Line positions, isotropic spectra

In these spectra, the protein has been regenerated with retinal specifically 13 C labeled at positions 11,12 and 13, and in each case the retinal resonance exhibits a sharp centerband at the isotropic chemical shift and is flanked by rotational sidebands. Other lines in the spectrum are the natural-abundance 13C resonances of the protein carbonyls ca 175 ppm) and aliphatic carbons (0-100 ppm). Contributions from the Ammonyx-LO detergent in these spectra are seen in the different intensities in the 0-100 ppm region. Ammonyx-LO does not exhibit NMR resonances above 100 ppm. Spectra of the 9-cis pigment isorhodopsin are similar. Table 38 summarizes the isotropic chemical shifts from the solid-state NMR spectra of rhodopsin regenerated with retinal13 C labeled at each position along... 

In these liquids, for all the observed nuclei, the high-temperature NMR spectrum consists of a single, narrow line, characterized by its position (isotropic chemical shift) and its line width. This single sharp line reflects rapid exchange between the different available environments (rapid as compared to NMR time scales ranging from 10 to 10 Hz). Consequently, the observed peak position is the average of the chemical shifts of individual species, weighted by their respective populations. 

Methods of Spectrum Analysis For simple molecules the line positions and the intensities can be expressed explicitly in terms of the chemical shifts (isotropic and anisotropic) and the coupling constants Djj and J. In these special cases a system of equations may be derived which allows the determination of the coupling parameters (D and Jy) from the experimental line positions in a straightforward manner [37, 38, 46]. A number of these simple cases has been summarized by Diehl and Khetrapal [43]. For more complex molecules the spectra can only be analyzed by computer methods, either by a simulation or an iteration procedure. 

Figure 4-2. One-dimensional proton decoupled C CP spectra of THE6 in the columnar phase at 85 °C. Line positions in static (top) and MAS spectrum (bottom) are determined by one of the principal values of the residual CSA tensor and by isotropic chemical shift, respectively...

The isotropic average of 3 cos 0—1 over all orientations is zero, so the dipolar interactions do not contribute to line positions in a liquid phase NMR spectrum (cf. the fact that the trace of D is zero). 

Fig. 0.3. Raman spectrum of liquid oxygen [6]. The positions of the free rotator s. /-components are shown by vertical lines and the isotropic scattering contour is presented by the dashed line.

In the isotropic potential approximation, the complete binary spectrum is obtained by superimposing basic line profiles, Ga,a2al( T), shifted by sums of molecular rotational frequencies which may be positive,... 

These workers (Adrian et al., 1962) also studied the spin resonance spectrum of DCO radicals and obtained remarkably narrow lines and shoulders which gave sufficient detail that the anisotropic hyperfine tensor could be deduced. This result then enabled them to extract the data tabulated from the spectrum of HCO. In particular, it is pointed out that as the g- and hyperfine-anisotropies have different principal axes, there has to be an extra term (Ayz) where the hyperfine tensor is expressed in terms of the axes of the gr-tensor. A careful analysis of all the data led these authors to the conclusion, based entirely upon experiment, that the large isotropic hyperfine coupling must be positive. 

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