ISSN:
1432-1017
Keywords:
Key words Phosphatidylcholine
;
Temperature jump
;
Small-angle X-ray scattering
;
Wide-angle X-ray scattering
;
Sodium chloride
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Physics
Notes:
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.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s002490050257
Permalink