  The influence of hydroxyectoine on the properties of the aqueous solution in
presence of DPPC lipid bilayers is studied via semi-isotropic constant pressure
(NPT) Molecular Dynamics simulations. We investigate the solvent-co-solute
behavior in terms of Kirkwood-Buff integrals as well as hydrogen bond life
times for an increasing hydroxyectoine concentration up to 0.148 mol/L. The
observed preferential exclusion mechanism identifies hydroxyectoine as a
kosmotropic osmolyte. Our findings in regards to the DPPC lipid bilayer
indicate an increase of the surface pressure as well as the solvent accessible
surface area in presence of higher hydroxyectoine concentrations. The results
are in agreement to the outcome of recent experiments. With this study, we are
able to validate the visibility of co-solute-solute-solvent effects for low and
physiologically relevant osmolyte concentrations.
