Molecular short covalent

While nonbonded atom pairs will typically not come within 1A of each other, it is possible for covalently bound pairs, either directly bounds, as in 1-2 pairs, or at the vertices of an angle, as in 1-3 pairs. Accordingly it may be considered desirable to omit the 1-2 and 1-3 dipole-dipole interactions as is commonly performed on additive force fields for the Coulombic and van der Waals terms. However, it has been shown that inclusion of the 1-2 and 1-3 dipole-dipole interactions is required to achieve anistropic molecular polarizabilites when using isotropic atomic polariz-abilites [50], For example, in a Drude model of benzene in which isotropic polarization was included on the carbons only inclusion of the 1-2 and 1-3 dipole-dipole interactions along with the appropriate damping of those interactions allowed for reproduction of the anisotropic molecular polarizability of the molecule [64], Thus, it may be considered desirable to include these short range interactions in a polarizable force field. 

To our knowledge, there have been no previous attempts to develop a broad class of molecular catalysts that have temperature-dependent solubilities. When molecular catalysts are covalently bound to polymeric supports, they generally assume the solubihty properties of the host polymer. In the above fluorous catalysts, we Hke to think that a short segment of polymer is being grafted onto a molecular catalyst, hi other words, the ponytails can be viewed as pieces of Teflon , which impart more and more of the solubility characteristics of the polymer as they are lengthened. 

The stability of the molecular conformation of organic solids Is determined by the nature and distribution within the molecular network of both covalent crosslinks and the various non-covalent Interactions. The latter Include localized (e.g. hydrogen bonds) and non-locallzed electrostatic Interactions and the short-range non-polar Interactions between molecular units due to the ubiquitous and weak van der Waals Induction and dispersion forces (7 ). 

In many ways, the molecular models that we have used as the basis for our CAMD studies describe coal structure very well. However, none of the models investigated thus far contains explicit three-dimensional covalent cross-links. Actualfy, the models we have studied are primarily constructed of long chains of one-dimensionally-linked clusters with a number of short side-chains. However, it has been established on the basis of solvent swelling studies (11.15.16) that bituminous coal is primarily made up from a three-dimensional network of clusters held together by covalent bonds and by an even higher density of hydrogen bonds. These macromolecular models of coal, which are less concerned with the molecular structure than with the ways that clusters are bonded to one another, provide a complementary way of describing coal structure. 

The basic extensins. These are hydroxyproline-, lysine- and tyrosine-rich glycoproteins consisting of rigid molecular rods about 80 nm long (14,15), bearing short mono- to tetrasaccharide side-chains (2,14). When newly secreted they bind ionically to the acidic polysaccharides of the cell wall and can be extracted with cold salt solutions later they become much more resistant to salt-extraction and are said to be covalently bound, probably via dimerization of their tyrosine residues to form isodityrosine (15). 

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