Hartmann-Hahn transfer coupling constant determination

Even in the absence of relaxation, Hartmann-Hahn transfer depends on a large number of parameters pulse sequence parameters (multiple-pulse sequence, irradiation frequency, average rf power, etc.) and spin system parameters (size of the spin system, chemical shifts, /-coupling constants). For most multiple-pulse sequences, these parameters may be destilled into effective coupling tensors, which completely determine the transfer of polarization and coherence in the spin system. This provides a general classification scheme for homo- and heteronuclear Hartmann-Hahn experiments and allows one to characterize the transfer properties of related... 

For the qualitative and quantitative determination of coupling constants, Hartmann-Hahn transfer can be of assistance and also provides a number of new approaches. These approaches are based on Hartmann-Hahn transfer functions or on the efficient transfer of coherence in one subset of the spin system while the polarization of a second subset of spins remains untouched (E.COSY principle). Furthermore, in combination with other experiments, the in-phase multiplets of Hartmann-Hahn experiments can be used as a reference in an iterative fitting of coupling constants in antiphase multiplets. 

Homonuclear and heteronuclear coupling constants can be determined from the mixing-time dependence of Hartmann-Hahn transfer (see Sections II and VI). For example, for two heteronuclear spins 1 /2, the ideal polarization-transfer frequency under planar Hartmann-Hahn mbdng is 7,5/2 (see Section VI). Heteronuclear H- Si coupling constants have been determined in IS, I2S, and I S spin systems by Fourier analysis of the cross-polarization intensity as a function of the mbdng time (Bertrand et al., 1978a) and by an iterative fitting procedure (Murphy et al., 1979). 

Broadband Hartmann-Hahn transfer can also be of assistance in alternative approaches to determine coupling constants that do not rely on E.COSY-type multiplets that are separated by large one-bond couplings. The homonuclear two-dimensional PICSY (pure in-phase correlation spectroscopy) experiment (Vincent et al., 1992, 1993), which is based on selective Hartmann-Hahn transfer using doubly selective irradiation, can... 

Finally, broadband and multiple-step selective Hartmann-Hahn transfer can be of assistance in the determination of long-range heteronuclear coupling constants in crowded spectra, van Halbeek and co-workers used broadband and multiple-step selective Hartmann-Hahn transfer in onedimensional experiments to determine long-range heteronuclear coupling constants in oligosaccharides (Poppe and van Halbeek, 1991 Poppe et al., 1994). 

In favorable cases, intensities of cross-peaks between the resonances of two spins i and m that are not directly coupled may yield qualitative information about couplings that are involved in the transfer pathway. Clore et al. (1991) showed that in homonuclear Hartmann-Hahn spectra of proteins, the relative size of the two cross-peaks between the amide and the two H protons yields semiquantitative information about the relative size of the two involved V(H , H ) coupling constants in each amino acid residue. In order to reduce overlap, a three-dimensional N-separated H- H Hartmann-Hahn experiment was employed. With a relatively short mixing time of 30 ms, the relative size of V(H ,H ) coupling constants could be determined with sufficient accuracy to allow stereospecific assignment of the j8-methylene protons. Constantine et al. (1994) used cross-peak and diagonal-peak intensity ratios derived from three-dimensional C-edited TOCSY-HMQC spectra to obtain qualitative or semiquantitative estimates of vicinal H- H coupling constants. 

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