Heteronuclear dipolar coupling Hamiltonians

The geometric part of the heteronuclear dipolar coupling Hamiltonian is as follows ... 

There are several ways to enhance spin diffusion in such systems. One can broaden the zero-quantum line to such an extent that the intensity at frequency zero is non vanishing for all relevant chemical-shift differences. However, due to the normalization of the zero-quantum line, a broad line implies that the intensity/,y(0) is low and that the spin diffusion proceeds slowly. A broadening of the zero-quantum line can often naturally be achieved by the coupling to a strongly-coupled proton spin system in so-called proton-driven spin diffusion while the form of the heteronuclear dipolar-coupling Hamiltonian (Equation (4.3)) prevents polarization exchange with the protons, the... 

The PAR experiment may be described by considering two heteronuclear dipolar coupling interactions with one proton (7) in common, i.e., a Hamiltonian of the type... 

In the simplest setup, the two strong field components may be set identical to Ci = Cs = C. The relatively large CIX or CSX term averages isotropic and anisotropic chemical shift effects as well as the heteronuclear dipolar coupling interaction between 15N or 13C and H. The difference of - or the sum of - the B coefficients selects the form of the recoupled heteronuclear dipole-dipole coupling interaction, as expressed in terms of the effective Hamiltonian in the interaction frame of the rf irradiation... 

Rotational-echo double resonance (REDOR), originally introduced by Gullion and Schaefer [102], is a method to recouple heteronuclear spin pairs. The sequence relies on a train of rotor-synchronized n pulses applied to the I spin to interrupt the spatial averaging of the heteronuclear dipolar coupling under MAS to give a nonvanishing dipolar Hamiltonian over a full rotor cycle (Fig. 11.8). Typically, REDOR data are collected by col-... 

Fourier transformation over an incremented Hartmann-Hahn evolution period yields the eigenfrequencies of the (effective) Hartmann-Hahn Hamiltonian. In solid samples with resolved heteronuclear dipolar couplings (Muller et al., 1974), this approach yields heteronuclear dipolar oscillation spectra (Hester et al., 1975) if the heteronuclear spins are Hartmann-Hahn matched during the evolution period of the experiment. In liquid state NMR, Fourier transformation over incremented homonu-clear Hartmann-Hahn transfer periods yields so-called coherence-transfer... 

D is ealled the dipolar coupling constant and resonance frequency of the observed nuclei. The heteronuclear dipolar Hamiltonian can be expressed as... 

If no chemical-shift differences existed, an abundant low-y spin system in the absence of further spins (or in the presence of efficient heteronuclear spin decoupling) would behave in the same way as an abundant high-y spin system. In practice, however, the chemical-shift differences tend to be comparable to and often larger than the dipolar couplings and they must be included in the system Hamiltonian... 

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