Mixtures of tetraetherlipids from Thermoplasma acidophilum with varying degree of cyclization show a kinetic effect for a metastable phase

Abstract The main glycophospholipid of Thermoplasma acidophilum is composed of a di-isopranol-2,3-glycero-tetraether. Depending on the growth temperature of the source organism it shows an increasing fraction of pentane cyclizations of its hydrocarbon chains. The thermotropic properties of hydrated samples of its main glycophospholipid, isolated from organisms grow at 39°C. 49°C and 59°C (designated as MPL39, MPL49 and MPL59) and mixtures of these lipids have been characterized by calorimetry. Whereas MPL59 merely shows a broad transitions at sub-zero temperatures. MPL49 and MPL39 exhibit complex thermotropic properties which include competing transition between a metastable and a stable gel phase as well as a liquid-crystalline phase. The formation of the stable gel phase was found to be dependent on the fraction of acyclic hydrocarbon chains and the pretreatment conditions of the sample. Its kinetics were studied in mixed samples and revealed that cyclic hydrocarbon chains act as “impurities”; they quench the formation of the stable gel phase and drastically increase its time constant.