W. Mastle et al., CONFORMATIONAL STUDY OF LINEAR ALTERNATING AND MIXED D-PROLINE AND L-PROLINE OLIGOMERS USING ELECTRONIC AND VIBRATIONAL CD AND FOURIER-TRANSFORM-IR, Biopolymers, 36(5), 1995, pp. 623-631
Vibrational CD (VCD) spectra of a series of blocked linear, alternatin
g D- and L-proline containing oligopeptides, dissolved in D2O and in C
DCl3, are reported For the BoC-LDL-Pro(3) to BOC-DLDLDLDL-Pro(8) oligo
mers, the VCD spectra in the amide I band is a positive couplet, oppos
ite in sense to that obtained for (L-Pro)(n) oligomers. While this adm
its the possibility of their favoring a right-handed helical chain con
formation, the amide I ir spectra for these DL oligomers in D2O indica
te a mixed, apparently alternate, cis-trans conformation that prevents
a simple conclusion. Their VCD in D2O evidence no narrowing and has a
progressive loss in intensity (measured as Delta AA/A) with an increa
se in chain length. In CDCl3 a similar pattern of positive VCD coupler
s decreasing in intensity with length was seen, but the iv spectra are
narrower. Their electronic CD (ECD), in the uv, also indicates a loss
in intensity with increasing length. Oligomers with odd or even numbe
rs 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 couplin
g of the amides in the helical structure. All the spectra are consiste
nt 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. (C) 1995
John Wiley & Sons, Inc.