Exploring Fluorescent Dyes at Biomimetic Interfaces with Second Harmonic Generation and Molecular Dynamics.
The adsorption of a DNA fluorescent probe belonging to the thiazole orange family at the dodecane/water and dodecane/phospholipid/water interfaces has been investigated using a combination of surface second harmonic generation (SSHG) and all-atomistic molecular dynamics (MD) simulations. Both approaches point to a high affinity of the cationic dye for the dodecane/water interface with a Gibbs free energy of adsorption on the order of -45 kJ/mol. Similar affinity was observed with a monolayer of negatively charged DPPG (1,2-dipalmitoyl-sn-glycero-3-phospho-rac-(1-glycerol)) lipids. On the other hand, no significant adsorption could be found with the zwitterionic DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) lipids. This was rationalized in terms of Coulombic interactions between the monolayer surface and the cationic dye. The similar affinity for the interface with and without DPPG, despite the favorable Coulombic attraction in the latter case, could be explained after investigating the interfacial orientation of the dye. In the absence of a monolayer, the dye adsorbs with its molecular plane almost flat at the interface, whereas in the presence of DPPG it has to intercalate into the monolayer and adopt a significantly different orientation to benefit from the electrostatic stabilization.
Department of Physical Chemistry, University of Geneva , 30 quai Ernest-Ansermet, CH-1211 Geneva 4, Switzerland.
Giuseppe
G
Licari
J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences , Dolejškova 2155/3, 182 23 Prague 8, Czech Republic.
Lukasz
L
Cwiklik
Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences , Flemingovo nam. 2, 16610 Prague 6, Czech Republic.
Pavel
0000-0002-6892-3288
P
Jungwirth
Department of Physical Chemistry, University of Geneva , 30 quai Ernest-Ansermet, CH-1211 Geneva 4, Switzerland.
Eric
0000-0002-9580-9683
E
Vauthey