Über die Phasenumwandlung von Monoschichten des synthetischen Phospholipids DPPA und Vergleich mit DPPC

Abstract

AbstractThe monolayer phase transition from the liquid‐condensed to the liquid‐expanded phase of the unusual synthetic phospholipid DPPA has been studied with the Langmuir film balance and compared with literature data of DPPC. DPPA and DPPC have different head groups. DPPA has a quarternary acridine orange (AO) residue instead of the quarternary nitrogen atom of DPPC. – The equilibrium pressure π of the phase transition of DPPA increases linearly with the transition temperature Tu: dπ/dTu = 3.1 · 10−5 N cm−1 K−1. The area change ΔFu = 6.6 · 10−16 cm2 per molecule DPPA at the phase transition is within the limits of error independent of π, in contrast to DPPC and other phospholipids. The transition entropy ΔSu = 125 J K−1 mol−1 and transition enthalpy ΔHu = 38 kJ mol−1 are large in comparison to DPPC under equal experimental conditions. The difference is related to the association of the head groups of DPPA in condensed phase. It agrees qualitatively with the thermodynamic parameters of the dissociation of dimers of AO and N‐alkyl AOs.