Dichroic ratios in polarized Fourier transform infrared for nonaxial symmetry of beta-sheet structures
Abstract
The transition moments for the amide bands from beta-sheet peptide structures generally do not exhibit axial symmetry about the director in linearly polarized Fourier transform infrared (FTIR) measurements on oriented systems. The angular dependences of the dichroic ratios of the amide bands are derived for beta-sheet structures in attenuated total reflection (ATR) and polarized transmission experiments on samples that are oriented with respect to the normal to the substrate and are randomly distributed with respect to the azimuthal angle in the plane of the orienting substrate. The orientational distributions of both the beta-strands and the beta-sheets are considered, and explicit expressions are given for the dichroic ratios of the amide I and amide II bands. The dichroic ratio of the amide II band, which is parallel polarized, can yield the orientation of the beta-strands directly, but to specify the orientations of the beta-sheets completely requires measurement of the dichroic ratios of both the amide I and amide II bands, or generally two bands with parallel and perpendicular polarizations. A random distribution in tilt of the planes of the beta-sheets does not give rise to equal dichroic ratios for bands with perpendicu...Continue Reading
Citations
Structure, dynamics and composition of the lipid-protein interface. Perspectives from spin-labelling
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