Gradient HSQC spectra

Figure 7-15 HSQC spectrum (left) and gradient HSQC spectrum (right) of T-2 toxin.

Fig. 10.16. (A) GHSQC spectrum of strychnine (1) using the pulse sequence shown in Fig. 10.15 without multiplicity editing. (B) Multiplicity-edited GHSQC spectrum of strychinine showing methylene resonances (red contours) inverted with methine resonances (black contours) with positive phase. (Strychnine has no methyl resonances.) Multiplicity-editing does have some cost in sensitivity, estimated to be 20% by the authors. For this reason, when severely sample limited, it is preferable to record an HSQC spectrum without multiplicity editing. Likewise, there is a sensitivity cost associated with the use of gradient based pulse sequences. For extremely small quantities of sample, non-gradient experiments are preferable.

Load the spectrum of the gradient-assisted, inverse detected, 2D CH-HSQC-TOCSY experiment acquired with the echo-antiecho technique, D NMRDATA GLUCOSE 2D CH GCHICOTO 001999.RR. Check and if necessary correct its calibration in both dimensions. Set up a layout as for the basic HSQC spectrum. Compare the spectrum with the spectra of the basic HSQC and HMQC experiments. Use the same rows or columns to identify the additional TOCSY-peaks. 

Figure 6.11. A gradient-selected HSQC spectrum of the carbopeptoid 6.3 at natural N abundance plotted at high and at low contour levels to show the thermal noise floor. No ti-noise artefacts remain from the parent resonances ( N is referenced to external liquid ammonia).

Fig. 14.51 (A) HSQC spectrum of a 1-mM spectrometer using the gradient selected sen-...

Fig. 3. Sections of two-dimensional 31P/15N H correlation spectra of the azido-substituted monophosphazene derivative shown. The 2D spectra were recorded by using a conventional 31P/15N HMQC pulse scheme with phase-cycling (left), and the gradient-enhanced enhanced sensitivity HSQC pulse sequence of Fig. 2 (right). The onedimensional spectra on top of the 2D-maps were acquired with the lD-versions of both pulse sequences. The right spectrum is distinguished by a substantially lower artefact level and displays an additional clearly visible correlation of the 31P with nitrogen atom N3. Reproduced from Ref. 25 by permission of Elsevier Ltd.

The assignment of the carbohydrate chains of an intact glycoprotein (de Beer et al., 1994) with the help of a gradient-selected natural abundance HSQC-TOCSY spectrum is a recent example of the use of Hartmann-Hahn-type experiments in the assignment of oligosaccharides (Dabrowski, 1994). 

HSQC pulse sequence with gradient selection. The CTP for an N-type spectrum is shown by the full line and for the P-type spectrum by the dashed line. 

The HMQC or HSQC sequences may be transformed into their ID equivalents by simply removing the incremental t time period (Fig. 6.22) so that the experiment becomes just a heteronuclear filter. Only magnetisation that has passed via the X spin will be observed in the final spectrum and again the suppression of all unwanted signals is greatly improved by the use of pulsed field gradients. The selective observation of C-labelled glycine in an aqueous mixture is illustrated in Fig. 6.23. 

Fig. 3. Contour plot of the 500.1 MHz gradient enhanced HSQC NMR spectrum...

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