Lipase-mediated selective acetylation of primary alcohols in ethyl acetate

An environmental friendly process to selectively acetylate primary alcohols was demonstrated. The esterification process consists of treatment of a primary alcohol in the presence of immobilized C. antarctica lipase (Novozyme-435) in ethyl acetate at room temperature. Primary alcohols were acetylated in the presence of secondary alcohols and phenols.     

A Spectroscopy-based Methodology for Rapid Screening and Characterization of Phytochrome Photochemistry in Search of Pfr-favored Variants

Phytochromes are photosensitive proteins with a covalently bound open-chain chromophore that can switch between two principal states: red light absorbing Pr and far-red light absorbing Pfr. Our group has previously shown that the bacteriophytochrome from Xanthomonas campestris pv. campestris (XccBphP) is a bathy-like phytochrome that uses biliverdin IXα as a co-factor and is involved in bacterial virulence. To date, the XccBphP crystal structure could only be solved in the Pr state, while the structure of its Pfr state remains elusive. The aims of this work were to develop an efficient screening methodology for the rapid characterization and to identify XccBphP variants that favor the Pfr form. The screening approach developed here consists in analyzing the UV-Vis absorption behavior of clarified crude extracts containing recombinant phytochromes. This strategy has allowed us to quickly explore over a hundred XccBphP variants, characterize multiple variants and identify Pfr-favored candidates. The high-quality data obtained enabled not only a qualitative, but also a quantitative characterization of their photochemistry. This method could be easily adapted to other phytochromes or other photoreceptor families.     

Mild TiIII- and Mn/ZrIV-catalytic reductive coupling of allylic halides: efficient synthesis of symmetric terpenes

Two new efficient methods for the regioselective homocoupling of allylic halides using either catalytic TiIII or the combination Mn/ZrIV catalyst have been developed. The regio- and stereoselectivity of the process proved to increase significantly when the Mn/ZrIV catalyst is used as the coupling reagent and when cyclic substituted allylic halides are used as substrates. The use of Lewis acids such as collidine hydrochloride allowed the quantity of catalyst to be lowered up to 0.05 equiv. We have proved the utility of these protocols with the synthesis of different terpenoids such as (+)-beta-onoceradiene (1), (+)-beta-onocerine (2), squalene (5), and advanced key-intermediates in the syntheses of (+)-cymbodiacetal (3) and dimeric ent-kauranoids as xindongnin M (4a).     

Mapping dynamical heterogeneity in structural glasses to correlated fluctuations of the time variables

Dynamical heterogeneities--strong fluctuations near the glass transition--are believed to be crucial to explain much of the glass transition phenomenology. One hypothesis for their origin is that they emerge from soft (Goldstone) modes associated with a broken continuous symmetry under time reparametrizations. To test this hypothesis, we use numerical simulation data to construct coarse grained observables and decompose their fluctuations into two transverse components associated with the postulated soft modes and a longitudinal component unrelated to them. We find that as temperature is lowered and time scales are increased, the time reparametrization fluctuations become increasingly dominant, and that their correlation volumes grow together with those of the dynamical heterogeneities, while the correlation volumes for longitudinal fluctuations remain small.     

Band renormalization and spin polarization of MoS2 in graphene/MoS2 heterostructures

Transition metal dichalcogenides exhibit spin–orbit split bands at the K‐point that become spin polarized for broken crystal inversion symmetry. This enables simultaneous manipulation of valley and spin degrees of freedom. While the inversion symmetry is broken for monolayers, we show here that spin polarization of the MoS₂ surface may also be obtained by interfacing it with graphene, which induces a space charge region in the surface of MoS₂. Polarization induced symmetry breaking in the potential gradient of the space charge is considered to be responsible for the observed spin polarization. In addition to spin polarization we also observe a renormalization of the valence band maximum (VBM) upon interfacing of MoS₂ with graphene. The energy difference between the VBM at the Γ‐point and K‐point shifts by ～150 meV between the clean and graphene covered surface. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

A Novel Series of 3,4‐Disubstituted Dihydropyrazoles: Synthesis and Evaluation for MAO Enzyme Inhibition

In this study, the authors have designed and synthesized a novel series of 3‐acyl‐4‐aryl‐4,5‐dihydropyrazoles, with the aim to obtain new potential scaffolds for the inhibition of both isoforms of monoamine oxidase (MAO) enzyme. The synthetic pathway to these compounds includes as a key step the 1,3‐dipolar cycloaddition reaction of diazomethane with a chalcone. All the compounds were fully characterized by means of spectroscopic and analytical data and showed specific inhibition against MAO A.     

Solvent‐Free Approach to 3,4‐Dihydropyrimidin‐2(1H)‐(thio)ones: Biginelli Reaction Catalyzed by a Wells–Dawson Reusable Heteropolyacid

The Biginelli reaction is performed in an efficient, simple, solvent‐free procedure, using a small amount of H₆P₂W₁₈O₆₂ · 24H₂O, a reusable heteropolyacid catalyst with Wells–Dawson structure. Both aromatic and aliphatic aldehydes, and different β‐dicarbonyl compounds and urea or thiourea, were used as starting materials. Seventeen examples of dihydropyrimidinones and dihydropyrimidinethiones were prepared by heating the reactants either in refluxing acetonitrile or in the absence of solvent. Operational simplicity, the use of a noncorrosive, reusable catalyst in solventless conditions, short reaction times, and very good to excellent yields in most of the selected examples are the main advantages of the method.     

Seasonal variability of optical properties in a highly turbid lake (Laguna Chascomús, Argentina)

We study the underwater light field seasonality in a turbid lake, Laguna Chascomús (Buenos Aires, Argentina). We report (1) relationships between optical properties (OPs) and optically active substances (OASs); (2) relationships between inherent (IOPs) and apparent (AOPs) optical properties; and (3) the seasonal variability in OASs and OPs. Light absorption was dominated by the particulate fraction. The contributions of phytoplankton pigments and unpigmented components were similar. The best predictors of total particulate absorption, unpigmented particulate absorption, turbidity and vertical attenuation coefficient were total suspended solids or their ash content. Many OASs and OPs varied seasonally. The concentrations of OASs were higher during spring and summer, resulting in lower transparency and higher turbidity. However, mass-specific absorption coefficients displayed lower values during spring and summer. Thus, the higher light attenuation observed during spring and summer resulted from higher concentrations of relatively less absorptive OASs. Collectively, these results suggest that: (1) light extinction is enhanced during spring and summer; (2) the enhanced light extinction is due to changes in the particulate fraction; (3) the enhanced light extinction is mostly due to an increase in the amount of particulate material; and (4) the increase of particulate matter also enhanced light extinction through increased scattering.     

Near-field-optical-microscopy studies of micro-modifications caused by femtosecond laser irradiation in lithium niobate crystals

Near-field-optical-microscopy has been used to study the micro-modifications caused by femtosecond laser pulses focused at the surface and in the volume of lithium niobate crystals. We have found experimental evidence of the existence, close to femtosecond ablation craters, of periodic modifications in the surface reflectivity. In addition, the potential application of near-field-optical microscopy for the spatial location of permanent modifications caused by femtosecond pulses focused inside lithium niobate crystals has been also demonstrated.     

Use of synchrotron radiation X‐ray fluorescence and X‐ray absorption spectroscopy to investigate bioaccumulation,molecular target,and biotransformation of volcanic elements

Because environment pollutants have a strong impact on ecosystems, including human health, methods of their determination and mitigation have received special attention in recent years. Taking advantage of the wide range of data that can be obtained by synchrotron radiation X‐ray fluorescence spectroscopy (SRXRF) in the field of environmental sciences, different instrumental setups were used to study the biological fates of toxic elements in volcanic environments. The elemental composition of plants, algae, and bacteria in Copahue and Domuyo volcanoes from Argentinean Patagonia was determined by SRXRF and the volcanic elements Ti, Fe, and Zn were abundant in these organisms. Interestingly, a high As concentration was found in cyanobacteria (26.2 μg/g) living in As contaminated stream (250 μg/ml). Because arsenic is toxic and human carcinogen, element‐retention capacity, element‐protein associations, and arsenic metabolism in this As resistant organism were analyzed by SRXRF. A high capacity (100–95%) of Ti > Fe > Cr > Sr > Ni > Cu > Mn > Zn > As retention was found after aqueous/alcoholic extraction assisted by ultrasonication. The cyanobacterial proteins were separated by SDS‐PAGE, electro‐transferred to nitrocellulose, and mapped by SRXRF. Defined protein bands containing Ca, Ti, Mn, Fe, and/or Zn were observed. Their ability to metabolize arsenic was revealed by combining SRXRF and X‐ray absorption near edge spectroscopy and Dimethylarsenic was found. Based on results, we speculate that these cyanobacteria could be interesting candidates for water treatment. Finally, we conclude that SRXRF is a valuable tool to study the biological cycle of environmental pollutants, including their accumulation, molecular targets, and metabolism. The SRXRF may also assist in remediation researches.