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Conformational study of linear alternating and mixed D ‐ and L ‐proline oligomers using electronic and vibrational CD and fourier transform IR
Author(s) -
Mästle Werner,
Dukor Rina K.,
Yoder Gorm,
Keiderling Timothy A.
Publication year - 1995
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360360508
Subject(s) - chemistry , fourier transform infrared spectroscopy , fourier transform , proline , stereochemistry , amino acid , biophysics , biochemistry , chemical engineering , mathematical analysis , mathematics , engineering , biology
Vibrational CD (VCD) spectra of a series of blocked linear, alternating D ‐ and L ‐proline containing oligopeptides, dissolved in D 2 O and in CDCl 3 . are reported. For the Boc‐ LDL ‐Pro 3 to Boc‐DLDLDLDL‐Pro 8 oligomers. The VCD spectra in the amide I band is a positive couplet, opposite in sense to that obtained for ( L ‐Pro) n oligomers. While this admits the possibility of their favoring a right‐handed helical chain conformation, the amide I ir spectra for these dl oligomers in D 2 O indicate a mixed, apparently alternate, cis‐trans conformation that prevents a simple conclusion. Their VCD in D 2 O evidence no narrowing and has a progressive loss in intensity (measured as Δ /A,) with an increase in chain length. In CDCl 3 a similar pattern of positive VCD couplets decreasing in intensity with length was seen, but their spectra are narrower. Their electronic CD (ECD) in the uv, also indicates a loss in intensity with increasing length. Oligomers with odd or even numbers of Pro residues have different ECD patterns, indicating that those spectra are strongly influenced by local contributions arising in the N‐terminal groups. The VCD arises from dipolar and vibrational coupling of the amides in the helical structure. All the spectra are consistent with the chiral end groups leading to formation of an excess of one helical handedness. With an increase in length, the influence of this selectiveness is less and the overall CD measured decreases. © 1995 John Wiley & Sons, Inc.