Cryogenic Ion Spectroscopy Studies of Ion-Receptor Interactions in Water Soluble Molecular Recognition Complexes and Their Hydrated Clusters

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In this project funded by the Chemical Structure, Dynamics and Mechanisms-A program of the Chemistry Division, Professor J. Mathias Weber and his team will study how charged atoms and molecules (ions) bind to molecules designed to capture them (receptors) in a process called molecular recognition, and how the presence of water molecules changes this recognition process. Ion receptors can be used to measure and control the concentration of ions in numerous chemical contexts, ranging from a group of antibiotics to sensors and materials science. Ion recognition also has impact on important issues regarding food and water sources, such as the safety of public water supplies, or pollution with some types of molecular ions from industrial and agricultural sources. Professor Weber plans to develop outreach and educational activities related to his scientific studies, including developing simulations for use in teaching advanced undergraduate chemistry topics, which would provide a valuable resource, particularly for students who cannot participate in hands-on activities on campus.The project focuses on the role of the solvent in receptor-ion interactions, which is one of the most difficult problems for understanding molecular recognition in solutions. The complexity of solutions presents many obstacles to investigating the interplay of ion, receptor, and solvent, from the presence of multiple species in the same sample with similar responses to experimental probes, to the bulk solvent masking key spectroscopic signatures, to the fluctuating number of solvent molecules interacting with the host-guest pair. The charged nature of many ion-receptor complexes allows selective preparation and mass spectrometric isolation of relevant species, including their hydrated clusters, and circumvents the obstacles mentioned above. The Weber group employs cryogenic ion spectroscopy in concert with electrospray ionization mass spectrometry to measure the infrared spectra of ionic complexes consisting of anions and synthetic receptors binding such ions. These spectra and the accompanying quantum chemical calculations will yield information on the structures and intermolecular forces governing molecular recognition of negative ions. Additionally, the Weber group will characterize the interaction of these complexes with water molecules. The knowledge gained in this work will help in developing predictive methods for the design of synthetic ion receptors. The broader impacts from the expected outcome of this work has the potential to change the way scientists think about ion molecular recognition, which is a frontier in chemical science. The development of applications that address the impact of ions in environmental as well as technical scenarios, including the nexus of food and water, can have significant societal impact. Professor Weber will also continue outreach and educational work, including development of web-based simulations for teaching quantum mechanics, chemical kinetics, and spectroscopyThis 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.