3 research outputs found
Water-Soluble Molecularly Imprinted Nanoparticle Receptors with Hydrogen-Bond-Assisted Hydrophobic Binding
Molecularly
imprinted nanoparticles (MINPs) were prepared when
surfactants with a tripropargylammonium headgroup and a methacrylate-functionalized
hydrophobic tail were cross-linked in the micelle form on the surface
and in the core in the presence of hydrophobic template molecules.
With the surfactants containing an amide bond near the headgroup,
the MINPs had a layer of hydrogen-bonding groups in the interior that
strongly influenced their molecular recognition. Templates/guests
with strong hydrogen-bonding groups in the midsection of the molecule
benefited most, especially if the hydrophobe of the template could
penetrate the amide layer to reach the hydrophobic core of the cross-linked
micelles. The location and the orientation of the hydrophilic groups
were also important, as they determined how the template interacted
with the surfactant micelles and, ultimately, with the MINP receptors
Artificial Zinc Enzymes with Fine-Tuned Active Sites for Highly Selective Hydrolysis of Activated Esters
Zinc
enzymes are ubiquitous in nature and are frequently used to
catalyze the hydrolysis of carboxylic acid esters, phosphate esters,
and amides. Although many models and mimics of zinc enzymes have been
reported, it remains difficult to construct active sites with accurately
positioned catalytic groups and tunable substrate selectivity. By
imprinting a substrate-like amino template coordinated to a polymerizable
zinc complex inside cross-linked micelles, we prepared water-soluble
nanoparticles with well-defined active sites. The position of the
zinc ion could be tuned systematically with respect to the ester bond
to be cleaved in the substrate (<i>p</i>-nitrophenyl esters),
as well as the rigidity of the active site. Our imprinted zinc catalysts
were able to distinguish substrates that differed by the position
of a single methyl group, chain length of the acyl chain, and substitution
of the phenyl ring. The turnover number (>460 at pH 7) was 1 order
of magnitude higher than those previously reported for artificial
zinc enzymes in the literature
Surface ligands in the imprinting and binding of molecularly imprinted cross-linked micelles
<p>Molecular recognition in water is challenging but water-soluble molecularly imprinted nanoparticle (MINP) receptors were produced readily by double cross-linking of surfactant micelles in the presence of suitable template molecules. When the micellar surface was decorated with different polyhydroxylated ligands, significant interactions could be introduced between the surface ligands and the template. Flexible surface ligands worked better than rigid ones to interact with the polar moiety of the template, especially for those template molecules whose water-exposed surface is not properly solvated by water. The importance of these hydrophilic interactions was examined in the context of different substrates, density of the surface ligands, and surface-cross-linking density of the MINP. Together with the hydrophobic interactions in the core, the surface hydrophilic interactions can be used to enhance the binding of guest molecules in water.</p