Molecular Oxygen 1O2 Research Articles

Photophysical Behavior of Angelicins and Thioangelicins: Semiempirical Calculations and Experimental Study

AbstractThe decay processes of the lowest excited singlet and triplet states of five methylated angelicins (4,6,4′‐trimethyl‐angelicin, MA, and four methylated thioangelicins, MTA; see Scheme 1) were investigated in live solvents by stationary and pulsed fluorometric and flash photolytic techniques. In particular, the solvent effects on absorption, fluorescence, quantum yields of fluorescence (φF) and triplet formation (φT), lifetimes of fluorescence (τF) and the triplet state (τT) and the quantum yields of singlet oxygen production (φΔ) were investigated. Semiempirical (ZINDO/S‐CI) calculations were carried out to obtain information (transition probabilities and nature) on the lowest excited singlet and triplet states. The quantum mechanical calculations and the solvent effect on the photophysical properties showed that the lowest excited singlet state (S1) is a partially allowed π,π* state, while the close‐lying S2 state is n,π* in nature. The efficiencies of fluorescence, S1→T1 intersystem crossing (ISC) and S1→ S0 internal conversion (IC) strongly depend on the energy gap between S1, and S2 and are explained in terms of the so‐called proximity effect. In fact, for MA in cyclohexane, only the S1→ S0 internal conversion is operative, while in acetonitrile and ethanol, where the n.π* state is shifted to higher energy, the efficiencies of fluorescence and ISC increase significantly. The energy gap between S1 and S2 increases in MTA, where the furanic oxygen is replaced by a sulfur atom. Consequently, the solvent effect on the photophysical parameters of MTA is less marked than for MA; e.g. fluorescence and triplet‐triplet absorption are also detectable in the nonpolar cyclohexane. The lowest excited singlet state of molecular oxygen O2(1Dg) was produced efficiently in polar solvents by energy transfer from the T1 state of MA and MTA.

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.

Reactions of Sodium Clusters with Oxygen Molecules

In a crossed molecular beam experiment, the reactive scattering of sodium clusters Nan (n ≤ 33) with molecular oxygen O2 is investigated. By measuring the angular and the velocity distributions of the scattered reaction products, direct information on the reaction mechanisms is obtained. The sodium clusters are generated in a supersonic expansion of sodium vapor from an oven with a refilling system with argon carrier gas. The products are detected by photoionization at a wavelength of 308 nm and mass analyzed in a time-of-flight mass spectrometer (TOF-MS). In addition, a fast chopper with a pseudorandom sequence modulating the sodium cluster beam allows us to determine at the same time the velocity distributions of the products. The scattering of Na clusters with O2 shows two series of reaction products. The monoxides NanO are centered around Na3O with 2 ≤ n ≤ 5, while the metal-rich dioxides NanO2 are detected for 3 ≤ n ≤ 32 with varying intensities and a maximum at Na5O2. For all products, the measured ...

Time‐Resolved Near Infrared Studies on Singlet Oxygen Production by the Photosensitizing 2‐Arylpropionic Acids*

Abstract— Time‐resolved near infrared emission studies have been carried out on a series of nonsteroidal anti inflammatory 2‐arylpropionic acids, in order to assess their ability to photosensitize the production of singlet molecular oxygen O2(1Δg). Benoxaprofen, naproxen, tiaprofenic acid, suprofen, ketoprofen and carprofen showed quantum yields for this process (φΔ) in the range 0.2‐0.7 in acetonitrile. Deprotonation of the propionic acid moiety in mixtures of acetonitrile‐ethanol (4:1) basified with KOH produced a systematic decrease in φΔ for all compounds with the exception of naproxen. This effect was even more dramatic in D2O‐based phosphate buffer, where no singlet oxygen could be detected for benoxaprofen, ketoprofen or carprofen. The above results are consistent with the occurrence of competing photochemical reactions of 2‐arylpropionic acids in different media and particularly with the enhanced photodecarboxylation from the carboxylate anions.

Excited Electronic States and Ionic States of Molecular Oxygen

Abstract Since molecular oxygen O2 is one of the most fundamental and practically important molecules in its chemical and biochemical reactions, it is very important to clarify its excited electronic states, including various Rydberg states, as much as possible. So far, two comprehensive review articles have been published on molecular oxygen by Krupenie [I] and Michels [2], summarizing the experimental and theoretical spectroscopic data of O2 and its ions O− 2, O+ 2, and O2+ 2 published up to 1976. Molecular constants of O2 and its ions have been compiled in detail by Huber and Herzberg [3]. All these spectroscopic data [1–3] are predominantly associated with one-photon-allowed excited electronic states.

Ozone generation in an oxygen-fed wire-to-cylinder ozonizer at atmospheric pressure

A numerical simulation, including transport phenomena, is presented in this paper for the calculation of ozone generation in an oxygen-fed wire-to-cylinder ozonizer. The ozone density dependence on the first excited states of atomic and molecular oxygen and ozone is analysed, introducing three kinetic models. The influence of excited states on ozone production is shown as well as the correlation between the first excited state of atomic oxygen O(1D) and the second excited state of molecular oxygen O2(1 Sigma +g). Furthermore, these results confirm the validity of the plug-flow reactor hypothesis in the case of an oxygen-fed ozonizer.

A MORE EXACT THEORETICAL INTERPRETATION OF RECENT EXPERIMENTAL DATA OBTAINED USING THE SEPARATED SENSITIZER AND SUBSTRATE METHOD TO INVESTIGATE O2(lδg) INTERACTIONS. POSSIBLE IMPORTANCE OF O2(1σg+)

Abstract— Recent experimental data obtained using the separated sensitizer and substrate method to investigate the interaction of O2(1δg) with various substances has been re‐interpreted by means of a more complete theory. Comparison of experimental and recalculated values of the dependence of relative reaction rates on the sensitizer‐substrate separation indicate general accord for experiments in which singlet oxygen acceptors in aqueous solution were used. The presumption is therefore that singlet molecular oxygen O2(1δg) is indeed the active oxidizing agent and that the theory presented and experiment are entirely in agreement.For experiments in which bacterial targets were used a very distinct disagreement between theory and experiment is evident, the conclusion being that the kill rate does not depend linearly on the O2(1δg) concentration in the immediate proximity of the bacteria. However, the data is consistent with a quadratic dependence on the 1δg concentration. A possible conclusion therefore is that the cytotoxic species is actually O2(1σ+g), formed by an energy pooling reaction involving two O2(1δg) molecules.

Chemistry of singlet oxygen. 40. Enhanced molecular oxygen 1O2 formation in cyanoaromatic-sensitized photooxidations by substrate-enhanced intersystem crossing

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTChemistry of singlet oxygen. 40. Enhanced molecular oxygen 1O2 formation in cyanoaromatic-sensitized photooxidations by substrate-enhanced intersystem crossingLewis E. Manring, Chee Liang Gu, and C. S. FooteCite this: J. Phys. Chem. 1983, 87, 1, 40–44Publication Date (Print):January 1, 1983Publication History Published online1 May 2002Published inissue 1 January 1983https://doi.org/10.1021/j100224a012RIGHTS & PERMISSIONSArticle Views131Altmetric-Citations62LEARN 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 (595 KB) Supporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Electronic Energy Transfer from Sinclet Molecular Oxygen to Carotenoids

Abstract Aerated benzene solutions containing anthracene together with one of the carotenoids, β-carotene, β-apo-8′-carotenal, ethyl β-apo-8′-carotenate and canthaxanthin were subjected to laser photolysis. Under these conditions oxygen quenching of triplet anthracene produces the excited singlet state of molecular oxygen O2∗ (1δg) which in turn transfers energy to the carotenoid thereby yielding its triplet state, the absorption of which was monitored thereby confirming electronic energy transfer as the mechanism of quenching of O2 ∗(1δg) by these carotenoids and enabling the bimolecular quenching constansts which vary from 1.2 – 1.45 × 1010 1 mol−1s−1 to be measured.

Collisional deactivation of laser excited singlet molecular oxygen by ozone

The effect of small amounts of ozone (5–38 mm) on the rate of collisional deactivation of singlet molecular oxygen O2(1Δg) excited by means of laser radiation at 1.064 μ has been investigated. Due to the fact that high oxygen pressures were used (35 atm), the rate of deactivation of O2(1Δg) by collision with ground electronic state oxygen O2(3Σ−g) competes with deactivation by O3, a situation not encountered by previous investigators at much lower pressures. In the case of minimum O3 partial pressure (5 mm), the effect of O3 in direct deactivation of O2(1Δg) is negligible, with the controlling process being an intersystem crossing (electronic–vibration) O2(1Δg)(v′=0) →O2(3Σ−g)(v=5). Analysis of the data indicates that transfer of this large amount of vibrational energy to O3 en bloc must take place with high efficiency, producing O3 in a highly excited vibrational state lying just below the dissociation limit. Dependence of the overall deactivation rate of O2(1Δg) on O3 partial pressure exhibits a quadratic term in addition to the linear variation observed by other investigators at lower pressures. The effect of adding a third component (He, SO2, CO2, and NO2) with the ozone partial pressure held constant was also studied.

Seasonal Effects on Distributions of Minor Neutral Constituents in the Mesosphere and Lower Thermosphere

Calculations have been made of the diurnal variations in minor neutral constituents in the mesosphere and lower thermosphere for the condition of 60° latitude, summer and winter, using the method developed by the authors [Shimazaki and Laird, 1970]. The excited molecular oxygen O2(1Δg) has been added and the effects of absorption of Schumann‐Runge bands have been taken into account. The results show significant seasonal differences, which may be interpreted mainly in terms of the difference of penetration of solar radiation and the duration of sunlit hours. However, the comparison of the observed seasonal and diurnal variations in the airglow emissions from hydroxyl, atomic oxygen (5577 Å), and O2(1Δg) with those calculated from models suggests that effects of large‐scale meridional circulation (horizontal and vertical transports) may be important in explaining these observations. It is shown that the concentration of the constituents whose main loss mechanism is recombination with atomic oxygen decreases sharply above ˜80 km. These constituents include OH, HO2, H2O2, and NO2 (nighttime) and the extension of this general theory may explain the sudden decrease observed by rockets in the water‐cluster ion concentration above ∼80 km. Ion‐neutral chemistry should be important in explaining an observed increase in [NO] above ∼85 km.

Determination of parameters appearing in the “dry” and the “wet” photochemical theories for ozone in the stratosphere

Existing photochemical theories of the ozone in the stratosphere have been investigated. It is indicated in this work that the ozone concentrations above 30 km between 0° and 45° latitude during the summer months are mainly determined by photochemical processes.Parameters appearing in the schemes proposed by Chapman and Hampson are determined by fitting them to the mean ozone observations obtained from the Umkehr method. The results obtained simply that it is unlikely that any of the above mentioned theories alone can explain the ozone distributions. Numerical conditions on critical parameters are given. An alternative theory involving water vapour dissociation by excited molecular oxygen O2(3Σ+u) is also discussed.