Ligand-exchange adsorbents that are enantioselective for underivatized alpha-amino acids have been synthesized by molecular imprinting using only achiral monomers. Bulk polymers were prepared by allowing the functional monomer, Cu(II)-N-(4-vinylbenzyl)iminodiacetic acid, to form complexes with the template amino acid in solution, followed by crosslinking with ethylene glycol dimethacrylate. To make supports suitable for chromatography, the imprinted polymer was grafted to derivatized silica particles. Racemic mixtures of various underivatized alpha-amino acids are resolved on the imprinted adsorbents. Adsorbents prepared from amino acids with larger, aromatic side chains exhibit the highest selectivities (alpha = 1.65 for the enantioresolution of d,l-phenylalanine). Cross-selectivity for similar amino acids also depends on side chain size: materials templated with l- or d-phenylalanine exhibit good enantioselectivity when challenged with racemic tyrosine (alpha ~ 1.4) and much reduced enantioselectivities towards d,l-tryptophan or aliphatic amino acids. Materials imprinted with alanine show no selectivity. The ability of a material imprinted with an amino acid enantiomer to resolve an analogous chiral amine is also demonstrated. The mechanisms underlying the observed enantioselectivity are discussed in light of the three-point interaction model for conventional chiral ligand exchange separations.

"A Glucose-Sensing Polymer," G. Chen, Z. Guan, C.-T.Chen, D. Lee, L. Fu and F. H. Arnold, Nature Biotechnology, 15, 354-357 (1997).

We have prepared a robust polymer that can be used to measure glucose concentrations in complex biological media. At alkaline pH, this metal-complexing polymer binds glucose and instantly release protons in proportion to the glucose concentration over a clinically relevant range (0-25 mM). The inexpensive polymer is sufficiently selective to provide an easily measurable response to glucose in porcine plasma. The polymer's ability to function at nonphysiological pH's (at which the buffer capacity of biological samples is small) makes it possible to design simple and inexpensive sensing devices based on measurement of changes in proton concentration.

"Substrate Selectivity of Molecularly Imprinted Polymers Incorporating a Rigid Chelating Monomer, Bis-Methacrylato-(4-methyl, 4'-vinyl)2,2'-bipyridine Cu(II)," P. K. Dhal and F. H. Arnold, New J. Chemistry, 20, 695-698 (1996).

The substrate binding selectivities of imprinted polymers prepared using bis-methacrylato (4-methyl, 4'-vinyl) 2,2'-bipyridine Cu(II) (1) as the metal-chelating monomer have been investigated. This monomer was designed to minimize the flexibility of the metal ions in the binding sites formed by molecular imprinting. A series of bisimidazole derivatives (3-5) were used as the templates for the preparation of imprinted polymers. Formation of monomer:template assemblies in solution was investigated by visible and ESR spectroscopy. Polymerization of these assemblies with ethylene glycol dimethacrylate yielded macroporous, insoluble polymers. In competitive rebinding experiments, the resulting polymers showed greater selectivity for their bisimidazole templates than imprinted polymers prepared previously using an iminodiacetate metal-chelating monomer (2).

"Polymeric Sensor Materials for Glucose," C.-T. Chen, G. Chen, D. Lee and F. H. Arnold, Polymer Preprint, 37, 217-218 (1996).

"Multipoint Binding in Metal Affinity Chromatography II. Effect of pH and Imidazole on Chromatographic Retention of Engineered Histidine-Containing Cytochromes c," R. D. Johnson, R. J. Todd and F. H. Arnold, Chromatography A, 725, 225 (1996).

"Surface Site Hetereogeneity and Lateral Interactions in Multipoint Protein Adsorption," R. D. Johnson, Z.-G. Wang and F. H. Arnold, J. Phys. Chem., 100, 5134- 5139 (1996).