Experimental and Theoretical Studies on Arene‐Bridged Metal–Metal‐Bonded Dimolybdenum Complexes

The bis(hydride) dimolybdenum complex, [Mo₂(H)₂{HC(N‐2,6‐iPr₂C₆H₃)₂}₂(thf)₂], 2 , which possesses a quadruply bonded Mo₂^II core, undergoes light‐induced (365 nm) reductive elimination of H₂ and arene coordination in benzene and toluene solutions, with formation of the Mo^I₂ complexes [Mo₂{HC(N‐2,6‐iPr₂C₆H₃)₂}₂(arene)], 3?C₆H₆ and 3?C₆H₅Me , respectively. The analogous C₆H₅OMe, p‐C₆H₄Me₂, C₆H₅F, and p‐C₆H₄F₂ derivatives have also been prepared by thermal or photochemical methods, which nevertheless employ different Mo₂ complex precursors. X‐ray crystallography and solution NMR studies demonstrate that the molecule of the arene bridges the molybdenum atoms of the Mo^I₂ core, coordinating to each in an η² fashion. In solution, the arene rotates fast on the NMR timescale around the Mo₂‐arene axis. For the substituted aromatic hydrocarbons, the NMR data are consistent with the existence of a major rotamer in which the metal atoms are coordinated to the more electron‐rich C?C bonds.     

Fluorescence of New o‐Carborane Compounds with Different Fluorophores: Can it be Tuned?

Two sets of o‐carborane derivatives incorporating fluorene and anthracene fragments as fluorophore groups have been successfully synthesized and characterized, and their photophysical properties studied. The first set, comprising fluorene‐containing carboranes 6 – 9 , was prepared by catalyzed hydrosilylation reactions of ethynylfluorene with appropriate carboranylsilanes. The compound 1‐[(9,9‐dioctyl‐fluorene‐2‐yl)ethynyl]carborane ( 11 ) was synthesized by the reaction of 9,9‐dioctyl‐2‐ethynylfluorene and decaborane (B₁₀H₁₄). Furthermore, reactions of the lithium salt of 11 with 1 equivalent of 4‐(chloromethyl)styrene or 9‐(chloromethyl)anthracene yielded compounds 12 and 13 . Members of the second set of derivatives, comprising anthracene‐containing carboranes, were synthesized by reactions of monolithium or dilithium salts of 1‐Me‐1,2‐C₂B₁₀H₁₁, 1‐Ph‐1,2‐C₂B₁₀H₁₁, and 1,2‐C₂B₁₀H₁₂ with 1 or 2 equivalents of 9‐(chloromethyl)anthracene, respectively, to produce compounds 14 – 16 . In addition, 2 equivalents of the monolithium salts of 1‐Me‐1,2‐C₂B₁₀H₁₁ (Me‐o‐carborane) and 1‐Ph‐1,2‐C₂B₁₀H₁₁ (Ph‐o‐carborane) were reacted with 9,10‐bis(chloromethyl)anthracene to produce compounds 17 and 18 , respectively. Fluorene derivatives 6 – 9 exhibit moderate fluorescence quantum yields (32–44 %), whereas 11 – 13 , in which the fluorophore is bonded to the C_cluster (C_c), show very low emission intensity (6 %) or complete fluorescence quenching. The anthracenyl derivatives containing the Me‐o‐carborane moiety exhibit notably high fluorescence emissions, with ?_F=82 and 94 %, whereas their Ph‐o‐carborane analogues are not fluorescent at all. For these compounds, we have observed a correlation between the C_c?C_c bond length and the fluorescence intensity in CH₂Cl₂ solution, comparable to that observed for previously reported styrene‐containing carboranes. Thus, our hypothesis is that for systems of this type the fluorescence may be tuned and even predicted by changing the substituent on the adjacent C_c.     

Understanding Stability Trends along the Lanthanide Series

The stability trends across the lanthanide series of complexes with the polyaminocarboxylate ligands TETA^4? (H₄TETA=2,2′,2′′,2′′′‐(1,4,8,11‐tetraazacyclotetradecane‐1,4,8,11‐tetrayl)tetraacetic acid), BCAED^4? (H₄BCAED=2,2′,2′′,2′′′‐{[(1,4‐diazepane‐1,4‐diyl)bis(ethane‐2,1‐diyl)]bis(azanetriyl)}tetraacetic acid), and BP18C6^2? (H₂BP18C6=6,6′‐[(1,4,10,13‐tetraoxa‐7,16‐diazacyclooctadecane‐7,16‐diyl)bis(methylene)]dipicolinic acid) were investigated using DFT calculations. Geometry optimizations performed at the TPSSh/6‐31G(d,p) level, and using a 46+4fⁿ ECP for lanthanides, provide bond lengths of the metal coordination environments in good agreement with the experimental values observed in the X‐ray structures. The contractions of the Ln³⁺ coordination spheres follow quadratic trends, as observed previously for different isostructural series of complexes. We show here that the parameters obtained from the quantitative analysis of these data can be used to rationalize the observed stability trends across the 4f period. The stability trends along the lanthanide series were also evaluated by calculating the free energy for the reaction [La( L )]^n+/?_(sol)+Ln³⁺_(sol)→[Ln( L )]^n+/?_(sol)+La³⁺_(sol). A parameterization of the Ln³⁺ radii was performed by minimizing the differences between experimental and calculated standard hydration free energies. The calculated stability trends are in good agreement with the experimental stability constants, which increase markedly across the series for BCAED^4? complexes, increase smoothly for the TETA^4? analogues, and decrease in the case of BP18C6^2? complexes. The resulting stability trend is the result of a subtle balance between the increased binding energies of the ligand across the lanthanide series, which contribute to an increasing complex stability, and the increase in the absolute values of hydration energies along the 4f period.     

Characterization of a New Bacteriocin from Lactobacillus plantarum LE5 and LE27 Isolated from Ensiled Corn

Bacteriocins are low molecular peptides with antimicrobial activity, which are of great interest as food bio-preservatives and for treating diseases caused by pathogenic bacteria. In this study, we present the characterization of bacteriocins produced by Lactobacillus plantarum LE5 and LE27 isolated from ensiled corn. Bacteriocins were purified through ammonium sulfate precipitation and double dialysis by using 12- and 1-kDa membranes. Bacteriocins showed activity against Listeria innocua, Listeria monocytogenes, and Enteroccocus faecalis. Molecular weight was estimated through Tricine-SDS-PAGE and overloading the gel onto Mueller-Hinton agar seeded with L. monocytogenes, showing an inhibition zone between 5 and 10 kDa. NanoLC-MS/MS analysis allowed the identification of UPF0291 protein (UniProtKB/Swiss-Prot Q88VI7), which is also presented in other lactic acid bacteria without assigned function. Ab initio modeling showed it has an α-helix-rich structure and a large positive-charged region. Bacteriocins were stable between 4 and 121 °C and pH 2 and 12, and the activity was inhibited by SDS and proteases. Mode of action assay suggests that the bacteriocin causes of target microorganism. Taken together, these results describe a possible new class IIa bacteriocin produced by L. plantarum, which has a wide stability to physicochemical conditions, and that could be used as an alternative for the control of foodborne diseases.     

Human skin thermal properties determination using a calorimetric sensor

Journal of Thermal Analysis and Calorimetry - The purpose of the calorimetric sensor developed is to measure the heat flux transmitted by conduction between the human body surface and a thermostat...     

Optimization of STEM-HAADF Electron Tomography Reconstructions by Parameter Selection in Compressed Sensing Total Variation Minimization-Based Algorithms

A novel procedure to optimize the 3D morphological characterization of nanomaterials by means of high angle annular dark field scanning-transmission electron tomography is reported and is successfully applied to the analysis of a metal- and halogen-free ordered mesoporous carbon material. The new method is based on a selection of the two parameters (μ and β) which are key in the reconstruction of tomographic series by means of total variation minimization (TVM). The parameter-selected TVM reconstructions obtained using this approach clearly reveal the porous structure of the carbon-based material as consisting of a network of parallel, straight channels of ≈6 nm diameter ordered in a honeycomb-type arrangement. Such an unusual structure cannot be retrieved from a TVM 3D reconstruction using default reconstruction values. Moreover, segmentation and further quantification of the optimized 3D tomographic reconstruction provide values for different textural parameters, such as pore size distribution and specific pore volume that match very closely with those determined by macroscopic physisorption techniques. The approach developed can be extended to other reconstruction models in which the final result is influenced by parameter choice.     

Simulation of the ion beam-plasma interaction processes for point-like ions in doped DT plasmas

The purpose of this work is to study the interaction between an ion beam and a doped deuterium-tritium (DT) plasma in a fast ignition nuclear fusion context. In order to analyze the influence of the dopants in the interaction process, we present a physical model to carry out spatial-temporal simulations of the stopping of an ion beam interacting with a doped plasma target, the plasma heating processes, and the formation of the ignition regions. We perform a set of numerical experiments where different concentrations of dopants are added to a fully ionized DT plasma. These simulations allow us to characterize the increase in the stopping power and the maximum temperatures achieved with the presence of impurities, as well as the reduction of the heated and ignition regions. This reduction in the ignition region indicates difficulties for the formation of an efficient hot spot when there are dopants in the DT plasma.     

Solid-phase extraction and determination of trace aroma and flavour components in cider by GC-MS

Summary Minor volatile compounds are responsible for the aromas of cider. A simple technique for the analysis of these components is described based on solid-liquid phase extraction followed by quantitation by gas chromatography-mass spectrometry (GC-MS). The method is quantitative for analysis of alcohols, esters, lactones, phenols, and medium and long chain-length fatty acid.     

High-performance liquid chromatography with evaporative light-scattering detection for the determination of phospholipid classes in human milk,infant formulas and phospholipid sources of long-chain polyunsaturated fatty acids

We developed and validated a new high-performance liquid chromatographic method for the separation of phospholipid classes in human milk, infant formulas and phospholipidic sources of long-chain polyunsaturated fatty acids (LC-PUFAs) used in paediatric nutrition. Phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, phosphatidylserine and sphingomyelin were separated in less than 25 min using an Extrasil silica column (150 x 4.0 mm I.D., 3-microm particle size) by isocratic elution with a mixture of isopropanol-hexane-water. Phospholipids were determined by an evaporative light-scattering detector. Several chromatographic conditions were assayed to optimise the method, whose suitability is shown by the detection limits, linearity ranges and precision rates obtained. The main advantages of the proposed method are its speed and the direct determination of the main phospholipids present in human milk, infant formulas and the phospholipid sources of LC-PUFAs used in paediatric nutrition.     

Dynamic properties of soy globulin adsorbed films at the air-water interface

In this paper we present surface dilatational properties of soy globulins (beta-conglycinin, glycinin, and reduced glycinin with 10 mM of dithiothreitol (DTT)) adsorbed onto the air-water interface, as a function of adsorption time. The experiments were performed at constant temperature (20 degrees C), pH (8.0), and ionic strength (0.05 M). The surface rheological parameters were measured as a function of protein concentration (ranging from 1 to 1x10(-3)% wt/wt). We found that the surface dilatational modulus, E, increases, and the phase angle, phi, decreases with time, theta, which may be associated with protein adsorption. These phenomena have been related to protein adsorption, unfolding, and/or protein-protein interactions (at long-term adsorption) as a function of protein concentration in solution. From a rheological point of view, the surface viscoelastic characteristics of soy globulin films adsorbed at the air-water interface are practically elastic. The main conclusion is that the dilatational properties of the adsorbed films depend on the molecular structure of the protein.