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Biophys J, December 2002, p. 3558-3569, Vol. 83, No. 6

eSpectroscopic and Structural Properties of Valine Gramicidin A in Monolayers at the Air-Water Interface

Hugo Lavoie,* Daniel Blaudez,dagger David Vaknin,Dagger Bernard Desbat,§ Benjamin M. Ocko, and Christian Salesse*

 *Département de Chimie-Biologie, Université du Québec à Trois-Rivières, Trois-Rivières, Québec G9A 5H7, Canada;  dagger Centre de Physique Moléculaire Optique et Hertzienne and  §Laboratoire de Physico-Chimie Moléculaire, Université Bordeaux I, 33405 Talence, France;  Dagger Ames Laboratory and Department of Physics, Iowa State University, Ames, Iowa 50011 USA; and  Brookhaven National Laboratory, Department of Physics, Upton, New York 11973 USA

Monomolecular films of valine gramicidin A (VGA) were investigated in situ at the air-water interface by x-ray reflectivity and x-ray grazing incidence diffraction as well as polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). These techniques were combined to obtain information on the secondary structure and the orientation of VGA and to characterize the shoulder observed in its pi -A isotherm. The thickness of the film was obtained by x-ray reflectivity, and the secondary structure of VGA was monitored using the frequency position of the amide I band. The PM-IRRAS spectra were compared with the simulated ones to identify the conformation adopted by VGA in monolayer. At large molecular area, VGA shows a disordered secondary structure, whereas at smaller molecular areas, VGA adopts an anti-parallel double-strand intertwined beta 5.6 helical conformation with 30° orientation with respect to the normal with a thickness of 25 Å. The interface between bulk water and the VGA monolayer was investigated by x-ray reflectivity as well as by comparing the experimental and the simulated PM-IRRAS spectra on D2O and H2O, which suggested the presence of oriented water molecules between the bulk and the monolayer.

Biophys J, December 2002, p. 3558-3569, Vol. 83, No. 6
© 2002 by the Biophysical Society   0006-3495/02/12/3558/12  $2.00




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Copyright © 2002 by the Biophysical Society.