The g-Value

The negative sign in equation (b 1.15.26) implies that, unlike the case for electron spins, states with larger magnetic quantum number have smaller energy for g O. In contrast to the g-value in EPR experiments, g is an inlierent property of the nucleus. NMR resonances are not easily detected in paramagnetic systems because of sensitivity problems and increased linewidths caused by the presence of unpaired electron spins. 

From a knowledge of various values of P it is possible to calculate F values for specific polymers and G values for specific gases if the G value for one of the gases, usually nitrogen, is taken as unity. These values are generally found to be accurate within a factor of 2 for gases but urtreliable with water vapour. Some... 

From the experimental data for the free resulting jet, the g value in Eq, (7.162) is equal to 0.075. Tests in field showed that the influence of the re-... 

Pauli spin susceptibility for the aligned CNTs has been measured and it is reported that the aligned CNTs are also metallic or semimetallic [30]. The temperature dependence of gn and gx s plotted in Fig. 5(a). Both values increase with decreasing temperature down to 40 K. A similar increase is observed for graphite. The g-value dependence on the angle 0 at 300 K is shown in Fig. 5(b) (inset). The g-value varies between gn = 2.0137 and gx= 2.0103 while the direction of magnetic fields changes from parallel to perpendicular to the tubes. These observed data fit well as... 

In the simple model of CNTs described earlier, its g-value can be estimated using the g-values of graphite at 300 K,... 

The XRD peaks characteristic of Co and Ni disappeared after the treatment, as did the broad ESR line, successfully leaving only the narrow asymmetric line with 26 G linewidth as shown in Fig. 8 [40]. The g-value of the narrow line is =2.002 0.001. The narrow ESR line shows Dysonian at all temperatures in the range of 4-300 K. Furthermore, the ESR intensity is quite independent of T and thus the density of conduction electrons is invariant as a function of temperature as shown in Fig. 9. These show that the material is highly metallic, even at low 7. 

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 ... 

Shear modulus is also changed with the blending type (Fig. 11). Preheated blends provide higher modulus than the preblends. It is obvious that shear modulus either decreases or remains the same at the initial level of NBR for preblends, but beyond 45% of NBR there is a further rise in the G value irrespective of shear rates whereas at the lower shear rate, preheated blends show the continuous rise in the shear modulus for the entire composition range. 

The shear modulus varies with the blend ratios in the preblend system, G remains constant up to 50 50 blend ratio and then it decreased with the further addition of AU in the blend at higher shear rate. At lower shear rate, G increased up to the 50 50 blend ratio and then it fell. Preheating of the blends resulted in increasing the G values. At both shear rates G increased up to 50 50 blend ratio and then decreased with further addition of AU in the blends. 

On the basis of these results, the relative scale of radiation resistance of aliphatic, alicyclic, aromatic, and ionic solid compounds may be immediately deduced. Table I summarizes these data including the G values, which have been obtained on assuming for vr an average value of 200. 

Table 16. Composition", frequency (co) beginning from which one may achieve coincidence of the G values and the shift factors b(c) at 190 °C [344]...

If the flow is accompanied with CBA decomposition, the G value in Eq. (5) should be substituted with its time function, G(t). In the general case, thermal decomposition of a solid substance with gas emission is a heterogeneous topochemical reaction [22]. Kinetic curves of such reactions are S -shaped the curves representing reaction rate changes in time pass a maximum. At unchanging temperature, the G(t) function for any CBA is easily described with the Kolrauch exponential function [20, 23, 24] ... 

If the solvent is water, the electron pulse produces several stable and unstable species. They arise from the energy transferred to water molecules by the electron beam and include e, HO", H, H+, H2, and H2O2. It is customary to express the yields of these products by referring to their G-values. They represent the number of a given species formed per 100 eV of energy absorbed by the water. The following equation uses the G-values as the coefficients ... 

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). 

An estimate for the G value for ethylene removal by ionic reactions can be made from the ion intensities of the 5-torr spectrum. First, the total intensity of accounted ions is set equal to unity. Then we multiply the intensities of the given ions by the number of ethylene molecules used up in their formation. Some of the weighing factors used were ... 

Fig. 13. Plot of the g values g,gz) and of the average g value vs rhombicity (Uj) of the Rieske and Rieske-type proteins listed in Table VIII. The lines represent linear fits to the data points.

Fig. 14. Plot of the g values g,g ) and of the average g value g vs rhombicity (UJ of (a) wild type (open symbol) and variant forms (closed symbols) of the Rieske protein in yeast bci complex where the residues Ser 183 and Tyr 185 forming hydrogen bonds into the cluster have been replaced by site-directed mutagenesis [Denke et al. (35) Merbitz-Zahradnik, T. Link, T. A., manuscript in preparation] and of (b) the Rieske cluster in membranes of Rhodobacter capsulatus in different redox states of the quinone pool and with inhibitors added [data from Ding et al. (79)]. The solid lines represent linear fits to the data points the dashed lines reproduce the fits to the g values of all Rieske and Rieske-type proteins shown in Fig. 13.

In general there are few reproducible data on binding of reducible substrates to the isolated MoFe proteins. However, the S = EPR signal from the FeMoco centers of Kpl is pH dependent, the g values changing with a pKa of 8.7 (50). Of course, the proton is a substrate of nitrogenase however, there is no direct evidence for the proton associated with the pKa being bound directly to FeMoco. Nevertheless, this pKa can be perturbed by addition of the analog substrate acety-... 

Almost simultaneously, Lindahl and co-workers proposed that Cluster C is the CO oxidation site based on EPR and ENDOR studies of the cyanide adduct of the enzyme (134). That proposal was based on the premise that CO and cyanide compete for the same binding site. Additionally, Xia and Lindahl have shown that, by mild SDS treatment, they can partially dissociate CODH/ACS, which is a tetra-meric enzyme with an subunit composition, into an isolated a subunit and an form (135). The form has the same level of CO oxidation activity as the native protein indicating that the a subunit is not involved in CO oxidation and that the /8 subunit must contain the clusters required for CO oxidation (135). In addition, CO2 alters the g values of the Credi form of the enzyme (136). 

Like [3Fe-4S] centers, these centers display an EPR spectrum centered at 2 in the oxidized form. However, the g values and the... 

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