title: Physicochemical characterization of tetraether lipids from Thermoplasma acidophilum. V. Evidence for the existence of a metastable state in lipids with acyclic hydrocarbon chains.
abstract: The main glycophospholipid of Thermoplasma acidophilum, grown at 39 degrees C, is composed of a di-isopranol-2,3-glycerotetraether. It has been characterized in hydrated systems by calorimetry. Unlike its equivalent grown at 59 degrees C, it shows complex phase properties, which include at least three different phases, (1) a liquid-analogue state (C), which is stable above 20 degrees C, (2) a metastable solid-analogue state (A) formed by supercooling of the liquid-analogue state (C) and (3) a stable solid-analogue state (B), which is slowly formed and may include a close chain packing of lipids and a network of hydrogen bonds between the headgroups. A high fraction of acyclic isopranol chains seems to be a prerequisite for the formation of state (B). A phase diagram, displaying the observed states and the transitions between them is proposed.
authors.affiliation: King Faisal Specialist Hospital & Research Centre, Biomedical Physics Department, Riyadh, Saudi Arabia.
authors.forename: D
authors.initials: D
authors.lastname: Blöcher
authors.forename: R
authors.initials: R
authors.lastname: Gutermann
authors.forename: B
authors.initials: B
authors.lastname: Henkel
authors.forename: K
authors.initials: K
authors.lastname: Ring
mesh_terms: D002151:Calorimetry; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004987:Ethers; D006017:Glycolipids; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D008563:Membrane Lipids; D010743:Phospholipids; D013329:Structure-Activity Relationship; D013816:Thermodynamics; D013822:Thermoplasma / Q000502:physiology*
chemical_list: D004987:Ethers; D006017:Glycolipids; D008563:Membrane Lipids; D010743:Phospholipids