Separation of tryptophan enantiomers with polypyrrole electrode column by potential-induced technique

Polypyrrole (PPy), synthesized by chemical oxidation in the presence of L-tryptophan (L-Trp) as template molecules, was packed into a porous ceramic column as the conductive stationary phase to fabricate an electrode column which can be regarded as a working electrode of a three-electrode system from an electrochemical point of view. The electric potential of this column can be easily controlled by a potentiostat. L-Trp anions were ejected from the PPy backbone after overoxidation of PPy, and thus cavities complementary to L-Trp were left in the stationary phase. When the solution containing L- or D-Trp was pumped through the column packed with imprinted overoxidized polypyrrole (oPPy), a negative potential was applied on the electrode column for re-binding Trp enantiomers. The novel electrode column offers an excellent chiral selectivity for L-Trp over D-Trp as the result of stereochemistry, and it also displays satisfactory selectivity for tyrosine (Tyr) enantiomers which is analogous to Trp in structure. The advantage of this method proposed over previously reported is that the separation of amino acids enantiomers can be performed in a high efficiency by controlling the potential applied on the electrode column. (C) 2011 Elsevier Ltd. All rights reserved.