Residual anisotropy, determination

Deuterium nuclei in water molecules have negligible asymmetry parameters and residual anisotropies. After correcting for the paramagnetic impurities present, that affect relaxation rates somewhat (35), one obtains from the experimental data a value of the longitudinal relaxation rate for the water deuterons in the bound state of 650 s 1. This value incorporates the quadrupolar coupling constant (above determined) and the correlation time for bound waters. Using the standard expression for quadrupolar relaxation (29,35) yields a value for t 1.6 ns. 

An independent method of determining stress, especially useful for materials under flow, is from the optical birefringence. Of course, it is limited to transparent materials, which precludes application to filled polymers. Because of the need for transparency, stress birefringence has been used more often for plastics than rubber. Residual anisotropy due to unrelaxed orientation can also be assessed using birefringence this is commonly known as the photoelastic effect. Generally the birefringence is directly proportional to the tme stress... 

The isotropic g-value and F lt/-couplings were determined by averaging the measured parameters for a spectrum showing residual anisotropy. 

An often employed model for the interpretation of NMR relaxation data, which was developed for amphiphilic molecules, is based on a separation of the molecular motions into two well separated time regimes, and has been termed two-step model [13] Local anisotropic motions, such as bond rotations, are fast motions determining the longitudinal relaxation rate f /. Isotropic motions, which are averaging the residual anisotropy, such as aggregate rotation or diffusion, occur on much slower time scales, described by the slow motion correlation time ts-... 

Nondestmctive testing (qv) can iaclude any test that does not damage the plastic piece beyond its iatended use, such as visual and, ia some cases, mechanical tests. However, the term is normally used to describe x-ray, auclear source, ultrasonics, atomic emission, as well as some optical and infrared techniques for polymers. Nondestmctive testing is used to determine cracks, voids, inclusions, delamination, contamination, lack of cure, anisotropy, residual stresses, and defective bonds or welds in materials. 

The sensitivity of the NMR anisotropy to the conformation of the glycol residue, which was a complication in polyethylene terephthalate, can be turned to advantage in 4GT, as shown by some recent research 36). The anisotropy of the second moment was determined for three cases, starting with a highly oriented tape ... 

Instead of measuring only the time-dependent dipolar interaction via NOE, it is also possible to determine dipolar couplings directly if the solute molecule is partially aligned in so-called alignment media. The most important resulting anisotropic parameters are RDCs, but residual quadrupolar couplings (RQCs), residual chemical shift anisotropy (RCSA) and pseudo-contact shifts (PCSs) can also be used for structure determination if applicable. 

The anisotropy decay of the tryptophan fluorescence of both model peptides and biologically active peptides containing a single tryptophan residue has been determined in various studies. Even in the case of the tripeptide H-Gly-Trp-Gly-OH quenched by acrylamide the anisotropy decay displayed two correlation times with values of 39 and 135 ps. 44 The shorter correlation time was thought to be due to motions of the indole ring relative to the tripeptide. In the case of ACTH(l-24) the fluorescence anisotropy decay of the single tryptophan residue in position 9 of the peptide sequence obtained in phosphate buffer (pH 7, 3.5 °C) was also double-exponential. 29 The shorter rotational correlation time (0 = 92ps)... 

Most studies of the strength of glass ceramics have determined modulus of rupture as a function of crystal size (strength increases as crystal size decreases), volume fraction of crystalline phase (strength increases with the volume fraction of crystalline phase), and internal stresses generated either by the difference in thermal expansion between the crystalline phases and residual glass or by anisotropic thermal expansion of the crystalline phase (strength decreases as the difference or anisotropy increases). 

A graphical approach was also used by Millet and Pons to analyse anisotropy of rotational diffusion in proteins. The values of Z)j and DJD compatible with R IRi ratios are presented as a contour plot. The intersection of the contour plots for different residues provides the values of anisotropy parameters compatible with experimental data. The obtained parameters can be used as starting values for further optimisation. The method is apphcable to axially symmetric rotation. A combination of approximate and exact methods was used by Ghose et al. to reduce the computational time of the determination of rotational diffusion tensor from NMR relaxation data. The initial values of the tensor components and its orientation are evaluated from the approximate solution, which substantially reduces the search space during the exact calculations. The method was applied for the estimation of relative domain orientation of a dual domain protein. 

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