Chemistry Reference
In-Depth Information
NONA solubilization had a minor, yet consistent swelling effect on the
cylinders. The initial lattice parameter in the blank system was 57.9
±
0.5 Å ,
0.5 Å
at 6 wt % NONA. Its effect was found to be focused mostly on the water
and the GMO carbonyls. The stretching mode of the water was gradually
shifted from 3361 to 3346 cm
− 1
with increasing NONA concentration in the
mesophase, indicating stronger hydrogen bonding of the water with the
peptide.
It was summarized that structural investigation revealed that the solubiliza-
tion sites of the different guest molecules depend on their molecular structure
and differ signifi cantly. Na-DFC populates the interfacial region, enhances the
interactions between GMO tails, and shrinks and stabilizes the H
II
mesophase
(Fig. 8.9c). PEN solubilization is concentration dependent. The initial PEN
loads populate the hydrophilic head-group area, whereas the higher PEN
loads pack closer to the GMO tails (Figs. 8.9e and 8.9f). The hydrophilic
NONA populated the inner channels region and swelled the mesophase (Fig.
8.9d). RALA acted as a chaotropic agent at the H
II
mesophase, interacting
mostly with the water within the channels and enhancing the hydration of the
GMO head groups.
Furthermore, the effect of the various peptides on skin permeation effi -
ciency was determined by diffusion experiments of Na-DFC through porcine
skin using Franz diffusion cells. All systems were composed of H
II
mesophases
loaded with 1 wt % Na-DFC and 1 wt % of each CPP (the control was a
system with Na-DFC and no CPP). These experiments indicated that all
three peptides increased signifi cantly the diffusion of Na-DFC through the
skin (Fig. 8.10 a).
NONA was found to be the most effi cient CPP, signifi cantly enhancing the
transdermal penetration (a 2.2-fold increase in the total amount of Na-DFC
that diffused through the skin). PEN and RALA caused 1.9- and 1.5-fold
increases, respectively, compared with the control system. In all tested systems,
there was a gradual and linear increase in the cumulative penetration of
Na - DFC with time.
A calculation of Na-DFC percentage that permeated through the skin
showed that at the blank systems the total amount that diffused through the
skin during the 24-h experiment was 0.9% from the initial applied dose. The
amount released at the NONA, PEN, and RALA systems was 1.9, 1.8, and
1.3%, respectively. The permeability coeffi cients (
K
p
, calculated as cm·h
− 1
),
derived from the steady-state fl ux of Na-DFC, revealed the same tendency
(Fig. 8.10b), a 1.5-fold increase in the presence of RALA and 2.3- and 2.2-fold
increases with PEN and NONA, respectively. Since the skin permeation studies
revealed different profi les for each of the three peptides, a more detailed
analysis using the well-established technique of “emptying experiments” was
conducted by the authors. These experiments aimed to determine whether the
rate-determining step of Na-DFC skin permeation from the mesophase is
migration out of the mesophase or permeation through the skin. In addition,
and it slightly increased with NONA loading to a maximal value of 60.5
±
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