Infrared and Raman microscopy of fowl feather barb

Abstract

A fowl feather barb 10 μm in thickness was subjected to a polarized infrared spectroscopic measurement by the use of a microscopic device. Nearly 50% of its peptide groups were found to give the 1633 and 1684 cm−1 bands characteristic of the antiparallel-chain pleated sheet structure, and the remaining 50% gave the 1659 cm−1 band assignable to unordered polypeptide chains. The orientation of the pleated sheet was determined to be on average θ = 52° and χ = 39°, where θ and χ are the angles for the transformation of the XYZ coordinate system fixed on the pleated sheet and the abc coordinate system fixed on the sample barb. The Raman spectra of the barb were also examined with another microscopic device and a 488.0-nm laser beam. A sharp aa component of the Raman scattering tensor was observed at 1667 cm−1. Based on this fact, a revised set of parameters for the vibrational couplings among the peptide groups in the pleated sheet has been proposed. Some discussions have been made on the amide I Raman tensor of the antiparallel-chain pleated sheet. Key words: fowl feather barb, Raman microscope, infrared microscope, antiparallel-chain pleated sheet, Raman scattering tensor.