Electron density modeling and reconstruction of
infinite periodic minimal surfaces (IPMS) based phases in
lipid-water systems.
II. Reconstruction of D surface based phases
P.E. Harper1 - S.M. Gruner1 - R.N.A.H. Lewis2 - R.N. McElhaney2
1 Department of Physics, Joseph Henry Laboratories,
Jadwin Hall, Princeton University, Princeton NJ 08544, USA
2 Department of Biochemistry, The University of Alberta, Edmonton,
Alberta, Canada T6G 2H7
smg26@cornell.edu
Received 15 January 1999 and Received in final form 20 October 1999
Abstract
This is the second of two papers dealing with the structure of
lipid-water phases based on Infinite Periodic Minimal Surfaces
(IPMS). The first paper describes mathematical modeling of such
phases. In this paper, a new reconstruction method, called the
methyl trough search, is described and used to solve the
structures based on powder pattern X-ray diffraction data.
Structures are derived for both a single chain lipid-water system
(mono-olein) and a diacyl phospholipid-water system (2-2 methyl
butyl 16:0 phosphatidylcholine). The methyl trough search uses
the low electron density of the lipid methyl tails to determine
the correct phasing for the electron density reconstruction. The
data are consistent with a structure based on the IPMS D surface.
The results are compared to other methods used to solve the
mono-olein structure; the structure of the diacyl lipid has never
before been solved. We discuss the subtleties involved in
reconstruction of D surface based phases and the substantial
artifacts that arise in low-resolution reconstructions of
hydrocarbon lipids lacking heavy-atom sites.
PACS
61.30.Cz Theory and models of liquid crystal structure -
87.15.By Structure and bonding -
83.70.Jr Liquid crystals: nematic, cholesteric, smectic,
discotic, etc
Copyright EDP Sciences, Società Italiana di Fisica, Springer-Verlag
