Chain Radical Reactions Research Articles

Effects of Maillard reaction products on myoglobin-mediated lipid oxidation during refrigerated storage of carp

Lipid oxidation is the major cause of quality deterioration in freshwater fish, especially mediated by myoglobin (Mb). This study aimed to investigate the antioxidant mechanism of Maillard reaction products (MRPs) in Mb-mediated lipid oxidation in common carp (Cyprinus carpio). MRPs exhibited promising antioxidant and antimicrobial capacities based on the reduced content of peroxide and thiobarbituric acid-reactive substances and inhibited microbial growth. MRPs inhibited the oxidation of Mb by lowering the transfer from oxymyoglobin to metmyoglobin and improving the stability of heme iron. The correlation analysis showed that MRPs regulated the formation of free radicals by maintaining the reduced structure of Mb and the integrity of heme iron, and also directly inhibited the formation of oxidation products in a chain radical reaction. The texture and electronic nose analysis indicated that MRPs could delay the structural disruption and flavor deterioration of surimi. Therefore, MRPs could effectively inhibit Mb-induced lipid oxidation and further control the resulting changes in the flavor and texture of surimi.

Investigation of photochemical conversion processes in aromatic hydrocarbons of Balakhani oil

In this paper, Balakhani oil, as the case study, was separated into 4 groups of aromatics by adsorption column chromatography. With the aid of GC-MS and UV/vis spectrometers, it was proved that the composition of the separated groups is mainly composed of mono-, di-, tri- and a trace amount of tetracyclic aromatics. The conversion process of separated aromatics under photo-irradiation was investigated by IR, UV, 1H NMR and GC-MS spectroscopies. It was found that the components of aromatic groups undergo photo-conversion processes at different rates depending on their composition. In the 3rd and 4th groups, the mentioned process occurs slowly, so their use as petroleum luminophores (PLs) may be recommended. It was found that the PLs based on these groups have variable luminescence properties, and the variation range of their spectral-luminescence properties was also determined. Finally, the role of singlet (1O2) and triplet (3O2) oxygens in reversible and irreversible photooxidation reactions with aromatics was investigated as well as, the significance of molecular and chain-radical reactions in this process was also determined.

Free Radical Reaction Pathway, Thermochemistry of Peracetic Acid Homolysis, and Its Application for Phenol Degradation: Spectroscopic Study and Quantum Chemistry Calculations

The homolysis of peracetic acid (PAA) as a relevant source of free radicals (e.g., *OH) was studied in detail. Radicals formed as a result of chain radical reactions were detected with electron spin resonance and nuclear magnetic resonance spin trapping techniques and subsequently identified by means of the simulation-based fitting approach. The reaction mechanism, where a hydroxyl radical was a primary product of O-O bond rupture of PAA, was established with a complete assessment of relevant reaction thermochemistry. Total energy analysis of the reaction pathway was performed by electronic structure calculations (ab initio and semiempirical methods) at different levels and basis sets [e.g., HF/6-311G(d), B3LYP/6-31G(d)]. Furthermore, the heterogeneous MnO2/PAA system was tested for the elimination of a model aromatic compound, phenol from aqueous solution. An artificial neural network (ANN) was designed to associate the removal efficiency of phenol with relevant process parameters such as concentrations of both the catalyst and PAA and the reaction time. Results were used to train and test ANN to identify an optimized network structure, which represented the correlations between the operational parameters and removal efficiency of phenol.

Initiation of a superoxide-dependent chain oxidation of lactate dehydrogenase-bound NADH by oxidants of low and high reactivity

In cells, NADH and NADPH are mainly bound to dehydrogenases such as lactate dehydrogenase (LDH). In cell-free systems, the binary LDH–NADH complex has been demonstrated to produce reactive oxygen species via a chain oxidation of NADH initiated and propagated by superoxide. We studied here whether this chain radical reaction can be initiated by oxidants other than LDH largely increased the oxidation of NADH (but not of NADPH) by O2, H2O2 and during the intermediacy of HNO2. LDH also increased the oxidation of NADH by peroxynitrite. The increases in NADH oxidation were completely prevented by superoxide dismutase (SOD). In contrast, the nitrogen dioxide-dependent oxidation of NADH and NADPH was decreased by LDH in a SOD-independent manner. These experimental data strongly indicate that oxidation of LDH-bound NADH can be induced from reaction of either weak oxidants with LDH-bound NADH or of strong oxidants with free NADH thus yielding which is highly effective to propagate the chain. Our results underline the importance of SOD in terminating superoxide-dependent chain reactions in cells under oxidative stress.

Determination of Hydrogen Peroxide in Water by Chemiluminescence Detection, (II)

The authors previously developed a flow injection type hydrogen peroxide detection system based on chemical photoluminescence spectroscopy. This system has the lowest detectable limit of 0.3 ppb. The relationships between the hydrogen peroxide concentration and luminous intensity were expressed as a linear function and a quadratic function of the H2O2 concentration. In the present study, the chemiluminescence processes were theoretically evaluated by analyzing the chain radical reactions to confirm the effect of major parameters on the chemiluminescent intensity and to understand the complex relationship between H2O2 concentration and luminous intensity. Then delay in luminescence was empirically analyzed by calculating diffusion of chemical species in the sample water and mixed reagent solution. The calculated results showed dependencies of the chemiluminescent intensity on luminol concentration and pH of the mixed reagent were mainly determined by a balance between OH radical concentration and luminol concentration. Furthermore the presence of O2 - radicals in the mixed reagent might explain the linear relation between chemiluminescent intensity and H2O2 concentration at low values.

An Oxidative Dimeric Product of (+)-Catechin by Radical Reaction in the Dark

In the course of our study on the antioxidative mechanism of (+)-catechin (1), we have examined the reaction products of 1 in the dark with radical initiator. Compound (2) was isolated as a major product by chromatographic methods and was identified as a known dehydro-dicatechin A on the basis of spectroscopic and chemical evidences. It was an oxidative dimeric flavan-3-ol, in which two units of 1 and the oxidative derivatives of 1 are linked each other. It can therefore be presumed that in the radical reaction in the dark, the A ring as well as the B ring of 1 could possess the H-atom donating ability, thus the chain radical reaction was terminated. Compound 2 was different from the reaction products under photoirradiation of 1. This is the first report on 2 derived from 1 without enzyme.

“Surprising kinetics” or the major role of trace quantities in radical chain mechanisms

AbstractAlthough hydrogen abstraction from 1,1,1,2‐tetrachloroethane should produce only one kind of radical, CCl3CHCl, the presence of small amounts of trichloroethene, as impurity as well as product of reaction, induces the formation of the a priori unexpected CHCl2CCl2 radicals. The importance of this radical in the reaction pathways of the chlorination and the chlorine induced dehydrochlorination of CCl3CH2Cl, under different experimental conditions, is computed and discussed. For example, at 380 K, and for small partial pressures of chlorine (2 torr), the CHCl2CCl2 radicals account for more than 70% of the formation of the reaction products after only 2% reaction. The major role of trace quantities in long chain radical reactions is emphasized. © 1993 John Wiley & Sons, Inc.

ChemInform Abstract: Free Radical Processes in Heterogeneous Oxidation Catalysis

The well known phenomenon of heterogeneous-homogeneous catalysis is believed to involve surface formation of free radicals, their escape to the gas phase, and subsequent radical, possibly chain reactions [i]. However, the chain and chain radical reactions are most frequent also in strictly heterogeneous catalytic reactions [2]. It is widely accepted that radical oxygen forms Oand 02 are involved in the catalytic oxidation of hydrocarbons (see review [3]). Large amounts of radical sites can be obtained on the catalyst surface by mechanical treatment.

Free radical processes in heterogeneous oxidation catalysis

The well known phenomenon of heterogeneous-homogeneous catalysis is believed to involve surface formation of free radicals, their escape to the gas phase, and subsequent radical, possibly chain reactions [i]. However, the chain and chain radical reactions are most frequent also in strictly heterogeneous catalytic reactions [2]. It is widely accepted that radical oxygen forms Oand 02 are involved in the catalytic oxidation of hydrocarbons (see review [3]). Large amounts of radical sites can be obtained on the catalyst surface by mechanical treatment.

Antioxidant activity of flavonoids and reactivity with peroxy radical

The autoxidation of linoleic acid and methyl linolenate is inhibited by flavonoids. The antioxidant efficiency of these flavonoids increases with their concentration and in the order fustin < catechin < quercetin < rutin = luteolin < kaempferol < morin for linoleic acid and rutin < catechin < morin = kaempferol for methyl linolenate. Flavonoids are more effective on linoleic acid than on methyl linolenate. The antioxidant activity offlavonoids is related to an inhibition of the formation of trans,trans hydroperoxide isomers of linoleic acid. This inhibition exhibited the great H-atom donating ability of flavonoids to peroxy radical, thus terminating the chain radical reaction.

Mechanism of photo-oxidation of an elastomer

Ultraviolet irradiation in air of various elastomeric substances results in crosslinks, chain scissions and oxidation functions. The quantum yields of the different processes and the oxygen balance have been determined in the case of a model system. These results make it possible to propose a mechanism of photo-oxidation which agrees well with the experimental data. The rôle played by hydroperoxide functions has been recognised and demonstrated; their sensitised generation and decomposition have been explained in terms of energy transfer phenomena. Lastly, changes in the macromolecular chains and network formation have been followed. The results demonstrate quantitatively how light energy is absorbed by impurity in a polymer and is transferred to potential radical sites (hydroperoxides). Chain radical reactions develop in the material, leading predominantly to photocrosslinking simultaneously with a chain scission process which allows spatial reorganisation of the polymer medium.

Effects of the exciting light intensity on the selectivity of consecutive chain reactions

The mixing time in a photochemical reactor can have a great importance on the rate of long chain radical reactions when the free radical chain carriers have a short lifetime with respect to this time. We show here that the imperfect regeneration of the reagents (and of the free radicals) in the reactor is at the root of the lowering of selectivity when consecutive reactions come into play.

Kinetics of the initial stage of initiated thermal oxidation of caprolactam and N-octylbutyramide

The thermal oxidation of ε-caprolactam or N-octylbutyramide in the liquid phase is a chain radical reaction. In the initial stage, the only reaction product is the corresponding amide hydroperoxide, formed from peroxy radicals by a second-order termination reaction. The rates of thermal oxidation reactions initiated with 7,7'-dicumenyl peroxide or 1,1'-azodi(cyclohexanecarbonitrile) and the rates of initiation reactions were measured in the temperature range 80-130 °C. Using the values thus obtained, the ratios of rates of the propagation and termination steps, k2 . k6-1/2, characterizing the oxidizability compounds, were calculated.

Low-level chemiluminescence of bovine heart submitochondrial particles.

Submitochondrial particles from bovine heart mitochondria showed low-level chemiluminescence when supplemented with organic hydroperoxides. Chemiluminescence seems to measure integratively radical reactions involved in lipid peroxidation and related processes. Maximal light-emission was about 1500 counts/s and was reached 2-10min after addition of hydroperoxides. Ethyl hydroperoxide, cumene hydroperoxide and t-butyl hydroperoxide were effective in that order. Antimycin and rotenone increased chemiluminescence by 50-60%; addition of substrates, NADH and succinate did not produce marked changes in the observed chemiluminescence. Cyanide inhibited chemiluminescence; half-maximal inhibitory effect was obtained with 0.03mm-cyanide and the inhibition was competitive with respect to t-butyl hydroperoxide. Externally added cytochrome c (10-20mum) had a marked stimulatory effect on chemiluminescence, namely a 12-fold increase in light-emission of antimycin-inhibited submitochondrial particles. Stimulation of hydroperoxide-induced chemiluminescence of submitochondrial particles by cytochrome c was matched by a burst of O(2) consumption. O(2) is believed to participate in the chain radical reactions that lead to lipid peroxidation. Superoxide anion seems to be involved in the chemiluminescence reactions as long as light-emission was 50-60% inhibitible by superoxide dismutase. Singlet-oxygen quenchers, e.g. beta-carotene and 1,4-diazabicyclo[2,2,2]-octane, affected light-emission. beta-Carotene was effective either when incorporated into the membranes or added to the cuvette. The present paper suggests that singlet molecular oxygen is mainly responsible for the light-emission in the hydroperoxide-supplemented submitochondrial particles.

Initiation of free-radical addition reactions of alcohols by tertiary butyl hydroperoxide

1. Tert-Butyl hydroperoxide can be used as an initiator of the chain radical reaction for the addition of alcohols to the methyl esters of acrylic and maleic acids. 2. The decomposition of tert-butyl hydroperoxide in butanol and cyclohexanol at 115° obeys the first-order reaction. 3. tert-Butyl hydroperoxide in butanol at 115° undergoes mainly induced decomposition, with a small proportion of the decomposition going through the stage of forming the complex with the alcohol.