Counterion‐Controlled Self‐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 host-guest complex with the calixarene behaving like a traditional host-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 self-sorting behavior.

Delving into the Variability of Supramolecular Affinity: Self‐Ion Pairing as a Central Player in Aqueous Host‐Guest Chemistry

“…As aforementioned, one of the main challenges in using charged supramolecular receptors is the ubiquitous presence of their counterions, which not only alter the net charge of these hosts but also compete with the targeted guests for the complexation at the binding sites. [56,58,[62][63][64] For this reason, as a preliminary step, it is necessary to determine the extent of the coordination of bromide ion to P5A within the concentration range under investigation. Only then can a rigorous analysis of the complexation capacity of this macrocycle be conducted.…”

Selective Heavy Element Sensing with a Simple Host–Guest Fluorescent Array

“…43 The affinity of 4 for cavitands 1−3 varies from 2.8 μM (2, pH 3.3) to 190 nM (3, pH 9.0), and >98% quenching of the fluorescence of 4 is observed upon binding. DSMI 5 has a size, shape, and charge profile that suggest it would be an excellent guest for 1−3 in water, and it is well-known to display enhanced fluorescence upon binding in hydrophobic environm e n t s , s u c h a s t h e c a v i t y o f h o s t m o l e c u l e s hexasulfonatocalix[6]arene 53,54 or cucurbit[7]uril. 55 Interestingly, DSMI 5 behaves quite differently to RhB guest 4: upon its binding to anionic cavitand 1, a strong enhancement in fluorescence of 5 is observed.…”

Assembling features of calixarene-based amphiphiles and supra-amphiphiles

“…Later, Fernandez-Abad and coworkers reported that DSMI (G7) could also decrease the CAC of 3 to 1.4 mM. 57 Moreover, it is also reported that the CAC of analogue 6 decreases in the presence of G45. 88 Aggregation of calixarenes bearing sulfonic groups at the lower rim could also be induced by cationic guests.…”