Multiplicity edited HMBC

The edited HMBC experiment edits into two subspectra according to the number of protons attached to ¹³C nuclei being odd or even.

Sequence

a) Standard sequence

b) Up-down sequence

HMBC pulse sequences with a 3^rd order low-pass J filter for editing into two subspectra according to the number of directly attached protons being odd or even:

Filled and open bars refer to /2 and pulses, respectively, while the dashed box represents ¹³C decoupling. = (2×¹J_CH)^-1 and is the delay necessary for a gradient.

The initial four gradients of the low-pass J filter can be set an order of magnitude weaker than the other gradients for formation of heteronuclear gradient echoes.

The recommended phase cycle is:

• ₁ = {x, -x, -x, x},
• ₂ = {x, x, 4(-x), x, x},
• ₃ = {4(x), 4(y), 4(-x), 4(-y)},
• with receiver phase {x, -x}.

The delays for the 3rd order low-pass J filter is

• ₁ = ½ [¹J_min + 0.07(¹J_max - ¹J_min)]^-1,
• = ₂ = [¹J_max + ¹J_min]^-1,
• ₃ = ½ [¹J_max - 0.07(¹J _max - ¹J_min)]^-1.

a) Standard HMBC pulse sequence where the echo is selected by the filled gradients and the antiecho by the open gradients;

b) up-down HMBC pulse sequence inverting ¹³CH and ¹³CH₃ peaks relative to the standard sequence and where the echo is selected by the +5G/-5G gradients and the antiecho by the -3G /+3G gradients.

References

• Nils T. Nyberg and Ole W. Sørensen Multiplicity-edited Broadband HMBC NMR spectra Magnetic Resonance in Chemistry xx in press 2006


• Schulte-Herbrüggen, T., Meissner, A., Papanikos, A., Meldal, M., and Sørensen, O.W. Optimizing delays in the MBOB, broadband HMBC, and broadband XLOC NMR pulse sequences J.Magn.Reson. 156 282-294 2002

Code and procedures

For Bruker. The Varian code is incorporated into the improved edited HMBC and can be downloaded from here