Unexpected Bilayer Formation
in Langmuir Films of
Nucleolipids
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Abstract
Langmuir monolayers have been extensively investigated
by various
experimental techniques. These studies allowed an in-depth understanding
of the molecular conformation in the layer, phase transitions, and
the structure of the multilayer. As the monolayer is compressed and
the surface pressure is increased beyond a critical value, usually
occurring in the minimal closely packed molecular area, the monolayer
fractures and/or folds, forming multilayers in a process referred
to as collapse. Various mechanisms for monolayer collapse and the
resulting reorganization of the film have been proposed, and only
a few studies have demonstrated the formation of a bilayer after collapse
and with the use of a Ca<sup>2+</sup> solution. In this work, Langmuir
isotherms coupled with imaging ellipsometry and polarization modulation
infrared reflection absorption spectroscopy were recorded to investigate
the air–water interface properties of Langmuir films of anionic
nucleolipids. We report for these new molecules the formation of a
quasi-hexagonal packing of bilayer domains at a low compression rate,
a singular behavior for lipids at the air–water interface that
has not yet been documented