Добірка наукової літератури з теми "Oxygen-containing radicals"

The radiolytic reduction of uranyl ions in degassed sulphuric acid solutions containing various organic solutes was studied. It was shown that while ĊOOH, CO2−, and α-hydroxy-alkyl radicals reduced uranyl ions, the β-hydroxy-alkyl radicals and those derived from gluconic acid could not affect the reduction. The oxidation of uranium(IV) by hydrogen peroxide at pH 0.7 involves hydroxyl radicals in a chain mechanism but at pH 2.0 the oxidation proceeds by a non-radical reaction pathway. From the enhancement of the rate of oxidation of uranium(IV) by oxygen in the presence of 2-propanol, a mechanism involving the perhydroxyl radical, which reconciles earlier published data on kinetics and oxygen tracer studies, is proposed for the oxygen-uranium(IV) reactions.

Hydrocarbon (HC) contamination is a persistent problem for users of electron microscopes (EMs), often leading to image distortion and interference with nanoprobing. The Evactron De-Contaminator (D-C) has been available for HC contamination removal in EMs since 1999. The Evactron D-C uses low power radio frequency (RF) generated plasma in order to produce oxygen radicals that clean the EM. The Oxygen Radical Source (ORS) is attached to the EM chamber, and a controlled leak of oxygen containing gas such as room air is passed through the plasma in order to produce oxygen radicals. The oxygen radicals chemically react with the HCs to form volatile oxidation products such as H2O, CO and CO2. These volatile compounds are pumped out of the EM chamber.

Mitochondrial dysfunction is associated with a wide range of human diseases, including neurodegenerative diseases, and is believed to cause or contribute to the etiology of these diseases. These disorders are frequently associated with increased levels of reactive oxygen species. One of the design strategies for therapeutic intervention involves the development of novel small molecules containing redox cores, which can scavenge reactive oxygen radicals and selectively block oxidative damage to the mitochondria. Presently, we describe recent research dealing with multifunctional radical quenchers as antioxidants able to scavenge reactive oxygen radicals. The review encompasses ubiquinone and tocopherol analogs, as well as novel pyri(mi)dinol derivatives, and their ability to function as protective agents in cellular models of mitochondrial diseases.

Boron derivatives are becoming key reagents in radical chemistry. Here, we describe reactions where an organoboron derivative is used as a radical initiator, a chain-transfer reagent, and a radical precursor. For instance, B-alkylcatecholboranes, easily prepared by hydroboration of alkenes, represent a very efficient source of primary, secondary, and tertiary alkyl radicals. Their very high sensitivity toward oxygen- and heteroatom-centered radicals makes them particularly attractive for the development of radical chain processes such as conjugate addition, allylation, alkenylation, and alkynylation. Boron derivatives have also been used to develop an attractive new procedure for the reduction of radicals with alcohols and water. The selected examples presented here demonstrate that boron-containing reagents can efficiently replace tin derivatives in a wide range of radical reactions.

Visible light photocatalytic radical carbonylation has been established as a robust tool for the efficient synthesis of carbonyl-containing compounds. Acyl radicals serve as the key intermediates in these useful transformations and can be generated from the addition of alkyl or aryl radicals to carbon monoxide (CO) or various acyl radical precursors such as aldehydes, carboxylic acids, anhydrides, acyl chlorides or α-keto acids. In this review, we aim to summarize the impact of visible light-induced acyl radical carbonylation reactions on the synthesis of oxygen and nitrogen heterocycles. The discussion is mainly categorized based on different types of acyl radical precursors.

The hex-5-enyl (1), 3-oxahex-5-enyl (6), 2-oxahex-5-enyl (9) and 2,2-dimethylbut-3- enoyloxymethyl (13) radicals have been generated by interaction of the corresponding bromides with trialkyltin or trialkylgermanium radicals, and their rate constants and activation parameters for cyclization have been determined by kinetic e.s.r . spectroscopy. The 3-oxa species (6) undergo 1,5-ring closure more rapidly than does hex-5-enyl radical (1) because of favourable stereoelectronic factors. Spectral evidence has been obtained for restricted rotation about the O-CH2* bond in the 2-oxa radical (9) as a consequence of which its ring closure is relatively slow. Similarly, 1,5-ring closure of the ester derived radical (13) is slow because of unfavourable conformational effects arising from restricted rotation about the CO-O bond. The radical (22) formed from allyl bromoacetate does not undergo ring closure. Spectral data have been obtained for various radicals (16), (19), (23), (24) formed by intermolecular addition.

The cellular utilization of oxygen leads to the generation of free radicals in organisms. The accumulation of these free radicals contributes significantly to aging and several age-related diseases. Angiotensin II can contribute to DNA damage through oxidative stress by activating the NAD(P)H oxidase pathway, which in turn results in the production of reactive oxygen species. This radical oxygen-containing molecule has been linked to aging and several age-related disorders, including renal damage. Considering the role of angiotensin in aging, melatonin might relieve angiotensin-II-induced stress by enhancing the mitochondrial calcium uptake 1 pathway, which is crucial in preventing the mitochondrial calcium overload that may trigger increased production of reactive oxygen species and oxidative stress. This review highlights the role and importance of melatonin together with angiotensin in aging and age-related diseases.

Робота виконана на кафедрі хімічних технологій та водоочищення Черкаського державного технологічного університету Міністерства освіти і науки України.
Дисертація присвячена питанням розробки технологій інтенсифікації первинних ендотермічних стадій реакцій горіння та окиснення сировини, що містять вуглеводневі гази і тверді вуглеводні, які базуються на використанні направленої дії штучно створеної низькотемпературної плазми з упорядкованим рухом «повільних» електронів в присутності гетерогенного каталізатору та визначення оптимальних умов проведення цих процесів. Розроблений новий напрям в проведенні окиснювальних процесів, який базується на використанні для інтенсифікації первинних ендотермічних стадій реакцій горіння та окиснення сировини, що містить вуглеводневі гази і тверді вуглеводні, низькотемпературної плазми з упорядкованим рухом «повільних» електронів в присутності гетерогенного каталізатору. Штучно створена низькотемпературна нерівноважна плазма, при її короткотривалій дії на об’єкт горіння або окиснення, дає можливість проводити хімічні реакції, які в звичайних умовах можливі при значних енерговитратах або не протікають, або протікають дуже повільно. Мінімізація енерговитрат в процесах, що пропонуються, досягається з використанням каталізу в зоні розряду. Для створення низькотемпературної плазми запропоновано використання бар′єрного та об′ємного розрядів. Цей напрям отримав назву електронно-каталітичний метод. Використання цього методу в процесах горіння і окиснення дозволяє витрачати на процес інтенсифікації ендотермічних стадій значно меншу кількість енергії завдяки використанню енергії «повільних» електронна, на утворення яких впливає нерівноважна плазма. При горінні паливної суміші в предполумьяній зоні значно зменшується вміст води, на руйнування якої витрачалося велика кількість енергії. Замість неї утворюються радикали і іони, теплоємність яких значно менше теплоємності води і завжди має негативне значення. Енергія, яка витрачалася на руйнування, додається до сумарної енергії, що надають електрони і протони. Сумарний енергетичний внесок всіх утворюються при з'єднань, достатній, щоб ініціювати як процес горіння, так і окислення різних з'єднань. Для газової фази досягався додатковий енергетичний ефект в розмірі 12-15% від кількості енергії, що виділяється при звичайному згорянні палива.
Dissertation is devoted to the development of technologies for the intensification of endothermic stages of combustion and oxidation reactions on hydrocarbon gases and solid hydrocarbons based on the directional action of artificially created low-temperature plasmas with the ordered motion of "slow" electrons in the presence of a heterogeneous catalyst and determining the optimum conditions for carrying out these processes. A new direction has been developed in carrying out oxidation processes, which are based on the use of a low-temperature plasma with the ordered motion of "slow" electrons in the presence of a heterogeneous catalyst for the intensification of the endothermic stages of combustion and oxidation reactions on hydrocarbon gases and solid hydrocarbons. An artificially created low-temperature nonequilibrium plasma, with its short-term action on the object of combustion or oxidation, makes it possible to conduct a chemical reaction, which under normal conditions is possible at considerable energy costs, or proceed very slowly. Minimization of energy consumption in the proposed processes is achieved by using catalysis in the discharge zone. To create a low-temperature plasma, it is proposed to use a barrier and volume discharge. This direction was called the electron-catalytic method. The use of this method in combustion and oxidation processes allows a much smaller amount of energy to be expended on the process of intensification of endothermic stages due to the use of the energy of "slow" elecrons, the formation of which is affected by the nonequilibrium plasma. When the fuel mixture burns in the presumed zone, the water content significantly decreases, and a large amount of energy is consumed to destroy it. Instead, radicals and ions are formed, the heat capacity of which is much less than the heat capacity of water and always has a negative value. Energy, which was spent for destruction, is applied to the total energy that exerts electrons and protons. The total energy contribution of all compounds formed during the compounds is sufficient to initiate both the burning process and the oxidation of various compounds. For the gas phase, an additional energy effect was achieved in the amount of 12-15% of the amount of energy released during the usual combustion of fuel.
Диссертация посвящена вопросам разработки технологий интенсификация эндотермических стадий реакций горения і окисления углеводородные газы и твердые углеводороды, которые базируются на использовании направленного действия искусственно созданной низкотемпературной плазм с упорядоченным движением «медленных» электронов в присутствии гетерогенного катализатора и определении оптимальных условий проведения этих процессов. Разработано новое направление в проведении окислительных процессов, которые базируются на использовании низкотемпературной плазмы с упорядоченным движением «медленных» электронов в присутствии гетерогенного катализатора для интенсификация эндотермических стадий реакций горения і окисления на катализаторах углеводородные газы и твердые углеводороды,. Искусственно созданная низкотемпературная неравновесная плазма, при её кратковременном действии на объект горения или окисления, дает возможность проводить химическую реакцию, которые в обычных условиях возможны при значительных энергозатратах, или протекают очень медленно. Минимизация энергозатрат в предлагаемых процессах достигаются при использовании катализе в зоне разряда. Для создания низкотемпературной плазмы предложено использовать барьерный и объемный разряд. Это направление получило название электронно-каталитический метод (ЭКМ). Использования этого метода в процессах горения и окисления позволяет расходовать на процесс интенсификации эндотермических стадий значительно меньшее количество энергии благодаря использованию энергии «медленных» элекронов, на образование которых влияет неравновесная плазма. При горении топливной смеси в предполумьяний зоне значительно уменьшается содержание воды, на разрушение которой расходовалось большое количество энергии. Вместо нее образуются радикалы и ионы, теплоемкость которых значительно меньше теплоемкости воды и всегда имеет отрицательное значение. Энергия, которая тратилась на разрушение, прилагается к суммарной энергии, оказывающих электроны и протоны. Суммарный энергетический вклад всех образующихся при соединений, достаточный, чтобы инициировать как процесс горения, так и окисления различных соединений. Для газовой фазы достигался дополнительный энергетический эффект в размере 12-15% от количества энергии, выделяемую при обычном сгорании топлива. В условиях ЭКМ на химический процесс влияют факторы: упругое и неупругое соприкосновения электронов и частиц, Ионизация, колебательное возбуждение и диссоциация молекул, температурная неоднородность между газовым потоком и потоком низкотемпературной плазмы, резонанс частоты колебаний молекул и электрического разряда. Существенное влияние оказывают диссоциативное прилипания, которое протекает при соприкосновении электронный с молекулой с образованием промежуточного агента - отрицательно заряженного иона, который затем разлагается на фрагменты, один из которых имеет отрицательный заряд и электронное возбуждение. При использовании низкотемпературной плазмы перед зоной реакции возникают резонансные частоты колебаний, которые могут вступать в резонанс с молекулой и инициировать первичные стадии горения и окисления сырья. Для электрического барьерного разряда характерно ряд температурных неоднородностей. При наложении электрического разряда на пламя под действием электромагнитного поля и потока электронов происходит направленное движение положительных частиц, которые образуются в пламени. Под действием электронов количество этих ионов увеличивается. Действие этого направленного движения ионизированных частиц увеличивает скорость процесса горения, благодаря более интенсивному движению частиц и изменении поверхности контакта. Использование ЭКМ интенсификации процесса горения твердого топлива позволяет повысить выход летучих соединений, в составе которых содержатся вещества, теплоты сгорания которых значительно выше, чем теплота сгорания веществ, которые образовались при обычном термолизе. Кроме того, использование ЭКМ приводит к образованию летучих соединений при значительно меньших температурах, что позволяет использовать избыток теплоты, образовавшийся на целевые нужды. Были проведены исследования горения и окисления углеводородных газов, в результате которых установлено: - оптимальные условия проведения электронно-каталитической интенсификации первичных стадий процессов горения и окисления газообразного и твердого топлива. Достигнуты значительные повышения выделения тепла для различных видов топлива. - влияние состава катализаторов на процесс окисления и горения газообразного топлива. Для ЭКМ наиболее эффективны катализаторы, содержащие никель и хром. - влияние параметров напряжения и формы синусоиды тока на процесс горения газообразного топлива. Наибольший эффект достигается при увеличении напряжения разряда и нижней синусоиде тока. Исследован процесс неполного окисления метана с использованием ЭКМ с образованием формальдегида и метанола. Получены зависимости формальдегида при разных составах исходной смеси и температуре. Для процесса сжигания твердого топлива определено влияние напряжения на процесс выделения газообразных веществ при термолизии топлива. Полученные зависимости выделение тепла от напряжения при сжигании антрацита, древесины и пеллет. При использовании ЭКМ в процессах горения достигнуто уменьшение выбросов оксидов углерода (II) до 52% и оксидов азота до 80% при сжигании твердого топлива. Составлены и решены математические модели процессов горения углеводородных газов, угля и древесины, процесса неполного окисления метана и формальдегид. Были предложены методы электронно-каталитической интенсификации процесса горения газообразного топлива, угля и древесины; метод синтеза формальдегида при атмосферном давлении.

Today, many factors such as advancing technology, environmental pollution, radiation, contaminated water, pesticides, heavy metals, stress and oxygen metabolism in living cells inevitably cause the formation of free radicals in the human body. Free radicals are very reactive forms of oxygen that destroy the cells of the organism. This calls for cardiovascular disease, cancer, cataracts, diabetes and many more diseases. To provide solutions to these diseases, firstly, we can eliminate the negative effects of free radicals and prevent the formation of diseases. While there is an antioxidant defense system in the human body that can prevent this, the environmental factors encountered break down this defense resistance and sometimes make it inadequate. We can strengthen our weakened antioxidant defense systems by eating a natural and balanced diet and consuming fruits and vegetables containing antioxidants, thus preventing illness. Research shows that free radicals have a significant effect on aging, free radical damage can be controlled with adequate antioxidant defense, and optimal antioxidant nutrient intake can contribute to improved quality of life. This review is intended to highlight once again the importance of alternative antioxidants in the body to eliminate free radicals and their harmful effects.

Reactive oxygen species (ROS) is the collective term for several oxygen containing free radicals, such as hydrogen peroxide. ROS is important in innate immunity, protein folding in the endoplasmic reticulum and as a cell signalling molecule involved in cellular proliferation, survival, differentiation, and gene expression. ROS has been implicated in both hematopoietic stem cell quiescence and hematopoietic differentiation. Consequently, ROS is of considerable interest as a therapeutic target, with both pro-oxidant and anti-oxidant cellular modulation being explored. Recently, it has been established that increased ROS production in acute myeloid leukemia (AML) leads to increased glycolysis and metabolic reprogramming. It is often stated as a key tenet of the Warburg effect, that transformed cells, including AML, show increased aerobic glycolysis accompanied by increased cellular glucose uptake and lactate secretion. This review will summarize ROS state of the art in acute leukemia and how these reactive molecules re-wire metabolism in cancer cells. The review will focus on what are ROS? What are the sources of ROS in hematopoietic cells and their function and how this relates to the Warburg effect and regulation of metabolic pathways in acute leukemias.

Dielectric barrier discharges (DBD) are the configurations for the production of electrical discharges using a dielectric medium between the metallic electrodes. Plasma treatment produces negative radicals, which increase the adhesion of fabric for nanoparticles. The plasma treatment made the fabric surface rougher because of the etching effect. UV-vis spectra of the Plasmon resonance band observed at 253-400 nm. X-ray diffraction results showed that AgNPs has a cubical structure and the average crystalline size is 25 nm. SEM results determined that the morphology of the silver nanoparticles are flower shaped. The energy bandgap of AgNPs was observed at 2.59 eV. The silver nanoparticles were found to have enhanced antimicrobial properties and showed better zone of inhibition against isolated bacteria (Escherichia coli). DBD plasma treatment changed the chemical as well as physical properties of the cotton fabric. FTIR spectrum revealed that oxygen-containing groups, such as C-O, C=O, O-C-O, as well as O-C=O, increased on DBD treatment of cotton samples.

The action of most xenobiotics ends in either excretion or metabolic inactivation. Some compounds, on the other hand, require metabolic activation before they can exert any biological action. In most cases these biotransformations, activations as well as inactivations, are carried out by specialized enzyme systems. The essential role of these enzymes is to facilitate elimination of xenobiotics. Water-soluble compounds usually do not need to be metabolized, as they can be excreted in their original forms. Lipophilic compounds can be disposed of through biliary excretion, or they may undergo metabolism to become more polar and thus more water-soluble so that they can be disposed of through the kidneys. The metabolism of xenobiotics is usually carried out in two phases. Phase 1 involves oxidative reactions in most cases, whereas phase 2 involves conjugation (combination) with highly water-soluble moieties. Occasionally the products of biotransformation are unstable and decompose to release highly reactive compounds such as free radicals, strong electrophiles, or highly stressed three-member rings (epoxides, azaridines, episulfides, and diazomethane; Figure 3.1) that have a tendency toward nucleophilic ring opening. For order to be retained within the cells, the chemical reactions have to occur through enzymatic processes in which the substrate is activated while bound to the enzyme. Only after the desired reaction takes place is a stable product released. Freely roaming reactive compounds are not welcome in a living organism because they react randomly with macromolecules such as DNA, RNA, and proteins. Alteration of DNA leads to faulty replication and transcription. Alteration of RNA causes faulty messages that, in turn, lead to the synthesis of abnormal proteins and thus alter enzymatic and regulatory activity. Phase 1 processes are carried out by a series of similar enzymes (commonly designated as mixed-function monooxidases) or cytochrome P-450. The basic reactions catalyzed by cytochrome P-450 enzymes involve introduction of oxygen into a molecule. In most cases the oxygen is retained, but sometimes it is removed from the end product. The oxygen carrier is a prosthetic group containing porphyrin-bound iron. The overall reaction catalyzed by these enzymes is hydroxylation.

Organic acids, particularly formic and acetic acid, are ubiquitous components of the troposphere (Chebbi and Carlier, 1996); see table I-D-1. However, the atmospheric budget of these species is at present poorly constrained, and global models often underestimate their abundance (von Kuhlmann et al., 2003). The presence of organic acids in the atmosphere can be attributed to two distinct mechanisms: direct emission from anthropogenic and natural sources; and in situ production via gas-phase or condensed-phase chemistry. Direct emissions result from biomass burning (e.g., Christian et al., 2007), from motor vehicle use (Kawamura et al., 2000) and other anthropogenic activities (see chapter I), and from biogenic sources (e.g., Seco et al., 2007). Production in the gas phase can occur via the reactions of acylperoxy radicals with HO2: . . . CH3C(O)O2 + HO2 → CH3C(O)OOH + O2 . . . . . . CH3C(O)O2 + HO2 → CH3C(O)O + OH + O2 . . . . . . CH3C(O)O2 + HO2 → CH3C(O)OH + O3 . . . or via the ozonolysis of unsaturated species (Orzechowska and Paulson, 2005a, b). Additional in situ acid production (particularly with multi-functional species and diacids) likely occurs in the condensed phase as well, via the oxidation of carbonyl and other oxygen-containing and multi-functional organics (e.g., Ervens et al., 2004). In general, the organic acid moiety, —C(O)OH, is rather unreactive in the gas phase. This is in large part due to the strength of the O—H bond, ∼460 kJ mole−1 versus 400–420 kJ mole−1 for typical C—H bonds (Sander et al., 2006). The organic acid moiety also acts to inhibit somewhat the reactivity of neighboring sites (Kwok and Atkinson, 1995), further decreasing the reactivity of small saturated acids. UV spectra for unsubstituted acids are located at relatively short wavelengths, [e.g., λmax< 210 nm for acetic acid, Orlando and Tyndall (2003); see figure IX-A-1], so tropospheric photolysis is of negligible importance. Thus, the gas-phase lifetime for small saturated organic acids (e.g., formic and acetic acid) can be quite long, about 1 month.

Although the HO radical is present in the sunlight-irradiated troposphere at very low concentrations, only about 106 molecules cm−3, it is the most important trace component in our atmosphere. It is a highly reactive transient species and is responsible for initiating the oxidation of the majority of organic compounds in the troposphere. It initiates the chain reactions that produce ozone. All the saturated, H-atom containing molecules react with HO through abstraction of an H atom. In the case of the simplest alkane, methane, reaction (1) leads to the formation of a water molecule and an alkyl (CH3) radical: . . . HO + CH4 → H2O + CH3 (1) . . . The CH3 radical released into the oxygen-rich atmosphere quickly adds O2 to give the methyl peroxy radical in reaction (2), which in NO-containing atmospheres can react to form NO2, and an alkoxy radical, CH3O, in reaction (3). In turn, this radical reacts with O2 to give an HO2 radical and a molecule of formaldehyde in (4). An HO radical can be regenerated as the HO2 molecule oxidizes NO to NO2 in (5), and the chain of events, reactions (1) through (5), leads to ozone generation through the photolysis of the NO2 molecule in reactions (6) and (7): . . . CH3 + O2 → CH3O2 (2) . . . . . . CH3O2 + NO → CH3O + NO2 (3) . . . . . . CH3O + O2 → HO2 + CH2O (4) . . . HO2 + NO → HO + NO2 (5) . . . . . . NO2 + hν → O + NO (6) . . . . . . O + O2 (+ M) → O3 (+ M) (7) . . . Methane is the least reactive of the alkanes with HO. Urban atmospheres contain a complex mixture of the more reactive larger alkanes (RH). The number of different possible geometric isomers and stereoisomers of the alkanes that can be formed by association of C and H atoms is astounding (Calvert et al., 2008). For example, there are more than a thousand structurally different molecules of molecular formula C12H26, more than a million C20H22, more than a billion of formula C25H52, and more than a trillion possible different isomers of molecular formula C31H64.

Coals contain considerable amounts of oxygen in their structures ranging from 30% in brown coal to about 1.5% in anthracites. The distribution of coal oxygen in various functionalities changes drastically with increasing rank. The hetero-atom functionalities in coal and coal products are of importance in the processing of coal. The process of coal conversion relevant to the steam and gas turbine applications are pyrolysis, oxidation and combustion processes. Initial stages of pyrolysis and oxidation (combustion) are the thermal decomposition of the solid coal matrix to free radicals. Oxygen, sulfur, nitrogen and mineral containing free radicals play an important role during combustion thermodynamically. The differences between the coal functionalities in the solid coal matrix contribute to oxidation reactions of first and second order. The first and second order reactions affect the corrosion and deposition rates of the machine components differently. In this paper functionality differences of various coals with respect to their oxidation characteristics will be discussed.

A quartz crystal microbalance (QCM)/Parr bomb system with a headspace oxygen sensor is used to measure oxidation and deposition during thermal oxidative stressing of jet fuel. The advantages of the oxygen sensor technique in monitoring fuel oxidation is demonstrated. Simultaneous measurement of deposition using the QCM shows a strong correlation between oxidation and deposition in jet fuels. Studies performed over the temperature range 140 to 180°C show that surface deposition peaks at an intermediate temperature, while bulk deposition increases with temperature, in studies of jet fuel antioxidants, we find that rapid increases in oxidation rate occur upon consumption of the antioxidant. The antioxidant appears to be consumed by reaction with alkylperoxy radicals. In studies of metal deactivator (MDA) additives, we find that MDA is consumed during thermal stressing, and this consumption results in large increases in the oxidation rate of metal containing fuels. Mechanisms of MDA consumption are hypothesized.