Saturation recovery experiment

Figure 7 The saturation-recovery experiment. The dynamic range is equal to the equilibrium magnetization.

Fig. 5 Effect of varying relaxation delays between on- and off-resonance experiments in STD NMR experiments, a Experimental setnp for interleaved measnrements in STD NMR spectroscopy, n represents the nnmber of scans. The inter-scan delay Adi is varied while keeping on- and off-resonance freqnencies constant at -4 and -t300 ppm, respectively, b The resulting STD effects for the 0-methyl group of a-L-Fuc-O-methyl in the presence of RHDV VLPs. The equation that was used for non-linear least squares data fitting is based on the saturation recovery experiment [98], With Ti(iig) = 0.91 s as measured independently (unpublished results) and a Monte Carlo error estimation yields Ti(virus) = 10.06 0.41 s. This value does not directly correspond to a Tl relaxation time of the virus protons, because other factors also influence the observed relaxation [99]. According to these findings a relaxation delay Adi = 25 s was employed in all STD experiments. This results in a recovery of 92% of the virus resonance, and thereby reduces errors in epitope mapping that are introduced otherwise by non-homogeneous recovery of the binding site.

When the primary electron donation pathway in photosystem II is inhibited, chlorophyll and p-carotene are alternate electron donors and EPR signals for Chl+ and Car+ radicals are observed.102 At 130 GHz the signals from the two species are sufficiently resolved to permit relaxation time measurements to be performed individually. Samples were Mn-depleted to remove the relaxation effects of the Mn cluster. Echo-detected saturation-recovery experiments were performed with pump pulses up to 10 ms long to suppress contributions from cross relaxation and spin or spectral diffusion. The difference between relaxation curves in the absence of cyanide, where the Fe(II) is S = 0, and in the presence of cyanide, where the Fe(II) is S = 2, demonstrated that the relaxation enhancement is due to the Fe(II). The known distance of 37 A between Fe(ll) and Tyrz and the decrease of the relaxation enhancement in the order Tyrz > Car+ > Chl+ led to the proposal of 38 A and > 40A for the Fe(II)-Car+ and Fe(II)-Chl+ distances, respectively. Based on these distances, locations of the Car+ and Chl+ were proposed. 

Fig. 2.28. Motion of the magnetization vector during a saturation-recovery experiment the first 90J pulse rotates the magnetization vector M0 to the x y plane (a -> b). where the resultant transverse magnetization is dispersed by a field gradient pulse (homo-spoil) after r s (d), a second 90 pulse monitors the partially relaxed magnetization Mt (d - f), and the resultant FID signal is Fourier transformed to the NMR signal with amplitude Ax. (Reproduced by permission of the copyright owner from E. Breitmaier and G. Bauer ...

Fig. 45. Time/temperature scaling of spin lattice relaxation curves in a saturation-recovery experiment. At each temperature the raw amplitude data arc first normalized by the amplitude of the fully relaxed signal so that all values fall between zero (saturation at short times) and 1 (lull recovery at long times). The time points t are multiplied by the temperature at which the relaxation curve was obtained. If the relaxation is governed by the Korringa process, the scaled points fall on a temperature-independent curve, even if the relaxation is not simply exponential, as in the cases shown here. The sample is Pt/Ti02 of dispersion 0.60 (determined by electron microscopy) at several hydrogen coverages (calculated from the dispersion) 0.1, 0.5, and 1.0 monolayers. The squares in c show data at 110 K for another Pt/TiOi catalyst of dispersion 0.36.

Temperature-dependent saturation recovery experiments by pulsed EPR have been performed on the RNR radicals, to assess the interactions between the radical and the iron center in the R2 proteins from different species (95,49). The J couplings of the diferric sites evaluated from these and other studies are shown in Table III. The interaction with iron explains why the EPR signal of the tyrosyl radical of mouse RNR-R2 is nearly impossible to saturate with microwave power at 77 K. 

The factor two appears because the echo recovers from an inverted intensity -lo at T = 0. In the corresponding saturation recovery experiment the echo signal is zero at time t = O.The echo grows as ... 

The Ti relaxation refers to the time it takes for the z-component of the magnetization Mz to achieve an equilibrium value Mq. Two different equations could be used to extract Ti from a series of measurements, depending on whether a saturation-recovery experiment or an inversion recovery experiment (explained in the subsequent section) is used. In the former case, the following equation is used ... 

To measure the longitudinal relaxation time Ti, an inversion or saturation pulse is applied, followed, after a variable time T, by a two-pulse echo experiment for detection (Fig. 5b). The inversion or saturation pulse induces a large change of the echo amplitude for T < T. With increasing T, the echo amphtude recovers to its equilibriiun value with time constant Ti. The echo amphtude of the stimulated echo (Fig. 5c) decays with time constant T2 when the interpulse delay T is incremented, and with the stimulated-echo decay time constant Tse < T1 when the interpulse delay T is incremented. A faster decay, compared to inversion or saturation recovery experiments, can arise from spectral diffusion, because of a change of the resonance frequency for the observed spins, of the order of Av = 1/t on the time scale of T. Quantitative analysis of spectral diffusion can provide information on the reorientation dynamics of the paramagnetic centers. 

If we further limit discussion to the saturation recovery experiment, eq. 10 for the three cases of interest can be explicitly written as eqs. 11-13. In addition to these coefficients. 

The spin-lattice relaxation time (Tj) can be determined by either the inversion-recovery (IR) or the saturation-recovery experiment. The IR experiment (Figure 6.3a) employs a 180° pulse, which inverts the magnetisation, Mj( = 0) = -Mq, followed by a recovery time (x) and a 90° observe... 

Figure 6.3 Radio-frequency pulse sequences for (a) the IR and (b) the saturation-recovery experiments for determination of spin-lattice (T,) relaxation times. The recovery time (x) is incremented in both experiments. The saturation-recovery sequence employs typically 10-20 saturation pulses (n,t) with a length corresponding to 90° pulses (Xp = 90°).

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