Centro de Química y Materiales de Aragón

Nowadays, the eutectic liquids (DESs) are considered an adequate alternative to the traditional solvents. Therefore, there is an increasing interest in the study of the structure, properties and applications of these mixtures. In this paper, several NMR spectroscopic techniques have been used in order to evaluate the molecular structure of three ternary DESs, composed of choline chloride, urea or glycerol or ethylene glycol, and water. The use of routine and non-routine NMR techniques, such as 1H, 13C, correlation experiments, NOESY, ROESY, and diffusion experiments gave us some important evidences pointing to a supramolecular structure of the DES, which may be the origin of their particular behaviour. The mixture containing ethylene glycol shows the feeblest structure. In these ternary solvents, the water is found within the structure that is still retained when DESs are diluted at 10% wt.

Unusual magnetic behaviour is observed in compounds with three Cl ligands in fac -mode coordination to dysprosium, cerium and even gadolinium.

Quantum chemical topology analyses provide a new way of understanding the synchronicity of organic reactions.

The cycloaddition of azomethine ylide N-oxides (nitrone ylides) with aldehydes provides 3-oxazolines in a completely stereoselective manner in the presence of a catalytic amount of n-butyllithium. The process involves an initial nucleophilic attack on the aldehyde, followed by intramolecular oxygen addition to the nitrone moiety and lithium-assisted elimination of water, regenerating the catalytic species. Various Li-based catalytic systems are possible and the in situ generated water is required for continuing the catalytic cycle. The best results are observed with 20 mol % of n-butyllithium, whereas the use of stoichiometric amounts inhibit the rate of catalysis. Experimental, spectroscopic, and computational mechanistic studies have provided evidence of lithium-ion catalysis and rationalized several competing catalytic pathways.

The Leloir donors are nucleotide sugars essential for a variety of glycosyltransferases (GTs) involved in the transfer of a carbohydrate to an acceptor substrate, typically a protein or an oligosaccharide. A series of less-polar nucleotide sugar analogues derived from uridine have been prepared by replacing one phosphate unit with an alkyl chain. The methodology is based on the radical hydrophosphonylation of alkenes, which allows coupling of allyl glycosyl compounds with a phosphate unit suitable for conjugation to uridine. Two of these compounds, the GalNAc and galactose derivatives, were further tested on a model GT, such as GalNAc-T2 (an important GT widely distributed in human tissues), to probe that both compounds bound in the medium-high micromolar range. The crystal structure of GalNAc-T2 with the galactose derivative traps the enzyme in an inactive form; this suggests that compounds only containing the β-phosphate could be efficient ligands for the enzyme. Computational studies with GalNAc-T2 corroborate these findings and provide further insights into the mechanism of the catalytic cycle of this family of enzymes.

Abstract A full experimental study of the activation energy required for the hitherto unknown neutral 2‐aza‐Cope rearrangement is presented. A kinetic study of the process showed activation energies in the range of 22.91–24.06 kcal/mol, in agreement with a process operating at moderate temperature (70 °C). Calculations at B3LYP/6‐311+G(d,p) and M06‐2X/6‐311+G(d,p) levels of theory considering solvent (dimethyl sulfoxide (DMSO) and toluene) effects (PCM model) predict reaction energy barriers that are in agreement with the values obtained from 1H NMR‐based kinetic experiments. Results obtained by using enantiomerically pure substrates demonstrate that the rearrangement takes place with complete transfer of chirality, in contrast to previously described cationic processes. The effects of solvent and acid catalysis, which converts the process into the more common cationic rearrangement, have also been studied. DFT calculations also predict correctly the acceleration of the process under acid catalysis, estimating energy barriers in the range of 16.80–18.57 kcal/mol.

Liquid-Assisted Pulsed Laser Ablation (LA-PLA) is a promising top-down method to directly synthesize colloidal dispersions of nanoparticles in a eco-friendly manner. However, the role of LA-PLA synthesis parameters is not yet fully agreed. This work seeks to optimize the production of nanoscale zero-valent iron (nZVI) particles suitable for biomedical or environmental applications using nanosecond LA-PLA on iron targets with different ablation media, laser and target scanning parameters. The use of alcohols as solvents produces iron-iron oxide core-shell nanoparticles with amorphous cores, except for a small crystalline fraction corresponding to the biggest core sizes. Decreasing carbon chain length and complexity leads to a thinning of the carbonaceous material coatings and an increase of the colloidal stability and the nanoparticle productivity. Moreover, a decrease of solvent density and surface tension allows obtaining reduced sizes and polydispersity values. Among, laser and scanning parameters, the pulse accumulation per spot displayed a clear effect in boosting size and productivity. As main outcome, aqueous dispersions with suitable colloidal properties are obtained, either by transferring to water of optimized nZVI particles produced in ethanol, or by direct formation of nZVI particles and in situ coating with hydrophilic molecules in aqueous solutions of these molecules.

Abstract Homogeneous polycrystalline FexOy nanoparticles were generated by ablation of iron targets in water by nanosecond laser pulses at 532 nm. In ethanol, crystalline core‐shell Fe/FexOy structures with size medians around 20 nm were produced. The ablation of FeWxOy targets in water resulted in crystalline hollow shells and homogeneous FeWxOy nanoparticles. In contrast, amorphous core‐shell FeWxOy nanoparticles with a median size of 17 nm were produced in ethanol. The size distribution of both the FexOy and the FeWxOy particles showed a slight dependence on fluence and pulse number. This may be related to primary and secondary ablation and modification mechanisms.

-pronucleophiles in the initial oxa-Michael reaction, also leading to the formation of a single stereoisomer under a dynamic kinetic resolution (DKR) process. Importantly, by using β-aryl or β-alkyl substituted α,β-unsaturated substrates as initial Michael acceptors either kinetically or thermodynamically controlled diastereoisomers were formed with high stereoselection through the careful selection of the reaction conditions. Finally, a complete experimental and computational study confirmed the initially proposed DKR process during the catalytic oxa-Michael/Michael cascade reaction and also explained the kinetic/thermodynamic pathway operating in each case.

Abstract The experimental and computational study of the mechanism of the iminium‐organocatalyzed formation of N‐hydroxypyrrolidines from nitrones, revealed up to three activation levels of the Schreiner's thiourea used as co‐catalyst, i.e: (i) formation of the iminium ion through hydroxyl anion recognition forming a stable ion pair; (ii) enolization of the nitrone through a H‐bond network and (iii) activation of the nitrone moiety towards the final ring closure. The computational model supports the mechanism and the catalytic cycle. This mechanistic rationale is supported by the lack of reactivity of preformed iminium ion with the nitrone in the absence of thiourea‐hydroxyl complex and the observed reactivity when a complex thiourea‐tetrabutylammonium hydroxide is added. magnified image

This study aims to develop a low invasive and selective laser cleaning procedure for the removal of reactive corrosion products on Cu-based artefacts without damage the substrate. In a preliminary step, laser cleaning was performed on two typologies of artificially corroded copper reference samples. The effect of the variation of laser parameters as pulse duration and output power, was thus evaluated on an oxide layer, simulating a protective patina, and a hydroxychloride layer, simulating a reactive corrosion products layer to be removed. The optimized cleaning procedure was validated on an archaeological artefact, a bronze coin. Morphological, microchemical and microstructural characterizations were performed by means of optical microscopy, confocal microscopy, field emission scanning electron microscopy, X-Ray diffraction and Raman spectroscopy, before and after laser cleaning. The experimental findings show that laser cleaning, in optimized conditions, can reduce the thickness of the hydroxychloride layers slightly affecting the oxide layers. The difference in the interaction with laser radiation of these two layers seems to be mainly related to the difference in grain size and porosity. Notwithstanding these encouraging results, in order to define the real feasibility of the laser cleaning procedure, a further validation on real artefacts is mandatory due to the variation in thickness and composition of the corrosion products formed during long-lasting uncontrolled degradation processes.

Thlaspi arvense (Pennycress) is an emerging feedstock for biofuel production because of its high seed oil content enriched in erucic acid. A transcriptomic and a lipidomic study were performed to analyze the dynamics of gene expression, glycerolipid content and acyl-group distribution during seed maturation. Genes involved in fatty acid biosynthesis were expressed at the early stages of seed maturation. Genes encoding enzymes of the Kennedy pathway like diacylglycerol acyltransferase1 (TaDGAT1), lysophosphatidic acid acyltransferase (TaLPAT) or glycerol 3-phosphate acyltransferase (TaGPAT) increased their expression with maturation, coinciding with the increase in triacylglycerol species containing 22:1. Positional analysis showed that the most abundant triacylglycerol species contained 18:2 at sn-2 position in all maturation stages, suggesting no specificity of the lysophosphatidic acid acyltransferase for very long chain fatty acids. Diacylglycerol acyltransferase2 (TaDGAT2) mRNA was more abundant at the initial maturation stages, coincident with the rapid incorporation of 22:1 to triacylglycerol, suggesting a coordination between Diacylglycerol acyltransferase enzymes for triacylglycerol biosynthesis. Genes encoding the phospholipid-diacylglycerol acyltransferase (TaPDAT1), lysophosphatidylcholine acyltransferase (TaLPCAT) or phosphatidylcholine diacylglycerolcholine phosphotransferase (TaPDCT), involved in acyl-editing or phosphatidyl-choline (PC)-derived diacylglycerol (DAG) biosynthesis showed also higher expression at the early maturation stages, coinciding with a higher proportion of triacylglycerol containing C18 fatty acids. These results suggested a higher contribution of these two pathways at the early stages of seed maturation. Lipidomic analysis of the content and acyl-group distribution of diacylglycerol and phosphatidyl-choline pools was compatible with the acyl content in triacylglycerol at the different maturation stages. Our data point to a model in which a strong temporal coordination between pathways and isoforms in each pathway, both at the expression and acyl-group incorporation, contribute to high erucic triacylglycerol accumulation in Pennycress.

This paper presents a new method for the fabrication of metal-like decorative layers on glazed ceramic tiles. It consists of the laser treatment of Cu thin films prepared by electron-beam evaporation at glancing angles. A thin film of discontinuous Cu nanoparticles was electron-beam-evaporated in an oblique angle configuration onto ceramic tiles and an ample palette of colors obtained by laser treatment both in air and in vacuum. Scanning electron microscopy along with UV-vis-near-IR spectroscopy and time-of-flight secondary ion mass spectrometry analysis were used to characterize the differently colored layers. On the basis of these analyses, color development has been accounted for by a simple model considering surface melting phenomena and different microstructural and chemical transformations of the outmost surface layers of the samples.

Ethynylation and propargylation of chiral nonracemic polyhydroxylated cyclic nitrones with Grignard reagents are efficient methods for preparing building blocks containing an alkyne moiety to be used in copper-catalyzed azide alkyne cycloaddition click chemistry. Whereas ethynylation takes place with excellent diastereoselectivity, propargylation afforded mixtures of diastereomers in some cases. The use of (trimethylsilyl)propargyl bromide as precursor of the Grignard reagent is necessary to avoid the formation of undesired allene derivatives. DFT calculations explain, within the experimental error, the observed behavior. Cycloaddition of the obtained pyrrolidinyl alkynes with sugar azides derived from β-(1,3)-glucans provides glycomimetics suitable to be used against fungal transglycosylases.

This work describes the preparation of HKUST-1 layers on brass supports by a thermal gradient approach. Supports were perforated using laser irradiation to create 30–50 μm microholes. Perforation improved the adhesion and loading of the MOF. The microhole environment generated during the laser treatment led to well-anchored coatings. Two distinct samples were synthesized with the reaction temperature (100 and 150 °C) as the main difference. A continuous HKUST-1 coating was only achieved with the higher temperature of 150 °C. However, the microholes were totally filled with crystals in both samples reaching weight fractions of crystallized material of 2.4 and 6.6 wt%. PXRD and N2 physisorption studies confirmed the formation of HKUST-1 crystals with high quality (SBET = 1105 m2 g−1). Water adsorption was performed on both samples, showing the main sorption event below a relative pressure of 0.4 and obtaining uptakes (0.48 and 0.45 g g−1 at 293 K and p/p0 = 0.9) among the reported values for HKUST-1 powder. The HKUST-1 properties and the enhanced MOF–support interaction make these coatings candidates for use in gas storage and separation, sensing and water-based adsorption applications, such as chillers or heat pumps.

Abstract Representative derivatives of uridine‐conjugated amino acids that have been suitably protected for Fmoc solid‐phase chemistry have been prepared through efficient procedures that use “click” reactions as key steps, including thiol–ene radical reactions and copper‐catalyzed azide alkyne cycloaddition (CuAAC) reactions. Several linkers between the amino acid and nucleoside units, including alkyl chains and a triazole ring, have been successfully employed. Alkyl chains offer retention of flexibility, to allow the bisubstrate analogues to adopt an appropriate orientation, whilst the triazole ring can promote additional interactions at the active sites of target enzymes. Furthermore, a neutral surrogate of the pyrophosphate unit has been prepared by using a Staudinger–Vilarrasa reaction as a key step. Neutral analogues are promising surrogates for avoiding difficulties owing to cell‐membrane permeability.

The transglycosylase Saccharomyces cerevisiae Gas2 (ScGas2) belongs to a large family of enzymes that are key players in yeast cell wall remodeling. Despite its biologic importance, no studies on the synthesis of substrate-based compounds as potential inhibitors have been reported. We have synthesized a series of docking-guided glycomimetics that were evaluated by fluorescence spectroscopy and saturation-transfer difference (STD) NMR experiments, revealing that a minimum of three glucose units linked via a β-(1,3) linkage are required for achieving molecular recognition at the binding donor site. The binding mode of our compounds is further supported by STD-NMR experiments using the active site-mutants Y107Q and Y244Q. Our results are important for both understanding of ScGas2-substrate interactions and setting up the basis for future design of glycomimetics as new antifungal agents.

Abstract This paper reports a new methodology for the coloring of glazed ceramic tiles consisting of the near infrared pulsed laser processing of copper containing oxide coatings prepared by magnetron sputtering. As a second approach, the employ for the same purpose of a novel laser furnace technique is also described. Changing the laser parameters and using the laser furnace to treat the tiles at high temperature during irradiation has resulted in a wide color palette. The optical characterization of the modified tiles by UV ‐Vis spectroscopy has been complemented with their microstructural and compositional analysis by Scanning Electron Microscopy ( SEM ), Transmission Electron Microscopy ( TEM ), and Time Of Flight Secondary Ion Mass Spectrometry (TOF‐SIMS). The chemical composition of the surface was obtained by X‐ray Photoemission Spectroscopy ( XPS ) and its structure determined by X?ray diffraction (XRD). The chemical resistance was characterized by several tests following the norm ISO 10545‐13. Color changes have been attributed to surface microstructural and chemical transformations that have been accounted for by simple models involving different ablation, melting, diffusion, and segregation/agglomeration phenomena depending on the laser treatments employed.

Nowadays, multimodal diagnosis by combining several imaging techniques, such as mammography, magnetic resonance imaging and computed X-ray tomography is playing a leading role in the diagnosis of breast cancer.[1]However clinical application of this multimodal approach is still problematic due the lack of appropriate commercial contrast agents showing capabilities to distinguish between malignant tumours and benign abnormal masses. Hybrid nanoparticles, which contain both magnetic and radiopaque elements are a promising alternative for the generation of these multimodal contrast agents due to their unique characteristics, such as: high biocompatibility, contrast enhancement efficacy, cost effectiveness and colloidal stability in the physiological environment.[2]Unfortunately, conventional chemical procedures to synthesize multimodal nanoparticles in liquid media used in laboratory are not well standardized and cost-effective methods to produce large quantities of nanoparticles.[3]

Laser tailoring has been used for increasing the active area of the yttria stabilised zircona (YSZ) electrolyte interface in solid oxide fuel cells to reduce the polarisation losses and improve the cell electrochemical performance.