Single quantum coherence transfer

DEPT (distortionless enhancement by polarization transfer) A onedimensional C-NMR experiment commonly used for spectral editing that allows us to distinguish between CH, CH2, CH, and quaternary carbons. Detectable magnetization The magnetization processing in the x y -plane induces a signal in the receiver coil that is detected. Only single-quantum coherence is directly detectable. 

Use a coherence transfer pathway for a noncoupled 13C similar to that in Eq. 12.4 or prepare a suitable vector diagram to show its coherence state after the evolution period of Fig. 12.4. Verify that the phase cycling procedure described for INADEQUATE cancels the single quantum coherence from this 13C. 

Heteronuclear multiple-quantum correlation Experiment for tailored correlation spectroscopy of H and H resonances in peptides and proteins Homonuclear Hartmann-Hahn spectroscopy Heteronuclear quadruple-quantum coherence Heteronuelear triple-quantum coherence Heteronuclear single-quantum coherence TOCSY sequences developed at the Indian Institute of Chemical Technology Insensitive nucleus enhancement by polarization transfer... 

Figure 1. Gradient-enhanced heteronuclear single quantum coherence pulse sequence with coherence transfer selection and artifact suppression gradients. All pulses are of phase x unless otherwise indicated.

The HSQC (Heteronuclear Single Quantum Coherence) experiment is another widely used inverse detection experiment. It provides essentially the same information as HMQC, but relies on a different sequence of pulses to effect the transfer of magnetization between H and the heteronucleus. A direct comparison of HMQC and HSQC in the study of a natural product has indicated some advantages of the latter-sequence, which may provide improved sensitivity and narrower crosspeaks for improved resolution. ... 

Using fast amplitude modulation pulses it is possible to redistribute the population of the spin energy levels. This is the Rotor Assisted Population Transfer (RAPT) method introduced by Yao et al. [57]. It has been shown that enhancement by a factor of 1.5-2 is achieved in a MAS experiment of spin-3/2 nuclei when RAPT is applied before the excitation pulse. It is also possible to combine RAPT with MQMAS in an experiment which uses single-quantum coherences for the excitation of multiple-quantum coherences. Madhu and Levitt [58] have shown that a combination of RAPT and RIACT-FAM gives the best performance for MQMAS experiments of spin-3/2 systems. 

The transverse magnetisation we observe directly in an NMR experiment is known as single quantum coherence. Multiple quantum coherence, however, cannot be directly observed because it induces no signal in the detection coil. For multiple quantum coherence to be of use to us, it must be transferred back into signal quantum coherence by the action of rf pulses. The concept of coherence is developed further in Chapter 5. 

The coherence transfer pathway must start with p = 0 as this is the order to which equilibrium magnetization ("-magnetization) belongs. In addition, the pathway has to end with p = 1 as it is only single quantum coherence that is observable. If we use quadrature detection (section 9.2.2) it turns out that only one of p = 1 is observable we will follow the usual convention of assuming that p = -1 is the detectable signal. 

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