Thermodynamics of Host−Guest Interactions in Lower Rim Functionalized Calix[4]arenes and Metal Cations:  The Medium Effect

Abstract

A new calix[4]arene derivative containing mixed pendant arms in its lower rim, 5,11,17,23-tetra-tert-butyl[25,27-bis(ethylethanoate)oxy-26,28-bis(ethylthioethoxy)]-calix[4]arene, 1, has been synthesized and characterized by 1H and 13C NMR. 1H NMR data carried out in CDCl3, CD3CN, CD3OD, and C3D7NO suggest that as far as acetonitrile is concerned, the hydrophobic cavity is likely to embrace a solvent molecule. It is shown that the hosting capacity of 1 toward metal cations is greater in acetonitrile than in N,N-dimethylformamide and in methanol. Thus, in the former solvent, complexation with various cations (Li+, Na+, Ag+, Ca2+, Cu2+, Hg2+, and Pb2+) occurs while in the latter media, 1 interacts only with Ag+ and Hg2+. This statement is corroborated by 1H NMR, conductance, calorimetric and potentiometric measurements. It is concluded that through molecular inclusion of acetonitrile in the hydrophobic cavity of 1, the hydrophilic cavity of the resulting adduct becomes more receptive to host metal cations than that of the free ligand. In propylene carbonate, the results show that the ligand loses its ability to interact with metal cations. Thus in acetonitrile, selective recognition of 1 for Hg2+ is demonstrated to an extent that the selectivity for this cation is greater by factors of 1.8 × 103, 1.9 × 103, 6.9 × 103, 1.8 × 104, 4.1 × 104 and 4.5 × 104, relative to Pb2+, Na+, Li+, Cu2+, Ag+, and Ca2+, respectively. This statement is supported by the thermodynamic characterization of the complexation process involving these systems in acetonitrile, N,N-dimethylformamide and in methanol. Thus, the medium effect on the binding process is carefully assessed. The results show that replacement of two ester groups in two alternate pendant arms of the tetraester calix[4]arene derivative by thioethyl moieties has altered significantly the binding capacity and the selective behavior of the latter relative to the former. Final conclusions are given.

Coordination chemistry of calix[4]arene derivatives with lower rim functionalisation and their applications

“…Her work in this area, prior to 2000, has been extensively reviewed [57]. She has published a number of detailed studies, since 2000, on a range of calix [4]arene derivatives including complexation studies of calix [4]arene ketone derivatives with sodium ions [58,59], complexation of calix [4]arene ester, ketone and acetamide derivatives with lanthanides [60], complexation of calix [4]arene pyridine derivatives with lead and mercury cations [61], complexation of calix [4]arene amines and amides with lanthanides [62], complexation of a partially substituted calix [4]arene aminophosphate derivative with a range of cations [63], complexation of calix [4]arene ester and ketone derivatives with lead and cadmium ions [64], complexation of calix [4]arene with mixed pendant arms (di-functionalised with ethylethanoate and ethylthioethoxy groups) with a range of cations [65,66]. Many of these studies offered a comprehensive investigation into the role of solvation of host and guest species in a given medium, and indeed medium effects feature as one of the main areas of focus of investigation in all of these studies.…”

“…This group was particularly interested in studying cation-interactions. The ligands they studied (63)(64)(65) are shown in Fig. 32.…”

A calix[4]arene derivative and its selective interaction with drugs (clofibric acid, diclofenac and aspirin)

“…38 Conductometric titrations were carried out by the gradual addition of the receptor solution in acetonitrile to the conductivity cell containing the targeted guest in the same solvent at 298.15…”

Formation of a Unique 1:2 Calcium-Calixquinone Complex in Aqueous Media

“…6 They found that the medium was a very important factor that affects complex stability and selectivity. [7][8][9] The calix [4]arene derivatives bound with Ca 2+ ion in acetonitrile while they formed no complex in methanol and N,N-dimethylformamide. The solvent effect on the structure of the complexes in acetonitrile and water was examined by using molecular dynamics simulation on tertbutylcalix [4]arene tetraamide ligand and its complex with metal ions.…”