CD and Fourier transform ir spectroscopic studies of peptides. II. Detection of β‐turns in linear peptides

Publisher Website
Google Scholar
Abstract
Comparative CD and Fourier transform ir (FTIR) spectroscopic data on N‐Boc protected linear peptides with or without the (Pro‐Gly) β‐turn motif (e.g., Boc‐Tyr‐Pro‐Gly‐Phe‐Leu‐OH and Boc‐Tyr‐Gly‐Pro‐Phe‐Leu‐OH) are reported herein. The CD spectra, reflecting both backbone and aromatic contributions, were not found to be characteristic of the presence of β‐turns. In the amide I region of the FTIR spectra, analyzed by self‐deconvolution and curve‐fitting methods, the β‐turn band shewed up between 1639 and 1633 cm−1 in trifluoroethanol (TFE) but only for models containing the (Pro‐Gly) core. This band war‐also present in the spectra in chloroform but absent in dimethylsulfoxide. These findings, in agreement with recent ir data on cyclic models and 310‐helical polypeptides and protein in D2O [see S. J. Prestrelski, D. M. Byler, and M. P. Thompson (1991), International Journal of Peptide and Protein Research, Vol. 37, pp. 508–512; H. H. Mantsch, A. Perczel. M. Hollósi, and G. D. Fasman (1992), FASEB Journal, Vol. 6, p. A341; H. H. Mantsch. A. Perczel, M. Hollósi, and G. Fasman (1992), Biopolymers. Vol. 33, pp. 201–207; S. M. Miick, G. V. Martinez, W. R. Fiori, A. P. Tedd, and G. L. Millhauser (1992). Nature, Vol. 359, pp. 653–655], suggest that the amide I band, with a major contribution from the acceptor C  O of the 1 ← 4 intramolecular H bond of β‐turns, appears near or below 1640 cm−1, rather than above 1660 cm−1. In TFE, bands between 1670 and 1660 cm−1 are mainly due to “free” carbonyls, that is, C  O's of amides that are solvated but not involved in the characteristic H bonds of periodic secondary structures or β‐turns. © 1994 John Wiley & Sons, Inc.