Rate constants for the reactions of halogenated organic radicals

Reactive Oxygen Species-Induced Lipid Peroxidation in Apoptosis, Autophagy, and Ferroptosis

Reactive oxygen species- (ROS-) induced lipid peroxidation plays a critical role in cell death including apoptosis, autophagy, and ferroptosis. This fundamental and conserved mechanism is based on an excess of ROS which attacks biomembranes, propagates lipid peroxidation chain reactions, and subsequently induces different types of cell death. A highly evolved sophisticated antioxidant system exists that acts to protect the cells from oxidative damage. In this review, we discussed how ROS propagate lipid peroxidation chain reactions and how the products of lipid peroxidation initiate apoptosis and autophagy in current models. We also discussed the mechanism of lipid peroxidation during ferroptosis, and we summarized lipid peroxidation in pathological conditions of critical illness. We aim to bring a more global and integrative sight to know how different ROS-induced lipid peroxidation occurs among apoptosis, autophagy, and ferroptosis.

Kinetic and thermodynamic studies of chlorinated organic compound degradation by siderite-activated peroxide and persulfate

The efficacy of two oxidant systems, iron-activated hydrogen peroxide (H₂O₂) and iron-activated hydrogen peroxide coupled with persulfate (S₂O₈^2-), was investigated for treatment of two chlorinated organic compounds, trichloroethene (TCE) and 1,2-dichloroethane (DCA). Batch tests were conducted at multiple temperatures (10-50 °C) to investigate degradation kinetics and reaction thermodynamics. The influence of an inorganic salt, dihydrogen phosphate ion (H₂PO₄^-), on oxidative degradation was also examined. The degradation of TCE was promoted in both systems, with greater degradation observed for higher temperatures. The inhibition effect of H₂PO₄^- on the degradation of TCE increased with increasing temperature for the iron-activated H₂O₂ system but decreased for the iron-activated hydrogen peroxide-persulfate system. DCA degradation was limited in the iron-activated hydrogen peroxide system. Conversely, significant DCA degradation (87% in 48 hours at 20 °C) occurred in the iron-activated hydrogen peroxide-persulfate system, indicating the crucial role of sulfate radical (SO₄^-·) from persulfate on the oxidative degradation of DCA. The activation energy values varied from 37.7 to 72.9 kJ/mol, depending on the different reactants. Overall, the binary hydrogen peroxide-persulfate oxidant system exhibited better performance than hydrogen peroxide alone for TCE and DCA degradation.

Photosensitized degradation kinetics of trace halogenated contaminants in natural waters using membrane introduction mass spectrometry as an in situ reaction monitor

On-line membrane introduction mass spectrometry used to directly measure the photosensitized reductive dehalogenation kinetics of trace aqueous halocarbons in the presence of naturally occurring dissolved organic matter.

QSAR models for oxidation of organic micropollutants in water based on ozone and hydroxyl radical rate constants and their chemical classification

Ozonation is an oxidation process for the removal of organic micropollutants (OMPs) from water and the chemical reaction is governed by second-order kinetics. An advanced oxidation process (AOP), wherein the hydroxyl radicals (OH radicals) are generated, is more effective in removing a wider range of OMPs from water than direct ozonation. Second-order rate constants (k(OH) and k(O3) are good indices to estimate the oxidation efficiency, where higher rate constants indicate more rapid oxidation. In this study, quantitative structure activity relationships (QSAR) models for O(3) and AOP processes were developed, and rate constants, k(OH) and [Formula: see text] , were predicted based on target compound properties. The k(O3) and k(OH) values ranged from 5 * 10(-4) to 10(5) M(-1)s(-1) and 0.04 to 18 * (10(9)) M(-1) s(-1), respectively. Several molecular descriptors which potentially influence O(3) and OH radical oxidation were identified and studied. The QSAR-defining descriptors were double bond equivalence (DBE), ionisation potential (IP), electron-affinity (EA) and weakly-polar component of solvent accessible surface area (WPSA), and the chemical and statistical significance of these descriptors was discussed. Multiple linear regression was used to build the QSAR models, resulting in high goodness-of-fit, r(2) (>0.75). The models were validated by internal and external validation along with residual plots.

Reactivity of aqueous phase hydroxyl radical with halogenated carboxylate anions: experimental and theoretical studies

With concerns about emerging contaminants increasing, advanced oxidation processes have become attractive technologies because of potential mineralization of these contaminants via radical involved reactions that are induced by highly reactive hydroxyl radical. Considering the expensive and time-consuming experimental studies of degradation intermediates and byproduct, there is a need to develop a first-principles computer-based kinetic model that predict reaction pathways and associated reaction rate constants. In this study, we measured temperature-dependent hydroxyl radical reaction rate constants for a series of haloacetate ions and obtained their Arrhenius kinetic parameters. We found a linear correlation between these reaction rate constants and theoretically calculated aqueous-phase free energies of activation. To understand the quantitative effects on entropy of solvation due to solvent water molecules, we calculate each portion of the entropic energies that contribute to the overall aqueous phase entropy of activation; cavity formation is a dominant portion. For the series of reactions of hydroxyl radical with carboxylate ions, the increase in the entropy of activation during the solvation process is approximately 10-15 cal mol(-1)K(-1) because of interactions with solvent water molecules and the transition state. Finally, charge distribution analysis for the aqueous-phase reactions of hydroxyl radical with acetate/haloacetate ions reveals that in the aqueous phase, the degree of polarizability at the transition state is less substantial than those that are in the gaseous phase resulting in a high charge density. In the presence of electronegative halogenated functional groups, the transition state is less polarized and hydrogen bonding interactions are expected to be weaker.

Ozone oxidation for the alleviation of membrane fouling by natural organic matter: A review

Membrane fouling by natural organic matter is one of the main problems that slow down the application of membrane technology in water treatment. O(3) is able to efficiently change the physico-chemical characteristics of natural organic matter in order to reduce membrane fouling. This paper presents the state-of-the-art knowledge of the reaction mechanisms between natural organic matter and molecular O(3) or *OH radicals, together with an in-depth discussion of the interactions between natural organic matter and membranes that govern membrane fouling, inclusive the effect of O(3) oxidation on it.

Degradation of 1,2-dichloroethane from wash water of ion-exchange resin using Fenton's oxidation

BACKGROUND, AIM, AND SCOPE

Chlorinated volatile organic compounds (CVOCs), widely used in industry as solvents and chemical intermediates in the production of synthetic resins, plastics, and pharmaceuticals, are highly toxic to the environment and public health. Various studies reported that Fenton's oxidation could degrade a variety of chlorinated VOCs in aqueous solutions. In acidic conditions, ferrous ion catalyzes the decomposition of H2O2 to form a powerful *OH radical. In this study, wastewater from wash of ion-exchange resin containing typical CVOC, 1,2-dichloroethane, was treated using Fenton's oxidation. To reduce environmental load and processing costs of wastewater, Fenton process as a simple and efficient treatment method was applied to degrade 1,2-dichloroethane of wash water.

MATERIALS AND METHODS

The water samples were collected from three different washing stages of ion-exchange resin. The degradation of 1,2-dichloroethane and total organic carbon (TOC) of wash water of ion-exchange resin by Fenton process was studied with response surface method (RSM). Design of the experiments was conducted by central composite face, and factors included in three models were Fe2+ and H2O2 doses and treatment time. Relevant quadratic and interaction terms of factors were investigated.

RESULTS

According to ANOVA, the model predicts well 1,2-dichloroethane reduction of all water samples and TOC reduction of samples 2 and 3. The Fe2+ and H2O2 doses used in the present study were most suitable when 1,2-dichloroethane concentration of the wash water is about 120 mg L(-1). In that case, Fenton's oxidation reduced 1,2-dichloroethane and TOC up to 100% and 87%, respectively, according to the RSM model. With 90-min reaction time and H2O2 dose of 1,200 mg L(-1), the required Fe2+ doses for 1,2-dichloroethane and TOC were 300 and 900 mg L(-1), respectively. The optimal H2O2/Fe2+ stoichiometric molar ratio was between 4-6. Then, concentration of Fe2+ was low enough and the amount of residual sludge can thus be reduced. It seems that most of TOC and part of 1,2-dichloroethane were removed by coagulation.

DISCUSSION

Up to a certain extent, increase of Fe2+ and H2O2 doses improved the removal of 1,2-dichloroethane and TOC. High Fe2+ doses increased the formation of ferric-based sludge, and excessive H2O2 doses in sample 2 decreased the degradation of 1,2-dichloroethane. Excess amount of hydrogen peroxide may scavenge hydroxyl radicals, thus leading to loss of oxidative power. Also, the residual hydrogen peroxide of different samples increased with increasing H2O2 dose and H2O2/Fe2+ molar ratio and decreasing treatment time probably also due to scavenging reactions. Due to the saturated nature of 1,2-dichloroethane, the oxidation mechanism involves hydrogen abstraction before addition of hydroxyl radical, thus leading to lower rate constants than for direct hydroxyl radical attack, which for one increases the treatment time.

CONCLUSIONS

Complete removal of 1,2-dichloroethane was attained with initial concentration<120 mg L(-1). Also, TOC degraded effectively. Wash water with higher concentration of 1,2-dichloroethane requires longer treatment times and higher concentrations of Fe2+ and H2O2 for sufficient 1,2-dichloroethane removal.

RECOMMENDATIONS AND PERSPECTIVES

Due to the results achieved in this study, Fenton's oxidation could be recommended to be used for organic destruction of wash water of ion-exchange resin. Residual sludge, the main disadvantage in Fenton process, can be reduced by optimizing the ferrous dose or by using heterogeneous treatment where most of the reusable iron remains in the solid phase.

Trichloroethylene transformation in aerobic pyrite suspension: pathways and kinetic modeling

The pathways and kinetics of trichloroethylene (TCE) degradation in aerobic pyrite suspension were investigated. The detection of hydroxyl radical in aqueous pyrite suspension suggested that TCE was degraded by this strong oxidant The reaction pathways of TCE degradation were proposed in which the degradation of TCE to formic acid and finally to CO2 was the main route. Degradation of TCE to oxalic acid and to dichloroacetic acid were found as minor pathways. Degradation rates of TCE to formic acid, glyoxylic acid, and dichloroacetic acid were obtained using kinetic model at 1.2 x 10(-2), 9.8 x 10(-4) and 4.6 x 10(-4) h(-1), respectively.

Reactions of 2,2‘-Azinobis-(3-ethylbenzthiazoline-6-sulfonate) Dianion, ABTS2-, with •OH, (SCN)2•-, and Glycine or Valine Peroxyl Radicals

ABTS2-, 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulfonate) dianion, was used as a reference to compare the reactivity of peroxyl radicals of two amino acids, glycine and valine, in aqueous solutions at natural pH. Peroxyl radicals were produced by pulse radiolysis and the product of their reaction with ABTS2- the ABTS*- radical was observed spectrophotometrically. Experimental kinetic traces were fitted using chemical simulation. The rate constants of reactions of glycine and valine peroxyl radicals with ABTS2- were (6.0+/-0.2)x10(6) and (1.3+/-0.1)x10(5) M-1.s-1, respectively. Moreover, it was found that only 60% of glycine radicals formed upon its reaction with *OH radicals reacted with molecular oxygen to yield peroxyl radicals. Comparison of experimental data with simulations of chemical reactions in irradiated ABTS and ABTS/NaSCN solutions showed that ABTS*- forms in the reaction with *OH with a yield of 43% and rate constant of (5.4+/-0.2)x10(9) M-1.s-1 and in the reaction with (SCN)2*- with a yield of 57% and rate constant of (8.0+/-0.2)x10(8) M-1.s-1.

Chain Photoreduction of CCl3F in TiO2 Suspensions: Enhancement Induced by O2

Trichlorofluoromethane (CFC 11) was photoreduced in aqueous suspensions of TiO2 particles containing HCO2- ions and air. Dissolved O2 inhibited the reaction during an induction period that preceded the rapid formation of chloride ions. Reaction rates were higher in systems containing O2 as compared to analogous reactions that occurred in anaerobic suspensions. High photonic efficiencies of Cl- formation (> or =15) were achieved using suspensions with pH > or = 5. As was the case for studies with air-free suspensions, reactions are best described using a photoinitiated chain mechanism that produced CHCl2F and Cl- during the propagation steps. The enhanced yields obtained in the presence of air are attributed to the removal by O2 of electrons trapped in the oxide, which are converted first into H2O2 and then into reducing radicals that participate in the chain process. Enhanced yields of Freon photoreduction were also observed during illumination of air-free suspensions containing hydrogen peroxide, which were interpreted using a similar mechanism.

Rate Coefficient Measurements of Hydrated Electrons and Hydroxyl Radicals with Chlorinated Ethanes in Aqueous Solutions

Rate coefficients for the reactions of hydrated electrons and hydroxyl radicals with various chloroethanes were determined in aqueous solutions using pulse radiolysis techniques. The rate coefficients for the hydrated electron increase from 0.17 x 10(9) to 16.3 x 10(9) M(-1) s(-1) with increasing number of chlorine atoms from monochloroethane to hexachloroethane. Very little difference in rates is found between the isomers. Rate coefficients for the OH radicals range from 1 to 5 x 10(8) M(-1)s(-1) and have very little variation with the number of chlorine atoms except when no H atom is available on a carbon atom. The use of competition kinetics with low concentrations of SCN(-) as a reference is reviewed and suitable model simulations proposed. Possible explanations for the discrepancies between the previously published rate coefficients and the present values are offered.

Kinetic model for phenolic compound oxidation by Fenton's reagent

A kinetic model is developed for the oxidation of phenolic compounds by Fenton's reagent. In the first stage a rigorous kinetic model is applied to calculate the different kinetic rate constants for the oxidation process of p-hydroxybenzoic acid. In a second phase a competitive method is applied to calculate these kinetic constants for another 10 phenolic compounds present in agroindustrial and pulp paper wastewaters. These 10 phenolic compounds were: beta-resorcylic acid, 3-(4-hydroxyphenyl)-propionic acid, ferulic acid, protocatechuic acid, caffeic acid, p-coumaric acid, vanillic acid, syringic acid, veratric acid and 3,4,5-trimethoxybenzoic acid.

High dose propofol enhances red cell antioxidant capacity during CPB in humans

PURPOSE

To compare low vs. high dose propofol and isoflurane on red cell RBC antioxidant capacity in patients during aortocoronary bypass surgery (ACBP).

METHODS

Twenty-one patients, for ACBP, were anesthetized with sufentanil 0.5-10 microg x kg(-1) and isoflurane 0-2%; ISO = control; n = 7), or sufentanil 0.3 microg x kg(-1), propofol 1-2.5 mg x kg(-1) bolus then 100 microg x kg(-1) min(-1) before, and 50 microg x kg(-1) x min(-1) during CPB (LO; n = 7), or sufentanil 0.3 microg x kg(-1), propofol 2-2.5 mg x kg(-1) bolus then 200 microg x kg(-1) x min(-1) (HI; n = 7). Venous blood was drawn pre- and post-induction, after 30 min CPB, 5, 10, and 30 min of reperfusion, and 120 min post-CPB to measure red cell antioxidant capacity (malondialdehyde (MDA) production in response to oxidative challenge with t-butyl hydrogen peroxide) and plasma propofol concentration. Pre- induction blood samples were analyzed for antioxidant effects of nitrates on red cells. The tBHP concentration response curves for RBC MDA in ISO, LO and HI were determined.

RESULTS

Preoperative nitrate therapy did not effect RBC MDA production. Perioperative RBC MDA production was similar in ISO and LO groups. Sustained intraoperative decrease in RBC MDA was seen with propofol 8.0+/-2.4 - 11.8+/-4.5 microg x ml(-1) in HI (P<0.05-0.0001). MDA production vs. log plasma propofol concentration was linear in HI dose.

CONCLUSIONS

During CPB, RBC antioxidant capacity is enhanced and maintained with HI dose propofol. Propofol, at this dose, may prove useful in protecting against cardiopulmonary ischemia-reperfusion injury associated with ACBP.

Interaction of hydroxycinnamic acid derivatives with the Cl3COO radical: a pulse radiolysis study

The electron transfer reactions between the trichloromethylperoxyl radical (Cl3COO*) and hydroxycinnamic acid derivatives, including chlorogenic acid, sinapic acid, caffeic acid, ferulic acid and 3,4-(methylenedioxy)cinnamic acid, have been studied by pulse radiolysis. The hydroxycinnamic acid derivatives, especially sinapic acid, are identified as good antioxidants for reduction of Cl3COO* via electron transfer reactions. From buildup kinetic analysis of phenoxyl radical, the rate constant for reaction of Cl3COO* with sinapic acid has been determined to be 8.2x10(7) dm3 mol(-1) s(-1), while the rate constants of electron transfer from other hydroxycinnamic acid derivatives to Cl3COO* were obtained to be about 2x10(7) dm3 mol(-1) s(-1). The reaction of 3,4-(methylenedioxy) cinnamic acid with Cl3COO* was investigated as an evidence for the electron transfer mechanism.

Propofol enhances red cell antioxidant capacity in swine and humans

PURPOSE

To determine the effect of an anaesthetic with antioxidant potential, propofol, on red blood cell (RBC) antioxidant enzyme activities and RBC susceptibility to peroxidative challenge.

METHODS

Propofol was administered by intravenous bolus (2.5 mg.kg-1) and continuous infusion (36 and 72 ml.hr-1 in nine swine; 216 ml.hr-1 in two swine), to achieve serum concentrations between 5 and 30 micrograms.ml-1 for two hours at each rate. Arterial blood sampling was at 0, 10, 30, 60, and 120 min for each rate of infusion, for measurement of plasma propofol concentration, activities of plasma and RBC superoxide dismutase, glutathione peroxidase, glutathione reductase, RBC catalase, and RBC malondialdehyde (MDA) formation in response to ex vivo oxidative challenge with t-butyl hydrogen peroxide (tBHP; 1.5 mM). Antioxidant mechanisms were determined by in vitro study of MDA formation, GSH depletion, and oxidation of haemoglobin to methaemoglobin in human erythrocytes exposed to propofol 0-75 microM. The antioxidant potential of propofol was compared with that of alpha-tocopherol utilising the reaction with 2,4,6-tripyridyl-s-triazine (TPTZ).

RESULTS

Propofol had no effect on plasma or RBC antioxidant enzyme activities. It inhibited RBC MDA production over the range of 0-20 micrograms.ml-1 (y = -18.683x + 85.431; R2 = 0.8174). Effective propofol concentrations for 25% and 50% reductions in MDA levels were 7-12 and 12-20 micrograms.ml-1, respectively. Propofol has a similar effect on human erythrocytes in vitro (R2 = 0.98).

CONCLUSION

Propofol antagonises the effects of forced peroxidation of red cells at anaesthetic and sub-anaesthetic concentrations in swine. Its actions include scavenging of oxygen derived free radicals in a tocopherol-like manner.

Alterations in the course of acid-induced lung injury in rats after general anesthesia: volatile anesthetics versus ketamine

Pulmonary aspiration of gastric acid is a complication that occurs during anesthesia. The effects of the often used anesthetics on the inflammatory response after aspiration of acid are not known. We examined the effects of three different inhaled anesthetics--halothane, enflurane, and isoflurane--as well as parenteral ketamine, on the associated immediate mortality, alveolar protein leakage, and morphometric changes after intrapulmonary instillation of acidic solution in rats. Animals in deep state of anesthesia had a higher mortality after the instillation of acidic solutions than those in lighter stages (82.5% vs 31.6%). Protein leakage over 5 h was greater in the animals receiving volatile anesthetics (range 0.9-1.2) compared with those receiving ketamine (0.6 +/- 0.05). Desferoxamine did not decrease protein leakage in acid-injured animals (1.1 +/- 0.06 vs 1.02 +/- 0.08). Furthermore, volatile anesthetics resulted in an increase in the acute inflammatory response and leukocytic infiltration compared with ketamine in acid-injured lungs. We conclude that the administration of inhaled anesthetics was associated with exacerbation of an acute inflammatory response after aspiration of acidic solution. Lung injury was not increased with ketamine anesthesia. This difference was the result of the hypotensive effects of inhaled anesthetics.

IMPLICATIONS

This study reveals that the use of inhaled anesthetics aggravates inflammation secondary to gastric aspiration and should be avoided on diagnosis of the situation.

Oxidation reactions of a bovine serum albumin-bilirubin complex. A pulse radiolysis study

Using the technique of pulse radiolysis, oxidation studies of the bovine serum albumin-bilirubin (BSA-BR) system with radicals like CCl3OO., N3., (SCN)2.-, Br2.- and OH. generated in neutral and alkaline medium are reported. In a neutral solution, BSA protects the bound BR very efficiently from the attack of these radicals. The experimental k/k' values for the reaction of CCl3OO., N3. and Br2.- radicals are 2.46, 1.78 and 2.55 respectively, where k and k' are the bimolecular rate constants for the formation of the semi-oxidized BSA and BR radicals respectively. The calculated ratios from our measurements of rate constants k and k' are 0.16, 0.28 and 1.38 for CCl3OO., N3. and Br2.- respectively. These values indicate protection of BR by BSA from free radical attack. For Br2.- radical-induced oxidation of the BSA-BR system, a radical transfer from protein to BR was observed. OH. shows very fast adduct formation with both BSA and BR. The bimolecular rate constant for the formation of BR-OH adducts at PH 8+/- 0.2 is 9.5 x 10(9) dm3 mol-1 s-1 (540 nm). OH. adds to BSA at neutral pH with a rate constant of 3.0 +/- 1.0 x 10(10) dm3 mol-1 s-1 (305 nm). In the BSA-BR complex, BSA fully protects BR from OH. attack and the (BSA-BR)-OH adduct further reacts with free BR molecule if present in solution.

The characterization of antioxidants

The role of antioxidants in nutrition is an area of increasing interest. Antioxidants are used (1) to prolong the shelf life and maintain the nutritional quality of lipid-containing foods, and (2) to modulate the consequences of oxidative damage in the human body. This review discusses what an antioxidant is and how the properties of antioxidants may be characterized.

Characterization of the potential antioxidant and pro-oxidant actions of some neuroleptic drugs

It has been suggested in the literature that neuroleptic drugs may be able to exert antioxidant and/or pro-oxidant actions in vivo. The feasibility of this was tested by measuring the ability of chlorpromazine, prochlorperazine, metoclopramide, methotrimeprazine and haloperidol to scavenge biologically relevant oxygen-derived species in vitro. None of the drugs reacted with superoxide radical at a significant rate. Chlorpromazine, prochlorperazine, metoclopramide and methotrimeprazine were very powerful scavengers of hydroxyl radicals, reacting at almost a diffusion-controlled rate. Chlorpromazine showed some ability to inhibit iron ion-dependent hydroxyl radical formation. Chlorpromazine, methotrimeprazine, promethazine and prochlorperazine were powerful inhibitors of iron ion-dependent liposomal lipid peroxidation, scavengers of organic peroxyl radicals and inhibitors of haem protein/hydrogen peroxide-dependent peroxidation of arachidonic acid. Chlorpromazine, prochlorperazine, metoclopramide, methotrimeprazine and haloperidol were powerful scavengers of hypochlorous acid. Haloperidol showed no ability to inhibit lipid peroxidation or to scavenge peroxyl radicals, and reproducibly increased lipid peroxidation catalysed by haem proteins, in both the presence and absence of hydrogen peroxide. The relevance of these in vitro observations to events in vivo is discussed.

Lipoic and dihydrolipoic acids as antioxidants. A critical evaluation

A detailed evaluation of the antioxidant and pro-oxidant properties of lipoic acid (LA) and dihydrolipoic acid (DHLA) was performed. Both compounds are powerful scavengers of hypochlorous acid, able to protect alpha 1-antiproteinase against inactivation by HOCl. LA was a powerful scavenger of hydroxyl radicals (OH.) and could inhibit both iron-dependent OH. generation and peroxidation of ox-brain phospholipid liposomes in the presence of FeCl3-ascorbate, presumably by binding iron ions and rendering them redox-inactive. By contrast, DHLA accelerated iron-dependent OH. generation and lipid peroxidation, probably by reducing Fe3+ to Fe2+. LA inhibited this pro-oxidant action of DHLA. However, DHLA did not accelerate DNA degradation by a ferric bleomycin complex and slightly inhibited peroxidation of arachidonic acid by the myoglobin-H2O2 system. Under certain circumstances, DHLA accelerated the loss of activity of alpha-antiproteinase exposed to ionizing radiation under a N2O/O2 atmosphere and also the loss of creatine kinase activity in human plasma exposed to gas-phase cigarette smoke. Neither LA nor DHLA reacted with superoxide radical (O.2-) or H2O2 at significant rates, but both were good scavengers of trichloromethylperoxyl radical (CCl3O2.). We conclude that LA and DHLA have powerful antioxidant properties. However, DHLA can also exert pro-oxidant properties, both by its iron ion-reducing ability and probably by its ability to generate reactive sulphur-containing radicals that can damage certain proteins, such as alpha 1-antiproteinase and creatine kinase.

Evaluation of the antioxidant actions of ferulic acid and catechins

We have evaluated the abilities of ferulic acid, (+/-) catechin, (+) catechin and (-) epicatechin to scavenge the reactive oxygen species hydroxyl radical (OH.), hypochlorous acid (HOCl) and peroxyl radicals (RO2.). Ferulic acid tested at concentrations up to 5 mM inhibited the peroxidation of phospholipid liposomes. Both (+/-) and (+) catechin and (-) epicatechin were much more effective. All the compounds tested reacted with trichloromethyl peroxyl radical (CCl3 O2.) with rate constants > 1 x 10(6) M-1 s-1. A mixture of FeCl3-EDTA, hydrogen peroxide (H2O2) and ascorbic acid at pH 7.4, has often been used to generate hydroxyl radicals (OH.) which are detected by their ability to cause damage to the sugar deoxyribose. Ferulic acid, (+) and (+/-) catechin and (-) epicatechin inhibited deoxyribose damage by reacting with OH. with rate constants of 4.5 x 10(9)M-1 s-1, 3.65 x 10(9) M-1 s-1, 2.36 x 10(9) M-1 s-1 and 2.84 x 10(9) M-1 s-1 respectively. (-) Epicatechin, ferulic acid and the (+) and (+/-) catechins exerted pro-oxidant action, accelerating damage to DNA in the presence of a bleomycin-iron complex. On a molar basis, ferulic acid was less effective in causing damage to DNA compared with the catechins. A mixture of hypoxanthine and xanthine oxidase generates O2-. which reduces cytochrome c to ferrocytochrome c. (+) Catechin and (-) epicatechin inhibited the reduction of cytochrome c in a concentration dependent manner. Ferulic acid and (+/-) catechin had only weak effects. All the compounds tested were able to scavenge hypochlorous acid at a rate sufficient to protect alpha-1-antiproteinase against inactivation. Our results show that catechins and ferulic acid possess antioxidant properties. This may become important given the current search for "natural" replacements for synthetic antioxidant food additives.

Reactivity of ebselen and related selenoorganic compounds with 1,2-dichloroethane radical cations and halogenated peroxyl radicals

The reactivity of ebselen, 2-phenyl-1,2-benzisoselenazol-3(2H)one, and structurally related analogues was studied by pulse radiolysis. The rate constant for the reaction of ebselen with trichloromethylperoxyl radicals was determined to be 2.9 X 10(8) M-1 s-1, while its sulfur analogue, 2-phenyl-1,2-benzisothiazol-3(2H)one, was oxidized at much lower rates, k less than or equal to 10(7) M-1 s-1. Among several derivatives studied, the only other compound that exhibited a high rate constant was 2-(methylseleno)-benzoic acid-N-phenylamide. Oxidation of ebselen by other halogenated peroxyl radicals was also carried out and revealed a direct relationship between rate constant and the degree of halogenation of the oxidant. The transient radicals generated during oxidation of ebselen and the analogues were characterized by optical absorption and conductivity measurements and were attributed to one-electron-oxidized radical cations. The oxidation potentials were determined by cyclic voltammetry. Comparative evaluation of the in vitro behavior during microsomal lipid peroxidation revealed ebselen to be the most potent antioxidant of the compounds investigated, 2-(Methylseleno)-benzoic acid-N-phenylamide, despite its high rate constant for oxidation by halogenated peroxyl radicals, was found to be a poor antioxidant. The rate constant of oxidation of ebselen by trichloromethylperoxyl radicals is comparable to that of alpha-tocopherol under similar conditions, underscoring the potential pharmacological interest of ebselen as an antioxidant.

Subcellular distribution of an inhalational anesthetic in situ

To better understand the mechanisms and sites of anesthetic action, we determined the subcellular partitioning of halothane in a tissue model. A method was found to fix the in vivo distribution of halothane in rat atrial tissue for subsequent electron microscopy and x-ray microanalysis. Atrial strips were exposed to various concentrations of halothane, rapidly frozen, cryo-sectioned, and cryo-transferred into an electron microscope. Irradiation of the hydrated cryosections with the electron beam caused halothane radiolysis, which allowed retention of the halogen-containing fragments after dehydration of the sections. The bromine from halothane was detected and quantified with x-ray microanalysis in various microregions of atrial myocytes. Halothane (bromine) partitioned largely to mitochondria, with progressively lower concentrations in sarcolemma, nuclear membrane, cytoplasm, sarcomere, and nucleus. Partitioning could not be explained solely by distribution of cellular lipid, suggesting significant and differential physicochemical solubility in protein. However, we found no saturable compartment in atrial myocytes within the clinical concentration range, which implies little specific protein binding.

The formation and structure of the sulfoxyl radicals RSO(.), RSOO(.), RSO2(.), and RSO2OO(.) from the reaction of cysteine, glutathione and penicillamine thiyl radicals with molecular oxygen

This work reports an electron spin resonance study of the reactions of cysteine, glutathione and penicillamine thiyl radicals with molecular oxygen in frozen aqueous solutions at low temperatures. For all three thiols, the thiyl radical, RS., is found to react with oxygen to form the thiol peroxyl radical, RSOO(.). On the absorption of visible light, RSOO(.) photoisomerizes to the sulfonyl radical, RSO2(.), which subsequently reacts with molecular oxygen to form RSO2OO(.), the sulfonyl peroxyl radical. The identities of the sulfonyl and sulfonyl peroxyl radicals were confirmed by their production by a different route, from sulfinic acid. Sulfinyl radicals, RSO(.), are found as the final radical species in the reactions of thiyl radicals and oxygen. Parallel 17O hyperfine couplings (A parallel) are reported for each sulfoxyl radical and a correlation between the spin density on oxygen and the reactivity of the radical is suggested. As a result of this correlation sulfonyl peroxyl radicals are predicted to be far more reactive than thiol peroxyl radicals. We also report molecular orbital calculations on the nature of the spin density distribution and the molecular geometry of the model radicals CH3SO2(.) and CH3SO2OO(.).