Inversion-recovery method

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... 

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... 

Whereas in the case of monomer siloxanes, Tj values may be measured by the inversion recovery method [1], we recommend the saturation recovery method for polymer siloxanes due to the very long measuring times. 

Fig. 13 Determination of 31P Tx values for fosinopril sodium using the inversion-recovery method. The spectra represent approximately a 50/50% w/w mixture of polymorphic forms A (8 = 52 ppm) and B (8 = 55 ppm). Spinning sidebands are represented by asterisks. 

Longitudinal relaxation times (T]) and NOE measurements The relevant data are reported in Table III. The T values were measured by the inversion-recovery method. 

Spin-lattice relaxation times were measured by the fast inversion-recovery method (24) with subsequent data analysis by a non-linear three parameter least squares fitting routine. (25) Nuclear Overhauser enhancement factors were measured using a gated decoupling technique with the period between the end of the data acquisition and the next 90° pulse equal to eibout four times the value. Most of the data used a delay of eibout ten times the Ti value. (26)... 

Morris and coworkers have studied trans-[OsH(H2)(depe)2] (depe = diethylpho-sphinoethane) using several spectroscopic methods, and in particular by Ti(H2) inversion-recovery methods in solution between 190 and 300 K [200]. They conclude that if the motion of the H2 ligand is much faster than the tumbling frequency, Eq. (11) applies. If the motion of the H2 ligand is slower than the tumbling frequency. 

A first improvement, aiming at reasonable measuring times [2], consists of choosing an arbitrary waiting time (though of the order of Ti). This is the Fast Inversion Recovery method whose results must be analyzed according to... 

Frye, J. S., Comparison of Inversion-Recovery Methods for Measuring Longitudinal Relaxation Rates, Concepts in Magnetic Resonance An Educational Journal, 1989, ... 

Spin-lattice relaxation times 7j of individual nuclei (13C, H) present in a molecule can be obtained by Fourier transformation of the FID signal following a 180°, r, 90° pulse sequence. The technique is referred to as inversion-recovery method [39, 40, 41] or... 

FIGURE 38. 29Si GHDMAS NMR spectra of CPTMPS/DMS in the solid state at 80 °C using the inversion recovery method (180 ° — z — 90 ° — 150 s) as a function of z. Reproduced by permission of Elsevier Science from Reference 144... 

By using the inversion recovery method with the standard pulse sequence (180°-t-90°-T), it is possible to determine the spin-lattice relaxation times in the supercritical state. The values of benzyl-n-butylphthalate have been... 

The latter technique is particularly appreciated by coordination chemists because of its simple mathematical formulation and the limited amount of experimental data to be collected (longitudinal relaxation times at a single magnetic field obtained by the inversion-recovery method (Void et al., 1968)). However, the a priori choice of a reference distance (rref) requires a partial modeling of the complex and the extracted distances strongly depend on the accuracy of this original choice. 

It is sometimes necessary to measure 7 i s so that weak signals are not lost in the noise or in order to obtain quantitative results. The inversion-recovery method to determine 7 1 s is demonstrated in Figure 4.4. Generally, 7 s decrease as the number of protons directly attached to the l3C nucleus increases. In other words, a quaternary l3C nucleus gives a peak of lowest intensity as shown in Figure 4.4a it also gives the slowest recovery in the inversion-recovery method. However, it is often difficult to differentiate between CH3, CH2, and CH on the basis of 7 , s alone since other factors are involved. 7) values cover a range of several... 

T, relaxation times can be determined with the inversion recovery method (part of the spectrometer software package) using the 180°, r, 90° sequence and varying x... 

Figure 2 shows the results of a J, determination for (T)3-cyclo-C8H13)-Ni(Br)P[CH(CH3)2]3 (7) using the inversion recovery method. All carbon atoms in this compound are directly bonded to at least one proton, and Tt lies in the range 0.7-1.5 sec, whereby the relaxation times within the cy-clooctenyl ring are approximately proportional to the number of associated protons a result expected for predominantly dipole-dipole relaxation. 

Suppose we wish to measure T, for a nuclear spin that gives only a single NMR line. There are a number of ways in which this can be done, but one of the simplest and most accurate is the inversion-recovery method, in which a 180° pulse inverts the magnetization, and its recovery by spin—lattice relaxation is monitored by application of a 90° pulse. Figure 2.12 shows that an initial 180° pulse flips M... 

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. 

The spin-lattice rehucation times Ti are measured by the inversion-recovery method By the capillary method, we have measured the spin-lattice relaxation times Tj for heavy water (D2Q) over a wide range of temperature. The results are in good agreement with those given by Hindman and co-workers - within the expe ental uncertainties our and their uncertainties ate 1% and 12%, respectively. The uncertainty of tempm ture is 0.1 C in the present work. 

The inversion recovery method was used for measuring the relaxation time. The instruments and the procedure were described previously. 1... 

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. 

Spin-lattice relaxation times for the carbon atoms of L-ascorbic acid treated with Chelex-100 (Bio-Rad Laboratories) were determined on 0.25 M solutions in deuterium oxide purged with nitrogen. The inversion-recovery method (33-35) with alternating phases and 8-10 t values was used for the protonated carbons, and the homo-spoil technique with 6-8 t values was used for the non-protonated atoms. The spin-lattice relaxation times (Tj) were calculated from the data using the appropriate Nicolet (25) digital computer programs. The Ti-values for the nonprotonated carbon atoms were repeated using the inversion recovery method and were virtually identical to those reported in Table 1. 

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