Efficiency Of Radical Production Research Articles

Hypoxia-Induced Photogenic Radicals by Eosin Y for Efficient Phototherapy of Hypoxic Tumors.

The current reported photosensitizers generally show a decreased reactive oxygen species (ROS) generation property under hypoxia conditions, which is the main reason for the clinical failure of photodynamic therapy (PDT) in treatment of solid tumors. Herein, for the first time, hypoxia-induced photogenic radicals by eosin Y (Eos) were reported for efficient phototherapy of hypoxic tumors. More importantly, Eos shows a higher ROS and radical production efficiency under hypoxia conditions than under normoxia conditions. The photogenic radicals were captured by electron paramagnetic resonance and further verified by ROS and radical probe. Introducing CoCl2 as a hypoxia inducer, the photoinduced therapy of the hypoxia cancer cell model and tumor-bearing mice indicated that bovine serum albumin-Eos in hypoxic tumor sites can produce even higher tumor toxicity, thereby crossing the clinical obstacles of hypoxic tumor therapy. This non-oxygen-dependent PDT may open up an avenue for fighting with hypoxia.

The Effect of TiO2 Catalyst on the NO Reduction by Barrier Discharge in Nitrogen

The study investigated NO reduction by N radicals produced by barrier discharge in nitrogen and the possible effect of TiO2 catalyst on this reaction. The experiments for NO reduction were carried out at temperatures ranging from room temperature to 140 °C and at NO concentrations ranging from 200 to 800 ppm. The experimental results were described by a model which was based on six main reactions for the calculation of the NO and NO2 concentrations. The analysis of model suggested two simple methods for the estimation of nitrogen radical production efficiency which in present study was 2 ppm/(J/L). The model also confirmed that N radicals are used very efficiently in the reduction of NO and this process can’t be improved by the catalyst. Nonetheless, experiments showed that the presence of TiO2 catalyst improved the removal of NO. The experimental results can be explained by surface processes taking place with NO2 with the help of other plasma produced nitrogen species.

Radical production efficiency and electrical characteristics of a coplanar barrier discharge built by multilayer ceramic technology

The present study investigated the electrical characteristics and radical production efficiency of a coplanar barrier discharge (CBD) device manufactured by Kyocera by multilayer ceramic technology. The device consisted of a number of linear electrodes with electrode and gap widths of 0.75 mm, immersed into a ceramic dielectric barrier. A closed flow-through system necessary for the measurements was prepared by placing a quartz plate at a height of 3 mm from the ceramic barrier. The production of nitrogen radicals was determined from the removal of a trace amount of NO in pure N2 gas, while the production of oxygen radicals was determined by ozone production in pure O2 or synthetic air. The production efficiency of N and O radicals and NO oxidation in synthetic air was comparable with the efficiency of a volume barrier discharge device. The power density per unit of surface area of the CBD device was more than two times larger than that of a similar volume barrier discharge setup, which makes the CBD device a compact alternative for gas treatment. The production of ozone and different nitrogen oxides was also evaluated for the open system of the CBD which is usable for surface treatment. The ozone concentration of this system was nearly independent from the input power, while the concentration of nitrogen oxides increased with input power. The open system of the CBD was additionally tested for the treatment of a silicon surface. An increase of applied power decreased the time required to reduce the water contact angle below 10 degrees but also started to have an impact on the surface roughness.

Numerical simulation of nanosecond pulsed DBD in lean methane–air mixture for typical conditions in internal engines

Detailed two-dimensional numerical simulations of a high energy loading nanosecond dc pulse DBD in a lean methane–air mixture were conducted for plasma-assisted combustion by integrating individual models of plasma chemistry, photoionization and energy loading. The DBD streamer propagation process with radical productions was clarified at 10 atm and 600 K as under the condition of actual internal engines at ignition. Energy is loaded to the streamer first by the formation of plasma channel and then ceased due to the self-shielding effect. Because of the inversed electric field in a discharge space during decrease in applied voltage, energy is loaded to the discharge again. It was found that higher energy is loaded to the DBD streamer for larger dielectric constant even at lower applied voltage, and higher number density of oxygen radical is produced at almost the same radical production efficiency.

Large Area Pulsed Corona Discharge in Water for Disinfection and Pollution Control

To investigate the efficiency of submerged pulse corona (SPC) discharges in water we built a laboratory scale, parallel-plate reactor that is part of a closed loop water circulation system. A pulsed voltage is applied across the electrodes. One of the electrodes is coated with a porous ceramic layer to create local field enhancements to initiate corona discharges. For energization of the SPC reactor a pulse generator was developed which is based on a capacitor discharge initiated by a semiconductor switch. A pulse transformer, followed by two magnetic pulse compression stages, produces voltage pulses with amplitudes of up to 30 kV at a pulse width of 0.3 ?s. Simulation of the circuit behavior leads to good agreement with voltage and current measurements. Details of the pulse generator and first experimental results concerning the efficiency of radical production are presented. Depending on the conductivity of the water to be treated, pulse currents of > 600 A at a voltage of 20 kV to > 30 kV are obtained for electrode sizes of around 50 cm2. The efficiency of the radical production is measured in terms of the hydrogen peroxide (H2O2) concentration, which is formed by recombination of hydroxyl radicals (OH.) at sufficiently high concentrations downstream of the plasma reactor. At pulse repetition rates of 20 to 100 Hz, H2O2 concentrations of several mg/l are produced, at efficiencies in the range of up to ?1 g/kWh.

Combined effect of electrode gap and radio frequency on power deposition and film growth kinetics in SiH4/H2 discharges

The combined effect of the variation of the interelectrode gap (1.3–2.5 cm) and radio frequency (13.56–50 MHz) on the properties of highly diluted silane in hydrogen discharges used for the deposition of microcrystalline silicon thin films is presented. The investigation included electrical and optical discharge measurements as well as the in situ determination of the film growth rate. In the lower frequencies regime, the increase of the interelectrode gap for the same applied voltage results in higher current flows and higher total power dissipation. On the other hand, at 50 MHz the variation of the interelectrode space has only a slight effect on the total power dissipation, due to the low excitation voltage. However, at all frequencies, the increase of the interelectrode space results in a drop of the power dissipation per discharge volume. This is related to the less effective energy transfer to the electrons that is due to the enhancement of the bulk relative to the sheath ohmic heating. The variation of the relative importance of the electron heating modes is reflected in the discharge radical production efficiency and the film growth rate.

Nucleotide Oxidation Mediated by Naphthalimide Excited States with Covalently Attached Viologen Cosensitizers¶

Abstract The ground- and excited-state interactions of polymethylene-linked 1,8-naphthalimide–viologen dyads with calf-thymus DNA have been investigated. By virtue of the covalently attached viologen, the compounds represent the first example of linked chromophore/cosensitizer systems in the photooxidation of duplex DNA. The compounds associate strongly with DNA. Analysis of ground-state spectral changes yield binding constants of 0.7–2.5 × 106 M−1. Upon 355 nm pulsed irradiation of the compounds in the presence of calf-thymus DNA, reduced viologen is observed within the laser pulse. Photoproducts are not observed on this time scale in the absence of DNA. Since ground-state bleaching of the naphthalimide was not observed, the results suggest that DNA nucleobases are the species being oxidized. The quantum efficiency of radical production increases with the extent of binding to DNA. Under conditions where the compounds are bound predominantly to DNA, the quantum efficiencies were found to range from 0.02 t...

Two-dimensional simulation of filaments in barrier discharges

We present a fluid model for barrier discharges in air at atmospheric pressure with spectral resolved photonic secondary processes, implemented with general finite-element software. The results show five different discharge phases, a homogenous and a space-charge dominated avalanche phase, a phase of dielectric charging with field enhancement due to positive ions causing streamer formation, a cathode streamer and a subsequent glow-discharge phase with a cathode-fall region. Quenching of the microdischarge occurs after a few nanoseconds by the increasing charge on the dielectric. While the capacity of the dielectric has nearly no influence on the energetic efficiency of radical production and vacuum-UV-irradiation of the dielectric, a higher voltage causes a small decrease in radical efficiency and a significant increase in the efficiency of VUV-irradiation of the dielectric.

1 kW Pulse Corona Reactor for Voc Destruction

A I kW pulse corona reactor has been developed capable of treating gas flows up to 100 m3/h. The discharge efficiency reaches 80 % in air and nearly 100 % in nitrogen flows. The efficiency of radical production has been proofed by ozone synthesis as weil as by NO to N2 conversion.

Simulation of microdischarges in a dielectric-barrier discharge

The results of simulation of microdischarges in a dielectric-barrier discharge are presented. These simulations have been carried out in two dimensions with an adaptive grid. The results presented are for oxygen at atmospheric pressure. The dielectric has little effect on the propagation of the streamerlike discharge until the very last stage. The dielectric capacitance has been found to have very little effect on the radical production efficiency.

Nature and ESR anisotropy of trapped radicals in UV‐irradiated isotactic polypropylene at 4.2 K and 77 K

AbstractA comparative ESR study of low‐temperature photolysis at 77 and 4.2 K of isotactic polypropylene, preoxidized under controlled conditions, and of 2.6.8 trimethylnonane‐4‐one as a model compound of the inchain PP ketones CH2COCH2 is presented. The results show conclusively that the ESR spectra of low‐temperature PP photolysis reported in the literature arise from the decomposition of tertiary hydroperoxides, whereas the contribution by the Norrish I photolytic cleavage of ketones is of minor importance; the relative efficiency of radical production at 77 K (λ ≥ 300 nm) by both types of photoactive compound has been measured by ESR and found to be about 15 times greater for the hydroperoxides. The mechanism of solid‐state photolysis of PP hydroperoxides is dominated by the nearly complete decay of excited alkoxyls during the photolytic events that yield the chain end radicals CH(CH3)CH2· by β scission (87.8%) and the inchain radicals CH2C(CH3)CH2 by hydrogen abstraction (10.4%). The low yield of methyl radicals detected (1.8%) and their delayed appearance strongly suggest that these species are of secondary origin and that the decomposition of alkoxyls via CCH3 scission is of negligible importance. From the ESR anisotropy of the deliberately prepared peroxyradicals CH(CH3)CH2O2· and CH2C(CH3)(O2)CH2 evidence of the misalignment of terminal chain segments following scission of alkoxyls at 77 K was obtained. An unexpected result of the measurements at 4.2 K is represented by the identification of a clear signal by H atoms: the H atoms apparently are not trapped in perprotiated matrices, even at 4.2 K, because of their unusually high reactivity toward the hydrogen abstraction assisted by tunneling effects.

Free radicals from eumelanins: Quantum yields and wavelength dependence

Formation of light-induced free radicals from natural eumelanin (from bovine eyes) and synthetic melanin (from oxidation of 3,4-dihydroxyphenylalanine) has been studied by electron spin resonance spectroscopy. Action spectra measured for natural melanins are very similar to that found for synthetic melanin, and are unaffected by the removal of associated protein. A comparison of action spectra with optical absorbance spectra shows that the former has a more marked wavelength dependence, suggesting that the chromophore that is most active in free-radical production is not the major melanin chromophore that absorbs visible light. Measurements of quantum yields for freeradical production have been made over a wavelength range from 600 to 230 nm. The efficiency of radical production from natural eumelanin is about three times greater than from the synthetic material. Although production of the melanin radicals detected is independent of oxygen, some correlation with oxygen consumption is evident; quantum yields for radical production are approximately three times those for oxygen consumption obtained under similar conditions. Possible reasons for this are discussed.

Solvent Effects in the Oxidation of Hydrocarbons. I. Chain Initiation by Azobisisobutyronitrile

Abstract The effects of solvents on the rate of decomposition and the efficiency of radical production by AIBN were studied by measuring the rate of evolution of nitrogen from AIBN and the inhibition time in the oxidation of tetralin. The rates of decomposition of AIBN were larger in aromatic solvents than in aliphatic solvents. The efficiency of AIBN was found to depend more on the viscosity of the medium than on the polarity of the solvents. The requirements for the determination of the inhibition time are discussed.

REACTIONS OF RADICALS. III. MEASUREMENT OF THE TRANSFER CONSTANT OF t-BUTYL PEROXIDE USING RADIOACTIVE PEROXIDE1,2

The decomposition of C14-labeled tert-butyl peroxide (TBP) in the polymerization of styrene in the presence of inactive azobisisobutyronitrile was investigated. The efficiency of radical production from TBP was found to be very high. (D.L.C.)

The efficiency of radical production by x-rays in dry proteins and nucleic acids.

Data are tabulated on the yields of radicals per 100 ev of absorbed energy for several proteins and nucleic acids exposed in the dry state to various doses of x radiation. Spectrographic recordings of paramagnetic absorption in the irradiated.samples were analyzed and findings compared with previous results on amino acids. Results indicate that yields in proteins and nucleic acids are of the same orders as those in amino acid;. Applications of the findings in efforts to elucidate the part played by radicals in primary mechanisms of radiation damage in biological systems are discussed briefly. (C.H.)

The Efficiency of Radical Production from Azo-bis-isobutyronitrile

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe Efficiency of Radical Production from Azo-bis-isobutyronitrileGeorge S. Hammond, Jyotirindra N. Sen, and Charles E. BoozerCite this: J. Am. Chem. Soc. 1955, 77, 12, 3244–3248Publication Date (Print):June 1, 1955Publication History Published online1 May 2002Published inissue 1 June 1955https://doi.org/10.1021/ja01617a028RIGHTS & PERMISSIONSArticle Views472Altmetric-Citations84LEARN 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 (601 KB) Get e-Alerts Get e-Alerts