REPT-HDOR experiment

Quantitative analysis of PDMS chain dynamics was derived from both the REPT-HDOR experiment and analysis of the ID signal intensity as a function of recoupling time. The conclusion is that PDMS seem to exist in a highly symmetric conformation, with all methyl groups experiencing the same local en-... 

Finally, we note that an analysis of H-13C spinning-sideband patterns obtained using the REPT-HDOR experiment (see Figure 16) has also been used to provide evidence of restricted dynamics in a shape-persistent polyphenylene dendrimer.184... 

Both REREDOR and REPT-HDOR experiments are used in an assessment of segmental dynamics in a dendritic polymer28 by examining the residual dipolar couplings through simulation of the /i sideband patterns arising from the two types of experiment. Fig. 19 shows the results for the phenyl rings in the polymer. 

The REDOR experiment has formed the basis for a large number of ideal pulse type recoupling experiments, and later finite pulse variants, for heteronuclear dipolar recoupling. These include experiments such as frequency selective REDOR (FS-REDOR) [80], TEDOR (Transferred Echo DOuble Resonance) [25], and 3D variants of TEDOR [81, 82], which have found important applications, e.g., for measurement of intemuclear 13C-15N distances in biological solids. We should also mention that rotor-encoded variants of TEDOR, such as REPT, HDOR [83], and REREDOR [84], have been proposed for 1H13C dipolar recoupling under high-speed MAS conditions. 

Figure 16. Pulse sequence and coherence transfer pathway diagram for the REPT-HDOR heteronuclear ( H-13C) experiment, which is suitable for recording rotor-encoded spinning-sideband patterns. Dark- and light-shaded rectangular blocks represent rf pulses of flip angle 90° and 180°, respectively. For more details, see ref 125.

An alternative to the REREDOR experiment is the REcoupled polarization transfer-heteronuclear dipolar order (REPT-HDOR),27 shown in Fig. 18(b). This experiment uses initial 1H transverse magnetization, rather than 13C as in the REREDOR experiment, to create a heteronuclear 1H-13C coherence (corresponding to dipolar order, described by a term 3IZSZ - IS in the density operator, where / = JH and S = 13C) in tx after dipolar... 

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