Chains internal mobility

As noted previously, internal mobility along a carbohydrate chain is more pronounced if one end of the chain-like molecule is fixed by chemical or physico-... 

One of the most widely used tools to assess protein dynamics are different heteronuclear relaxation parameters. These are in intimate connection with internal dynamics on time scales ranging from picoseconds to milliseconds and there are many approaches to extract dynamical information from a wide range of relaxation data (for a thorough review see Ref. 1). Most commonly 15N relaxation is studied, but 13C and 2H relaxation are the prominent tools to characterize side-chain dynamics.70 Earliest applications utilized 15N Ti, T2 relaxation as well as heteronuclear H- N) NOE experiments to characterize N-H bond motions in the protein backbone.71 The vast majority of studies applied the so-called model-free approach to translate relaxation parameters into overall and internal mobility. Its name contrasts earlier methods where explicit motional models of the N-H vector were used, for example diffusion-in-a-cone or two- or three-site jump, etc. Unfortunately, we cannot obtain information about the actual type of motion of the bond. As reconciliation, the model-free approach yields motional parameters that can be interpreted in each of these motional models. There is a well-established protocol to determine the exact combination of parameters to invoke for each bond, starting from the simplest set to the most complex one until the one yielding satisfactory description is reached. The scheme, a manifestation of the principle of Occam s razor is shown in Table l.72... 

The experimental spectrum, which has been taken after a single 12 h freezing step, shows narrow lines superimposed on a solid-state spectrum for the polymer. The result was reproduced by a simulated spectrum based on data for an aliphatic chain (Table 1) assuming two fractions of different mobility. Fraction A represents the dehydrated solid and is merely subject to particle tumbling at a rate which is expected for particles of a = 50-70 nm in aqueous dispersion (r = 0.1 ms). Fraction B represents the particles with the gel matrix in this case, the molecular reorientation is dominated by the internal mobility which is assumed to be equivalent to an isotropic tumbling of a short correlation time... 

Measurements of i N iH -NOEs, and longitudinal and transverse spin relaxation times can provide supplementary information on the globular PrP domain in the form of data on the internal mobility along the polypeptide chain (Peng and Wagner, 1992). Furthermore, realtime... 

Besides using side chains, internal double bonds were added among thiophene rings to produce a more soluble derivative. Bis(bithienylethenyl)thiophene was spin-coated from N-methylpyrrolidone solution [33]. The mobility was reported as 0.0014 cmWs. 

The large deformability of elastomeric materials is due to the pre sence of a certain internal mobility that allows rearranging the chain orientation, the absence of which in linear chain plastic materials (at normal temperature) constitutes the essential difference between die two groups. Polyethylene, which has" weak mter-... 

Side chains (even when modeled as single-interaction spheres) should have some conformational freedom that reflects their internal mobility in real proteins. Pairwise interaction potentials should be as specific as possible, and in the absence of explicit solvent, a burial potential that reflects the hydrophobic effect may be necessary... 

A new transversal correlation length is established at about 37 % strain. By shearing the lamellar blocks break down to a size which later represents the dimensions of the fibrils. According to the relatively low internal mobility the aligned chains are not able to form new crystallites. Their mean dimension in transversal direction is with 8.4 nm clearly below the lamellar thickness. This correlates with the WAXS results, which also indicate the final disappearance of the lamellar transversal order during cold drawing. Ultimately, at high strains, this transversal correlation dominates the whole CDF. 

The extensibility of the swollen objects depends on the conditions of preparation and on the degree of swelling, but lies in the order of magnitude of 100% (for the air-dry filaments, which contain about 15% water, the extensibility is usu Jly smaller and below 100%). Fully dried filaments cannot be extended at all, they are hard and brittle as glass and can be pulveris ed in a mortar. The presence of water is essential in order to make a cellulose gel deformable. Dry cellulose is comparable with rubber cooled to temperatures far below 2 ero, say — 100°. In both cases the cohesion between the chains is so considerable that there is no more question of an internal mobility, which is essential in order to render large deformations possible,... 

Measurements of Smyth and Walls on long saturated hydrocarbon chains, carrying two equal dipoles at their ends, have shown in fact that, within the limits of error of the method, the total moment fulfills the requirement of equation 14 (see Table 32). These molecules clearly form no rigid, flat zig-zag chain in the dissolved or liquid state, but exhibit a certain internal mobility. These results are thus in excellent agreement with previous ideas on the behavior of long hydrocarbon chains. 

If, however, we desire the ends of the chain to be at some other distance apart, e.g. a distance r, when r < r ax, this can be effected in a number of different ways indeed, because of the internal mobility of the chain, we may arrange the individual links in many different ways and still have the two terminal C atoms separated by the distance r. If we imagine a large number—say, 1000—of such chains scattered at random on the floor, and then measure the distances between the ends for every chain and draw up statistics, it is very unlikely on grounds of probability that the maximum distance will be found frequently, since it can be obtained only in one way any shorter distance can be obtained by a large number of configurations and will, consequently, be found much more frequently in actual conditions. 

Up to now we have confined our considerations to the behavior of an isolated chain molecule with a certain amount of internal mobility. We may summarize by saying that this preliminary study gives a) A range of elasticity of the correct order of magnitude ... 

The present short treatise, which is intended merely to illustrate general principles of internal molecular statistics and to indicate their application to rubber elasticity, was chosen in view of this latter point and of the possibility of explaining certain features of the viscous flow of high polymeric substances (compare page 290). It may, however, be remarked that many other characteristic constants of high polymeric substances— osmotic pressure, double refraction etc.—are related to the internal mobility of long chain or reticulate structures. 

This corresponds to the equation (17) on page 74 and shows that rather considerable entropy gains are to be expected if long chain molecules, after being frozen in a lattice-like arrangement, are liberated and acquire their full internal mobility. 

Summarizing, we may say Vapor pressure and osmotic measurements both point to the probability that long chain molecules, under certain conditions, have a high internal mobility in solution and certainly do not behave as stiff rods. 

For a simple understanding of equation (105) it seems much more feasible to assume a certain internal mobility of long chain particles. H. Mark 2 suggested this possibility W. Kuhn, simultaneously with E. Guth, formulated it quantitatively, I. Sakurada, Hess and Philippoff and, especially, Huggins have recently carried out an exhaustive examination on a large amount of experimental material. 

R. Richarz, K. Nagayama, K. Wiithrich, Carbon-13 nuclear magnetic resonance relaxation studies of internal mobility of the polypeptide chain in basic pancreatic trypsin inhibitor and a selectively reduced analog. Biochemistry 19 (1980) 5189—5196. 

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