Extraction of Unprotected Amino Acids by Mixed-Ligand Nickel(II) and Copper(II) Chelates

Summary.  Six mixed-ligand Nickel(II) and Copper(II) chelates with square-planar geometry of the formula [Ni/Cu(O-O)(S-tmpn)]B(C₆H₅)₄ were prepared, where O-O represents acetylacetonate, tropolonate, or hinokitiolate and S-tmpn is (S)-tetramethyl-1,2-propanediamine. The compounds were investigated with respect to their function as receptor for unprotected amino acids, taking advantage of their high solubilities in non-polar organic solvents. In liquid-liquid extraction experiments between a 1,2-dichloroethane phase containing the metal chelates and an aqueous phase containing amino acids (rac-phenylglycine, rac-phenylalanine, or rac-tryptophan), the nickel(II) chelates effectively extracted amino acids from the aqueous phases under neutral conditions, forming octahedral ternary chelates. Received February 19, 2001. Accepted April 2, 2001