Figure 2 1H NMR data of beta-CD (a), aldehyde
group functionalized beta-CD (b), crosslinked beta-CD nanocage (c) and
crosslinked beta-CD nanocage loaded with DOX (d).
The assembly process of the beta-CD nanocage was further examined using
FTIR. For beta-CD, the broad peaks at 3300 cm-1 and
1420 cm-1 are assigned to the OH stretching and
bending vibrations, respectively. The absorption peak at 2920
cm-1 corresponds to CH stretching vibrations, while
the prominent peak at 1020 cm-1 is attributed to the
CO stretching vibration of the glucose
unit25[]. Upon oxidation of beta-CD,
a clear characteristic peak at 1740 cm-1 emerged,
corresponding to the C=O stretching vibration of the CHO
group2426[,
]. Another prominent peak at 2730 cm-1 is associated
with the CH stretching vibrations of the CHO group. Other characteristic
peaks remained relatively unchanged compared to pure beta-CD. After
crosslinking with cystamine, the characteristic peak of the CHO group
weakened, indicating the reaction between the aldehyde
group-functionalized beta-CD and cystamine. Additionally, two new
absorption peaks appeared at 1650 cm-1 and 570
cm-1, respectively assigned to the C=N stretching
vibration and the SS bond, indicating the successful introduction of the
acid-sensitive imine and reduction-sensitive disulfide bonds. Following
the loading of DOX into the beta-CD nanocage, the DOX signal was
observed, including the absorption peak at 3000 cm-1assigned to the CH stretching vibrations of the DOX benzene ring, the
absorption peak at 3300-3500 cm-1 assigned to the OH
and NH stretching vibrations of DOX, the absorption peak at 1750
cm-1 assigned to the C=O stretching vibration, and the
absorption peaks at 1650 cm-1 and 1500
cm-1 assigned to the C=C stretching vibration of the
benzene skeleton. The FTIR spectrum of pure DOX is also provided in
Figure S2. Some characteristic peaks overlapped between DOX and the
beta-CD nanocage, but the loaded DOX signals were
distinguishable27[]. Through the
combination of FTIR and 1H NMR analysis, we were able
to identify the components of the beta-CD nanocage and its derivatives.