Evidence of a new intermediate compound of the chitin biogenesis found in a marine-derived fungus
- Toledo-Marante, Francisco javier
Copper ion substituted hercynite (Cu0.03Fe0.97Al2O4): A highly active catalyst for liquid phase oxidation of cyclohexane
- Mistri, Rajib; Maiti, Sayantani; Llorca Piqué, Jordi; Domínguez Escalante, Montserrat; Mandal, Tapas Kumar; Mohanty, Paritosh; Ray, Bidhan Chandra; Gayen, Arup
Copper ion substituted MAl2O4 (M = Mg, Mn, Fe, Ni and Zn) spinels, CuxM1-xAl2O4 (x = 0.03 and 0.05), have been synthesized by a single step solution combustion method. Of the various compositions studied the 3 at.% copper ion substituted hercynite, Cu0.03Fe0.97Al2O4, reported here for the first time, is shown to be much more active (similar to 92% conversion with similar to 99% selectivity) than other spinet analogues towards liquid phase oxidation of cyclohexane in acetonitrile with H2O2 as oxidant in air. Powder XRD analyses have revealed formation of pure hercynite phases. The least-square refined lattice parameters obtained from XRD...
Letter to the Glyco-Forum Relative efficacy of lactose-related donors for Trypanosoma cruzi trans-sialidase
- Dto Química Orgánica; Facultad Ciencias; Exactas Naturales; Rosa M. De Lederkremer; Alberto C. C. Frasch
We read the letter of Dr Previato with regard to one experiment in the publication by Agusti et al. (Agusti et al., 2004). As indicated by the title of the article, the aim of our work was to study the properties of lactose derivatives as substrates and inhibitors of the Trypanosoma cruzi trans-sialidase (TcTS), and is based in the 3D structure of TcTS (Amaya et al., 2003; Buschiazzo et al., 2002; Buschiazzo et al., 2000). In these articles, it was described that glucose, in the lactose, also interacts with the enzyme. Thus, our study was oriented in this direction for...
Films de PLA y PLA-PHB plastificados para su aplicación en envases de alimentos. Caracterización y análisis de los procesos de degradación
- Arrieta, Marina Patricia
El uso de envases plásticos, constituidos por materiales poliméricos derivados del petróleo, se ha extendido en muchas aplicaciones debido a su disponibilidad a gran escala, bajo coste de producción, gran versatilidad y buenas propiedades barrera. Sin embargo, representan un importante impacto medioambiental y una fuente enorme de generación de residuos de difícil eliminación. Como respuesta a este problema se ha planteado la prevención de la contaminación ambiental mediante el uso de biopolímeros como el poli(ácido láctico), PLA.
Tras el uso de estos productos, el PLA puede ser recuperado a través de procesos mecánicos (triturado-transformación térmica) o químicos (hidrólisis), o bien ser...
Formation and stability of 3-5 atom gold clusters from gold complexes during the catalytic reaction: dependence on ligands and counteranions
- Oliver Meseguer, Judit; Leyva Perez, Antonio; Al-Resayes, Saud I.; Corma Canós, Avelino
Gold complexes and salts decompose to catalytically active 3¿5 atom gold clusters during the one-pot acylation¿hydration of propargyl alcohols. Kinetic and spectroscopic studies show that released ligands and counteranions exert a direct effect on the formation and stability of the clusters.
Estudio de sistemas y tratamientos de estabilización de capas pictóricas no protegidas en pintura contemporánea. Criterios y metodologías de actuación.
- PASTOR VALLS, MARÍA TERESA
El propósito de esta investigación se centra en profundizar en las metodologías y criterios de intervención aplicados a la adhesión y consolidación de capas pictóricas contemporáneas sin proteger, así como en el estudio del comportamiento frente al envejecimiento de diversos polímeros y su posible viabilidad en el tratamiento de pintura vinílica, un tipo de aglutinante muy empleado en pintura actual.
Los problemas de estabilidad presentados (levantamientos y pulverulencia) comprometen la integridad de las obras y plantean tratamientos de limitada reversibilidad y elevada complejidad técnica. Además de los cambios de tipo óptico y de la afectación del concepto de la obra,...
Gold-catalyzed carbon-heteroatom bond-fiorming reactions
- Corma Canós, Avelino; Leyva Perez, Antonio; Sabater Picot, Mª José
We have seen the work on gold catalysis to increase exponentially
in the last few years. This is specifically true for homogeneous
gold(I) and some gold(III) catalysts. Despite further
expansion of gold catalysts to form C-O and C-N bonds, new
developments are now starting for selective formation of C-S
and, especially, C-P, C-Si, and C-B bonds. This is a field that
may offer new possibilities for gold catalysis.
Potential phototoxicity of rosuvastatin mediated by its dihydrophenanterene-like photoproduct
- Nardi, Giacomo; Lhiaubet, Virginie Lyria; Leandro García, Paula; Miranda Alonso, Miguel Ángel
In this work, rosuvastatin has been used to gain insight into the molecular basis of statin photosensitization. This lipid-lowering drug, also known as ¿superstatin¿, contains a 2-vinylbiphenyl-like moiety and has been previously described to decompose under solar irradiation, yielding stable dihydrophenanthrene analogues. During photophysical characterization of rosuvastatin, only a long-lived transient at ca. 550 nm was observed and assigned to the primary photocyclization intermediate. Thus, the absence of detectable triplet¿triplet absorption and the low yield of fluorescence rules out the role of the parent drug as an efficient sensitizer. In this context, the attention has been placed on the rosuvastatin...
Commercial metal-organic frameworks as heterogeneous catalysts
- Amarajothi ., Dhakshina Moorthy; Alvaro Rodríguez, Maria Mercedes; García Gómez, Hermenegildo
Metal¿organic frameworks (MOFs) are porous crystalline materials that have promising
applications as heterogeneous catalysts. After describing the composition, textural properties and
crystal structure of four commercially available MOFs, we summarize organic transformations for
which these commercial MOFs exhibit higher catalytic activity than the corresponding soluble
metal salts or metal ion-exchanged zeolites. In the present article, we have focused on reactions
requiring Lewis-acid sites or redox centers to illustrate the potential applications and limitations
of commercial MOFs. In a ¿nal section, we provide our views on future developments whose
ultimate target will be the use of a commercial MOF as a heterogeneous catalyst for a real
industrial process in...
Oxetane ring enlargement through nucleophilic trapping of radical cations by acetonitrile
- Pérez Ruiz, Raul; Jiménez Molero, María Consuelo; Miranda Alonso, Miguel Ángel; Domingo, Luis R.; Sáez Cases, José Antonio
Oxidative electron transfer cycloreversion of trans,trans-2-cyclopropyl-4-methyl-3-phenyloxetane, using triphenylthiapyrylium perchlorate as a photosensitizer, leads to distonic 1,4-radical cations; subsequent cleavage gives rise to fragmentation products (pathway a), whereas nucleophilic trapping by acetonitrile affords a ring expanded oxazine (pathway b).
Catalysis by supported gold nanoparticles: Beyond aerobic oxidative processes
- García Gómez, Hermenegildo; Stratakis, Manolis
Bulk gold, being the most stable among all metals, was for
many years considered as an inert catalyst. However, gold
particles with size on the scale of nanometers (gold
nanoparticles, Au NPs) have been recognized as surprisingly
active and extraordinary e¿ective green catalysts, generating a
highly popular research topic in the frontier between
homogeneous and heterogeneous catalysis
Benzophenone photosensitized DNA damage
- Cuquerella Alabort, Maria Consuelo; Lhiaubet ., Virginie Lyria; Cadet, Jean; Miranda Alonso, Miguel Ángel
A lthough the carcinogenic potential of ultraviolet radiation is well-known, UV light may interact with DNA by direct absorption or through photosensitization by endogenous or exogenous chromophores. These chromophores can extend the ¿active¿ fraction of the solar spectrum to the UVA region and beyond, which means that photosensitizers increase the probability of developing skin cancer upon exposure to sunlight. Therefore researchers would like to understand the mechanisms involved in photosensitized DNA damage both to anticipate possible photobiological risks and to design tailor-made photoprotection strategies. In this context, photosensitized DNA damage can occur through a variety of processes including electron transfer,...
Enantioselective intramolecular (2+2)-photocycloaddition reactions of 4-substituted quinolones catalyzed by a chiral sensitizer with a hydrogen-bonding motif
- Miranda Alonso, Miguel Ángel; Cuquerella Alabort, Maria Consuelo; Müler, Christiane; Bauer, Andreas; Maturi, Mark M.; Bach, Thorsten
Six 2-quinolones, which bear a terminal alkene linked by a three- or four-membered tether to carbon atom C4 of the quinolone, were synthesized and subjected to an intramolecular [2 + 2]-photocycloaddition. The reaction delivered the respective products in high yields (78-99%) and with good regioselectivity in favor of the straight isomer. If conducted in the presence of a chiral hydrogen-bonding template (2.5 equiv) at low temperature in toluene as the solvent, the reaction proceeded enantioselectively (83-94% ee). An organocatalytic reaction was achieved when employing a chiral hydrogen-bonding template with an attached sensitizing unit (benzophenone or xanthone). The xanthone-based organocatalyst proved...
A New Aluminosilicate Molecular Sieve with a System of Pores between Those of ZSM-5 and Beta Zeolite
- Moliner Marin, Manuel; Portilla Ovejero, Mª Teresa; Tom Willhammar; Rey Garcia, Fernando; FRANCISCO JAVIER LLOPIS ALONSO; Xiaodong Zou; Corma Canós, Avelino; Gonzalez, Jorge
A new aluminosilicate zeolite (ITQ-39) has been synthesized. This is an extensively faulted structure with very small domains that makes the structure elucidation very difficult. However, a combination of adsorption spectroscopy and reactivity studies with selected probe molecules suggests that the pore structure of ITQ-39 is related to that of Beta zeolite, with a three-directional channel system with large pores (12-MR), but with an effective pore diameter between those of Beta and ZSM-5, or a three-directional channel system with interconnected large (12-MR) and medium pores (10-MR). The pore topology of ITQ-39 is very attractive for catalysis and shows excellent results...
Efficient visible-light photocatalytic water spilitting by minute amounts of golds supported on nanoparticulate CeO2 obtaines by a biopolymer templating method
- Corma Canós, Avelino; Primo Arnau, Ana Maria; García Gómez, Hermenegildo; MARINO, TIZIANA; Molinari, Raffaele
When irradiated with visible light (¿ > 400 nm) 1wt%gold-supported ceria nanoparticles generate oxygen from water (10.5 ¿mol 3 h 1)moreefficiently than the standardWO3 (1.7 ¿mol 3 h 1) even under UV irradiation (9.5 ¿mol 3 h 1). This remarkable photocatalytic activity arises from a novel preparation method to reduce the particle size of ceria (5 nm) by means of electrostatic binding of Ce4¿ to alginate gel, subsequent supercritical CO2 drying, and calcination. The low loading of Au is crucial for the observed high catalytic activity.
Virtues and Vices of an Organic Dye and Ti-Doped MCM-41 Based Dye-Sensitized Solar Cells
- García Gómez, Hermenegildo; Ziólek, Marcin; Martín, Cristina; Cohen, Boiko; Douhal, Abderrazzak
We report on femtosecond to millisecond (fs-ms) studies of the interactions
of an e¿cient triphenylamine organic dye (TPC1) for photovoltaics with titanium-doped
high porous MCM-41 (TiMCM-41) silicate materials in half and complete dye-sensitized
solar cells (DSSCs). Stationary UV visible absorption results indicate a higher dye loading
(3 5 times) per Ti atom in the TiMCM-41-based solar cells in comparison with those
based on typical titania nanoparticles (NPs). However, the dye loading per Ti atom
decreases with increasing the Ti doping, and the total dye content is still smaller in the
TiMCM-41 solar cells than in the NP ones. Time-resolved emission studies showed that the
average electron injection times...
Different routes for preparing mesoporous organosilicas containing the Tröger's base and their textural and catalytic applications
- Merino Marcos, Estibaliz; DÍAZ MORALES, URBANO MANUEL; Poli ., Evelyne; BRUNEL, DANIEL; Corma Canós, Avelino
Organosilica materials with different contents of
Tr¿oger¿s base (TB) as builder moieties have been synthesized
from previously synthesized bis-trialkoxysilylated Tr¿oger¿s base.
Three well-nanostructured hybrid mesoporous materials were
prepared through different approachs: (a) anchoring the TB on
a preformed silica SBA-15 material by postsynthesis grafting,
(b) incorporating the TB fragments into the rigid and ordered
periodic mesoporous organosilica (PMO) with hexagonal
structure (HMS) by self-assembling process, and (c) using
anion fluoride as catalyst for a sol gel synthesis process in the
absence of structural directing agents (SDAs), at neutral pH and
low synthesis temperature, to introduce the TB units into the
walls of high surface orderless mesoporous materials with
flexible structure. The degree of...
Molecular Dynamics Simulations of the Diffusion of Small Chain Hydrocarbons in 8-Ring Zeolites
- Combariza Montañez, Aldo F.; SASTRE NAVARRO, GERMAN IGNACIO; Corma Canós, Avelino
Molecular dynamics (MD) simulations were performed to study the microscopic motion of methane, ethane, propene, and propane adsorbed in three pure silica zeolites with windows made of 8 SiO(4) tetrahedral units: Si-LTA, Si-IHW, and Si-ITE. The zeolite framework and guest structures have been simulated allowing full flexibility, using the well-known BKS model and the potential of Oie et al., respectively. The MD approach followed allows us to calculate the intra-and intercage dynamics of the smaller adsorbates, that is, methane and ethane, in statistically meaningful time and length scales in the temperature range studied, whereas for the larger size guest molecules...
Photobehavior of mixed Nn*/nn* triplets. Simultaneous detection of the two transients, solvent-depend hydrogen abstraction and reequilibration upon protein binding.
- Miranda Alonso, Miguel Ángel; Jornet Olivé, Mª Dolors; Tormos Faus, Rosa Esperanza
[EN] In the present work, a systematic study on hydrogen abstraction by the excited triplet states of 4-methoxybenzophenone (1) and
4,40-dimethoxybenzophenone (2) from 1,4-cyclohexadiene (3), 4-methylphenol (4), 1,2,3,4-tetrahydroquinoline (5), and
1-methyl-1,2,3,4-tetrahydroquinoline (6) in different media has been undertaken. Laser flash photolysis (LFP) revealed that in
nonpolar solvents, 1 and 2 triplets have a n¿* configuration with the typical benzophenone-like T-T absorption spectrum (¿max ca.
525 nm). Conversely, in aqueous solution, transient absorption spectra with maxima at 450 and 680 nm, attributed to the ¿¿* triplet,
were obtained. Quenching of 1 or 2 triplet by 3 led to ketyl radical formation with rate constants in the...
Site-dependent photo-fries rearrangement within serum albumins
- Miranda Alonso, Miguel Ángel; Marin Melchor, Mireia; Lhiaubet ., Virginie Lyria
[EN] : In the present work, the in¿uence of serum albumins as biological
hosts on the well-established photo-Fries rearrangement has been investigated. For this purpose,
4-methoxy-1-naphthyl hydrogen succinate and glutarate (1a,b) as well as the corresponding
acetate (1c), have been selected as substrates. Special
attention has been devoted to the e¿ect of the binding site location and serum albumin species on
the outcome of the reaction. In a ¿rst stage, the stabilizing e¿ect
of the biomacromolecule on the intramolecularly catalyzed hydrolysis of succinate
1a was observed. Then, 1b and 1c were considered for their interaction with proteins in site II and
site I, respectively....