Pulse Radiolysis Of Aqueous Solutions Research Articles

One-electron transfer reactions of the couple NAD.cntdot./NADH

One-electron transfer reactions involving nicotinamide-adenine dinucleotide in its oxidized and reducd forms (NAD./NADH) were studied by pulse radiolysis in aqueous solutions. One-electron oxidation of NADH by various phenoxyl radicals and phenothiazine cation radicals was found to take place with rate constants in the range of 10/sup 5/ to 10/sup 8/ M/sup -1/ s/sup -1/, depending on the redox potential of the oxidizing species. In all cases, NAD. is formed quantitatively with no indication for the existence of the protonated form (NADH/sup +/.). The spectrum of NAD., as well as the rates of oxidation of NADH by phenoxyl and by (chlorpromazine)/sup +/. were independent of pH between pH 4.5 and 13.5. Reaction of deuterated NADH indicated only a small kinetic isotope effect. All these findings point to an electron transfer mechanism. On the other hand, attempts to observe the reverse electron transfer, i.e., one-electron reduction of NAD. to NADH by radicals such as semiquinones, showed that k was less than 10/sup 4/ to 10/sup 5/ M/sup -1/ s/sup -1/, so that it was unobservable. Consequently, it was not possible to achieve equilibrium conditions which would have permitted the direct measurement of the redox potential for NAD./NADH. One-electron reduction of NAD. appearsmore » to be an unlikely process. 1 table.« less

Investigation of Hydrogen Atom Addition to Vinyl Monomers by Time Resolved ESR Spectroscopy

AbstractBy means of time resolved ESR spectroscopy in the microsecond time scale the H atom addition to different vinyl monomers was investigated. The H atoms produced by pulse radiolysis of aqueous solutions show a strong recombination CIDEP effect which also allows the recombination rate constant of H atoms to be determined. By analysis of ESR time profiles with the modified Bloch equations the relaxation times T1, T2, the polarization factors and the chemical rate constants with scavengers were obtained. Besides the H atom addition rate constants to different vinyl monomers the structure of the monomer radical was determined for acrylic acid.

A pulse radiolysis investigation of the reactions of bromine dioxide radical (BrO2.cntdot.) with hexacyanoferrate(II), manganese(II), phenoxide ion, and phenol

The single-electron reductions of BrO/sub 2/. by Fe(CN)/sub 6//sup 4 -/, phenoxide ion, Mn(II), and phenol have been investigated. The BrO/sub 2/. was produced by pulse radiolysis of aqueous solutions of BrO/sub 3//sup -/ which also contained one of these reductants. All experiments were carried out at pH 6-12. The reductions by Fe(CN)/sub 6//sup 4 -/ and phenoxide ion were rapid and clean and led to the products Fe(CN)/sub 6//sup 3 -/ and phenoxy radical. The rate constants for these reductions were found to be, respectively, (1.9 +- 0.1) x 10/sup 9/ and (2.6 +- 0.2) x 10/sup 9/ M/sup -1/ s/sup -1/. The reductions of BrO/sub 2/. by Mn(II) and phenol were found to be much slower as well as more complex than the reductions by Fe(CN)/sub 6//sup 4 -/ and phenoxide ion. The products were, as expected, Mn(III) and phenoxy radical. However, there was a component of BrO/sub 2/. reduction by Mn(II) whose rate did not depend upon (Mn(II)). Furthermore, the rate of BrO/sub 2/. reduction by phenol did not depend at all upon the concentration of phenol. It is suggested that these slower reductions were complicated by the well-known dimerization equilibrium between BrO/sub 2/. and Br/sub 2/O/submore » 4/. If the rate of reduction of this dimer by Mn(II) or phenol is comparable to or faster than the rate of its return to BrO/sub 2/., then the dimerization process itself will become partially or completely rate determining. 8 figures, 1 table.« less

On the free radical-induced aggregation of ribonuclease - a pulse radiolysis study using the light scattering detection method.

The aggregation of bovine ribonuclease (RNase) induced by either .OH or Br(2) radicals has been studied. These radicals, which were generated by pulse radiolysis of aqueous solution with 16 MeV electrons, readily attack the enzyme thus producing RNase-radicals which subsequently combine. At initial radical concentrations low enough (less than 0.1 radical per enzyme molecule) to prevent multimerizations other than dimerization, rate constants for the latter process were determined from the increase of the light scattering intensity after the pulse: 2k2 = (22 +/- 0.3) 106 l/mol s (Br(2) initiated dimerization) and (5.4 +/- 0.4) 106 l/mol s (.OH initiated dimerization). The G-values for dimerization are: 1.3 (Br(2) and 0.85 (.OH). Transient optical absorption measurements revealed the existence of phenoxyl radicals of tyrosine (TyrO.) that decayed with a rate constant of 2 K2 (total) = (5.5 +/- 0.7) 106 l/mol s (Br(2)-case). The difference between k2 and k2 (total) presumably indicates the occurrence of disproportionation.

Radiation chemistry of xenon trioxide, xenate and perxenate, and photochemistry of perxenate. A pulse radiolysis and laser flash photolysis study

Unstable species containing xenon in the formal oxidation states five, XeV, and seven, XeVII, were observed by pulse radiolysis of aqueous solutions of xenon trioxide, XeO3, at pH 8–9 and of xenate, HXeO–4, at pH 11–13. XeVII and species containing xenon in the formal oxidation state nine, XeIX, were observed in pulse radiolysis and flash photolysis of aqueous solutions of perxenate, HXeO3–6, at pH 11–13. The formulae HXeO3 and H3XeO2–7 are assumed for XeV and XeIX, whereas the observations suggest that XeVII corresponds to three different species for which the formulae HXeO4, HXeO2–5 and H3XeO2–6 are assumed. HXeO3 and H3XeO2–6 are formed in reactions of the hydrated electron with XeO3 and HXeO3–6, respectively. HXeO4 and H3XeO2–7 are formed in reactions of the hydroxyl radical with XeO3 and HXeO3–6 in which the hydroxyl radical adds to a ligand oxygen atom to form peroxy compounds. HXeO2–5 is formed in a reaction with the hydroxyl radical anion in which the hydroxyl radical anion adds to the xenon atom and by photolysis of HXeO3–6: HXeO3–6 [graphic omitted] HXeO2–5+ O–. XeV, XeVII and XeIX and corresponding iodine species in the oxidation states four, six and eight have similar spectra and kinetics of disappearance. Estimated values of standard Gibbs energy of formation of the xenon species are used for selecting thermodynamically feasible mechanisms for one-electron reduction of perxenate and for the decomposition of perxenate in acid solution.

The reactions of the sulfate radical ion with phenylacetic and 4-phenylbutanoic acids

The reactions of the sulfate radical ion (SO4-) were studied by pulse radiolysis of aqueous solutions of aromatic acid and peroxydisulfate ions. With phenylacetic acid, the major reaction is decarboxylation; the resulting ultra-violet absorption spectrum shows that the main product is the benzyl radical, Ph-·CH2, and that only minor amounts of hydroxylation products are formed. However, decarboxylation is unimportant with 4-phenylbutanoic acid and the spectrum has been assigned to the benzylic Ph-·CH-CH2-CH2-COO- radical ion. The same spectrum is obtained if the hydrogen abstraction reaction of the O-· radical ion is used with 4-phenylbutanoic acid to form the latter radical.

Reactivity of semiquinone radicals and its relation to the biochemical role of superoxide

Semiquinone radicals derived from 9, 10-anthraquinone-2-sodium sulphonate (AQS), menadione (MD), duroquine (DQ) and 2,5-dimethylbenzoquinone (DMBQ) by pulse radiolysis of aqueous solutions containing propan-2-ol and quinone are shown to reduce methaemoglobin and cytochrome c at rates which greatly exceed those of the corresponding reductions by superoxide. Reasons for this are suggested. Rate constants are reported for these and related reactions, including dismutation of the semiquinones.From studies of the γ radiolysis of similar quinone–haem solutions containing oxygen, it is shown that the equilibrium O–2+ Q ⇄ O2+ Q–(4), is maintained in these systems, and in similar ones in which superoxide is generated by enzymes, thereby converting superoxide to the more reactive radical, semiquinone. Addition of superoxide dismutase to these systems suppresses reactions caused by semiquinone, a conclusion of current biochemical significance. Measurements of the equilibrium constant K4, and hence of redox properties of the semiquinones, have been obtained from studies of this suppression, and agree with previous measurements by other methods.

Pulse radiolysis of aqueous solutions of substituted phosphonium ions

The reactions of substituted phosphonium ions Me n P +Ph 4− n ( n = 1 ∼ 3) with e - aq have been investigated. All the phosphonium ions are reduced with e - aq at the diffusion-controlled rates producing the respective phosphoranyl radicals. The absorption spectra of these radicals have major absorption peaks at 300–305 nm (ϵ ∼ 9000 dm 3 mol -1 cm -1) and minor ones at 380 nm. The phosphoranyl radicals decay in both unimolecular and bimolecular reactions. They react also with H +. The rate constants both for decay of these radicals and for reactions of these radicals with H + increases with increasing the number of the methyl group. In the case of Me nPPh, the unimolecular decay of Me 3>.;PPh produces another transient species with an absorption maximum at 330 nm. It is proposed that this transient species is the methyl radical adduct (Me 2P>.;PhMe) yielded by the intramolecular reaction of Me 3>.;PPh or the reaction of Me 2PPh and Me in a solvent cage.

Pulse radiolysis of aqueous solutions of sodium azide: Reactions of azide radical with tryptophan and tyrosine

Azide radicals (N . 3) are formed on reactions of axide anions (N - 3aq) and hydroxyl radicals in aqueous solutions. Mechanisms of formation of N . 3 and its reactions with the amino acids tryptophan (trpH) and tyrosine(tyrH), which gave the radicals trp and tyr, respectively, and with some inorganic transients, have been studied by use of the pulse radiolysis technique. Variation of pH has no significant effect on the formation or decay of the azide radical. Its decay rate increases with the concentration of N ⨪ 3aq; this is consistent with the formation of the diazide radical anion ((N 3) - 2aq). Electron transfer reactions of N - 3aq with the isopropyl radical and the dithiocyanate radical anion have been studied. The formation of the radicals trp and tyr most likely occurs by hydrogen atom transfer to N . 3 from the amino acids. The efficiencies of reactions of N . 3 and (N 3) ⨪ 2aq, with the two amino acids appear to be different.

Pulse radiolysis of aqueous solutions of benzyltrialkylammonium cations. Reactions with the primary transients from water radiolysis

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPulse radiolysis of aqueous solutions of benzyltrialkylammonium cations. Reactions with the primary transients from water radiolysisK. BobrowskiCite this: J. Phys. Chem. 1981, 85, 4, 382–388Publication Date (Print):February 1, 1981Publication History Published online1 May 2002Published inissue 1 February 1981https://doi.org/10.1021/j150604a016RIGHTS & PERMISSIONSArticle Views109Altmetric-Citations16LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (770 KB) Get e-Alerts

Radiolysis of aqueous solutions of nucleosides halogenated at the sugar moiety.

SummaryThe pulse radiolysis of aqueous solutions of nucleosides halogenated at the sugar moiety (2′-bromo-2′-deoxyuridine 4, 3′-deoxy-3′-iodothymidine 5, 5′-deoxy-5′-iodouridine 6) has been studied. G(Hal) were determined by conductometry varying the experimental conditions (pH, saturation with Ar, N2O or air, addition of t-butanol). The results indicate that solvated electrons both add to the nucleobases and eliminate halogen ions from the halogenated sugar moiety. In the case of 4 (and possibly of 5) the radical anion of the base transfers (k ≈ 105s−1) an electron to the sugar-bound halogen atom thus cleaving the C-Hal bond. In competition with this reaction there is a protonation of the radical anion of the base by protons and by water. For the latter reaction a rate constant of k = 5 × 103 M−1s−1 was estimated.Compound 4 has also been investigated by product analysis after 60-Co-γ-irradiation. In aerated solutions erythrose is formed with a G-value of 0·12. Its precursor radical is the 2′-radical generated from 4 by dissociative electron capture which reacts with O2 to the corresponding peroxyl radical. Erythrose is formed after a sequence of reactions, one of which involves the scission of the C-1′–C-2′ bond. Under this condition G(HBr) as measured by pulse radiolysis is 0·8. Thus erythrose is formed in 15 per cent yield with respect to its precursor radical. This result is of importance in assessing the precursor radical of a similar product observed in irradiated DNA.

Nanosecond proton pulse radiolysis of aqueous solutions. Part 2.—Improved measurements and isotope effects

The use of a signal sampling and averaging technique has improved the time resolution of the measurements of G(eaq–) following irradiation of aqueous solutions by 3 MeV protons in a pulse of ca. 1 ns. The maximum measured G(eaq–) for pure water and for water containing concentrated scavengers for H+ ions and OH radicals was in all cases significantly higher than previously reported. The maximum G(eaq–) for a solution of both 1 mol dm–3 OH– and 2 mol dm–3 ethanol in H2O was 6.3. Except for this case values of G(eaq–) for solutions in D2O were slightly higher than, or the same as, values for H2O solutions. Analysis of the effect of pulse shape and detection response shows that the maximum signal occurs 3.5 ns after the start of the pulse. Comparison with results of diffusion kinetic modelling shows the observation to diverge even further from the predictions than is the case for low LET radiation.

Pulse radiolysis of aqueous solutions of acetophenone

It was shown that the interaction of the hydrated electron with acetophenone results in the formation of short-lived particles with peaks at 315 and 440 nm. The comparison of the data obtain lead us to suggest that the former ( λ max = 315 nm) is a cyclohaxadienyl radical, while the latter ( λ max = 440 nm) is the product of the e - hydr, with carbon atoms of the acetophenone carbonyl group.

Kinetics of reactions and yield of hydrogen ions from pulse radiolysis of aqueous solutions of potassium chromate

The pulse radiolysis method has been used to determine the rate constants of reactions: H 3O + + CrO 4 2− and HCrO 4 - + OH -. They are equal, respectively, to (3.1 ± 0.4) × 10 11 on condition that k(H 3O + + OH −) = 1.4 × 10 11 dm 3 mol −1 s −1) and (4.3 ± 0.3) × 10 9 dm 3 mol −1 s −1. The yield of H 3O + in a bulk of the solution has been estimated from the decrease of CrO 4 2− concentration in solutions containing oxygen. For a neutral medium it is 3.45 ± 0.5 ions/100eV. It has been found, that the yield depends on chromate concentration. This has been explained by scavenging of hydrogen ions in “spurs” by chromate. For ∼10 −4 − 5 × 10 −5 mol dm −3 solution of CrO 4 2− (this corresponds to time of ca. (3–6) × 10 −8s after passing the ionising particle) H 3O + yield is 4.25 ± 0.15 ions/100eV.

Carbon-13 CIDNP from reactions of some simple organic and inorganic radicals during pulse radiolysis

Examples of carbon-13 NMR spectra exhibiting chemically induced dynamic nuclear polarization (CIDNP) during pulse radiolysis of aqueous solutions of simple organic and inorganic compounds in D/sub 2/O are presented. The following aspects of carbon-13 CIDNP are illustrated: (A) detection of CIDNP in a reaction where all protons have been replaced by deuterons, (B) generation of a theoretically ideal radical pair with only one I = 1/2 nucleus, and (C) use of isotopic enrichment to distinguish two different polarization pathways, and (D) comparison of proton and carbon-13 CIDNP from the same sample. The chemical systems studied include the radiolysis of CD/sub 3/OD in D/sub 2/O (D. and .CD/sub 2/OD radicals) and the radiolysis of sodium formate in D/sub 2/O (CO/sub 2//sup -/.radical), sodium carbonate (CO/sub 3//sup -/.), and sodium chloroacetate (.CH/sub 2/COO/sup -/).

Resonance Raman spectrum of the transient (SCN) −2 free radical anion

The resonance Raman spectrum of the transient species (λ max = 475 nm, τ 1 2 = 1.6 μs) formed by pulse radiolysis of aqueous solutions of thiocyanate, SCN 2−, is reported. The spectrum is discussed in terms of the previous assignment of this transient to the radical anion, (SCN) − 2. The observed vibrational frequencies of the radical anion are consistent with substantial weakening of the SS and the CN bonds are compared with neutral thiocyanogen.

Fast electron transfer processes in cytochrome C and related metalloproteins

Various free radicals formed on pulse radiolysis of aqueous solutions have been used to investigate the mechanisms of reduction of cytochrome(III) c by inter- and intramolecular electron transfer. The rapid formation of free radicals (t less than 1 mus) and their high reactivity with cytochrome (k approximately 10(8)(-5) x 10(10)M(-1)s(-1)) make such studies feasible. Reduction of cytochrome by free radicls is monitored by optical methods. Fast optical changes in the 1(-500)-mus region correspond to reduction of the iron center; whereas the slower changes in the 10(-500)-ms region are attributed to postreduction conformational changes. It has been concluded that the reduction path is mediated through the crevice and that no reduction intermediates are being formed.

Chemically induced dynamic electron polarization. Pulse radiolysis of aqueous solutions of micelles

Pulse radiolysis of aqueous micelle systems has been studied by time-resolved EPR. Chemically induced dynamic electron polarization (CIDEP) is observed in the spectra of the alkyl radicals produced. At all surfactant concentrations S–T O contributions to polarization are observed. At concentrations greater than the critical micelle concentration (CMC) excess emission is also observed in the CIDEP of radicals produced from micelles. The latter, S–T −1 contributions to polarization, apparently become important because of the reduction in diffusion in micelle solutions.

Radiation chemistry studies on chemotherapeutic agents. Part 1.—Pulse radiolysis of adrenalin in aqueous solutions

Adrenalin has been studied as a model radiation protective agent by means of pulse radiolysis in aqueous solutions. The rate constants for the reactions of adrenalin with e–aq and OH were determined : k(e–aq+ adr—NH+2)= 7.5 × 108 dm3 mol–1 s–1, k(e–aq+ adr—NH)= 2.5 × 108 dm3 mol–1 s–1, and k(OH + adr)= 2.2 × 1010 dm3 mol–1 s–1(pH = 9.2). e–aq attacks the amino group by splitting off methylamine, whereas OH and O–aq lead to the formation of the corresponding adducts of the cyclohexadienyl type. OH radicals can also abstract an electron from an O– group at pH > 8.

Selenium dioxide free radicals: A study by pulse radiolysis

It is shown that, in the pulse radiolysis of aqueous solutions of SeO 2, the primary water radicals react with the anionic forms of selenium dioxide (HSeO 3 -/SeO 3 2-). Hydrated electrons (and H atoms) and OH radicals give rise to different species with an absorption maximum at 330 and 430 nm, ascribed respectively to the SeO 2 - and SeO 3 - radicals. The p K's of the radicals in acid-base equilibrium have been determined as well as the rates of reaction of hydroxyl and hydrated electron with the mono- and di-negative oxy-selenites. A comprehensive reaction mechanism is proposed together with spectral and kinetic data for the various species involved.