Robert H. Schuler

Oxidation of Ascorbate Anion by Electron Transfer to Phenoxyl Radicals

Most phenoxyl radicals rapidly oxidize ascorbate anion (rate constants from 4 to 20 x 10/sup 8/ M/sup -1/ sec/sup -1/) by a simple electron transfer process. The product radical anion is relatively unreactive and has a well-characterized absorption at 360 nm where it has an extinction coefficient of 3300 M/sup -1/ cm/sup -1/. In the case of a phenoxyl radical produced by OH attack on phenol, oxidation appears to be quantitative. Ascorbate is oxidized only slowly or not at all by less reactive radicals, such as the alcohol radicals, para-semiquinones, or the phenyl radical. Ascorbate can, therefore, be used to selectively remove phenoxyl radicals from many mixed radical systems. Because ascorbate radical anion absorbs only weakly above 390 nm, where phenoxyl and para-semiquinone radicals absorb more strongly, ascorbate can be used to examine the oxidation of substrates in cases where phenoxyl and semiquinone radicals are produced simultaneously. This application is illustrated by a study of the attack of OH at the fluorine position of para-fluorophenol. A second illustrative example is provided by a study of the tertiary oxidation of ascorbate following reduction of the bromophenols by e/sub aq//sup -/. It is shown, in agreement with previous optical and ESR studies,morexa0» that phenoxyl radicals are produced by rapid protonation of the hydroxyphenyl radical anion in the case of the ortho- and para-isomers but not in the case of the meta-isomer.«xa0less

RATE CONSTANTS FOR REACTION OF HYDROGEN ATOMS WITH COMPOUNDS OF BIOCHEMICAL INTEREST.

The rate constants for the reaction of hydrogen atoms with a large number of amino acids, hydroxy acids, sugars, purines, pyrimidines, sulfur-containing compounds, and related substances have been ...

Radical Production in the Radiolysis of the Hydrocarbons

Previously (1), in a discussion of detailed experiments on the radiation-induced reaction between iodine and heptane, we have proposed the use of iodine for the quantitative determination of radical production in hydrocarbon radiolysis. It was shown that the yield of iodine disappearance in air-free iodine-heptane solutions is independent of concentration in the range 0.0001 to 0.0006 M and also independent of temperature and of radiation intensity. The disappearance of iodine was ascribed to reaction with free radicals. The radical yield measured by the uptake of iodine, G(RI) = 6.8 radicals per 100 ev, was found to be in approximate agreement with the value obtained by Chapiro et al. (2, 3), who used diphenylpicrylhydrazyl radical (DPPH) as the radical detector. The present work extends these iodine absorption studies to other hydrocarbons.

The Mode of Reaction of O - Radical with Aromatic Systems

The rate constants for reaction of

Radiation‐Induced Reaction between Iodine and Heptane

{rm O}^{-}

E.s.r. studies of energy transfer in ethane + ethylene mixtures

with a number of substituted benzenes and toluenes have been measured. While the values for abstraction from the methyl group of the toluenes

Radiation Chemistry Studies with Cyclotron Beams of Variable Energy: Yields in Aerated Ferrous Sulfate Solution1

(ksim 10^{9} M^{-1} {rm sec}^{-1})

Radiation-Chemical Studies With Cyclotron Beams1

are considerably greater than for addition to the ring

OXIDATION OF FERROUS SULFATE BY IONIZING RADIATIONS FROM (n,/cap alpha/) REACTIONS OF BORON AND LITHIUM

(k<10^{8} M^{-1} {rm sec}^{-1})

THE FAST ELECTRON AND X-RAY DECOMPOSITION OF THE ALKYL HALIDES

they are not strongly influenced by additional substitution. The dependence of rate constants on the substituents indicates that