STAR-HMBC for Bruker (hmbcacbigpl2ndqf)

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Basic facts about hmbcacbigpl2ndqf

Synopsis: STAR-HMBC

Family: 2D HMBC

Code authors:

Copyright: Bruker, Inc.

Introduction

The hmbcacbigpl2ndqf is a pulse sequence for Bruker epuipment. It is a variation of 2D HMBC technique where it is possible to differentiate ²J_CH and ³J_CH correlations[1]. It's very useful in structural elucidation of natural products. A drawback of this experiment is the lower sensitivity detection compared to the common HMBC.

Delays

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

d2 - Calculed autmatically based in cnst2

d6 - Calculed autmatically based in cnst14 - evolution of long range coupling. (83 ms from cnst14 = 6 Hz)

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

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 8.

Carrier frequencies

O1 (or O1P for the value in ppm) - in the middle of ¹H spectrum.

O2 (or O2P for the value in ppm) - in the middle of ¹³C spectrum.

Hard 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 (p2) 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.

If waveform Crp60,0.5,20.1 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
• gpnam2 SINE.100
• gpnam3 SINE.100
• gpnam4 SINE.100
• gpnam5 SINE.100
• gpnam6 SINE.100
• gpnam7 SINE.100
• gpnam8 SINE.100

Strengths of gradients are set by parameters:

• gp1:gp2:gp3:gp4:gp5:gp6:gp7:gp8 - 50:30:40.1:60:-40:-20:11:-11

Setup Constants

• cnst2 - coupling constant for ¹J_CH (recommended - 145 Hz)

• cnst6 - minimal coupling constant for ¹J_CH (recommended - 125 Hz)

• cnst7 - maximum coupling constant for ¹J_CH (recommended - 165 Hz)

• cnst14 - minimal coupling constant for long range J_CH (recommended - 6 Hz)

• cnst15 - maximum coupling constant for long range J_CH (recommended - 10 Hz)

• cnst16 - scaling factor for splitting pattern of the multiples (recommended - 15-24)

References

1. Krishnamurthy, VV and Russell, DJ and Hadden, CE and Martin, GE. 2J, 3J-HMBC: a new long-range heteronuclear shift correlation technique capable of differentiating 2JCH from 3JCH correlations to protonated carbons. Journal of Magnetic Resonance 146(1):232--239, 2000. BibTeX [star-hmbc]

2. Hadden, CE and Martin, GE and Krishnamurthy, VV. Improved Performance Accordion Heteronuclear Multiple-Bond Correlation Spectroscopy--IMPEACH-MBC. Journal of Magnetic Resonance 140(1):274--280, 1999. BibTeX [impeach-mbc]

3. Hadden, CE and Martin, GE and Krishnamurthy, VV. Constant time inverse-detection gradient accordion rescaled heteronuclear multiple bond correlation spectroscopy: CIGAR-HMBC. Magnetic Resonance in Chemistry 38(2):143--147, 2000. BibTeX [cigar-hmbc]

4. Wagner, R and Berger, S. ACCORD-HMBC: a superior technique for structural elucidation. Magnetic Resonance in Chemistry 36(S1):S44--S46, 1998. BibTeX [accord-hmbc]