Rigid Calix[4]arene as a Building Block for the Synthesis of New Quaternary Ammonium Cation Receptors

Abstract

The synthesis of a new series of neutral hosts derived from the head-to-head linkage of two calix[4]arene-bis(crown-3) units fixed in the rigid cone conformation with bridges of different nature and length is described. The binding abilities of the new receptors towards tetraalkylammonium and Nmethylpyridinium cations of different size and shape in CDCl 3 solution have been extensively investigated by 1 H NMR spectroscopy. In this solvent, ion-pairing is found to have a strong effect on the binding efficiency. In the more polar CDCl 3 /CD 3 CN solvent mixture, a substantial decrease in the K ass values is observed, which can be attributed, in [a]

Electronic Tuning of Host-Guest Interactions within the Cavities of Fluorophore-Appended Calix[4]arenes

“…The overall numbers (~4000–6000 M −1 ) are higher than K ass obtained by the 1 H NMR technique ( K ass = 162 ± 13 M −1 for 3c ) at higher concentrations. The latter compares well with the literature data for NMP cation complexation obtained by the 1 H NMR technique for calixarene hosts with a single cavity [ 9 , 10 ]. Importantly, the most significant drop in the fluorescence intensity was observed for compound 3b , bearing an electron-rich piperidine moiety at the ring C opposite to the fluorophore unit.…”

“…It is generally accepted that π interactions (cation-π and/or π-stacking) play an important role in the overall complexation of N-alkyl pyridinium salts within the calixarene hosts [ 6 ]. With nearly all studied calix[4]arene hosts having four alkyl ether groups at the lower rim, the average C4v conic structure of the cavity is not optimized for such interactions [ 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ]. Naturally, π interactions would be maximized if a pair of the opposite aromatic groups adopted a parallel disposition, where two opposite aromatic groups are parallel to each other in a C 2v symmetrical conformation ( 1d , flattened cone), which for the symmetrically substituted calixarenes can be observed only at low temperatures [ 16 , 17 , 18 ].…”

Molecular recognition of organic ammonium ions in solution using synthetic receptors

“…The binding abilities of a head-to-head linked bis-calix[4]arene-bis(crown-3) ( 127 ) fixed in the rigid cone conformation with bridges of different nature and length was described [ 384 ]. Tetraalkylammonium and N -methylpyridinium cations different in size and shape were investigated by 1 H NMR spectroscopy in CDCl 3 solution and in the more polar CDCl 3 /CD 3 CN solvent mixture.…”

Two-Dimensional Supramolecular Polymers Embodying Large Unilamellar Vesicles in Water

“…As discussed earlier, a greater diamagnetic shielding of the resonances corresponding to H a/c than H d/e protons in 4 suggests the inclusion of the pyridinium rings in the cavity of 1 ; in fact, similar magnetic perturbations of proton resonances were already measured for a guest bridging two adjacent and aromatic cavities of a host (see Figure S7). On the contrary, the vertical insertion of guests 4 (Figure B) is expected to show a smaller perturbation of the pyridinium H a/c while greater shielding of H d/e resonances. A computational study of the [ 1 ⊂ 4 ] 2 complex (MMFFaq, Spartan), with energy corrections for water solvation, revealed a family of comparable conformers (Figure C) with greater than 97% of the Boltzmann population distribution at 298 K (Monte Carlo conformational search, 500 steps; see Figure S8).…”