Two-state structure

Structural solution obtained by minimization in the absence of distance constraint pseudoenergies. One state structural solution obtained by minimization with distance constraint pseudoenergies. Two state structural solution obtained by minimization with distance constraint pseudoenergies. 

In Figure 7, we present a stereo view of the superposition of the dominant conformers from the lowest energy two-state structural solutions, D A and D B and the one-state structural solutions B and C when all atoms in the oligosaccharide moiety of globoside were included in the comparison. In Figure 7, we also present... 

Figure 6. Ball and stick drawing of the dominant (1) and minor (2) conformers from the lowest energy two-state structural solution D A. (Reproduced from ref. 40. Copyright 1986 American Chemical Society.)...

From the data in Table VI and Figure 7, it is clear that the dominant conformer from the lowest energy two-state structural solution is quite similar to the lowest energy one-state structural solution, the chief difference being in the orientation of the terminal /3-D-GalNAc residue. We conclude, therefore, that structures which are similar to the lowest energy one-state structural solution A", represent the predominant conformer present in solution. The one-state procedure thus provides a reasonable and time efficient approach to structural analysis for this molecule. 

This does not mean that minor conformers and/or motional averaging are unimportant. The presence of even small amounts of minor conformers or limited conformational averaging as is suggested by the lowest energy two state structural solution could significantly affect the observed cross relaxation rate. The inverse sixth power dependence of the cross relaxation rate on interproton distance serves to strongly weight contributions from conformers with short interproton distances. Therefore the presence of even small amounts of conformers with short interproton distances can exert a disproportionate amount of influence on the observed cross relaxation rate. 

This is the case with the second reaction (with CHal). Because of this the solution will be in equilibrium between the two states (structures V VI). For the first reaction, this is not the case and it is essentially an irreversible reaction under the given conditions. The reversible reaction will yield a different product because there is a slow reaction which can occur under these conditions ... 

For the treatment of chain conformation problems in biomacromolecules such as two-state structural transitions to be discussed in the next section, a partition function can be constructed as follows ... 

The requirements for hydrogen bond preservation in the folded structure result in the cooperative formation of hydrogen-bonded secondary structure regions in proteins. The secondary structure specifies regular polypeptide chain folding patterns of helices, sheets, coils and tnms that are combined/folded into tertiary structure. Studies of two-state structural transition suggest that a statistical method can be developed to predict the... 

Another type of packing defect occurs when a "multi-state" structure is possible. This happens when each successive chain may enter the crystallite in any of several spatially different conformations. Thus, if a chain may be accommodated into the crystal lattice in either an "up" or a "down" position a two-state structure will result] if a side group may assume any of three different angular positions in the solid phase, then a three-state structure is possible. These defects may occur sporadically with low probability or they may occur randomly each time the opportunity presents itself. In the latter case it is likely that a statistical distribution of several different models will have to be invoked in order to obtain satisfactory agreement to the experimental data. 

Ise and coworkers [102 -104] studied solutions of charged latex particles by SAXS and ultramicroscopy. Their micrographs showed a particifiarly interesting phenomenon, the formation of a two-state structure. Within hours after the sample preparation, a dense, ordered phase is formed coexistent with a dilute disordered phase. Using video-techniques, Ise and coworkers were able to study the Brownian motion of the particles in the ordered and disordered phase, thus obtaining information about the dynamics of lattice defects, motion of single particles around their lattice position, and the dynamics of particles at the interphase between the ordered and disordered regime. 

Motion along Xi stretches the intermolecular N-H distance whereas displacement along X2 causes an out-of-plane pyrazoline ring distortion, both translations lifting the degeneracy between the two states. Structural evolution along both displacements is illustrated in O Scheme 39-8. Translation along Xi leads to the radical pair (RP) while displacement... 

Bragg Spacing and Average Spacing The Two-State Structure... 

Hi y simpHfkd sctematic fepresentation of the two-state structure . The circles imlicate ma[Pg.200]

For latex dispersions, the two-state structure has been confirmed by microscopy. In polyelectrolyte solutions it has been inferred from the fact that 2D xp < 2Do as described in Sect. 2. However, the size of the ordered duster was not estimated. For polyelectrolyte solutions, the intermoleculm- distmice calculated from the Bragg peak position was of the order of 100 A. Hence, it may be a reasonable estimate that the size of the polyel arolyte cluster would be of the order of several thousand A to several micrometers. Because the USAXS intensity was not sufficiently high enough for solutions of ionic polymers such as NaPSS, we determined the size of the duster by using neutron scattering [65]. In the following the SANS measurements for NaPSS-D20 solutions are described. 

In our original paper, d was assumed to be 1.576 and it was found that 2D p values were very dose to 2Do values, indicating the one-state structure. This seemed to be reasonable in Ught of the low charge density of the particles. Further study is certainly necessary to reach the final conclusion as to which of the two-state structure or the one-state structure is real for this system... 

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