Antiphase component

The basic INEPT spectrum cannot be recorded with broad-band proton decoupling, since the components of multiplets have antiphase disposition. With an appropriate increase in delay time, the antiphase components of the multiplets appear in phase. In the refocussed INEPT experiment, a suitable refocusing delay is therefore introduced that allows the C spin multiplet components to get back into phase. The pulse sequences and the resulting spectra of podophyllotoxin (Problem 2.21) from the two experiments are given below ... 

Fig. 8.5 Downfield (a) and upfield (b) compo-nents of 15N doublets of a I PAP-[ H-15N]-HSQC for the protein saposin in Pfl viruses, a results from the subtraction and b from the addition of the spectra containing the in-phase and antiphase components, respectively. The sum of the...

Figure 11 Spectral region of a conventional f2-coupled HSQC (A) and a CLIP-HSQC spectrum (B) of strychnine in CDCl3 for a mismatched delay for heteronuclear coherence transfer. The conventional HSQC has strong dispersive antiphase components and contributions from long-range connectivities which are practically absent in the CLIP-HSQC.144...

Equations 9.4 represent the actual situation correctly. At all times the magnitude of the vector sum P + A = 2 M as it should, and each component has the required oscillatory behavior. In Chapter 11 we discover how to express P and A in terms of the familiar spin operators Ix, Iy, and Iz, and in Chapter 12 we see that the presence of both in-phase and antiphase components is fundamental to the operation of many two-dimensional NMR experiments. 

Evolution based on spin coupling is indicated by the appropriate operator and time. Because the product operator treatment applies solely to weakly coupled systems, the operator is JisIzSz, with only the ar components considered. As we saw in Section 9.6, we must consider both in-phase and antiphase components of a magnetization (or coherence) as it precesses in the xy plane. In line with Eq. 9.4, we can now use the product operator terminology to note that, for example,... 

For most applications, the phase anomalies that are created by zero-quantum coherence can be ignored in practice, because the long dispersive tails of the antiphase components have opposite signs and tend to cancel each other (Ranee, 1987). However, the zero-quantum terms must be suppressed if TOCSY spectra with pure two-dimensional in-phase absorp-... 

Figure 5.16. Coupling evolution during ti produces in-phase and antiphase magnetisation components. Only the antiphase component contributes to magnetisation transfer and hence to crosspeaks in the 2D spectrum.

Anisotropic interactions, orientational dependence, 26f Anisotropic rotation, polyformal spin relaxation, local motion, 70,78t Anisotropy, chemical shift (CSA), solid sample NMR, 22 Antiphase components, undesirable INEPT properties, 106 Areas, integrated, quantitative NMR studies, 1371... 

Most 2D NMR methods in solids have low sensitivity because of fast transverse relaxation. In particular, for the COSY experiment the system must evolve for sufficiently long time periods in both dimensions before satisfactory intensities of cross-peaks can be obtained. Accordingly, Fyfe et al. [30,31 ] introduced two extra deiays into their solid-state COSY pulse sequence, a concept originally conceived for so-called long range or delayed COSY in liquids [40]. If transverse relaxation is too fast on the time scale of the required evolution and acquisition periods, there will be no cross-peak magnetization to detect. Furthermore, rapid transverse relaxation leads to wide lines, so that diaganol peaks can overlap with adjacent cross-peaks, which are already very weak because of the destructive interference of their broad antiphase components. 

Another critical issue in CPMG R2 dispersion is the magnitude of R large molecules. Since Rex is extracted from the measuredR2, the accuracy of Rex decreases when R° is large. In a pulse sequence that averages the inphase and antiphase components, HRj contributes to R° as does NR2 [109,116]. Thus, as the molecular... 

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