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Atomic-scale dynamical structures of fatty acid bilayers observed by ultrafast electron crystallography

Chen, Songye and Seidel, Marco T. and Zewail, Ahmed H. (2005) Atomic-scale dynamical structures of fatty acid bilayers observed by ultrafast electron crystallography. Proceedings of the National Academy of Sciences of the United States of America, 102 (25). pp. 8854-8859. ISSN 0027-8424.

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The structure and dynamics of a biological model bilayer are reported with atomic-scale resolution by using ultrafast electron crystallography. The bilayer was deposited as a Langmuir-Blodgett structure of arachidic (eicosanoic) fatty acids with the two chains containing 40 carbon atoms (50 Å), on a hydrophobic substrate, the hydrogen terminated silicon(111) surface. We determined the structure of the 2D assembly, establishing the orientation of the chains and the subunit cell of the CH2 distances: a0 = 4.7 Å, b0 = 8.0 Å, and c0 = 2.54 Å. For structural dynamics, the diffraction frames were taken every 1 picosecond after a femtosecond temperature jump. The observed motions, with sub-Å resolution and monolayer sensitivity, clearly indicate the coherent anisotropic expansion of the bilayer solely along the aliphatic chains, followed by nonequilibrium contraction and restructuring at longer times. This motion is indicative of a nonlinear behavior among the anharmonically coupled bonds on the ultrashort time scale and energy redistribution and diffusion on the longer time scale. The ability to observe such atomic motions of complex structures and at interfaces is a significant leap forward for the determination of macromolecular dynamical structures by using ultrafast electron crystallography.

Item Type:Article
Additional Information:Contributed by Ahmed H. Zewail, May 13, 2005. Freely available online through the PNAS open access option. We thank Prof. J. Heath for the use of his facilities and Drs. Y. Luo and H. Yu for the preparation of the LB bilayer. This work was supported by the National Science Foundation.
Subject Keywords:dynamics, ultrafast electron diffraction, Langmuir-Blodgett films
Record Number:CaltechAUTHORS:CHEpnas05b
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:492
Deposited By: Archive Administrator
Deposited On:11 Jul 2005
Last Modified:14 Nov 2014 19:18

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