Overview
The Weber group will measure the infrared spectra of ionic complexes consisting of anions and synthetic receptors binding such ions. These complexes form in solution and are transferred to the gas phase by electrospray ionization. The final targets for study are then prepared in a series of temperature-controlled ion traps. The target ions are irradiated with pulsed infrared light from a tunable infrared light source. Photon absorption and subsequent fragmentation of the target ions is used to measure their vibrational spectra. 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.
Intellectual Merit
The molecular recognition of ions in aqueous solution by synthetic receptors addresses the need to measure and control the concentration of ionic species in numerous chemical contexts, ranging from ionophoric antibiotics to sensing, materials science, and separation/extraction 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 nitrate and phosphate from agriculture. Despite decades-long developments with enormous progress in the science of molecular recognition, a complete, predictive understanding of the interactions in aqueous “host-guest” systems has not been achieved. Consequently, there is still a need for a detailed, molecular level understanding of ion receptors and binding competitiveness in solution, in order to advance the rational design of synthetic hosts for ionic guests.
Currently, the most difficult problem for understanding molecular recognition in solutions is the role of the solvent in receptor-ion interactions. 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. In concert with laser spectroscopy, this strategy is a powerful approach to investigate the molecular properties of complexes, and the effect of solvent molecules on these properties. A comparison of experimental data with quantum chemical predictions will permit benchmarking of computational approaches to describe molecular recognition. The knowledge gained in this work will help in developing predictive methods for the design of synthetic ion receptors.
Broader Impacts
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. Most of the proposed work will be carried out by graduate student researchers, contributing to the education of the next generation of scientists, who will be trained in a broad range of experimental and computational techniques.
As part of a long-standing educational part of their NSF funded research program, the Weber group will continue their work on web-based simulations for teaching quantum mechanics, chemical kinetics, and spectroscopy. These simulations transport the fundamentals of the science at the heart of their research into the classroom, aiming to enhance student learning in chemistry. This activity will result in interactive teaching tools, which will be freely available to any instructor.
The PI will be involved in the highly successful CU Wizards outreach program. This is a continuing Saturday morning lecture series, which treats topics the STEM fields, and is intended primarily for students in grades five through nine. The PI contributes an interactive lecture to this series with many experimental demonstrations, introducing the audience to the world of buoyancy and water displacement.