Structural characterization of a phenolic lipid and its derivative using vibrational spectroscopy

The thermodynamic properties of 3-pentadecylphenol (PDP) and 3-pentadecyl-2-(N-piperidinemethyl)phenol (PPMP) were investigated using vibrational spectroscopy. The PDP lipid forms a medium strong intermolecular H-bond, with characteristic OH stretching at 3330 cm−1. The PPMP lipid forms a stronger intramolecular H-bond with broad OH stretching between the 3200 and 2700 cm−1. Both types of H-bonds prevent hydration of lipid films. The differences in H-bonding are also reflected in the diverse temperatures of the main transition (Tm). The Tm in PDP films is 9 °C higher than in PPMP films (43 °C). In mixtures with dipalmitoylphosphatidylcholine lipid (DPPC), both lipids significantly reduce the Tm for DPPC. The OH group of the PDP lipid strongly interacts with the phosphate group from DPPC. For PPMP no such interaction can be observed. Mixing of PPMP with various amounts of DPPC preserves the intramolecular H-bond between the piperidinic nitrogen and the OH group, which is characteristic of pure PPMP films.