Dielectric and calorimetric studies of hydrated purple membrane.
Purple membranes (PM) from halobacteria were hydrated to approximately 0.4 and approximately 0.2 g H(2)O/g of PM and studied by dielectric spectroscopy and differential scanning calorimetry between 120 and 300 K. The dielectric process, attributed to a local (beta) relaxation of the confined supercooled water, shows an Arrhenius temperature behavior at low temperatures. In the case of the most hydrated PM a small deviation from the Arrhenius behavior occurs at 190-200 K together with a pronounced endothermic process and an increased activation energy. The observed crossover is accompanied by a reduction of the interlayer spacing due to the partial loss of the intermembrane water. All these effects at approximately 200 K are consistent with a scenario where the local relaxation process merges with a nonobservable alpha-relaxation of the interlayer water, giving rise to a more liquid-like behavior of the interfacial water. For the less hydrated sample the effects are less pronounced and shift to a slightly higher temperature.
Berntsen
Peter
P
Department of Applied Physics, Chalmers University of Technology and Göteborg University, SE-51296 Göteborg, Sweden. peterber@fy.chalmers.se
Bergman
Rikard
R
Jansson
Helén
H
Weik
Martin
M
Swenson
Jan
J
D002151:Calorimetry / Q000379:methods*; D002152:Calorimetry, Differential Scanning; D004594:Electrophysiology; D019605:Euryarchaeota / Q000378:metabolism; D007700:Kinetics; D008055:Lipids / Q000737:chemistry; D015233:Models, Statistical; D018717:Purple Membrane / Q000378:metabolism*; D013057:Spectrum Analysis; D013696:Temperature; D014867:Water / Q000737:chemistry
D008055:Lipids; D014867:Water