Steric potential

For spherical particles, some of these interactions can be described by simple formulas. The hard-core steric potential is simply... 

In order to optimise the steric repulsion, the steric potential as expressed by Napper can be considered [8] ... 

Adsorbed layer thickness 5 The steric interaction starts at h = 28 as the chains begin to overlap and increases as the square of the distance. Here, the important point is not the size of the steric potential but rather the distance h at which it begins. 

The final interaction potential is the superposition of the steric potential and the van der Waal s attractions, as shown in Figure 11.3b. 

The concept of Brownian ratchets has been applied to construct asymmetric obstacle courses that provide a spatially asymmetric steric potential for biomolecule separation [20, 21], The basic idea is to use such asymmetric obstacles to rectify the Browiuan motion laterally and thereby to deflect diffusing biomolecules based on their sizes. So far, the Brownian ratchet systems have been successfully demonstrated for long DNA and phospholipids [15, 16], even though the separation resolution reported so far was not ideal. 

The crystal structure of 2,2,2, 2 -tetrachloro-3,3,3, 3 -tetramethyl-1,1 -bicyclopropyl has appearedand the photoelectron spectrum of parent l,r-bicyclopropyl has been analysed. The present molecule shows strong conformationally dependent conjugative interaction of the Walsh orbitals of approximately the same magnitude as the interaction between the double bonds of buta-1,3-diene. However, in sterically fixed disubstituted bicyclopropyls the substituents considerably reduce this interaction. Steric potential curves for several bicyclopropyls and substituted cyclopropanes have... 

Each of the N molecules is compared with every other to generate an N X N similarity matrix, which is compared to the biological potency values using PLS60.63,198 or a neural network. Frequently, the cross-validation statistics are slightly better for models based on similarities than for those using the full matrix of electrostatic and steric potentials. 

This discrqumt between the experimait and the above calculations may be naturally explained by the fact that the latta do not take into account the steric potential, Le. the term Q ra in the expression (13) for Q( ). This term is a result of indispensable involvement (because correlation in the motion) of the groups adjacent to the rotation axis into the event of torsional motion, especially for rotation at large angles when the torsicmal vibrations the neighbouring monomeric units caimot be considered as independent ones. Thus, the real potential barrier for torsional vibrations in the maoomolecules is rather controlled by nonbonded (intermolecular) interactions betv n the nearest units of the chain involvol in the motion rather than by the value of Qq, Le. = Qq + where the sum extends over all units of the correlation drain part. 

Naturally, there are many grid points with only minor variation in the field values, e.g., the steric potential within the common overlap volume of all molecules or the steric and electrostatic potentials far outside the molecules. To eliminate such grid points, a minimum sigma condition is defined, i.e., all points are eliminated which have a lower variance in their field values than defined by this minimum sigma option. ... 

Bartell treats the vibrations as harmonic, so that the linear terms and cross terms in eq. (III-28) drop out, leaving only the square and higher even terms. He then, somewhat arbitrarily, assumes functional forms and assigns attractive and repulsive parameters for the H H, C H, and C C interactions. Since the functional form of the combined interactions is such that the second derivative of the potential energy is positive in the isotopic displacements, i.e., repulsive forces predominate, the smaller mean-square amplitudes in the deuterated molecules lead to a lower average steric potential energy. This means that release of steric compression in the product... 

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