Studies of heteronuclear dipolar interactions between spin-1/2 and quadrupolar nuclei by using REDOR during multiple quantum evolution

A new technique for measurements of dipolar interactions in rotating solids is presented that combines the capabilities of multiple quantum magic angle spinning (MQMAS) with the rotational echo double resonance (REDOR). It employs the dipolar recoupling between spin-1/2 (I) and quadrupolar (S) nuclei by applying a series of pi pulses to the I spins. In contrast to the previously reported MQ-REDOR method, the recoupling sequence is applied during the triple quantum, rather than single quantum evolution. As the dipolar effect is enhanced by the MQ coherence order, this new technique exhibits improved sensitivity toward weak dipolar interactions. (C) 1999 Elsevier Science B.V. All rights reserved.