The Structure of Lipids and Proteins Studied by Attenuated Total-Reflection (ATR) Infrared Spectroscopy: I. Oriented Layers of Tripalmitin

The structure of tripalmitin multilayers prepared by the Langmuir-Blodgett technique has been investigated within room temperature and 62°C using infrared internal reflection spectroscopy (ATR). It was found that the bilayer structure exhibits crystalline features with pseudo hexagonal structure. The methylene groups of the hydrocarbon chains are in the all-trans-zig-zag conformation, oriented perpendicularly to the germanium internal reflection plate. Increasing temperature produces at first a continuous conformational change in the glycerol part of the molecule. This process is extended over nearly 10° and followed by sudden melting (disordering) of the hydrocarbon chains within 1°. In comparison microcrystalline tripalmitin shows an identical infrared spectrum and analogous behaviour at increased temperatures. This indicates that the bilayer structure (head-head, tail-tail) also exicts in the crystal.