Conformational symmetry

Of course the conformational symmetry breaking may appear or disappear depending on the level of sophistieation of the eomputation, which may unduly favor one term of the crucial (relaxation/resonance) ratio. As an example we would like to mention an open... 

Ultraviolet/visible absorption, fluorescence, infrared and Raman spectroscopies are useful for studying structures (configuration, conformation, symmetry etc.) of electronically ground and excited states of linear polyenes, which have attracted much attention of... 

The first structure of an Ned motor domain (Sablin et al., 1996) was that of a monomeric construct (amino acids 335-700) including only part of the neck (amino acids 328-348). Later, several crystal structures of dimeric constructs were published. These constructs dimerize by coiled-coil interaction of the neck/stalk helices. The PDB database now contains three crystal structures of dimeric DmNcd constructs that differ mainly by the overall conformation (symmetry) of the dimers, whereas the individual motor domains are very similar in all known structures. 

The conformational symmetry is maintained such that all protomers of the protein must be in the same conformation, either all T or all R at any instance. Therefore, a protein with n subunits is limited to only two conformational states, T and R . Thus only a single equilibrium constant L = T / R is sufficient to express the equilibrium between them. 

There is no requirement for conformational symmetry therefore mixed conformations are permitted. The stability of any particular state is determined by a product of equilibrium constants including a term Kt for each subunit in the B conformation expressing the free energy of the conformational transition from A to B of an isolated subunit, a term KAB for each contact between a subunit in the A conformation with one in the B conformation, and a term ABB for each contact between a pair of subunits in the B conformation. 

This general rule would seem to have some exceptions, as in the case of the /V-(p-chlorobenzylidene)-p-chloroaniline (B ACL), in which the crystal imposes on the molecule a conformational symmetry which the isolated molecule does not possess [7J5],... 

Conformal symmetry is very common in nature e.g. we can find it in the nautilus shell and the sunflower. These structures are clearly ordered, even if they do not give sharp diffraction patterns. Here the repetition is non-Euclidean, on a logarithmic spiral (nautilus), or on a torus (sunflower). We are inclined to say that any kind of repetition, conformal or isometric, even in non-Euclidean space, is ordered. However, classification of these more chaotic structures, as for liquids, is less certain. It may be that a liquid can be described as a structure with some of the characteristics of conformal symmetry or perhaps by a representation even more exotic, like a manifold of constant negative curvature. 

Table 1.2. Simple symmetry operations and conforming symmetry elements...

Molecules in LCPs may develop correlated rotations about their chain axes, or correlated side chain rotations may develop, over optically resolvable distances. The optical properties of a correlated domain depend both on the configurational and conformational symmetry of the individual molecules and on the extent to which this symmetry is preserved on a larger scale by the correlations. 

Role in Nature, Hydrate Form, Unit-Cell Type and Conformational Symmetry of Various Polysaccharides... 

In the A conformers (symmetry 2/1) the 9-9 ethylenic moiety remains planar while the benzene rings are rotated about the single bonds of the ethylenic system. 

B. Strong Segregation Theories Conformational Symmetry and Asymmetry Microphases and Microdomains of Neat Copolymers... 

Eqs. (8.2) and (8.3) is that the effective interaction between two sites on the polymer depends on their instantaneous position, and only on the entire macromolecule conformation in an average (implicit) sense via the direct and collective pair correlations. This simplification does not preclude describing situations of broken conformational symmetry, such as polymer collapse, solvated electron localization, or spatially inhomogeneous conformational characteristics such as occur in star polymers (see Section IX)... 

Table 11.4 Optimized singlet and triplet geometry of acrolein (jtrans conformer, symmetry B3LYP/6-311++G level), with net shifts As t- ...

Conformer symmetry and geometry, equilibrium ratios of con-formers, barrier heights and conversion rates can be analysed by many techniques, mainly diffraction and spectroscopic experiments. Examples are given in a short review by Woldbye and Rasmussen . ... 

---