Double-selective relaxation rates

According to these equations, the effect of selectively perturbing the spin states of spins i and j is to isolate the cross-relaxation paths common to these two spins. Combining Eqs. 15 and 19, the individual cross-relaxation terms are readily determined from single-selective and double-selective relaxation-rate measurements, that is. 

Single- and double-selective relaxation-rates, together with n.O.e. experiments, have been used to examine the configuration and conformation of asperlin (1) in benzene solution." " Comparing experimental distances for the proton pairs H-4,H-7 and H-5,H-7 with those obtained from molecular models, it was possible to confirm earlier evidence that the oxirane ring is trans, and also to show that, of the two possible diastereoisomeric forms (49a and 49b), the data are more fully compatible with structure 49a, the... 

However, the relaxation contributions obtained from Eq. 22 were not satisfactorily compared with those obtained from specific, deuterium-substitution experiments and single- and double-selective relaxation-rates. Moreover, the errors estimated for the triple-pulse experiments were very much larger than those observed for the other techniques. This point will be discussed next. 

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... 

The effect of temperature on relaxation rate of selected signals from aspen MWL in DMSO has been reported and is shown in Table 5.6 [399], As indicated from the Tj values, heating the sample from 30° to 70° doubles the required relaxation delay, if valid quantification is desired over the entire spectral range. This viscosity effect is much more noticeable in DMSO than in acetone or chloroform. 

Intra-residue selectivity have been introduced into the CANCO experiment to detect (C ,COi,Ni+i) correlations. The coherence transfer starts with C , converted into the double-anti-phase C zCOzNy coherence and subsequently refocused into the observable CO transverse magnetisation. Two variants of the experiment were described, that either achieved refocusing through the constant time evolution of N or used non-constant time period to detect the N evolution, followed by the refocusing through the transverse CO evolution. The choice of the optimal experiment depends on the relaxation rates of the nuclei. 

Saturation transfer has been used commonly to obtain information about the connectivity of exchanging sites (24). Selective irradiation of one site causes transfer of magnetization to another site with which it is exchanging. The changes in peak intensities may be analyzed to obtain rate constants. For example, measurement of intensities at site A prior to double irradiation at site B (M2 (0)) and after equilibrium has been attained during irradiation (M2 ( >)) can give the rate constant from eq. 9, in which Ti is the relaxation time at site A and... 

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