Inversion recovery

I and the measured line intensities are fitted to an exponential expression. S (-e) =A + B exp(-i / T ). The inversion-recovery experiments are often perfonned for multiline spectra of low-natural abundance nuclei,... 

Figure Bl.13.3. The inversion-recovery experiment. (Reproduced by pennission of VCFI from Banci L, Bertini I and Luchinat C 1991 Nuclear and Electron Relaxation (Weinlieim VCFI).)...

Figure Bl.13.4. The inversion-recovery detennination of the carbon-13 spin-lattice relaxation rates in melezitose. (Reproduced by pemiission of Elsevier from Kowalewski J and Maler L 1997 Methods for Structure Elucidation by High-Resolution N R ed Gy Batta, K E Kover and Cs Szantay (Amsterdam Elsevier) pp 325-47.)...

NMR spectroscopy is always struggling for increased sensitivity and resolution, as well as more efficient use of the instrument time. To this end, numerous improvements of the simple inversion-recovery method have been proposed over the years. An early and unportant modification is the so-called fast mversion recovery... 

FIR) [25], where the recycle delay is made shorter than 5T and the experiment is carried out under the steady-state rather than equilibrium conditions. A still more time-saving variety, the super-fast inversion recovery (SUFIR) has also been proposed [26]. 

Canet D, Levy G C and Peat I R 1975 Time saving in C spin-lattice relaxation measurements by inversion-recovery J. Magn. Reson. 18 199-204... 

The Davies-ENDOR teclmique is based on an inversion recovery sequence (see figure B1.15.13(A ). The experiment starts by interchanging the populations of levels 1 and 3 of one of the EPR transitions of the. S-/=i... 

The values of the time constants and are important in understanding both internal and overall motional behavior of the sample molecule. values are measured by the inversion recovery pulse sequence ... 

The technique for measurement which is most easily interpreted is the inversion-recovery method, in which the distribution of the nuclear spins among the energy levels is inverted by means of a suitable 180° radiofrequency pulse A negative signal is observed at first, which becomes increasingly positive with time (and hence also with increasing spin-lattice relaxation) and which... 

Figure 2.27. Sequence of measurements to determine the C spin-lattice relaxation times of 2-octanol (42) [(CD3)2C0, 75% v/v, 25 °C, 20 MHz, inversion-recovery sequence, stacked plot]. The times at which the signals pass through zero, xo, have been used to calculate, by equation 10, the T values shown above for the nuclei of 2-octanol...

H longitudinal relaxation time, measured by the inversion-recovery technique, at 293 K. 

The chemical shifts are obtained from the spectra of the T1 measurements in relation to the signal for the methyl carbon (20.6 ppm). The T1 measurements were performed using the inversion recovery (IR) method (180 deg. (12.7 us)-tau — 90 deg. (6.1 us)) with MAS 2200 scans were collected and the pulse delay time was veryshort, + 10 sec. 

Fig. 7. A C-13 relaxation time measurement of solid state wetted cellulose acetate (6% by weight water) using the inversion recovery (IR) method at 50.1 MHz and spinning at 3.2 kHz at the magic angle (54.7 deg) with strong proton decoupling during the aquisition time (136.3 ms), (upper part of the Figure). Tau represents the intervals between the 180 deg (12.2 us) inverting and 90 deg (6.1 us) measuring pulse. 2200 scans were collected and the pulse delay time was 10 s, Cf. Table 3 and Ref.281...

The most popular, and also a very accurate, experimental method for measuring nonselective spin-lattice relaxation-rates is the inversion recovery (180°-r-90°-AT-PD)NT pulse sequence. Here, t is the variable parameter, the little t between pulses, AT is the acquisition time, PD is the pulse delay, set such that AT-I- PD s 5 x T, and NT is the total number of transients required for an acceptable signal-to-noise ratio. Sequential application of a series of two-pulse sequences, each using a different pulsespacing, t, gives a series of partially relaxed spectra. Values of Rj can... 

Fig. 1.—Diagrammatic Representation of the Recovery of Magnetization along the z-Axis (Mj), from Its Initial Value (-M ) to +Mo, Following Its Inversion by a 180° Pulse. The exponential recovery curve shown in [A] depicts the return of magnetization that would be found in a typical inversion-recovery experiment. The curve in [B] would be obtained from a three-pulse sequence, and is a plot of which decreases from an initial value of...

Another method used to measure relaxation rates is the three-pulse (180°-t-90°-AT-PD—90°)nt sequence. This method is similar to the inversion recovery, with the addition of a third 90° pulse after the pulse... 

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... 

It is important to avoid saturation of the signal during pulse width calibration. The Bloch equations predict that a delay of 5 1] will be required for complete restoration to the equilibrium state. It is therefore advisable to determine the 1] values an approximate determination may be made quickly by using the inversion-recovery sequence (see next paragraph). The protons of the sample on which the pulse widths are being determined should have relaxation times of less than a second, to avoid unnecessary delays in pulse width calibration. If the sample has protons with longer relaxation times, then it may be advisable to add a small quantity of a relaxation reagent, such as Cr(acac) or Gkl(FOD)3, to induce the nuclei to relax more quickly. 

Figure 1.39 Representation of an inversion-recovery 7) experiment. (Reprinted from W. R. Croasmun and R. M. K. Carlson, Two-dimensional NMR spectroscopy applications for chemists and biochemists, copyright 1987, p. 13, with permission, from VCH Publishers Inc., 220 East, 23rd Street, New York 10010-4606.)...

Inversion recovery A pulse sequence used to determine spin-lattice relaxation times. 

Perkins CJ, Kahya E, Roque CT, Roche PE, Newman GC. Fluid-attenuated inversion recovery and diffusion- and perfusion-weighted MRI abnormalities in 117 consecutive patients with stroke symptoms. Stroke. 2001 32 2774-2781. 

The idea of exploration of relaxation correlation was first reported in 1981 by Peemoeller et al. [23] and later by English et al. [24] using an inversion-recovery experiment detected by a CPMG pulse train. This pulse sequence is shown in Figure 2.7.1. 

Hiirlimann and Venkataramanan [43] have derived the kernel for the inversion-recovery CPMG experiment in an inhomogeneous field ... 

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