title: Recoupled separated-local-field experiments and applications to study intermediate-regime molecular motions.
abstract: A specific separated-local-field NMR experiment, dubbed Dipolar-Chemical-Shift Correlation (DIPSHIFT) is frequently used to study molecular motions by probing reorientations through the changes in XH dipolar coupling and T₂. In systems where the coupling is weak or the reorientation angle is small, a recoupled variant of the DIPSHIFT experiment is applied, where the effective dipolar coupling is amplified by a REDOR-like π-pulse train. However, a previously described constant-time variant of this experiment is not sensitive to the motion-induced T₂ effect, which precludes the observation of motions over a large range of rates ranging from hundreds of Hz to around a MHz. We present a DIPSHIFT implementation which amplifies the dipolar couplings and is still sensitive to T₂ effects. Spin dynamics simulations, analytical calculations and experiments demonstrate the sensitivity of the technique to molecular motions, and suggest the best experimental conditions to avoid imperfections. Furthermore, an in-depth theoretical analysis of the interplay of REDOR-like recoupling and proton decoupling based on Average-Hamiltonian Theory was performed, which allowed explaining the origin of many artifacts found in literature data.
authors: Instituto de Física de São Carlos, Universidade de São Paulo, Caixa Postal 369, CEP 13560-970 São Carlos, São Paulo, Brazil.
authors: Marcio Fernando
authors: MF
authors: Cobo
authors: Anja
authors: A
authors: Achilles
authors: Detlef
authors: D
authors: Reichert
authors: Eduardo Ribeiro
authors: ER
authors: Deazevedo
authors: Kay
authors: K
authors: Saalwächter