Substrate binding pockets of ω‐transaminase (ω‐TA) consist of a large (L) pocket capable of dual recognition of hydrophobic and carboxyl substituents, and a small (S) pocket displaying a strict steric constraint that permits entry of a substituent no larger than an ethyl group. Despite the unique catalytic utility of ω‐TA enabling asymmetric reductive amination of carbonyl compounds, the severe size exclusion occurring in the S pocket has limited synthetic applications of ω‐TA to access structurally diverse chiral amines and amino acids. Here we report the first example of an ω‐TA whose S pocket shows a non‐canonical steric constraint and readily accommodates up to an n‐butyl substituent. The relaxed substrate specificity of the (S)‐selective ω‐TA, cloned from Paracoccus denitrificans (PDTA), afforded efficient asymmetric syntheses of unnatural amino acids carrying long alkyl side chains such as L‐norvaline and L‐norleucine. Molecular modeling using the recently released X‐ray structure of PDTA could pinpoint an exact location of the S pocket which had remained dubious. Entry of a hydrophobic substituent in the L pocket was found to have the S pocket accept up to an ethyl substituent, reminiscent of the canonical steric constraint. In contrast, binding of a carboxyl group to the L pocket induced a slight movement of V153 away from the small‐pocket‐forming residues. The resulting structural change elicited excavation of the S pocket, leading to formation of a narrow tunnel‐like structure allowing accommodation of linear alkyl groups of carboxylate‐bearing substrates. To verify the active site model, we introduced site‐directed mutagenesis to six active site residues and examined whether the point mutations alleviated the steric constraint in the S pocket. Consistent with the molecular modeling results, the V153A variant assumed an elongated S pocket and accepted even an n‐hexyl substituent. Our findings provide precise structural information on substrate binding to the active site of ω‐TA, which is expected to benefit rational redesign of substrate specificity of ω‐TA.magnified image

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The first gold-catalyzed intermolecular coupling of alkynoates and allylic ethers invoking alkoxy addition and [3,3]-sigmatropic rearrangement as the key mechanism has been developed. Remarkably, the reaction showed complete chemoselectivity toward the pathway initiated by the alkoxy addition to alkynes. This unprecedented reactivity led to a new access to diversely substituted β-alkoxyacrylates in a highly efficient manner.

Lithium-ion batteries have been rapidly expanding in portable electronic devices, electric vehicles (EVs) and energy storage systems. In lithium-ion batteries, a separator is a critical component which prevents physical contact of the positive and negative electrodes while permitting free ionic transport within the cell. Most of the separators currently used in lithium-ion batteries are based on microporous polyolefin membranes. Although these separators offer excellent mechanical strength and chemical stability, they shrink, soften and even melt at high temperature, which cause short circuiting between electrodes. Furthermore, the large difference in polarity between the non-polar polyolefin separator and the polar organic electrolyte leads to poor wettability. As a result, there is a high resistance when the pores in the separator are not completely filled with liquid electrolyte. In our previous studies, we synthesized silica nanoparticles with vinyl groups, which permitted the surface reaction with vinyl monomers by radical polymerization [1-3]. With the goal of developing high performance separators with high thermal stability, good transport properties and enhanced wettability for non-aqueous liquid electrolytes, we prepared electrospun hybrid polymer membrane based on polyacrylonitrile (PAN) and reactive SiO2 nanoparticles. Due to the presence of reactive silica particles, it could be thermally cross-linked, resulting in good thermal stability and improved wettability for liquid electrolyte. Using the cross-linked electrospun hybrid polymer membranes, we assembled lithium-ion cell composed of carbon anode and LiNi0.6Co0.2Mn0.2O2 cathode. The cycling performances of the cells with cross-linked hybrid polymer membrane were evaluated, and the results were compared to those obtained with a pristine PE separator. References 1. Y.S.Lee, S.H.Ju, J.H.Kim, S.S.Hwang, J.M.Choi, Y.K.Sun, H.Kim, B.Scrosati, D.W.Kim, Electrochem. Commun., 17, 18, 2012. 2. S.H.Ju, Y.S.Lee, Y.K.Sun, D.W. Kim, J. Mater. Chem. A, 1, 395, 2013. 3. Y.S.Lee, J.H.Lee, J.A.Choi, W.Y.Yoon, D.W.Kim, Adv. Funct. Mater., 23, 1019, 2013.