New evidence for gel-liquid crystalline phase coexistence in the ripple phase of phosphatidylcholines |
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Authors: | Michael Rappolt Georg Pabst Gert Rapp Manfred Kriechbaum Heinz Amenitsch Christian Krenn Sigrid Bernstorff Peter Laggner |
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Institution: | (1) Institute of Biophysics and X-ray Structure Research, Austrian Academy of Sciences, Steyrergasse 17, 8010 Graz, Austria, AT;(2) European Molecular Biology Laboratory, Hamburg Outstation, c/o DESY, Notkestrasse 85, 22603 Hamburg, Germany, DE;(3) Synchrotron Trieste (ELETTRA), Strada Statale 14, km 163.5, 34012 Basovizza (TS), Italy, IT |
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Abstract: | Experimental evidence supporting the hypothesis of gel-liquid crystalline phase coexistence in the stable ripple phase of
diacylphosphatidylcholines has been obtained from time-resolved X-ray small- (SAXS) and wide-angle diffraction (WAXS) in the
millisecond to second time domain. The pretransition of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) exhibits a thin lamellar liquid crystalline intermediate phase (designated Lα*) if driven far away from equilibrium by an infrared temperature jump (T-jump) technique. The findings can be described by
a two-step model. (1) Instantaneously with the T-jump, an anomalously thin lamellar liquid crystalline intermediate phase
(d = 5.6–5.8 nm) forms, coexisting with the original gel-phase Lβ′. Within the first seconds, the lamellar repeat distance of the intermediate increases to a value of about 6.7 nm. A closer
examination of these kinetics reveals two relaxation components: a fast process, proceeding within tenths of a second, and
a slow process, on the time scale of a few seconds. (2) Finally, both the liquid crystalline and the gel-phase relax into
the stable ripple phase Pβ′. The total process time of the transition is nearly independent of the addition of NaCl, but varies strongly with the chain
length of the lecithin species.
Received: 24 November 1999 / Revised version: 25 February 2000 / Accepted: 25 February 2000 |
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Keywords: | Phosphatidylcholine Temperature jump Small-angle X-ray scattering Wide-angle X-ray scattering Sodium chloride |
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