Spatial Organization of Ions in Supramolecular Nanostructures

With the support of the Macromolecular, Supramolecular and Nanochemistry Program in the Division of Chemistry, Professor Samuel Stupp and Professor Monica Olvera de la Cruz of Northwestern University will explore nano-sized structures formed by the assembly of molecules (named amphiphiles) containing two distinct segments: one that has affinity for water and one that does not mix well with water. Specifically, the investigators will study how the arrangement of various species that bear one or more charged species (ions or electrolytes) can be used to change the structure and function of the nano-sized structures.

The building blocks will be based on peptides, and therefore the findings can illuminate several biologically important processes. This work is inspired by the natural functions of cells, including signaling, movement, and ultimately survival, all of which depend on the tight regulation of ions inside and outside the cell membrane. The researchers will use a simultaneous experimental and computational approach to understand how added electrolytes interact with nanomaterials and how they impact critical cellular functions such as catalysis, energy storage, and bioactivity.

This work is expected to have a broad impact on education as it is a risky approach that attempts to innovate beyond traditional scientific inquiries and therefore has a great deal of potential for unexpected discoveries, a good motivator for early career scientists.

The planned research under this study is to investigate how the presence of ions affects the shape and dimensions of supramolecular nanostructures based on self-assembling peptide amphiphile molecules. The work will also probe how the spatial positioning of these ions within nanostructures and in their immediate environment affects their mobility. The study is motivated by a recent discovery in the Stupp laboratory, which surprisingly showed that ion clouds can be engineered around supramolecular nanostructures and controlled by internal interactions between ionic liquids and the self-assembling PA molecules.

The hypothesis is that large organic ions can act as dopants that produce denser clouds as electrolyte reservoirs that will impact in turn on properties such as bioactivity and external control of charge transport. By varying ionic strength of solutions and ion type, it is expected that hydration of the supramolecular structures will change as well as polarize associated water molecules and, in this way, provide for an opportunity to possibly tune ionic mobility.

This work could lead to novel materials and also have great impact on our understanding of the role of environmental ions in biological systems.

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.