Collaborative Research: Cooperative Processes at Surfaces: Ligand Binding at the Single Molecule Level

With support from the Chemical Structure, Dynamics, and Mechanisms-A (CSDM-A) Program in the Division of Chemistry, Ursula Mazur and Kerry Hipps of Washington State University and Bhaskar Chilukuri of Illinois State University are exploring cooperative binding events using highly sensitive imaging and computational methods. Chemical processes such as chemical reactivity and detection sensitivity depend on cooperativity. Studying these cooperative interactions requires both surface techniques that are capable of single molecule detection and computational tools for quantifying the degree of interactions. Drs. Chilukuri, Hipps, and Mazur and their students will investigate how single molecules interact with one reactive site and how that system impacts beyond other nearby domains using both experimental and computational methods. The interplay among intermolecular, intramolecular, and substrate-induced effects on chemical reaction cooperativity at surfaces will be studied and analyzed. High school, graduate, and undergraduate students will be mentored in research, and an undergraduate course in nanoscale physical chemistry will be developed. Scanning tunneling microscopy (STM) measurements reveal contributions of both inter- and intramolecular communications to cooperativity on the submolecular level while density functional theory (DFT) and molecular dynamics provide a mechanism for quantifying the role of the substrate, inter and intramolecular interactions, spatial effects, and spin-spin interactions in producing cooperativity in axial complexation. Real-time STM imaging will be used to monitor the reaction between molecules in solution and/or the gas phase and reactive sites on surface supported metal complexes containing two or more reactive sites. Reactivity will be monitored as a function of temperature, reactant concentration, solvation environment, and nature of the support for the metal complexes. Several approaches will be used to model the STM experiments, including the grand canonical ensemble to parameterize the energetics of binding for each distribution over the reactive sites and periodic DFT calculations to provide insight into how electronic distributions affect binding cooperativity at reactive sites. Molecular dynamics calculations will be employed to model solvent effects. By developing a comprehensive model of reaction cooperativity at surfaces, improved predictability of reactivity in surface chemistry, catalysis, and sensor development is envisioned. 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.