Effective residue rotation

In this equation, [m ]x is the effective residue rotation at wavelength X,... 

In order to avoid complications caused by excitation energy transfer between tryptophan residues, most investigations have been performed with proteins containing one tryptophan residue per molecule. When studying protein solutions, there are difficulties in separating the effects of rotation of entire protein molecules and of the chromophores themselves relative to their environment in the protein matrix. It is usually assumed that intramolecular motions are more rapid and manifest themselves as short-lived components of anisotropy decay curves or in depolarization at short emission lifetimes. 

Cotton effects which result from the random coil and a-helical forms of polylysine (37). The ordinate is the reduced mean residue rotation, which is defined as... 

Figure 5. Effect of pH upon aggregation and ORD of mitochondrial structural protein in xoater. The curves are trough position (O), absorbance (%), and reduced mean residue rotation (V). Dashed lines show region where precipitation prevented dependable measurements, but spectra of the precipitate in glycerol suggest that here the trough position may be at about...

Figure 2. Effect of rotation of the residue about the virtual bond on the bridge angle r (for trimethyl amylose (5))...

Figure 4. Effect of chain length on Cu(II)-induced changes in rotation for single-stranded poly(A) and oligo(A) in water at 25°. Presented as % change in mean residue rotation at trough (see...

The assumption underlying this equation, that the mean residue rotations obtained from measurements on long random coils and helical structures will adequately represent shorter lengths of chain expected in mixtures, must, however, be examined in the light of end effects. Because the rotatory power of a residue is dependent upon its environment, its proximity to the end of a structure will endow it with a rotation that is not representative of residues at the interior, each of which may be considered to exist in an equivalent environment. Residues at the ends of random coils and helical segments therefore will not contribute to the net rotation in a manner proportional to the length of the structure. 

Petkova and Tycko have described investigations of the effects of rotational resonance (R ) on solid state C NMR spectra of uniformly C-labelled samples obtained under MAS." The utility of R measurements as structural probes of peptides and proteins with multiple uniformly labelled residues has been demonstrated. Results for uniformly C-labelled L-alanine and L-valine in polycrystalline form and for amyloid fibrils formed by the 15-residue peptide with uniform labeling of a four-residue segment have been reported. The MAS NMR spectra revealed a novel J-decoupling effect at R conditions that may be useful in spectral assignments for systems with sharp C MAS NMR lines. Pronounced dependences of the apparent isotropic NMR chemical shifts on MAS frequency near R conditions were also observed. The feasibility of quantitative distance determinations in L-valine, and qualitative determinations of inter-residue contacts in fibrils has been demonstrated. In addition, it has... 

The crossed polarizer effects of both types are used in analysis work. The concentration of optically active organic materials is determined by the degree of rotation. In plastic processing the residual strains in molded materials as well as the degree of orientation of polymers is determined by the effect on polarized light. Crossed polarizers are used with special wave plates to control the amount of light that passes through an optical system. 

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