Biophysical Journal 49: 597-605 (1986)
© 1986 the Biophysical Society

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Church, S E Articles by Wickman, H H Search for Related Content PubMed PubMed Citation Articles by Church, S E Articles by Wickman, H H

X-ray structure study of thermotropic phases in isoacylphosphatidylcholine multibilayers.

ABSTRACT

Structures of lamellar phases in aqueous dispersions of diisoacylphosphatidylcholines (17iPC and 20iPC) were determined by x-ray diffraction methods. In agreement with previous DSC studies, subgel, gel, and liquid crystal phases were observed in each homolog. The subgel Lc(c') phases of both homologs show significant two-dimensional long range order and can be described by rectangular lattices. The dimensions of the two rectangular unit cells differ in that the side chains are canted (approximately 33 degrees) in the 20iPC homolog, while in 17iPC the side chains are normal to the bilayer plane. The gel L beta phases of 17iPC (Tgg = 17-19.5 degrees C) and 20iPC (Tgg = 44 degrees C) are similar but not identical and are consistent with a distorted, pseudohexagonal lattice for the rotationally disordered side chains. The liquid crystal phases of 17iPC (Tgl = 28 degrees C) and 20iPC (Tgl = 52 degrees C) are structurally similar and are typical of lipids with fluid side chains. Significant but different changes occur in the long spacings at Tgg and Tgl for the two homologs. This implies that interfacial states (particularly in the subgel phases) differ in the two homologs below the liquid crystal phase transition temperature.