Unique binding behaviour of water-soluble polycationic oxacalix[4]arene tweezers towards the paraquat dication

Abstract

The first water-soluble polycationic oxacalix[4]arene molecular tweezers able to recognize - under pH control - the paraquat dication as a result of a delicate balance between electrostatic repulsion, Coulombic shielding and attractive π-stacking interactions are reported.

Attraction by repulsion: compounds with like charges undergo self-assembly in water that improves in high salt and persists in real biological fluids

“…26 (4) For good measure, a simple tetracationic oxacalixarene host was recently shown to bind to the dicationic guest paraquat in water, although salt effects were not reported. 27 The motif that is common among these systems is the use of hydrophobic attraction tempered by like-charged electrostatic elements within a rigid, concave molecular host framework.…”

A water-soluble hybrid[4]arene: synthesis, host–guest complexation and application in the construction of a supra-amphiphile

“…The paraquat guest nestles within the wider p-rich cleft generated by two 1,2-substituted benzenes of WH4 with stable host-guest complexation. 21 Moreover, the complexation between WH4 and G is pHresponsive 22 because anionic carboxylate groups on WH4 can be reversibly transformed into neutral carboxylic groups by adjusting the solution pH, which means the association and disassociation of the complex can be effectively controlled by sequential addition of DCl and NaOD aqueous solutions (Fig. 4).…”

Solution- and gas-phase study of binding of ammonium and bisammonium hydrocarbons to oxacalix[4]arene carboxylate

“…28,29 For the purpose of ammonium sensing, Gattuso and co-workers synthesized a polycationic oxacalix [4]arene in 2015, which showed affinity towards paraquat and neutral aromatic compounds in aqueous media. 30,31 Previously, our group has investigated complexation properties of "naked" oxacalixarenes 32 and shown in 2020 that 1 can bind paraquat in methanol and water. 33 To the best of our knowledge, there are only a few examples where calixarene complexation with amine molecules has been investigated in polar protic solvents.…”