Line widths in NMR

The narrowing of the viscoelastic spectrum as salinity increases is analogous to motional narrowing of line widths in NMR spectroscopy. The narrowing process occurs when the breakage time Tbr becomes smaller than the reptation time Trep. In the limit Tbr Trep, the Gates model predicts that G(t) is monoexponential, with a time constant t given by... 

Using a solvent-reagent system gives narrow line-widths in NMR spectra of phospholipid extracts when applied to human amniotie fluid. Resolution of the major components is achieved by manipulating... 

Figure 7. Concentration dependence of the line widths in NMR spectra of the complexes ...

TABLE 1 31P NMR chemical shifts (ppm) and line width (in parentheses Hz) of the wild... 

Line shape analysis was performed for the binding of some dihydroxycholate ions to /1-cyclodextrin.205 The dihydroxycholates show different 18-CH3 signals for the complexed and free dihydroxycholate ions. To extract exchange rate constants from the NMR spectra, a complete line-shape simulation was performed. The simulation requires input of the chemical shift difference between the two sites, the line width in the absence of exchange, the residence time in each site (thg and Tg), and the relative population (fHG and fG) of each site (Equation (11)). The values were varied until the simulated and experimental spectra could be superimposed. The dissociation rate... 

Composite-pulse decoupling schemes like WALTZ [36, 37], DIPSI [38], or GARP [39], which are used in solution-state NMR, have failed to offer any significant improvements in the solid state compared to CW decoupling. The residual line width in CW-decoupled spectra is dominated by a cross term between the chemical-shielding tensor of the protons and the heteronuclear dipolar-coupling tensor [40, 41]. 

It should be noted that the activation energies for motional processes in the same crosslinked polymer gel calculated from line widths in 13C NMR spectra are higher than those calculated from 1H NMR spectra under the magic angle conditions (residual line width). These findings indicate that 13C line widths (which are of the order of 10 Hz) are probably more affected by sample inhomogeneity and by relatively small residual chemical shift anisotropies 162). 

Since crosslinked polymer networks exhibit anisotropic internal motions, the effect of MAS on the line narrowing is explained assuming that the rigid lattice second moment AM2 consists of two terms, analogous to Eq. (34). Then, the residual line width in the NMR MAS experiment, Acomas, can be described by the following relation ... 

The non-rotation of the sapphire flow cell, together with the detection volume and the employed flow rate, determine the resulting NMR line width. Whereas with rotation of the NMR tube in a conventional NMR probe, the signal line width of chloroform at the height of the 13C satellites in degassed acetone-d6 is about 3-4 Hz, SFC continuous-flow probes show values of the order of 15-18 Hz in the liquid and in the supercritical state. This hump test also indicates that there is no change in the signal line width in the H NMR spectra in the liquid and in the supercritical state. 

A recommended method for the estimation of natural line-widths in the dynamic range of an NMR spectrum is based on the line-width of a standard signal, w0, which is not affected by the exchange ... 

Doskocilova D, Tao DD, Schneider B, Effects of macroscopic spinning upon line width of NMR signals of liquid in magnetically inhomogeneous systems, Czech. J. Phys. B, 25 202-209, 1975. 

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