ISSN:
0006-3525
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Vibrational circular dichroism (VCD) spectra for the principal amide stretching vibrations, amide A (N—H stretch) and amide I (predominantly C=O stretch), are presented and analyzed for a variety of polypeptides dissolved in chloroform, as well as for two examples in D2O. Our results for poly(γ-benzyl-L-glutamate) confirm the first and only previous report of VCD in polypeptides carried out by Singh and Keiderling [(1981) Biopolymers 20, 237-240]. Collectively, our spectra show that the sense of the bisignate VCD in these two regions depends on the sense of α-helicity and not on the absolute configuration of the constituent amino acids. This conclusion is established by obtaining VCD for the two polypeptides, poly(β-benzyl-L-asparate) and poly(im-benzyl-L-histidine), that form left-handed as opposed to right-handed α-helices. A new amide band having significant VCD intensity owing to its Fermi resonance interaction with the N—H stretching mode has been identified as a weak shoulder on the low-frequency side of the amide A band near 3200 cm-1 and is assigned as a combination band of the amide I and amide II vibrations. VCD spectra of polypeptides in D2O solution, although weak, have been successfully measured in the amide I region, where spectra appear to be more complicated due to the presence of solvated and internally hydrogen-bonded amide groups. Strong monosignate contributions to the VCD in the amide A and amide I regions for some of the polypeptides indicate coupling of an electronic nature between these two regions and is deduced by an application of the concept of local sum rules of rotational strength. It appears that a detailed understanding of the VCD obtained for polypeptides will not only be diagnostic of secondary structure, but also of more subtle structural and vibrational effects that give rise to local, intrinsic chirality in the amide vibrations.
Additional Material:
5 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/bip.360211106
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