Hydrophilic Macroionic Solutions - the Roles of Counterions, Co-ions and Surface Water Layers

University Of Akron, Akron OH

Investigators

Abstract

In this project funded by the Macromolecular, Supramolecular and Nanochemistry Program of the Chemistry Division, Professor Tianbo Liu of the University of Akron explores the solution properties of macroions. These macroions are between 1 and 10 nanometers (nm) in size and represent a missing link between simple ions and large colloids. The project aims to explore the microscopic features of macroions and their interactions with local environments, that is, the counterions, the co-ions, and the layered structures they make in water. These interactions are being explored in order to unveil the fundamental reasons behind the unique solution properties of the macroions such as their self-assembly into blackberry-like structures. The blackberry formation process is found to mimic the virus capsid formation process. This research could have broad impacts on other fields, such as physical chemistry, supramolecular chemistry, biochemistry, materials sciences and nanotechnology. The project involves training graduate and undergraduate students, and encouraging high school students to participate in national science competitions and scientific careers. The research infrastructure is being enhanced through scientific collaborations. The research has three complementary components. First, the macroion-counterion interaction is being characterized by determining the radial distributions of counterions around macroions and the stability of the macroions in the presence of an excess number of counterions. Secondly, the effect of co-ions on the macroions are being examined, particularly for the preferential interactions between chiral macroions and chiral co-ions. Third, the detailed changes of surface water structures of both counterions and macroions during their interaction are being studied. Relatively simple models, mainly polyoxometalate clusters and metal-organic nanocages, are employed for the study. The solution studies employ a combination of techniques, such as static and dynamic laser light scattering, synchrotron small-angle X-ray scattering, isothermal titration, nuclear magnetic resonance, electron microscopy, and Zeta potential analysis. The conclusions are expected to be universal and may be instructive for understanding more complex systems such as polyelectrolyte and biomacromolecular solutions.