Inorganic Free Radicals Research Articles

Perceptions of peroxynitrite reactivity – Then and now

Many chemical and biological reactions involving peroxynitrite3 occur by unusual rate laws that are independent of the identity of the reacting partner. The true nature of these reactions and the identities of actual reactive species have been the subject of considerable debate ever since the notion that peroxynitrite is an important component of oxidative stress was first introduced in the early 1990s. We present herein a succinct historical review of this topic written from the perspective that intermediary inorganic free radicals are the causative agents in these reactions. This viewpoint provides a complete self-consistent rationalization of all verified data from multiple laboratories, whereas other explanations have been unable to do so. Recognition of the radical nature of peroxynitrite decomposition has also allowed a reassessment of the quantitative mechanism of CO2-catalyzed peroxynitrite decomposition. Detailed analyses indicate that the constant for rate-limiting formation of the putative reactive carbon dioxide adduct (ONOOCO2−)3 is actually ∼20% less than previously recognized and CO2 turnover numbers for catalysis (that is, the number of reaction cycles that CO2 undergoes before being removed as bicarbonate) are relatively large and dependent upon the [CO2]/[ONOO−] ratio in the reaction environment.

The endotoxin binding and antioxidative properties of ceramic granules

To investigate the possible antimicrobial activities and the detoxification (endotoxin binding and free radical scavenging) properties of Cerdak. In order to measure the antimicrobial activity of Cerdak, microorganisms were separately inoculated into nutrient agar in the presence of Cerdak, and growth was observed over 48 hours. Cerdak was incubated with 4000EU/ml endotoxin, and the residual endotoxin was determined over 24 hours. The decrease in the colour of ABTS and DPPH (inorganic free radicals) in the presence of Cerdak was colourimetrically monitored as a measure of Cerdax's free radical scavenging ability. DNA was exposed to hydrogen peroxide and ultraviolet irradiation in the presence and absence of Cerdak. The DNA strand break was then observed through electrophoresis. While Cerdak had little or no antibacterial activities, it demonstrated a high water and endotoxin-binding capacity. It also protected DNA from damage by reactive oxygen species. The detoxification properties of Cerdak could contribute to its healing abilities.

234 REGION SPECIFIC ABUNDANCE OF INDUCIBLE NITRIC OXIDE SYNTHASE (iNOS) IN THE BOVINE OVIDUCT DURING THE ESTROUS CYCLE

Nitric oxide synthases (NOS) are involved in a large number of biochemical processes. By generating inorganic free NO radicals, which are important modulatory agents, NOS are supposed to contribute to the regulation of mammalian reproduction. We have, therefore, studied the expression and localization of inducible NOS (iNOS) in the bovine oviduct during the estrous cycle. Simmental heifers were synchronized and slaughtered at Days 0, 3.5, 12, or 18 after standing heat. Bovine oviduct epithelial cells (BOEC) of ampulla and isthmus were collected separately for ipsi- and contralateral oviducts, as determined by the ovulatory follicle or the functional corpus luteum. In addition, a BOEC in vitro suspension culture from heifers of day 3.5 was established and stimulated with physiological doses of progesterone and estradiol-17β (10 ng/mL and 10 pg/mL, respectively). Total RNA was extracted and iNOS mRNA was absolutely quantified using real-time RT-PCR. For statistical analysis, the MIXED procedure of the SAS program package (SAS Institute, Inc., Cary, NC, USA) was used to model the experimental design (n = 4). Differences were indicated as statistically significant in the case of P < 0.05. Furthermore, immunoreactive iNOS protein was localized on serial oviductal cryosections. Transcripts of iNOS mRNA were detected in bovine oviducts throughout the estrous cycle. Since the level of 18S rRNA did not differ significantly the data were not normalized. Positive immunohistochemical staining for iNOS in the luminal epithelium gave evidence for the presence of iNOS protein in the bovine oviduct. At estrus (Day 0) and Day 18, the mRNA abundance of iNOS in epithelial cells of both ipsi- and contralateral isthmus was significantly lower than in epithelial cells of the ampulla. At Day 3.5, iNOS expression was significantly reduced in the contralateral but not the ipsilateral isthmus, whereas the abundance in the ipsilateral isthmus reached levels similar to those in the ampulla. At Day 12 the mRNA abundance was low without region specific differences. A down-regulation of iNOS could be associated with an accelerated oviductal transport due to higher contractility and increased ciliary motion in the luminal epithelium of the oviduct. This might be of special importance around ovulation time for gametes as well as for the formation of a homogeneous oviductal fluid. A modulated expression pattern of iNOS during the estrous cycle points towards a possible hormonal regulation. Preliminary in vitro results showed that in BOEC iNOS responded to progesterone, while no such up-regulation was observed after estradiol-17β stimulation. As Day 3.5 coincides with early embryonic development shortly after fertilization, the possible progesterone-dependent increase of iNOS transcripts in the ipsilateral isthmus might lead to a necessary local quiescence. Due to region-specific different transcript abundance, the presence of a local NO-system in the bovine oviduct can be postulated. Therefore, these findings point out a possible important role of iNOS in the oviduct for reproductive success. This work was supported by the DFG Ei 296/10-1 and the Ev. Studienwerk eV.

On the Chemistry of Inorganic Free Radicals in Cloud Water

The chemistry by which the inorganic free radicals •OH, HO2•, O2•-, SOx•- (x = 3, 4, 5), NO3•, Cl• and Cl2•- lead to the formation of acid rain by the oxidation of sulfur dioxide and organic pollutants in cloud water is discussed in detail. Also considered are the sources of the radicals, their relative reactivities, their inter-conversion and the origins of the pollutants with which they react.

Theoretical Estimation of the Redox Potentials Involving Organic and Inorganic Free Radicals

Abstract A simple theoretical expression for the redox potential of a redox couple (X/X−• or X•/X−) has been presented by using a modified Born equation and has been successfully applied to the organic and inorganic redox couples the reliable standard redox potentials of which are directly measured electrochemically, and to polarographic half-wave redox potentials of organic compounds. The expression has also been applied to inorganic redox couples the provisional standard redox potentials of which are estimated indirectly by using thermodynamic cycles, to examine the validity of the provisional potentials. At least, the provisional redox potentials, with which the potentials calculated approximately agree, seem to be reliable.

Physical-Chemical Properties of Selenium-Containing Inorganic Radicals and their Reactivity with Amino Acids and Enzymes

Abstract The physical-chemical properties of some selenium-containing inorganic radicals have been studied by using the pulse radiolysis technique. These inorganic free radicals can be formed readily in irradiated aqueous solutions by scavenging of OH primary radicals with anions such as selenocyanate and the anionic forms of selenium dioxide (HSeO− 3/SeO2- 3). Particular attention has been paid to the spectral and kinetic properties of the radical species involved. The investigations on the reactivity of these radicals with amino acids and enzymes have allowed information both on oxidation mechanism and on the preferential site of attack.

ChemInform Abstract: Reduction Potentials Involving Inorganic Free Radicals in Aqueous Solution

Publisher Summary This chapter discusses the reduction potentials involving inorganic free radicals in aqueous solution. Because free radicals are usually transients, knowing their thermodynamic properties is primarily useful in mechanistic studies. Thus, the useful redox couples associated with a given free radical correspond to plausible elementary steps in reaction mechanisms. All potentials are expressed against the normal hydrogen electrode (NHE). Apart from the NHE, the standard state for all solutes is the unit molar solution at 25 °C. This violates the usual convention for species, such as O 2 that occur as gases, but because the rates of bimolecular reactions in solution are significant, the unit molar standard state is most convenient. The emphasis is on electron transfer reactions in which no bonds are formed or broken, electron transfer reactions in which concerted electron transfer and bond cleavage could occur, and certain atom transfer reactions. The chapter also presents a tabulation of ∆ f G ° values for all the radicals. A common approach in estimating the thermochemistry of aqueous free radicals is to use gas-phase data with approximations of solvation energies.

Reactivity of Ions of Actinides Towards Inorganic Free Radicals in Irradiated Aqueous Solutions

The paper is a short review of experimental data obtained during the study of reactivity of ions of actinides towards inorganic free radicals in irradiated aqueous solutions by pulse radiolysis method. The values of rate constants of reactions of these ions with primary products of water radiolysis (eaq −, H, OH, O−) and secondary radicals formed via reactions of these products with solutes and/or as a result of direct action of ionizing radiation on solutes (SO4 −, NO3, Cl2 −, CO3 −, O2 − etc.) are listed. The peculiarities of the reactivity are discussed. The examples of application of the obtained data for the simulation of radiolytical transformations of ions of actinides are presented.

Reactions of inorganic free radicals with liver protecting drugs

Liver protecting drugs, silibinin, a flavonolignane, and the dihydroquinoline derivates, CH 402 and MTDQ-DA, were shown to inhibit processes in which enzymatically or non-enzymatically generated free radicals were involved. Inorganic free radicals (N 3, (SCN) - 2, OH, Trp, CO - 2, O - 2) produced by pulse radiolysis readily react with the compounds, which transform into exceptionally long-lived, unreactive transients. Time evolution of the UV and visible spectra indicate that oxidising radicals form a phenoxyl type radical from silibinin, while OH forms an adduct by attacking, simultaneously, at various sites of the molecule. Superoxide radicals reduce silibinin and oxidise CH 402 and MTDQ-DA. It is concluded that the drugs might exhibit antioxidant behavior in living systems.

Study of the kinetics of the oxidation of palladium(II) by inorganic free radicals in acidic aqueous solutions by pulse radiolysis

The rate constants for the reactions of OH., NO3., and SO4−. with Pd(II) ions in aqueous solutions of the acids have been measured by the pulse radiolysis method. An inner-sphere mechanism of electron transfer.occurs in such reactions.

Some radiation chemical aspects of nuclear engineering

Some radiation chemical aspects of nuclear engineering are discussed (predominantly on the base of the works performed in the Soviet Union). The data on the influence of temperature within the range of 0–300°C on the yields of water radiolysis products are considered. The results obtained from the study of reactivity of actinide ions towards inorganic free radicals in acid aqueous solutions are summarized. The information on composition and properties of the products of radiolytic transformations of different extragents and diluents and on their influence on the behaviour of extraction systems during processing of irradiated nuclear fuel is presented.

Kinetics of one-electron transfer reactions involving chlorine dioxide and nitrogen dioxide

Rate constants for the one-electron oxidation of ClO/sub 2//sup -/ and NO/sub 2//sup -/ by several organic and inorganic free radicals have been measured along with rate constants for several reactions of ClO/sub 2/, NO/sub 2/, and BrO/sub 2/. The kinetics of the reactions of ClO/sub 2/ and NO/sub 2/ are consistent with simple electron-transfer theory, except for the reaction of NO/sub 2/ with SO/sub 3//sup 2 -/, which appears to be oxygen atom transfer. Equilibrium constants have been determined for the reactions of ClO/sub 2/ with aniline at pH 6.9 and N,N-dimethylaniline at pH 9.6. This leads to one-electron redox potentials of 1.03 and 0.87 V for these aromatic amines, respectively, at the corresponding pH. 55 references, 3 figures, 2 tables.

A pulse radiolysis study of the reactivity of neptunoyl ions relative to inorganic free radicals

1. Pulse radiolysis was used to find the rate constants for the reactions of OH, HSO4, NO3, and Cl2 radicals with neptunoyl ions.

Horseradish peroxidase. XL. The oxidation of native enzyme to Compound II

The oxidation of native horseradish peroxidase to Compound II by photochemically generated inorganic free radicals [Formula: see text], [Formula: see text], and [Formula: see text] was observed. The rates of Compound II accumulation for different rates of free radical generation and different reagent concentrations have been measured. The interpretation of the experimental data allowed us to estimate the rates of the reactions [Formula: see text], [Formula: see text], and [Formula: see text]: (3–6) × 106 M−1 s−1, (2.2–3.0) × 106 M−1, and [Formula: see text] respectively. Also obtained for all three oxidants were the ratios of the number of free radicals responsible for the heme oxidation to the total number of them attacking the enzyme.

Nitrite photolysis as a source of free radicals in productive surface waters

Sunlight photolyzes nitrite in natural waters, producing free radicals by NO2− + HOH + hν = NO + OH + OH−. The primary and secondary radicals may react irreversibly with the medium, or regenerate nitrite as proposed for pure water. We measured net nitrite loss to estimate the irreversible component. Compositionally varied nitrite‐rich surface seawaters from the Peruvian coastal upwelling were sealed in glass bulbs, sterilized, and exposed to ambient sunlight or held in darkness. Samples showed light‐dependent nitrite losses of 5‐27% per day, providing the first field evidence for generation of inorganic free radicals in surface seawater and their interaction with the chemical milieu (∼ 90 nmole/ℓ/day). The rate in filtered samples correlated positively with initial chlorophyll a content and negatively with nitrite concentration, indicating that biogenic scavengers and nitrite may compete in a product‐determining secondary step. Although nitrate is photolyzable and was present, it did not show photochemical loss.

One-electron redox reactions of free radicals in solution. Rate of electron transfer processes to quinones

A large number of biologically-important organic and inorganic free radicals have been produced in aqueous solutions, using the fast-reaction technique of pulse radiolysis and kinetic absorption spectrophotometry. The reactions of these free radicals with menaquinone (vitamin K 3, E 0 = 0.42 V) were followed by observing the formation kinetics of the semiquinone radical anion of menaquinone, •MK −. The absorption spectrum of •MK − has maxima at 395 nm and 300 nm, with extinction coefficients of 1.1·10 4 and 1.25·10 4 M −1·cm −1, respectively. The p K a of the radical •MK −-H + is 4.6±0.1. The free radicals were produced by a one-electron oxidation or reduction of various compounds by hydroxyl radicals and solvated electrons, e aq −. Alcohols, sugars, carboxylic acids, amino acids, peptides, aliphatic amines and amides, aromatic and heterocyclic molecules, pyridine derivatives (nicotinamide, NAD +), and transition metal ions have been examined. Significant differences have been observed in both the efficiency (expressed in percentage) and the rate constants of the electron transfer reactions from these free radicals to menaquinone. Absolute rates of electron transfer from approx. 5·10 8–5·10 9 M −1·s −1 have been observed for most of the free radicals studied. Information relating to the nature of the radicals and the acid-base properties of these radicals for effective one-electron redox reactions with quinones is indicated.

A Novel Method of Determining Certain Group VIII Metal Ions by Electron Paramagnetic Resonance Measurements

Abstract Although electron paramagnetic resonance (EPR) has long proven itself a valuable technique for the study of various organic free radicals1 including those that are biochemically interesting, only recently has it come into use as a convenient and sensitive method for inorganic analysis. Guilbault and coworkers have demonstrated the usefulness of EPR methods for the determination of low concentrations of various ions of the first transition metal series both in aqueous solution2, 3, 4 and extracted into organic solvents.5 Moyer and McCarthy6 have also demonstrated the application of EPR to quantitative inorganic analysis. Inasmuch as the area under the EPR first derivative curve is related to the number of unpaired electrons, this can serve as a measure of the concentration of a relatively large number of inorganic free radicals including most paramagnetic metal ions. Some of the Group VIII metal ions such as Ni(II), Pd(II), and Pt(II), while paramagnetic in their high spin complexes, however, do n...

Aqueous chemistry of inorganic free radicals. VI. Effect of oxygen on the rate of photolysis of hydrogen peroxide in aqueous solutions containing carbon monoxide

Aqueous chemistry of inorganic free radicals. VI. Effect of oxygen on the rate of photolysis of hydrogen peroxide in aqueous solutions containing carbon monoxide

Reactions of halogenoaliphatic acids with free radicals in aqueous solution. Part III. Reactions with inorganic free radicals

The ions CO2–, Cd+, Ni+, Co+, Al-+, Zn+, and Mn+ were found to induce dehalogenation of ClCH2·CO2–,ClCH2·CH2·OH, and BrCH2·CO2–, the order of reactivity being RCl < RBr. On the other hand, N2O–, O2–, NO32– and Cu+, do not induce dehalogenation. Whereas CO2– seems to react by a charge-transfer mechanism, the metal ions at their lower state of oxidation seem to react by an inner-sphere mechanism involving halogen atom transfer from the halogenoaliphatic compound.

II(a). Oxidation-reduction reactions involving inorganic substrates. Aqueous chemistry of inorganic free radicals. Part 3.—The kinetics and mechanism of the reaction of peroxydisulphate ion and hydrogen peroxide

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