Extraction of amino acid derivatives using calixarene amide derivatives

The extraction of amino acid derivatives using calix[n]arene (n=4, 6, 8) amide derivatives was studied. A calix[6]arene amide derivative exhibited the highest extractabilities for cationic amino acid derivatives in the series of calix[n]arene derivatives in the presence of perchlorate ion. The extraction is independent of the aqueous pH under acidic conditions. Based on the slope analysis as a function of perchlorate ion concentration and the extractant concentration, the calix[6]arene was found to form a 1:1:1 complex with tryptophan methyl ester and the perchlorate ion. The results suggest the possibility of using the calix[6]arene amide derivative as a recognition tool for cationic biomolecules, however, the extraction selectivity was simply based on the hydrophobicity of the guest molecule.