NON-ELECTROSTATIC BONDS

The conception of the electrostatic bond has been found to be most valuable in the field of inorganic chemistry and has helped to clarify a great many phenomena. It has frequently made it possible to predict properties both of unknown compounds and of those which have been little investigated. Nevertheless, a number of difficulties have been encountered. For example, in Section 43, it was shown that the theory did not really provide a satisfactory explanation of the low symmetry of molecules. Again, the theory failed to explain the volatility and small dipole moment of the compounds CO, NO, C120, etc., and lastly, it threw no light whatever on the reason for the existence of molecules of elements such as H2, Cl2, Oa, N2, etc., especially as dipole measurements show that the formulae H+H, Ci+ci are excluded. 

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Further, in the case of virtually non-existent ion-solvent interactions (low degree of solvation), so that solute-solute interactions become more important, Kraus and co-workers47 confirmed that in dilute solutions ion pairs and some simple ions occurred, in more concentrated solutions triple ions of type M+ X M+ orX M+X andinhighly concentrated solutions even quadrupoles the expression triple ions was reserved by Fuoss and Kraus48 for non-hydrogen-bonded ion aggregates formed by electrostatic attraction. 

Noncovalent interactions, both inter- and intramolecular, are of considerable importance in determining the physical properties of molecules. Such interactions can be classified as hydrogen-bonding or non-hydrogen-bonding. In this section we will explore some recent uses of the electrostatic potential in the analysis of both types. 

The Analysis of Non-Hydrogen-Bonding Noncovaient Interactions Using Surface Electrostatic Potentials... 

Murray, J. S., K. Paulsen, and P. Politzer. 1994. Molecular Surface Electrostatic Potentials on the Analysis of Non-Hydrogen-Bonding Noncovalent Interactions. Proc. Ind. Acad. Sci. (Chem. Sci.) 106, 267. 

CNT can markedly reinforce polystyrene rod and epoxy thin film by forming CNT/polystyrene (PS) and CNT/epoxy composites (Wong et al., 2003). Molecular mechanics simulations and elasticity calculations clearly showed that, in the absence of chemical bonding between CNT and the matrix, the non-covalent bond interactions including electrostatic and van der Waals forces result in CNT-polymer interfacial shear stress (at OK) of about 138 and 186MPa, respectively, for CNT/ epoxy and CNT/PS, which are about an order of magnitude higher than microfiber-reinforced composites, the reason should attribute to intimate contact between the two solid phases at the molecular scale. Local non-uniformity of CNTs and mismatch of the coefficients of thermal expansions between CNT and polymer matrix may also promote the stress transfer between CNTs and polymer matrix. 

Thus, non-covalent hydrophobic interactions, hydrogen bonds, and electrostatic bonds all contribute to the overall shape of a protein (Figure 13.3). As we shall see (Section 13.3.2), many pertinent properties of a protein are then provided by the appropriate combination of the remaining amino acid side-chains that reside on the surface, allowing specific binding to various molecules. This is the essence of enzymic activity and drug-receptor interactions. 

Eq. (9.12) does not require any specification of bonding - all atoms electrically interact with all other atoms. Sefcik et al. (2002) have combined QEq electrostatics with Morse potentials for non-electrostatic non-bonded interactions between all atom pairs to create a... 

Other energetic components associated widi the solvation process include non-electrostatic aspects of hydrogen bonding and solvent-structural rearrangements like the hydrophobic effect. Despite many years of study, the fundamental physics associated with both of these processes remains fairly controversial, and physically based models have not been applied with any regularity in the context of continuum solvation models. 

Fat absorption of protein additives has been studied less extensively than water absorption and consequently the available data are meager. Although the mechanism of fat absorption has not been explained, fat absorption is attributed mainly to the physical entrapment of oil (7). Factors affecting the protein-lipid interaction include protein conformation, protein-protein interactions, and the spatial arrangement of the lipid phase resulting from the lipid-lipid interaction. Non-covalent bonds, such as hydrophobic, electrostatic, and hydrogen, are the forces involved in protein-lipid interactions no single molecular force can be attributed to protein-lipid interactions ( ). 

J.S. Murray et al., Molecular surface electrostatic potentials in the analysis of non-hydrogen-bonding noncovalent interactions. Proc. Indian Acad. Sci. 106, 267-275 (1994)... 

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