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Bhattacharjee N, Gao X, Nathani A, Dobscha JR, Pink M, Ito T, Flood AH. Solvent Acts as the Referee in a Match-Up Between Charged and Preorganized Receptors. Chemistry 2023; 29:e202302339. [PMID: 37615829 DOI: 10.1002/chem.202302339] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2023] [Revised: 08/21/2023] [Accepted: 08/22/2023] [Indexed: 08/25/2023]
Abstract
The prevalence of anion-cation contacts in biomolecular recognition under aqueous conditions suggests that ionic interactions should dominate the binding of anions in solvents across both high and low polarities. Investigations of this idea using titrations in low polarity solvents are impaired by interferences from ion pairing that prevent a clear picture of binding. To address this limitation and test the impact of ion-ion interactions across multiple solvents, we quantified chloride binding to a cationic receptor after accounting for ion pairing. In these studies, we created a chelate receptor using aryl-triazole CH donors and a quinolinium unit that directs its cationic methyl inside the binding pocket. In low-polarity dichloromethane, the 1 : 1 complex (log K1 : 1 ~ 7.3) is more stable than neutral chelates, but fortuitously comparable to a preorganized macrocycle (log K1 : 1 ~ 6.9). Polar acetonitrile and DMSO diminish stabilities of the charged receptor (log K1 : 1 ~ 3.7 and 1.9) but surprisingly 100-fold more than the macrocycle. While both receptors lose stability by dielectric screening of electrostatic stability, the cationic receptor also pays additional costs of organization. Thus even though the charged receptor has stronger binding in apolar solvents, the uncharged receptor has more anion affinity in polar solvents.
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Affiliation(s)
- Nabarupa Bhattacharjee
- Department of Chemistry, Indiana University Bloomington, 800 E. Kirkwood Ave., Bloomington, IN, 47405, USA
| | - Xinfeng Gao
- Department of Chemistry, Indiana University Bloomington, 800 E. Kirkwood Ave., Bloomington, IN, 47405, USA
| | - Akash Nathani
- Department of Chemistry, Kansas State University, 213 CBC Building, 1212 Mid-campus Dr North, Manhattan, KS 66506, USA
| | - James R Dobscha
- Department of Chemistry, Indiana University Bloomington, 800 E. Kirkwood Ave., Bloomington, IN, 47405, USA
| | - Maren Pink
- Department of Chemistry, Indiana University Bloomington, 800 E. Kirkwood Ave., Bloomington, IN, 47405, USA
| | - Takashi Ito
- Department of Chemistry, Kansas State University, 213 CBC Building, 1212 Mid-campus Dr North, Manhattan, KS 66506, USA
| | - Amar H Flood
- Department of Chemistry, Indiana University Bloomington, 800 E. Kirkwood Ave., Bloomington, IN, 47405, USA
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