Molecular conformation, influence

Stereochemistry. Cyclohexane can exist ia two molecular conformations the chair and boat forms. Conversion from one conformation to the other iavolves rotations about carbon—carbon single bonds. Energy barriers associated with this type of rotation are low and transition from one form to the other is rapid. The predominant stereochemistry of cyclohexane has no influence ia its use as a raw material for nylon manufacture or as a solvent. 

Rotations around torsional barriers induce changes in chain conformation. For conjugated systems like polydiacetylenes, flow-induced changes in chain conformation can have a profound influence on the photon absorption and electronic conductivity properties of the material [73]. Flow-induced changes in molecular conformation form the basis for several technically important processes, the best known examples are the production of oriented fibers by gel spinning [74], the compatibility enhancement [75] and the shear-induced modification of polymer morphology [76]. 

Electrochemistry. The cyclic voltammogram of Compound 87a was measured and is compared to octa. S -benzyl porphyrazine, Ni[pz(A4)] A = difS -benzyl), 60a (from Section IV.B.l) in Table XXIV. Compound 87a has two reversible ring reductions, which are more positive than those measured for H2 pc and more negative than those measured for Ni[pz(.V-benzyl)8], 60a, suggesting that the conformational influences of the peripheral seven-membered ring make this pz harder to reduce than the pz with unconstrained peripheral thioethers. Because these compounds are of limited solubility and cannot be oxidized or reduced readily, they appear to be unsuitable for use as building blocks for molecular conductors. 

Strong evidence of the dominant Influence of molecular conformation on the properties of coals Is Implicit In the several data sets which show an extremum In the measured property when plotted against carbon rank. Examples are the extrema which occur In the solid state properties of mass density (22,23) and proton spin-lattice relaxation rate (24) as well as In solvent swelling and extractablllty ( ). 

It is noteworthy that most of the chemical shift values for all three polymers may be closely approximated ( ) by calculations based on data for monomeric reference compounds. These findings illustrate, therefore, the general validity of studies on low molecular weight model compounds for einalysis of spectra of carbohydrate polymers. Many examples of equally satisfactory comparisons of this kind are to be found in studies on other polysaccharides (11,23). These polymers include glucans (l6), mannans (2k, 2 ), limit dextrins (26), lichenin (2j), agarose (28) and various polysaccharides of fungal and microbial orgins (e.g., 7,8,29-31). Observed departures from expectation have been attributed to specific conformational influences ( 8). 

Emulsification is a stabilizing effect of proteins a lowering of the interfacial tension between immiscible components that allow the formation of a protective layer around oil droplets. The inherent properties of proteins or their molecular conformation, denaturation, aggregation, pH solubility, and susceptibility to divalent cations affect their performance in model and commercial emulsion systems. Emulsion capacity profiles of proteins closely resemble protein solubility curves and thus the factors that influence solubility properties (protein composition and structure, methods and conditions of extraction, processing, and storage) or treatments used to modify protein character also influence emulsifying properties. 

The conformational influence of Saa2, Saa3, and Saa4 on the peptide backbone of three cyclic peptides 27-29 (Figure 1) has been investigated in more detail by NMR spectroscopy, distance geometry (DG), and subsequent molecular dynamic (MD) calculations.1451... 

Small oscillatory torsions of molecular units within the segment produce a de-localization of the electronic density according to the Debye-Waller effect . In a very distorted structure as in the melt its smooth intensity distribution is not affected to a measurable extent. Rotational isomers, on the other hand, induce remarkable changes of the ru involved. Moreover, it is easily shown that the Boltzmann weighting factor of the molecular conformation ensemble also has a substantia] influence on the ru. It is strictly not possible to calculate the... 

Balakrishnan C, Gordon RJ (1975) Influence of molecular conformation and intermolecular interactions on turbulent drag reduction J Appl Polym Sci, 19 909... 

Dschagarowa E, Mennig G (1977) Influence of molecular weight and molecular conformation of polymers on turbulent drag reduction Rheol Acta 16 309... 

How Important is the Influence of Intermolecular H-Bonds on Molecular Conformation in the Solid State ... 

The rarity of the phenomenon of conformational polymorphism (one of the rare examples of conformational polymorphism is D,L-methionine (30)) is an indication that it is unusual for the crystal field forces to exercise a dominant influence on molecular conformation. It appears that the differences in the lattice sums of the crystal field forces for different conformations are in most cases an order of magnitude too small to induce conformational changes—i.e., tenths of kilocalorie per interaction rather than kilocalories. 

For polyelectrolytes, the salt concentration has a strong influence on the molecular conformation and the adsorption. The charges on the polymer repel each other electrostatically and in this way tend to elongate the chain. This elongation is reversible if a salt is added, the charges on the polymer chain are screened and the conformation becomes more compact (Fig. 10.9). Addition of salt has a similar effect as improving the quality of the solvent (see Section 6.7). As a result they tend to adsorb in a more bulky conformation. 

We consider now a class of models that introduce particle heterogeneity through random rate coefficients. In this conceptualization, the particles are assumed different due to variability in such characteristics as age, size, molecular conformation, or chemical composition. The hazard rates h are now considered to be random variables that vary influenced by extraneous sources of fluctuation... 

Kroon-Batenburg LMJ, Kanter JA (1983) Influence of hydrogen bonds on molecular conformation. Molecular mechanics calculations on a -D-glucose. Acta Cryst B39 749-754... 

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