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Nanosecond Relaxation Processes of Phospholipid Bilayers in the Transition Zone

Gamble, Ronald C. and Schimmel, Paul R. (1978) Nanosecond Relaxation Processes of Phospholipid Bilayers in the Transition Zone. Proceedings of the National Academy of Sciences of the United States of America, 75 (7). pp. 3011-3014. ISSN 0027-8424.

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Ultrasonic relaxation spectra of dipalmitoyl lecithin vesicles have been recorded as a function of temperature over the frequency range 14-265 MHz. A relaxation process is observed with a time constant of about 10-8 sec. At the mid-point of the crystalline-liquid crystalline transition (about 41.3 degrees), the relaxation amplitude is maximal. This suggests that the relaxation process is intimately associated with the order-disorder transition. Further support for this conclusion comes from the finding that the volume change of the reaction, as calculated from the relaxation amplitude at the transition midpoint, agrees with that determined independently by equilibrium dilatometry measurements of the Delta V of the transition. The results show that a major step in the transition occurs on a far shorter time scale than previously recognized. Similar fast processes have also been detected in dimyristoyl and distearoyl lecithin vesicles. From a consideration of various lines of evidence, it appears that the relaxation monitors the elementary step associated with the isomerization of lipid chains, such as kink formation through internal bond rotations, as the bilayer transforms between ordered and disordered phases.

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Additional Information:Copyright © 1978 by the National Academy of Sciences Communicated by John D. Baldeschwieler, April 7, 1978 Helpful conversations concerning this work with S. I. Chan and J. S. Waugh are gratefully acknowledged. This work was supported by Grants GM-15539 and GM-21111-05 from the National Institutes of Health. This paper is contribution 5711 from the California Institute of Technology. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.
Subject Keywords:thermal transition; chain isomerizations; ultrasonics
Issue or Number:7
Record Number:CaltechAUTHORS:GAMpnas78
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:4909
Deposited By: Archive Administrator
Deposited On:12 Sep 2006
Last Modified:02 Oct 2019 23:17

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