COMBINED SAMPLE ROTATION AND MULTIPLE-PULSE NMR SPECTROSCOPIC STUDIES ON PROTONS BONDED TO N-14 NUCLEI IN SOLID AMINO-ACIDS

Solid-state high-resolution proton nuclear magnetic resonance spectra (NMR) of glycine, alanine, N-acetylglycine, and L-histidine hydrochloride monohydrate were recorded by using the CRAMPS technique. The protons bonded to N-14 nuclei showed characteristic line shapes which are explained by the N-14 quadrupole effects on the N-14-H dipolar interactions. The BR-24 pulse sequence was generally more effective than the MREV-8 sequence in yielding well-resolved H-1 CRAMPS spectra. In the case of the peptide proton bonded to an N-14 nucleus in N-acetylglycine, however, better resolved spectra were obtained by decoupling with the MREV-8, than with BR-24 pulse sequence, because a faster rotor-spinning frequency was required in this case to reduce the N-H dipolar interactions. Theoretical computer simulations of the line shapes show good agreement with those observed experimentally.