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Yin D.,University of Minnesota | Purpero V.M.,University of Minnesota | Purpero V.M.,Lucigen Corporation | Fujii R.,University of Minnesota | And 4 more authors.
Chemistry - A European Journal | Year: 2013

Some serine hydrolases also catalyze a promiscuous reaction - reversible perhydrolysis of carboxylic acids to make peroxycarboxylic acids. Five X-ray crystal structures of these carboxylic acid perhydrolases show a proline in the oxyanion loop. Here, we test whether this proline is essential for high perhydrolysis activity using Pseudomonas fluorescens esterase (PFE). The L29P variant of this esterase catalyzes perhydrolysis 43-fold faster (kcat comparison) than the wild type. Surprisingly, saturation mutagenesis at the 29 position of PFE identified six other amino acid substitutions that increase perhydrolysis of acetic acid at least fourfold over the wild type. The best variant, L29I PFE, catalyzed perhydrolysis 83-times faster (kcat comparison) than wild-type PFE and twice as fast as L29P PFE. Despite the different amino acid in the oxyanion loop, L29I PFE shows a similar selectivity for hydrogen peroxide over water as L29P PFE (β0=170 vs. 160 M-1), and a similar fast formation of acetyl-enzyme (140 vs. 62 U mg-1). X-ray crystal structures of L29I PFE with and without bound acetate show an unusual mixture of two different oxyanion loop conformations. The type II β-turn conformation resembles the wild-type structure and is unlikely to increase perhydrolysis, but the type I β-turn conformation creates a binding site for a second acetate. Modeling suggests that a previously proposed mechanism for L29P PFE can be extended to include L29I PFE, so that an acetate accepts a hydrogen bond to promote faster formation of the acetyl-enzyme. Ulterior motif: An esterase variant (L29I; see figure) uses a new mechanism for perhydrolysis of acetic acid, likely involving a second acetate molecule. X-ray crystal structures of L29I PFE with and without bound acetate show an unusual mixture of two different oxyanion loop conformations that creates a binding site for the second acetate. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Makio H.,Mitsui Chemicals Singapore Randnter | Ochiai T.,Mitsui Chemicals Inc. | Mohri J.-I.,Mitsui Chemicals Inc. | Takeda K.,Mitsui Chemicals Inc. | And 4 more authors.
Journal of the American Chemical Society | Year: 2013

Multinuclear alkylene zinc (MAZ) compounds of the type EtZn-(R″-Zn) n-Et (R″ = ethyl and propyl branched alkylene groups) were synthesized by a simple one-step procedure in nonpolar hydrocarbon solvents from α,ω-dienes (e.g., 1,7-octadiene or 1,9-decadiene) and diethylzinc using a bis(salicylaldiminato)Zr(IV) complex, [(2-methylcyclohexyl)N=CH(2-O- C6H3-3,5-di-tert-butyl)]2ZrMe2, as a catalyst. The MAZ serves as a divalent reversible chain-transfer agent for olefin polymerization, resulting in telechelic Zn-metalated polyolefins whose molecular weights are controllable over a wide range. The Zn-terminated telechelics serve as a polymer precursor for further reactions and can be converted into a variety of telechelic functionalized polyolefins in high yield. © 2013 American Chemical Society.

Iwashita A.,Mitsui Chemicals Inc. | Chan M.C.W.,City University of Hong Kong | Makio H.,Mitsui Chemicals Singapore Randnter | Fujita T.,Mitsui Chemicals Singapore Randnter
Catalysis Science and Technology | Year: 2014

The deployment of fluorinated moieties to engender electronic effects through non-covalent attractive interactions is a new concept for olefin polymerization catalysts, and was proposed to account for the unprecedented living polymerization mediated by certain catalysts bearing fluorine-containing ancillary ligands. This strategy is distinct from conventional approaches based on steric influences to control olefin polymerization processes. In this perspective, the concept, generality and beneficial effects of applying non-covalent interactions to control polymerization reactions are discussed, with particular emphasis given to intramolecular C-H⋯F-C interactions between a fluorinated ligand and growing polymer chain. © 2014 The Royal Society of Chemistry.

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