Hartmann-Hahn match

The spin-locking and CP behavior of the most commonly used SQ coherence (CT) in quadrupolar nuclei under static and MAS conditions has been described in detail by Vega using the fictitious spin-1/2 approximation [223]. In a static sample, the Hartmann-Hahn matching condition requires that co = nut where co ut is one of the nutation frequencies associated with the SQ coherence of the quadrupolar S spin (see Sect. 2.3.4). In the simple case of on-resonance SQ-CP this translates to [224]... 

Fig. 17 Efficiency of H — nB CPMAS in borax measured as a function of co (Hartmann-Hahn matching curve). The spectra were measured on-resonance at 9.4 T using = 6 kHz,...

Adamantane (C10H16) External referencing for 13C spectra, optimizing Hartmann-Hahn match, linewidth measurement, sensitivity measurement [30]... 

Hexamethylbenzene (Ci2H18) Optimizing Hartmann-Hahn match [30]... 

Hartmann-Hahn match, and cross-polarization mixing time are discussed in relation to obtaining quantitative NMR results. 

If we used a continuous-wave spin lock (ROESY mixing scheme) for TOCSY mixing, the only way efficient transfer could occur via 7 couplings within a spin system would be if the two protons have opposite resonance offsets (v0 - vr), where vr is the carrier or reference frequency. This is a special case of the Hartmann-Hahn match ... 

Radiofrequency (RF) power output levels should be adjusted for a Hartmann-Hahn match. The pulse sequence illustrated in Fig. 4.5.2 should be used with the following parameters ... 

The Hartmann-Hahn match can be found by varying the B S) power level so that maximum intensity is observed. It is important to ensure that the observed spectrum results from the CP (the best indication of this is the absence of the signal after increase of the power beyond the H-H matching condition). 

The derivative A of the effective field Iv Kv,) = ( y/2 7r) fi (r, ) is central to the theory of heteronuclear decoupling, where it represents the effective scaling factor of heteronuclear coupling constants (Waugh, 1982b). The parameter A is also a measure of the degree to which spins with similar chemical shifts are Hartmann-Hahn matched, because... 

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... 

Figure 2.23. A. Schematic representation of the CP sequence for H —> X. B. the changes of the energy levels from the laboratory frame and in the rotating frame showing the Hartmann-Hahn match (separations are not to scale). C. The build-up of magnetisation for the C signals in the 2 carbons of glycine as a function of contact times with an inset of short contact times showing the effect of different Tis for each carbon.

Cis is a constant. In cases where the CP occurs between relatively isolated spins (e.g. pairs) the spin thermodynamic description cannot be applied. Rather than a smooth, continuous build-up of magnetisation, the CP curve shows structure, termed dipolar oscillations (Muller et al. 1974). The magnetisation oscillates between the proton and the X-nucleus. In the case where the system is exactly Hartmann-Hahn matched, the magnetisation of the S-spin is given by (Levitt et al. 1986)... 

Figure 2.24. A. One of the pulse sequences for modulating the Hartmann-Hahn match condition by ramping the X-nucleus transmitter amplitude. B. Comparison of H —> C CP for conventional CP (SACP) matched on the centreband and a sideband with RAMP-CP on a sideband of N-t-Boc-alanine showing the very much improved quantitative data for the six equally populated carbon sites. Taken from Metz, Ziliox and Smith (1996) with permission of the copyright owners.

Cross-polarization between spin 1=112 and S=l/2 systems is a relatively simple and well-understood process. For a static sample, under on-resonance conditions, there is a unique Hartmann-Hahn matching condition [73] at which polarization is transferred between the two sets of nuclei, given by... 

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