Calixarenes carboxyllic acid derivatives

Fig. 27.14 pH depended complexation of the biomolecules and calixarene-carboxylic acid derivative... 

Calixarenes, which are macrocyclic compounds, are one of the best building blocks to design molecular hosts in supramolecular chemistry [158]. Synthesis of calix[4]arenes, which have been adamantylated, has been reported [105, 109]. In calix[4]arenes, adamantane or its ester/carboxylic acid derivatives were introduced as substituents (Fig. 29). The purpose of this synthesis was to learn how to employ the flexible chemistry of adamantane in order to construct different kinds of molecular hosts. The X-ray structure analysis of p-(l-adamantyl)thiacalix[4]arene [109] demonstrated that it contained four CHCI3 molecules, one of which was located inside the host molecule cavity, and the host molecule assumed the cone-like conformational shape (Fig. 30). 

Continuing our studies in the functionalization of calixarene macrocycles to build up new specific ligands for ions and neutral molecules we have synthesized three new carboxylic acid derivatives (3-5) of p.t-butyIcalix[4]arene (1), determined their structures and checked their complexing ability. 

Co, Ni, Cu, and Pb thus, the separation of rare earths from a large amount of zinc is important. Conventional carboxylic acid extractant, Versatic 10, extracts yttrium, europium, and zinc at neutral pH and their mutual separation is difficult. On the other hand, calixarene carboxyl derivative was shown to extract rare earths at acidic pH preferentially to zinc, particularly in the presence of sodium ions in the aqueous phase. 

The solvent extraction of trivalent lanthanides (La, Nd, Eu, Er, and Yb) in three calixarene-type cyclophanes was described by Ludwig et al. (1993). Calixarenes are (1, w)-cyclophanes with a cavity formed by bridged phenyl units and various derivatives are formed with the introduction of substituents onto the skeleton. The three calixarenes studied are /7-tert-butylcalix/6/arene hexacarboxylic acid (LI), /i-tert-butylcalix/4/arene tetracarboxylic acid (L2) and [3,1,3, l]-cyclophane (L3). LI, L2 and L3 have different cavity sizes and contain carboxylic acid groups at the lower rim to achieve a high coordination number for Ln and to prevent the phase transfer of counter anions. 

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