Authors Marsh, D. ; Müller, M. ; Schmitt, F.-J.
Title Orientation of the Infrared Transition Moments for an a-Helix
Date 04.05.2000
Number 8636
Abstract Appropriate values for the orientation of the amide transition dipoles are essential to the growing use of isotopically edited vibrational spectroscopy generally in structural biology and to infrared dichroism measurements on membrane-associated a-helices, in particular. The orientations of the transition moments for the amide vibrations of an a-helix have been determined from the ratio of intensities of the A- and E1-symmetry modes in the infrared spectra of poly(·-methyl-l-glutamate)x-co-(·-n-octadecyl-l-glutamate)y oriented on silicon substrates. Samples possessing a high degree of alignment were used to facilitate band fitting. Consistent results were obtained from both attenuated total reflection and transmission experiments with polarized radiation, yielding values of TI = 38°, TII = 73°, and TA = 29°, relative to the helix axis, for the amide I, amide II, and amide A bands, respectively. The measurements are discussed both in the context of the somewhat divergent older determinations, and in relation to the helix geometry and results on model amide compounds, to resolve current uncertainties in the literature.
Publisher Biophysical Journal
Citation Biophysical Journal 78 (2000) 2499-2510
Tags linear dichroism spectroscopy proteins membranes bacteriorhodopsin polymers ratios order

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