Application of gold, silica and titania surfaces for the PM IRRAS: structural studies of biologically relevant films
|Izabella Brand 1, Martina Nullmeier 1, Michael Ahlers 1, Sabine Szunerits 2, Rabah Boukherroub 3, Gunther Wittstock 1|
1. Institut für Reine und Angewandte Chemie der Universität Oldenburg, Carl von Ossietzky-Str. 9-11, Oldenburg 26111, Germany
|Polarization modulation infrared reflection absorption spectroscopy (PM IRRAS) is an excellent tool for structural studies of organized organic layers on surfaces reflecting the IR radiation, such as Au or Pt. IR transmitting or absorbing substances such as silica, or titania are not suitable for IRRAS analysis. However, these surfaces are of large importance for implants development and design, creating a large need to understand properties of a biological substance on their surfaces. Despite the fact that silica and titania, depending on the wavelength of the IR light, are either transparent or absorptive to the IR radiation, when deposited in the form of thin films on a reflecting material such as gold fulfill surface selection rules.
The PM IRRAS is applied for structural analysis of bilayers of 1,2dimyristoyl-sn-glycero-3-phosphocholine (DMPC) deposited using the Langmuir-Blodgett and Langmuir-Schaefer techniques on gold, silica and titania surfaces. Lipid films formed on Au, Au|SiO2 and Au|Ti|TiO2 surfaces show two-dimensional long range order. The hydrocarbon chains exist in a liquid and a gel phase, depending on the surface pressure of the film transfer. Interactions between positively charged choline and the negatively charged silica and titania surfaces influence the arrangement of the polar head group of the lipid molecule at the interface. On the titania surface in a loosely packed bilayer the polar head group has an open conformation. In a densely packed bilayer on all surfaces interactions between the choline and phosphate groups of DMPC predominate interactions with the surface, changing the conformation of the polar head group.
A lipid bilayer exposed to the electric field mimics a natural cell membrane. The lipid bilayer assembled on the gold electrode was exposed to protein solutions interacting specifically either with a glycolipid or with a phospholipid. Charge accumulated on the membrane, capacity, potential window of film adsorption were determined electrochemically.
A successful adaptation of an implant material in an organism is governed by the adsorption processes of the extracellular matrix. The great success of titania implants is connected with a formation of collagen rich layer on its surface. The process of adsorption of collagen helices on the Au|Ti|TiO2 surface was monitored by the PM IRRAS. In an electrolyte solution, however, a collagen coating is unstable. A significant improvement of the stability of the collagen layer was obtained, when the protein was coadsorbed with a polysaccharide (heparine) on the surface of titania pre-treated in 20 mM CaCl2 solution. The PM IRRA spectra of collagen on the titania surface show a blue-shift of the amide I band, as compared to an IR spectrum in aqueous solution. The collagen helix is less hydrated / weaker hydrogen bonded in the adsorbed state, indicating that a hydrogen bonding network in the triple helix of collagen changes upon adsorption.
Presentation: Tutorial lecture at SMCBS'2009 International Workshop, by Izabella Brand
See On-line Journal of SMCBS'2009 International Workshop
Submitted: 2009-08-14 14:43 Revised: 2009-10-30 12:06