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Syntheses of ester and amide derivatives of calix[6]arene and their complexation affinities towards La3+, Eu3+, and Yb3+

One hexaester (1) and three hexaamide derivatives (2-4) of calix[6]arenes were prepared for the first time in one synthetic step, under microwave radiation. Compounds 2 and 3 were novel ones, while ester calix6arene derivative 1 and amide derivative 4 were prepared previously, by conventional syntheses. Microwave-assisted syntheses shortened the reaction times from 48 to 2 hours. The binding properties of calix6arenes towards selected lanthanide cations (La3+, Eu3+, Yb3+) were studied by spectroscopic and mass spectrometric techniques. No complexation was observed with the ester derivative, while compounds 2-4 formed 1:1 complexes. Based on spectrophotometric titrations, the stability constants of resulting complexes could only be estimated (lg K ≥ 6). Calixarene derivatives as well as their complexes were analysed by ESI MS and MS/MS spectrometry. Corresponding fragmentation pathways were proposed, and in some cases confirmed by MS3 experiments. The results obtained by different techniques were in accordance.

calix[6]arene ; lanthanides ; complexation ; UV spectroscopy ; mass spectrometry

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