Hydrogen Peroxide in Biocatalysis. A Dangerous Liaison

Hydrogen peroxide is a substrate or side-product in many enzyme-catalyzed reactions. For example, it is a side-product of oxidases, resulting from the re-oxidation of FAD with molecular oxygen, and it is a substrate for peroxidases and other enzymes. However, hydrogen peroxide is able to chemically modify the peptide core of the enzymes it interacts with, and also to produce the oxidation of some cofactors and prostetic groups (e.g., the hemo group). Thus, the development of strategies that may permit to increase the stability of enzymes in the presence of this deleterious reagent is an interesting target. This enhancement in enzyme stability has been attempted following almost all available strategies: site-directed mutagenesis (eliminating the most reactive moieties), medium engineering (using stabilizers), immobilization and chemical modification (trying to generate hydrophobic environments surrounding the enzyme, to confer higher rigidity to the protein or to generate oxidation-resistant groups), or the use of systems capable of decomposing hydrogen peroxide under very mild conditions. If hydrogen peroxide is just a side-product, its immediate removal has been reported to be the best solution. In some cases, when hydrogen peroxide is the substrate and its decomposition is not a sensible solution, researchers coupled one enzyme generating hydrogen peroxide “in situ” to the target enzyme resulting in a continuous supply of this reagent at low concentrations thus preventing enzyme inactivation. This review will focus on the general role of hydrogen peroxide in biocatalysis, the main mechanisms of enzyme inactivation produced by this reactive and the different strategies used to prevent enzyme inactivation caused by this “dangerous liaison”.This work has been supported by grant CTQ2009-07568 from Spanish Ministerio de Ciencia e Innovación. A. Berenguer-Murcia thanks the Spanish Ministerio de Ciencia e Innovación for a Ramon y Cajal fellowship (RyC-2009-03813). Mr. Hernandez is a holder of a MAEC-AECID fellowship

Single wall carbon nanotubes loaded with Pd and NiPd nanoparticles for H2 sensing at room temperature

Pd and bimetallic Ni50Pd50 nanoparticles protected by polyvinylpyrrolidone (PVP) have been synthesized by the reduction-by-solvent method and deposited on single wall carbon nanotubes (SWCNTs) to be tested as H2 sensors. The SWCNTs were deposited by drop casting from different suspensions. The Pd nanoparticles-based sensors show a very reproducible performance with good sensitivity and very low response times (few seconds) for different H2 concentrations, ranging from 0.2% to 5% vol. H2 in air at atmospheric pressure. The influence of the metal nanoparticle composition, the quality of SWCNTs suspension and the metal loading have been studied, observing that all these parameters play an important role in the H2 sensor performance. Evidence for water formation during the H2 detection on Pd nanoparticles has been found, and its repercussion on the behaviour of the assembled sensors is discussed. The sensor preparation procedure detailed in this work has proven to be simple and reproducible to prepare cost-effective and highly efficient H2 sensors that perform very well under real application conditions.We thank the MINECO, Generalitat Valenciana and FEDER (Projects CTQ2012-31762 and PROMETEO/2009/047) for financial support. A.B.M. thanks the Spanish Ministry Science and Innovation for a Ramón y Cajal fellowship (RyC 2009-03913). Jaime Garcia Aguilar and Izaskun Miguel García also thank the University of Alicante for their fellowships

Zn-Promoted Selective Gas-Phase Hydrogenation of Tertiary and Secondary C4 Alkynols over Supported Pd

We have investigated the gas-phase (P = 1 atm; T = 373 K) hydrogenation of (tertiary alkynol) 2-methyl-3-butyn-2-ol (MBY) and (secondary) 3-butyn-2-ol (BY) over a series of carbon (C), non-reducible (Al2O3 and MgO), and reducible (CeO2 and ZnO) supported monometallic [Pd (0.6–1.2% wt) and Zn (1% wt)] and bimetallic Pd–Zn (Pd:Zn mol ratio = 95:5, 70:30, and 30:70) catalysts synthesized by deposition–precipitation and colloidal deposition. The catalysts have been characterized by H2 chemisorption, hydrogen temperature-programmed desorption (H2-TPD), specific surface area (SSA), X-ray photoelectron spectroscopy (XPS), and transmission (TEM) and scanning transmission electron microscopy (STEM) analyses. Reaction over these catalysts generated the target alkenol [2-methyl-3-buten-2-ol (MBE) and 3-buten-2-ol (BE)] through partial hydrogenation and alkanol [2-methyl-butan-2-ol (MBA) and 2-butanol (BA)]/ketone [2-butanone (BONE)] as a result of full hydrogenation and double-bond migration. The catalysts exhibit a similar Pd nanoparticle size (2.7 ± 0.3 nm) but a modified electronic character (based on XPS). Hydrogenation activity is linked to surface hydrogen (from H2 chemisorption and H2-TPD). An increase in H2:alkynol (from 1 → 10) results in enhanced alkynol consumption with a greater rate in the transformation of MBY (vs BY); H2:alkynol had negligible effect on product distribution. Reaction selectivity is insensitive to the Pd site electron density with a similar response (SMBE = 65 ± 9% and SBE = 70 ± 8%) over Pdδ− (on Al2O3 and MgO) and Pdδ+ (on C and CeO2). A Pd/ZnO catalyst delivered enhanced alkenol selectivity (SMBE = 90% and SBE = 96%) attributed to PdZn alloy phase formation (proved by XRD and XPS) but low activity, ascribed to metal encapsulation. A two-fold increase in the consumption rate was recorded for Pd–Zn/Al2O3 (30:70) versus Pd/ZnO with a similar alloy content (32 ± 4% from XPS), ascribed to a contribution due to spillover hydrogen (from H2-TPD) where high alkenol selectivity was maintained.This research was funded by the Engineering and Physical Sciences Research Council (EPRSC; grant number EP/L016419/1; Ph.D. studentship to A.G.-F., CRITICAT program), the Spanish Ministerio de Ciencia Innovación y Universidades, Generalitat Valenciana and FEDER (RTI2018-095291-B-I00, MAT2017-87579-R MINECO/FEDER and PROMETEO/2018/076)

Preparation of homogeneous CNT coatings in insulating capillary tubes by an innovative electrochemically-assisted method

Preparation of homogeneous CNT coatings in insulating silica capillary tubes is carried out by an innovative electrochemically-assisted method in which the driving force for the deposition is the change in pH inside the confined space between the inner electrode and the capillary walls. This method represents a great advancement in the development of CNT coatings following a simple, cost-effective methodology.Authors gratefully acknowledge the Explora program (MAT2011–13877–e) and funding from the Generalitat Valenciana, Ministerio de Economía y Competitividad and FEDER (Projects CTQ2012-31762, MAT2010-15273, PROMETEO /2009/047 and RyC 2009-03913)

Switchable surfactant-assisted carbon nanotube coatings: innovation through pH shift

The inner surface of fused-silica capillaries has been coated with a dense/homogeneous coating of commercial multi-wall carbon nanotubes (MWCNTs) using a stable ink as deposit precursor. Solubilization of the MWCNTs was achieved in water/ethanol/dimethylformamide by the action of a surfactant, which can switch between a neutral or an ionic form depending on the pH of the medium, which thus becomes the driving force for the entire deposition process. Careful control of the experimental conditions has allowed us to selectively deposit CNTs on the inner surface of insulating silica capillaries by a simple, reproducible, and easily adaptable method.The authors gratefully acknowledge the funding from the Ministerio de Economía y Competitividad, Generalitat Valenciana, and FEDER (Projects CTQ2012-31762, MAT2013-42007-P, PrometeoII/2014/10, JCI-2012-12664, and RyC 2009-03913)

K- and Ca-promoted ferrosilicates for the gas-phase epoxidation of propylene with O2

In the propylene epoxidation reaction with Fe-SiO2 catalysts the presence of iron oxide particles has a detrimental effect due to the total combustion of propylene on these iron species. Thus, the complete elimination of the iron oxide particles is presented as a preliminary strategy in order to increase the selectivity towards propylene oxide in iron-based catalysts. In this sense, a simple post-treatment of the catalysts with alkali or alkaline-earth elements (such as K or Ca, respectively) has proven effective in the total elimination of these iron oxide particles. Furthermore, the addition of K and Ca has modified the physico-chemical properties of the catalysts, decreasing their superficial acidity and (for higher K or Ca loadings) masking/blocking the active sites responsible for the catalytic reaction. With all this, it is shown that K has a higher efficiency removing the iron oxide particles compared with Ca (for the same molar ratios) and that a higher amount of K (compared to Fe) is required for the complete elimination of the iron oxide particles. A considerable propylene oxide selectivity enhancement (up to 65%) has been obtained for the K-promoted Fe0.005SiO2 and Fe0.01SiO2 catalysts using O2 as sole oxidant.We thank the Spanish Ministry of Economy and Competitiveness (MINECO), Generalitat Valenciana and FEDER (CTQ2015-66080-R MINECO/FEDER and PROMETEOII/2014/010) for financial support. J.G.A. thanks the Spanish Ministry of Economy and Competitiveness (MINECO) for his fellowship (BES-2013-063678)

Photocatalytic Oxidation of VOCs in Gas Phase Using Capillary Microreactors with Commercial TiO2 (P25) Fillings

The elimination of volatile organic compounds (VOCs) at low concentration is a subject of great interest because these compounds are very harmful for the environment and human health. In this work, we have developed an easy methodology to immobilize a benchmark photocatalyst (P25) inside a capillary microreactor (Fused silica capillary with UV transparent coating) without any previous treatment. For this purpose, a dispersion of the sample (P25) in EtOH was used obtaining a packed bed configuration. We have improved the immobilization of the benchmark photocatalyst (P25) inside the capillary incorporating a surfactant (F-127) to generate porosity inside the microreactor to avoid severe pressure drops (∆P < 0.5 bar). The resulting capillaries were characterized by Scanning Electron Microscopy (SEM). These microreactors show a good performance in the abatement of propene (VOC) under flow conditions per mol of active phase (P25) due to an improved mass transfer when the photocatalyst is inside the capillary. Moreover, the prepared microreactors present a higher CO2 production rate (mole CO2/(mole P25·s)) with respect to the same TiO2 operating in a conventional reactor. The microreactor with low pressure drop is very interesting for the abatement of the VOCs since it improves the photoactivity of P25 per mol of TiO2 operating at near atmospheric pressure.The authors thank MINECO (Project CTQ2015-66080-R, MINECO/FEDER) for financial support. JFC thanks MINECO for a researcher formation grant (BES-2016-078079)

La evaluación formativa a través de un aprendizaje basado en proyectos: conectando la educación universitaria con la investigación aplicada

En el presente trabajo se plantea y se analiza la posibilidad de aplicar un modelo de evaluación formativa a través de un aprendizaje basado en proyectos en asignaturas con una elevada asignación de créditos prácticos, de los nuevos grados de las universidades. Este modelo se basa en el desarrollo de proyectos de investigación tutelados y la evaluación continua de los estudiantes, los cuales deberían desarrollar tanto competencias específicas de la disciplina, como competencias genéricas orientadas a su inserción profesional en el mercado laboral. Con el modelo de evaluación formativa a través de un aprendizaje basado en proyectos que se realizar en este trabajo, un estudiante ha desarrollado, a lo largo de una asignatura práctica de laboratorio, la cual tiene un número considerable de horas dentro del laboratorio (al menos 3 créditos CTS), un “proyecto” determinado con unos objetivos muy concretos que suponen el desarrollo de diversas competencias. Con el término “proyecto”, se incluye una serie de actividades coordinadas e interconectadas, de carácter tanto teórico como práctico, con unos objetivos específicos, que pretenden potenciar el aprendizaje de conocimiento y habilidades en el estudiante, de forma que resulte de gran ayuda en su desarrollo, realización personal, y en su futuro profesional

Glutaraldehyde in bio-catalysts design: a useful crosslinker and a versatile tool in enzyme immobilization

Glutaraldehyde is one of the most widely used reagents in the design of biocatalysts. It is a powerful crosslinker, able to react with itself, with the advantages that this may bring forth. In this review, we intend to give a general vision of its potential and the precautions that must be taken when using this effective reagent. First, the chemistry of the glutaraldehyde/amino reaction will be commented upon. This reaction is still not fully clarified, but it seems to be based on the formation of 6-membered heterocycles formed by 5 C and one O. Then, we will discuss the production of intra- and inter-molecular enzyme crosslinks (increasing enzyme rigidity or preventing subunit dissociation in multimeric enzymes). Special emphasis will be placed on the preparation of cross-linked enzyme aggregates (CLEAs), mainly in enzymes that have low density of surface reactive groups and, therefore, may be problematic to obtain a final solid catalyst. Next, we will comment on the uses of glutaraldehyde in enzymes previously immobilized on supports. First, the treatment of enzymes immobilized on supports that cannot react with glutaraldehyde (only inter and intramolecular cross-linkings will be possible) to prevent enzyme leakage and obtain some enzyme stabilization via cross-linking. Second, the cross-linking of enzymes adsorbed on aminated supports, where together with other reactions enzyme/support crosslinking is also possible; the enzyme is incorporated into the support. Finally, we will present the use of aminated supports preactivated with glutaraldehyde. Optimal glutaraldehyde modifications will be discussed in each specific case (one or two glutaraldehyde molecules for amino group in the support and/or the protein). Using preactivated supports, the heterofunctional nature of the supports will be highlighted, with the drawbacks and advantages that the heterofunctionality may have. Particular attention will be paid to the control of the first event that causes the immobilization depending on the experimental conditions to alter the enzyme orientation regarding the support surface. Thus, glutaraldehyde, an apparently old fashioned reactive, remains the most widely used and with broadest application possibilities among the compounds used for the design of biocatalyst

Strategies for the one-step immobilization–purification of enzymes as industrial biocatalysts

In this review, we detail the efforts performed to couple the purification and the immobilization of industrial enzymes in a single step. The use of antibodies, the development of specific domains with affinity for some specific supports will be revised. Moreover, we will discuss the use of domains that increase the affinity for standard matrices (ionic exchangers, silicates). We will show how the control of the immobilization conditions may convert some unspecific supports in largely specific ones. The development of tailor-made heterofunctional supports as a tool to immobilize–stabilize–purify some proteins will be discussed in deep, using low concentration of adsorbent groups and a dense layer of groups able to give an intense multipoint covalent attachment. The final coupling of mutagenesis and tailor made supports will be the last part of the review.This work has been supported by grant CTQ2013-41507-R from Spanish MINECO, grant no.1102-489-25428 from COLCIENCIAS and Universidad Industrial de Santander (VIE-UIS Research Program) (Colombia) and CNPq grant 403505/2013-5 (Brazil). A. Berenguer-Murcia thanks the Spanish MINECO for a Ramon y Cajal fellowship (RyC-2009-03813)