  Basic understanding of biological membranes is of paramount importance as
these membranes comprise the very building blocks of life itself. Cells depend
in their function on a range of properties of the membrane, which are important
for the stability and function of the cell, information and nutrient transport,
waste disposal and finally the admission of drugs into the cell and also the
deflection of bacteria and viruses.
  We have investigated the influence of ibuprofen on the structure and dynamics
of L-alpha-phosphatidylcholine (SoyPC) membranes by means of grazing incidence
small-angle neutron scattering (GISANS), neutron reflectometry and grazing
incidence neutron spin echo spectroscopy (GINSES). From the results of these
experiments we were able to determine that ibuprofen induces a two-step
structuring behavior in the SoyPC films, where the structure evolves from the
purely lamellar phase for pure SoyPC over a superposition of two hexagonal
phases to a purely hexago- nal phase at high concentrations. Additionally,
introduction of ibuprofen stiffens the membranes. This behavior may be
instrumental in explaining the toxic behavior of ibuprofen in long-term
application.
