Electrostatic model, simple

The concept of electrostatic complimentarity is somewhat meaningless without the ability to estimate its contribution to AAg. Thus, it is quite significant that the electrostatic contribution to AAthat should be evaluated by rigorous FEP methods can be estimated with a given enzyme-substrate structure by rather simple electrostatic models (e.g., the PDLD model). It is also significant that calculated electrostatic contributions to A A g seem to account for its observed value (at least for the enzymes studied in this book). This indicates that simple calculations of electrostatic free energy can provide the correlation between structure and catalytic activity (Ref. 10). 

But why linearly and why with a slope of-1, or something thereabout, the reader may righteously ask. In anticipation of the quantum mechanical treatment in Chapter 5 we can briefly discuss here a simple electrostatic model which fully accounts for the observed behaviour. After all, as the detailed quantum mechanical treatment has shown, direct electrostatic... 

Godt, R.E. (1981). A simple electrostatic model can explain the effect of pH upon the force-pCa relation of skinned muscle fibers. Biophys. J. 35, 385-392. 

In a first part of this paper, we will discuss results of a 27A1 NMR study of the binding of Al ions on acrylamide-acrylic acid copolymers as a function of pH, at the light of a simple electrostatic model. The second part deals with the phase diagrams, physical gelation and precipitation phenomenon, for different copolymer compositions and under various conditions of concentrations, pH and salinity. 

The effective CF models, intended to include covalence effects via effective charges and shielding parameters [46] (superposition model [47], effective charge model [48], simple overlap model [49, 50]), keep the radial (M-L distance) dependence of the CF parameters as in the simple (point charge) electrostatic model. Dedicated studies have shown, however, that the radial dependence of these parameters deviates strongly from the latter for the whole series of lanthanide ions [51, 52]. 

The simple iib-ctah predictions (5.30a)-(5.30e) can be tested and compared with expectations of classical electrostatic models for each of the H-bonded complexes to be discussed below. 

In the o.s. reaction, the ion pair A+ - B is formed in a first step. The corresponding equilibrium constant can usually be obtained from simple electrostatic models. In this "ideal" case specific chemical interactions can be neglected and the rate constant of the E.T. step follows the theory of R.A. Marcus (see for example Marcus, 1975, or Cannon, 1980). In the i.s. reaction each of the three steps in reaction (9.2) may determine the reaction rates. The lability of the coordinated ligands at the... 

Permittivity measurements have been used to study hydrogen bonding of phenol or carboxylic acids with trialkylphosphine oxides (154). The results can be explained in terms of a simple electrostatic model. The properties of trimethylphosphine oxide were different from the general properties of the series.189... 

If the fi C—X bond is free to rotate away from periplanarity, then fi C—H bonds will adopt the geometry reqnired for hyperconjugation [as shown for carbocation (6)] and Markovnikov regiochemistry will be favoured. The results are consistent with ab initio theoretical calculations and can be rationalized using a simple electrostatic model."... 

Benson, S. W., and Hougen, G. R., A simple, self-consistent electrostatic model for quantitative prediction of the activation energies of four-center reactions, J. Amer. Chem. Soc. 18,4036 (1965). 

According to the simple electrostatic model, the hydrogen bond between H2O molecules consists of electrostatic interaction between the O—H bond dipole of one water molecule and the unshared lone pair of electrons on the oxygen of another water molecule (Fig. 2.6). The resulting bond is a hydrogen bond. 

It is quite remarkable that electrostatic calculations based on a simple model of integral point charges at the nuclear positions of ionic crystals have produced good agreement with values of the cohesive energy as determined experimentally with use of the Born-Haber cycle. The point-charge model is a purely electrostatic model, which expresses the energy of a crystal relative to the assembly of isolated ions in terms of the Coulombic interactions between the ions. 

These uncertainties are increased when the existence of compounds of CO with metals, the carbonyls such as Fe(CO)5, for which no electrostatic model is conceivably possible are considered. The iron obviously is not present in the compound as an ion how then can the attraction for the CO molecules be explained Even in the straight ammoniates there is some doubt regarding the validity of the simple electrostatic representation of the structure for it is found experimentally that the magnetic properties of halides are radically altered by the taking up of molecules of ammonia. This shows that - some of the electrons of the positive ions are influenced by the ammonia molecules in a way which an electrostatic picture cannot explain. 

JST. D. Sokolov (Moscow) (i) It is not difficult to show that a simple electrostatic model of the hydrogen bond is not sufficient to explain the fundamental spectroscopic manifestation of the hydrogen bond, namely the shift of the A—H frequency in the direction of longer waves. Indeed, in the electrostatic treatment the energy of the hydrogen bond is written, for example, as follows ... 

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