Rotational-echo adiabatic-passage double resonance

It was shown that REDOR or its variants can be used when one coupling partner is a quadrupolar spin.113,114 However, there are some limitations, such as the fact that only a fraction of the spin-1, nuclei are involved in the dephasing.115 Accordingly, more specific dephasing methods have been proposed for this type of system. One is TRAPDOR (transfer of population in double resonance), which uses continuous irradiation.116 The other is REAPDOR (rotational-echo, adiabatic passage, double resonance),117,118 which is a more straightforward extension of REDOR. 

There have been many papers reporting the biological applications of solid-state 170 NMR.89-100 This section briefly describes several notable examples of 170 NMR for biological solids, including 13C-170 Rotational Echo Adiabatic Passage Double Resonance (REAPDOR) experiments,100 the ONIOM methods for NMR calculations27 and 170 NMR studies of carbohydrates98 and a peptide-lipid complex.92... 

The REDOR experiment has been proposed for spin-1/2 pairs. For quadmpolar nuclei-spin-1/2 pairs, the use of this experiment is limited. The main reason behind this is the fact that a significant quadmpolar broadening (in order of several MHz) makes the Sn pulses inefficient for the inversion of S populations. For such systems REDOR experiments can be applied if the n pulses are apphed to the spin-1/2 nucleus and only central transition is observed for a halfinteger spin. The transfer of population in double resonance (TRAPDOR) or rotational-echo adiabatic passage double resonance (REAPDOR) experiment offer a much better choice for the measurement of quadmpolar nuclei-spin-1/2 pair dipolar couplings. 

The development of the double resonance experiments described in Section 3.8.2 was targeted at spin- /i systems. TRAPDOR and Rotational-Echo Adiabatic Passage Double Resonance (REAPDOR) experiments are designed specifically for quadrupolar nuclei and do not work on systems containing only spin- /2 nuclei. These MAS experiments still rely on the modulation of the heteronuclear dipolar coupling (as in the REDOR experiment) to prevent an echo from refocusing, but the modulation is no longer by 180° pulses. 

The synthesis of a range of silicon boron carbonitride ceramics can conveniently be carried out by thermal treatment of suitable amorphous precursor molecules in which the desired atomic linkages are already in place. A series of new amorphous precursor molecules has been investigated by "B MAS NMR and double resonance techniques such as Si- B) Rotational Echo Adiabatic Passage DOuble Resonance (REAP-DOR) and B-j Si) Rotational Echo DOuble Resonance (REDOR) (van Wiillen and Jansen 2001). The results indicate the presence of hexagonal BN and (3-Si3N4 in some... 

HETCOR), MQ REDOR (Rotational Echo Double Resonance), TRAPDOR (TRAnsfer of Populations in DOuble Resonance) and REAPDOR (Rotational Echo Adiabatic Passage Double Resonance), and the recently introduced /-cou-phng based experiments. A few other excellent reviews on MQMAS NMR have been recently pubhshed and complement the present review [1,2]. 

It proved to be possible to identify ordered Si-O-Al environments in molecular sieves by 27Al -29Si REAPDOR (i.e. rotational echo adiabatic passage double resonance) NMR techniques.350 NMR studies have been reported for the following silicoaluminophosphate molecular sieves SAPO-5 351 SAPO-11 and -31 352,353 H-SAPO-34 and -37 354 and SAPO-44.355... 

The most powerful tool to study the intermediate range order in amorphous Si/B/N/(C) networks is MAS-NMR spectroscopy including advanced double resonance techniques such as B- Si rotational echo double resonance (REDOR), Si- B] rotational echo adiabatic passage double resonance (REAPDOR), and C- B] REAPDOR. These methods utilize the heteronu-clear coupling between the observed nucleus and a nucleus in the second coordination sphere to get information about the internuclear distance of the two nuclei. 

Gulion et al. [169]. The C- REAPDOR (rotational echo adiabatic passage double resonance) NMR measurement was carried out using one part of and four parts of singly labelled samples prepared as P P-sheet and P P-sheet structures. The final results are presented in Fig. 2.36. 

Heteronuclear dipolar-coupling-based double-resonance NMR techniques such as rotational-echo double-resonance [98], rotational-echo adiabatic passage double-resonance (REAPDOR) [99] and transfer of populations in double-resonance [100] are useful tools for the characterization of intermediate-range ordering phenomena involving two unhke spins in a wide variety of materials. These techniques utilize the distance-dependent heteronuclear dipole—dipole interaction to obtain information on intemuclear distance between the two spins involved under the MAS conditions. 

T. Gulhon, Measurement of dipolar interactions between spin-12 and quadrupolar nuclei by rotational-echo, adiabatic-passage, double-resonance NMR, Chem. Phys. Lett. 246 (1995) 325-330. 

Ganapathy et al. (2004) studied molecular sieve ETAS-10 and showed that the silicon sites tetrahedrally connected to aluminum in framework positions of a molecular sieve can be identified by a selective reintroduction of the heteronuclear Al- Si dipolar interaction through Rotational Echo Adiabatic Passage DOuble Resonance (REAPDOR) NMR. They used an effective dipolar dephasing of the Si-O-Al, over Si-O-Si, environments to identily silicon sites in the immediate vicinity of aluminum. The direct NMR estimation of Al-Si distance gave =0.323 nm. REAPDOR... 

REAPDOR rotational echo adiabatic passage double resonance... 

In this context, we must at least briefly mention the REAPDOR experiment [94] (rotational-echo adiabatic-passage double resonance), a technique that is very similar to the BJ3DOR pulse sequence, although it is more efficient, as it is designed especially for quadrupolar nuclei utilizing an adiabatic pulse of length for the polarization transfer (Fig. 25). In this... 

These techniques can be applied also for S-X (with X having / > 0.5) dipole couplings in its REAPDOR (rotational-echo adiabatic-passage double-resonance) version. ... 

---