Poly(amidoamine)
and Poly(propyleneimine) Dendrimers
Show Distinct Binding Behaviors with Sodium Dodecyl Sulfate: Insights
from SAXS and NMR Analysis
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Abstract
We
investigate the interactions of generation 3 (G3) poly(amidoamine)
(PAMAM) and G3 poly(propylenimine) (PPI) dendrimers with sodium dodecyl
sulfate (SDS) in aqueous solution. Size and structure of the dendrimer–SDS
aggregates as a function of SDS/dendrimer molar ratio were revealed
by SAXS and NMR. G3 PAMAM has a relatively open and dense-core structure,
while G3 PPI with the same number of surface amine groups possesses
a compact and uniform structure. Upon addition of SDS, much more SDS
monomers were encapsulated in the interior of PPI rather than in PAMAM.
More significant size increase in PAMAM–SDS aggregate is observed
at low SDS concentrations, due to the binding of SDS on PAMAM surface
and further assembly into larger supramolecular structures. Both noncooperative
and cooperative binding of SDS on G3 PPI surface are observed, while
only noncooperative binding is proposed on G3 PAMAM, due to its open
surface and large surface group distance. The size of the PPI–SDS
complex is larger than that of PAMAM–SDS at higher SDS concentrations.
Within the investigated SDS concentrations, SDS exhibits much stronger
interactions with G3 PPI than with G3 PAMAM. These results provide
new insights into dendrimer–surfactant interactions and explain
why PPI is much more cytotoxic than PAMAM