Measurement, critical role

The critical role of the latter process was clearly shown in the extremely elegant work of Wegner and Riihe (1989) who measured the temperature dependence of the DC conductivity of a range of polythiophene and polypyrrole derivatives as a function of the interchain separation. The derivatives... 

The charge distribution in the immediate vicinity of the interface will play a critical role in transferring the hybridization-induced signal to the FED. Only effects of charge-density changes that occur directly at the surface of the FED or within the order of the Debye length D from the surface can be detected as a measurable biosensor signal (see also Eq. (3)) ... 

The critical role of the ion-radical pair in the cycloaddition reactions in equation (75) is demonstrated by a careful measurement of the quantum yields as a function of the dienophile concentration and by a study of the effect of solvent and salt on the dynamics of the ion pair ANT+ , MA-. 212 However, in the reported cases, back electron transfer effectively competes with the coupling within the ion-radical pair and thus limits the quantum yields for the formation of the Diels-Alder adduct.212... 

Experiments have also played a critical role in the development of potential energy surfaces and reaction dynamics. In the earliest days of quantum chemistry, experimentally determined thermal rate constants were available to test and improve dynamical theories. Much more detailed information can now be obtained by experimental measurement. Today experimentalists routinely use molecular beam and laser techniques to examine how reaction cross-sections depend upon collision energies, the states of the reactants and products, and scattering angles. 

ATP (Adenosine 5 -triphosphate) plays a critical role in all living beings as an energy source for various enzyme activities and as a direct precursor in RNA synthesis. ATP is rapidly regenerated mainly by the glycolytic pathway and oxidative phosphorylation. A conventional luciferin-luciferase method was established a, 2), and many investigators have been using it to measure static ATP concentration (3). However it has been difficult to measure cellular ATP synthetic activity (4). Recendy, we developed... 

The authors finish by predicting a quantity that has not yet been measured, the secondary KIE that would be obtained with -ND2 in place of -NI Q as the reactive base. They also note the critical role of the Mg counterions in facilitating the reaction. The binding to the two cations of the phosphoenolpyruvate tetraanion compared to the reactant trianion is predicted to be increased by some 240 kcal mol this offsets the highly unfavorable pKa of the C-2 proton sufficiently to render the overall reaction thermochemistry only 2.8 kcal mol endergonic. 

Here, the potentiometric selectivity coefficient is given with respect to the hydroxyl ion. Single-crystal lanthanum fluoride is a wide bandgap semiconductor in which the electrical conductivity is due only to the hopping mobility of fluoride ions through the defects in the crystal. It does not respond to the La3+ ion because of the slow ion exchange of that ion. Hydroxyl ion is the only other ion that has appreciable mobility, and is the only known interference. For this reason, the measurements with a fluoride electrode are always done below pH 7, which circumvents this interference. As shown later, the consideration of ionic and/or electronic conductivity of the membrane plays a critical role also in the design of the internal contact in nonsymmetric potentiometric sensors. 

When calcination was performed at 470°C, the sample turns light yellow, indicating the conversion of intermediates probably into oxides and other species, accompanied by further V migration to the gel (Fig. 11c). Luminescence measurements from our laboratory (33) have shown that calcination at 470°C results in complete disappearance of vanadyl porphyrin peaks and appearance of some new excitation peaks which can not be observed in the corresponding excitation spectrum of the EuYV(p)AAAC sample. These data suggest that intermediates exist after calcination and that these species may play a critical role during V migration. 

---