2 research outputs found
Impact of Lipid Oxidization on Vertical Structures and Electrostatics of Phospholipid Monolayers Revealed by Combination of Specular X‑ray Reflectivity and Grazing-Incidence X‑ray Fluorescence
The influence of phospholipid oxidization
of floating monolayers
on the structure perpendicular to the global plane and on the density
profiles of ions near the lipid monolayer has been investigated by
a combination of grazing incidence X-ray fluorescence (GIXF) and specular
X-ray reflectivity (XRR). Systematic variation of the composition
of the floating monolayers unravels changes in the thickness, roughness
and electron density of the lipid monolayers as a function of molar
fraction of oxidized phospholipids. Simultaneous GIXF measurements
enable one to qualitatively determine the element-specific density
profiles of monovalent (K<sup>+</sup> or Cs<sup>+</sup>) and divalent
ions (Ca<sup>2+</sup>) in the vicinity of the interface in the presence
and absence of two types of oxidized phospholipids (PazePC and PoxnoPC)
with high spatial accuracy (±5 Å). We found the condensation
of Ca<sup>2+</sup> near carboxylated PazePC was more pronounced compared
to PoxnoPC with an aldehyde group. In contrast, the condensation of
monovalent ions could hardly be detected even for pure oxidized phospholipid
monolayers. Moreover, pure phospholipid monolayers exhibited almost
no ion specific condensation near the interface. The quantitative
studies with well-defined floating monolayers revealed how the elevation
of lipid oxidization level alters the structures and functions of
cell membranes
Three-Legged 2,2′-Bipyridine Monomer at the Air/Water Interface: Monolayer Structure and Reactions with Ni(II) Ions from the Subphase
The behavior of compound <b>2</b> [1,3,5-triÂ(2,2′-bipyridin-5-yl)Âbenzene]
with three bipyridine units arranged in a star geometry is investigated
in the presence and absence of NiÂ(ClO<sub>4</sub>)<sub>2</sub>. Its
properties at the air–water interface as well as after transfer
onto a solid substrate are studied by several techniques including
Brewster angle microscopy, X-ray reflectivity, neutron reflectivity,
X-ray photoelectron spectroscopy, Rutherford backscattering spectrometry,
and atomic force microscopy combined with optical microscopy. It is
found that compound <b>2</b> within the monolayers formed stays
almost vertical at the interface and that at high Ni<sup>2+</sup>/<b>2</b> (Ni<sup>2+</sup>/<b>2</b> = 4000, 20′000) ratios
two of the three bipyridine units of <b>2</b> are complexed,
resulting in supramolecular sheets that are likely composed of arrays
of linear metal–organic complexation polymers