Secondary structures of peptides: 5 · 15N n.m.r. CP/MAS spectroscopy of solid polypeptides and gramicidin-S

摘要: Abstract 30.5 MHz 15 N m.m.r. ( CP/MAS ) spectra of various solid polypeptides were measured using the cross-polarization/magic angle spinning technique. In order to obtain optimum signal-to-noise ratios, relatively short contact times (1 ± 0.5 ms) are required, because cross-polarization T NH and proton rotating-frame relaxation 1p in 20 ms. The n.m.r. signals copolypeptides may be sensitive sequence effects; yet they most cases more nature secondary structure. α-helices absorb ca. 8–10 ppm upfield β-sheet structures, whereas polyglycine II helix absorbs downfield. natural abundance spectrum crystalline gramicidin-S exhibits a signal at −247 ppm, characteristic chemical shift antiparallel pleated sheet