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Issue 2, 2011
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pH Responsiveness of polyelectrolyte dendrimers: a dynamical perspective

Xin Li,ab  Michaela Zamponi,bc  Kunlun Hong,d  Lionel Porcar,e  Chwen-Yang Shew,f  Timothy Jenkins,g  Emily Liu,a  Gregory S. Smith,b  Kenneth W. Herwig,*b  Yun Liu*gh  and  Wei-Ren Chen*bij 
Author affiliations

* Corresponding authors

a Department of Mechanical, Aerospace & Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, USA

b Neutron Scattering Science Division, Oak Ridge National Laboratory, Oak Ridge, USA
E-mail: chenw@ornl.gov, herwigkw@ornl.gov

c Jülich Centre for Neutron Science, Forschungszentrum Jülich, Jülich, Germany

d The Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, USA

e Institut Laue-Langevin, B.P. 156, Grenoble Cedex 9, France

f Department of Chemistry, City University of New York, College of Staten Island, Staten Island, USA

g The NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, USA
E-mail: yunliu@nist.gov

h Department of Chemical Engineering, University of Delaware, Newark, USA

i Joint Institute for Neutron Sciences, Oak Ridge National Laboratory, Oak Ridge, USA

j Department of Chemical & Biomolecular Engineering, the University of Tennessee, Knoxville, USA

Abstract

A combined quasi-elastic neutron scattering (QENS) and high-resolution solution NMR spectroscopy study was conducted to investigate the internal dynamics of aqueous (D2O) G5 PAMAM dendrimer solutions as a function of molecular protonation at room temperature. Localized motion of the dendrimer segments was clearly exhibited in the QENS data analysis while the global, center-of-mass translational diffusion was measured by NMR. Our results unambiguously demonstrate an increased rapidity in local scale (∼ 3 Å) motion upon increasing the molecular protonation. This is contrary to an intuitive picture that increased charge stiffens the dendrimer segments thereby inhibiting local motion. These charge-induced changes may be a result of interactions with the surrounding counterions and water molecules as the segments explore additional intra-dendrimer volume made available by slight electrostatic swelling and redistribution of mass in the dendrimer interior. This observation is relevant to development of a microscopic picture of dendrimer-based packages as guest-molecule delivery vehicles because reorganization of the confining dendrimer segments must be a precursor to guest-molecule release.

Graphical abstract: pH Responsiveness of polyelectrolyte dendrimers: a dynamical perspective

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Publication details

The article was received on 12 Jul 2010, accepted on 28 Oct 2010 and first published on 23 Nov 2010


Article type: Paper
DOI: 10.1039/C0SM00671H
Citation: Soft Matter, 2011,7, 618-622
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    pH Responsiveness of polyelectrolyte dendrimers: a dynamical perspective

    X. Li, M. Zamponi, K. Hong, L. Porcar, C. Shew, T. Jenkins, E. Liu, G. S. Smith, K. W. Herwig, Y. Liu and W. Chen, Soft Matter, 2011, 7, 618
    DOI: 10.1039/C0SM00671H

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