RUI: Exploring Halogen Bonding as a Fundamental Interaction Toward the Development of Nanoparticle-Based Screening Methods for Explosive Molecule Detection

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With the support of the Macromolecular, Supramolecular, and Nanochemistry (MSN) Program in the Division of Chemistry, Professor Michael C. Leopold of the University of Richmond and his undergraduate students will explore the chemistry of the halogen bond in an effort to exploit its unique attractive interactions to develop nanoparticle sensing platforms for explosives and structurally-related compounds. The long-term practical objective is to develop halogen bonding nanoparticle-based explosive sensing tools that are fast, operable by non-experts, field portable and deployable by law enforcement and the military. On the fundamental side, the project advances knowledge and fundamental understanding of structure-dependent halogen bond interactions and adapts this knowledge to the design of nanomaterials that serve a functional role within sensing schemes. The project engages undergraduate students in fundamentally-sound, multidisciplinary, practical outcome-oriented research. In addition to an immersive laboratory experience, undergraduate students will assist in the development of curriculum-based undergraduate research material and will actively participate in community educational and outreach programs aimed at inspiring and retaining interest in STEM fields at local under-resourced K-12 schools. This project focuses on structure-optimized halogen bonding (XB) as a fundamental intermolecular interaction between strategically-designed XB selector molecules coupled to gold nanoparticles (NPs) and the targeted explosive molecules. Promotion of strong XB interactions between these functionalized NPs and non-aromatic explosives should lead to analytical signaling, spectroscopic or electrochemical, that indicates the presence of targeted molecules. To accomplish this overarching goal, there are a number of specific objectives including: (1) the use of 19F and 1H NMR (nuclear magnetic resonance) titration measurements to identify specific halogenated chemical structure and experimental conditions for the strongest X-B interactions with explosives and/or explosive-related molecules; (2) synthesis of thiol-terminated ligands with optimized X-B promoting chemical structure; (3) exploration of the surface structure/chemistry of monolayer protected nanoclusters (MPCs) to effectively functionalize their peripheral layer with X-B selector ligands via place-exchange reactions monitored with NMR measurements; (4) the use of sophisticated 2-D NMR, NOESY (Nuclear Overhauser Enhancement Spectroscopy) and HOESY (Heteronuclear Overhauser Enhancement Spectroscopy) methods, to characterize X-B interactions between functionalized MPCs and explosive/explosive-related target molecules; (5) exploration of X-B induced solution aggregation of selector-modified MPCs in the presence of explosive molecules; (6) demonstration of X-B selector functionalized MPCs within assembled films as an interface for detecting explosives and/or explosive-related molecules in chemical vapor via electrochemical measurements.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.