Effect of flexibility

This is called the Kratky-Porod model, and the length (2A) is referred to as the persistence length. 

Equation (8.173) indicates the analogy between the change of (.y) of the Kratky-Porod model and the time evolution of u(i) in rotational Brownian motion both processes are Gaussian with the constraint 1,2 = 1,35 pjqjj gqn (g.i74) it can be shown that for small s 

To develop a complete theory for the dynamical properties is difiicult, but various approximate treatments have been proposed. Crudely speaking, the flexibility affects the dynamical properties in two respects. 

Firstly, the flexibility changes the transport coefficients. As the size of the chain decreases with the increase in the flexibility, the diffusion constant Do, which is roughly proportional to increases, and the 

Secondly, the flexibility gives a relaxation in the high-firequency region. For example, according to the rigid rod model, the complex intrinsic viscosity [ (a )] approaches the finite value 

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Optical and electro-optical behavior of side-chain liquid crystalline polymers are described 350-351>. The effect of flexible siloxane spacers on the phase properties and electric field effects were determined. Rheological properties of siloxane containing liquid crystalline side-chain polymers were studied as a function of shear rate and temperature 352). The effect of cooling rate on the alignment of a siloxane based side-chain liquid crystalline copolymer was investigated 353). It was shown that the dielectric relaxation behavior of the polymers varied in a systematic manner with the rate at which the material was cooled from its isotropic phase. 

It is not known if the effect of flexibility is an equilibrium or kinetic effect. The flexibility might allow the compounds to expand or contract to fill available space in the VP1 hydrophobic pocket. Alternatively, the flexibility may allow the compounds to achieve a conformation required to enter or leave the pocket, but this conformation would not be seen in the crystallographic experiment. If this is true, modeling of the equilibrium structure of compounds in the pocket will not be accurate predictors of compound potency. 

Portoghese and coworkers also considered other naltrindole derivatives substituted in position 6 or 7 with aryl, benzyl or aniline moieties to evaluate the effect of flexible aryl groups on selectivity, but obtained non-selective compounds only. This result demonstrates that the conformational flexibility of these aryl groups causes them to reside preferentially in regions of space that are not accepted by the 8 opioid receptor (Portoghese et al., 1994). A more rigid compound however, 7-benzylidene-naltrindole (BNTX) proved to be a potent and highly... 

The opioid alkaloids are classic examples of non-peptide ligands that have later been discovered to be mimetics of endogenous peptides. For example, morphine 5 (Figure 1.4.3) imitates the effect of flexible peptides, for example Met-enkephalin 4, at the common recognition site of the receptor for both compounds... 

Haouas, M., Kogelbauer, A. and Prins, R. The effect of flexible lattice aluminum in zeolites during the nitration of aromatics, Stud. Surf. Sci. Catal., 2001, 135, 2113-2120. 

More recent studies on the effect of flexible spacers now include the use of either poly(ethylene oxide) or polysiloxane segments. Each such spacer brings with it certain unique characteristics to the final polymer, and it is clear that the role of the spacer... 

The expoimental data on the non-steady state Ken effect of flexible-chain polymers dissolved in solvents with moderate viscosities reveal that at frequences up to lO Hz no dispersion of B is observed (just as in solutions of low molecular weight substances and monomers). This is also an indication of mutually independent orientation of single monomer units in the electric field which is only sightly related to the structure and conformation of the polymer chain as a whole. 

Figure 6. Excitation spectra of synthesized PMDA and 6FDA based polyimides with same cure history indicating effect of flexibility of diamine on relative intensity of PMDA-ODA vs PMDA-IPDA and effect of flexible dianhydride on spectral structure and relative intensity of PMDA-IPDA vs 6FDA-IPDA.

We next provide an approximate method to estimate the effects of particle flexibility (the fact that the elastic moduli of the dispersed particles are not infinite). Assuming that the effects of flexibility can be described completely by making 4>m0 a function of flexibility, calculated so that as y—the flexibility effects vanish in the same manner as < > —> d>ocp, we use Equation 13.43 where P is a flexibility parameter ranging from 0 in the limit of infinite rigidity to 1 in the limit of complete flexibility, with Equation 13.44 where E is Young s modulus (in MPa, for consistency with how the equation was calibrated to obtain the factor of 22.5) which is valid for both cylindrical fibers of aspect ratio Af>l and cylindrical platelets of aspect ratio (1/Af)[Pg.574]

P-22 - The effect of flexible lattice aluminum in zeolites during the nitration of aromatics... 

Figure 8. Effect of Flexible Oxygen Linkage on Rigidity...

Recently, the effects of flexible and rigid caps introduced to the primary rim of y-CD (50a-d, 57a-c) on the photodimerization of AC were investigated, as capping is known to significantly modify the binding and reaction behavior of native CDs. " The chemical... 

In discussing the influence of steric features on mechanical properties, it is convenient to consider the side chains and the main chain separately. The effects of flexible side chains differ completely from those of stiff side chains. Long, flexible side chains reduce the glass transition temperature, while stiff side chains increase it. Long, flexible side chains increase the free volume and ease the steric hindrance from neighboring chains and as such facilitate the movement of the main chain. Figure 13.28 illustrates... 

The polemic also spread out to U.S.A., where the Vice President decided to order a rigorous investigation regarding the health effects of flexible PVC. Results obtained by the American Council on Science and Health were pubhshed in June 1999. The use of DINP in toys was favored ...Based on its review of available scientific data and exposure estimates for DINP, the panel concludes that DINP in flexible toys is unlikely to pose a health risk to children... . In spite of all the work done so far, various associations show little confidence in reports, arguing that scientists may have been influenced by PVC manufacturers. 

Huiskes, R., Weinans, H., and van Rietbergen, R. (1992), The relationship between stress shielding and bone resorption around total hip stems and the effects of flexible materials, Clin. Orthop. 274 124-134. 

This is because the sample, especially the central portion will be denser under the strong constraints of the rigid boundary. In addition, two volume strain curves of the specimen with the same rock block shape under different boundary types are almost coincide at the very beginning stage which means that the effect of flexible boundary is not obvious when the deformation is small. 

The effect of flexibility of the zeolite on the diffusivity A flexible zeolite yields better results with smaller molecules and lower loading (number of atoms per unit cell of the sorbate molecules). 

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