Extraction of amino acids by calixarenes in an aliphatic organic solvent

The extraction behavior of amino acid esters was investigated with a series of calixarene carboxylic acid derivatives. A small addition of alcohol enables the use of an aliphatic organic solvent in the calixarene extraction system. The extraction performance of the calixarenes was significantly influenced by the cavity size of the extractants. Calix[6]arene was the strongest extractant for the target tryptophan ester. The key interaction in the extraction was found to be the electrostatic interaction between the amino group of the amino acid and the oxygen atoms of the calixarene. Based on slope analysis and the Job method, a 1:1 complex was shown to form in isooctane containing 15 v/v% 1-octanol. Stripping was also accomplished by contacting the organic solution with an acidic solution.