quenching singlet oxygen enabled us to use this property for the analysis of the otherwise experimentally difficult-to-determine parameter of heme upon exposure to solvents as highly similar conformational states of cyt c in the molten globule states are induced by different salts at acidic pH. Our results from singlet oxygen quenching experiments correlate well with other spectroscopic methods, such as circular dichroism and fluorescence measurements, and suggest increasing availability of heme in the order: perchlorate < chloride < sulfate. Based on our findings we propose that singlet oxygen phosphorescence measurements are useful in determining the differences in the protein conformation of their heme regions, particularly regarding the relative heme exposure to the solvent.

Theoretical study of new promising conjugated psoralens in psoralen ultraviolet A therapy

AbstractIn our previous report (J. Phys. Org. Chem., 2019), we discussed novel silicon photosensitizers (PSs) in psoralen ultraviolet A (PUVA) therapy. Continuing this quest, we have scrutinized a new brand of PSs, via density functional theory (DFT) and time‐dependent density functional theory (TD‐DFT) methods. These PSs show intense narrow absorption peaks in the therapeutic window with very high molar absorption coefficients ( ). Calculated vertical ionization potential (VIP) and vertical electron affinity (VEA) values indicate that our PSs can produce reactive oxygen species (ROS) through type I mechanism. Also, energies of the first triplet excited states (T1) and spin–orbit coupling (SOC) constants verify the possibility and efficiency of type II mechanism for the generation of the singlet excited state of molecular oxygen (1O2). The results introduce new potential PSs in PDT and PUVA therapy.

Singlet Oxygen Metabolism: From Genesis to Signaling.

Singlet oxygen (1O2) is an excited state of molecular oxygen with an electron spin shift in the molecular orbitals, which is extremely unstable and highly reactive. In plants, 1O2 is primarily generated as a byproduct of photosynthesis in the photosystem II reaction center (PSII RC) and the light-harvesting antenna complex (LHC) in the grana core (GC). This occurs upon the absorption of light energy when the excited chlorophyll molecules in the PSII transfer the excess energy to molecular oxygen, thereby generating 1O2. As a potent oxidant, 1O2 promotes oxidative damage. However, at sub-lethal levels, it initiates chloroplast-to-nucleus retrograde signaling to contribute to plant stress responses, including acclimation and cell death. The thylakoid membranes comprise two spatially separated 1O2 sensors: β-carotene localized in the PSII RC in the GC and the nuclear-encoded chloroplast protein EXECUTER1 (EX1) residing in the non-appressed grana margin (GM). Finding EX1 in the GM suggests the existence of an additional source of 1O2 in the GM and the presence of two distinct 1O2-signaling pathways. In this review, we mainly discuss the genesis and impact of 1O2 in plant physiology.

Quenching of singlet oxygen by natural and synthetic antioxidants and assessment of electronic UV/Visible absorption spectra for alleviating or enhancing the efficacy of photodynamic therapy

&#x0D; Photodynamic therapy (PDT) is one of the methods involved in cancer therapy exploiting singlet oxygen as a weapon to kill cancer cells. Singlet oxygen, a bizarre reactive oxygen species as it is not related to electron transfer to O2 but it is one of the most active intermediate involved in biochemical reactions as it directly reacts with all the major macromolecules like DNA, protein, lipids etc, various photosensitized oxidations and in the photodegradation of dyes and polymers. Recent studies about the usage of antioxidant along with the photo-sensitizer involved in photodynamic therapy have shown concentration- dependent dual behavior like usually it retards the efficacy of PDT but at a higher dose mostly, it actually enhances the damaging effect of PDT. The natural and synthetic antioxidants are being used in our day to day life in order to increase the shelf life of various food ingredients and processed foods. In this paper, we have compared natural and synthetic antioxidants along with the known singlet oxygen quencher (DABCO) in order to understand the quenching potential of singlet oxygen (1O2) which is lowest electronically excited state of molecular oxygen. The singlet oxygen can be artificially generated through various methods such as sunlight, phosphate, ozonides, NaOCl &amp; H2O2 etc. We have studied the mechanisms of the few antioxidant effects on the bleaching of RNO linked with the energy decay of 1O2 produced by the Mallet reaction (H2O2+HOCl → HCl+H2O+1O2). β-Carotene, α-Tocopherol, Ascorbic acid and Quercetin exhibited best dose-dependent singlet quenching ranging from 92.3 to 56.5 % at 100μM among others. Overall singlet oxygen is a major concern of light-related properties so we have analyzed the theoretical aspect of electronic UV/visible absorption spectra of the antioxidants studied through ZINDO CI semi-empirical Hamiltonian method. We have compared only the first singlet state of molecules in order to understand whether the structure of the molecules has any influence on the quenching potential. Considering the main features associated with singlet states, we have seen a drastic correlation between known sensitizer of singlet oxygen, i.e. Rose Bengal and DABCO, known scavenger of singlet oxygen in terms of energy and wavelength. This study is important as it highlights the behavior of antioxidant which can improve the effects of photosensitizer used in photodynamic therapy.&#x0D;

Quenching of singlet oxygen by natural and synthetic antioxidants and assessment of electronic UV/Visible absorption spectra for alleviating or enhancing the efficacy of photodynamic therapy

Photodynamic therapy (PDT) is one of the methods involved in cancer therapy exploiting singlet oxygen as a weapon to kill cancer cells. Singlet oxygen, a bizarre reactive oxygen species as it is not related to electron transfer to O2 but it is one of the most active intermediate involved in biochemical reactions as it directly reacts with all the major macromolecules like DNA, protein, lipids etc, various photosensitized oxidations and in the photodegradation of dyes and polymers. Recent studies about the usage of antioxidant along with the photo-sensitizer involved in photodynamic therapy have shown concentration- dependent dual behavior like usually it retards the efficacy of PDT but at a higher dose mostly, it actually enhances the damaging effect of PDT. The natural and synthetic antioxidants are being used in our day to day life in order to increase the shelf life of various food ingredients and processed foods. In this paper, we have compared natural and synthetic antioxidants along with the known singlet oxygen quencher (DABCO) in order to understand the quenching potential of singlet oxygen (1O2) which is lowest electronically excited state of molecular oxygen. The singlet oxygen can be artificially generated through various methods such as sunlight, phosphate, ozonides, NaOCl & H2O2 etc. We have studied the mechanisms of the few antioxidant effects on the bleaching of RNO linked with the energy decay of 1O2 produced by the Mallet reaction (H2O2+HOCl → HCl+H2O+1O2). β-Carotene, α-Tocopherol, Ascorbic acid and Quercetin exhibited best dose-dependent singlet quenching ranging from 92.3 to 56.5 % at 100μM among others. Overall singlet oxygen is a major concern of light-related properties so we have analyzed the theoretical aspect of electronic UV/visible absorption spectra of the antioxidants studied through ZINDO CI semi-empirical Hamiltonian method. We have compared only the first singlet state of molecules in order to understand whether the structure of the molecules has any influence on the quenching potential. Considering the main features associated with singlet states, we have seen a drastic correlation between known sensitizer of singlet oxygen, i.e. Rose Bengal and DABCO, known scavenger of singlet oxygen in terms of energy and wavelength. This study is important as it highlights the behavior of antioxidant which can improve the effects of photosensitizer used in photodynamic therapy.

Antioxidant β-Carotene Does Not Quench Singlet Oxygen in Mammalian Cells

Carotenoids, and β-carotene in particular, are important natural antioxidants. Singlet oxygen, the lowest excited state of molecular oxygen, is an intermediate often involved in natural oxidation reactions. The fact that β-carotene efficiently quenches singlet oxygen in solution-phase systems is invariably invoked when explaining the biological antioxidative properties of β-carotene. We recently developed unique microscope-based time-resolved spectroscopic methods that allow us to directly examine singlet oxygen in mammalian cells. We now demonstrate that intracellular singlet oxygen, produced in a photosensitized process, is in fact not efficiently deactivated by β-carotene. This observation requires a re-evaluation of β-carotene's role as an antioxidant in mammalian systems and now underscores the importance of mechanisms by which β-carotene inhibits radical reactions.

Generation of Singlet Oxygen from Fragmentation of Monoactivated 1,1-Dihydroperoxides

The first singlet excited state of molecular oxygen ((1)O(2)) is an important oxidant in chemistry, biology, and medicine. (1)O(2) is most often generated through photosensitized excitation of ground-state oxygen. (1)O(2) can also be generated chemically through the decomposition of hydrogen peroxide and other peroxides. However, most of these "dark oxygenations" require water-rich media associated with short (1)O(2) lifetimes, and there is a need for oxygenations able to be conducted in organic solvents. We now report that monoactivated derivatives of 1,1-dihydroperoxides undergo a previously unobserved fragmentation to generate high yields of singlet molecular oxygen ((1)O(2)). The fragmentations, which can be conducted in a variety of organic solvents, require a geminal relationship between a peroxyanion and a peroxide activated toward heterolytic cleavage. The reaction is general for a range of skeletal frameworks and activating groups and, via in situ activation, can be applied directly to 1,1-dihydroperoxides. Our investigation suggests the fragmentation involves rate-limiting formation of a peroxyanion that decomposes via a Grob-like process.

Mapping viscosity in cells using molecular rotors

This article describes an emerging method for quantitative measurement and spatial imaging of microviscosity within individual domains of live cells. The method is based on fluorescence detection from small synthetic molecules termed 'molecular rotors', which are characterised by a strong response of fluorescence lifetimes or spectra to the viscosity of their immediate environment. Alongside this new method, two complementary techniques are discussed, which provide further insights into diffusion controlled processes on a microscopic scale in a biological environment. These are time resolved fluorescence anisotropy and imaging of short-lived excited state of molecular oxygen, termed 'singlet oxygen'. It is possible to utilise all three approaches for the quantitative determination of viscosity in individual organelles of live cells. Finally, it is discussed how the major advantage of molecular rotor imaging, fast signal acquisition, can be used to monitor changing viscosity during dynamic biological processes within cells, such as photoinduced cell death.

Dissociative Excitation Energy Transfer in the Reactions of Protonated Cysteine and Tryptophan with Electronically Excited Singlet Molecular Oxygen (a1Δg)

We report a study on the reactions of protonated cysteine (CysH(+)) and tryptophan (TrpH(+)) with the lowest electronically excited state of molecular oxygen (O(2), a(1)Δ(g)), including the measurement of the effects of collision energy (E(col)) on reaction cross sections over the center-of-mass E(col) range of 0.05 to 1.0 eV. Electronic structure calculations were used to examine properties of complexes, transition states and products that might be important along the reaction coordinate. For CysH(+) + (1)O(2), the product channel corresponds to C(α)-C(β) bond rupture of a hydroperoxide intermediate CysOOH(+) accompanied by intramolecular H atom transfer, and subsequent dissociation to H(2)NCHCO(2)H(+), CH(3)SH and ground triplet state O(2). The reaction is driven by the electronic excitation energy of (1)O(2), the so-called dissociative excitation energy transfer. Quasi-classical direct dynamics trajectory simulations were calculated for CysH(+) + (1)O(2) at E(col) = 0.2 and 0.3 eV, using the B3LYP/6-21G method. Most trajectories formed intermediate complexes with significant lifetime, implying the importance of complex formation at the early stage of the reaction. Dissociative excitation energy transfer was also observed in the reaction of TrpH(+) with (1)O(2), leading to dissociation of a TrpOOH(+) intermediate. In contrast to CysOOH(+), TrpOOH(+) dissociates into a glycine molecule and charged indole side chain in addition to ground-state O(2) because this product charge state is energetically favorable. The reactions of CysH(+) + (1)O(2) and TrpH(+) + (1)O(2) present similar E(col) dependence, i.e., strongly suppressed by collision energy and becoming negligible at E(col) > 0.5 eV. This is consistent with a complex-mediated mechanism where a long-lived complex is critical for converting the electronic energy of (1)O(2) to the form of internal energy needed to drive complex dissociation.

Experimental and Trajectory Study on the Reaction of Protonated Methionine with Electronically Excited Singlet Molecular Oxygen (a1Δg): Reaction Dynamics and Collision Energy Effects

The reaction of protonated methionine with the lowest electronically excited state of molecular oxygen O(2)(a(1)Δ(g)) was studied in a guided ion beam apparatus, including the measurement of reaction cross sections over a center-of-mass collision energy (E(col)) range of 0.1-2.0 eV. A series of electronic structure and RRKM calculations were used to examine the properties of various complexes and transition states that might be important along the reaction coordinate. Only one product channel is observed, corresponding to generation of hydrogen peroxide via transfer of two hydrogen atoms (H2T) from protonated methionine to singlet oxygen. At low collision energies, the reaction approaches the collision limit and may be mediated by intermediate complexes. The reaction shows strong inhibition by collision energy, and becomes negligible at E(col) > 1.25 eV. A large set of quasi-classical direct dynamics trajectory simulations were calculated at the B3LYP/6-21G level of theory. Trajectories reproduced experimental results and provided insight into the mechanistic origin of the H2T reaction, how the reaction probability varies with impact parameter, and the suppressing effect of collision energy. Analysis of the trajectories shows that at E(col) = 1.0 eV the reaction is mediated by a precursor and/or hydroperoxide complex, and is sharply orientation-dependent. Only 20% of collisions have favorable reactant orientations at the collision point, and of those, less than half form precursor and hydroperoxide complexes which eventually lead to reaction. The narrow range of reactive collision orientations, together with physical quenching of (1)O(2) via intersystem crossing between singlet and triplet electronic states, may account for the low reaction efficiency observed at high E(col).

Effect of the granule size in porous silicon on the photosensitization efficiency of molecular oxygen on the surface of silicon nanocrystals

Photoluminescence is used to study the effect of the granule size in porous silicon on the generation efficiency of the excited state of molecular oxygen (1O2) on the surface of silicon nanocrystals. The generation efficiency is found to increase as the granule size becomes smaller than 100 nm, which can be explained by a change in the conditions of exciton diffusion along a network of silicon nanocrystals.

Differential cross section for electron impact excitation of the a 1Δ g state of molecular oxygen in the 15–180° angular range

The absolute differential cross section has been measured for excitation of the v = 0 vibrational level of the a 1Δ g excited state of molecular oxygen in a wide scattering angle range from 15° to 180° at an electron impact energy of 10 eV. The integral excitation cross section for the above state has been also obtained through integration of the measured differential cross section. Detailed comparison of the determined cross sections with the results of previous measurements and existing theoretical calculations has been given.

GOMOS serendipitous data products: The mesospheric sodium layer and various limb emissions

We present first results of the analysis of fine details present in GOMOS co-added transmittances. In particular, mesospheric sodium (around 589 nm) and the oxygen green line (at 557 nm) have been unambiguously identified and the Na concentration profile can be obtained by standard inversion techniques. Two other unusual spectral signatures have been observed, both exhibiting a strong altitude dependence, in absorption (511.7 nm) and in emission (601.2 nm), the first one perhaps being related to a transition c 1 Σ u - - b 1 Σ g + involving an excited state of molecular oxygen. The general usefulness of averaging limb transmittances data is discussed.

Measurement of Concentration of Singlet Molecular Oxygen in the Gas Phase by Electron Paramagnetic Resonance

Abstract The concentration of the lowest excited state of molecular oxygen, O2(1Δg), generated by gas-phase photosensitization with octafluoronaphthalene has been determined by electron paramagnetic resonance spectroscopy. The ground-state oxygen molecule, O2(3Σg−), was used as a quantitative standard. At low pressures, ≈0.12 Torr, about 30% of O2(3Σg−) was converted to O2(1Δg) under steady-state conditions.

Detection of Near-IR Singlet Oxygen Luminescence with an FT-Raman Spectrometer

The first excited state of molecular oxygen, O2(1Δg), lying at 0.98 eV above the ground state, O2(3Σg-), is relatively long-lived as a consequence of the multiple forbiddenness of the O2(1Δg) → O2(3Σg-) transition. As a result, O2(1Δg-) shows high reactivity to organic substrates, and irreversible photo-oxidative damage may occur. A typical example is that singlet oxygen is believed to be the cytotoxic species generated in the photodynamic therapy (PDT) of cancer.

8] Singlet oxygen DNA damage: Chromatographic and mass spectrometric analysis of damage products

Publisher Summary This chapter focuses on singlet oxygen DNA damage and discusses chromatographic and mass spectrometric analysis of damage products. Singlet oxygen ( 1 O 2 )—the lowest excited state of molecular oxygen—may be generated through energy transfer involving a type II photosensitized reaction and by thermal decomposition of endoperoxides and dioxetanes. Additionally, the formation of 1 O 2 in biological systems may be mediated by several enzymatic reactions and by chemiexcitation during lipid peroxidation. Like the highly reactive hydroxyl radical (.OH), but in a more specific manner, 1 O 2 is capable of inducing genotoxic, carcinogenic, and mutagenic effects and is likely involved in aging. The major biological target of 1 O 2 is DNA. The chapter describes that DNA synthesis blocking lesions induced by a chemical source of singlet oxygen are targeted to guanine residues in single-stranded DNA. This may be accounted for by the specific oxidation of the guanine moiety of DNA, which is the most reactive nucleobase toward the electrophilic addition of 1 O 2.

The collision-induced radiation of O 2(a 1Δ g)

Emissions from the first excited state of molecular oxygen, O 2 (a 1Δ g), have been observed over the pressure range 1–30 Torr in a flow system and from 5 to 1000 Torr in a static system. The relative intensities of the (0, 0) band at λ = 1.27 μm and of the (0, 1) band at λ= 1.58 μm were seen to change as a function of oxygen pressure. Further, at higher pressures a continuum was observed under the discrete lines of the (0, 1) molecular emission. Comparison of the intensities of the two bands enables rate constants for the collision-induced radiative processes to be deduced. These rate constants for the (0,0) and (0,1) bands respectively were found to be 4.1 × 10 −23 and 1.2 × 10 −23, 3.4 × 10 −23 and 9.9 × 10 −24, 2.4 × 10 −23 and 7.2 × 10 −24 cm 3 s −1 at 217, 293 and 336 K.