Inversion-recovery spectra

Fig. 21. inversion-recovery spectra of germanium. Reproduced, with permission, from... 

Fig. 27. Experimental (left) and simulated (right) central transition inversion recovery spectra of 47% enriched poly crystalline cristoballite for the temperatures given, recorded as a function of the length t of the relaxation delay.40 All simulations assume a six-site motion between six equally probable sites on a circle orthogonal to the Si-Si axis between adjacent Si04 tetrahedra, with rate constants log( ) = 3.50 at T= 298 K, log(Jfc) = 3.95 at T= 473K and log(fc) = 5.80 at T= 528 K.

Inversion-recovery deuterium NMR spectra were obtained by performing a 180°-r-90° pulse sequence, followed by the quadrupolar echo sequence (12). Spin lattice relaxation times were estimated from the null points in the inversion-recovery spectra. 

Figure 8.6 (a) A plot of Tj versus inverse temperature for PP -d. This temperature dependence is typical of slow, large-amplitude motion, (b) Experimental and (c) simulation inversion recovery spectra near the null-point showing the expected anisotropy for a ring-flip. (Reprinted from J.H. Simpson, D.M. Rice and F.E. Karasz, J. Polym, ScL B, Polym. Phys. Ed. 30 (1992) 11-18,... 

Figure 8. Inversion-recovery spectra of vanadate species, with interpulse delays from 0.5 to 10 ms. a = monomer, b = dimer, c = cyclic tetramer, d = cyclic pentamer. Note that T, is slightly less for the cyclic pentamer, but that because of faster exchange the linewidth is slightly greater for the cyclic tetramer.

For a jump mechanism, is also anisotropic. The anisotropy, measured with an inversion recovery experiment near the null-point, can provide a signature pattern for a particular mechanism. Figure 8.6 also shows an inversion recovery spectrum, obtained at 220°C and a simulation [88], Wittebort et al have described the theoretical calculation of anisotropy for a jump model [113,134]. For C-D bond orientations close to the PAS axes, Tj has a larger value and therefore these signals are inverted. This particular pattern is unique to the ring-flip mechanism and distinguishes it from other motions which might coincidently cause a spectrum of the same shape. 

Selective, spin-lattice relaxation-rates are measured by the inversion-recovery technique. A rather weak, 180° pulse of very long duration (10-50 ms) inverts a multiplet (single-selective) or two multiplets (double-selective) in the spectrum of asperlin (1 see Fig. 2 ) and the recovery of the... 

In some cases, CP is not necessary to obtain a suitable solid state NMR spectrum. In these cases, the SPE/MAS sequence may be used and for quantitative analysis only the X-nucleus T time needs to be determined. The standard inversion-recovery experiment (Fig. 10C) can be used to measure this... 

Because the excitation/detection coil is in the x-y plane and the longitudinal component relaxes along the z axis, T cannot be measured directly from an NMR spectrum, but must be obtained using a pulse sequence. The most commonly used pulse sequence to measure T is an inversion recovery pulse sequence (Kemp, 1986). Other commonly used pulse sequences for measuring 7j are given in Ernst et al. (1987). 

FIGURE 31. Typical data set for measurement of the spin-lattice relaxation times of the sp2-hybridized carbon atoms of, 6-carotene at 11.7 T. The chemical shift values are shown across the bottom of the figure. The t-value for each spectrum is the delay time in the inversion-recovery pulse sequence. Reprinted with permission from Reference 49. Copyright (1995) American Chemical Society... 

Finally, a coupled and decoupled 13C NMR spectrum of 2,2 -bipyrrole (Fig. 4.14(a,b) and an inversion-recovery series of 2,2 -bi pyridine (Fig. 4.15 [73 i]) illustrate signal assignments of heteroaromatic compounds by means of carbon-proton couplings and spin-lattice relaxation times. These spectra also exemplify the characteristic shift differences between n-excessive (2,2 -bipyrrole) and n-deficient heteroaromatic compounds (2,2 -bipyridine). 

Figure 5.17 shows the H inversion-recovery experiment for sucrose. Recovery values of 0, 0.1, 0.2, 0.3, 0.5, 0.75,1.0, and 2.0 s were used, plotting the whole spectrum for each experiment. In the analysis of these data, we use the proton assignments for sucrose derived... 

Figure 3.23. Spin inversion/recovery H NMR spectrum of artimisinin as a function of delay time (x). (Courtesy of David Lankin.)...

EXAMPLE 3.10 In the complex molecule artemisinin (the structure of which can be seen in Chapter 13) each hydrogen exhibits its own signal. Figure 3.23 shows the H spectrum of this compound, obtained by the inversion-recovery pulse sequence. Estimate the value of T, for each signal. 

The above multipulse inversion-recovery sequence is our first example of a 2D NMR spectrum. That is, it is a plot of signal intensity versus both the frequency of the signal (Av,)... 

FIGURE 2.12 Determination of T, by the inversion-recovery method, (a) M is inverted by a 180° pulse at time 0. (b) After a time interval T, during which spin—lattice relaxation occurs, a 90° pulse rotates the remaining magnetization to the y (or — y ) axis, (r) The initial height of the FID or the height of a given line in the Fourier-transformed spectrum (see Chapter 3) is plotted as a function of t. Note that each point results from a separate 180°, T, 90° pulse sequence. 

NMR samples contained 0.6 ml receptor (0.5-2.0 mM) dissolved in refolding buffer (vide supra) with 10% DjO. One-dimensional F NMR spectra were obtained at 470 mHz on a General Electric GN 500 spectrometer fitted with a 5 mm F probe. Parameters included 16K data points, 3.0 second relaxation delay and 25 Hz linebroadening for processing spectra. T, relaxation times were measured by the inversion recovery method. The two-dimensional F NOESY NMR spectrum was obtained on a Varian Unity Plus 500 using the standard Varian pulse sequence. A total of 128 experiments with a mixing time of 0.3 seconds were performed with collection of 1024 data points. Quadrature detection in the second dimension was obtained through the method of States and Haberkom. C ( H NMR spectra were obtained on a Varian 500 Unity Plus fitted with a 10 mm broadband probe. 

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