CAREER: Pnictogen Bonding in Solution: Developing Tools for the Self-assembly of Inverted Bilayer Membranes, Heteromolecular Dyads and Supramolecular Catalysts.

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Nature builds complexity through a clever combination of strong and weak chemical bonds/interactions. Weak interactions are used to assemble larger molecules, frameworks and scaffolds. For example, DNA strands are held together by hydrogen bonds to form a double-stranded structure (double helix). These hydrogen bonds can be broken relatively easily to allow separation of the strands when single-stranded DNA is needed for cell replication and protein synthesis. Hydrogen bonds are well studied and widely used not only in nature but also for controlling the assembly and properties of man-made materials. With the support of the Macromolecular, Supramolecular and Nanochemistry Program of the NSF Division of Chemistry, the research group of Professor Cozzolino at Texas Tech University studies weak interactions that lead to larger assemblies of molecules and explores their potential applications. Possible applications range from molecular sensing to crystal engineering, self-assembly of large polymers and gels to solar cells and liquid crystals - all of which are beneficial to society and the economy. This research project also engages high school and undergraduate students (including members of underrepresented groups) in the development of a code for the computational studies of weak interactions, providing an inquiry-based opportunity for involvement in STEM fields.This project seeks to gain a better fundamental understanding of pnictogen bonding and to develop this type of bonding into a useful and predictable supramolecular interaction. There are three main objectives in this project. The first objective is to prepare and study antimony(III) and bismuth(III) compounds that self-assemble through multiple, homo-complementary secondary bonding interactions. The research plan takes advantage of the unique ability of these pnictogens to support up to three interactions at three well-defined sigma-holes. By examining the influence of the pnictogen element, the polarity of the primary bond, the symmetry of the supporting ligand, bond angles, and steric factors on the secondary interactions, this project develops/refines a set of rules for designing supramolecular systems (e.g., inverted bilayer membranes and vesicles) that exploit pnictogen bonding. The second objective of the resesarch is to design and study pnictogen compounds that self-assemble through heteromolecular recognition events that are analogous to the self-assembly of Watson-Crick base pairs. The third objective is to design systems that bind anions through antimony(III) or bismuth(III) secondary bonding interactions. The experimental studies are complemented by the parameterization of a molecular mechanics force field to account for pnictogen secondary bonding interactions.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.