Host–Guest Chemistry
of Dendrimer–Drug
Complexes: 7. Formation of Stable Inclusions between Acetylated Dendrimers
and Drugs Bearing Multiple Charges
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Abstract
Drug molecules bearing multiple charges usually form
precipitates
with cationic dendrimers, which presents a challenge during the preparation
of dendrimer inclusions for these drugs. In the present study, fully
acetylated polyamidoamine (PAMAM) dendrimers were proposed as stable
vehicles for drug molecules bearing two negative charges such as Congo
red and indocyanine green. NMR techniques including <sup>1</sup>H
NMR and <sup>1</sup>H-<sup>1</sup>H NOESY were used to characterize
the host–guest chemistry of acetylated dendrimer and these
guest molecules. The cationic PAMAM dendrimer was found to form a
precipitate with Congo red and indocyanine green, but the acetylated
one avoided the formation of cross-linking structures in aqueous solutions.
NOESY studies revealed the encapsulation of Congo red and indocyanine
green within the interior cavities of PAMAM dendrimers at mild acidic
conditions and acetylated dendrimers show much stronger ability to
encapsulate the guest molecules than cationic ones. Also, UV–vis–NIR
studies suggest that acetylated dendrimers significantly improve the
photostability of indocyanine green and prevent the formation of indocyanine
green J-aggregates in aqueous solutions. The present study provides
a new insight into dendrimer-based host–guest systems, especially
for those guest molecules bearing multiple charges