Heteronuclear magnetization-transfer filters

Using this expression to compare excitation of with direct detection of C involving a single coherence transfer step from H to and with indirect detection of by double transfer from H to C to H shows that indirect detection provides an S/N which is (yiH/yi3c) = 8 times better than for direct detection. 

The SEDOR method is based on subtraction of large signals leading to small signal differences. It is sensitive to small signal errors and critically depends on spectrometer adjustments. The HYCAT method is illustrated in Fig. 7.2.33(a) [Kim4]. The initial 

Heteronuclear incoherent magnetization transfer is the transfer of longitudinal magnetization. It can proceed in the laboratory frame and in the rotating frame. The nuclear Overhauser effect (NOE) [Nogl] is a manifestation of polarization tranter in the laboratory frame. In the extreme narrowing limit saturation of dipolar relaxation of the I doublet of a heteronuclear IS two-spin- system leads to an enhancement of the S-spin polarization by a factor 

For C coupled to the Overhauser enhancement assumes a maximum value of = 3, 

The standard cross-polarization scheme due to Hartmann and Hahn requires the simultaneous application of spin-lock fields to both nuclear species, e. g. H and C. For optimum polarization transfer, the amplitudes Beff of the fields effective in the rotating frames of each nucleus have to match the Hartmann-Hahn condition (cf. Section 3.3.1) 

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The application of three and more gradients is necessary if multiquantum states are to be suppressed as in the double-quantum filtered COSY experiment or if CT pathways in heteronuclear spin systems should be selected in sequences which include magnetization transfer steps. 

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