title: Effect of counterion valence on the pH responsiveness of polyamidoamine dendrimer structure.
abstract: 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.
authors.affiliation: The NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-6100, USA.
authors.forename: Yun
authors.initials: Y
authors.lastname: Liu
authors.forename: Lionel
authors.initials: L
authors.lastname: Porcar
authors.forename: Kunlun
authors.initials: K
authors.lastname: Hong
authors.forename: Chwen-Yang
authors.initials: CY
authors.lastname: Shew
authors.forename: Xin
authors.initials: X
authors.lastname: Li
authors.forename: Emily
authors.initials: E
authors.lastname: Liu
authors.forename: Paul D
authors.initials: PD
authors.lastname: Butler
authors.forename: Kenneth W
authors.initials: KW
authors.lastname: Herwig
authors.forename: Gregory S
authors.initials: GS
authors.lastname: Smith
authors.forename: Wei-Ren
authors.initials: WR
authors.lastname: Chen