INEPT Insensitive Nucleus Enhancement by Polarization Transfer

J splittings cannot be directly resolved. In addition to the obvious advantage of providing a map of chemical bonds between the spins, /-based transfers do not require spin-locking and are not disturbed by molecular motions. The major drawback of polarization transfer through J coupling is that the delays involved in the pulse sequences, such as insensitive nuclei enhanced by polarization transfer (INEPT) [233] or heteronuclear multiple-quantum coherence (HMQC)... 

Insensitive Nuclei Enhanced by Polarization Transfer (INEPT) method (see Table 3.13). 

The NMR signals of insensitive nuclear spins can be enhanced by transferring polarization from a more sensitive species to which they are coupled. The well-known pulse sequences as the polarization transfer techniques are insensitive nuclei enhanced by polarization transfer (INEPT), distortionless enhancement by polarization transfer (DEPT), and reverse insensitive nuclei enhanced by polarization transfer (RINEPT) The INEPT sequence is an alternative to the nuclear Overhauser effect. The INEPT experiment does not require any particular relaxation mechanism and therefore a better enhancement factor can be obtained. Furthermore it is demonstrated that INEPT sequence can be used to determine the multiplicity of each signal in a NMR spectrum. More recently, the INEPT and DEPT experiments were used for the coherence transfer via heteronuclear J-coupling between spin-1/2 and quadrupolar nuclei in the solids. " Fyfe et showed that coherence transfer via the scalar coupling between spin-1/2 and quadrupolar nuclei can be obtained in the solid state by using INEPT experiment. 

With the adaptation of NMR techniques for larger molecules, it becomes possible to analyze proteins with molecular weights reaching 50 kDa. These techniques include H-, N-TROSY (transverse relaxation-optimized spectroscopy, with the mutual cancellation of H-, N-dipole-dipole coupling and the N chemical shift anisotropy) and CRINEPT (Cross-correlated Relaxation-Enhanced Polarization Transfer, combining insensitive nuclei enhanced by polarization transfer (INEPT) transfer with cross-correlated relaxation-induced polarization transfer). They are used in conjunction with the N-, c-labeling of the protein for increased sensitivity. 

During the multidimensional NMR experiments, effective coherence transfer is important, which can be accomplished via accurate J-modulation (e.g.. Insensitive Nuclei Enhanced by Polarization Transfer, INEPT) or dipole-dipole (Nuclear Over-hauser Effect, NOE) interaction. As seen in the table, the couplings with F are quite different from those with H and The large and varied F couplings create opportunities and permit a larger variety of experiments, while at the same time, it also create complicated spectra with complex cross-peak patterns. The Vcf and Jcp in Table 24.2 is sufficient for the heteronuclear 2D-NMR experiments... 

Detection of insensitive nuclei enhanced by polarization transfer (INEPT) Morris and Freeman, J. Am. Chem. Soc. 101 760... 

The Insensitive Nuclei Enhanced by Polarization Transfer (INEPT) experiment is useful to discuss for two reasons. First is its utility in enhancing the S/N level in X-nucleus-detected spectra such as NMR. Second is because it is the basis for building many 2D- and 3D-NMR experiments described below. 

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