Correlated spectroscopy delayed-COSY

SECSY (spin-echo correlated spectroscopy) is a modified form of the COSY experiment. The difference in the pulse sequence of the SECSY experiment is that the acquisition is delayed by time mixing pulse, while the mixing pulse in the SECSY sequence is placed in the middle of the period. The information content of the resulting SECSY spectrum is essentially the same as that in COSY, but the mode... 

Standard correlation spectroscopy (COSY) experiments were run on the same four samples and the results are displayed in Figure 8.2.16. Since the acquisition time was approximately an order of magnitude less than the recycle delay, a full factor of four for improvement in throughput was achieved in fact, the number of coils could be increased for yet further improvements in temporal efficiency. No signal bleedthrough was observed from one spectrum to another. Similar results were reported in this paper with a two-coil probe used at 500 MHz [19]. 

Laurie was one of the first to apply two-dimensional (2D) NMR to carbohydrates. With students Subramaniam Sukumar and Michael Bernstein, and visiting scientist Gareth Morris, he demonstrated and extended the application of many of the directly observed 2D NMR techniques of the time. These included the homo- and hetero-nuclear 2D /-resolved techniques, delayed proton /-resolved NMR that allowed broad resonances to be suppressed, for example, those of dextran in the presence of methyl /Lxvlopyranoside. proton-proton chemical shift correlation spectroscopy (COSY), nuclear Overhauser enhancement spectroscopy (NOESY), proton-carbon chemical shift correlation (known later as HETCOR), and spin-echo correlated spectroscopy (SECSY). Trideuteriomethyl 2,3,4,6-tetrakis-<9-trideuterioacetyl-a-D-glucopyranoside served as a commonly used model compound for these studies. 

Stop-flow requires the calibration of the delay time, which is the time required for the sample to travel from the UV detector to the NMR flow cell, which depends, in turn, on the flow rate and the length of the tubing connecting HPLC with NMR. Because the chromatographic run is automatically stopped when the chromatographic peak of interest is in the flow cell, the amount of sample required for the analysis can be reduced and 2-D NMR experiments, such as correlation spectroscopy (COSY), total correlation spectroscopy (TOCSY), and others, can be obtained because the sample can remain inside the flow cell for days. It is possible to obtain NMR... 

The pulse sequence for J-resolved spectroscopy is (90) — fj — (180). The FID is observed as an echo, so there needs to be an additional delay ty before the detection period ti, and the complete sequence is (90) — tj — (180) — tj — f2, as shown in Figure 26. For COSY the basic pulse sequence is (90) — ty— (90) — tj and for NOESY it is (90) — ty— (90) — D — (90) — 2, with a pulsed field gradient applied during the delay, D. A large number of other pulse sequences has been designed both to improve detection and to permit other forms of correlation spectroscopy. 

Fig. 8.10 Pulse sequence for homonuclear correlation spectroscopy, COSY/GCCOSY [46-48]. Although the gradient version of the experiment is shown, the pulse sequences are the same except for the two gradients and their associated delays. The non-gradient experiment employs a four-step phase cycle the gradient experiment allows the acquisition of data with a...

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