Ethanol Radicals Research Articles

Analysis of resolved ESR spectra of neutral nitroxide radicals in ethanol and pyridine: the dynamic behavior in fast motion conditions

The ESR spectra of ethanol and pyridine solutions of the spin probes 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (Tempol) and 3-carbamoyl-2,2,5,5-tetramethylpyrroline-1-oxyl (Tempyo) were analyzed to obtain information on the dynamic behavior of the radicals in solution. In order to evaluate the true line widths, the dependence of the proton and carbon-13 hyperfine coupling constants on temperature and on solvent polarity were analyzed as a function of a/sub N/. Tempol and Tempyo showed an opposite dependence of a/sub H/ on a/sub N/. Furthermore the structure of Tempol was affected more than that of Tempyo by variations of solvent polarity. From the line widths the correlation times for motion were evaluated. A weak hydrogen bond was formed by Tempol and Tempyo with ethanol. However, only Tempol in ethanol gave rise to an anisotropic rotational reorientational motion, with the fastest rotation about the x axis. All samples, except for Tempol in pyridine, showed a deviation from the Debye spectral densities. The hydrodynamic rotational radii were about 3 times lower than the effective geometric spherical radii. However, Tempyo exerted slightly greater torques than Tempol during its rotational motion. At the highest temperatures (T > 298 K), the dynamic behavior was as expected on the basis of the free volumemore » model, whereas at lower temperatures an increase in the H-bonding strength was found between radical and ethanol molecules.« less

Role of water and ethanol radicals in the radiation destruction of human deoxyhemoglobin.

In this study destruction of human deoxyhemoglobin (deoxy-Hb) induced by the action of primary products of water radiolysis, mainly .OH, eaq-, H, and of secondary ethanol radicals was investigated. The extent of destruction was estimated on the basis of absorbance ratio A505/A563 after conversion of hemoglobin into methemoglobin (MetHb) and the changes in the parameters of hemoglobin oxygenation. Deoxy-Hb solutions were irradiated under the atmosphere of argon and N2O, in the absence and presence of ethanol. In each case the radiation-chemical yield for hemoglobin destruction Gd = sigma i fi gi was determined (where: fi--fractional efficiency of destruction by the individual radicals, gi-fraction of radicals reacting with deoxy-Hb). Results were elaborated statistically estimating, by the method of least squares, the parameters of a multidimensional regression function which for each experiment with deoxy-Hb conc. 5 mg ml-1 was of the form: Gd = 0.09 gOH + 0.018 geaq- -0.099 gH + 0.03 g R.Et. The destruction efficiencies f.OH and fR.Et were statistically significant while feaq- and fH were not.

Reactions of reducing radicals with ribonuclease.

Radiation-induced reactions of hydrated electrons, formate- and ethanol radicals with ribonuclease were studied by pulse radiolysis and by electrophoresis. Initially formate radicals react rapidly and very specifically with the disulphide bonds of ribonuclease. This reaction leads to aggregation by intermolecular S-S-interchange, the process being more effective at pH 4, since formation and decay of S-S-.-radical anions increases with decreasing pH. With high doses additional unreducible aggregates are formed. Radical formation at the positively charged histidine residues seems to be involved. Hydrated electrons do not react as selectively as the formate radicals, but with several sites in native ribonuclease. Thus with low doses unreducible aggregates are formed. Electrophoresis shows that reaction of the electrons causes fragmentation of the peptide chain, when OH-radicals are scavenged. Very weak transient spectra and very little degradation result on reaction of ethanol radicals with ribonuclease.

Temperature Effect on Decay of Ions and Radicals in Supercooled Liquids as Studied by Pulse Radiolysis and γ-Radiolysis: 1-Propanol and Ethanol

Abstract The decay-rate constants, k, of dipentyl disulfide anions or benzyl radicals in 1-propanol and ethanol were measured over a temperature range of 107–230 K by pulse- and γ-radiolysis method. The decay-rate constants were found to range over nine orders of magnitude. The decay kinetics is a composite first-order reaction. Since the decay rates of reaction intermediates observed are diffusion-controlled, the decay-rate constants represent directly the rates of molecular transport in the supercooled liquids. It was found that the temperature dependence of the decay-rate constants could be expressed by the following equation. log\frackT=−\fracAT–Tg+B, where T is the absolute temperature, A and B are constants. Tg is the glass transition temperature. The molecular diffusion of the ions or radicals in the supercooled liquids was completely suppressed at the glass transition temperature. The temperature dependence of the decay-rate constant was compared with that of the viscosity of the matrix. It was found that the temperature, at which the molecular diffusion is completely suppressed is much higher than the temperature at which the viscosity is infinite.

Formation of lipoamide anion radicals by hydroxyl, formate and alcohol radicals at pH 6–9

Lipoamide anion radicals (LS - 2·) produced by the reaction of ·OH with dihydrolipoamide, L(SH) 2, or ·CO - 2 with lipoamide (LS 2) at pH 9 have an absorption ( λ max = 400 nm, ϵ max = 7750 M −1 cm −1) similar to the anion radical formed from lipoate ions by the same reactants in previous studies, and they decay at similar rates. The yields G(LS 2) and G(L(SH) 2) in λ-radiolyses show that the radicals disproportionate. As with lipoate, the absorbance of the protonated form LS 2H is less intense and slightly blue shifted. At pH 7 the latter reacts with formate ion. This causes a chain LS 2H + HCO - 2→L(SH) 2 + ·CO - 2 sequence which leads to G(SH)≃ 45 and precludes the use of formate radicals as stoichiometric reductants of lipoamide at pH ⩽ 7. The alcohol radicals formed by ·OH attack on ethanol, isopropanol and ter-butanol also produced transients with λ max near 400 nm on reaction with LS 2. However, the absorbances were weaker and the yields of G(SH) demonstrated that LS - 2· was not the only species present. The alcohol radicals evidently react rapidly to form adducts with LS 2, which then decay by electron transfer to LS 2, opening of the disulphide ring or other subsidiary reactions. Based on this study, quantitative (i.e. g ⋍ 6/100 eV) formation of lipoamide radicals at pH ≃ 6 is best accomplished by abstraction of H atoms from L(SH) 2 or by a combination of e - aq and ethanol radicals reacting with LS 2.

Reactions of formate and ethanol radicals with bovine serum albumin studied by electrophoresis.

Radiation-induced reactions of formate and ethanol radicals with bovine serum albumin were studied by electrophoresis. The reaction products were separated as reduced and unreduced SDS-protein-complexes on polyacrylamide gel. Quantitative evaluation of the densitometric measurements gives information about the reaction mechanisms. Initially formate radicals react rapidly and very selectively with the disulphide groups which then form partly intermolecular S-S-bonds. This formation of reducible aggregates causes a massive loss of serum albumin. With increasing dose unreducible aggregates are formed. Formate radicals show a high efficiency in both degradation processes, which are not caused by ethanol radicals. Formate radicals are much more effective in degrading serum albumin than ethanol radicals. Both radicals show a third degradation process which has low G-values and is presumably caused by H-abstraction.

Radiation-induced reduction reactions with bovine serum albumin.

The reduction of bovine serum albumin (BSA) by hydrated electrons, formate and ethanol radicals leads to the formation of S-S-radicals. The reaction of the hydrated electrons becomes faster, if BSA was preirradiated in the presence of formate or ethanol, but the rate does not change if radiolysis is done in the presence of t-butanol or without scavenger. The reduction of BSA by formate radicals is 10 times slower but gives a higher yield of S-S-radicals than by hydrated electrons. The rate and yield of the reduction by the formate radicals are increased by preirradiation of BSA. The reduction by ethanol radicals is five times slower than by formate radicals and gives lower yields of S-S-radicals which are increased by preirradiation. All rates and yields of the reduction reactions are decreased by changing the pH from 6.3 to 7.3.

A Pulse‐Radiolysis Study of Cytochrome c3

Pulse‐radiolysis experiments were performed in the presence of methyl viologen and cytochrome c3. After the pulse, methyl viologen radicals are formed and the kinetics of these radicals with cytochrome c3 are studied. The reaction between cytochrome c3 and methyl viologen radicals (MV+) is diffusion controlled. The ionic strength dependence and the pH‐dependence of this reaction were studied. From the ionic strength dependence (at pH 7.8) we found that the net charge of the fully oxidized cytochrome c3 molecule was Z =+ 4.7 ± 0.7. After the pulse an equilibrium is reached for the reaction of MV+ with cytochrome c3. From this equilibrium an apparent midpoint potential can be obtained. The apparent midpoint potential of this multihaem molecule was found to depend on the degree of reduction, α. With the help of the Nernst equation an empirical equation is obtained to describe this dependence of the midpoint potential: E0=− 0.250–0.088α (in V). An estimation is made of the energy of interaction between the haems due to electrostatic interactions (Δɛ < 32 mV) and due to ionic strength effects (−12 mV < Δɛ < 26 mV). The results suggest that the redox properties of the individual haems in the cytochrome c3 molecule are dependent on the degree of reduction of the other haems in the molecule. The reaction of cytochrome c3 with MV+ or with ethanol radicals (EtOH) has been compared with the reactions of horse‐heart cytochrome c and of metmyoglobin with the same radicals. The reaction of MV+ or EtOH with horse‐heart cytochrome c is found to be diffusion controlled; the reactions with metmyoglobin on the other hand are most probably controlled by an activation energy.

Electron spin resonance saturation analysis of solvated electrons. On the applicability of Zhidkov's treatment

Electron spin resonance saturation measurements of e/sub sol//sup -/ in ethanol glass were carried out to test the applicability of Zhidkov's treatment for the first derivative signals. The treatment turned out to be unsatisfactory for e/sub sol//sup -/, because: (1) there were saturation curves providing q/sub 0/ /sub 5/ 9.2. Cross relaxation between e/sub sol//sup -/ and ethanol radicals became evident, being thought important for the saturation behavior of e/sub sol//sup -/.

ChemInform Abstract: AN ESR STUDY OF ELECTRON REACTIONS WITH CARBOXYLIC ACIDS, KETONES, AND ALDEHYDES IN AQUEOUS GLASSES

AbstractDie auf 77 Kgekühlte Lösung von 12 M LiCl, l0 mM K4[Fe‐ (CN)6] und O.l‐0.5 M Carbonsäure, Keton oder Aldehyd wird mit 2537 Å photolysiert ( 1 min).

An ESR study of electron reactions with carboxylic acids, ketones, and aldehydes in aqueous glasses

Electron reactions with a number of carboxylic acids, ketones, and aldehydes were investigated in a deuterated neutral aqueous glass at 77 K by ESR spectroscopy. Free radical reactions which took place upon warming the glasses to temperatures at which the electron adducts become mobile were studied. For carboxylic acids (C/sub n/H/sub 2n+1/CO/sub 2/D, n = 2,3) the deuterated anion radicals (RCH/sub 2/C(OD)/sub 2/) give results which suggest abstraction of a hydrogen from the parent acid to produce radicals of structure RCHCO/sub 2/D. The formic acid deuterated anion is found to undergo a similar mechanism. The acetic acid deuterated anion is not found to abstract from acetic acid, but is found to abstract from isopropyl alcohol. Ketone electron adducts are also found to abstract from their parent compounds to yield radicals of structure RCHC(O)R' with R and R' = CH/sub 3/, C/sub 2/H/sub 5/. Electron reactions with five aldehydes (RCHO with R = H, CH/sub 3/, C/sub 2/H/sub 5/, C/sub 3/H/sub 7/, and i-C/sub 3/H/sub 7/) gave their corresponding alcohol radicals (RCHOD) after deuteration at 77 K. Radicals with R = C/sub 2/H/sub 5/, C/sub 3/H/sub 7/, and i-C/sub 3/H/sub 7/ were found to abstract from the parent aldehyde to formmore » radicals of structure RR'CCHO. The methanol radical (CH/sub 2/OD) showed no further reaction while the ethanol radical (CH/sub 3/CHOD) resulted in the production of the diacetal anion. The results for acids, aldehydes, and ketones show that radicals of structure RC(OD)R' with R' = OD, H, or an alkyl group can act as hydrogen atom abstracting agents.« less

Reduction of ferricytochrome c, methemoglobin and metmyoglobin by hydroxyl and alcohol radicals

We have studied the reaction of ferricytochrome c, methemoglobin and metmyoglobin with OH and alcohol radicals (methanol, ethanol, ethylene glycol and glycerol). These radicals can be divided into three groups: 1. 1.|The OH radicals which reduce the ferricytochrome c with a yield of (30 ± 10)% and methemoglobin with a yield of (40 ± 10)%. They do not reduce metmyoglobin. The reduction is not a normal bimolecular reaction but is most probably an intramolecular electron transfer of a protein radical. 2. 2.|Methanol and ethanol radicals which reduce all three hemoproteins with a yield of (100 ± 5)%. This reduction is a normal bimolecular reaction. 3. 3.|Glycerol radicals which do not reduce the ferrihemoproteins under our experimental conditions. Ethylene glycol radicals do not reduce ferricytochrome c and metmyoglobin but they do reduce methemoglobin with a yield of (30 ± 10)%.

The Influence of the Interface Potential on the Reactions of Hydrated Electrons and Neutral Radicals with Acceptors in Micelles

AbstractThe rates of reaction of the hydrated electron and ethanol radical with various acceptors whose electron affinities range between 0.6 and 6.5 eV were investigated. The acceptors were solubilized in cationic and anionic micelles of various surface potentials. In the case of the ethanol radical, the rate constants (ca. 3.5 · 109 M−1 s−1) of the electron transfer reactions were independent of the electron affinity of the acceptors and the surface charge of the micelles. In contrast, the rate constants of the hydrated electron were only independent of these factors for the cationic micelles of high positive surface potential, presumably because of the long residence time of the hydrated electron near the micellar surface. As the interface potential of the micelle becomes more negative, that is, in going from cationic to anionic micelles, the rate constants become more dependent on the electron affinity of the acceptors. In anionic micelles, acceptors with electron affinities from 1.6 to 2 eV reacted with a rate constant (ca. 2 · 1010 M−1 s−1) determined by the diffusion‐controlled encounters between eaq− and micelles. Acceptors with lower or higher electron affinities showed a marked decrease in reactivity towards the hydrated electron. These effects are interpreted on the basis of current theories on electron transfer reactions and are ascribed to the relative favorableness of electron tunneling through the electrical double layer of the micelles.

Reaction of ethanol radicals with ribonuclease.

Ribonuclease was irradiated under conditions such that ethanol radicals were the main reactive species in solution. Sephadex gel filtration of the irradiated solution demonstrated that ethanol radicals had reacted with the ribonuclease and had become firmly bound to the enzyme molecule. The number of ethanol molecules bound to ribonuclease was a function of dose and correlated with the loss of enzymatic activity and with the changes in the molecular configuration of the enzyme molecule.

Effect of ethanol on the radiolysis of ribonuclease.

The dependence of D 37 on the ribonuclease concentration was measured for depolymerase and hydrolase activity. Ethanol gives different radiation protection to the two functions by OH-scavenging. Evidence for the reaction of ethanol radicals was obtained by simultaneously scavening hydrated electrons, OH-and most of the H-radicals without increase in the radiation protection. The efficiency of the individual primary radicals and the ethanol radicals in inactiviating ribonuclease is calculated from the measured inactivation yield.

ChemInform Abstract: FURTHER STUDIES ON THE SOLID‐STATE CHEMISTRY OF IRRADIATED CHOLINE CHLORIDE

The remarkable radiation sensitivity of crystalline choline chloride has been investigated by studies of infrared and ESR spectra, photochemical transformation of radicals, microwave electrodeless conductivity, and exposure to hydrogen atoms, vacuum ultraviolet, and thermal electrons. These studies lend support to the involvement of both ethanol radicals and electrons in the chain decomposition. They also show that hydrogen atoms can induce the decomposition. These observations indicate that during subsequent thermal treatment of γ‐irradiated choline chloride, the detrapped electrons interact with ethanol radicals to form hydrogen atoms, which propagate the chain decomposition.

Further studies on the solid-state chemistry of irradiated choline chloride

The remarkable radiation sensitivity of crystalline choline chloride has been investigated by studies of infrared and ESR spectra, photochemical transformation of radicals, microwave electrodeless conductivity, and exposure to hydrogen atoms, vacuum ultraviolet, and thermal electrons. These studies lend support to the involvement of both ethanol radicals and electrons in the chain decomposition. They also show that hydrogen atoms can induce the decomposition. These observations indicate that during subsequent thermal treatment of γ-irradiated choline chloride, the detrapped electrons interact with ethanol radicals to form hydrogen atoms, which propagate the chain decomposition.

Kinetic electron spin resonance spectroscopy. Part III. Proton exchange rates for ketyl radicals in organic solvents

Measurements of linewidths and hyperfine splittings in the e.s.r. spectra of some photochemically generated ketyl radicals have been used to determine the rates of acid-catalysed carboxy-proton exchange reactions in these species. For CH3Ċ(OH)CO2H radicals in chloroform, ethanol, and propan-2-ol the second-order rate constants k are 1·7, 2·0, and 2·8 × 107 l mol–1s–1 respectively at 298 K and for HO2CCH2Ċ(OH)CO2H radicals in ethanol k= 2·8 × 107 l mol–1s–1. Measured activation energies are ca. 30 kJ mol–1.

Pulse Radiolytic Polarography: The Kinetics of the Oxidation of the Ethanol Radical at the Mercury Electrode

AbstractThe ethanol radical was produced in N2O saturated, 2 · 10−3 molar aqueous ethanol solutions by a 20 ns pulse of high energy electrons. The anodic current of the radical was recorded as a function of time at various potentials of the mercury electrode and at various pH‐values of the solution. The concentration of the radical in the bulk of solution as a function of time was simultaneously recorded by optical measurements. Analysis of the data shows that the electrode process is reversible in the 10−5 s range at pH > 12, i.e. when the base form of the radical is mainly present. Transfer rate constants of more than 1.0 cm s−1 are calculated. Below pH = 12, the electrode process becomes more irreversible with decreasing pH. The kinetics of the oxidation of the acid form of the radical is strongly influenced by its adsorption at the mercury electrode. The influence of electrochemically inactive adsorbed solutes is also investigated: Adsorbed sulfate ions strongly decrease the anodic current at potentials more positive than ‐ 0.5 V. Fluorid ions exert a less pronounced effect. Adsorbed alcohol molecules have a promoting effect on the oxidation of the ethanol radical.

Pulse Radiolytic Polarography: Adsorption Effects in the Electrode Kinetics of Short‐Lived Free Radicals

AbstractMathematical solutions for the polarographic current as a function of time are given for the case of two‐step electrode reactions: R → Ra → P (R: radicals produced homogeneously in solution by a short pulse of high energy electrons; Ra: radical adsorbed at the electrode; P: product of oxidation or reduction). If R is long‐lived or disappears according to first order kinetics, the differential equations involved are amenable to solution. If R disappears by second order kinetics, an explicit solution cannot be given; the solution for first order disappearance, however, may well be applied to such cases at times shorter than the first half‐life time of the radical. The current‐time curves exhibit a maximum whose magnitude and position with respect to time can be expressed in terms of the ratio V = k/k1 where k is the transfer rate constant in s−1 and k1 the time constant of the disappearance of the radicals in the solution, k1 is measured by recording the optical absorption of the radicals as a function of time.The current‐time curves obtained for the oxidation of the ethanol radical at a mercury electrode are described by the above two‐step electrode reaction, k is obtained at different electrode potentials. The transfer coefficient for the oxidation of the ethanol radical at pH = 6 is 0.37.