Exploring the contributions of multiple physical forces towards the self-assembly of complex macroions in solution

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Many biological molecules, such as proteins and DNA, contain many charged (ionic) groups of the same kind. A phenomenon observed in these molecules is that they can associate with each other in water despite the fact that positively-charge groups repel other positively-charged groups (or negative charges repel negative charges). Professor Tianbo Liu of the University of Akron designs and studies complex charged molecules that are large and water-soluble, and that attract each other even when they carry the same charge (positive or negative). Through an investigation of how different kinds of inter-molecular forces cooperate and compete with each other in solution, the Liu group gains a better understanding of how such ions attract one another. The conclusions are expected to be applicable to many other solution systems, and instructive for understanding biological solutions. The project contributes fundamentally to many science disciplines including physical chemistry, supramolecular chemistry, biochemistry, and materials sciences. In addition, the ability to manipulate the strengths and the effects of different inter-molecular forces would enable the design of novel self-assembled structures for applications in nanotechnology or biotechnology. This project provides research training to high school, undergraduate and graduate students, preparing them for further education or careers in STEM fields.Between simple ionic solutions (e.g., sodium chloride) and the suspensions of bulky colloidal particles, there exists a region of macroions - nanoscaled soluble ions. Supported by the Macromolecular, Supramolecular and Nanochemistry Program, Professor Liu expands his research project from the study of purely hydrophilic macroions, dominated by electrostatic interactions in polar solvents, to more complicated macroions with other forces (hydrophobic, cation-pi, pi-pi, etc.) also being present. The cooperation and competition of various intermolecular forces in such macroionic solutions are expected to demonstrate rich assembly phenomena. There are three main objectives in this project. First, the project aims to understand the effect of functionalization of macroions with organic groups on the properties of such ions in polar solvents. Secondly, dumbbell-shaped macroions with polymerizable hydrophobic linkers are designed, synthesized, then assembled into single-layered hollow, spherical "blackberry-like" structures. Polymerization of the linkers is expected to create stable, porous nanocontainers. Finally, the effects of aromatic groups on the counterion distribution around the macroions and how it leads to various controllable assembly structures are examined.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.