Electron Adduct Research Articles

A Pulse Radiolysis Study on Oxidation of Cystine by SO 4

1 Introduction Oxidation and reduction of disulfide have been widely studied owing to its importance in the enzyme kinetics. The electron adduct of disulfide RSSR~(.-) has been proved to be a critical intermediate of the disruption of the disulfide bridge that leads to the inactivation of enzymes. However, the transient radicals produced by the radiation oxidation of cystine, such as CySSCy~+, CySS, can also make inactive enzymes. Oxidation

Pulse radiolysis of aqueous solutions of ethyl acrylate and hydroxy ethyl acrylate

Ethyl- and hydroxy ethyl acrylate show high reactivities with hydrated electron and hydroxyl radical intermediates of water radiolysis. The electron adduct reversibly protonate with pK values of 5.7 and 7.3. The adducts may take part in irreversible protonation at the β carbon atom forming α-carboxyl alkyl radicals. Same type of radical forms in reaction of acrylates with OH: at low concentration the adduct mainly disappear in self termination reactions. Above 5 mmol dm -1 the signals showed the startup of oligomerization.

ChemInform Abstract: Reaction of Hydrated Electrons with Guanine Nucleosides: Fast Protonation on Carbon of the Electron Adduct

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Radiolysis of hydroxy ethylacrylate in dilute aqueous solutions

The reaction of e - aq and OH radicals with hydroxy ethylacrylate was investigated, the intermediates formed were identified and their decay characteristics were established by pulse and steady state radiolysis. The electron adduct decays by protonation at the β carbon atom forming thus α-carboxyalkyl radical. The OH adduct also has the α-carboxyalkyl radical structure. The radicals under pulse radiolytic conditions, in the hydroxy ethylacrylate concentration range investigated (0.05–1 mmol dm -3) mostly disappear in bimolecular self termination reactions.

Photo-InducedP-Methylbenzylation of 1,3-Dimethylthymine and 1, 3-Dimethyluracil in the Presence of Trifluoroacetic Acid

Abstract Abstract Photolysis of a solution of a pyrimidine (i. e., 1, 3-dimethylthymine and 1, 3-dimethyluracil) in p-xylene in the presence of trifluoroacetic acid afforded mainly the 5, 6-dihydropyrimidine derivative together with the 5-p-methylbenzylated product and the 6-isomer as well. It is suggested that the first two products result from the C6-protonated pyrimidine electron adduct (III), while the 6-isomer is derived from the O4-protonated isomer (II).

Reactions of water radiolysis intermediates with pyrimidine and purine bases in aqueous BeF2 glasses: an EPR study.

Free radical formation by reaction of water radiolysis intermediates produced by X-irradiation in aqueous glasses containing 7 M BeF2 at 77 K with pyrimidine and purine constituents of DNA (10 mM) was studied by electron paramagnetic resonance (EPR) spectroscopy. Reactions of electrons and .OH radicals were observed; H. form a minority and their contribution was difficult to establish. The electrons form substrate radicals at 77 K, while .OH radicals, stabilized in the matrix at 77 K, become mobile at about 140K and in part react with solute molecules. The radicals formed by both reactions were characterized after isolation of the corresponding components by thermal annealing up to about 190 K and spectra simulation using literature parameters whenever possible. The spectra from cytosine gave strong evidence for heteroatom protonation following electron addition while those from adenine were somewhat less clear. The spectra of uracil and all methylated pyrimidines gave no evidence for the protonation state of the electron adduct. For the .OH radical, the reaction with uracil and cytosine was found to be addition to the 5,6-double bond, in line with studies using aqueous solutions. For all methylated pyrimidines, however, H-abstraction from the methyl group was dominant. .OH addition to adenine was found to take place at C2.

Reaction of hydrated electrons with guanine nucleosides: fast protonation on carbon of the electron adduct

The reactions of hydrated electrons (e aq - ) and hydrogen atoms (H . ) with guanosine, 2'-deoxyguanosine, and 1-methylguanosine (G) were studied by pulse radiolysis with optical and conductometric detection. In neutral solution, the reaction of both e aq - and H . with these purines leads to the same neutral radical. This is suggested to be the H adduct to the C8 position (G(C8H) . ) formed by H . addition and by protonation at C8 of the electron adducts, via tautomerization (k=1.2×10 6 s -1 for the case of guanosine) following protonation of the radical anion at a hetero atom (k≥10 7 s -1 )

Pulse radiolysis of ethyl propionate in aqueous solution

Abstract Hydrated electrons (e aq – ) formed in water radiolysis react with ethyl propionate with a rate parameter of 7.5×107 mol–1 dm3 s–1. The electron adduct in acidic solutions immediately (<100 ns) dissociates, yielding CH3CH2C=0 radical. This process in alkaline solutions is slower, k=1.4×105 s–1. The hydroxyl radicals abstract H atoms in about 50% from the -position of propionate.

One-electron-reduction potentials of pyrimidine bases, nucleosides, and nucleotides in aqueous solution. Consequences for DNA redox chemistry

The reduction potentials in aqueous solution of the pyrimidine bases, nucleosides, and nucleotides of uracil (U) and thymine (T) were determined using the technique of pulse radiolysis with time-resolved spectrophotometric detection. The electron adducts of U and T were found to undergo reversible electron exchange with a series of ring-substituted N-methylpyridinium cations with known reduction potential. From the concentrations of the pyrimidine electron adducts and the reduced N-methylpyridinium compounds at electron-transfer equilibrium, the thermodynamical equilibrium constants wereobtained and from these the reduction potentials

Electron transfer from nucleobase electron adducts to 5-bromouracil. Is guanine an ultimate sink for the electron in irradiated DNA?

Electron transfer to 5-bromouracil (5-BrU) from nucleobase (N) electron adducts (and their protonated forms) has been studied by product analysis and pulse radiolysis. When an electron is transferred to 5-BrU, the ensuing 5-BrU radical anion rapidly loses a bromide ion; the uracilyl radical thus formed reacts with added t-butanol, yielding uracil. From the uracil yields measured as the function of [N]/[5-BrU] after gamma-radiolysis of Ar-saturated solutions it is concluded that thymine and adenine electron adducts and their heteroatomprotonated forms transfer electrons quantitatively to 5-BrU. Like the electron adduct of adenine, those of cytosine and guanine are rapidly protonated by water. The (protonated) electron adduct of guanine does not transfer an electron to 5-BrU, and in the case of the (protonated) cytosine electron adduct only partial electron transfer is observed. The results can be modelled if the protonated electron adduct (protonated at N(3) or at the amino group) of cytosine, CH., which can transfer its electron to 5-BrU (k approximately 2 x 10(7) dm3 mol-1 s-1) is transformed in a slow tautomerization reaction (k approximately 2.5 x +/- 10(3) s-1) into another form C'H. (possibly protonated at C(6) or C(5)) which does not transfer an electron to 5-BrU. There is also electron transfer from the electron adduct of thymine to cytosine and guanine which serve as electron sinks. The rate constant of electron transfer from the thymine electron adduct to cytosine is about 250 times greater than that of the reverse reaction. The heteroatom-protonated electron-adduct of thymidine transfers an electron to 5-BrU more slowly (k = 2.3 x 10(7) dm3 mol-1 s-1) than the electron-adduct itself (k = 7.2 x 10(8) dm3 mol-1 s-1). Phosphate buffer-induced protonation of the electron-adduct of thymine at carbon (C(6)) prevents electron transfer to 5-BrU. Such phosphate catalysis is also observed as an intramolecular process (k approximately 2 x 10(4) s-1) with thymidine-5'-phosphate but not with the 3'-phosphate. Phosphate-induced protonation at carbon also reduces transfer efficiency for the electron adducts of dinucleoside phosphates such as dTpdT and dTpdA. The data raise the question whether in DNA the guanine moiety may act as the ultimate sink of the electron in competition with other processes such as protonation at C(6) of the thymine electron adduct.

Electron adducts of adenine nucleosides and nucleotides in aqueous solution: protonation at two carbon sites (C2 and C8) and intra- and intermolecular catalysis by phosphate

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTElectron adducts of adenine nucleosides and nucleotides in aqueous solution: protonation at two carbon sites (C2 and C8) and intra- and intermolecular catalysis by phosphateL. P. Candeias and S. SteenkenCite this: J. Phys. Chem. 1992, 96, 2, 937–944Publication Date (Print):January 1, 1992Publication History Published online1 May 2002Published inissue 1 January 1992https://doi.org/10.1021/j100181a074RIGHTS & PERMISSIONSArticle Views146Altmetric-Citations52LEARN 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 (1 MB) Get e-Alerts

Pulse Radiolysis Study of Initiation, Dimerization, and Propagation Steps of 3,3-Dimethylacrylic Acid in Aqueous Medium

Abstract Rates of initiation, dimerization, and first propagation steps originating from the hydrated electron and hydroxyl radical reactions with 3,3-dimethylacrylic acid monomer have been investigated using the technique of pulse radiolysis. The initiation step for the protonated monomer is found to be faster than that of the deprotonated form. The dimerization step is about two orders of magnitude faster than the first propagation step. Radical species are more reactive than the corresponding radical-anionic species, and the β-protonated electron adduct to the monomer is found to propagate faster than other electron adduct species. The different transient species have been characterized by their absorption spectra, λmax, extinction coefficient, pK, and redox behavior. Based on these observations, the most probable structures are suggested.

The Polymorphism of a Cytosine Anion Studied by Electron Paramagnetic Resonance Spectroscopy

Electron addition to the nucleic acid base cytosine and several derivatives was studied in frozen aqueous solution and in aqueous glasses containing 10 M glucose, 7 M BeF2, 10 M LiCl and 8 N NaOH. Electron paramagnetic resonance spectroscopy revealed that three major types of spectra are obtained which can be classified into a group D giving a doublet (ca. 1.6 mT) and a group of triplet patterns T and T1 (ca. 3.0 mT total spread) which differ slightly in coupling values but which are both distinct from D by showing the loss of one sizeable proton coupling (ca. 1.0 mT) in deuterated solvents. Varying the type of glasses and other parameters such as pH, together with modification of the cytosine exocyclic groups, indicated that the triplet patterns represent electron adducts protonated at the amino group, whereas the doublets D should probably involve N3-protonated species. The equilibrium between doublets and triplets was found to depend strongly on the presence of Li+ and Be2+ and less strongly on pH or the presence of Na+, the former group of ions inducing the triplets. It is suggested that the influence of the ions derives mostly from their strength in stabilizing the amino-protonated tautomer of the electron adducts.

Intermolecular-directed reactivity in solid media. Radiogenic formation of phosphorus-centered radicals in chiral diphosphine disulfides studied by ESR

AWct Singlecrystal, powder, and frozen-matrix ESR experiments have been performed to study the radiogenic electron-capture properties of several diastereoisomeric and asymmetric diphosphine disulfides (R,RzP(S)P(S)R3R4). The principal values of the hyperfine couplings of several phosphorus-centered radical configurations are determined and related to the spin density distribution. Attention is focused on the strong differences in radiogenic properties, observed between the meso and racemic forms of phenyl- and tolyl-substituted diphosphine disulfides. The most striking result is that X irradiation of the crystalline meso compounds MePhP(S)P(S)MePh, Me@-Tol)P(S)P(S)Me@-Tol), and Ph(PhCHz)P(S)P(S)Ph(CH2Ph) does not lead to the formation of a three-electron bond PAP u* radical but invariably results in configurations in which the unpaired electron is primarily localized on one half of the molecule. X irradiation of the corresponding racemic forms, on the other hand, gives rise to PLP u* configurations. The observed discrimination between symmetric and asymmetric configurations is explained in terms of intermolecular steric interactions affecting the geometry relaxation of the precursor molecule after initial electron addition. For a quantitative assessment, the change in van der Waals energy resulting from elongation of the P-P bond of the molecules in their respective crystal lattices was calculated with X-ray crystallographic data. The calculations reveal significantly stronger steric interactions for the aromatic meso compounds than for their racemic forms, in agreement with the absence of PAP u* configurations in the first. X irradiation of diphosphine disulfides in a frozen THF matrix almost invariably results in a single radical product, being the PAP u* configuration, and differences between meso and racemic isomers disappear. This is a consequence of the fact that in a randomly oriented solid matrix the molecular packing is less tight than in a molecular crystal, making more space available to the precursor molecule. It is concluded that in case stabilization of the initial electron adduct via P-P bond length elongation is unfavorable because of steric interactions, other relaxation pathways become accessible, resulting in alternative phosphoranyl radical configurations. In recent years the radiochemistry of organophosphorus compounds has received considerable attention. The phosphoruscentered radicals, formed in the radiation process, are of special interest because of their diverse structural and dynamical prop erties and their possible relevance to radiation damage in biochemical systems.’” It has been shown from a number of single-crystal ESR studies that the precise nature of the configuration of a phosphoranyl radical depends on the type of ligands surrounding the central phosphorus nucleus. Only recently have effects other than the nature of the substituents been envisaged as being essential to the formation of radiogenic phosphoruscentered radicals. In this respect, aspects of conformation and configuration of the precursor molecules and the involvement of the precursor environment in the electron-capture process have been studied.4d Substituted diphosphine disulfides (R,R,P(S)P(S)R,R,) can serve as good probes to study phosphoranyl radical formation because of their intrinsic ability to adopt various radical configurations from a single molecule (Figure l).’ X irradiation of a diphosphine disulfide almost invariably results in the formation of an electron-capture radical in which the unpaired electron is accommodated in the antibonding u* orbital of the inter-phosphorus bond. As a consequence, the electron is symmetrically distributed over the two phosphorus nuclei. Complementary to this symmetrical PAP u* configuration, several radical structures with an asymmetrical spin density distribution have been established. One of the asymmetric structures frequently observed is a radical in which the odd electron is located in the vacant equatorial position of a trigonal-bipyramidal configuration (TBP-e). Another asymmetric structure has been identified as a phosphoranyl radical in which the unpaired electron resides in an antibonding u* orbital of the phosphorussulfur bond (PS U’).

Pulse radiolysis of solutions of sodium tetraphenylborate

Pulse radiolysis of solutions of sodium tetraphenylborate (NaBPh/sub 4/) indicates that the absorption observed in organic amides with lambda/sub max/ in the range 650-724 nm is not due to Na/sup -/, an electron adduct to BPh/sub 4//sup -/, a triplet excited state, or a proton-donating solvent cation. Experiments in aqueous solution are described in which the reactions of selected radicals with NaBPh/sub 4/ are studied. One-electron oxidation of NaBPh/sub 4/ by N/sub 3//sup .-/ radicals yields a species, assumed to be NaBPh/sub 4//sup ./, with absorption maxima at 335 and 800 nm. A similar spectrum is observed on pulse radiolysis of solutions of NaBPh/sub 4/ in tetramethylurea (TMU), but the long-wavelength absorption is shifted to 725 nm. The formation of an oxidizing radical in irradiated TMU was confirmed by the observation of I/sub 2//sup .-/ on pulse radiolysis of solutions of KI in this solvent. Pulse radiolysis of solution of NaBPh/sub 4/ and KI in TMU demonstrated that these solutes compete for the oxidizing intermediate.

TRANSIENT PHENOMENA IN THE PULSE RADIOLYSIS OF RETINYL POLYENES—7. RADICAL ANIONS OF VITAMIN A AND ITS DERIVATIVES

Abstract— Upon e‐‐pulse irradiation in nonprotic solvents, all‐trans retinol (ROH) and retinylmethyl ether (ROMe) form transient species (τ= 0.5–7μs, λmax=575–590 nm) identifiable as radical anions. Similar species are also formed upon laser pulse photoexcitation of these retinyl derivatives in the presence of N,N‐dimethylaniline in acetonitrile. In contrast, electron transfer or attachment to all‐trans retinyl acetate (ROAc) and palmitate (ROPa) results in ‘instantaneous’ loss of carboxylate anions from electron adducts giving the retinylmethyl radical (R‐, λmax= 395 nm, τk &gt; 100 μ,s); the radical anions in these cases are too short‐lived to be detected by nanosecond pulse radiolysis. The lifetimes of radical anions of ROH and ROMe are very sensitive to water and alcohols (e.g. kq= 107M‐1 s‐1 with methanol as quencher for ROH‐ in tetrahydrofuran). Based on these findings, the spectral dissimilarity of the one‐electron reduction products from ROH and ROAc in alcohols and aqueous micelles becomes explainable in terms of fast formation of protonated radical anions (RH(OH), τ1/2, &gt; 100 μs, λmax=370–375 nm) in the case of ROH and of retinylmethyl radical via loss of AcO‐ from radical anion in the case of ROAc. In tetrahydrofuran, the complexation of ROH‐ with cations such as Na+ and Bu4N+ affects the relative importance of its major decay modes, namely, protonation and dehydroxylation, the latter process being significantly enhanced by the presence of Na+.

Spectral and kinetic properties of intermediates induced by reaction of hydrated electrons with adenine, adenosine, adenylic acid and polyadenylic acid: A multicomponent analysis

The overlapping transient optical absorption spectra obtained from pulse radiolysis experiments in which the hydrated electron reacted with adenine, adenosine, 5'-adenosine monophosphate and polyadenylic acid were measured and analysed. The analysis consists of a multicomponent analysis which yields the number of different species and a set of orthonormal basis spectra. From this set of basis spectra together with a number of trial models for the possible kinetics of the different species the best model is determined by fitting the original data. In this way the molar absorptivity spectra and the kinetics of the species can be found. To describe all the spectra of the adenine-containing compounds in a consistent way we need, at most, three different species. The following reaction scheme is obtained: e - aq + A → A -., A -. + H 2O →2 A′H . + OH -, A -. → A″H . and A'H .(A″H .) + A'H .(A″H .). The radicals A'H . and A″H . are both protonated electron adducts, while P appears to be “stable” product with a decay time of the order of 1 day.

Radiation-induced reduction of vanadium(IV) to vanadium(II) in aqueous picolinate-formate solutions

Quantitative reduction of V(IV)(pic) to V(III)(pic) n and then to V(II)(pic) n (1 ⩽ n ⩽3) occurs when N 2O-saturated formate solutions (pH 4.2–6.3) containing V(IV) and picolinic acid (2-carboxypyridine) are irradiated. Pulse radiolysis measurements show that CO - 2 reacts with picolinate only when the N-atom is protonated ( k = 2.7 × 10 8 dm 3 mol -1 s -1). Reduction of V(IV)(pic) and V(III)(pic) n is effected by the electron adduct of the protonated picolinate (picH) . with rate constants at pH 4.2 of (3.5 ± 0.2) × 10 7 dm 3 mol -1 s -1 for V(IV)(pic) and (6.9 ± 0.4) × 10 8 dm 3 mol -1 s -1 for V(III)(pic) n . No reduction of V(II)(pic) n is observed.

Radiolysis of Spin-Labeled DNA: An Electron Spin Resonance Investigation

The reactions of free and DNA-bound 2,2,5,5-tetramethylpyrrolidine-N-oxyl (PROXYL) probes with radicals generated during radiolysis of dilute aqueous solutions of DNA were examined. For the free PROXYL probe in deaerated solution with each of the four nucleotides (dAMP, dCMP, dGMP, and TMP) it was found that the pyrimidine radicals were more reactive toward the probe than were the purine radicals. Reactions of the electron adduct of TMP and the hydroxyl radical adducts of dAMP, dGMP, and TMP with the probe resulted in little or no reduction of the probe. For TMP these results are consistent with the fact that both the protonated electron and hydroxyl radical adducts of TMP will covalently bind to the nitroxide function of the probe. Reduction of the PROXYL probe was observed in reactions with the hydroxyl radical adduct of dCMP and with the electron adducts of dAMP, dCMP, and dGMP. Results of the radiolysis of the free PROXYL probe in deaerated dilute solution of DNA suggest that the PROXYL probe protects the DNA from water radical attack as the ratio of DNA bases to PROXYL probe increases above 50:1. Reactions of DNA-bound probes are dependent on the depth of the nitroxide function in relation to the major groove of the DNA helix. Two probes with tether lengths which are less than the depth of the major groove show an expected increase in reactions with DNA base radicals as compared to a probe with a tether that extends beyond the groove. The longer probe is involved largely in reactions with sugar and water radicals along the periphery of the DNA helix. In the presence of oxygen, there is a dramatic decrease in the loss of both the free and DNA-bound probes due to the lack of reaction of these probes with peroxyl radicals formed by the addition of molecular oxygen to DNA radicals.

Radioprotection of pyrimidines by oxygen and sensitization by phosphate: a feature of their electron adducts.

The reactions of the electron adducts of thymine, uracil and 1,3-dimethylthymine in the presence of phosphate buffer and low oxygen concentrations have been investigated. Oxygen reacts with the pyrimidine electron adducts and their O(4)-protonated forms to restore the pyrimidine and produce O2-./HO2.. Thus oxygen acts as a radiation protector. In the presence of high buffer concentrations the electron adducts are irreversibly protonated at C(6). On reaction of this radical with oxygen no restitution of the original pyrimidine occurs and the pyrimidine is destroyed. Thus phosphate buffer acts as a radiation sensitizer. Some speculations are made as to the possible relevance of these reactions to biological systems.