Selective TOCSY

In a ID TOCSY-NOESY experiment [39], the proton magnetization is aligned along the spin-lock axis after the initial selective TOCSY step. The... 

In the subsequent ID ROESY-TOCSY experiment (pulse sequence of fig. 7(c)), a selective TOCSY transfer was applied from H-4c. During the... 

Fig. 8. ID ROESY-TOCSY. (a) H spectrum of the oligosaccharide 3 (5 mg/0.5 ml D2O). (b) ID ROESY spectrum of 3 acquired using the pulse sequence of fig. 7(a) with selective excitation of the H-lb proton. Duration of the 270° Gaussian pulse and the spin-lock pulse ( yBi/ K = 2.8 kHz) was 49.2 ms and 0.5 s, respectively. The spin-lock pulse was applied 333.3 Hz downfield from the H-lb resonance. The time used for the frequency change was 3 ms. (c) ID ROESY-TOCSY spectrum acquired using the pulse sequence of fig. 7(c) and the selective ROESY transfer from H-lb followed by a selective TOCSY transfer from H-4c. Parameters for the ROESY part were the same as in (b). A 49.2 ms Gaussian pulse was used at the beginning of the 29.07 ms TOCSY spin lock. 256 scans were accumulated. A partial structure of 3 is given in the inset. Solid and dotted lines represent TOCSY and ROESY...

The ID TOCSY-ROESY experiment is illustrated on the same molecule using the pulse sequence of fig. 7(d). This time the magnetization of H-4c was generated during the initial selective TOCSY transfer from H-lc (fig. 9(b), pulse sequence of fig. 7(b)). In the subsequent ID TOCSY-ROESY experiment, the ROE transfer from H-4c confirmed the expected... 

The double-selective TOCSY-ROESY and TOCSY-NOESY techniques are particularly useful. They allow one to measure NOE and ROE correlations in spectra with high degree of overlap as often found in carbohydrates. In addition to the DANTE, DANTE-Z [66], and Gaussian pulses as described earlier for selective excitation, self-refocusing shaped pulses such as BURP (EBURP and UBURP) [67] have also been used for this purpose [64]. 

Encapsulation of herbicides within anionic clays was readily identified by the loss of HRMAS NMR signal associated with immobilization of the molecules between clay layers.103 The application of HRMAS to soil samples has been shown to provide important results on the interaction of herbicide and other organic components with the soil matrix, using ID lH HRMAS, selective TOCSY and 2D TOCSY experiments.104 Significant advantages to the HRMAS approach are its reduced samples preparation needs, with no extraction, pre-treatment or purification required. 

Sandusky, P. and Raftery, D. (2005). Use of selective TOCSY NMR experiments for quantifying minor components in complex mixtures Application to the metabolomics of amino acids in honey. Anal. Chem. 77, 2455-2463. 

A selective TOCSY experiment starts with putting the net magnetization of just one resonance in the x -y plane and locking it with the TOCSY mixing spin lock. After an appropriate mixing time, the spin lock field is turned off and we simply start acquiring the FID. These steps can be summarized as follows ... 

Figure 5.69. Gradient-selected TOCSY. Sequence (a) is suitable for absolute-value presentations with a 1 1 gradient combination selecting the N-type spectrum. Sequence (b) provides phase-sensitive data sets via the echo-antiecho method for which separate P- and N-type data are collected through inversion of the first gradient.

Figure 5.70. The general sequence for ID selective TOCSY. Any suitable selective 90 pulse scheme (see Chapter 9) can be used to selectively excite the target resonance from which transfer is initiated.

In Check it 5.4.2.1 the ID selective COSY, ID selective relayed COSY without and with z-filter and a ID selective TOCSY spectrum are simulated for the same spin system and the results compared. As already mentioned the spinlock for isotropic mixing can be generated in different ways and this has lead to the development of improvements and elements being added to the spinlock sequence. Of these improvements the trim pulse and z-filter, adapted to the spinlock sequence [5.154], are the most popular. 

FIGURE 8 Grouping of PCA scores derived from the F2-selective TOCSY spectra of rice wines for PC1-PC2 (left) and PC1-PC2-PC3 (right). Modified from Ref. [76]. 

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