Binding of inorganic and organic cations by p-sulfonatocalix[4]arene in water: a thermodynamic study

Abstract

We report a microcalorimetry study of the association of various inorganic and organic cations with p-sulfonatocalix[4]arene at 298.15 K. First, we have studied the electrostatic attraction between host 1 and seven rare-earth-metal cations representative of the whole lanthanide series (La 3+ , Nd 3+ , Sm 3+ , Eu 3+ , Gd 3+ , Dy 3+ and Yb 3+ ) in an acidic solution (pH 2). In order to compare the charge effects in the electrostatic interactions we have also studied the attraction between host 1 and two alkaline-earth-metal cations (Ca 2+ and Mg 2+ ). Next, we investigated the binding of a series of quaternary ammonium cations in an acidic solution (pH 2). For each system, both the apparent association constant and enthalpy of complexation have been extracted from the calorimetric data. In all cases, our results are consistent with the formation of 1 : 1 complexes. Whereas for the inorganic cations (alkaline-earthmetal and lanthanide cations) the association process is enthalpically unfavoured (∆ r H Њ>0) and entropically favoured (∆ r SЊ>0), the complexation is driven by a favourable enthalpy change for the organic cations. These thermodynamic properties show that the organic and inorganic cations bind in very different modes.

Molecular Selective Binding of Pyridinium Guest Ions by Water‐Soluble Calix[4]arenes

“…In the present study, the T∆S°values are also plotted against the ∆H°values by using the thermodynamic parameters obtained in this work and the published data for water-soluble calix [4]arenes. [5,7,9,10,12,19,28,29] As can be seen from Figure 6, the plot of ∆H°against T∆S°gives an excellent straight line with a correlation coefficient of 0.95. The obtained slope (α) and the intercept (T∆S°) values for water-soluble calix [4]arenes as well as the corresponding values for some natural and synthetic receptors are summarized in Table 3.…”

Effect of Lower‐Rim Alkylation of p‐Sulfonatocalix[4]arene on the Thermodynamics of Host–Guest Complexation

“…They show high complex stabilities on the order of 10 5  -1 due to strong ionic interactions with the sulfonate groups of the hosts, frequently accompanied by C-H-π interactions with the π-electronrich cavity of the calixarene. [27] Herein, two quaternary ammonium cations, trimethyl(phenyl)ammonium chloride (TMA) and tetramethylammonium chloride (TEMA), were selected to compare the inclusion complexation of SC4A and SC4A-Bu. The complexation of SC4A and SC4A-Bu with TMA was measured at two pH values (pH = 2.0 and 6.0).…”

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

“…0 and TD r S o < 0) whereas it is entropy driven for processes involving divalent and trivalent metallic cations (D r H o > 0 and TD r S o @ 0). [21,23] In the former case, the host and the organic cation form an inclusion complex; the cation is inserted into the calixarene cavity with predominant van der Waals interactions between the host and guest. For an inorganic cation such as La 3 + , the association occurs outside the cavity where the cation forms, with the SO 3 À groups of the host, an outer-sphere complex (solvent separated) marked by positive entropy changes, resulting from the desolvation of the species.…”

“…[18] The p-sulfonatocalix [4]arene is able to complex a variety of organic compounds as well as inorganic ions in water. [19][20][21][22][23] For the tetramethylammonium cation, the binding process is enthalpy driven (D r H o ! 0 and TD r S o < 0) whereas it is entropy driven for processes involving divalent and trivalent metallic cations (D r H o > 0 and TD r S o @ 0).…”