Dual processing of two-dimensional exchange data in magic angle spinning NMR of solids

We discuss procedures for processing data in rotor-synchronized two-dimensi onal magic angle spinning (2D MAS) NMR exchange measurements for both struc tural and dynamical studies. We show, both mathematically and experimentall y, that there are two distinct data processing procedures that lead to 2D M AS exchange spectra with purely absorptive crosspeaks. One procedure is tha t described previously by Hagemeyer, Schmidt-Rohr, and Spiess (HSS), The ot her procedure is related, but different, and leads to crosspeak intensities given by the formulae of Herzfeld, Roberts, acid Griffin (HRG), In 2D MAS exchange experiments on doubly C-13-labeled L-alanylglycylglycine, we demon strate that the HSS and HRG crosspeak intensities can be extracted separate ly from the same data set and contain independent information. Processing a nd analysis of 2D MAS exchange data with both the HSS and the HRG procedure s may enhance utilization of the information content of 2D MAS exchange mea surements.