Rate Of Peroxide Formation Research Articles

Studies with primaquine in vitro: superoxide radical formation and oxidation of haemoglobin.

1. The production of superoxide radicals from primaquine diphosphate in aqueous solution has been demonstrated, using as indicator the reduction of cytochrome C with inhibition of the reaction by superoxide dismutase. 2. Primaquine-mediated oxidation of haemoglobin to methaemoglobin was reduced by the addition of catalase and increased by superoxide dismutase. Mannitol, a hydroxyl radical scavenger, abolished the increase in methaemoglobin observed in the presence of superoxide dismutase. EDTA reduced the oxidation of haemoglobin with and without superoxide dismutase. 3. Although the oxidation of haemoglobin in the presence of primaquine includes the effects of hydrogen peroxide, superoxide and hydroxyl radicals and metal ions, the results indicate that hydrogen peroxide, rather than the superoxide radical, is the main oxidizing species. The increase in haemoglobin oxidation occurring with superoxide dismutase may result from the augmented rate of hydrogen peroxide formation from superoxide radicals.

Autoxidation of polyunsaturated fatty acids. Part I. Effect of ozone on the autoxidation of neat methyl linoleate and methyl linolenate.

Neat samples of polyunsaturated fatty acids were exposed to ozone in air in a flow system, and the formation of peroxides, conjugated dienes and thiobarbituric acid (TBA)-reactive material was followed as a function of time. The effect of ozone is to shorten the induction period normally observed in autoxidation studies, but the ozone, at the concentrations used here (0-1.5 ppm), appears to have no effect on the rates of product formation after the induction period. During the induction period, increasing ozone concentrations give rise to substantially increased rates of peroxide (or materials which titrate like peroxide) formation, a slightly increased rate of conjugated diene formation, and no significant increase in the rate of production of TBA-reactive material. Vitamin E lengthens the induction period but appears to have no other effect. Some of these data are in conflict with earlier reports of Menzel et al.

Chemistry of ultrasound. III. The irradiative behavior of simple aliphatic amines

The ultrasonic irradiation of water was effected under an argon atmosphere with an 800-kHz transducer at several intensities. The rates of hydrogen peroxide formation were followed by spectrophotometric analyses. The results were utilized to relate intensity to reaction rate for standardization purposes. Irradiations of several alkyl amines in aqueous solution or suspension were next accomplished under conditions similar to those applied to pure water. Products included aldehydes, an alcohol, amines, an N-oxide, methane, ethane, ethylene, carbon monoxide, and hydrogen. The products and their ratios were dependent on the structure of the amine used in the reaction. Reaction rates were only slightly different when an oxygen atmosphere was used instead of argon. The reactivity order for the amines was observed to be primary > secondary > tertiary. Methylamines reacted somewhat faster than did n-butylamine.

Hepatic microsomal ethanol oxidation. Hydrogen peroxide formation and the role of catalase.

Microsomes from rat liver form hydrogen peroxide in the presence of an NADPH‐generating system in proportion to protein concentrations as determined by three independent methods: ferrithiocyanate, cytochrome c peroxidase, and scopoletin fluorescence. Maximal rates observed were about 15 μmol H2O2/g microsomal protein per minute. The oxygen concentration for half‐maximal rates was 50 μM. It is suggested that NADPH‐dependent hydrogen peroxide formation in microsomes is mainly due to NADPH oxidase; however, partial inhibition by carbon monoxide suggests that about one third arises from the autoxidation of cytochrome P‐450.Similarities exist between microsomal acetaldehyde production from ethanol (i.e. the microsomal ethanol‐oxidizing system of Lieber and DeCarli [4]) and hydrogen peroxide formation: viz. requirement for NADPH and oxygen, identical oxygen concentrations for halfmaximal rates, and sensitivity to carbon monoxide. Microsomal acetaldehyde production in the presence of either an NADPH‐ or an H2O2‐generating system exhibits identical characteristics as follows: (a) ethanol concentration for half‐maximal rates (i.e. 12 mM); (b) dependency of maximal rates on rates of hydrogen peroxide formation; (c) competitive inhibition by peroxidatic substrates for catalase, e.g. formate (half‐maximal effect: 150 μM); (d) inhibition by catalase inhibitors, e.g. azide (half‐maximal effect: 50 μM), with identical azide insensitive rates; (e) diminished acetaldehyde production in microsomes from rats pretreated with aminotriazole or pyrazole with identical residual rates. Moreover, NADPH‐dependent acetaldehyde production is suppressed in the presence of an active H2O2‐utilizing system.Thus, it is concluded that the NADPH‐dependent microsomal ethanol‐oxidizing system of Lieber and DeCarli [4] is due to a hydrogen peroxide formation from NADPH and a subsequent peroxidation of ethanol by contaminating catalase. The data indicate that the existence of a unique system in addition to the peroxidatic reaction of catalase as postulated recently [4] is highly doubtful.

Radiolytic oxidation of 2-methyl tetrahydrofuran

Abstract The γ-ray oxidation of 2-methyl tetrahydrofuran proceeds with a chain reaction giving an organic hydroperoxide as the major product at low doses. The rate of peroxide formation is given by and the rate constant ratio for the chain propagation to the chain termination is given by at room temperature. An ionic chain termination by O2- was found to be important only in aqueous solutions but not in pure MTHF or mixtures of cyclohexane + MTHF where the low dielectric constant of the medium seems to inhibit the O2- formation in appreciable yield.

The nature of the sex-linked differences in glutathione peroxidase activity and aerobic oxidation of glutathione in male and female rat liver.

1. Glutathione peroxidase activity in the livers of sham-operated female rats was about 60% higher than in similarly treated male rats. The value in the ovariectomized female was about the same as that in the castrated or sham-operated male. 2. Glutathione peroxidase activity changed during the oestrous cycle. The highest value was in oestrus, and was about 50% higher than the lowest activity, which was found in dioestrus. The activity in proestrus and in metoestrus was respectively about 20 and 30% higher than in dioestrus. 3. In the pregnant female 1 or 2 days before term, glutathione peroxidase activity was about 20% higher than that in the female in oestrus. 4. Subcutaneous implants of both oestra-diol and progesterone in the gonadectomized rats increased the glutathione peroxidase activity approximately to the values found in the female at oestrus. 5. The rate of aerobic oxidation of GSH in the female rat liver was about 80% higher than in the male and about 110% higher than in the gonadectomized rats. Treatment of gonadectomized rats with subcutaneous implants of oestradiol and of progesterone increased the rate of oxidation of GSH by about 100%. 6. In the presence of azide the rate of GSH oxidation in the male and in the female was respectively about 3.5- and 2.1-fold that in the absence of azide. In castrated or ovariectomized rats the increase due to the presence of azide was about 2.4-fold. In the gonadectomized rats treated with oestradiol or progesterone the rate of GSH oxidation in the presence of azide was about 2.2-fold that in its absence. 7. The rate of lipid peroxidation in female was 15-30-fold that in male or in gonadectomized rats. Treatment of the gonadectomized rats with oestradiol or with progesterone increased the rate of lipid peroxidation up to values that were even higher than in the female. In the presence of GSH the formation of malonaldehyde from peroxides was virtually eliminated. 8. The results suggest that the sex-linked differences in glutathione peroxidase activity, in the rate of GSH oxidation and in the rate of lipid peroxidation are due to the female sex hormones. 9. It is suggested that both the catalase activity and the rate of hydrogen peroxide formation are higher in the male than in the female. 10. Sex-linked changes in glutathione peroxidase, in the rate of GSH oxidation and in the rate of lipid peroxide formation are discussed in relation to the metabolism of oestrogens in the liver and also to the possible nature of those sex-linked changes.

Lipid peroxide formation in microsomes. General considerations.

1. Liver microsomes form lipid peroxide when incubated with ascorbate or NADPH, but not with NADH. Increasing the concentration of ascorbate beyond the optimum (0.5mm) decreases the rate of lipid peroxide formation, but this effect does not occur with NADPH. Other reducing agents such as p-phenylenediamine or ferricyanide were not able to replace ascorbate and induce lipid peroxide formation. 2. The rate of ascorbate-induced peroxidation is optimum at pH6.0 whereas the rate of the NADPH system is optimum at pH7.0. Both systems require phosphate for maximum activity. 3. Lipid peroxide formation occurs at the maximum specific rate in very dilute microsome suspensions (0.15mg. of protein/ml.). 4. Treatment of microsomes with deoxycholate and other detergents causes membrane disintegration and inhibits lipid peroxide formation. 5. Lipid peroxide formation is accompanied by a rapid uptake of oxygen and there is a large excess of oxygen utilized for each molecule of malonaldehyde measured in the peroxide method. 6. Boiled microsomes form lipid peroxide in the presence of ascorbate, but not if NADPH is added. 7. Lipid peroxide formation induced by NADPH is strongly inhibited by p-chloromercuribenzoate, weakly inhibited by N-ethylmaleimide and unaffected by iodoacetamide. Ascorbate-induced peroxidation in untreated microsomes is unaffected by p-chloromercuribenzoate, but inhibited if boiled microsomes are used. These experiments may be interpreted on the basis that a ferredoxin-type protein forms part of the system in which NADPH induces lipid peroxide formation. 8. Most heavy-metal ions, with the exception of inorganic iron (Fe(2+) or Fe(3+)), which activates, inhibit both ascorbate-induced and NADPH-induced peroxidation. Mg(2+) increases the rate of peroxidation whereas Ca(2+) inhibits it. 9. Lipid peroxide formation is inhibited strongly by GSH and weakly by cysteine. Ascorbate-induced peroxidation is much more sensitive than NADPH-induced peroxidation. 10. Peroxidation is strongly inhibited by addition of low concentrations (0.01-0.1mm) of cytochrome c or of haemoglobin. 11. It is considered that lipid peroxide formation occurs as a result of the operation of the microsomal electron-transport chain switching from hydroxylation to oxidize unsaturated lipids of the endoplasmic reticulum.

Determination of hydroperoxides in ultraviolet-irradiated nylon 66

According to mechanisms described in the literature, photodecomposition of nylon 66 proceeds through the abstraction of the hydrogen on the carbon α to the amide NH group by a free radical which has been activated by photo absorption. In the propagation phase, the α-carbon radical could readily react with atmospheric oxygen to form a hydroperoxide. The formation of a hydroperoxide in the photodecomposition scheme for nylon 66 has been detected but has not been measured quantitatively. With the colorimetric method described in this paper, it is now possible to determine the peroxide content in a polyamide to a level of 1 μmole/g. with a relative precision of less than 5%. The polyamide is dissolved in tetrafluoropropanol, to which aliquots of potassium iodide and glacial acetic solutions are added. The absorbance of the liberated iodine is measured in a 1-cm. cell at 400 mμ and the hydroperoxide concentration determined from a calibration curve constructed from hydrogen peroxide solution standards. The rate of peroxide formation, which is dependent on the wavelength of ultraviolet radiation, can be correlated to the strength loss exhibited by a nylon 66 yarn free from antioxidant and delustrant. In addition, an increase in the level of thermal degradation will accelerate yarn strength loss and peroxide formation under ultraviolet exposure. The hydroperoxide begins to decompose at about 100°C. Yarn finish will contribute to the peroxide formation during exposure.

Influence of Cobalt on Leaf Expansion and Oxidative Phosphorylation

The cobaltous ion, as well as many other chemicals, particularly the purine analogs, are known to affect the growth of etiolated leaves in the presence or absence of photomorphogenically active light (11, 18, 19). Additionally, cobalt has been shown to promote growth of other etiolated tissue such as the oat (Avena) coleoptile (2, 21) and pea roots (6). There have been different explanations of the mode of action of Co+ +. Busse (2) presented evidence that Co+ + delays the deposition of secondary cell wall material, thereby prolonging the action of IAA. Galston (6) observed that the rate of peroxide formation in etiolated tissue is lowered by the addition of Co+ +, which in turn results in a decreased peroxidative destruction of IAA. Thimann (21) by using specific inhibitors came to the conclusion that Co+ + modifies some step in oxidative metabolism which makes energy available for growth by diverting it from other metabolic roles. The present investigation arose from an observation that leaf disks given Co+ + plus DNP5 responded quite differently from those given BAP plus DNP. In view of the diversity of opinion on the mechanism of Co++ action, it was of interest to obtain information about the primary site of action of Co+. The main emphasis during the present investigations was placed on the way by which Co+ + might modify oxidative phosphorylation. Evidence is presented showing that Co+ +-induced leaf expansion is not susceptible to inhibition by DNP. The amount of ATP in leaf tissue decreases sharply in the presence of DNP, but remains unchanged when Co+ + is supplied in addition to DNP. Furthermore, experiments with mitochondria isolated from sweet potato tubers show that Co+ + increases the yield of oxidative phosphorylation. Results from other experiments indicate that Co++ has an inhibiting effect on ATPase activity.

Peroxide genesis in plant tissues and its relation to indoleacetic acid destruction

1. 1. All tissues of etiolated pea plants and the stems of green pea plants produce peroxides from endogenous substrates. Such peroxides are not accumulated; in the absence of exogenous peroxidizable substrate, they decay, and in the presence of exogenous pyrogallol, they result in the appearance of purpurogallin in the tissue and in the medium. 2. 2. The rate of peroxide formation is increased by visible light, 2,4-dichlorophenol, and manganous ion. Thus, the enhancement of IAA oxidase activity by these three agents is believed due to their effect on peroxide genesis. 3. 3. Peroxide formation in suitably starved tissue may be increased by the addition of typical flavoprotein substrates, such as glycolic acid, xanthine, butanal, and alanine, or by indoleacetic acid itself. Peroxide generation from such substrates is unaffected by Mn ++ or dichlorophenol. These peroxigenic materials must therefore be presumed to operate via other peroxide-generating pathways. 4. 4. Some implications of the metabolic role of peroxides are discussed.

The keeping quality of elaïdinated fats

SummaryThe causes of the considerably better keeping quality of elaïdinated oils and fats have been investigated through the rate of peroxide formation. They are physical as well as chemical in nature. The more solid composition of elaïdinated fats is the physical cause.Traces of selenium have been proved to behave as a strong antioxidation agent. The elimination of traces of metals in the course of the process of elaïdination with Se also has a very favorable influence.The elaïdo configuration of the unsaturated acids, however, has been shown to be the principal factor in retarding oxidation.

Antioxygenic properties of molecularly distilled fractions of peanut oil

1. Samples of unhydrogenated and hydrogenated peanut oils, which had been refined, bleached, and deodorized, were separated into two comparable series of fractions by molecular distillation. The various fractions were analyzed for tocopherols (and related chromogens) by the method of Furter and Meyer, and stability tests by the Swift method were made on the larger distilled fractions. 2. Molecular distillation at 140°, 160°, and 180° C. yielded antioxidant concentrates (presumably of tocopherols) from each oil; distillation at 240° yielded fractions almost devoid of antioxygenic substances. 3. In the unhydrogenated and hydrogenated oils, approximately 40 percent and 20 percent, respectively, of the chromogenic substances reacting in the Furter-Meyer tests were undistillable and remained in the residue comprising 10 percent of the original oil. 4. Evidence was found of the presence of distillable antioxidants other than tocopherols, which either do not respond to the Furter-Meyer test or else respond to it weakly, in proportion to their antioxygenic activity. 5. Hydrogenation of the oil had no appreciable effect on the activity of its distillable antioxidants. 6. The progressively increased addition of tocopherol-rich concentrates to fractions almost devoid of antioxidants resulted in first decreasing and then increasing the initial rate of peroxide formation in the stability tests. 7. In the case of the unhydrogenated oil, there was an optimum level of antioxidant concentration above which the addition of these substances had no stabilizing action. However, hydrogenated oil showed an increase in stability with the addition of antioxidants up to the highest level to which the concentration of the latter was carried (approximately 0.15 percent, calculated asa-tocopherol).

Photochemical studies of rancidity: Antioxidants vs. green light protection

1. The antioxidants used in this investigation showed antioxygenic activity in delaying the development of rancidity, but they were not so effective as green wrappers which absorb all light except that delimited by 4900–5800 Angstrom units. 2. The use of a protective green container or wrapper alone or in conjunction with an antioxidant increased the period during which the oil or fat remained fresh at room temperature and, incidentally, decreased the rate of peroxide formation. 3. Oils or fats stored at low temperatures and with light excluded remained fresh longer than if treated with an antioxidant or packaged in green and exposed to light at room temperature. 4. Packaging in green or opaque wrappers has a special advantage in that they can be used to protect those oil-bearing food products, such as shelled nuts and ground whole grain, to which it is difficult to add an antioxidant. 5. Protecting oil-bearing foods from rancidity by packaging in green or opaque containers is practical.

Stability tests on fats containing oxidation accelerators and inhibitors

1. Purified gossypol has been shown to have marked antioxidant strength at low concentration. 2. The combined effect of added pro- and antioxidants on the rate of peroxide formation in cottonseed oil is shown graphically. 3. A modification of Wheeler's accelerated oxidation apparatus is described, which shortens the aging period by means of irradiation. 4. The methylene blue test has been checked against peroxide titration for the estimation of fat stability.