Two new functional monomers for molecular imprinting, 5-(4′′′-vinyl)benzyloxy-1,3-bis[2′-(3′′,3′′,4′′,4′′-tetramethyl-2′′,5′′-dioxaborolanyl)phenylcarbomoyl]benzene (3) and 2-(4-vinylphenyloxy)-3,5,6-trichlorobenzoquinone (4), designed to interact with carboxylate and amino groups, respectively, were synthesized. NMR titrations confirmed the interactions of 3 with tertabutylammonium acetate and ampicillin carboxylate in d 6-DMSO and of 4 with the free amino group of ampicillin in the same solvent. Polymers were prepared, using DMSO or THF as porogen, imprinted with ampicillin carboxylate using 3 and 4 present in the polymerization mixture in only stoichiometric amounts. The polymer made in DMSO was shown to bind ampicillin from aqueous buffer at pH 8.0 with two populations of binding sites, the first characterized by Kd ) (3.0 ( 0.3) × l0 -5 mol/L at a capacity of 5.8 ( 0.3 µmol/g and the second by Kd ) (9.6 ( 1.1) × l0 -4 mol/L and 48 ( 3.4 µmol/g.

The aim of this investigation was to determine whether relatively weak interactions, such as hydrogen bonds to aromatic chlorine atoms and interactions involving aromatic π electrons could be exploited within artificial receptors, constructed using the technique of molecular imprinting. For the purposes of this investigation we chose 2,3,7,8-tetrachlorodibenzodioxin (TCDD) as the model target. Imprinted polymers have been prepared with two new templates designed to create recognition sites for TCDD. The first of these, the bis-N-(4-vinylphenyl)urea derivative of 2,8-dichloro-3,7-diaminodibenzodioxin, employed a carbonyl spacer to introduce aromatic amines into the polymer after reductive cleavage of the template. The second, N-(2-(3,7,8-trichlorodibenzodioxinyl))-2-methacryloyloxybenzamide, incorporated a salicylic acid spacer and introduced a methacrylic acid residue into the polymer following hydrolysis. Both amine and acid groups were positioned in such a way as to interact with TCDD through the formation of weak hydrogen bonds to aromatic chlorine atoms. A second recognition element was introduced into the binding sites by the inclusion of a polymerizable, electron-rich, aromatic ether capable of forming π−π interactions with the electron-deficient dioxin molecule. Polymers imprinted with either template showed significantly higher uptake of TCDD than the corresponding nonimprinted controls, even at concentrations as low as 2 nM.

Interactions between a well-characterized protein, beta-lactoglobulin, and two flavor compounds, beta-ionone and gamma-decalactone, were studied by 2D NMR spectroscopy. NMR spectra were recorded in aqueous solution (pH 2.0, 12 mM NaCl, 10% D(2)O) under conditions such that beta-lactoglobulin is present in a monomeric state. TOCSY and NOESY spectra were recorded on the protein and the complexes between protein and ligands. The spectra of the NH-CH(alpha) region showed the cross-signals due to the coupling between N- and C-bonded protons in the polypeptide backbone. The observed chemical shift variations in the presence of ligands can be assigned to changes in the protein conformation. It appears that the side chains of several amino acids are affected by binding of gamma-decalactone point into the central cavity (Leu46, Ile56, Met107, and Gln120), whereas binding of beta-ionone affects amino acids located in a groove near the outer surface of the protein (Leu104, Tyr120, and Asp129), as illustrated by molecular visualization. This NMR study provides precise information of the location of binding and confirms the existence of two different binding sites for aroma compounds on beta-lactoglobulin, which was suggested in previous competition studies by fluorometry or affinity chromatography and by structural information obtained from infrared spectroscopy.