scholarly journals Formation of super-reduced Chromatium high-potential iron–sulphur protein in aqueous solution by pulse radiolysis

1980 ◽  
Vol 189 (3) ◽  
pp. 641-644 ◽  
Author(s):  
J Butler ◽  
A G Sykes ◽  
G V Buxton ◽  
P C Harrington ◽  
R G Wilkins
Keyword(s):  
Aqueous Solution ◽  
Rate Constant ◽  
Rate Constants ◽  
Pulse Radiolysis ◽  
High Potential ◽  
Single Stage ◽  
Process Rate ◽  
Stage Process ◽  
Reduced Forms

Both the oxidized and reduced forms of Hipip (high-potential iron–sulphur protein) are reduced (approx. 30% yields) by eaq.- in a single-stage process, rate constants 1.7 × 10(10) and 1.8 × 10(10) M-1 . s-1 respectively, at 25 degrees C, pH 7.0 (5 mM-phosphate). Super-reduced Hipip, which is formed in the latter case, has a spectrum which closely resembles that of reduced ferredoxin, i.e. Fe4S4 (SR)4(3-) clusters. The spectrum is stable over 2 s periods investigated. Super-reduced Hipip is reoxidized with O2, rate constant 4.8 × 10(6) M-1 . s-1 at 25 degrees C.

Studies of radiation-induced reactions of ethylene in aqueous solution II. Reactions in the presence of oxygen as studied by pulse radiolysis and γ -irradiation techniques

1967 ◽  
Vol 300 (1463) ◽  
pp. 443-454 ◽  
Keyword(s):  
Aqueous Solution ◽  
Hydrogen Peroxide ◽  
Rate Constants ◽  
Pulse Radiolysis ◽  
Major Product ◽  
Peroxy Radicals ◽  
Ferrous Ions ◽  
Constant Composition ◽  
Γ Irradiation ◽  
Radiation Induced

The radiolysis of dilute aqueous solutions containing ethylene and oxygen has been investigated. Pulse radiolysis was used to measure the rate constants for the addition of hydroxyl radicals to ethylene, the binary decomposition of the resulting hydroxyethyl radicals and their addition to ethylene and reaction with oxygen to yield peroxy radicals. The rate constants have also been determined for the mutual interaction of the peroxy radicals and their reaction with ferrous ions. The principal products of γ -irradiation were aldehydes and organic hydroperoxides. Hydrogen peroxide was found in yields close to the molecular yield from water. The polymer produced in the absence of oxygen was not formed, and glycollaldehyde, reported as a major product by previous workers, could not be detected. At constant composition of the gas mixtures, product yields were unaffected by total pressure in the range up to 40 atm, but were strongly dependent on the proportion of oxygen. Aldehyde yields were markedly greater at pH 1.2 than in neutral solution. The influence of ferrous ions an d of added hydrogen peroxide has been determined. The pulse radiolysis and γ -irradiation experiments complement one another and show that the radiation-induced oxidation of ethylene in aqueous solution involves the same primary reactions as occur in the absence of oxygen, followed by the formation and further reactions of peroxy radicals.

Conductometric Pulse Radiolysis Study on the Reaction of the Solvated Electron with 5-Bromouracil in Aqueous Solutions at Different pH Values

1974 ◽  
Vol 29 (1-2) ◽  
pp. 86-88b ◽  
Author(s):  
Burkhard O. Wagner ◽  
Herbert Klever ◽  
Dietrich Schulte-Frohlinde
Keyword(s):  
Aqueous Solution ◽  
Hydrogen Atom ◽  
Aqueous Solutions ◽  
Hydroxyl Radical ◽  
Rate Constant ◽  
Pulse Radiolysis ◽  
Solvated Electron ◽  
Ph Values

To study the reaction of the solvated electron with 5-bromouracil an aqueous solution has been examined by conductometric pulse radiolysis at pH values between 4.68 and 8.74. Alcohol was added to scavenge the hydrogen atom and the hydroxyl radical. G(Br—) = (2.64 ± 0.08)/100 eV was found to be independent of the pH. The mobility of the bromouracil mono-anion was measured to be (2.7 ± 0.2) 10-4 cm2 V-1 s-1 at 20°C, and the rate constant of reaction (3b) was determined to be k(H+ BrUr-) = (2.3 ± 0.2) 1010 I mole-1 s-1*.

Nanosecond pulse radiolysis of methanolic and aqueous solutions of readily oxidizable solutes

1972 ◽  
Vol 328 (1572) ◽  
pp. 23-36 ◽  
Keyword(s):  
Aqueous Solution ◽  
Rate Constants ◽  
Pulse Radiolysis ◽  
Nanosecond Pulse ◽  
Forward Rate ◽  
Mechanism Of Formation ◽  
Methoxy Radicals ◽  
Nanosecond Pulses ◽  
Radiation Induced ◽  
Pure Methanol

The formation of I ̅ 2 and (CNS) ̅ 2 has been observed in aqueous solution of KI and KCNS respectively following irradiation with nanosecond pulses of 3 MeV electrons. In both cases it is necessary to invoke the intermediate and consecutive formation of two species which do not absorb light at the monitoring wavelength. The following mechanism is invoked for the formation of X ̅ 2 (where X ̅ = I ̅ or CNS ̅ ): OH + X ̅ → HOX ̅ , (5 a ) HOX ̅ → OH ̅ + X , (5 b ) X ̅ + X ̅ ⇌ X ̅ 2 (6) For the iodide solutions the rate constants were evaluated as k 5 a = k 6 = (1.21 + 0.08) x 10 10 1 mol -1 s -1 and k 5 b = (1.2 ± 1.0) x 10 8 s -1 . In the case of the thiocyanate solutions k 5 a = k 6 = (1.08 ± 0.10) x 10 10 1 mol -1 s -1 and HOCNS ̅ is estimated to have a lifetime of about 5 ns. The radiation induced oxidation of N, N , N', N' -tetramethyl- p -phenylenediamine (TMPD) to Wurster’s Blue cation (TMPD + ) has been observed by nanosecond pulse radiolysis of solutions of TMPD in methanol. It is concluded that the oxidation of TMPD is by methoxy radicals and the rate constants k CH 2 O. +TMPD and k CH 2 O.+CH 3 OH are evaluated to be (6·10 ± 0·05) x 10 9 1 mol -1 s -1 and 2·63 + 0·10 x 10 5 1 mol -1 s -1 respectively. Thus the half-life of methoxy radicals in pure methanol is 106 ns. The formation of I ̅ 2 was observed in methanolic solutions of KI. The oxidizing species is thought to be the m ethoxy radical and the mechanism of formation of I ̅ 2 is by the reactions CH 3 O + I ̅ → CH 3 O ̅ + I ̅ , I + I ̅ ⇌ I ̅ 2 . The rate constant of reaction (1) and the forward rate of the equilibrium (2) are estimated to be (3·7 ± 0.3) x 10 9 1 mol -1 s -1 an d (2·6 ± 0·4) x 10 10 1 mol -1 s -1 respectively. Observations on the transient u.v. absorption band of pulse irradiated methanol suggest that the spectra of CH 3 O and CH 2 OH are very similar for λ = 250 to 320 nm.

scholarly journals Evidence for catalytic dismutation of superoxide by cobalt(II) derivatives of bovine superoxide dismutase in aqueous solution as studied by pulse radiolysis

1982 ◽  
Vol 205 (1) ◽  
pp. 181-187 ◽  
Author(s):  
P O'Neill ◽  
E M Fielden ◽  
D Cocco ◽  
G Rotilio ◽  
L Calabrese
Keyword(s):  
Aqueous Solution ◽  
Superoxide Dismutase ◽  
Rate Constants ◽  
Redox Reactions ◽  
Pulse Radiolysis ◽  
Turnover Rate ◽  
Copper Site ◽  
Initial Interaction ◽  
Derivatives Of ◽  
Reaction Schemes

By using the technique of pulse radiolysis to generate O2-., it is demonstrated that Co(II) derivatives of bovine superoxide dismutase in which the copper alone and both the copper and zinc of the enzyme have been substituted by Co(II), resulting in (Co, Zn)- and (Co, Co)-proteins, are capable of catalytically dismutating O2-. with ‘turnover’ rate constants of 4.8×10(6) dm3.s-1.mol-1 and 3.1×10(6) dm3.s-1.mol-1 respectively. The activities of the proteins are independent of the pH (7.4-9.4) and are about three orders of magnitude less than that of the native (Cu, Zn)-protein. The rate constants for the initial interaction of O2-. with the Co-proteins were determined to be (1.5-1.6) X 10(9) dm3.s-1.mol-1; however, in the presence of phosphate, partial inhibition is apparent [k approximately (1.9-2.3) X 10(8) dm3.s-1.mol-1]. To account for the experimental observations, two reaction schemes are presented, involving initially either complex-formation or redox reactions between O2-. and Co(II). This is the first demonstration that substitution of a metal into the vacant copper site of (Cu, Zn)-protein results in proteins that retain superoxide dismutase activity.

Pulse radiolysis: evidence for the reaction of HO2 with NO2 in aqueous solution

1978 ◽  
Vol 56 (14) ◽  
pp. 1961-1964 ◽  
Author(s):  
Harry Callender Sutton ◽  
William Arthur Seddon ◽  
Fred Charles Sopchyshyn
Keyword(s):  
Aqueous Solution ◽  
Formic Acid ◽  
Rate Constant ◽  
Pulse Radiolysis ◽  
First Order ◽  
Data Support ◽  
Radiation Induced ◽  
Three Stages ◽  
Ph Range ◽  
Saturated Solutions

Nitroform is the major radiation induced species observed after the pulse radiolysis of acidic oxygen saturated solutions of tetranitromethane (TNM) and formic acid. It is formed in three stages, of which a major component at pH < 3 is first order with t1/2 = 49 s, independent of [TNM] and pH. Evidence is provided for the reactions[Formula: see text]in which k14 = 0.014 ± 0.002 s−1. The data support similar conclusions reached previously in rapid mixingexperiments (1) from which it was concluded that k3 = 4 × 109 dm3 mol−1 s−1.Analysis of the fastest component of nitroform production over the pH range 1–4 shows that the COOH radical reduces TNM to nitroform with a rate constant about four times greater than that for its reaction with oxygen to produce HO2.

scholarly journals The kinetics of oxygen exchange between the sulfite ion and water

1970 ◽  
Vol 48 (13) ◽  
pp. 2035-2041 ◽  
Author(s):  
R. H. Betts ◽  
R. H. Voss
Keyword(s):  
Aqueous Solution ◽  
Ionic Strength ◽  
Rate Constant ◽  
Rate Constants ◽  
Time Rate ◽  
A Value ◽  
First Time ◽  
Kinetics Of ◽  
Sulfite Ion ◽  
Gross Rate

Oxygen of mass 18 was used as a stable tracer to measure the rate of exchange between the sulfite ion and water as a function of pH and total sulfite concentration. A value for the rate constant of hydration of SO2 in aqueous solution was determined. The gross rate constants k1 and k−1 for the overall reaction[Formula: see text]at 24.7 °C and ionic strength = 0.9 were evaluated from exchange results to be [Formula: see text]Also, for the first time, rate constants for the pyrosulfite equilibrium[Formula: see text]Were obtained[Formula: see text]at 24.7 °C and ionic strength = 0.9

Pulse radiolysis of aqueous solutions of N-Vinylpyrrolidin-2-one and Poly(N-vinylpyrrolidin-2-one)

1981 ◽  
Vol 34 (7) ◽  
pp. 1423 ◽  
Author(s):  
JE Davis ◽  
DF Sangster ◽  
E Senogles
Keyword(s):  
Aqueous Solutions ◽  
Hydroxyl Radical ◽  
Absorption Spectra ◽  
Rate Constant ◽  
Rate Constants ◽  
Pulse Radiolysis ◽  
Kinetic Method ◽  
Transient Species ◽  
Radical Scavengers ◽  
Dilute Aqueous Solutions

The absorption spectra of transient species produced when dilute aqueous solutions of N-vinylpyrrolidin-2-one (vp) and poly(N- vinylpyrrolidin-2-one) (pvp) are subjected to pulse radiolysis in the presence and absence of radical scavengers have been obtained and compared with those obtained from analogous compounds. The precise structure of the transients has not been established. Rate constants for the reaction of the hydroxyl radical with vp and pvp have been evaluated both by a competition kinetic method and by direct observation of the build-up of transient species: k(vp+·OH) = (6.4-8.1) × 109 dm3 mol-1 s-1 and k(pvp+·OH) = (1.5-2.3) × 108 dm3 mol-1 s-1 at 25°C. The rate constant for the reaction of the hydrated electron with vp has been determined as(1.6�0.3) × 109 dm3 mol-1 s-1 at 25°C. Rate constants for decay of the transient species have also been evaluated at 25°C: 2k(vp- OH·) = (8.1�1.0)× 108 dm3 mol-1 s-1; 2k(vp-e-) = (1.7�0.2) × 109 dm3 mol-1 s-1 and 2k(pvp-OH·) = (1.5�0.2) × 108 dm3 mol-1 s-1.

A pulse radiolysis study of the reaction of OH with I2 and the decay of I2−

1992 ◽  
Vol 70 (6) ◽  
pp. 1658-1661 ◽  
Author(s):  
A. John Elliot
Keyword(s):  
Ionic Strength ◽  
Hydroxyl Radical ◽  
Time Dependence ◽  
Rate Constant ◽  
Rate Constants ◽  
Pulse Radiolysis

The rate constant for the reaction of the hydroxyl radical with iodine was estimated to be (9.5 ± 1.0) × 109 dm3 mol−1 s−1 at 20 °C from fitting the time dependence of the decrease in the absorption of iodine at 460 nm. A number of rate constants associated with the decay of I2− that were required for this fitting process were also determined. They were the reaction of I2− with I2− (2k = (4.6 ± 1.6) × 109 dm3 mol−1 s−1) at an ionic strength of 1.2 × 10−2 mol dm−3; I2− with I (k = (4.6 ± 1.6) × 109 dm3 mol−1 s−1); and I with I (2k = (3.0 ± 1.0) × 1010 dm3 mol−1 s−1).

Notizen: OH-Radical-Induced Oxidation of Benzene in the Presence of Oxygen: R·+O2⇆RO2· Equilibria in Aqueous Solution. A Pulse Radiolysis Study

1990 ◽  
Vol 45 (9) ◽  
pp. 1337-1340 ◽  
Author(s):  
Xian-Ming Pan ◽  
Clemens von Sonntag
Keyword(s):  
Aqueous Solution ◽  
Kinetic Analysis ◽  
Rate Constants ◽  
Pulse Radiolysis ◽  
Room Temperature ◽  
Peroxyl Radical ◽  
Oh Radical ◽  
Transient Spectra ◽  
Equilibria In Aqueous Solution ◽  
Oxidation Of Benzene

The reaction of hydroxycyclohexadienyl radical with oxygen was studied by pulse radiolysis. At room temperature the establishment of the equilibria between the hydroxycyclohexadienyl radical (1), oxygen and the hydroxycyclohexadienperoxyl radicals 5-hydroxy-1,3-cyclohexadiene-6-peroxyl radical (3) and 6-hydroxy-1,4-cyclohexadiene-4-peroxyl radical (4), was observed. From the kinetic analysis of the decay of radical 1 at 310 nm overall forward and reverse rate constants of k = 3.1 xl08 dm3 mol-1 s-1 and k = 1.2 x 104 s-1 were obtained. From the analysis of the transient spectra and the products of pulse-irradiated solutions it is concluded that in the equilibrium radical 4 is much favoured over radical 3.

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