Copper–Oxygen Dynamics in the Tyrosinase Mechanism

The dinuclear copper enzyme, tyrosinase, activates O₂ to form a (μ-η²:η²-peroxido)dicopper(II) species, which hydroxylates phenols to catechols. However, the exact mechanism of phenolase reaction in the catalytic site of tyrosinase is still under debate. We herein report the near atomic resolution X-ray crystal structures of the active tyrosinases with substrate l -tyrosine. At their catalytic sites, CuA moved toward l -tyrosine (CuA1 → CuA2), whose phenol oxygen directly coordinates to CuA2, involving the movement of CuB (CuB1 → CuB2). The crystal structures and spectroscopic analyses of the dioxygen-bound tyrosinases demonstrated that the peroxide ligand rotated, spontaneously weakening its O−O bond. Thus, the copper migration induced by the substrate-binding is accompanied by rearrangement of the bound peroxide species so as to provide one of the peroxide oxygen atoms with access to the phenol substrate's ϵ carbon atom.     

Stereoselective Syntheses of all the Possible Stereoisomers of Coronafacic Acid

An efficient and stereoselective syntheses of all the possible stereoisomers of coronafacic acid (CFA) has been developed. The stereochemistries of C3a and C7a were controlled in a diastereoselective Diels-Alder type cycloaddition using a chiral auxiliary. CFA and 6-epi-CFA were synthesized by hydrogenation of a common intermediate. During the synthesis of 6-epi-CFA, we established that its cis-fused configuration is important for the introduction of C4-C5 double bond by dehydration. This report is the first practical synthesis of both 6-epi-CFA, and its enantiomer.     

Synthesis of polymers having a phospholipid polar group connected to a poly(oxyethylene) chain and their protein adsorption-resistance properties

New methacrylates having a phospholipid polar group which was connected to various lengths of poly(oxyethylene) chains to form a polymerizable group (MEOnPC) were synthesized. The MEOnPC could polymerize with n-butyl methacrylate (BMA) in ethanol using a conventional radical polymerization technique. The unit mole fraction of MEOnPC in the polymer corresponded to that in the feed monomer solution. The MEOnPC polymers were soluble in ethanol, insoluble in water, but swelled in water and became hydrated. On the surface of a poly(BMA) membrane coated with MEOnPC, the phosphorylcholine groups of the MEOnPC unit present were determined by x-ray photoelectron spectroscopy. As a fundamental evaluation for biomedical materials, adsorption of one of the plasma proteins, fibrinogen, on acrylic beads coated with the MEOnPC polymers was evaluated. The amount of fibrinogen adsorbed on the MEOnPC polymer was smaller than that on the original acrylic beads, poly(BMA) and poly(2-hydroxyethyl methacrylate). The increase in the MEOnPC unit mole fraction in the polymer showed more effective protein adsorption-resistant properties. © 1996 John Wiley & Sons, Inc.     

Enzymatic degradation of aliphatic polyesters copolymerized with various diamines

Poly(hexamethylene adipate) copolymers with 10–40 mol-% (in feed) of aliphatic diamines of various methylene chain lengths were prepared by melt polycondensation. In vitro degradation was performed in buffer solution at 37°C with a lipase and was evaluated by weight loss of the films. The weight loss increased greatly by the copolymerization and showed a maximum at 10 mol-% of comonomer content. Degradation also increased in a zig-zag fashion with decreasing number of methylene chains in the diamine comonomers. Both effects on the enzymatic degradation are discussed.     

Synthesis of a biodegradable polymeric supramolecular assembly for drug delivery

A novel design of a biodegradable carrier for drug delivery was established by constructing a supramolecular assembly of drugs and polymer backbones without any covalent bonds. A biodegradable polyrotaxane was synthesized in which α-cyclodextrins (α-CDs) as drug carriers were threaded onto poly(ethylene glycol) chains which then were capped at each chain end by L -phenylalanine via peptide linkages. The release of α-CDs was observed only when the terminal peptide linkages were degraded.     

Reactive-ion etch resistant polysulfones for microlithography

The various chemical approaches aimed at improving the reactive-ion etch resistance of poly(olefin sulfone)s are described. Resist systems based on incorporation of RIE-resistant moieties via random copolymerization, blending and block copolymer formation are described and lithographic properties noted.     

One‐Pot Synthetic Procedure for2,2′‐Disubstituted Biaryls via the Suzuki Coupling Reaction of Aryl Triflates in a Biphasic Solvent System

A one‐pot synthetic procedure for 2,2′‐disubstituted biaryls was developed via a Suzuki cross‐coupling reaction of aryl triflates in a biphasic solvent system. The effects of various bases and solvents were investigated. Results showed that the Na₂CO₃–toluene/H₂O combination gave the highest yields.