Enhanced cation recognition by a macrocyclic ionophore at the air–solution interface probed by mass spectrometry

Abstract

Interfacial environments have the potential to drive unexpected events of supramolecular recognition, leading to advances in the development of novel functional materials and molecular sensing techniques. We present experimental evidence for a noticeable enhancement of the cation binding specificity of a prototype calixarene macrocycle (cesium ionophore II) at the air-solution interface, in comparison to bulk solution and to isolated solvent-less conditions. A rationalization of this intriguing finding is outlined, with the support of quantum calculations, in terms of the 'half-solvation' conditions provided by the interface and of conformational effects posed by the backbone structure and the side chains of the macrocyclic ionophore. The investigation involves the introduction of a mass spectrometry method to determine the relative abundances of interfacial complexes that should be of general application in the field and guide future advances in analytical techniques based on molecular recognition.

Switching the Ion Selectivity from Fe3+ to Al3+ by a Triazole‐Appended Calix[4]arene‐Based Amphiphile†

“…The Π‐A isotherm studies carried out in presence of equimolar concentration of Al 3+ /Zn 2+ and Al 3+ /Mn 2+ supported strong binding as well as selectivity of Al 3+ to L (Figure h, Supporting Information, Figure S10). Similar results were reported for the selectivity of Cs + over Na + at the air‐water interface in case of a calix[6]arene derivative …”

“…Since the conjugates of calix[4]arenes possesses both hydrophobic and hydrophilic regions, these are well suited to make Langmuir films and hence can be used for the study of ion and molecular sensing on any substrate by using its functional moieties. The studies on Langmuir films of calixarenes are primarily focused on molecular, ion as well as gas sensing because of its supramolecular nature. The corresponding selectivity studies of the conjugates of calixarenes at air‐water interface is limited and hence deserves greater attention.…”

Recent advances in mass spectrometry studies of non-covalent complexes of macrocycles - A review

“…The study of interfacial environment gives the opportunity to accelerate the development of novel functional materials and molecular sensing techniques due to the potential to drive unexpected events of supramolecular recognition. Martinez-Haya et al [86] introduced a new mass spectrometry method searching for enhancement on Cs + selectivity when competitive binding of alkali cations take place at the air-water interface in comparison to bulk solution. For this purpose, the interfacial complex of 4-tert-butylcalix [6]arene-hexaacetic acid hexaethyl ester (or cesium ionophore II, henceforth CI) were transferred as Langmuir-Blodgett (LB) films for MALDI-MS analysis (LB-MALDI-MS).…”

Multipodal coordination and mobility of molecular cations inside the macrocycle valinomycin

“…19 Analogous studies have assessed supramolecular recognition effects mediated by macrocycles and by phosphoric and phosphate moieties. [20][21][22][23][24] This approach provides well-defined and tractable molecular benchmarks for the quantum chemical methods. For the present systems, the conformation of the isolated solvent-less valinomycin cation complexes can be expected to resemble the conformation adopted both in aqueous solution and in organic hydrophobic phases (e.g., cell membranes), at least for the smaller cations K + and NH 4 + .…”