Effect of counterion valence on the pH responsiveness of polyamidoamine dendrimer structure.
An accurate determination of the structure characteristics of protonated generation 5 polyamidoamine dendrimers in aqueous solution has been conducted by analyzing the small angle neutron scattering databased on a statistical mechanics model. In our investigation, the primary focus is to elucidate the effect of counterion valence on the counterion association and its impact on the intramolecular density profile within a dendrimer. In the range of our study for molecular protonation, a strong dependence of the structural properties of charged dendrimers on counterion valence is revealed. Our findings indicate that the association of a large amount of divalent counterions significantly reduces the effective charge of a dendrimer molecule. Surprisingly, no discernible transition of the density distribution profile is observed for the dendrimer charged by D(2)SO(4), as opposed to our previous observation of a pronounced transition in intramolecular density profile for the dendrimer charged by DCl. These findings may be understood from the thermodynamic processes of counterions.
Liu
Yun
Y
The NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-6100, USA.
Porcar
Lionel
L
Hong
Kunlun
K
Shew
Chwen-Yang
CY
Li
Xin
X
Liu
Emily
E
Butler
Paul D
PD
Herwig
Kenneth W
KW
Smith
Gregory S
GS
Chen
Wei-Ren
WR