Counterionâ Controlled Selfâ Sorting in an Amphiphilic Calixarene Micellar System

Abstract

Molecular recognition of small molecules and ions by artificial receptors in microheterogeneous media such as micelles and vesicles can, in principle, provide better models of biological systems in comparison with bulk solutions. In this work we have investigated the complexation of an organic fluorescent probe with amphiphilic calixarene receptor below and above the critical micelle concentration (CMC). For concentrations below the CMC, the probe forms a hostâ guest complex with the calixarene behaving like a traditional hostâ guest system operating in bulk solution. Above the CMC, multiple equilibrium processes are established and the probe can exchange between the recognition site of the calixarene in the monomeric state, micellized state and/or the micellar hydrophobic core. Careful analysis of the results obtained from NMR spectroscopy and fluorescence experiments allowed us to propose a quantitative model to describe the system. The increment of the local concentration of Na+ counterions at the Stern layer displace the dye to the micelle core through competitive binding of Na+ in the cavity of the receptor and is decisive for the observed selfâ sorting behavior.The sort code: In this work the complexation of an organic fluorescent probe with an amphiphilic calixarene receptor below and above the critical micelle concentration was investigated. It was found that guest translocation from the host cavity to the micellar core is affected by competitive counterion binding and is decisive for the selfâ sorting behavior.