Enantioselective uptake of amino acid with overoxidized polypyrrole colloid templated with L-lactate

An overoxidized polypyrrole colloid, which can recognise enantiomers of amino acids has been prepared by a newly developed molecular imprinting technique. A polypyrrole colloid, which had been polymerised from a mixture of pyrrole (monomer), polyvinylpyrrolidone (steric stabiliser), peroxodisulfate (oxidant) and l-lactate (dopant), was overoxidized to create a dopant-complementary cavity. The enantioselectivity of the overoxidized colloid was evaluated by comparing the uptake of l-alanine and l-cysteine with that of the respective d-enantiomers. The l/d uptake ratios for these amino acids were about 2, while phenylalanine showed suppressed uptake for both the enantiomers. The absence of phenylalanine uptake can be explained in terms of the molecular size, which is too large to be accommodated by the cavity created by l-lactate. In contrast, a colloid templated with l-phenyllactate took up l-phenylalanine with a higher enantioselectivity of about 7. A colloid templated with l-lactate was applied to surface chirality analysis through enantioselective adsorption on cysteine-modified gold surfaces. Quartz microbalance experiments and scanning electron microscope observation of the gold surface revealed that the colloidal particle has higher affinity to a surface modified with l-cysteine than to one modified with D-cysteine.