Molecular structures of edge-sharing square-planar dinuclear complexes with unsaturated bridges

The dinuclear complexes of transition metal ions of type [M(2)(mu,eta(1)-XY)(2)L(4)], where XY is an unsaturated ligand that can act as a four-electron or a two-electron donor through the X atom, appear in two molecular conformations depending on whether the coordination planes around the two metal atoms are coplanar or bent. In both structures the geometry of the X atom is planar, corresponding to an sp(2) hybridization. An ab initio theoretical study on 43 representative complexes, complemented with a structural database analysis, provides a rationale for the experimentally observed structures.     

Cluster beams from passivated nanocrystals

Stable, intense beams of large metal clusters (from 10² to 10³ Au or Ag atoms) can be produced by laser desorption of molecular films of passivated nanocrystals that have undergone fractionation by size and a separate structural characterization. The mass onset of the desorbed species corresponds directly to the dimensions of the nanocrystal core, indicating that only the surfactant shell is lost during desorption. Photofragmentation, photoionization, and photodetachment from beams of large metal clusters, generated in this way, have all been observed.     

Cationic copolymerization of tetrahydrofuran with propylene oxide. IV. Use of antimony pentachloride as catalyst

Propylene oxide and tetrahydrofuran were polymerized cationically by an in situ catalytic system composed of antimony pentachloride and 1,2-propanediol. The rates of polymerization were measured by vapor-phase chromatography in the temperature range from ?20°C to +20°C. The Arrhenius parameters pertaining to the reaction of each of the comonomers were evaluated and compared with data published earlier for other catalytic systems. The present catalyst system was incapable of initiating a homo-polymerization of tetrahydrofuran in the absence of propylene oxide, while the latter was readily homopolymerized. In a copolymerization system, the rates of consumption of both monomers were first-order in respect to the catalyst, but the reaction ceased when all of the propylene oxide had been consumed. The relative reactivity of the two monomers as characterized by the copolymerization parameters r₁ (PO) = 1.15 and r₂ (THF) = 0.70 suggests that in the copolymerization system, tetrahydrofuran is capable of a reaction with its own active center. This is discussed in terms of a possible mechanism involving the effects of penultimate units and extensive chain transfer. The latter is well evident from the molecular weights of resulting copolyethers, which do not exceed one thousand.     

Predictive models to describe VLE in ternary mixtures water + ethanol + congener for wine distillation

The modeling of liquid–vapor equilibrium in ternary mixtures that include substances found in alcoholic distillation processes of wine and musts is analyzed. In particular, vapor–liquid equilibrium in ternary mixtures containing water + ethanol + cogener has been modeled using parameters obtained from binary mixture data only. The congeners are substances that although present in very low concentrations, of the order of part per million, 10⁻⁶ to 10⁻⁴ mg/L, are important enological parameters [1] and [2]. In this work two predictive models, the PSRK equation of state and the UNIFAC liquid phase model and two semipredictive activity coefficient models: NRTL and UNIQUAC have been used. The results given by these different models have been compared with literature data and conclusions about the accuracy of the models studied are drawn, recommending the best models for correlating and predicting the phase equilibrium in this type of mixtures.     

Adsorption of crude oil on anhydrous and hydrophobized vermiculite

This publication reports the adsorption of crude oil on vermiculite samples, expanded and hydrophobized with carnauba (Copernícia Cerífera) wax. The adsorption studies were performed by using columns filled with the vermiculite matrices and by dispersion of the vermiculite samples in an oil-water (50 ppm of oil) emulsion. The hydrate vermiculite exhibits a very low adsorption capacity against crude oil. On the other hand, anhydrous (expanded) and hydrophobized matrices show a high adsorption capacity. The 10% hydrophobized matrix show a 50% increased adsorption capacity, in comparison with the expanded one. For adsorption performed in the water-oil emulsion, saturation of the solid hydrophobized matrix is achieved after 60 min. The hydrophobized samples exhibit adsorption factors in the 0.7-1.0 range.     

Rapid estmation of technetium in99Mo−99mTc generators

A nomogram is presented to estimate the radiooctivity of^99mTc in⁹⁹Mo−^99mTc generators, based on equations of radioactive equilibrium. Since the parent element decays through two isomeric states of the daughter, the ratio of the total mass of technetium per millicurie of^99mTc is a function of the time elapsed between two consecutive elutions. Values of the amount of^99mTc expressed as a mole fraction or in moles or grams of total technetium per millicurie of^99mTc^m are also presented.     

Glycan–protein cross-linking mass spectrometry reveals sialic acid-mediated protein networks on cell surfaces

A cross-linking method is developed to elucidate glycan-mediated interactions between membrane proteins through sialic acids. The method provides information on previously unknown extensive glycomic interactions on cell membranes. The vast majority of membrane proteins are glycosylated with complicated glycan structures attached to the polypeptide backbone. Glycan–protein interactions are fundamental elements in many cellular events. Although significant advances have been made to identify protein–protein interactions in living cells, only modest advances have been made on glycan–protein interactions. Mechanistic elucidation of glycan–protein interactions has thus far remained elusive. Therefore, we developed a cross-linking mass spectrometry (XL-MS) workflow to directly identify glycan–protein interactions on the cell membrane using liquid chromatography-mass spectrometry (LC-MS). This method involved incorporating azido groups on cell surface glycans through biosynthetic pathways, followed by treatment of cell cultures with a synthesized reagent, N-hydroxysuccinimide (NHS)–cyclooctyne, which allowed the cross-linking of the sialic acid azides on glycans with primary amines on polypeptide backbones. The coupled peptide–glycan–peptide pairs after cross-linking were identified using the latest techniques in glycoproteomic and glycomic analyses and bioinformatics software. With this approach, information on the site of glycosylation, the glycoform, the source protein, and the target protein of the cross-linked pair were obtained. Glycoprotein–protein interactions involving unique glycoforms on the PNT2 cell surface were identified using the optimized and validated method. We built the GPX network of the PNT2 cell line and further investigated the biological roles of different glycan structures within protein complexes. Furthermore, we were able to build glycoprotein–protein complex models for previously unexplored interactions. The method will advance our future understanding of the roles of glycans in protein complexes on the cell surface.

The cell surface glycocalyx is highly interactive defined by extensive covalent and non-covalent interactions. A method for cross-linking and characterizing glycan–peptide interactions in situ is developed.     

The complexation of Cr(III) and Cr(VI) with flavones in micellar media and its use for the spectrophotometric determination of chromium

The complexation of chromium by different flavonoid dyes in micellar media has been studied, in particular the reaction between chromium and quercetin. Micellar effects, the reaction pathway proposed and the application of the method to the determination of Cr(VI) and Cr(VI) + Cr(III) mixtures are discussed.     

Reactor power dependency of the neutron flux parameters fork 0-standardization

Using the facilities of the Triga Mark III reactor at the NNRI, Mexico and the HAV-1 multipurpose monitor, the reactor power dependency for thek ₀-standardization essential neutron flux parameters as: epithermal shape factor (), thermal to epithermal ratio (f) and neutron temperature (T _n ) were experimentally obtained. Evaluation of the obtained dependencies shows that it is unnecessary to analyze the possible introduction of correction factors in thek ₀-INAA experimental results. A single experimental procedure to determine throughf is suggested.