Chemistry Reference
In-Depth Information
pH7
pH2
pH7
1×10
−5
1×10
−5
1×10
−5
8×10
−5
6×10
−5
4×10
−5
2×10
−5
0
0
1
2
3
4
5
6
time
0.5
[h
0.5
]
Figure 8.19
Release profi les of phloroglucinol plotted against the square root of time,
upon sequential switch in the pH of the excess solution from pH 7 → pH 2 → pH 7
(Negrini and Mezzenga, 2011).
1 0
− 8
c m
2
/s and
D
pH7
1 0
− 8
c m
2
/s (slopes
1 0
− 8
at
D
pH2
=
2.2
×
=
30.6
×
=
1.34
×
1 0
− 8
at pH 7), respectively. It is therefore possible to conclude
that the bicontinuous cubic phase releases almost four times faster than the
reverse hexagonal phase, consistent with previous reported work. To demon-
strate a pH-triggered on-off release behavior and tunable release profi les in
dynamic conditions, the release study was also carried out by switching the
pH between the values of 7 and 2 using the same setup, and the resulting
release data are given in Figure 8.19. The values of the slopes obtained in
these conditions are 5.7
pH 2 and 5
×
1 0
− 8
in the initial pH 7 conditions, 2.58
1 0
− 8
after
×
×
1 0
− 8
upon reverting the pH to 7 again.
The values of the slopes at pH 7 agree well with those obtained by the static
release experiment, whereas that measured at pH 2 shows a slightly faster
release; this results from the relatively long time needed to induce a complete
change of Im3m into H
II
in bulk mesophases, leading to a long-living coexis-
tence of Im3m and H
II
upon the switch of the pH from 7 to 2. It can be easily
anticipated that, when applying these concepts to cubosomes and hexosomes
of a few hundred nanometers in diameter, the order-order transitions will
occur much faster, leading to a sharper pH-induced on-off-on release along
the gastrointestinal tract.
switching the solution at pH 2, and 5.3
×
8.6 MOLECULAR INTERACTIONS OF LYOTROPIC LIQUID
CRYSTALS WITH PROTEINS AND NUCLEOTIDES
Murgia et al. (2009) entrapped several nucleotides into cubic and lamellar
monoolein-based mesophases in order to protect them and enable their
release. Nucleoside and nucleotide analogs represent a class of innovative
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