Electrostatic effectiveness factor

As for 3M-type UTCLs, actual Pt loadings in them are in the range of 0.05-0.1 mg cm . This loading deviates from the ideal monolayer loading for several reasons Pt layers in UTCLs are about 5-10 monolayers thick, leading to a low surface atom ratio of Pt. Moreover, the electrostatic effectiveness factor in UTCLs is significantly below one. 

FIGURE 3.25 Solution of the single pore model in the ID Poisson-Boltzmann limit (a) the electrostatic effectiveness factor, as a function of the metal surface charge density, ctm, for various values of Rp (b) radial variation of the normalized proton concentration in the pore for various values of Rp at gm = —0.05 C (Reprinted from Chan, K. and Eikerling, M. 2011. /. Electrochem. Soc., 158(1), B18-B28, Figures 1,2,3,4,5,6. Copyright (2011), the Electrochemical Society. With permission.)... 

In view of the arguments presented in this chapter, as well as in previous chapters, it seems that electrostatic effects are the most important factors in enzyme catalysis. Entropic factors might also be important in some cases but cannot contribute to the increase of kcJKM. Furthermore, as much as the correlation between structure and catalysis is concerned, it seems that the complimentarity between the electrostatic potential of the enzyme and the change in charges during the reaction will remain the best correlator. Finally, even in cases where the source of the catalytic activity of a given enzyme is hard to elucidate, it is expected that the methods presented in this book will provide the crucial ability to examine different hypothesis in a reliable way. 

Other particular theories are confined to diffusion-controlled reactions (109), to the so called cooperative processes (113), in which the reactivity depends on the previous state, or to resistance of semiconductors (102), while those operating with hydrogen bridges (131), steric factors (132), or electrostatic effects (133, 175) are capable of being generalized less or more. 

As mentioned previously, in [FegS4] + clusters, the three Fe(III) ions are not completely equivalent. NMR spectroscopy may allow one to locate the iron with the lowest reduction potential, as being the one characterized by the weakest magnetic couplings with the other two irons. However, this is true only if the energetic contributions due to other factors, such as electrostatic effects or solvent accessibility 93), are less important than those due to the magnetic coupling of the... 

The inductive and electrostatic effects, steric constraints and conjugative interactions are the major factors that determine the configurational stability of a-sulfonyl carbanions. These are thought to be pyramidal with appreciable electrostatic inhibition to racemization by way of inversion. LCAO-MO-SCF calculations have indicated the conformer 195 in which the lone pair is directed along the bisector of the OSO angle to be the most stable in acyclic sulfones. ... 

The theory presented above accounts for the electrostatic effects on the apparent rate constant for ion transfer by relating the observed changes in to changes in c"(0), or equivalently to 0(0). In the following, we present the simulated electrical potential distributions and the corresponding enhancement factors for a cation transferring from the aqueous phase across the water-l,2-DCE interface (s" = 78.39, s° = 10.36). The rela-... 

Fitzgerald et al. (1984) measured pressure fluctuations in an atmospheric fluidized bed combustor and a quarter-scale cold model. The full set of scaling parameters was matched between the beds. The autocorrelation function of the pressure fluctuations was similar for the two beds but not within the 95% confidence levels they had anticipated. The amplitude of the autocorrelation function for the hot combustor was significantly lower than that for the cold model. Also, the experimentally determined time-scaling factor differed from the theoretical value by 24%. They suggested that the differences could be due to electrostatic effects. Particle sphericity and size distribution were not discussed failure to match these could also have influenced the hydrodynamic similarity of the two beds. Bed pressure fluctuations were measured using a single pressure point which, as discussed previously, may not accurately represent the local hydrodynamics within the bed. Similar results were... 

It is clear that above 15 kcal/mol, a region of saturation of the first-order electrostatic effect is entered, and a second-order effect can be discerned becoming the discriminating factor of hydrogen bond strength. 

Other factors also come into play in laboratory systems. For example, McMurry and Rader (1985) have shown that particle deposition at the walls of Teflon smog chambers is controlled by Brownian and turbulent diffusion for particles with Dp 0.05 yxm and by gravitational settling for particles with Dp > 1.0 yxm. However, in the 0.05- to 1.0-yxm range, the deposition is controlled by electrostatic effects Teflon tends to... 

Preference for the ds/irons-peptide bond in N-acylprolines, a condition for the stereochemistry of peptides and proteins, is governed mostly by steric factors due to substituents on C , by short-range electrostatic effects, and by intramolecular hydrogen bonding. 

The enhanced reactivity in the cupric ion-catalyzed hydrolysis cannot be due solely to the electrostatic effect of an attack of hydroxyl ion on a positively charged a -amino ester, since the introduction of a positive charge, two atoms from the carbonyl group of an ester, increases the rate constant of alkaline hydrolysis by a factor of 103 (10), whereas there is a difference of approximately 106 between the cupric ion-catalyzed and the alkaline hydrolyses of DL-phenylalanine ethyl ester. The effective charge on the cupric ion-glycine (buffer)-ester complex is +1, so that the factor of 106 cannot be explained by an increase in charge over that present in the case of betaine. Furthermore, the reaction cannot be due to attack by a water molecule on a positively charged a-amino acid ester, since the rate constant of the acidic hydrolysis of phenylalanine ethyl ester is very small. It thus seems... 

In addition to the effect of polar groups (discussed above) and the electrostatic effect of neighboring anionic charge, there are other factors that affect carbohydrate acidity. Among them are steric and entropy effects and intramolecular hydrogen bonding. 

The significance of these results for differences in reactivities of nucleophiles is that, despite the unfavorable relative equilibrium constants, Me2S is more reactive toward the quinone methide than chloride ion by a factor of nearly 3000. This mismatch of rate and equilibrium effects is summarized in Scheme 35. It must imply (a) that there is a relatively long partial bond between sulfur and carbon in the transition state so that the unfavorable steric and electrostatic effects are not developed and (b) that the favorable carbon-sulfur bonding interaction is well developed despite the long bonding distance. 

Product or reactant stabilizing factors that have been studied thus far include resonance/charge delocalization, solvation, hyperconjugation, intramolecular hydrogen bonding, aromaticity, inductive, jr-donor, polarizability, steric, anomeric, and electrostatic effects, as well as ring strain and soft-soft interactions. Product or reactant destabilization factors are mainly represented by anti-aromaticity, steric effects in some types of reactions, and, occasionally, electrostatic effects. What makes the PNS particularly useful is that it is completely general, mathematically provable,4 and knows no exception. 

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