Chain dimensions Temperature dependence

The 140-residue protein AS is able to form amyloid fibrils and as such is the main component of protein inclusions involved in Parkinson s disease. Full-length 13C/15N-labelled AS fibrils and AS reverse-labelled for two of the most abundant amino acids, K and V, were examined by homonuclear and heteronuclear 2D and 3D NMR.147 Two different types of fibrils display chemical shift differences of up to 13 ppm in the l5N dimension and up to 5 ppm for the backbone and side-chain 13C chemical shifts. Selection of regions with different mobility indicates the existence of monomers in the sample and allows the identification of mobile segments of the protein within the fibril in the presence of monomeric protein. At least 35 C-terminal residues are mobile and lack a defined secondary structure, whereas the N terminus is rigid starting from residue 22. In addition, temperature-dependent sensitivity enhancement is also noted for the AS fibrils due to both the CP efficiency and motional interference with proton decoupling.148... 

Extensive studies of the temperature dependence of the PD have been made by DXS and neutron scattering experiments.34-36 The PD at room temperature is incommensurate with the basic lattice with a repeat distance of 6.67 dpt—pt. At room temperature there is little correlation between the chains whereas at 37 K the PD/CDWs are partially ordered in three dimensions. At 80 K the correlation length along the chains is over 100 Pt atoms whereas the interchain correlation length is only about five interchain spacings.35... 

Fig. 34. Temperature dependence of the unperturbed chain dimension A, estimated by method 2B (Eq. (32)), for a cellulose diacetate (CDA) fraction in acetone (open circles), and of the number of the solvating solvent molecules at infinite dilution si of a CDA whole polymer in acetone (black circles) 7)...

CD molecules are partially free draining chains and the negative temperature dependence of the limiting viscosity number fn] can be attributed to the temperature dependence of the unperturbed chain dimension A. 

The parameter C is often considered independent of temperature and it has been shown to take a universal value of 0.0894 for long-chain hydrocarbons (Cutler et al., 1958). Nanda and Simha (1964) obtained excellent correlations for a number of polymers using this value of C. This value was therefore retained in the Handbook. The parameter B has the dimensions of pressure, but it is a function only of temperature. Different forms have been used in the literature to describe this temperature dependence, but the exponential form has proven to be a reliable representation. Thus B(T) is given by... 

The degree of chain expansion also depends on %, hence temperature (Equation 11-58). Clearly, as % approaches values of 1/2, a tends to zero and the chain becomes ideal. Flory reorganized his expression for the interactions in terms of a parameter, 6, and the temperature at which deviations from ideal chain dimensions occur is thus called... 

In this section we consider experimental results on the dependence of on molecular weight, polymer chain dimensions and architecture (whether linear or branched), temperature and diluent. We cast our results in forms suggested by theory whenever practicable. The existing theoretical calculations of 7j and comparisons with the empirical relations are reviewed in section 3. 

It has been established that Ko normally is independent of the solvent and the molecular weight of the polymer, though often dependent to some extent on the temperature. It is therefore possible to deduce values for the expansion factor in good solvents from intrinsic viscosities measured in them. From Eqs. (3.181) and (3.184) the linear expansion factor a.jj, which is a measure of long range interactions and pertains to hydrodynamic chain dimensions, is thus given by... 

Toxicity of many substances, their biological uptake and hpophilic storage in the body, their bioconcentrations (movements through the food chain resulting in higher concentrations), and so forth, as well as their fate in the environment can be predicted from their octanol/water partition coefficients, Poet-The partition or distribution coefficient of a substance is the ratio of its solubility in two immiscible solvents. It is a constant without dimensions, and depends on the temperature and pressure. Thus,... 

The annealing temperature dependence of such a surface mobile layer will now be discussed. At 370 K, the thickness of the surface mobile layer was 10 2.8 nm. It should be of interest to compare the thickness with the chain dimension. Twice the radius of gyration (2/fg) of an unperturbed PS with Mn of 29k is calculated to be 9.3 nm. This value is comparable to the surface layer thickness. At 365 and 355 K, the interfacial thicknesses similarly increased with time at first and then became invariant with respect to the annealing time, as shown in Fig. 8c, d. The evolved interfacial thickness at 365 and 355 K were 9.6 2.5 and 11.4 0.9 nm, respectively. Half of these values, namely surface mobile layer thicknesses, are much... 

To obtain a more quantitative picture of the temperature dependence of tr and R IR, specimens of TPBIO were dissolved in a proprietary mixture of low-molar-mass nematics, designated E5, which has a broad nematic temperature range [Chiang et al., 2000]. Experimental results for two TPBIO specimens having DP= 18 and 63 are shown in Eigure 1.10. Eirst, the temperature dependence of R and R may be considered in the context of pertinent statistical theories. An analysis by Halperin and William [1992] of the conformation of main-chain LCPs using an Ising chain model led to the conclusion that the chain dimensions, and R , each exhibit exponential temperature dependence ... 

Temperature dependence of the unperturbed dimensions of chains, d i. i )oldT... 

KUB Kubota, K., Kubo, K., and Ogino, K., The pressure and temperature dependence of the second virial coefficients and the chain dimensions of polydimethylsiloxane solutions. Bull. Chem. Soc. Japan, 49, 2410, 1976. 

Macromolecular desorption from a surface As briefly described above, in this situation we are applying a force perpendicular to an adsorbing surface to which a polymer chain is attached. At low temperature, surface attraction dominates, but at high temperatures entropy dominates, and the polymer is free of the surface. The temperature dependent force needed to extend the polymer is calculated. Let the polymer have N monomers, of which n lie in the surface. (In two dimensions the surface is a line). Let CN n, z) be the number of such SAW whose endpoint is at perpendicular distance from the surface. The model may be described by the partition function... 

A feature of chain dimensions is their temperature dependence that is expressed in terms of... 

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