Shape Recognition of Alkylammonium Ions by 1,3-Bridged Calix[5]arene Crown-6 Ethers:  Endo- vs Exo-Cavity Complexation

The structures and energies of p-tert-butylcalix [5]crown-6-ether (1) and its alkylammonium complexes have been calculated by DFT B3LYP/6-31G(d,p) method. We have studied the binding sites of these host-guest complexes focusing on the p-tert-butylcalix [5]arene pocket (endo) or the crown-6-ether moiety (exo) of 1. The smaller alkylammonium cations have the better complexation efficiency with p-tert-butylcalix [5]crown-6-ether than the bulkier alkylammonium ions. For the sec-and tert-butylammonium ions, the hydrogen-bond distances of the exo-complexes are shorter, therefore, stronger than the endo-cases. This DFT calculated result is in parallel with the trend of the experimental association constants of the branched butylammonium ions.

Section: Resultssupporting

confidence: 64%

Section: Resultsmentioning

confidence: 97%

Section: -3mentioning

confidence: 99%

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DFT Study of p-tert-Butylcalix[5]crown-6-ether Complexed with Alkylammonium Ions

Oh¹,

Choe

2007

“…12 More recently, 1,3-bridged calix[5]crown-6-ether was investigated as a tool for the shape recognition of alkylammonium ions in focusing the endo-versus exo-cavity complexation. 13 These interesting host-guest properties are mainly related to the calix[5]arene backbone fixed in cone-type C5v-symmetric structure by providing a highly preorganized three dimensional molecular framework assembled as efficient binding sites.…”

Section: Calixarenesmentioning

confidence: 99%

Ab Initio Study of the Complexation Behavior of Calix[5]arene Derivative toward Alkyl Ammonium Cations

2003

The structures and complexation energies of penta-O-alkylated 1b and penta-O-tert-butyl ester 1e of p-tertbutylcalix[5]arene and their simplified structures (2b and 2e) toward a series of alkyl ammonium guests have been calculated by a semi-empirical AM1 method. For AM1 calculations, complexation efficiencies of the simplified host 2e are very similar to the values of host 1e. The complexes of simplified host 2e with alkyl ammonium ions also have been optimized by ab initio HF/6-31G method. The calculated complexation efficiencies for 2e by ab initio method have been found to be bigger in magnitude than the values obtained by AM1 calculations for linear alkyl ammonium guests. Calculation results show that all of the calix[5]aryl derivatives investigated in this study have much better complexation ability toward ammonium cation without alkyl group compared with other alkyl ammonium guests. Ab initio calculations also well duplicate the molecular discriminating behaviors of calix [5]arene derivative 2e between butyl ammonium ions: n-BuNH3

“…1,3-Bridged calix [5]crown-6-ether was investigated as a tool for the shape recognition of alkylammonium ions in focusing the endo-versus exo-cavity complexation. 9 The cavity of calix[6]arene could not be exploited unless their flexibilities were restricted. Recently, Reinaud and Jabin have reported the three-step synthesis of the calix[6]arene capped with the TAC unit to immobilize the arms of the lower rim of calix[6]arene.…”

Section: Introductionmentioning

confidence: 99%

Ab Initio Study of the Complexation Behavior of Calix[6](aza)cryptand with Alkyl Ammonium Cations

Kim

Lee²,

Choe³

2005

The structures and complexation energies of p-tert-butylcalix [6](aza)cryptand 1 with a series of alkylammonium cations have been calculated by using ab initio HF/6-31G method. After geometry optimizations, B3LYP/6-31G(d) single point calculations of the final structures are carried out including the effect of an electron correlation and the basis set with a polarization function. The calculated complexation efficiencies of 1 for alkylammonium guests are better than those of the previously reported calix[5]arenes, and much better than those of the calix[4]crown-6-ether. The calculation results show that calix[6](aza)cryptand also has much better complexation ability with smaller ammonium cations than with bulky alkylammonium guests. The structural characterizations of the calculated complexes are described as the function of the nature of the alkyl substituents of the ammonium guests.