With this award, the Macromolecular, Supramolecular and Nanochemistry Program in the Division of Chemistry is funding Professor Sourav Saha of Florida State University to develop new strategies and receptors that can not only discriminate anions on the basis of their electronic properties, but also capture and release the target anions in a reversible fashion under the influence of electrons and light. Anions and cations are ubiquitous, and have diverse structures, properties, and functions. Some play important roles in biological, chemical, industrial, and environmental processes, while others are toxic and pollutants. For these reasons, it is important to regulate these charged species with high precision and selectivity. Selective ion receptors can provide scientists with systems that are recyclable, reusable, and better suited for applications in environmental protection. The graduate, undergraduate, and postdoctoral researchers working on this project will gain an array of scientific knowledge and technical expertise, from synthesis to molecular recognition. Integrated outreach activities are directed at local schools, the public library, and at students from Florida Agricultural and Mining University, an HBCU institution. Through these efforts, Dr. Saha plans to engage young and underrepresented students in hands-on experiments to motivate them to consider the pursuit of careers in science.
The goal of this research is to develop new strategies to (i) discriminate anions on the basis of their electronic properties, (ii) capture anions and cations simultaneously in a cooperative fashion, and (iii) bind and release ionic guests in a reversible fashion under the influence of electrons and light. To discriminate anions in aprotic solvents, the Saha research team is exploiting the ability of ð-acidic naphthalenediimide (NDI) receptors to accept electron(s) from strong Lewis basic anions, form charge-transfer complexes with less basic anions, and engage in anion?ð and CH···anion interactions with charge-diffuse anions. To overcome the ion-pairing effect that weakens the binding interactions between ionic guests and receptors, tweezers-shaped, ditopic ion-pair receptors are being developed by tethering two terminal NDI units with folded linkers that can bind cations. The hypothesis is that cation binding at the linker units should facilitate anion binding between the two overlapping NDI units and vice versa. During biphasic extractions, these ditopic receptors should selectively extract salts that contain less hydrated charge-diffuse anions from aqueous to organic medium, while the more hydrated hard anions should remain in water. NDI-based cationic metallacycles are being constructed to capture large charge-diffuse anions inside their cavities through anion/NDI interactions. The metal ion corners should mitigate the ion-pairing effects. The reversible redox chemistry of the NDI units and the tendency of their reduced forms to expel anions offer a new approach to release the captured anions from these receptors upon chemical, electrochemical, and/or photochemical reduction.
