Applying an Oleophobic/Hydrophobic Fluorinated Polymer Monolayer Coating from Aqueous Solutions.

Despite major advancements in the fabrication of low-surface-energy surfaces, the environmental consequences of their fabrication can be a serious issue, particularly in an industrial context. This is especially the case for fluorine-based coatings, which often require fluorinated solvents for their processing and applications. These solvents are not only detrimental to the ozone layer but also represent a potential workplace hazard because they tend to bioaccumulate. We describe the design, synthesis, and characterization of a new fluorinated-polymer coating that can be simply applied to surfaces from an aqueous environment using a dip-coating technique. This was made possible by copolymerizing three different methacrylate monomers, each serving a specific function. Namely, fluorinated methacrylate providing oleo/hydrophobicity, photocleavable polyethylene glycol (PEG) methacrylate promoting water solubility of the copolymer, and thioether-based methacrylate serving as an anchoring unit to a number of different substrates. This copolymer is initially grafted to the surface as a monolayer from an aqueous solvent, after which the system is treated with ultraviolet (UV) light, cleaving away the protecting PEG moieties to yield an oleo/hydrophobic surface.

Catalytic hydrogenation of meso-octamethylporphyrinogen (calix[4]pyrrole).

Hydrogenation of meso-octamethylporphyrinogen (calix[4]pyrrole) with a number of heterogeneous catalysts under different experimental conditions has been investigated. GC-MS analyses of the reaction mixtures showed the formation of one to four products in low to moderate yields: three of them were diastereoisomers of the product derived from half-hydrogenation of the substrate, and displayed alternating pyrrolidine and pyrrole rings, while the fourth was the all-cis saturated product. An acidic medium was necessary to achieve hydrogenation. However, the use of too strongly acidic solvents or additives was detrimental to the stability of the substrate and/or the catalyst.

Synthesis, structure, and complexation properties of partially and completely reduced meso-octamethylporphyrinogens (calix[4]pyrroles).

New tricks for an old dog: Calixpyrroles bind anions efficiently and can be transformed into transition-metal complexes only under forcing conditions. Reducing the macrocycle creates a ligand that easily forms classical Werner complexes with copper, nickel, and palladium ions. The metal complexes present an array of four directed hydrogen bonds, which specifically bind the counterions (see picture; blue N, white H, green Cl, red Cu, Ni, or Pd).

Artificial transfer hydrogenases based on the biotin-(strept)avidin technology: fine tuning the selectivity by saturation mutagenesis of the host protein.

Incorporation of biotinylated racemic three-legged d6-piano stool complexes in streptavidin yields enantioselective transfer hydrogenation artificial metalloenzymes for the reduction of ketones. Having identified the most promising organometallic catalyst precursors in the presence of wild-type streptavidin, fine-tuning of the selectivity is achieved by saturation mutagenesis at position S112. This choice for the genetic optimization site is suggested by docking studies which reveal that this position lies closest to the biotinylated metal upon incorporation into streptavidin. For aromatic ketones, the reaction proceeds smoothly to afford the corresponding enantioenriched alcohols in up to 97% ee (R) or 70% (S). On the basis of these results, we suggest that the enantioselection is mostly dictated by CH/pi interactions between the substrate and the eta6-bound arene. However, these enantiodiscriminating interactions can be outweighed in the presence of cationic residues at position S112 to afford the opposite enantiomers of the product.

Artificial metalloenzymes based on biotin-avidin technology for the enantioselective reduction of ketones by transfer hydrogenation.

Most physiological and biotechnological processes rely on molecular recognition between chiral (handed) molecules. Manmade homogeneous catalysts and enzymes offer complementary means for producing enantiopure (single-handed) compounds. As the subtle details that govern chiral discrimination are difficult to predict, improving the performance of such catalysts often relies on trial-and-error procedures. Homogeneous catalysts are optimized by chemical modification of the chiral environment around the metal center. Enzymes can be improved by modification of gene encoding the protein. Incorporation of a biotinylated organometallic catalyst into a host protein (avidin or streptavidin) affords versatile artificial metalloenzymes for the reduction of ketones by transfer hydrogenation. The boric acid.formate mixture was identified as a hydrogen source compatible with these artificial metalloenzymes. A combined chemo-genetic procedure allows us to optimize the activity and selectivity of these hybrid catalysts: up to 94% (R) enantiomeric excess for the reduction of p-methylacetophenone. These artificial metalloenzymes display features reminiscent of both homogeneous catalysts and enzymes.