Amplification of chiral recognition and discrimination among amino-acid-based nanoscale ions during assembly induced by electrostatic interaction

This award supports experimental research and education aimed at understanding how chirality is maintained and amplified during the formation of superstructures by charged macromolecules. Most biomacromolecules like proteins and DNA are chiral, that is, the same molecule has two different geometrical forms which cannot be superimposed onto its mirror image.

Although both forms are considered identical in chemical and physical properties except their handedness, exclusively L-amino acids in proteins and D-sugars are found in biological systems – a phenomenon called homochirality. Many interesting phenomena have been discovered, such as that charged chiral species only seek their own kind when forming large structures (chiral recognition), and under certain conditions only one form will assemble while the other one stays as molecules in solution (chiral discrimination, which leads to homochirality).

These are important topics in many fields from life sciences to catalysis and separation science. The PI will explore the conditions needed for achieving such phenomena in solution by studying nanoscale intermolecular physical interactions, especially the long-range electrostatic interaction between different chral components, which is the probable driving force.

The project engages graduate and undergraduate students through the NSF-REU center, and the newly established BS program in Polymers, both at the School of Polymer Science and Polymer Eng. at the University of Akron, and high school students from northeast Ohio. The PI’s team will specifically recruit from local schools that serve large numbers of students from groups traditionally under-represented in STEM fields, encouraging students to take science courses and pursue STEM related careers.

PI Tianbo Liu from the University of Akron will explore the nanoscale intermolecular interactions in dilute macroionic solutions containing multiple chiral components, by using metal-organic cages containing different chiral amino acid linkers as models . Such interactions are responsible for achieving chiral recognition (e.g., forming enantiomeric, chiral supramolecular structures instead of racemic mixed ones) and chiral discrimination and selection (e.g., only one enantiomer of chiral macroions will assemble, in the presence of small amount of chiral counterions or co-ions).

The PI plans to design experiments to explore the probable key role of the long-range electrostatic interaction, represented by the interactions of chiral counterions or co-ions with the central chiral macroions, behind such phenomena, by examining the following hypotheses: (1) long-range electrostatic intermolecular interaction is critical for achieving chiral recognition between chiral macroions, resulting in pure enantiomeric supramolecular structures in racemic solutions instead of forming mixed assemblies; (2) a minor chiral environment (e.g., low concentrations of minor chiral counterions) is sufficient to achieve chiral selection (i.e., promoting one type of enantiomer to self-assemble while suppressing the other type) in chiral macroionic solution; (3) chiral selection of the metal organic cage macroions might become much more significant when the counterions (amino acids, e.g., Alanine) and the ligands of the metal organic cages are of the same type (e.g., Alanine); (4) chiral co-ions (ions carrying the same charge as the macroions) themselves alone might also be able to achieve chiral recognition and chiral selection of chiral macroions; and (5) minor chiral components can lead to the formation of chiral gels with tunable chirality. The PI’s team expects to contribute to our fundamental understanding of nanoscale intermolecular interactions by identifying the critical force leading to the chiral recognition and chiral selection of biomacromolecules, which further lead to many critical phenomena such as the homochirality feature of lives.

The project engages graduate and undergraduate students through the NSF-REU center, and the newly established BS program in Polymers, both at the School of Polymer Science and Polymer Eng. at the University of Akron, and high school students from northeast Ohio. The PI’s team will specifically recruit from local schools that serve large numbers of students from groups traditionally under-represented in STEM fields, encouraging students to take science courses and pursue STEM related careers.

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.