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Susana Velasco-Lozano Maite Roca Alejandro Leal-Duaso Jos A. Mayoral Elisabet Pires Vicent Moliner Fernando Lpez-Gallego 《Chemical science》2020,11(44):12009
Enzymes acting over glyceryl ethers are scarce in living cells, and consequently biocatalytic transformations of these molecules are rare despite their interest for industrial chemistry. In this work, we have engineered and immobilised a glycerol dehydrogenase from Bacillus stearothermophilus (BsGlyDH) to accept a battery of alkyl/aryl glyceryl monoethers and catalyse their enantioselective oxidation to yield the corresponding 3-alkoxy/aryloxy-1-hydroxyacetones. QM/MM computational studies decipher the key role of D123 in the oxidation catalytic mechanism, and reveal that this enzyme is highly enantioselective towards S-isomers (ee > 99%). Through structure-guided site-selective mutagenesis, we find that the mutation L252A sculpts the active site to accommodate a productive configuration of 3-monoalkyl glycerols. This mutation enhances the kcat 163-fold towards 3-ethoxypropan-1,2-diol, resulting in a specific activity similar to the one found for the wild-type towards glycerol. Furthermore, we immobilised the L252A variant to intensify the process, demonstrating the reusability and increasing the operational stability of the resulting heterogeneous biocatalyst. Finally, we manage to integrate this immobilised enzyme into a one-pot chemoenzymatic process to convert glycidol and ethanol into 3-ethoxy-1-hydroxyacetone and (R)-3-ethoxypropan-1,2-diol, without affecting the oxidation activity. These results thus expand the uses of engineered glycerol dehydrogenases in applied biocatalysis for the kinetic resolution of glycerol ethers and the manufacturing of substituted hydroxyacetones.Design and fabrication of a robust heterogeneous biocatalyts for the selective oxidation of alkyl/aryl glyceryl monoethers through the engineering and immobilization of glycerol dehydrogenases. 相似文献
954.
For arbitrary values of a parameter ${\lambda \in \mathbb{R},}$ finite-time blow-up of solutions to the generalized, inviscid Proudman–Johnson equation is studied via a direct approach which involves the derivation of representation formulae for solutions to the problem. 相似文献
955.
Daniel E. Ceballos-Herrera Ismael Torres-Gómez Alejandro Martínez-Ríos José J. Sánchez-Mondragón 《Optical Review》2009,16(6):622-626
We present the spectral analysis of higher-order core mode resonances in a long period holey fiber grating induced mechanically
in an asymmetric holey fiber. Calculations based on a fast-Fourier transform mode solver shows that the mode resonances obtained
experimentally correspond to the odd- and even-LP1,1 core modes. Additionally, we analyze the twist and polarization response of these mode resonances in the long period holey
fiber grating. The results obtained in this work are of great importance in the design of new all-fiber optical devices that
involve couplings of higher order core modes in asymmetric holey fibers. 相似文献
956.
The minimization of general risk functions is becoming more and more important in portfolio choice theory and optimal hedging. There are two major reasons. Firstly, heavy tails and the lack of symmetry in the returns of many assets provokes that the classical optimization of the standard deviation may lead to dominated strategies, from the point of view of the second order stochastic dominance. Secondly, but not less important, many institutional investors must respect legal capital requirements, which may be more easily studied if one deals with a risk measure related to capital losses. 相似文献
957.
Using store level scanner data to improve category management decisions: Developing positioning maps
Óscar González-Benito María Pilar Martínez-Ruiz Alejandro Mollá-Descals 《European Journal of Operational Research》2009
This paper provides evidence of the usefulness of aggregated point-of-sale scanner data to infer the positioning of competing brands, providing valuable information for category management and hence facilitating decision making. Specifically, the authors propose a methodology to study the internal market structure based on market share models with latent heterogeneity when only macro-level time series data (not individual choices) are available. The proposed approach assumes a multidimensional decomposition, latent in the preference structure that is implicit to these types of models. By empirically applying this approach, the authors (1) simultaneously identify both latent dimensions of competing brands and latent segments with different brand preferences, (2) explain the competitive positioning of brands without using disaggregated consumer panel data, and (3) achieve greater predictive performance. The findings offer insights to academics and practitioners interested in improving the practice of category management. 相似文献
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959.
M. del Carmen Fernández-Fernández Rufina Bastida Alejandro Macías Paulo Pérez Lourido Laura Valencia 《Polyhedron》2009
The nitrate and perchlorate Ni(II) complexes of the stereo-isomeric hexazamacrocyclic ligands L1 (3,6,14,17,23,24-hexaazatricyclo[17.3.1.18,12]tetracosa-1(23),8,10,12(24),19,21-hexaene,2,7,13,18-tetramethyl) and L2 (3,7,15,19,25,26-hexaazatricyclo[19.3.1.19,13]hexacosa-1(25),9,11,13(26),21,23-hexaene,2,8,14,20-tetramethyl) derived from 2,6-diacetylpyridine have been synthesized and characterized by microanalysis, LSI-MS, conductivity measurements, IR, UV–Vis spectroscopy and magnetic studies. Crystal structures of L1·2H2O as well as of the complexes [NiL1](ClO4)2 and [NiL2](NO3)2 have been determined. The X-ray studies show the presence of mononuclear endomacrocyclic complexes with the metal ion coordinated to all the nitrogen donor atoms from the macrocyclic framework in a N6 core. The geometry around the metal ions can be described as distorted octahedral. The nitrate and perchlorate anions do not coordinate to the metal ions, but they are involved in intermolecular interactions through hydrogen bonds to the amine groups of the macrocyclic ligands. 相似文献
960.