Radiolysis Method Research Articles

Excimer emission of diphenyl derivatives in the pulse radiolysis of 3-methylpentane solutions at low temperature

Using the pulse radiolysis method the excimer formation of diphenyl derivatives in low temperature 3-methylpentane was investigated. For diphenyls two emission bands are found in the temperature range 140 – 230 K. The band at 320 nm is due to monomer fluorescence, whereas the second at 380 – 390 nm is as an excimer emission.

Deexcitation of He(2 1P) in collisions with rare gas atoms

Deexcitation (Penning ionization) cross sections of He(2 1P) by Kr and Xe have been obtained in a region of mean collisional energy between 18–38 meV by a pulse radiolysis method. Fairly large cross sections of above 100 Å2 and their collisional energy dependence are interpreted by the Penning ionization cross sections based on a long-range dipole–dipole interaction. Validity of the theoretical formula for the Penning ionization cross section (the Watanabe–Katsuura formula) is discussed. Two kinds of the cross sections have been further calculated by means of the impact parameter method with experimentally simulated classical trajectories; in one procedure, the polarization axis of the p-state helium has been assumed to rotate in order to keep collinear or perpendicular configuration with respect to the interatomic axis, in the other procedure, the polarization axis is fixed in a certain direction. The classical motion of the particles have been shown to cause considerable influence on the absolute values and the collisional energy dependence of the cross sections. The influence has increased accordingly to the attractive force of the interatomic potential, i.e., in order of Ar<Kr<Xe. Modified form of the dipole–dipole autoionization width with the electron exchange interaction is also discussed. It has also been suggested that rotation of the p-state atomic polarization depends strongly on the van der Waals interaction with the target atoms. The effect of the rotation has been shown to be most prominent for Xe but small for Ar.

The effect proved by pulse radiolysis and chemiluminometric methods of free radical scavengers in liver lesions

The effect proved by pulse radiolysis and chemiluminometric methods of free radical scavengers in liver lesions

The u.v. and visible emission bands of CF 3 radicals produced by pulsed electron beam excitation

Using time-resolved optical spectroscopy the kinetics of the u.v. and visible emission bands of electronically excited CF n ( n = 2,3) radicals were investigated by the pulse radiolysis method. In rare gases used as energy absorbing media, atomic and molecular transients which transfer their energy to foreign gases were formed by electron irradiation. In the presence of CF 3H, C 2F 6, C 3F 8 and CF 4 the decay of the absorption of the Ar(4s) as well as the Ar 2( 3Σ +) states and the growth of the Ar 2( 3Σ +) become faster. As, e.g. the argon absorption bands were influenced by the admixtures, new emission bands were obtained due to electronic transitions of excited CF 2 and CF 3 radicals in the spectral range 200–700 nm. Assuming that the emissions are generated by a transfer of electronic excitation energy from the rare gas excited states to the admixed gases, in which CF 2 and CF 3 radicals are formed by dissociation reactions, rate constants of the quenching reaction of the rare gas atomic and molecular states are obtained by numerical simulation of the experimental absorption time profiles. Collision free life-times of the emitting states were observed from simulations of the alkyl fluoride fluorescence decays as a function of the solute concentration.

Gas-phase collision dynamics by means of pulse-radiolysis methods

After a brief survey of recent advances in gas-phase collision dynamics studies using pulse radiolysis methods, the following two topics in our research programs are presented with emphasis on the superior advantages of the pulse radiolysis methods over the various methods of gas-phase collision dynamics, such as beam methods, swarm methods and flow methods. One of the topics is electron attachment to van der Waals molecules. The attachment rates of thermal electrons to O 2 and other molecules in dense gases have been measured in wide ranges of both gas temperatures and pressures, from which experimental evidence has been obtained for electron attachment to van der Waals molecules. The results have been compared with theories and discussed in terms of the effect of van der Waals interaction on the electron attachment resonance. The obtained conclusions have been related with investigations of electron attachment, solvation and localization in the condensed phase. The other is Penning ionization and its related processes. The rate constants for the de-excitation of He(2 1P), He(2 3S), Ne( 3P 0), Ne( 3P 1), Ne( 3P 2), Ar( 1P 1), Ar( 3P 1), by atoms and molecules have been measured in the temperature range from 100 to 300 K, thus obtaining the collisional energy dependence of the de-excitation cross sections. The results are compared in detail with theories classified according to the excited rare gas atoms in the metastable and resonance states.

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.

Critical Review of rate constants for reactions of hydrated electrons, hydrogen atoms and hydroxyl radicals (⋅OH/⋅O− in Aqueous Solution

Kinetic data for the radicals H⋅ and ⋅OH in aqueous solution,and the corresponding radical anions, ⋅O− and eaq−, have been critically pulse radiolysis, flash photolysis and other methods. Rate constants for over 3500 reaction are tabulated, including reaction with molecules, ions and other radicals derived from inorganic and organic solutes.

Deexcitation cross sections of He(2 1P) by atoms and molecules

The deexcitation cross sections of He(2 1P) by M (M=Kr, Xe, H2, D2, N2, CO, O2, NO, CO2, and CH4) have been obtained by a pulse radiolysis method at a mean collisional energy corresponding to room temperature. The cross sections have been explained fairly well by the Penning ionization process with a long-range dipole–dipole interaction. Bent trajectories appear to be important in the deexcitation by spherical atoms and molecules. An electron exchange process is also suggested to give an important contribution to the total decay width of the transient collision complex in highly excited autoionizing states of (HeM)*.

Stereochemical effects in the gas-phase pinacol rearrangement. 2. Ring contraction versus methyl migration in cis- and trans-1,2-dimethylcyclohexane-1,2-diol

The gas-phase pinacol rearrangement of cis- and trans-1,2-dimethylcyclohexane-1,2-diols, promoted by D/sub 3//sup +/, CH/sub 5//sup +//C/sub 2/H/sub 5//sup +/ and t-C/sub 4/H/sub 9//sup +/ ions, was studied by mass spectrometric and radiolytic methods in the pressure range 0.5-760 Torr. When product isomerization is inhibited, by using N(CH/sub 3/)/sub 3/ as a trapping reagent at high pressure, mixtures of 2,2-dimethylcyclohexanone and 1-acetyl-1-methylcyclopentane were recovered from the reaction. In methane, the trend of the measured relative rates for ring contraction (k/sub 5/), methyl or hydroxyl group migration (k/sub 6/) versus the rearrangement rate of pincaol itself (k/sub p/), is k/sub 6/(trans) approx. k/sub 5/(trans) greater than or equal to k/sub 5/(cis) > k/sub 6/(cis) greater than or equal to k/sub p/. No evidence for the formation of an intermediate carbenium ion was found. Stereochemical aspects of the mechanism are discussed and compared with solution data.

One-electron redox chemistry of amsacrine, mAMSA [9-(2-methoxy-4-methylsulphonylaminoanilino)acridinium], its quinone di-imine, and an analogue. A radiolytic study

The redox chemistry of the clinical antileukemia drug mAMSA (amsacrine) and of its dimethylamino analogue (diAMSA) has been investigated by radiolytic methods. Steady-state and pulse radiolysis experiments show that upon one-electron oxidation both compounds give quinone di-imine radicals (mAQDI˙ and diAQDI˙) which disproportionate to the parent compounds and the corresponding quinone di-imines (mAQDI and diAQDI). One-electron reduction of the quinone di-imines give the same intermediate radicals which are not oxidized by oxygen. Nanosecond pulse radiolysis experiments show that the initial one-electron reduction of the quinone di-imines also occurs at the acridine ring, but is followed by rapid intramolecular electron transfer to the quinone di-imine side-chain. One-electron reduction of mAMSA occurs at the acridine ring and leads to acridan formation. The redox potential at pH 7.4 of the mAMSA–mAQDI˙ couple is calculated as 915 mV (versus n.h.e.), while the redox potential of the mAMSA–mAQDI couple is 415 mV. The analogue diAMSA shows a similar reversible redox chemistry but is much more readily oxidizable, with a calculated redox potential diAMSA–diAQDI˙ of 635 mV, and a redox potential diAMSA–diAQDI of 330 mV.

A critical reevaluation of some assay methods for superoxide dismutase activity

We have compared the direct method of pulse radiolysis to the indirect methods of cytochrome c and nitroblue tetrazolium for assaying the superoxide activity of a compound. We have shown that with pulse radiolysis, where high concentrations of O 2 − are generated, the “turnover” rate constant, k cat, can be determined directly, while with the indirect methods, where relatively low steady state concentrations of O 2 − are formedl, the value of k cat determined by these methods, can be orders of magnitiude lower than that determined directly. The main reason for the lower values obtained with the indirect methods is due to the fast reoxidation of the reduced compound by molecular oxygen. Additional problems which arise with the use of indirect methods for determining superoxide dismutase catalytic activity are discussed.

Reactivity of H 2O 2 with radiation produced free radicals: Steady state radiolysis methods for estimating the rate constants

A new steady state radiolysis method for the determination of the rate constants of reaction of H 2O 2 with solute radicals derived by reaction with radiation produced OH radicals is described. The values so obtained are comparable with the ones obtained by the method described by Soylemez and Balkas in the past. A method similar to the latter has been employed to determine the rate constant of reaction of H 2O 2 with solute radicals derived from e - aq reaction. In the case of the (CH 3) 2 COH radical which can be generated by either reaction of OH with isopropanol or e - aq with acetone, the three methods give values agreeing with each other within ± 15% (viz. 2.7 ± 0.4 × 10 5 dm 3 mol -1 s -1). The reaction of the solute radicals with H 2O 2 is considered in the light of known one-electron redox potentials, and the limitations of the applicability of the methods described here are discussed.

The methoxatin semiquinone: A pulse radiolysis study

Methoxatin is a novel o-quinone found in bacterial dehydrogenases and mammalian plasma amine oxidase. This is the first report of the redox potential and spectrum of the 1-electron reduced methoxatin semiquinone obtained by the method of pulse radiolysis in aqueous solution.

Temperature dependence of the deexcitation of He(2 3S) by atoms and molecules as studied by pulse radiolysis method

The temperature dependence of the rate constants for deexcitation of He(2 3S) by Ar, Kr, N2, O2, CO, NO, CO2, and C2H4 has been measured in the temperature range from 133 to 300 K by a pulse radiolysis method, and thus the collisional energy dependence of the deexcitation cross sections is obtained. The results are interpreted in terms of an electron exchange mechanism. The value of α/β, the ratio of the exponential factor of the potential width Γ(R)=A exp(−αR) to that of the interaction potential V*(R)=B exp(−βR), is obtained for each target molecule. It is found that the value of α/β decreases with the increase of the deexcitation probability.

Resonance Raman, electron spin resonance and molecular orbital studies of m-benzosemiquinone radical anion

The resonance Raman spectrum of m-benzosemiquinone radical anion, examined by pulse radiolysis methods, shows this radical to have a CO stretching frequency of 1519 cm/sup -1/ that is similar to that of phenoxyl radicals and only 4 cm/sup -1/ lower than that for 3-hydroxyphenoxyl radical. A strong Raman band at 1093 cm/sup -1/ is assigned to a second CO stretching frequency. Theoretical molecular orbital studies suggest that the lowest electronic state is one of C/sub s/ symmetry, with one CO bond 0.04 A longer than the other. These findings are in accord with the relatively high reactivity of this radical, which indicates that it has substantial phenoxyl-like character, in contrast to the unreactive nature of its para isomer, which is strongly stabilized by resonance, making the CO bonds equivalent. The ESR spectrum indicates either that the radical has C/sub 2nu/ symmetry or that there is rapid exchange of unpaired spin between the two oxygen atoms in a structure of lower symmetry.

Temperature dependence of the rate constants for deexcitation of He(2 1P) by SF6 and Ar

The temperature dependence of the rate constants for deexcitation of He(2 1P) by SF6 and Ar has been measured in the temperature range from 133 to 300 K using a pulse radiolysis method, thus obtaining the collisional energy dependence of the deexcitation cross sections. The results agree well with the calculations of the Penning ionization cross sections based on a long-range dipole–dipole interaction. It is also suggested that bent trajectory due to an attractive potential is important, which influences greatly the absolute value and the collisional energy dependence of the cross sections.

Temperature dependence of the rate constants for deexcitation of Ar(1P1) and Ar(3P1) by SF6 and N2

The temperature dependence of the deexcitation rate constants of the resonance states of Ar, 1P1 and 3P1, by SF6 and N2 has been measured in the temperature range from 133 to 300 K using a pulse radiolysis method, thus obtaining the collisional energy dependence of the deexcitation cross sections. The results of the cross sections for SF6 are compared with the Watanabe–Katsuura theory and good agreement is obtained. The results for N2 agree with predictions of the cross sections for a nonresonant case. It is concluded that a long-range dipole–dipole interaction is important in the deexcitation processes of Ar(1P1) and Ar(3P1) by SF6, but that a short-range interaction with curve crossing dominates in the deexcitation of Ar(1P1) and Ar(3P1) by N2.

Reactions of cyclododecyl radicals in the pulse radiolysis of solutions of naphthalene and anthracene in liquid cyclododecane

1. It was established by the method of pulse radiolysis of solutions of naphthalene and anthracene in liquid cyclododecane with optical recording of the intermediate particles formed that cyclododecyl radicals form adducts ArH...R (in the absence of oxygen) and ArH...O2...R (in the presence of oxygen) with naphthalene and anthracene, respectively. 2. The rate constants of the formation of adducts ArH...R, their conversion to more stable particles in first-order reactions, as well as the destruction of the adducts ArH...O2...R in second-order reactions, were determined.

Intermolecular charge transfer involving tryptophan, tyrosine and three electron-bonded intermediates derived from methionine.

Oxidation processes of radiation-generated three-electron-bonded intermediates derived from methionine Met2[S+...S] and Met[S...X] (X=Cl,Br) were investigated through reaction with tryptophan and tyrosine, using the optical pulse radiolysis method. Bimolecular rate constants have been measured for the reactions Met2[S+...S] with TrpH(k=3.8 x 10(8) dm3 mol-1 s-1 and k = 4.9 X 10(8) dm3 mol-1 s-1 at at ph 1 and 4.3, respectively) and Met2[S+...S] with tyrosine, k=3.8 x 10(7) dm3 mol-1 s-1. Rate constants for intermolecular transformation of Met[S...Br] and Met[S...Cl] into TrpH+. or Trp. were also estimated. They varied from 4.7 X 10(8) dm3 mol-1 s-1 (bromide species) to 1.0 X 10(9)dm3 mol-1 s-1 (chloride species). It has also been established azide radicals N-6, N.3 in contrast to dihalide radicals (X-2) do not form transients of Met[S...X] (X = N3)-type. However, oxidation of N-3 by Met2[S+...S] occurs with a bimolecular rate constant of 2.8 X 10(8) dm3 mol-1 s-1. These results are discussed in the light of some equilibria which have been proposed earlier for methionine-halide systems.

Biochemical studies on the metabolic activation of halogenated alkanes.

This paper reviews recent investigations by Slater and colleagues into the metabolic activation of halogenated alkanes in general and carbon tetrachloride in particular. It is becoming increasingly accepted that free radical intermediates are involved in the toxicity of many such compounds through mechanisms including lipid peroxidation, covalent binding, and cofactor depletion. Here we describe the experimental approaches that are used to establish that halogenated alkanes are metabolized in animal tissues to reactive free radicals. Electron spin resonance spectroscopy is used to identify free-radical products, often using spin-trapping compounds. The generation of specific free radicals by radiolytic methods is useful in the determination of the precise reactivity of radical intermediates postulated to be injurious to the cell. The enzymic mechanism of the production of such free radicals and their subsequent reactions with biological molecules is studied with specific metabolic inhibitors and free-radical scavengers. These combined techniques provide considerable insight into the process of metabolic activation of halogenated compounds. It is readily apparent, for instance, that the local oxygen concentration at the site of activation is of crucial importance to the subsequent reactions; the formation of peroxy radical derivatives from the primary free-radical product is shown to be of great significance in relation to carbon tetrachloride and may be of general importance. However, while these studies have provided much information on the biochemical mechanisms of halogenated alkane toxicity, it is clear that many problems remain to be solved.