Selective Population Transfer SPT

Applying rf fields of lower intensity to selectively perturb a single resonance or satellite line is the basis of the SPT or selective population transfer experiment. Perhaps the most interesting example of the utilization of SPT experiments, which form the basis for the INEPT, DEPT and other spectral editing experiments that have been developed, is found in the consideration of an AX heteronuclear spin system, e.g. or where the heteronuclear spin is insensitive relative 

---

Enhancements between signals that are strongly spin-coupled to each other are best ignored as they are prone to another competing phenomenon, that of Selective Population Transfer (SPT). This makes it difficult to decide if any observed enhancement is down to a genuine NOE, or is merely an SPT. SPT... 

SELECTIVE POPULATION TRANSFER (SPT) AS A WAY OF UNDERSTANDING INEPT COHERENCE TRANSFER... 

The rationale for INEPT can best be understood by looking first at a somewhat simpler continuous wave experiment for transferring polarization, selective population transfer (SPT). SPT can be understood simply in terms of the populations of energy levels, whereas INEPT requires consideration of coherent precessing magnetization. Figure 9.9 shows the energy levels and populations of an AX spin system, which we take to be H and 13C, respectively, in this example. At equilibrium the populations conform to a Boltzmann distribution. Because the H... 

The experiment described above is termed selective population transfer (SPT), or more precisely in this case with proton spin inversion, selective population inversion, (SPI). It is important to note, however, that the complete inversion of spin populations is not a requirement for the SPT effect to manifest itself. Any unequal perturbation of the lines within a multiplet will suffice, so, for example, saturation of one proton line would also have altered the intensities of the carbon resonance. In heteronuclear polarisation (population) transfer experiments, it is the heterospin-coupled satellites of the parent proton resonance that must be subject to the perturbation to induce SPT. The effect is not restricted to heteronuclear systems and can appear in proton spectra when homonuclear-coupled multiplets are subject to unsymmetrical saturation. Fig. 4.20 illustrates the effect of selectively but unevenly saturating a double doublet and shows the resulting intensity distortions in the multiplet structure of its coupled partner, which are most apparent in a difference spectrum. Despite these distortions, the integrated intensity of the proton multiplet is unaffected by the presence of the SPT because of the equal positive and negative contributions (see Fig. 4.19d). Distortions of this sort have particular relevance to the NOE difference experiment described in Chapter 8. 

Figure 4.20. Selective population transfer (SPT) distorts proton multiplet intensities when the resonance of a coupled partner is unevenly saturated (b). These perturbations are more apparent in the difference spectrum (c), when the unperturbed spectrum (a) is subtracted.

The Selective Population Transfer (SPT) experiment is usually used in spin system analysis with a FT spectrometer. Normally the experimental SPT spectra are compared with calculated SPT spectra simulated using different combinations of coupling constant signs. In common with many textbooks the AMX spin system 2,3-dibromopropionic acid will be used to introduce the concepts behind the SPT experiment. The IH spin system parameters for 2,3-dibromopropionic acid are shown below. The only difference between Spin System A and Spin System B is the sign of the coupling constant J(H(2), H(3)), the results of SPT experiments will be used to distinguish between the two possible spin systems. 

The experiment described above is termed selective population transfer (SPT), or more precisely in tbis case with proton spin inversion, selective population inversion, (SPl). It is important to note, however, that the complete inversion of spin populations is not a requirement for the SPT effect to manifest itself. Any unequal perturbation of the lines... 

The relative signs of two-bond proton-carbon couplings in three quinolines, 6-ehloro-2-methylquinoline, 7-chloro-8-methylquinoline and 8-hydroxyquinoline, have been determined by Sakamoto and Ono by using hetero-nuclear Selective Population Transfer (SPT) Jh3C2 in... 

Selective population transfer (SPT) and selective population inversion (SPI) are FT equivalents of INDOR in the sense that the same type of information is obtained, though not yielding spectra that look exactly like INDOR spectra. In SPT,... 

---