Thermodynamics of Ethyl p-tert-Butylcalix[5]arene Pentanoate and Its Cation Complexes in Nonaqueous Media

Abstract

The solution behavior of ethyl p-tert-butylcalix[5]arene pentanoate, EtCalix(5), in various protic and aprotic solvents has been assessed from the standard Gibbs energies of transfer of this ligand from acetonitrile to other solvents. These data were derived from solubility measurements of EtCalix(5) in different media. It is concluded that in solvents in which metal cation salts are predominant as ionic species in solution (within a low concentration range), the solvation of the ligand will not contribute significantly to the thermodynamics of cation complexation as a result of the medium effect. Various analytical techniques were used to identify the sites of ligand-cation interaction (1H NMR) and the composition (conductance and calorimetric measurements) of the metal-ion complexes in the various solvents. Titration calorimetry (direct and competitive) was used to thermodynamically characterize the cation binding ability of EtCalix(5) and gain quantitative information on the complex stability and the factors controlling it. Given the large bulk of data reported in the literature wrongly placed under the thermodynamic umbrella, particular emphasis is made about the need of identifying the process taking place in solution prior to proceeding with its thermodynamic characterization. The results are compared with those for the ethyl ester derivative of the cyclic tetramer, EtCalix(4). It is concluded that in moving from EtCalix(4) to EtCalix(5), (i) the selectivity of the latter for cations is swallowed toward the larger cations and (ii) although the number of binding sites increases, these are not able to exert the efficient control upon the ligand-cation binding ability as that found for the tetramer ester and these cations in these solvents.

Calorimetric Study on Coordination of Tridentate Imidazolyl Calix[6]arene Ligands to Zinc Ion in Organic Solvents

“…Another benefit of ITC is that a stoichiometry of certain complexation can be easily determined. Many ITC studies have reported ion–dipole interactions between various metal ions and crown ethers, cryptands, and calix[ n ]arenes . In most cases, the complexation of these cyclic Lewis bases with metal ions is enthalpically dominated (Δ H 0 < 0, Δ S 0 < 0), and coordinating solvents such as acetonitrile and N , N -dimethylformamide (DMF) cause an increase in both Δ H 0 and Δ S 0 because of desolvation during complexation.…”

Ionic Recognition by 7-Nitro-1,3,5-triaza Adamantane: First Thermodynamic Study

“…If so, this compound can be used as pendant arms in the functionalization of calixarenes and calixpyrroles. This is an area of considerable interest for our Group given the possibility of anchoring this ligand to the polymeric matrices and then being used as recyclable decontaminating agents − for removal of heavy metals from water. However before proceeding with these studies, the complexing properties of this compound for these cations need to be investigated.…”

Physisorption of Three Calix[4]arenes on Alkyl-Functionalized Mesoporous Silica for Biomimetic Ligand Development

“…These calculated free energies are reasonable; the Gibbs free energy change for the transfer of 5,11,17,23,29-penta-tert-butyl-31,32,33,34,35calix [5]arene pentaethanoate from ethanol to n-hexane is −5.1 kJ mol −1 based on solubility measurements. 50 In another study, the Gibbs free energy change of solvation for hexane transfer from propanol to n-decane was −4 kJ mol −1 . 51 Thermodynamics of Calixarene Physisorption.…”