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Urea-Based Macrocycle Selective for Sulfate and Structurally Sensitive to Water

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journal contribution
posted on 01.06.2020, 11:03 by Sandeep Kaur, Victor W. Day, Kristin Bowman-James
An unsymmetrical semirigid tetraurea macrocycle, 1, selectively traps SO42– with high affinity in a 0.5% water:DMSO-d6 solution (Ka = 90,500 M–1). The macrocycle displays somewhat less affinity for HSO4 (Ka = 68,600 M–1), while Ka’s for OAc and H2PO4 are approximately half that seen for SO42– (49,800 and 52,600 M–1, respectively). Cl binds weakly (Ka = 3430 M–1), and essentially no affinity is observed for NO3. Structural results for the SO42– and Cl complexes indicate 1:1 1:anion complexes, with encapsulation of the SO42– but not for Clion, which hovers at the macrocyclic periphery. For the ditopic biphenyl-4,4′-dicarboxylate, each carboxylate binds to its own macrocycle in a sandwich-like mode, which shows a 2:1 1:dianion association. Binding studies indicate 1:1 binding for the monotopic anions in the 0.5% water:DMSO-d6 solutions, but as the water content of the solvent is increased, the binding mode changes to a 2:1 1:anion association according to the binding studies in solution. Binding studies indicate that 1 maintains a significant tolerance for water up to 1:1 mixtures of water:DMSO-d6.