Pulse-radiolysis studies. XIV. Rate constants for the reactions of hydrogen atoms with aromatic compounds in aqueous solution

1969 ◽  
Vol 73 (2) ◽  
pp. 413-417 ◽  
Author(s):  
P. Neta ◽  
Leon M. Dorfman
Keyword(s):  
Aqueous Solution ◽  
Rate Constants ◽  
Aromatic Compounds ◽  
Pulse Radiolysis ◽  
Hydrogen Atoms

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.

Site of H Atom Attack on Uracil and Its Derivatives in Aqueous Solution

1985 ◽  
Vol 40 (3-4) ◽  
pp. 292-294 ◽  
Author(s):  
Suresh Das ◽  
David J. Deeble ◽  
Clemens von Sonntag
Keyword(s):  
Aqueous Solution ◽  
Double Bond ◽  
Pulse Radiolysis ◽  
Hydrogen Abstraction ◽  
Methyl Groups ◽  
Oh Radicals ◽  
Hydrogen Atoms ◽  
Sugar Moiety ◽  
Reducing Properties

Hydrogen atoms from the radiolysis of water at pH 1.6 add to the 5,6-double bond of pyrimidines. The preferen­tial site of attack is the C(5) position (values in brackets) in the case of 6-methyluracil (87%), 1,3-dimethyluracil (71%), uracil (69%) and poly(U) (60%). This reaction yields a radical of reducing properties which can be monitored by its reaction with tetranitromethane in a pulse radiolysis experiment. In thymine (37%), thymidine (32%) and 1,3-dimethylthymine (25%) H-addition no longer pre­ferentially occurs at C(5), but addition is now mainly at C(6). Hydrogen abstraction from the methyl groups or the sugar moiety is negligible (≦ 5.5%). A comparison is made with literature values for the equivalent reactions of OH radicals.

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.

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.

Sign in / Sign up

Export Citation Format

Share Document