Molecular semi-flexible

Another viable method to compare experiments and theories are simulations of either the cell model with one or more infinite rods present or to take a solution of finite semi-flexible polyelectrolytes. These will of course capture all correlations and ionic finite size effects on the basis of the RPM, and are therefore a good method to check how far simple potentials will suffice to reproduce experimental results. In Sect. 4.2, we shall in particular compare simulations and results obtained with the DHHC local density functional theory to osmotic pressure data. This comparison will demonstrate to what extent the PB cell model, and furthermore the whole coarse grained RPM approach can be expected to hold, and on which level one starts to see solvation effects and other molecular details present under experimental conditions. 

It was this widespread, but misplaced, belief which caused the controversy over the interpretation of the observed rapid intra-molecular ET rates (= 107 s-1) in the radical anion of the semi-flexible traw.v-dinaphthyl-cyclohexane system 3(7), where the number in parentheses refers to the number of C-C bonds in one of the relays of the hydrocarbon bridge connecting the pair of chromo-phores.50 The observed rapid ET rate was tacitly attributed to a TS mechanism, rather than to a TB mechanism, even though the two naphthalene rings are about 7 A apart (edge-to-edge). A TS mechanism was likewise advanced to account for the observed rapid intra-molecular ET occurring in the radical anion of 4(6).51... 

The conformation parameter a (=A/Af, where Af is A of a hypothetical chain with free internal rotation) for cellulose and its derivatives lies between 2.8-7.5 2 119,120) and the characteristic ratio ( = A2Mb//2, where Ax is the asymptotic value of A at infinite molecular weight, Mb is the mean molecular weight per skeletal bond, and / the mean bond length) is in the range 19-115. These unexpectedly large values of a and Cffi suggest that the molecules of cellulose and its derivatives behave as semi-flexible or even inflexible chains. For inflexible polymers, analysis of dilute solution properties by the pearl necklace model becomes theoretically inadequate. Thus, the applicability of this model to cellulose and its derivatives in solution should be carefully examined. 

Urethane foams can be classified into two principle types, i.e., flexible and rigid foams. In some cases, flexible foams can be further subdivided into flexible and semi-flexible (or semi-rigid) foams. The differences in physical properties of the two foams are mainly due to the differences in molecular weight per cross-link, the equivalent weight and functionality of the polyols, and the type and ctionality of the isocyanate. 

The initial interest in liquid crystal dimers was triggered, therefore, by the similarity of their behaviour to that of the semi-flexible main chain liquid crystal polymers. It soon became apparent, however, that the dimers are of significant fundamental interest in their own right and exhibit quite different behaviour to conventional low molar mass liquid crystals. These studies, for example, have resulted in the discovery of a new family of intercalated smectic phases. This review focuses upon the novel behaviour of dimers and how it may be understood at a molecular level. 

Theoretical considerations are rare for the concentration dependence of LC cellulos-ic/solvent systems and the same is true for experimental studies. In many instances it is difficult to keep a constant concentration over a longer time during which experiments are carried out. If a functionality P=kc " is assumed k a constant, c concentration, m a variable that might depend on the stiffness of the molecules as well as on the solvent, the temperature, and the molecular mass), the value of m is 2 for somewhat stiff LC poly-y-benzyl-L-glutamate in dioxane and 3 for semi-flexible LC HPC in water. A detailed study of LC CTC/MAA [17] led to a value of m=2.4 for lower concentrations between 38 and 44 wt%, independent of the temperature. At a higher concentration of 44-50 wt%, a value of m = 1.1 at 20 °C was determined, which increases... 

Berry, G. C., Crossover behavior in the viscosity of semi-flexible polymers intermolecular interactions as a function of concentration and molecular weight, J. Rheol., 40, 1129-1154 (1996). 

PROPERTIES OF SPECIAL INTEREST Polymer model for a semi-flexible macromolecular chain material. Stiff-chain solution characteristics due to helical configuration liquid crystalline properties and molecular weight dependent chain dimensions in solution. ... 

For the present edition, we have modified the text in many places and have written new chapters on polymer synthesis, protein folding, polymer knots and new sections on molecular motors, semi-flexible and worm-like polymers, and several others. We have included many new figures. Overall, about 50% of the book is new. 

DNA is a highly charged, semi-flexible polyelectrol)Ae. In eukaiyotic cells, DNA chains are packed inside the microscopic volume of the nucleus in an ordered, yet dynamical way. To overcome the electrostatic repulsion that hinders compaction, DNA molecules associate with a variety of counterions and proteins to condensate into a hierarchical and tunable architecture named chromatin. Besides DNA condensation, chromatin also plays a key role in gene regulation by making DNA accessible for transcription in a dynamical and specific way. Consequently, understanding the physicochemical properties of DNA chains at the molecular and mesoscopic scales is a required step to elucidate how cells regulate... 

Bohdanecky found that published data on many semi-flexible polymers fit eq 3.5. Figure 5-8 shows this with the data [40] for poly (tere-phthalamide-p-benzohydrazide) (PPAH) in dimethyl sulfoxide (DMSO). The linear relation as observed here permits unequivocal estimation of I and S. If we have one more relation among q, Ml, and d, it becomes possible to determine these three unknowns. Molecular weight dependence data of (5 ) or / may be utilized as such an additional relation. Bohdanecky [39] proposed the use of the relation... 

One can describe polymer samples in a similar way. First of aU, a polymer chain possesses semi-flexibility, that characterizes the intra-chain interactions for the most stable conformation persisting along the chain axis. Secondly, a polymer chain also holds complex inter-chain interactions. These two intrinsic characteristic factors dictate the basic physical behaviors of the same species of polymers. Besides these two intrinsic factors, each individual polymer sample possesses certain extrinsic characteristic factors, i.e., molecular weights and their distributions, topological architectures, and sequence irregularities. These extrinsic characteristic factors are also important in determining the physical behaviors of the polymer samples. 

The stronger binding of Ca + than Na+ by chondroitin sulphate indicates that the association cannot be ascribed solely to electrostatic forces. Sedimentation coefficient and intrinsic viscosity measurements have indicated that chondroitin sulphate in solution can be represented by a semi-flexible coil with a molecular diameter of about 1.2 nm, a value which is consistent with the results of A -ray analysis. ... 

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