Recent Developments in Lyotropic Liquid Crystals as Drug Delivery Vehicles - Self-Assembled Supramolecular Architectures: Lyotropic Liquid Crystals - page 237

Figure 8.14 Schematic summary illustrating a (A) typical columnar hexagonal phase,
the (B, C) DNA entrapment and interactions with the surfactants forming the nonionic,
and (D, E) cationic H II systems. The molecular ratio between all the components is not
in scale in the image (Amar-Yuli et al., 2011a).
Quite in contrast, AFM examination of the excess water in the case of the
cationic hexagonal phase reveals no traces of DNA, including the smallest
fragments detectable by high - resolution AFM (Fig. 8.13 e), confi rming the
strong binding of the DNA to the cationic lipids.
Figure 8.14 summarizes the main fi ndings of this work. When confi ned
within nonionic columnar hexagonal phases, DNA interacts with the polar
heads of the lipids via hydrogen bonding (as illustrated in the fi gure), but this
enables a controlled release of the DNA in excess water following three main
release stages. When positive charges belonging to cationic lipids are decorat-
ing the water channels, binding between the lipid and DNA becomes strong,
and any release of DNA is completely suppressed at the charge ratio used. It
is reasonable to anticipate that further adjustment of the positive : negative
charge ratio or use of variable ionic strengths to partially screen electrostatic
attraction can be used as additional means to fi ne tune the DNA release
kinetics.