Interactions anisotropic, orientational

The second term in (29) is the anisotropic, orientation-dependent frequency shift due to the first-order quadrupolar interaction... 

Currently, the only other monoprotonated sapphyrin-monoanion complex to be solved by X-ray diffraction analysis is that of 3-HN,. As expected, in this complex the azide counteranion is bound above the sapphyrin plane by a combination of anisotropic electrostatic interactions and oriented hydrogen bonds (Figure 4). As such, this structure supports the conclusion, reached in the case of 3-HCl, that a single positive charge on the sapphyrin is enough to effect anion recognition of anionic substrates, at least in the solid state. 

Complementary to the analysis of conformation-dependent chemical shifts, two-dimensional experiments that correlate anisotropic interactions may be used to study backbone conformation by MAS NMR. This is possible in particular for dipolar interactions, whose orientations are along the intemuclear vector, and for the carbonyl CSAs, which generally adopt a particular orientation with respect to the peptide plane (Fig. 3a). Under MAS, these interactions may be recoupled during the evolution and/or detection period of a two-dimensional correlation experiment, as discussed earlier. The resulting spectrum will contain cross peaks whose pattern is characteristic of the relative orientation of the two interactions being correlated. An alternative approach is to excite a state of 2QC between two neighbouring nuclei, which then evolves under the influence of two anisotropic interactions. 

Anisotropic Interactions The Orientation Dependence of the Resonance Frequency [4]... 

The mesogenic side chains have to be in the liquid crystalline order. The anisotropic interactions induce an anisotropic orientation. 

The isotropic, or Fermi, hyperfine interaction a arises from the presence of nonzero electron density at the nucleus. Interaction between electrons and nuclear dipoles gives rise to the anisotropic, or dipolar, hyperfine coupling T. This interaction is orientation dependent, but averages to zero in freely tumbling solution. The total hyperfine interaction A is the sum of a and T, where A and T are tensors. 

R 226 M. Marjanska, R.H. Havlin and D. Sakellariou, Coherent Averaging and Correlation of Anisotropic Spin Interactions in Oriented Molecules , p. 45... 

Tensor of hyperfine interaction Anisotropic hyperfine interaction constant (mT) Orientation degree of chains Friction force... 

It is occasionally desirable to retain a small proportion of molecular orientation, in order to quantitate the dipolar interactions present, whilst minimizing their contribution to the linewidth. Partial orientation may be achieved by using a nematic solvent. In large, magnetically anisotropic molecules it may occur naturally at the highest magnetic fields. 

This can be inserted in equation (02.2.3) to give tlie orientational distribution function, and tlius into equation (02.2.6) to deteniiine the orientational order parameters. These are deteniiined self-consistently by variation of tlie interaction strength iin equation (c2.2.7). As pointed out by de Gemies and Frost [20] it is possible to obtain tlie Maier-Saupe potential from a simple variational, maximum entropy metliod based on tlie lowest-order anisotropic distribution function consistent witli a nematic phase. 

The range of systems that have been studied by force field methods is extremely varied. Some force fields liave been developed to study just one atomic or molecular sp>ecies under a wider range of conditions. For example, the chlorine model of Rodger, Stone and TUdesley [Rodger et al 1988] can be used to study the solid, liquid and gaseous phases. This is an anisotropic site model, in which the interaction between a pair of sites on two molecules dep>ends not only upon the separation between the sites (as in an isotropic model such as the Lennard-Jones model) but also upon the orientation of the site-site vector with resp>ect to the bond vectors of the two molecules. The model includes an electrostatic component which contciins dipwle-dipole, dipole-quadrupole and quadrupole-quadrupole terms, and the van der Waals contribution is modelled using a Buckingham-like function. 

The dipole density profile p (z) indicates ordered dipoles in the adsorbate layer. The orientation is largely due to the anisotropy of the water-metal interaction potential, which favors configurations in which the oxygen atom is closer to the surface. Most quantum chemical calculations of water near metal surfaces to date predict a significant preference of oxygen-down configurations over hydrogen-down ones at zero electric field (e.g., [48,124,141-145]). The dipole orientation in the second layer is only weakly anisotropic (see also Fig. 7). 

London23 has treated the case of the attractive force between anisotropic molecules on the dipole-dipole interaction basis as well as on the monopole basis mentioned above. The small anisotropy found for the chlorine atom makes the dipole-dipole formulation appropriate. For the symmetrical orientation in the Cl2 molecule the London formula is... 

Let us imagine that the liquid cage is a spherical cavity in a continuous medium. When the molecule is in its centre, the orienting field is equal to zero. At this point the anisotropic part of the rotator-neighbourhood interaction appears only in the case of asymmetrical breathing of the... 

As has been noticed by Gelbart and Gelbart [7], the predominant orientational interaction in nematics results from the isotropic dispersion attraction modulated by the anisotropic molecular hard-core. The anisotropy of this effective potential comes from that of the asymmetric molecular shape. The coupling between the isotropic attraction and the anisotropic hard-core repulsion is represented by the effective potential... 

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