Binding of monovalent metal cations by the p-sulfonatocalix[4]arene: experimental evidence for cation–π interactions in water

Abstract

Gibbs free energies, enthalpies and entropies for the binding of Na+, K+, Rb+, Cs+, Ag+, Tl+ and NH4+ by the p-sulfonatocalix[4]arene in water are determined by microcalorimetry. Whereas no significant heat effect is detected with Na+ or Ag+, suggesting that these cations are not complexed, weak but selective binding is observed with the other cations. The whole set of thermodynamic parameters, which demonstrate that the cations bind inside the cavity of the calixarene, evidence the importance of the cation-pi interactions for these complexes in water.

Methodology for the Calculation of the Potential of Mean Force for a Cation–π Complex in Water

“…The PMF profile does not show any negative Gibbs free-energy minimum to suggest any favorable interaction between the caesium and the calixarene. This result is not in line with the recent experimental determinations [22,24] of the thermodynamic properties of binding of this cation by the psulfonatocalixarene. In what follows, we tend to include in the PMF calculation a quantum contribution which is likely to describe the different types of energy contributions of the cation-p interaction.…”

“…These calculations are based upon recent microcalorimetry and 133 Cs diffusion NMR spectroscopy experiments [22,24] which have shown that Cs + binds inside the cavity of the calixarene and that the association process is enthalpy driven due to favorable cation-p interactions. The PMF profile calculated from a standard model [38] does not predict any Gibbs free energy minimum, suggesting, in contrast to the experimental observations, that the cation is not complexed by the calixarene.…”

“…This type of interaction has been recently studied by Morel and Morel-Desrosiers using microcalorimetry experiments; [22] the Gibbs free energies, enthalpies and entropies of binding determined for the first time in water indicate that Cs + , in contrast to the divalent and trivalent metal cations, forms with the calixarene an inclusion complex governed by cation-p interactions. This has been confirmed by 133 Cs diffusion NMR spectroscopy.…”

“…Thermodynamic properties for the binding of Cs + by the p-sulfonatocalix [4]arene in water calculated from Equations (5), (6) and (7). The corresponding experimental thermodynamic properties determined by microcalorimetry [22] and 133 Cs diffusion NMR [24] are reported for comparison. The cutoff distance is taken equal to r min + 1 .…”

Aromatische Ringe in chemischer und biologischer Erkennung: Energien und Strukturen

“…[256] Die Bindung von Cs + an p-Sulfonatocalix [4]aren wurde mithilfe von 133 Cs-Diffusions-NMR-Spektroskopie [257] untersucht, wobei eine Bindungsaffinität von K a = (22 AE 9) m À1 in wässriger Lösung ermittelt wurde, in guter Übereinstimmung mit Werten von 1 H-NMR-spektroskopischen Titrationen [257] und mikrokalorimetrischen Techniken. [258] Mikrokalorimetrische Studien der Bindung verschiedener Metallionen an pSulfonatocalix [4] [259] Pyrogallol [4]arene fungieren auch als Rezeptoren für Alkalimetallkationen, besonders K + , Cs + und Rb + , wie kristallographisch gezeigt wurde. [260] Ca 2+ -Indol-Wechselwirkungen wurden 13 C-NMR-und CD-spektroskopisch im Kontext der Entwicklung Trp-basierter fluoreszierender Chemosensoren für das Metallion untersucht (Abbildung 27 a).…”