Measurement of internuclear distances in solid-state NMR by a background-filtered REDOR experiment

A background-filtered version of the rotational-echo double resonance (REDO R) experiment is demonstrated. The experiment combines a traditional REDOR pulse sequence with a double-cross-polarization (DCP) sequence to select on ly those signals coming from spin pairs of interest. The relatively ineffic ient DCP sequence, which transfers polarization from H-1 to N-15 and subseq uently to C-13, is improved by the use of adiabatic passages through the (- 1) sideband of the Hartmann-Hahn matching condition. The result is an effic ient 2D-REDOR pulse sequence that does not require a reference experiment f or removal of background signals. The data produced by the experiment are i deally suited to analysis by newly developed dipolar transform methods, suc h as the REDOR transform. The relevant features of the experiment are demon strated on simple labeled amino acids. Relative efficiencies of several oth er potential filtering methods are also compared, (C) 2000 Academic Press.