Radical g- values

Radical g value Spin density an (ring protons)... 

Fig. 8. Superoxide radical G-values as a function of LET. The square symbol is the common yield accepted with y-rays and high energy electton beam irradiation. Plain lines are from scavenging experiments with C, Ne and Ni ion beam by Laverne and Schuler [Cited in Refs. 41 and 42]. The circle and triangle symbols are from track-segment pulse radiolysis experiments. Dash line is from Monte Carlo simulation.

Fig. 1. 2- >-Chlorophenyl-l,3-bis(diphenylene)allyl radical, g-value vs. temperature [77Yaml].

Un S, Gerez C, Elleingand E, Fontecave M. 2001. Sensitivity of tyrosyl radical g-values to changes in protein structure a high-field EPR study of mutants of ribonucleotide reductase. JAm Chem Soc 123 3048-3054. 

This EPR spectrum shows a considerable broadening of linewidth when comparing with an EPR spectrum of free TAM nitric oxide. An EPR characterization of nitroxyl radicals is based on the measurement of the signal intensity of an EPR spectrum. This measurement can provide fundamental information of free radicals, such as linewidth that bears a relationship to the tumbling motion of free radicals, g-value which largely depends on the immediate environments of the free radicals, and hyperfine splitting constants which describe the classical multiplicity of EPR spectrum due to the interaction of the unpaired electron spins with nuclear spins. 

Radical g-value Number of lines Line width Hyperfine constants, aH... 

FREE RADICAL g-VALUE HYPERFINE COUPLING (GAUSS) ... 

Tlie following summarizes g-values and hyperfine splitting values by ( h) and by ( 33s) in natural abundance for the representative 1,2-dithiete radical cations. 

The theory of radiation-induced grafting has received extensive treatment. The direct effect of ionizing radiation in material is to produce active radical sites. A material s sensitivity to radiation ionization is reflected in its G value, which represents the number of radicals in a specific type (e.g., peroxy or allyl) produced in the material per 100 eV of energy absorbed. For example, the G value of poly(vinyl chloride) is 10-15, of PE is 6-8, and of polystyrene is 1.5-3. Regarding monomers, the G value of methyl methacrylate is 11.5, of acrylonitrile is 5.6, and of styrene is >0.69. 

The rate of free radical production from Am and B are dependent on the G value of both ... 

Ionizing radiation is unselective and has its effect on the monomer, the polymer, the solvent, and any other substances present in the system. The radiation sensitivity of a substrate is measured in terms of its G value or free radical yield G(R). Since radiation-induced grafting proceeds by generation of free radicals on the polymer as well as on the monomer, the highest graft yield is obtained when the free radical yield for the polymer is much greater than that for the monomer. Hence, the free radical yield plays an important role in grafting process [85]. 

The radiation sensitivity of polymers and monomers is characterized by a G value the number of radicals formed per 100 e.v. (16 aJ) absorbed. Radiation sensitive groups include -COOH, C-halogen, -S02-, -NH2 and -C=C, Radiation resistant groups are aromatic rings. It appears that the presence of aromatic moieties also offers some degree of radiation protection to the polymer chain as a whole. 

The yields of radiolysis products are always expressed by the G value, which is defined as the number of particles (molecules, radicals, ions) produced or consumed per 100 eV of energy absorbed in the system. 

The authors did not give much quantitative information in their papers. The G values for decomposition are almost twice as large in ACSO (8.5) as compared to PCSO (4.6). The value in ACSO is higher than the yield of the radicals in aqueous solution and should be attributed to reactions of radicals produced from ASCO with other ASCO molecules, for... 

Typical values of g for some sulfonyl radicals are also listed in Table 2. Two main features stand out from these data. First, there is a decrease in the g-value as the electronegativity of the substituents increases, that is, MeSOj (2.0049), Me2NS02 (2.0036), MeOSOj (2.0032) and FSOj (2.0026), and second, there is an increase in the g-value when introducing atoms characterized by large spin-orbit couplings in positions of significant spin density of the radical (cf., for example, entries 7 and 9 as well as 10 and 11 in Table 2). 

Kemp and coworkers employed the pulse radiolysis technique to study the radiolysis of liquid dimethyl sulfoxide (DMSO) with several amines as solutes [triphenylamine, and N, A, A, N -tetramethyl-p-phenylenediamine (TMPD)]. The radiolysis led to the formation of transient, intense absorptions closely resembling those of the corresponding amine radical cations. Pulse radiolysis studies determine only the product Ge, where G is the radiolytic yield and e is the molar absorption. Michaelis and coworkers measured e for TMPD as 1.19 X 10 m s and from this a G value of 1.7 is obtained for TMPD in DMSO. The insensitivity of the yield to the addition of electron scavenger (N2O) and excited triplet state scavenger (naphthalene) proved that this absorption spectrum belonged to the cation. 

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