Intermolecular electrostatic effects

The link between UpophiUcity and point charges is given by intermolecular electrostatic interactions (Sections 12.1.1.2, 12.1.3 and 12.1.4 address this topic) and ionization constants. The mathematical relationships between Upophilicity descriptors and pKjS are discussed in detail in Chapter 3 by Alex Avdeef. Here, we recall how pKj values are related to the molecular electron flow by taking the difference between the pfCj of aromatic and aUphatic amines as an example. The pfCa of a basic compound depends on the equilibrium shown in Fig. 12.2(A). A chemical effect produces the stabilization or destabiUzation of one of the two forms, the free energy difference (AG) decreases or increases and, consequently. 

The form of this equation makes explicit the fact that intermolecular forces do depend upon their vibrational states as well as on their electronic states. Due to the antisymmetrization of the global electronic wave function, Vaia2(R R12) contains Coulomb exchange terms and a direct term formed by the Coulomb multipole interactions and the infinite order perturbation electrostatic effects embodied in the reaction field potential [21, 22],... 

Palecek, S.P. and Zydney, A.L., Intermolecular electrostatic interactions and their effect on flux and protein deposition during protein filtration, Biotechnol. Prog., 10, 207, 1994. 

When the intermolecular electrostatic energy cannot be neglected, we can use the methodology of London [30, 32] to obtain an expression accounting for the effective field" the chromophores experience... 

Based on DFT calculations on chlorophylls and, additionally, on ubiquinone and the RC main detergent, lauryl dimethylamine oxide or LDAO, we have then developed a force field for their classical modelization. Our approach to this undertaking was straightforward. We initially use the DFT optimized structures and the vibrational analysis to determine the bonded part of the potential parameters described by the AMBER potential function. Then, atomic ab initio partial charges on the chromophore are used to account for electrostatic effects. At a later stage, experimental data from X-ray crystallography are used to check the structural properties of the molecule in the condensed state and to refine the intermolecular Lennard-Jones parameters. 

A promising lead in the estimation of electrostatic interactions is the use of electrostatic molecular potentials [24]. This method simulates the coulombic contribution to the intermolecular interaction by substituting appropriately chosen point charges, which may be fractional, to replace actual neighbouring molecules. The potential is a function of the electronic distribution and the position of the nuclei in the molecule and is computed from molecular wave functions. It is the basic premise of the use of electrostatic potentials that - pol> - Ct and fi disp much less important than electrostatic effects in determining structural features of complex formation. The deformations of the special charge distribution of a set of atoms bound together to form a molecule are quite complex and the electrostatic potential, like all other... 

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