Journal of Molecular Structure, 220 (1990) 251-260 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands 251 zyxwvutsrqp SIDE-CHAIN CONFORMATION AND 13C-NMR CHEMICAL SHIFT OF POLY (L-PHENYLALANINE) AND OLIGOPEPTIDES CONTAINING L-PHENYLALANINE AND TYROSINE RESIDUES IN THE SOLID STATE HIDETOSHI MIYAMOTO’, TADASHI KOMOTO’s*, HIROMICHI KUROSU’, ISA0 ANDO’, TAKUO OZAKI* and AKIRA SHOJI* ‘Department of Polymer Chemistry, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo (Japan) 2Department of Industrial Chemistry, College of Technology, Gunma University, Tenjin-cho, Kiryu-shi, Gunma (Japan) (Received 3 July 1989) ABSTRACT The i3C cross-polarization, magic-angle-spinning (CP-MAS) NMR spectra of poly(L-phen- ylalanine) 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 phenyl- alanine and tyrosine residues. From these data it was found that the W chemical-shift difference between C, (main-chain carbon) and C!, (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(~-phenylalanine) in the a-helix, w-helix and P-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 i3C chemical shift. INTRODUCTION zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA It has been demonstrated that the main-chain conformation of a variety of polypeptides and peptides in the solid state such as the a-helix, P-sheet, 31- helix, collagen-like triple helix and w-helix, can be determined through the observation of 13C-NMR chemical-shift values of the main-chain carbon at- oms, which are not strongly influenced by specific amino acid residues but by the local conformation characterized by the dihedral angles q? and I,V [ I]. Such an approach has been successfully applied to the determination of the main- *Permanent address: Department of Polymer Chemistry, Gunma University, Tenjin-cho, Kiryu- shi, Gunma, Japan. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 0022-2860/90/$03.50 0 1990 Elsevier Science Publishers B.V.