HAT HMBC

HAT HMBC is a hybrid of H2BC and HMBC aiming at establishing two-bond correlations absent in H2BC spectra because of vanishing ³J_HH coupling constants. The basic idea is to create an additional phase difference in the multiplet structure in HMBC peaks with respect to the ⁿ⁺¹J_HH coupling constant between the proton(s) attached to a ¹³C and a ¹H separated by n bonds. Thus HMBC peaks associated with small J_HH will be the most attenuated in a HAT HMBC spectrum in comparison to a regular HMBC spectrum, i.e. peaks associated with ⁿ⁺¹J_HH and ⁿJ_CH will for n > 2 usually be strongly attenuated. The HAT HMBC pulse sequences contain the same number of pulses as regular HMBC and are only a few milliseconds longer. Multiplicity editing is an inherent part of HAT HMBC and the HAT (Homonuclear J ATtenuated) effect only applies for protonated carbons.

HAT HMBC pulse sequence pair with a 3^rd order low-pass J filter:

a) HAT+ HMBC sequence

b) HAT- HMBC sequence

Filled and open bars refer to /2 and pulses, respectively. = (2×¹J_CH)^-1 and is the delay necessary for a gradient. The delay is equal to the minimum t₁ time plus the time required for a proton pulse. The delay ' is the same as the delay but with the addition of the time needed for a carbon pulse.

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. In the HAT HMBC pulse sequences the echo is selected by the filled gradients and the antiecho by the open gradients;

The recommended phase cycle is an even number of scans out of:

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

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

• 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.

To produce the edited spectra simply combine the subspectra in the following manner:

¹³CH and ¹³CH₃ = a - b

Example Spectra

In the figure below are shown ¹³C and ¹³CH₂ spectrum (right) with the ¹³CH and ¹³CH₃ spectrum (left) of mannose in D₂O.

Reference

• Andrew J. Benie and Ole W. Sørensen HAT HMBC: A hybrid of H2BC and HMBC overcoming shortcomings of both J. Magn. Reson. in press 2006

Code and procedures

For Varian and Bruker.