title: Dipolar and J encoded DQ MAS spectra under rotational resonance.
abstract: A two-dimensional (2D) double-quantum (DQ) experiment under rotational resonance (R(2)) conditions is introduced for evaluating dipolar couplings in rotating solids. The contributions from the R(2)-recoupled dipolar interaction and the J coupling can be conveniently separated in the resulting 2D R(2)-DQ spectrum, so that the unknown dipolar coupling can readily be extracted, provided that the values of the involved J coupling constants are known. Since the measured parameters are integral intensity ratios between suitably chosen absorption peaks in the 2D spectrum, the proposed method is characterized by a reduced sensitivity to relaxation parameters. The effect of rotor-modulated terms, including chemical shift anisotropy, is efficiently averaged out by synchronizing the excitation/reconversion time with the rotor period. All of these features are demonstrated theoretically by the example of two model systems, namely, isolated spin-pairs and a three-spin system. The results of the theoretical models are applied to both (13)C and (1)H nuclei to extract dipolar couplings in uniformly (13)C labeled L-alanine and a crosslinked natural rubber.
authors.affiliation: Institute for Technical Chemistry and Macromolecular Chemistry, RWTH Aachen, Worringerweg 1, D-52074 Aachen, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Filip
authors.forename: X
authors.initials: X
authors.lastname: Filip
authors.forename: M
authors.initials: M
authors.lastname: Bertmer
authors.forename: D E
authors.initials: DE
authors.lastname: Demco
authors.forename: B
authors.initials: B
authors.lastname: Blümich