With a view to obtain (13)C chemical shift correlation spectra of uniformly labelled peptides/proteins at high magnetic fields and high magic angle spinning frequencies (omega(r)/2pi

Long-range (1)H,(13)C coupling constants ((n)J(CH)) are underutilized parameters for stereochemical structure determination, primarily because they are not easy to measure. This report describes a rapid and easily interpreted method for the measurement of one or more (n)J(CH) values based on a (13)C band-selective EXSIDE (SelEXSIDE), which reduces experiment times from many hours down to a few minutes while allowing a simple and straightforward readout of (n)J(CH) values from the resulting in-phase doublet signal.

An approach to the determination of the 2-(13)C' chemical shift (CS) tensor orientation in pyrimidine bases via heteronuclear MAS NMR spectroscopy is presented. Considering a dipolar coupled spin 1/2 network of the type S1-I-S2 consisting of directly bonded heteronuclear spins, we have carried out numerical simulations to assess the sensitivity of I-S REDOR spinning sidebands to the Euler angles defining the orientation of the I-S1 and I-S2 dipolar vectors in the I spin CS tensor principal axes system. Our investigations clearly demonstrate the potential of I-S REDOR studies in IS1S2 systems for obtaining with high reliability and accuracy the I spin chemical shift tensor orientation in the molecular frame spanned by the two internuclear vectors I-S1 and I-S2. The significant contribution to the observed REDOR sideband intensities from anti-phase operator terms which are present at the start of the data acquisition is illustrated. The procedure for the recording and analysis of the I-S REDOR spectra in IS1S2 systems is presented and the measurement of the 2-(13)C' CS tensor orientation in a polycrystalline sample of [1,3-(15)N2, 2-(13)C] uracil, which is one of the four bases in RNA, is experimentally demonstrated.

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