Preface

Abstract

The unique molecular architecture of calixarenes makes them a suitable platform for constructing host molecules that can selectively bind a variety of guest substrates that range from cations and anions to fullerenes. Substrates can be bound within the hydrophobic bowl-cavity of the calixarenes through noncovalent interactions or outside the cavity by introducing suitable ligand systems on the upper or lower rim. Also, the self-assembly of some calixarene derivatives via non-covalent interactions leads to a new class of encapsulation agents, inclu-sion complexes, and molecular networks.The fascinating conformational and chemical reactivity of the calixarene systems has led to their use in a variety of applications that range from de-velopment of efficient separation systems, specific sensors, and molecular switches to a new generation of catalysts. The scientific interest in the applications of this class of molecules to solve separation problems is demonstrated by the number of recent publications as well as the award of numerous patents that utilizes the chemistry of calixarenes. These patents include the use of calixarenes as extraction agents for separations, such as recovering uranyl ion from sea water and removing cesium from nuclear wastes. Calixarenes are also being used as selective agents for metal ion transport through supported liquid membranes. It is important to point out that efficient chemical separations are now integral not only to manu-facturing processes, but also for compliance with subsequent industrial waste-discharge requirements.This book is the outcome of a recent symposium titled "Calixarene Molecules for Separations" that was held at the 217 th

Tri-ionizable calix[4]arene ligands: synthesis and lanthanide ion complexation

“…The initial attempt to monomethylate p-tert-butylcalix [4]arene 9 by its reaction with K 2 CO 3 and MeI in MeCN at reflux 13 gave mostly dimethylated product. Subsequently, the monomethyl ether 10 was realized in 60% yield by reaction of 9 with CsF and MeI in DMF at 40 o C. 13 The reported reaction of 10 with K 2 CO 3 and ethyl bromoacetate in MeCN at reflux 14 gave a 50%…”

“…In the IR spectrum of 13, the carbonyl and O-H stretching absorptions of 12 were replaced by a new carbonyl absorption at 1809 cm -1 . From reactions of tri(acid chloride) 13 with the sodium salts of commercially available sulfonamides in THF, the tri-ionizable calix [4]arene ligands 5-8 were obtained in 52-65% overall yields from tri(carboxylic acid) 12. Structures of new compounds 5-8 and 12 were verified by IR and NMR spectroscopy and confirmed by combustion analysis.…”

“…[1][2][3][4][5][6][7][8][9] By attachment of functional groups to the lower rim of calix [4]arene, new metal ion complexing agents with high selectivity have been discovered. Of special interest in our laboratories are calix [4]arenes with pendent proton-ionizable groups 10,11 since these ligands generally provide stronger binding of cationic species than their neutral analogues. Also when the number of acidic sites in the side arms of the ligand matches the charge on the metal ion an electroneutral complex is formed.…”

“…This is especially important when highly hydrophilic aqueous phase anions of chloride, nitrate, and sulfate are involved. For example, we have found that lower-rim 1,3-disubstituted N-(X)sulfonyl tert-butylcalix- [4] arenecarboxamides 1-4 ( Figure 1) exhibit efficient and highly selective extraction of heavy metal Figure 1. Structures of previously studied di-ionizable p-tert-butylcalix [4]arene ligands.…”

“…Herein we report the synthesis of tri-ionizable p-tert-butylcalix [4]arene analogues 5-8 ( Figure 2) and the initial evaluation of their complexation of selected trivalent lanthanide ions in MeOH by potentiometric titration. In this series of ligands, variation of the electron-withdrawing properties of X should change the acidity.…”