Binding abilities of a chiral calix[4]resorcinarene: a polarimetric investigation on a complex case of study.

Marco Russo,Paolo Lo Meo

doi:10.3762/bjoc.13.268

Abstract

Polarimetry was used to investigate the binding abilities of a chiral calix[4]resorcinarene derivative, bearing L-proline subunits, towards a set of suitably selected organic guests. The simultaneous formation of 1:1 and 2:1 host–guest inclusion complexes was observed in several cases, depending on both the charge status of the host and the structure of the guest. Thus, the use of the polarimetric method was thoroughly revisited, in order to keep into account the occurrence of multiple equilibria. Our data indicate that the stability of the host–guest complexes is affected by an interplay between Coulomb interactions, π–π interactions, desolvation effects and entropy-unfavorable conformational dynamic restraints. Polarimetry is confirmed as a very useful and versatile tool for the investigation of supramolecular interactions with chiral hosts, even in complex systems involving multiple equilibria.

Highlights

During the last decades calix[n]arenes and calix[n]resorcinarenes (CAs) have emerged as versatile supramolecular host systems for various applications [1,2,3,4,5], spanning from sensors [6,7] to catalysis [8,9] and drug carriers [10,11,12,13]
Our data indicate that the stability of the host–guest complexes is affected by an interplay between Coulomb interactions, π–π interactions, desolvation effects and entropy-unfavorable conformational dynamic restraints
With the aim at gaining a deeper understanding of the microscopic and thermodynamic aspects of the binding phaenomena involving CAs, as well as at verifying the possibility to extend the use of polarimetry as an investigation tool to these systems, in the present work we studied the binding abilities of an accessible L-proline-derivatized calix[4]resorcinarene, namely 2,8,14,20-tetrapropyl-4,6,10,12,16,18,22,24-octahydroxy[5,11,17,23-(L-prolin-1-yl)methyl]calix[4]resorcinarene (CAP, Figure 1) towards a set of variously structured organic guests 1–12 (Figure 2)

Summary

Introduction

During the last decades calix[n]arenes and calix[n]resorcinarenes (CAs) have emerged as versatile supramolecular host systems for various applications [1,2,3,4,5], spanning from sensors [6,7] to catalysis [8,9] and drug carriers [10,11,12,13]. The simultaneous formation of 1:1 and 2:1 host–guest inclusion complexes was observed in several cases, depending on both the charge status of the host and the structure of the guest.

Results

Conclusion