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O: Fachverband Oberflächenphysik
O 75: Poster Session VI: Organic molecules on inorganic substrates: electronic, optical and other properties II
O 75.1: Poster
Wednesday, March 3, 2021, 13:30–15:30, P
Temperature induced conformational changes in phospholipid monolayers studied by sum-frequency spectroscopy — Damian Firla, •Tim Lämmerzahl, Matthias Linke, and Eckart Hasselbrink — Universität Duisburg-Essen, Germany
Phospholipids are a major component in cell membranes because they form bilayers due to their amphiphilic character. This was exploited to prepare monolayers on glass substrates using the Langmuir-Blodgett technique to study them by sum frequency spectroscopy (SFS). The main goal was to observe structural changes upon raising the temperature. SFS probes the local centrosymmetry of the methylene groups because of its inherent selection rules. Therefore, conformational disorder of the alkyl chains due to the increased temperature, and thus breaking of the local centrosymmetry, can be directly observed. Typically, gauche defects are observable by an increase of the intensities of CH2 vibrational modes. Different types of phospholipids and mixtures of phospholipids with varying chain lengths were studied. Monolayers prepared using a single phospholipid species showed only changes of the intensity of CH3 vibrational modes with rising temperatures. Furtheron, mixtures of phospholipids with different chain lengths were studied. In these cases CH2 modes were observed as well, consistent with the larger space being available for conformational changes. The thermal stability of phopholipid monolayers was also examined. We found that monolayers of single phospholipid species were more stable than monolayers of phospholipid mixtures. Divalent cations also increased the thermal stability of these monolayers.