Interactions problem with interpretation

Two product barrier layers are formed and the continuation of reaction requires that A is transported across CB and C across AD, assuming that the (usually smaller) cations are the mobile species. The interface reactions involved and the mechanisms of ion migration are similar to those already described for other systems. (It is also possible that solid solutions will be formed.) As Welch [111] has pointed out, reaction between solids, however complex they may be, can (usually) be resolved into a series of interactions between two phases. In complicated processes an increased number of phases, interfaces, and migrant entities must be characterized and this requires an appropriate increase in the number of variables measured, with all the attendant difficulties and limitations. However, the careful selection of components of the reactant mixture (e.g. the use of a common ion) or the imaginative design of reactant disposition can sometimes result in a significant simplification of the problems of interpretation, as is seen in some of the examples cited below. 

Intramolecular Isotope Effects. The data in Figure 2 clearly illustrate the failure of the experimental results in following the predicted velocity dependence of the Langevin cross-section. The remark has been frequently made that in the reactions of complex ions with molecules, hydrocarbon systems etc., experimental cross-sections correlate better with an E l than E 112 dependence on reactant ion kinetic energy (14, 24). This energy dependence of reaction presents a fundamental problem with respect to the nature of the ion-molecule interaction potential. So far no theory has been proposed which quantitatively predicts the E l dependence, and under these circumstances interpreting the experiment in these terms is questionable. 

Despite the fact that formalism of the standard chemical kinetics (Chapter 2) was widely and successfully used in interpreting actual experimental data [70], it is not well justified theoretically in fact, in its derivation the solution of a pair problem with non-screened potential U (r) = — e2/(er) is used. However, in the statistical physics of a system of charged particles the so-called Coulomb catastrophes [75] have been known for a long time and they have arisen just because of the neglect of the essentially many-particle charge screening effects. An attempt [76] to use the screened Coulomb interaction characterized by the phenomenological parameter - the Debye radius Rd [75] does not solve the problem since K(oo) has been still traditionally calculated in the same pair approximation. 

A problem with this interpretation relates to electrostriction, a process in which the density of the solvent changes about a solute. Shim et al. [243] noted evidence of electrostriction in molecular dynamics simulations of a model chromophore in an IL, and the degree of electrostriction was sensitive to the charge distribution of the solute. This observation does not necessarily contradict the framework above, as some local disruption of solvent structure due to dispersive interactions is inevitable. However, it is desirable to obtain a clearer understanding of the competition between these local interactions and the need to maintain a uniform charge distribution in the liquid. 

Extrinsic Cotton effects are due to the inherent dissymmetry of the enzyme-bound chromophore (an inherent effect) and/or to the interactions of the chromophore with the encompassing dissymmetric environment (interactive effects). The inherent effects are those which the free chromophore would exhibit if its conformation were identical with that of the enzyme-bound form. The interactive effects result from protein-ligand interactions or ligand-ligand interactions. The main problem in interpretation of die CD of enzyme-bound chromophores is distinguishing between the inherent and the interactive effects. 

Indeed, the solvent effects are usually small (< 1 ppm) compared with the changes arising from structural perturbations and are therefore generally not a problem in interpreting Si data. For cases in which specific solvent-solute interactions are possible, however, large solvent shifts can occur. 

The compound must be metabolically stable and capable of transport to the site for receptor interaction (interpretation of inactive compounds may be flawed by problems with bioavailability). 

Overall, the evidence to support suggestions that JT effects have been unequivocally observed in STM images [5] seems very thin. One problem with a JT interpretation of these images is that real STM images are influenced by many factors, some of which may be considerably more significant than the rather subtle JT interaction. In contrast, theoretical simulations can be specifically tailored to consider only the effects of a JT interaction, the results of which can be used as a guide to what may appear in actual experiments. 

A problem in interpreting the effect of different counterions on the mechanical properties of ionic polymers is the difficulty in evaluating how cation-anion interactions are changing from counterion to counterion. For example, metal counterions differ in ionicity as well as in size and valence, and they can have a partially covalent character. In contrast, quaternary phosphonium ions have a number of desirable characteristics that make them particularly attractive as model systems for the study of counterion effects. They have an essentially full positive charge on the heteroatom so partially covalent interactions, fractional charge transfer between the counterion and anion, and hydrogen bonding do not come into play. Furthermore, with quaternary ions there is no possibility of the tautomerism that can occur with nonquatemary ammonium or phosphonium counterions. 

This model has been criticized by Jewsbury and Holloway [344], who suggested on theoretical grounds that the second-order behaviour arose not from a pairwise interaction of As4 molecules, but simply because an As4 molecule could only desorb from an As site on the surface. The problem with this interpretation is that the sticking coefficient of As4 should become unity for a Ga-stable 100 surface, whereas experimentally its maximum value is 0.5 and then only for a Ga-saturated surface. 

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