Stability of monomolecular films of archaebacterial tetraether lipids on silicon wafers: a comparison of physisorbed and chemisorbed monolayers.

The monomolecular organisation of symmetric, chemically modified tetraether lipids caldarchaeol-PO(4) was studied using Langmuir film balance, ellipsometry, and atomic force microscopy (AFM). Solid silicon wafer substrates were modified to hydrophobic, hydrophilic, and amino-silanised surfaces; and Langmuir-Blodgett (LB)-films were transferred onto each. LB-caldarchaeol-PO(4) films were subjected to further rinsing with organic solvent and additional physical treatments, to compare their resistance and stability on chemisorbed (amino-silanised) and physisorbed (hydrophobic and hydrophilic) surfaces. The resistance and stability of these monolayer films was characterized by ellipsometry and AFM, and film thickness was determined using ellipsometry. AFM was also employed to observe surface morphology. Monolayer films on hydrophobic surfaces were found to be more resistant to rinsing with organic solvent and additional physical treatments than monolayer films on either amino-silanised or hydrophilic surfaces. The hydrophobic effect with hydrophobic surfaces appears to support the formation of stronger caldarchaeol-PO(4) films on silicon wafer substrates, with increased resistance and stability.

AFM and ellipsometric studies on LB films of natural asymmetric and symmetric bolaamphiphilic archaebacterial tetraether lipids on silicon wafers.

The monomolecular organisation of the natural asymmetric and symmetric bolaamphiphilic (archaebacterial tetraether lipids) was studied using a combination of Langmuir film balance, ellipsometry, and atomic force microscopy (AFM). Monolayer films were transferred onto silicon wafer substrates. After transfer of the lipids onto several kinds of silicon wafer substrates (hydrophobic, hydrophilic, and amino-silanised), the monolayer films were further investigated by ellipsometry and AFM in order to determined whether bolaamphiphiles are oriented differently at the water-air interface, including "horseshoe" and "upright" configurations. The thickness of the monolayer film, which was determined by ellipsometry, represents a combined mean value of the domains. The surface morphology, which was evaluated by AFM showed that in all films, the domains were arranged in small domains or the most homogeneous organisation, depending on the properties of the wafer silicon substrates. From all films, the hydrophobically transferred lipids showed the most homogeneous organisation on the substrates. After transfer onto hydrophilic and amino-silanised surfaces, the lipids were arranged in small islands on the substrates.