Side-chain conformation and 13C-NMR chemical shift of poly(l-phenylalanine) and oligopeptides containing l-phenylalanine and tyrosine residues in the solid state

Add time:09/02/2019    Source:sciencedirect.com

The 13C cross-polarization, magic-angle-spinning (CP-MAS) NMR spectra of poly (l-phenylalanine) and oligopeptides containing a l-phenylalanine or l-tyrosine residue in the solid state have been measured, in order to elucidate the side-chain conformational features of the phenylalanine and tyrosine residues. From these data it was found that the 13C chemical-shift difference between Cα (main-chain carbon) and Cγ (aromatic carbon) carbons in the l-phenylalanine and l-tyrosine residues in the oligopeptides of which the side-chain conformations in the solid state have already been determined from X-ray diffraction, depends significantly on the side-chain conformation. Using these results, the side-chain conformation of poly(l-phenylalanine) in the α-helix, ω-helix and β-sheet forms was determined. Furthermore, an FPT INDO MO calculation was carried out in order to allow detailed discussion of the side-chain conformation dependence of the 13C chemical shift.

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