Hartmann-Hahn transfer mixing periods

Fig. 31. Ideal coherence-transfer functions Tam> nd T/x> during multiple-step selective Hartmann-Hahn transfer in a three-spin system. In the first mixing step of duration T, = 1/(2/ ) coherence is selectively transferred from spin A to spin M. In a second mixing period of duration Tj = 1/(27mx) coherence is selectively transferred from spin M to spin X. (Adapted from Glaser and Drobny, 1989, courtesy of Elsevier Science.)...

Fig. 35. Experimental HCCH-COSY spectra of the fully C-labeled protein rhodniin with two heteronuclear Hartmann-Hahn transfer steps. The spectra were acquired at a spectrometer frequency of 600 MHz employing DIPST2 with = 4.8 kHz (A) and MGS-2 with = 3.78 kHz (B). In the experiments the heteronuclear Hartmann-Hahn mixing periods had a duration of 6 ms. The same plot levels were used for both spectra. (Adapted from Schwendinger et al., 1994, courtesy of Academic Press.)...

The combination of homonuclear Hartmann-Hahn transfer with homonuclear double- or zero-quantum spectroscopy yields the so-called DREAM experiment (double-quantum relay enhancement by adiabatic mixing Berthault and Perly, 1989) and the zero-quantum-(ZQ) TOCSY experiment (Kessler et al., 1990a), respectively. Multiplet-edited HOHAHA spectra can be obtained by adding a spin-echo sequence to the Hartmann-Hahn mbdng period (Davis, 1989a). 

The most important criteria for experimental Hartmann-Hahn mixing sequences are their coherence-transfer properties, which can be assessed based on the created effective Hamiltonians, propagators, and the evolution of the density operator. Additional criteria reflect the robustness with respect to experimental imperfections and experimental constraints, such as available rf amplitudes and the tolerable average rf power. For some spectrometers, simplicity of the sequence can be an additional criterion. Finally, for applications with short mixing periods, such as one-bond heteronuclear Hartmann-Hahn experiments, the duration Tj, of the basis sequence can be important. 

In multidimensional NMR experiments that contain several evolution and mixing periods, even more combinations are possible (Griesinger et al., 1987b). In these experiments, Hartmann-Hahn mixing periods with in-phase coherence transfer are of particular advantage, because the resolution is often limited in the indirectly detected frequency dimensions. 

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