Influence of salt on the solution dynamics of a phosphorylcholine-based polyzwitterion

[Display omitted] •Dimension of poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) does not change as a function of salt concentration.•Alkali cations have little effect on the radius of PMPC.•Halide anions, particularly iodide, have greater influence on the size of PMPC.•Interaction between salt...

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Bibliographic Details
Published in:European polymer journal 2017-02, Vol.87, p.449-457
Main Authors: Zhang, Zhenyu J., Madsen, Jeppe, Warren, Nicholas J., Mears, Matthew, Leggett, Graham J., Lewis, Andrew L., Geoghegan, Mark
Format: Article
Language:English
Subjects:
Alkali halides
Anions
Aqueous solutions
Coils
Correlation analysis
Diffusion
Diffusion coefficient
Divalent cations
Electrolytes
Enhanced diffusion
Fluorescence
Halides
Hydrogen bonds
Methacryloyloxyethyl phosphorylcholine
Phosphorylcholine
Polyelectrolyte
Potassium
Reduction
Salt
Solution dynamics
Spectroscopic analysis
Water chemistry
Zwitterionic
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Summary:[Display omitted] •Dimension of poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) does not change as a function of salt concentration.•Alkali cations have little effect on the radius of PMPC.•Halide anions, particularly iodide, have greater influence on the size of PMPC.•Interaction between salts and PMPC is ion specific. The diffusion of a polyzwitterion, poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC), in aqueous solution containing different alkali halides was studied by fluorescence correlation spectroscopy at single molecule level. It was found that the halide anion has a greater effect on the radius of zwitterionic PMPC molecules than alkali cations, which is due to the mechanism by which PMPC molecules interact with the surrounding hydrogen bond network of water molecules and adsorbed ions. With the addition of salt, the size of PMPC remains constant while its diffusion coefficient is reduced slightly, although larger cations (e.g. K+) result in slightly increased diffusion coefficient for 1M potassium chloride-based solutions. This enhanced diffusion coefficient is attributed to the decrease in the viscosity of the aqueous solution on the addition of salt. When the counter-ion was varied in potassium-based salts, different effects were observed for different anions, resulting a reduction in the diffusion coefficient as a function of salt concentration. This reduction was modest for KBr, but significant for KI. Overall, no discernible changes were observed as the size of the PMPC coil was varied, except in case of KI for which a significant increase was observed at higher ionic strength. Divalent cations (Ca2+ and Mg2+), produced similar effects to those found for monovalent cations. These effects are explained by the interaction of PMPC with the hydrogen bond network of water molecules and with the adsorbed ions.
ISSN:0014-3057
1873-1945
DOI:10.1016/j.eurpolymj.2016.12.001