Dipolar rotational spin echo

C NMR has been used to investigate the phenyl ring motions occurring at room temperature in BPA-PC, by using the dipolar rotational spin echo technique [40], Indeed, the reduction in dipolar coupling between carbons and directly attached protons arising from molecular motion (of frequency... 

Fig. 16. Dipolar rotational spin-echo C-NMR spectra of poly(styrene-co-sulfone) as a function of the number of evolution cycles used during dipolar evolution (left).

Double Cross Polarization and Dipolar Rotational Spin-Echo 226... 

Fig. 15. Pulse sequence for dipolar rotational spin-echo, SN NMR experiment...

The reduction in the strength of the dipolar interaction by molecular motions of frequencies comparable to or greater than the dipolar interaction itself is a measure of the amplitude of the motion. Essentially two techniques have been proposed for this purpose [64, 72]. The first method consists of measuring the intensity of the dipolar side-band patterns, obtained from dipolar rotational spin-echo NMR and arising from the heteronuclear dipolar interaction, while the homonuclear dipolar interactions are... 

In the case of plasticized poly(butyral-co-vinyl alcohol) [73], use of dipolar rotational spin-echo CNMR in conjunction with C) determinations, has shown that the frequencies but not the amplitudes of cooperative main-chain motions of the polymer in the hard regions, corresponding to solid polymer associated with partially immobilized plasticizer, are influenced by interactions with the soft regions attributed to liquid plasticizer containing mobile polymer. From this result, a schematic representation of the partitioning of the polymer and plasticizer in terms of a two-phase domain model has been proposed. 

Figure 2. Dipolar rotational spin-echo 15.1-MHz nmr spectra of poly(p-chlorostyrene)...

M. Mvmowitz, R. Griffin, G. Bodenhausen, T. Huang, Two-dimensional rotational spin-echo nuclear magnetic resonance in solids correlation of chemical shift and dipolar interactions, J. Am. Chem. Soc. 103 (1981) 2529—2533. 

The angles a and P define the orientation of the sample relative to the Bo-field cor denotes the rotation frequency. For the REDOR reference experiment, the rotor-synchronised spin-echo experiment for the S nuclei (cf. Figure lA), the dipolar Hamiltonian integrated over one rotor period Tr averages to zero... 

Various ID and 2D high-resolution solid-state NMR techniques have been applied to hydrous silicate and aluminosilicate glasses simple acquisition, CPMAS, HETCOR, dipolar dephasing, spin counting, DQ correlation, and rotational echo double resonance (REDOR). ... 

We discussed earlier (Section I.C.2.) that a magnetization which has decayed in the rotating x -y plane due to external field inhomogeneity can be refocussed into an echo by an appropriate pulse. Such an echo is called the ordinary spin echo or a Hahn echo. The usual sequence for a Hahn echo is (7i/2)Q-T-(7t)gQ-x-echo where the subscript indicates the relative phase of the carrier. Hahn echoes in this sense cannot be formed in dipolar coupled solids where the local field is not... 

From the success of the cross-polarization experiments, one may predict success for a variety of related experiments that depend on the dipolar interaction (such as those of Veeman [951, where spin echoes are observed under magic-angle spinning and double resonance conditions). Further experiments that allow determination of internuclear distances should also be possible, including rotational-echo double-resonance (REDOR) NMR [96], and transferred-echo double-resonance (TEDOR) NMR [97], the latter being related to INEPT experiments in liquids. 

When dealing with homonuclear multiple-spin systems, polarization transfer in the zero-quantum subspace of the effective dipolar Hamiltonian is advantageous as the spin dynamics of the process may be described by a kinetic matrix. The USEME (unified spin echo and magic echo) and RIL (rotating/laboratory frame) sequences follow this zero-quantum-subspace philosophy and aim at broadband properties of the pulse sequence. 

Having demonstrated the achievement of high-resolution sohd state NMR capability, the authors describe experiments that combine the high-resolution aspect of MAS NMR with methods that retain the structure and/or dynamic information inherent in the anisotropic interactions. Rotational-echo double resonance (REDOR) allows the determination of D between isolated heteronuclear spin pairs. D is related simply and without approximation to intemuclear separation. Hence, REDOR makes possible the unambiguous direct determination of intemuclear distance between the labeled spin pair, independent of pair orientation, i. e., in amorphous and /or microaystaUine solids, and extends our abihty to quantitatively explore complex materials. It is also possible to extract intemuclear distance from homonuclear dipolar coupled spin pairs, and these experiments are also reviewed. 

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