Generation of reactive oxygen species in water under exposure of visible or infrared irradiation at absorption band of molecular oxygen

It is found that in bidistilled water saturated with oxygen hydrogen peroxide and hydroxyl radicals are formed under the influence of visible and infrared radiation in the absorption bands of molecular oxygen. Formation of reactive oxygen species (ROS) occurs under the influence of both solar and artificial light sourses, including the coherent laser irradiation. The oxygen effect, i.e. the impact of dissolved oxygen concentration on production of hydrogen peroxide induced by light, is detected. It is shown that the visible and infrared radiation in the absorption bands of molecular oxygen leads to the formation of 8-oxoguanine in DNA in vitro. Physicochemical mechanisms of ROS formation in water when exposed to visible and infrared light are studied, and the involvement of singlet oxygen and superoxide anion radicals in this process is shown.     

Generation of reactive oxygen species in water under exposure to visible or infrared irradiation at absorption bands of molecular oxygen

It is found that in bidistilled water saturated with oxygen, hydrogen peroxide and hydroxyl radicals are formed under the influence of visible and infrared radiation in the absorption bands of molecular oxygen. Formation of reactive oxygen species (ROS) occurs under the influence of both solar and artificial light sources, including the coherent laser irradiation. The oxygen effect, i.e. the impact of dissolved oxygen concentration on production of hydrogen peroxide induced by light, is detected. It is shown that the visible and infrared radiation in the absorption bands of molecular oxygen leads to the formation of 8-oxoguanine in DNA in vitro. Physicochemical mechanisms of ROS formation in water when exposed to visible and infrared light are studied, and the involvement of singlet oxygen and superoxide anion radicals in this process is shown.     

Enhancement of oxygen absorption into sodium sulfite solutions

Oxygen absorption enhancement in a sodium sulfite solution was studied in the absence and presence of copper catalyst both for absorption across the liquid surface in a stirred cell and for absorption from individual bubbles rising through a turbulent liquid. The enhancement factor was determined from the ratio of oxygen and argon mass transfer coefficients, measured under identical experimental conditions in the same batch of liquid. It has been found that the oxygen absorption is not chemically enhanced, as long as the mass transfer coefficient, k_L⁰, is high enough, i.e., higher than the value 1.4 × 10^?4 m sec^?1 for the sulfite solution we used. An analysis of our data as well as literature data indicates that the sulfite system is poorly suited for studies of the volumetric mass transfer coefficient of physical absorption (k_L⁰a) in fermentors, inasmuch as oxygen absorption can be chemically enhanced while the degree of enhancement depends on the operating conditions of batch aeration, as well as on the concentration of trace impurities with catalytic effects upon the sulfite solution used.     

Surface solar ultraviolet radiation for paleoatmospheric levels of oxygen and ozone

Many investigators have concluded that the level of solar ultraviolet radiation (200–300 nm) reaching the surface was a key parameter in the origin and evolution of life on Earth. The level of solar ultraviolet radiation between 200 and 300 nm is controlled primarily by molecular absorption by ozone, whose presence is trongly coupled to the level of molecular oxygen. In this paper, we present a series of calculations of the solar ultraviolet radiation reaching the surface for oxygen levels ranging from 10^–4 present atmospheric level to the present level. The solar spectrum between 200 and 300 mn has been divided into 34 spectral intervals. For each spectral interval, we have calculated the solar ultraviolet radiation reaching the Earth's surface by considering the attenuation of the incoming beam due to ozone and oxygen absorption. A one-dimensional photochemical model of the atmosphere was used for these calculations.     

Activation of Molecular Oxygen by Infrared Laser Radiation in Pigment-Free Aerobic Systems

With the goal of mimicking the mechanisms of the biological effects of low energy laser irradiation, we have shown that infrared low intensity laser radiation causes oxygenation of the chemical traps of singlet oxygen dissolved in organic media and water saturated by air at normal atmospheric pressure. The photooxygenation rate was directly proportional to the oxygen concentration and strongly inhibited by the singlet oxygen quenchers. The maximum of the photooxygenation action spectrum coincided with the maximum of the oxygen absorption band at 1270 nm. The data provide unambiguous evidence that photooxygenation is determined by the reactive singlet ¹_g state formed as a result of direct laser excitation of molecular oxygen. Hence, activation of oxygen caused by its direct photoexcitation may occur in natural systems.     

Singular oxygen effects on the room-temperature phosphorescence of alcohol dehydrogenase from horse liver.

The room-temperature phosphorescence of alcohol dehydrogenase from horse liver in the presence of oxygen has the characteristics of a light-induced emission as it appears only after a certain amount of excitation has been absorbed. The initial lag period, the steady-state intensity, and the duration of the induced state are dominated by the oxygen content of the solution, the rate of light absorption, and the radiation dose. The phenomenon is not unique to this enzyme and the data are consistent with photochemical depletion of oxygen.     

X-ray absorption near edge structures of DNA or its components around the oxygen K-shell edge

The initial process of radiation damage in DNA was investigated by measuring the X-ray absorption near edge structures (XANES) within the energy region around the oxygen K-shell absorption edge for DNA, cytosine and 2-deoxy-d-ribose. Irradiation and XANES experiments were performed with the BL23SU soft X-ray beamline, using synchrotron radiation from the 8 GeV electron storage ring at SPring-8. Samples were mounted on gold-coated plates in a vacuum chamber. The XANES spectra were obtained by measuring the photoelectron current of the samples. 2-Deoxy-d-ribose was exposed to X rays at the absorption peak corresponding to the oxygen (O) 1s-->sigma* transition energy (538 eV); the XANES spectra were obtained after each irradiation. DNA and cytosine, possessing characteristic XANES spectra, both had two major energy bands corresponding to the O 1s-->pi* and 1s-->sigma* transitions. Two new peaks appeared and gradually increased in the XANES spectra of 2-deoxy-d-ribose during irradiation. These results suggest that C-O bonds in 2-deoxy-d-ribose are transformed to C=O bonds by O 1s-->sigma* transition, suggesting that the molecules undergo chemical changes into carbonyl-containing compounds.     

Photochemical investigation of the IR absorption bands of molecular oxygen in organic and aqueous environment

It is shown that the weak IR absorption bands corresponding to the forbidden triplet-singlet transitions in oxygen molecules can be reliably studied in air-saturated solvents under ambient conditions using measurements of the photooxygenation rates of singlet oxygen traps (1,3-diphenylisobenzofuran or uric acid) upon direct excitation of oxygen molecules by IR diode lasers. The best results were obtained from comparison of the oxygenation rates upon direct and photosensitized singlet oxygen excitation. In the present paper, this method was applied to estimation of the absorbance (A(ox)) and molar absorption coefficients (ε(ox)) corresponding to the oxygen absorption bands at 765 and 1273 nm in carbon tetrachloride, acetone, alcohols and water. In carbon tetrachloride, the band at 1073 nm was also investigated. Correlation of the obtained data with the luminescence spectra and radiative rate constants of singlet oxygen, contribution of oxygen dimols and biological significance of the studied effects are discussed.     

Superoxide dismutase and the oxygen enhancement of radiation lethality

Escherichia coli B were more susceptible to radiation lethality and showed a greater oxygen enhancement ratio when exposed in dilute suspension (1 × 10⁵ cells/ml) than when exposed in dense suspensions (1 × 10⁹ cells/ml). The oxygen enhancement, seen with dilute suspensions, was diminished by superoxide dismutase, catalase, mannitol, or histidine. Heat-denatured superoxide dismutase was without effect. The results are interpreted as indicating a role for O₂^? plus H₂O₂ in the oxygen enhancement of radiation lethality, and a scheme is proposed which is consistent with the observations.     

Glow discharge in singlet oxygen

Currently, there is no experimental data on the plasma balance in gas mixtures with a high content of singlet delta oxygen O₂(¹Δ_g). These data can be obtained by studying the parameters of an electric discharge in singlet oxygen produced by a chemical generator. The O₂(¹Δ_g) molecules significantly change the kinetics of electrons and negative ions in plasma. Hence, the discharge conditions at low and high. O₂(¹Δ_g) concentrations are very different. Here, the parameters of the positive column of a glow discharge in a gas flow from a chemical singlet-oxygen generator are studied. It is experimentally shown that, at an O₂(¹Δ_g) concentration of 50% and at pressures of 1.5 and 2 torr, the electric field required to sustain the discharge is considerably lower than in the case when all of the oxygen molecules are in the ground state. A theoretical model of the glow discharge is proposed whose predictions are in good agreement with the experimental data.     

Three-dimensional simulations of anomalous absorption of laser radiation by plasma with supercritical density

A three-dimensional (3D) model of the interaction of laser radiation with plasma in the framework of Maxwell-Vlasov equations has been used to calculate the anomalous optical absorption in plasma of supercritical density. The results of calculations confirmed the development of anomalous absorption that was previously revealed by 2D models, which were insufficient for comparison to the experiment. Calculations were performed for a system containing about 10⁶ macroparticles that allowed the absorption coefficient and other characteristics of anomalous absorption in plasma with an inhomogeneous surface to be determined as functions of various parameters of the incident radiation and plasma target. Results are analyzed and estimations are obtained for the contributions of ionization processes and pair collisions of electrons, which show that these factors were quite reasonably ignored in the model. All quantitative results are obtained for the third harmonic of neodymium laser (λ = 0.351 μm) at a tenfold excess of the substance density over a critical value for this radiation.     

Similarities and differences of hyperbaric oxygen and medical ozone applications

Abstract

Hyperbaric oxygen (HBO) treatment is based on the principle of having the patient breath 100% oxygen in an environment above atmospheric pressure. Ozone (O₃) is a colourless gas with a specific odour and consists of three oxygen atoms. The classical scientific understanding is that the world has become a place suitable for life for aerobic organisms with the increasing oxygen in the atmosphere billions of years ago. The formation of ozone after oxygen has then protected aerobic creatures from harmful rays. We now use these two gases for treatment purposes. It is noteworthy that the oxygen and ozone molecules that are formed by the same atom in different numbers are used for similar medical indications. We will try to emphasize the similarities and differences of HBO and medical ozone applications in this article.     

Fluorescence excitation profiles of beta-carotene in solution and in lipid/water mixtures

Intrinsic fluorescence from all-trans β-carotene molecules in solution and embedded in lipid/water mixtures has been observed under laser excitation and its excitation profiles measured. The profiles closely correspond to the absorption spectra. The observations can be explained in terms of a low-lying ¹A_g excited state.     

Correlation of liquid dispersion and oxygen transfer in bubble column

Summary In steady state, attained by continuous aeration after oxygen saturation of water in a bubble column, vertical composition distribution of liquid and gas phases has been determined. It has been assumed that, as a result of absorption at the bottom of the column, desorption in the upper section and vertical dispersion of dissolved oxygen flux, a closed oxygen circulation is created. Determination of the axial dispersion coefficient from hydrodynamic and oxygen transfer data verifies the mathematical model proposed. The results allow conclusions to be drawn about supersaturation and desorption and other phenomena expected in biological systems.Abbreviations C[-] Dimensionless oxygen concentration Unit=0.21 bar oxygen partial pressure or dissolved oxygen level in equilibrium with latter - E[m²/s] Axial dispersion coefficient - F[m²] Horizontal cross-section area - k _L a[s^-1] Overall oxygen transfer coefficient - u; u ₂[m/s; cm/s] Superficial velocity: related to state of bubbles leaving the sparger - x; x _atm[-] Signal registered in the experiment; signal recorded in O₂ saturated water, or water vapor saturated air stream, at temperature identical to the experiment under atmospheric pressure - y[m] Water column height - [s^-1] Dimensionless oxygen flux Indices a asorption - d desorption - g gas - l liquid - k dispersion - m measured value/in the case of hydrodynamically measured E/ Dedicated to Professor Dr. H. J. Rehm on the occasion of his 60th birthday     

Interaction of tyrosine with dissolved oxygen in solution and spectroscopic evidence for oscillations

Electronic absorption and fluorescence spectra of tyrosine have been studied, using aqueous solutions containing normal and excess amounts of dissolved oxygen, as a function of time. The absorption and fluorescence intensities are found to oscillate with time. Interaction between tyrosine and oxygen is appreciable but it seems that either the formation of a complex between the two molecules is not favoured, or the process of complexation is very slow and the complex weak.     

Production of singlet oxygen in a non-self-sustained discharge

The production of O₂(a¹Δ_g) singlet oxygen in non-self-sustained discharges in pure oxygen and mixtures of oxygen with noble gases (Ar or He) was studied experimentally. It is shown that the energy efficiency of O₂(a¹Δ_g production can be optimized with respect to the reduced electric field E/N. It is shown that the optimal E/N values correspond to electron temperatures of 1.2–1.4 eV. At these E/N values, a decrease in the oxygen percentage in the mixture leads to an increase in the excitation rate of singlet oxygen because of the increase in the specific energy deposition per O₂ molecule. The onset of discharge instabilities not only greatly reduces the energy efficiency of singlet oxygen production but also makes it impossible to achieve high energy deposition in a non-self-sustained discharge. A model of a non-self-sustained discharge in pure oxygen is developed. It is shown that good agreement between the experimental and computed results for a discharge in oxygen over a wide range of reduced electric fields can be achieved only by taking into account the ion component of the discharge current. The cross section for the electron-impact excitation of O₂(a¹Δ_g and the kinetic scheme of the discharge processes with the participation of singlet oxygen are verified by comparing the experimental and computed data on the energy efficiency of the production of O₂(a¹Δ_g and the dynamics of its concentration. It is shown that, in the dynamics of O₂(a¹Δ_g molecules in the discharge afterglow, an important role is played by their deexcitation in a three-body reaction with the participation of O(³P) atoms. At high energy depositions in a non-self-sustained discharge, this reaction can reduce the maximal attainable concentration of singlet oxygen. The effect of a hydrogen additive to an Ar: O₂ mixture is analyzed based on the results obtained using the model developed. It is shown that, for actual electron beam current densities, a significant energy deposition in a non-self-sustained discharge in the mixtures under study can be achieved due to the high rate of electron detachment from negative ions. In this case, however, significant heating of the mixture can lead to a rapid quenching of O₂(a¹Δ_g molecules by atomic hydrogen.     

Enhancement factor for oxygen absorption into fermentation broth

Values of the enhancement factor for oxygen absorption into fermentation broth, i.e., the ratio of the liquid phase mass transfer coefficients for oxygen absorption for both cases with and without respiration of microorganisms were predicted theoretically on the assumption of various cell concentration distributions. Calculations indicate that in the usual case the enhancement factor is only slightly or negligibly larger than unity, even when accumulation of microorganisms at or near the gas-liquid interface is assumed. Results of experiments with sparged-stirred fermentors on oxygen absorption into fermentation broths containing resting and growing cells of Candida tropicalis confirmed the theoretical prediction. Except for extreme cases, the effect of respiration of microorganisms on k_La, values can practically be ignored.     

Breakdown of highly excited oxygen in a DC electric field

The breakdown of oxygen in a dc electric field is studied. A high concentration of oxygen molecules in the a ¹Δ_g excited state is obtained in a purely chemical reactor. A decrease in the breakdown voltage at degrees of excitation exceeding 50% is observed. The theoretical decrement in the breakdown voltage obtained by solving the Boltzmann equation is in good agreement with the experimental data.     

State-dependent and site-directed photodynamic transformation of HCN2 channel by singlet oxygen

Singlet oxygen (¹O₂), which is generated through metabolic reactions and oxidizes numerous biological molecules, has been a useful tool in basic research and clinical practice. However, its role as a signaling factor, as well as a mechanistic understanding of the oxidation process, remains poorly understood. Here, we show that hyperpolarization-activated, cAMP-gated (HCN) channels–which conduct the hyperpolarization-activated current (I_h) and the voltage-insensitive instantaneous current (I_inst), and contribute to diverse physiological functions including learning and memory, cardiac pacemaking, and the sensation of pain–are subject to modification by ¹O₂. To increase the site specificity of ¹O₂ generation, we used fluorescein-conjugated cAMP, which specifically binds to HCN channels, or a chimeric channel in which an in-frame ¹O₂ generator (SOG) protein was fused to the HCN C terminus. Millisecond laser pulses reduced I_h current amplitude, slowed channel deactivation, and enhanced I_inst current. The modification of HCN channel function is a photodynamic process that involves ¹O₂, as supported by the dependence on dissolved oxygen in solutions, the inhibitory effect by a ¹O₂ scavenger, and the results with the HCN2-SOG fusion protein. Intriguingly, ¹O₂ modification of the HCN2 channel is state dependent: laser pulses applied to open channels mainly slow down deactivation and increase I_inst, whereas for the closed channels, ¹O₂ modification mainly reduced I_h amplitude. We identified a histidine residue (H434 in S6) near the activation gate in the pore critical for ¹O₂ modulation of HCN function. Alanine replacement of H434 abolished the delay in channel deactivation and the generation of I_inst induced by photodynamic modification. Our study provides new insights into the instantaneous current conducted by HCN channels, showing that modifications to the region close to the intracellular gate underlie the expression of I_inst, and establishes a well-defined model for studying ¹O₂ modifications at the molecular level.     

Thermal plasma irradiation under the action of the microwave-frequency-modulated laser beam

The results of the calculation of the thermal irradiation of the laser plasma formed by a powerful laser beam with the microwave-frequency-modulated intensity are presented. The analytical solution has been obtained for the case of the light detonation regime. It has been shown that the modulation of the gasdynamic parameters due to the absorption of the laser radiation leads to the modulation of the spectral and integral brightness observed from the thermal plasma irradiation.