Hartmann-Hahn transfer classification

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... 

Since the seminal paper of Braunschweiler and Ernst (1983), many experimental mixing schemes have been proposed for broadband homonuclear Hartmann-Hahn transfer. The most important mixing sequences are summarized in alphabetical order in Table 2. The listed names of the sequences are either acronyms that were proposed in the literature or acronyms composed from the initials of the authors who introduced them. For each sequence, the expansion scheme that is applied to the basic (composite) pulse R is indicated. For symmetric composite pulses R that can be decomposed into a composite pulse 5 and its time-reversed variant 5, only S is specified in Table 2 for simplicity and classification. For example, the composite 180° pulse R = 90 180 90 (Levitt and Freeman, 1979), which forms the basis of the MLEV-16 sequence, consists... 

A large number of polarization-transfer experiments already exist that are based on the Hartmann-Hahn principle, and the number of Hartmann-Hahn mixing sequences is still rapidly growing. Therefore, it is important to have classification schemes that allow one to disentangle the plethora of known (and potential) mixing sequences. In the NMR literature, a number of different classification schemes have been used for Hartmann-Hahn experiments. However, the nomenclature of different authors is not always uniform (and in some cases it is even contradictory). In this section, existing classification schemes are reviewed and discussed. This discussion also defines the nomenclature that is used in this review. 

Fig. 6. Classification schemes for Hartmann-Hahn experiments based on (A) the aggregation state of the sample, (B) nuclear species of the spins between which magnetization is transferred, (C) dynamics of magnetization transfer and its reach within a spin system, (D) isotropic or nonisotropic magnetization transfer, (E) magnitude of effective fields, (F) type of effective coupling tensors, (G) active bandwidth of the sequence, (H) type of multiple-pulse sequence, and (I) suppression of cross-relaxation.

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