AVS 46th International Symposium
    Surface Science Division Thursday Sessions
       Session SS3+BI-ThA

Invited Paper SS3+BI-ThA3
Thia(Ethylene Oxide) Alkanes: Tuning the Structure of a Supported Biomimetic Membrane via Spacer Length and Packing Density

Thursday, October 28, 1999, 2:40 pm, Room 613/614

Session: Biological Surface Science
Presenter: A.L. Plant, National Institute of Standards and Technology
Authors: D.J. Vanderah, National Institute of Standards and Technology
C.W. Meuse, National Institute of Standards and Technology
T. Petralli-Mallow, National Institute of Standards and Technology
A.L. Plant, National Institute of Standards and Technology
Correspondent: Click to Email
Interest in reconstituting transmembrane proteins in supported cell membrane mimics of phospholipid/alkanethiol hybrid bilayers has led to development of novel tethering molecules. In an attempt to introduce a disordered, hydrophilic region at the proximal side of the supported lipid bilayer, ethylene oxide moieties have been used as spacers between the sulfur and the alkane chain of alkanethiols. We have observed by infrared spectroscopy, neutron reflectivity, and electrochemistry that such ethyleneoxide moieties are not necessarily hydrated or disordered. The ethylene oxide of thiahexa(ethylene oxide) alkanes (HS(EO)@sub 6@-alkanes) form a highly ordered arrangement of 7/2 helices when allowed to self-assemble at gold from an ethanolic solution. This highly ordered conformation is apparently not driven by order in the alkane chains, since the helical structure occurs in both HS(EO)@sub 6@-decane and HS(EO)6-octadecane. The conformation is, however, determined in part by molecular density. Infrared analysis of mixed monolayers of HS(EO)@sub 6@-alkanes and phospholipids transferred from the air-water interface indicates that at low packing densities the EO region is disordered, but it assumes the helical structure at higher packing densities. Infrared spectroscopy and sum frequency generation suggest that the conformation of the EO region may be controlled by its length. For a series of self-assembled monolayers of HS(EO)@sub n@-decanes, the EO segment is an extended all-trains chain when n=4, a 7/2 helix when n=5-7, and a less ordered conformer when n=8. This effect of spacer length and packing may provide a means of tuning the molecular order of biomimetic matrices.