Modulation of Substrate-Membrane Interactions by Linear Poly(2-methyl-2-oxazoline) Spacers Revealed by X-ray Reflectivity and Ellipsometry

• Published in: Chemphyschem 2009-11, Vol.10 (16), p.2876-2883
• Main Authors: Seitz, Peter C., Reif, Michael D., Konovalov, Oleg V., Jordan, Rainer, Tanaka, Motomu
• Format: Article
• Language: English
• Subjects: Applied sciences; Chitin - analogs & derivatives; Chitin - chemistry; ellipsometry; Exact sciences and technology; Glycocalyx - chemistry; interfaces; Lipid Bilayers - chemistry; lipopolymers; membranes; Organic polymers; Physicochemistry of polymers; Polyamines; Properties and characterization; Refractometry; Surface properties; X-ray reflectivity; X-Rays
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.200900553

Hydrated polymer interlayers between planar lipid membranes and solid substrates provide a water reservoir and thus maintain a finite membrane–substrate distance. Linear polymer spacers attached to lipid head groups (lipopolymer tethers) can be used as a defined model of oligo‐ and polysaccharides covalently anchored on cell surfaces (glycocalyx). They can offer a unique advantage over membranes physisorbed on polymer films (called polymer‐cushioned membranes), owing to their ability to control both the length and density of polymer chains. In this study, a lipopolymer tether composed of a stable ether lipid moiety and a hydrophilic poly(2‐methyl‐2‐oxazoline) spacer with a length of 60 monomer units is used to fabricate supported membranes by the successive deposition of proximal (lower) and distal (upper) leaflets. Using specular X‐ray reflectivity and ellipsometry, we systematically investigate how the lateral density of polymer chains influences the membrane–substrate interactions. The combination of two types of reflectivity techniques under various conditions enables the calculation of quantitative force–distance relationships. Such artificial membrane systems can be considered as a half‐model of cell–cell contacts mediated via the glycocalyx, which reveals the influence of polymer chain density on the interplay of interfacial forces at biological interfaces. Keep your distance: Membrane–substrate interactions are influenced by hydrated polymer interlayers (see picture). The influence of lateral density and osmotic pressure exerted on the membrane is investigated by using two reflectivity techniques: ellipsometry and specular X‐ray reflectivity.