The ordering of branched chain glycerophosphoethanolamines (PE) with differ
ent side chain length (n = 1, 2, 5 and 14) is systematically studied and co
mpared with that of the corresponding double chain dipalmitoyl-phosphatidyl
ethanolamine (DPPE) monolayers. The PEs have a 2-branched (methyl, ethyl, p
entyl and tetradecyl) hexadecanoyl chain at the sn-1 position of the glycer
ol backbone and an unbranched hexadecyl residue at the sn-2 position. Therm
odynamic data obtained by pi-A isotherm measurements at different temperatu
res are coupled with two-dimensional (2D) texture and 2D structure informat
ion obtained by Brewster angle microscopy (BAM) and X-ray diffraction at gr
azing incidence (GIXD), respectively. With increasing side chain length up
to n = 5, the ordering of the long alkyl chains is increasingly disturbed s
o that n-16PE monolayers are highly disordered and cannot form a condensed
phase. Already the ethyl side chain reduces the ordering of 2-16PE monolaye
r so strongly that not only the polar tilt of the alkyl chains increases, b
ut also in a stretched lattice a varying tilt azimuth of the alkyl chains i
s indicated. A side chain elongation nearly to the length of the two main c
hains enhances the ordering to that of a triple chain phospholipid with the
alkyl chains oriented perpendicularly in a hexagonal lattice. Texture and
shape of the dendritic or fractal-like condensed phase domains are similar
to that known from DPPE monolayers. However, the individual differences in
the inner textures found for the different side chain lengths, corroborate
the GIXD results. At short side chains, domain regions of different tilt di
rection occur, whereas at long side chain the domains show no differences i
n the inner texture. (C) 1999 Elsevier Science S.A. All rights reserved.