Rotational-echo, adiabatic-passage, double-resonance: A new method for the recovery of dipolar interactions between spin-1/2 and quadrupolar nuclei during magic angle spinning.

摘要

In solid-state nuclear magnetic resonance (NMR), spectra are complicated by the directional dependance of various spin interactions, which are not motionally averaged in the solid state. To improve resolution, magic angle spinning (MAS) is employed to artificially average the interaction Hamiltonian to its isotropic chemical shift values. Unfortunately, such averaging removes dipolar coupling information from the spectrum, resulting in the loss of distance information between the coupled spins. Such information is desirable for structure determination.;Various techniques have been developed for recovering dipolar coupling between both homo- and heteronuclear spins, which involve changing the relative spacial coordinates of the spin Hamiltonians. However, such techniques depend on application of radio-frequency energy to irradiate the spins; for quadrupolar nuclei with broad resonances, this is technically difficult. A method is presented for measuring dipolar interactions between spin-1/2 nuclei and quadrupolar nuclei using rotational-echo, adiabatic-passage, double-resonance (REAPDOR) NMR. REAPDOR avoids the neccessity of fully irradiating the quadrupolar resonance by taking advantage of the modulation of the quadrupolar interaction during MAS in order to cause adiabatic transfer of magnetic coherence.;A three-tiered approach to evaluating the new technique of REAPDOR has been chosen. This evaluation is presented in terms of the scope, theory, and application of REAPDOR.