Solid–liquid extraction of ω-amino acids using ditopic receptors

Five heteroditopic ligands have been prepared to be used in solid–liquid extraction of ω-amino acids into DMSO solutions. The prepared ligands contain crown ethers as cation binding sites and thiourea or amide groups for anion recognition. The aliphatic zone of the 1H NMR spectra suggests that two different species related to the amino acid are present in solution. One of these species is the complexed zwitterionic form and the other seems to be free non-zwitterionic amino acid. The presence of these two species allows extraction efficiencies higher than 100%.