17 O MAS NMR Correlation Spectroscopy at High Magnetic Fields.

The structure of two protected amino acids, FMOC-l-leucine and FMOC-l-valine, and a dipeptide, N-acetyl-l-valyl-l-leucine (N-Ac-VL), were studied via one- and two-dimensional solid-state nuclear magnetic resonance (NMR) spectroscopy. Utilizing 17 O magic-angle spinning (MAS) NMR at multiple magnetic fields (17.6-35.2 T/750-1500 MHz for 1 H) the 17 O quadrupolar and chemical shift parameters were determined for the two oxygen sites of each FMOC-protected amino acids and the three distinct oxygen environments of the dipeptide. The one- and two-dimensional, 17 O, 15 N-17 O, 13 C-17 O, and 1 H-17 O double-resonance correlation experiments performed on the uniformly 13 C,15 N and 70% 17 O-labeled dipeptide prove the attainability of 17 O as a probe for structure studies of biological systems. 15 N-17 O and 13 C-17 O distances were measured via one-dimensional REAPDOR and ZF-TEDOR experimental buildup curves and determined to be within 15% of previously reported distances, thus demonstrating the use of 17 O NMR to quantitate interatomic distances in a fully labeled dipeptide. Through-space hydrogen bonding of N-Ac-VL was investigated by a two-dimensional 1 H-detected 17 O R3 -R-INEPT experiment, furthering the importance of 17 O for studies of structure in biomolecular solids.