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Palomo J.M.,CSIC - Institute of Catalysis
Methods in Enzymology | Year: 2017

This chapter describes the rational design and synthesis of semisynthetic lipases by site-directed incorporation of tailor-made peptides on the lipase-lid site to improve its activity, specificity, and enantioselectivity in specific biotransformations. Cysteine was genetically introduced at a particular point of the oligopeptide lid of the enzyme, and cysteine-containing peptides, complementary to the amino acid sequence on the lid site of Geobacillus thermocatenulatus lipase (BTL), were covalently attached on the lid of two different cysteine-BTL variants based on a fast thiol-disulfide exchange ligation followed by desulfurization. The BTL variants were initially immobilized on solid support to introduce the advantages of solid-state chemistry, such as quantitative transformations, easy purification, and recyclability. In the two different immobilized variants BTL-A193C and BTL-L230C, the cysteine was then activated with 2-dipyridyldisulfide to help the disulfide exchange with the peptide, generating the semisynthetic enzyme in high yield. Excellent results of improvement of activity and selectivity were obtained. For example, the peptide-BTL conjugate (at position 193) was 40-fold more active than the corresponding unmodified enzyme for the hydrolysis of per-acetylated thymidine at pH 5, or fourfold in the desymmetrization of dimethyl-3-phenylglutarate at pH 7. The new enzyme also exhibited excellent enantioselectivity in the desymmetrization reaction with enantiomeric excess (ee) of >. 99% when compared to that of the unmodified enzyme (ee = 78%). © 2017 Elsevier Inc.

Kubacka A.,CSIC - Institute of Catalysis | Fernandez-Garcia M.,CSIC - Institute of Catalysis | Colon G.,University of Seville
Chemical Reviews | Year: 2012

Advanced nanostructured materials that demonstrate useful activity under solar excitation in fields concerned with the elimination of pollutants, partial oxidation and the valorization of chemical compounds, water splitting and CO 2 reduction processes, are discussed. Point defects present in nanoparticulated anatase present both 5-fold- and 6-fold-coordinated titanium atoms, as well as 2-fold- and 3-fold-coordinated oxygens. The requirement of using sunlight as the excitation source for the degradation reaction demands, as a principal requirement, the modification of the electronic characteristics of a UV absorber system such as anatase-TiO 2. Some reports also indicate the need for large doping concentrations for N-doping in specific cases where notable changes in the valence band onset are subsequently observed. The effect of cetyltrimethylammonium bromide (CTAB) on the crystallization is reported by Yin et al. They showed that the presence of CTAB induces the appearance of BiOBr during the synthesis at 80°C using an aqueous method.

Mate D.M.,DWI Leibniz Institute for Interactive Materials | Alcalde M.,CSIC - Institute of Catalysis
Biotechnology Advances | Year: 2015

Laccases are multicopper oxidoreductases considered by many in the biotechonology field as the ultimate "green catalysts". This is mainly due to their broad substrate specificity and relative autonomy (they use molecular oxygen from air as an electron acceptor and they only produce water as by-product), making them suitable for a wide array of applications: biofuel production, bioremediation, organic synthesis, pulp biobleaching, textiles, the beverage and food industries, biosensor and biofuel cell development. Since the beginning of the 21st century, specific features of bacterial and fungal laccases have been exhaustively adapted in order to reach the industrial demands for high catalytic activity and stability in conjunction with reduced production cost. Among the goals established for laccase engineering, heterologous functional expression, improved activity and thermostability, tolerance to non-natural media (organic solvents, ionic liquids, physiological fluids) and resistance to different types of inhibitors are all challenges that have been met, while obtaining a more comprehensive understanding of laccase structure-function relationships. In this review we examine the most significant advances in this exciting research area in which rational, semi-rational and directed evolution approaches have been employed to ultimately convert laccases into high value-added biocatalysts. © 2014 Elsevier Inc.

Conesa J.C.,CSIC - Institute of Catalysis
Catalysis Today | Year: 2013

The electronic structure of ZnTiO3, Zn2TiO 4 and Zn2Ti3O8 is investigated using a hybrid DFT method in which the exchange mixing coefficient is obtained through its relation with the dielectric constant (also computed at the hybrid DFT level). Bandgaps higher than those of the simple oxides are predicted, in agreement with some experimental data; but in the case of spinel structures bandgaps also appear to depend significantly on the (dis)ordering of the cations at octahedral sites, implying a strong influence of the preparation details on the final gap values. The change in the electronic structure of the spinel titanates which occurs when they are nitrided can lead to photocatalytic activity with visible light, as is known to happen with TiO2 and other oxides; but here the cation vacancy suppression effect which accompanies the transformation makes the nitridation process much more favourable, as shown by total energy DFT calculations. These zinc titanate spinels are thus promising candidates to achieve via nitridation efficient and robust photocatalysts active with visible light. All these compounds show a lower conduction band edge constituted mainly by Ti-centred orbitals; this may have influence on the details of the photocatalytic reaction mechanisms. © 2012 Elsevier B.V.

Conesa J.C.,CSIC - Institute of Catalysis
Journal of Physical Chemistry C | Year: 2012

The band alignment at semiconductor interfaces can be theoretically computed using periodic slab models together with hybrid functional density functional theory methods in which Hartree-Fock exchange mixing coefficients are properly chosen (as justified by their relationship with the dielectric constant), and the calculated electrostatic potential inside each slab is used as reference for the band-edge energies. This principle is applied here to the interface between wurtzite-type ZnO and anatase-type TiO 2, two oxides with nearly identical band gap widths. According to the results, in a composite of both materials the conduction and valence bands of ZnO will lie ca. 0.3 eV lower in energy than those of anatase, influencing the way in which photogenerated electrons and holes will be routed in photocatalytic or photovoltaic systems which include interfaces between these two oxides. The performance improvement observed in dye-sensitized solar cells based on a nanostructured ZnO electrode when the surface of the latter is covered by a thin TiO 2 layer is thus justified. The system may serve as an example for the estimation of the band alignment in other semiconductor junctions of interest in different kinds of devices. © 2012 American Chemical Society.

Carrasco J.,CSIC - Institute of Catalysis | Hodgson A.,University of Liverpool | Michaelides A.,University College London
Nature Materials | Year: 2012

Water/solid interfaces are relevant to a broad range of physicochemical phenomena and technological processes such as corrosion, lubrication, heterogeneous catalysis and electrochemistry. Although many fields have contributed to rapid progress in the fundamental knowledge of water at interfaces, detailed molecular-level understanding of water/solid interfaces comes mainly from studies on flat metal substrates. These studies have recently shown that a remarkably rich variety of structures form at the interface between water and even seemingly simple flat surfaces. In this Review we discuss the most exciting work in this area, in particular the emerging physical insight and general concepts about how water binds to metal surfaces. We also provide a perspective on outstanding problems, challenges and open questions. © 2012 Macmillan Publishers Limited. All rights reserved.

Progress in nanomaterials and catalysis stands on three pillars: 1) synthesis of nanomaterials, including the preparation of hierarchically dispersed nanoparticles; 2) theoretical studies of materials that enable experimental results to be understood; and 3) advanced, in situ characterization during operation (operando methodology). This Research News brings a perspective on how these three pillars are blending for research in materials science, with particular emphasis on catalysis. Progress in nanomaterials and catalysis is founded on the simultaneous implementation of three strategies: the synthesis of nanomaterials and hierarchically dispersed nanoparticles; the theoretical study of materials that enable experimental results to be understood; and advanced, in situ characterization during operation (operando methodology). Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Serrano-Lotina A.,CSIC - Institute of Catalysis | Daza L.,CSIC - Institute of Catalysis
Journal of Power Sources | Year: 2013

A La-NiMgAlO catalyst, obtained after calcination of a hydrotalcite precursor, was evaluated in dry reforming of methane. The catalyst showed no sign of deactivation during a 300 h test. CH4 and CO2 conversion were higher than thermodynamic equilibrium estimation which suggests the participation of other reactions. Used catalyst was characterized by several techniques (TPO, XPS and Raman spectroscopy and SEM and TEM microscopy) in order to establish whether carbon was deposited and its nature. Two different types of carbon were present: carbon nanotubes (CNTs) and carbon nanofibres (CNFs). These filamentous carbons were well-crystallize but with many structural defects, which can increase the resistivity to fracture and therefore prevent the encapsulation of active sites. In addition, graphite can act as a CH x collector, limiting the deactivation process. The small Ni particles diameter, together with its broad distribution, seems to have also a beneficial effect on the catalytic performance.© 2013 Published by Elsevier B.V.

Conesa J.C.,CSIC - Institute of Catalysis
Journal of Physical Chemistry C | Year: 2010

The total energies of TiO2 and Al2O3 allotropic forms computed using density functional theory (DFT) methods that include dispersion interaction effects are compared. For TiO2, adding energy terms of r-6 form with coefficients derived from atomic polarizabilities leads to the correct result that rutile is more stable than brookite, anatase, and other forms, while previous DFT studies without this correction wrongly predicted rutile to be less stable. The magnitude of the correction is significant because of the high polarizability of the oxide ion, and produces energy differences between the titania phases that are reasonably close to available experimental values. The van der Waals density functional does not yield the correct result, but the error is significantly decreased. For Al2O3 the experimental energy difference between α and γ forms is also approached better when including dispersion corrections in DFT calculations. The results show that dispersion interaction should not be ignored when computing with DFT energy differences between oxide structures and that for the latter the dispersion coefficients appropriate for neutral species should not be used. It is proposed that the correct reproduction of these differences be included in the benchmarks used for testing van der Waals-type functionals. © 2010 American Chemical Society.

CSIC - Institute of Catalysis | Date: 2010-09-22

The present invention relates to a probe compound that can comprise any substrate or metabolite of an enzymatic reaction in addition to an indicator component, such as, for example, a fluorescence dye, or the like. Moreover, the present invention relates to means for detecting enzymes in form of an array, which comprises any number of probe compounds of the invention which each comprise a different metabolite of interconnected metabolites representing the central pathways in all forms of life. Moreover, the present invention relates to a method for detecting enzymes involving the application of cell extracts or the like to the array of the invention which leads to reproducible enzymatic reactions with the substrates. These specific enzymatic reactions trigger the indicator (e.g. a fluorescence signal) and bind the enzymes to the respective cognate substrates. Moreover, the invention relates to means for isolating enzymes in form of nanoparticles coated with the probe compound of the invention. The immobilisation of the cognate substrates or metabolites on the surface of nanoparticles by means of the probe compounds allows capturing and isolating the respective enzyme, e.g. for subsequent sequencing.

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