Side-chain motions

An important characteristic of biomolecular motion is that the different types of motion are interdependent and coupled to one another. For example, a large-scale dynamic transition cannot occur without involving several medium-scale motions, such as helix rearrangements. Medium-scale motions cannot occur without involving small-scale motions, such as side-chain movement. Finally, even side-chain motions cannot occur without the presence of the very fast atomic fluctuations, which can be viewed as the lubricant that enables the whole molecular construction to move. From the point of view of dynamic... 

The relaxation data for the anomeric protons of the polysaccharides (see Table II) lack utility, inasmuch as the / ,(ns) values are identical within experimental error. Obviously, the distribution of correlation times associated with backbone and side-chain motions, complex patterns of intramolecular interaction, and significant cross-relaxation and cross-correlation effects dramatically lessen the diagnostic potential of these relaxation rates. 

Fig. 22. Relaxation map for PBLG side chain motion. Experiments except 2H NMR measurements are open symbols, and PBLG-Kdi (filled circle) and PBLG-fd2 (filled triangle).

The jump rates obtained by the line shape simulations are plotted on the relaxation map in Fig. 22 together with values obtained by other experimental methods. The points of the mechanical and dielectric relaxations correspond to the process of the large-scale side chain motions refered to as the -process and follow the WLF equation very well above Jg,. 11 It should be noted that the present 2FI NMR results are located on the curve obtained by other relaxation experiments. This fact shows that... 

The symbols have their usual meanings (] ). From measured values of NTj and ri on a poly (butene-1 sulfone) of degree of polymerization 700 the values of t (in nanosec.) shown in Table III are obtained. The discrepancy between the values of from NT and from ri, particularly marked for the side-chain motions, indicates the inadequacy of the single-Tg model. Nevertheless it is evident that the backbone motions are relatively rapid. (Comparison to polybutene-1 (jW) shows that SO2 groups retard the motion of the copolymer chains by a factor of about 50.) The question now becomes why are these rapid motions NMR-active but dielectrically inactive One possible type of motion which would account for this is shown in Fig. 9. Five backbone bonds and six main-chain atoms are involved, i.e. the sequence C-S-C-C-S-C, with concerted segmental transitions about two C-S bond, allowing interconversion... 

Correlation Times for Backbone and Side-Chain Motions in Poly(but-1-ene sulfone) of P = 700 as a 25% w/v Solution in Chloroform-d, Deduced from the Simple Isotropic Single-T Motional Model... 

Poly(Propylene). In principle, resolution of individual carbon resonances in bulk polymers allows relaxation experiments to be performed which can be interpreted in terms of mainchain and side chain motions in the solid. This is a distinct advantage over the more common proton NMR relaxation experiments where efficient spin-diffusion usually results in the averaging of the relaxation behavior over the ensemble of protons. Thus, a direct... 

Influence of the Side Chain Motion on the Conformation of the Heterocyclic Ring... 

Relative importance of rigid-helix and side-chain motions were studied by Corbin et al. [14]. The contribution of two types of rigid-body motions were approximated. In the first set of calculations helices of deoxymyoglobin were treated as rigid units while in the second set side-chains were considered to be... 

Interestingly, we notice that the Cs(f) curve decays much faster for helix-2, compared with the other two helices. There could be several factors responsible for this, such as the relative hydrophilicity of the polar amino acid residues present in the three helices and their relative exposure to the solvent, the life-time of the hydrogen bonds between the "boimd" water molecules and the protein residues, the side chain motion of the residues, etc. Further investigation is necessary to obtain a microscopic level understanding of such solvation behavior. 

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