Conformational features

These chromisms were first recognized for a series of polydiacetylene [39] and polysilane [40] compounds. In these systems, extent of the disorder can be mea-smed by deviation from the fully-stretched aM-trans backbone conformation [41]. In the case of the poly thiophene and its derivatives, the conformational disorder is caused by the distortion around the cr-bonding interconnecting the thiophene rings [42]. The TT-delocalization along the polythiophene backbone will be maximized when the polymer chains assume the fully-stretched S-anti form. This delocalization will be hampered by the ring distortion of any amount. 

Similar spectral change can also be noticed when poor solvent is added to the system (solvatochromism). The color change caused by dissolving the polymer or removing the solvent from the polymer solution can also be referred to as the solvatochromism [38], 

Recently Leclerc et al. [45] and Sandstedt et al. [46] reported essentially the identical features using the regioregular polythiophenes. They found that both in solids and solutions those polymers display dramatic thermochromism. The 

The manifestation of the ordered phase in the solution is remarkable considering that dissolution of the materials in general brings about the disorder. This obviously explains how important role the energy stabilization due to the 7r-delocalization plays. At the same time, a sharp transition noted in Fig. 5 is contrasted with the spectra observed in the solid phase [5] where the transition is broadened. 

The aforementioned chromisms obviously indicate that no matter what processes and driving forces are responsible, the conformational change or transition of the TT-conjugated backbone is the major origin of the dramatic color change. In this 

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The conformational features of six membered rings are fundamental to organic chemistry so it is essential that you have a clear understanding of the directional prop erties of axial and equatorial bonds and be able to represent them accurately Figure 3 17 offers some guidance on the drawing of chair cyclohexane rings... 

The proposal of multiple crystalline forms in native celluloses implies that all native celluloses are compositions of two distinct forms, which has been earlier indicated for Acetobacter and Vallonia celluloses, 8). From the resolution of the NMR spectra an estimate of about 60-70 % of the la form in Acetobacter cellulose and of 60-70 % of the lb form in cotton was obtained. A further detailed analysis of conformational features in celluloses seemed to need X-ray diffractometric and Raman spectroscopic confirmation 19-56). 

Using NMR and CD studies,1 2 the conformation features were deduced (Pig. 1). 

In comparison, both the free ligand and the dinuclear Cu(I) cryptate of an analogous macrobicyclic structure possessing a diphenylmethane group as a central unit display only two resonances for the CH2CH2 fragment, as is the case here only for the complexes 91 and 92. This points to the special conformation features of the free macrobicycles 89 and 90. 

Studies on the Conformational Features of Neomycin-B and its Molecular Recognition by RNA and Bacterial Defense Proteins... 

Conformational Maos and surfaces. The conformational maps in Figures 3 and 4 are very small sections of the true conformational surfaces of 136 dimensions (3 coordinates per atom plus one for the energy). The special choice of

[Pg.188]

One result from the analysis of the MD simulation was the proposal of a new enzymic pathway for hydrolysis by lysozyme. We begin with a description of the alternative mechanism, and the basis on which it was proposed. The energetics of the individual GlcNAc units in the lysozyme cleft are then presented, followed by a graphical representation of the correlation between the atomic fluctuations of the substrate and those of the enzyme. Of particular interest is the fact that the binding interactions stabilize a bound state conformation for the two glycosides involved in hydrolysis that is optimum for catalysis by the alternative mechanism and which differs from the conformations of the other glycosides. These conformational features are described in the final two sections. 

However, the strikingly rapid development of instrumental analysis, and especially the NMR and X-ray techniques, has provided the possibility of investigation of these stereostructures, which contain several chiral centers possessing much more complicated steric and conformational features than... 

As a test of this hypothesis we decided to explore conformationally restricted auxiliaries such as 87 (Figure 26).48 We recognized that as long as the tartrate unit is held within an eight membered ring, the critical conformational features discussed for B become structural constants in D. 

Conformational feature in which a loop connects two parallel stems belonging to the same crystal. 

This section is about alkylcyclohexanes and related polycyclic molecules consisting of chair six-membered rings. Our work must thus accommodate conformational features such as those commonly described as hutanc-gauche interactions. 

Key conformational features of this model believed important for biological potency Include Phe-D-Trp-Lya-Thr and Thr-Phe-Pro-Phe B-turns of Types II and VI, respectively, the latter containing a els peptide bond between Phe and Pro. The model of 3b is very similar with N -methyl alanine replacing proline... 

Although abundant evidence supports the existence of snch an antoimmnne phenomenon, the causative event that heralds this self-directed immune-mediated attack remains uncertain. A number of mechanisms have been proposed to afford a molecular-level explanation of autoimmunity. One such explanation is molecular mimicry. Molecular mimicry occurs when a protein associated with a foreign substance bears structural similarities to a protein found in the host. For example, if a person experiences an infection from bacteria, there is a possibility that a protein in the bacterium shares certain similar geometrical and conformational features with a protein already existing in the person. Thus, an immune response directed against the bacteria will cross-react with organs in the host organism. 

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