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of the oleyl amine cationic surfactant. DNA was enzymatically treated to
generate a broad distribution of contour lengths and diffusion characteristic
times.
The impact of DNA confi nement on these two columnar hexagonal struc-
tures was investigated by SAXS. Both the neat neutral and cationic LLC
systems had a columnar hexagonal symmetry, the main difference being the
reduced lattice of 49.8 Å in the cationic system compared to the 55.5 Å of
the neutral formulation. This difference was interpreted to be the result of the
kosmotropic effect of the oleyl amine, which, due to its charged nature, dehy-
drates the surfactant polar heads and reduces the LLC lattice.
A very different effect on the H
II
lattice parameter was found when the
DNA (1.4 wt % from the aqueous phase) was incorporated into the two
systems. In the nonionic LLC system, the lattice parameter decreased from
55.5 to 50.8 Å (
0.5 Å) in the presence of DNA. In contrast, in the cationic
columnar phase the lattice parameter increased from 49.8 to 59.2 Å. These
effects can be rationalized by considering the negative charge of the DNA:
When added to the neutral formulation, DNA leads to a negative effective
charge that dehydrates the lipid polar heads and reduces the lattice parameter;
on the other hand, when added to the cationic formulation, DNA partially
neutralizes the overall positive charge, moderates the dehydration effect
caused by the cationic surfactants, and induces, at least partially, swelling of
the lattice.
Amar-Yuli et al. (2011a) postulated two different possibilities of arrange-
ments for the DNA within the nonionic and cationic columnar hexagonal
phases. Being strongly hydrophilic, the DNA double strands must be either
segregated outside the water channels, within the grain boundaries, or confi ned
within the relative narrow aqueous cylinders of the H
II
structure. The strong
impact of DNA on the lattice of the mesophases provides a robust indication
that the DNA molecules were indeed confi ned within the water channels of
the reverse hexagonal phases, although the different trends observed for the
lattice evolution in the nonionic and cationic case suggest two different types
of interactions among the lipids and the DNA.
This issue was directly addressed by performing ATR-FTIR analysis on the
two formulations and indirectly by following the release of the DNA from
each LLC system by ultraviolet (UV) spectrophotometry. In the nonionic-
based H
II
mesophase the results provided an evidence for a breakage of
GMO-GMO and GMO-D
2
O hydrogen bonds due to incorporation of DNA
molecules. Furthermore, the carbonyl absorption revealed a slight modifi ca-
tion in the area of their peaks, when the DNA was present. In the absence of
DNA, the number of hydrogen-bonded carbonyls was calculated to be 72%,
and it slightly increased to 78% in the presence of DNA. It was concluded
that the DNA molecules interfere with the interfacial region of the cylinders,
with tangible effects on the water (D
2
O) and GMO molecules, including
the hydroxyl and carbonyl groups and the ester moiety. The decrease in
lattice parameter upon the addition of DNA, as detected by the SAXS
±
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