J-HMBC for Bruker (hmbcetgpjcl2nd)

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Basic facts about hmbcetgpjcl2nd

Synopsis: J-HMBC

Family: 2D JHMBC

Code authors:

Copyright: Bruker, Inc.

Introduction

The hmbcetgpjcl2nd corresponds to the fig 1B. In the paper cited by the pulse sequence file, except that there is one less X-nucleus 90^o pulse in the low pass J-filter element (a second order J-filter is used instead of the third order).

Note: there is also a standard HMBC version of this pulse sequence - hmbcetgpl2nd which sets up in the same way, except it does not have p14 shaped pulse.

Delays

d1 - recycling delay (1-5 x T1)

d6 - calculated automatically from cnst13 - delay for evolution of long range couplings [1/(2 x J_{Long range}) - (500 ms from cnst13 = 1 Hz)

d16 - gradient recovery delay (depends on the probe) may be on the order of 100-200 μs.

in0 - 1/(2*SW), where SW is spectral window in the X-dimension

Acquisition in the indirect dimension and number of scans

The incremented delay used to record evolution in the indirect dimension is 2xd0. d0 is automatically calculated within the experiment using in0.

in0 equals 1/(2*SW) one half of the inverse of the spectral window width in X dimension. (1/2) is due to nd0=2 (below).

td1 - number of experiments to record in the X dimension

nd0 = 2 - there are two delays d0 within the X dimension evolution delay.

ns - number of scans must be a multiple of 16 as there are 16 steps in the phase cycle.

RF pulses

¹H channel

p1 - hard ¹H 90^o at power level pl1 - the only ¹H to set up for this experiment. Length of 180^o pulse is calculated automatically.

X-nucleus channel

p3 - hard X-nucleus 90^o at power level pl2.

Shaped 180 pulses

This sequence has two shaped 180 pulses at the X-nucleus channel - p14 and p24

p14 - is a refocusing pulse at power level sp3.

spnam3 must be set to the name of the waveform file.

p14 of 500μs is recommended for spnam3 set to Crp60,0.5,20.1.

p24 - is an inversion pulse at power level sp7

spnam7 must be set to the name of the waveform file.

p24 of 2ms is recommended for spnam7 set to Crp60comp.4.

If waveforms Crp60,0.5,20.1 and Crp60comp.4 are not available on the system they need to be prepared using the stdisp tool or an appropriate replacement used instead.

Gradient pulses

Duration of all gradients is set by:

• p16 (recommended default - 1 ms)

Shapes of all gradients are recommended to be sine bell implemented in 100 steps, i.e.:

• gpnam1 SINE.100
• gpnam3 SINE.100
• gpnam4 SINE.100
• gpnam5 SINE.100

Strengths of gradients are set by parameters:

• gp1, gp3, gp4, gp5.

Gradient gp1 is used for the Echo-AntiEcho coherence selection scheme, value of gp1 is recommended to set at 16/3 of gp3 (the first gradient within the LPJF element) - i.e. approximately 5x stronger.

Setup of the remaining gradients is described in the following section. gp1 is the strongest gradient in the pulse sequence - so its strength could be used as the "reference" and strengths of all the remaining gradients calculated using the recommended ratios.

Setup of the Low-pass J filter

Low pass J filter is an element that destroys coherence in the strongest J-coupling ¹H - heteroatom (X nucleus) pairs. Since those have the largest values of J coupling, frequency of the evolution of those coherences will be the fastest.

Therefore filter that removes those rapidly evolving coherences is called low-pass filter, i.e. one that will "let through" the coherences with the lowest frequencies of evolution.

hmbcetgpjcl2nd uses a second order low pass J-filter: ¹H 90^o excitation followed by two elements (gradient, X-nucleus 90^o) and finally, followed by one more gradient that must refocus the ¹H magnetization that did not take part in the ¹H-X-nucleus coupling.

Those gradients are gp3, gp4 and gp5 and they must have ratios: 3:-2:-1.

Strength of the last two gradients (gp4, and gp5) add up to the negative of the first one (gp3) - which recovers ¹H magnetization that survived after the filter.

Constant parameters: cnst6 and cnst7 are used to calculate delays before the first and second X 90^o pulses.

Recommended values for these are:

• cnst6 expected minimum of one-bond ¹H-X J coupling (¹JXH) (recommended default for ¹³C - 125 Hz)
• cnst7 expected maximum of ¹JXH (recommended default for ¹³C - 165 Hz)

Setup of the expected long range coupling

Parameter cnst13 - should equal the value of the optimally observed long range ¹H-X J coupling. (recommended default - 1 Hz for d6 equal to 500 ms (DELTA))

References

1. Meissner, A and Soerensen, OW. Measurement of J (H, H) and long-range J (X, H) coupling constants in small molecules. Broadband XLOC and J-HMBC. Magnetic Resonance in Chemistry 39(1):49--52, 2001. BibTeX [jhmbc]