Monolayer behavior of bolaamphiphiles and coupling of DNA

COLL 272

Xiuli Yue1, Gerald Brezesinski1, B Dobner2, and Helmuth Moehwald1. (1) Interfaces, Max-Planck Institute of Colloids and Interfaces, Golm, D-14476, Germany, (2) Institute of Pharmaceutical Chemistry, Martin-Luther-University, Halle, D-06120, Germany
Monolayers of bipolar lipids differing in head group structure and chain length have been in-vestigated by grazing incidence X-ray diffraction (GIXD), Brewster angle (BAM) and fluo-rescence microscopy at different temperatures. Pressure () Area (A) isotherms of 22-(sn-glycer-3-yl)-docosan-1yl-acetat exhibit a plateau region similar to a phase transition from liq-uid-expanded (LE) to condensed (LC). However, BAM shows a structured phase below this plateau. The lattice structure was investigated at pressures above the plateau by GIXD. The unit cell is rectangular and the tilt direction changes from NN to NNN at 40mN/m. The monolayer of 22-methoxydocosan-1-ol is fully condensed at all temperatures investi-gated. On compression, a transition from a rectangular phase with chains tilted towards next-nearest neighbors (NNN) to an orthorhombic phase with non-tilted molecules was observed below 35 C. At 35 C, the NNN-tilted molecules undergo a transition to a non-tilted hexago-nal phase (L2-LS). Compared with palmitic acid methyl ester, the hydroxy-group as the sec-ond polar moiety of 16-hydroxylpalmitic acid methyl ester shifts the LE/LC-phase transition to larger molecular area and lower temperature. Inserting the hydroxy-group does not change the lattice structure (NN-tilted rectangular) but increases the chain tilt. 16-hydroxypalmitic acid methyl ester cannot form a stable monolayer on pure water. The temperature effect on the transition pressure of the monolayers was also studied. Palmitic acid methyl ester shows a strong temperature dependence while the transition pressure of 16-hydroxypalmitic acid methyl ester is almost temperature independent. Replacing the ether group by a glycerol group leads to 3-0-(22-methoxydocosan-1-yl)-sn glycerol, which forms multilayers on pure water. Bolaamphiphiles with a positively charged headgroup, 22-hydroxydocosan-1-yl-trimethylammonium bromide and 22-(tetrahydro-2H-pyran-2-yloxy)-docosan-1-yl-trimethylammonium bromide, form only fluid phases. After coupling of DNA, GIXD experiments show that the lipid structure is still fluid but a one-dimensional ordering of DNA coupled to the oppositely charged monolayer was observed.