1D TOCSY for Bruker (selmlgp.2)

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Basic facts about selmlgp.2

Synopsis: selective 1D TOCSY with zero quantum filter

Family: DPFGSE 1D TOCSY

Code authors:

Copyright: Bruker, Inc.

Introduction

The selmlgp.2 is a pulse sequence for Bruker epuipment. It is a selective 1D version of 2D TOCSY using excitation sculpting technique with pulsed field gradients (PFG). This experiment can be used to identify impurities, analysis of mixtures, substances with glycosides units or peptides, overlaped signals and also to determine the coupling constant ^2,3J_CH.

Standard parameters might be accessible on your system under name SELMLGP or SELMLZF. If so, then typing rpar SELMLGP will load them, and only RF-pulse parameters will need to be adjusted. (the parameters is very similar to 1D NOESY (selnogp - Bruker))

This pulse sequence uses a single DPFGSE element for the selective excitation with a suppression of zero quantum coherence.

Delays

d1 - recycling delay (1-5 x T1) (usually 2 s)

d9 - mixing time (the value depends on how many step of magnetization transfer will desire. For 1D COSY type spectra, use 20-30 ms. For further steps can be used to transfer up to 120 ms.)

d16 - gradient recovery delay (depends on the probe) may be on the order of 100-500 μs.

Carrier frequencies

O1 (or O1P for the value in ppm) is the carrier frequency used for the hard pulses.

Parameter spoffs2 - may be used as an offset for the selective excitation.

If O1 is set exactly at the selectively excited resonance, then spoffs2 must be zero.

In most cases it will be more optimal to set O1 at the center of spectrum and enter spoffs2 as a difference in Hz between the resonance of interest and the carrier frequency applied to the hard pulses.

Hard RF pulses

p1 - ¹H 90^o pulse at power level pl1

Hard pulses are applied at O1 (or O1p) carrier frequency.

Selective RF pulse

There is one shaped selective pulse with the following adjustible parameters:

Note: pl0 must be at 120.

• p12 - length (default 30 ms, but generally length should be chosen according to desired selectivity)
• sp2 - power level
• spnam2 - waveform file name (default Gaus1.1000 - gaussian pulse with 1000 steps. Can be used a gaussian curve with 5% truncated to increase selectivity)
• spoffs2 - offset in Hz relative to O1 - the carrier frequency

Gradient pulses

• p16 (default 1 ms) - length used for the gradient pulses gp1 and gp2
• gp1 and gp2 strengths of the two gradient pulses.
• gpnam1 and gpnam2 - shapes of gradient pulses (default - SINE.100)

Suggested ratio of gp1/gp2 - 15/40

Processing Parameters

• EM - Exponential multiplication to reduce the noise from spectrum (usually 0.3)

Process the FID with command EM and FP (or use EFP - a combination of EM and FP command).

References

1. Kessler, H and Oschkinat, H and Griesinger, C and Bermel, W. Transformation of homonuclear two-dimensional NMR techniques into one-dimensional techniques using Gaussian pulses. Journal of Magnetic Resonance (1969) 70(1):106--133, 1986. BibTeX [kessler86]

2. Stonehouse, J and Adell, P and Keeler, J and Shaka, AJ. Ultrahigh-quality NOE spectra. Journal of the American Chemical Society 116(13):6037--6038, 1994. BibTeX [1d-noe]

3. Stott, K and Stonehouse, J and Keeler, J and Hwang, TL and Shaka, AJ. Excitation sculpting in high-resolution nuclear magnetic resonance spectroscopy: application to selective NOE experiments. Journal of the American Chemical Society 117(14):4199--4200, 1995. BibTeX [dpfgse]

4. Bax, AD and Davis, DG. MLEV-17-based two-dimensional homonuclear magnetization transfer spectroscopy. J magn Reson 65(2):355--360, 1985. BibTeX [mlev]