Electrochemical and PM-IRRAS Studies of the Effect of Cholesterol on the Properties of the Headgroup Region of a DMPC Bilayer Supported at a Au(111) Electrode

Xiaomin Bin† and Jacek Lipkowski*
Department of Chemistry, University of Guelph, Guelph, Ontario, Canada N1G 2W1
J. Phys. Chem. B, 2006, 110 (51), pp 26430–26441
DOI: 10.1021/jp0660132
Publication Date (Web): December 7, 2006
Copyright © 2006 American Chemical Society
†

 Present address:  Steacie Institute for Molecular Sciences, National Research Council, 100 Sussex Drive, Ottawa, Ontario, Canada K1A 0R6. E-mail:  Xiaomin.Bin@nrc-cnrc.gc.ca.

,
*

 To whom correspondence should be addressed. E-mail:  jlipkows@uoguelph.ca.

Abstract

Polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) was employed to investigate the interaction of cholesterol with the headgroups of dimyristoylphosphatidycholine (DMPC) molecules under a static electric field. DMPC/cholesterol (7:3 molar ratio) mixtures form a bilayer on a Au(111) electrode surface by fusion and spreading of small unilamellar vesicles. PM-IRRAS experiments provided detailed information concerning the conformation and hydration of headgroups of DMPC bilayers in the presence and absence of 30% cholesterol. The presence of 30% cholesterol increases the space between the headgroups of DMPC molecules and hence increases the hydration of the DMPC/cholesterol mixed bilayer. The conformational state of the headgroups of DMPC molecules in the mixed bilayer is also significantly changed. The phosphate group is closer to the surface compared with the pure DMPC bilayer. The conformation of the −O−C−C−N moiety changes from gauche to trans in the presence of cholesterol.

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History

  • Published In Issue December 28, 2006
  • Received September 14, 2006
    Revised October 20, 2006

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