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Effect on the Hydration and Orientation of the Phosphate Group of DPPC at Air-Water and Air-Hydrated Silica Interfaces
 

Summary: Na+
and Ca2+
Effect on the Hydration and Orientation of the Phosphate Group of DPPC at
Air-Water and Air-Hydrated Silica Interfaces
Nadia N. Casillas-Ituarte, Xiangke Chen, Hardy Castada, and Heather C. Allen*
Department of Chemistry, The Ohio State UniVersity, 100 West 18th AVenue, Columbus, Ohio 43210
ReceiVed: March 11, 2010; ReVised Manuscript ReceiVed: June 14, 2010
Hydration and orientation of the phosphate group of dipalmitoylphosphatidylcholine (DPPC) monolayers in
the liquid-expanded (LE) phase and the liquid-condensed (LC) phase in the presence of sodium ions and
calcium ions was investigated with vibrational sum frequency generation (SFG) spectroscopy at the air-
aqueous interface in conjunction with surface pressure measurements. In the LE phase, both sodium and
calcium affect the phosphate group hydration. In the LC phase, however, sodium ions affect the phosphate
hydration subtly, while calcium ions cause a marked dehydration. Silica-supported DPPC monolayers prepared
by the Langmuir-Blodgett method reveal similar hydration behavior relative to that observed in the
corresponding aqueous subphase for the case of water and in the presence of sodium ions. However, in the
presence of calcium ions the phosphate group dehydration is greater than that from the corresponding purely
aqueous CaCl2 subphase. The average tilt angles from the surface normal of the PO2
-
group of DPPC
monolayers on the water surface and on the silica substrate calculated from SFG data are found to be 59 (

  

Source: Allen, Heather C.- Department of Chemistry, Ohio State University

 

Collections: Chemistry