Dihalodimethyltin(IV) complexes of 2‐(pyrazol‐1‐ylmethyl)pyridine

Reaction of dichloro‐ and dibromodimethyltin(IV) with 2‐(pyrazol‐1‐ylmethyl)pyridine (PMP) afforded [SnMe₂Cl₂(PMP)] and [SnMe₂Br₂(PMP)] respectively. The new complexes were characterized by elemental analysis and mass spectrometry and by IR, Raman and NMR (¹H, ¹³C) spectroscopies. Structural studies by X‐ray diffraction techniques show that the compounds consist of discrete units with the tin atom octahedrally coordinated to the carbon atoms of the two methyl groups in a trans disposition (Sn? C = 2.097(5), 2.120(5) Å and 2.110(6), 2.121(6) Å in the chloro and in the bromo compounds respectively), two cis halogen atoms (Sn? Cl = 2.4908(16), 2.5447(17) Å; Sn? Br = 2.6875(11), 2.7464(9) Å) and the two donor atoms of the ligand (Sn? N = 2.407(4), 2.471(4) Å and 2.360(5), 2.455(5) Å). In both cases, the Sn? N(pyridine) bond length is markedly longer than the Sn? N(pyrazole) distance. Copyright © 2003 John Wiley & Sons, Ltd.     

Insecticidal Activity of Organic Extracts of Solidago graminifolia and Its Main Metabolites (Quercetin and Chlorogenic Acid) against Spodoptera frugiperda: An In Vitro and In Silico Approach

Spodoptera frugiperda (S. frugiperda) remains a global primary pest of maize. Therefore, new options to combat this pest are necessary. In this study, the insecticidal activity of three crude foliar extracts (ethanol, dichloromethane, and hexane) and their main secondary metabolites (quercetin and chlorogenic acid) of the species Solidago graminifolia (S. graminifolia) by ingestion bioassays against S. frugiperda larvae was analyzed. Additionally, the extracts were phytochemically elucidated by ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) analysis. Finally, an in silico study of the potential interaction of quercetin on S. frugiperda acetylcholinesterase was performed. Organic extracts were obtained in the range from 5 to 33%. The ethanolic extract caused higher mortality (81%) with a half-maximal lethal concentration (LC₅₀) of 0.496 mg/mL. Flavonoid secondary metabolites such as hyperoside, quercetin, isoquercetin, kaempferol, and avicularin and some phenolic acids such as chlorogenic acid, solidagoic acid, gallic acid, hexoside, and rosmarinic acid were identified. In particular, quercetin had an LC₅₀ of 0.157 mg/mL, and chlorogenic acid did not have insecticidal activity but showed an antagonistic effect on quercetin. The molecular docking analysis of quercetin on the active site of S. frugiperda acetylcholinesterase showed a −5.4 kcal/mol binding energy value, lower than acetylcholine and chlorpyrifos (−4.45 and −4.46 kcal/mol, respectively). Additionally, the interactions profile showed that quercetin had π–π interactions with amino acids W198, Y235, and H553 on the active site.     

Precise measurement of the W-boson mass with the CDF II detector

We have measured the W-boson mass M(W) using data corresponding to 2.2 fb(-1) of integrated luminosity collected in pp collisions at sqrt[s] = 1.96 TeV with the CDF II detector at the Fermilab Tevatron collider. Samples consisting of 470,126 W → eν candidates and 624,708 W → μν candidates yield the measurement M(W) = 80,387 ± 12(stat.) ± 15(syst.) = 80,387 ± 19 MeV/c2. This is the most precise measurement of the W-boson mass to date and significantly exceeds the precision of all previous measurements combined.     

Complexation of Dimethyl 2,3-Naphthalenedicarboxylate with 2-hydroxypropyl-α-, -β- and -γ-cyclodextrins in Aqueous Solution by Fluorescence,Circular Dichroism and Molecular Mechanics

Fluorescence, circular dichroism and molecular mechanics have been used to study the complexation of 2,3-dimethyl naphthalenedicarboxylate with 2-hydroxypropyl-α-, -β and -γ-cyclodextrins (HPCDs) in aqueous solution. Emission spectra upon excitation of the naphthalenedicarboxylate group show two bands whose intensity ratio R is quite sensitive to polarity. From the change of R and lifetimes averages <τ> with HPCD concentration and temperature were obtained the stoichiometry, the association constants and the enthalpy and entropy changes during the complexation. R, <τ> and the fluorescence anisotropies (r) extrapolated at [HPCD]→∞ allows us to estimate the polarity and microviscosity of the media surrounding the guest when complexed. In addition, the analysis of quenching and induced circular dichroism experiments and molecular mechanics calculations in the presence of water, provide information about the forces responsible for the complexation and the geometry of the complexes.     

Combustion wave propagation in mixtures of JSC-1A lunar regolith simulant with magnesium

Combustion of lunar regolith mixed with energetic additives is a potential method for production of construction materials in future moon missions. Recently, self-sustained combustion in the mixtures of JSC-1A lunar regolith and magnesium has been demonstrated. However, the concentration of magnesium in those mixtures was as high as 26 wt%. Note that magnesium must be either transported from Earth or recovered from lunar minerals or used structures. The present paper focuses on the minimization of magnesium content in JSC-1A/Mg mixtures. The mixtures were compacted into pellets and ignited in argon environment. Initial attempts to decrease magnesium concentration resulted in the observations of a spinning combustion wave at 23 wt% Mg. The observed spin combustion involved periodical motion of two counterpropagating hot spots along a helical path on the sample surface. These observations, including features such as formation of a faster hot spot after collision of the counterpropagating spots, confirm theoretical predictions for spin combustion in solid–solid mixtures. High-energy mechanical milling of JSC-1A in a planetary ball mill significantly increased its reactivity and improved combustion of its mixtures with magnesium. Mixtures of the obtained powder (the median diameter of about 3 μm) with 26 wt% Mg exhibit easy ignition and vigorous combustion. The minimum concentration of magnesium required for self-sustained propagation of a planar combustion front is as low as 13 wt%.     

XANES speciation of mercury in three mining districts – Almadén,Asturias (Spain), Idria (Slovenia)

The mobility, bioavailability and toxicity of mercury in the environment strongly depend on the chemical species in which it is present in soil, sediments, water or air. In mining districts, differences in mobility and bioavailability of mercury mainly arise from the different type of mineralization and ore processing. In this work, synchrotron‐based X‐ray absorption near‐edge spectroscopy (XANES) has been taken advantage of to study the speciation of mercury in geological samples from three of the largest European mercury mining districts: Almadén (Spain), Idria (Slovenia) and Asturias (Spain). XANES has been complemented with a single extraction protocol for the determination of Hg mobility. Ore, calcines, dump material, soil, sediment and suspended particles from the three sites have been considered in the study. In the three sites, rather insoluble sulfide compounds (cinnabar and metacinnabar) were found to predominate. Minor amounts of more soluble mercury compounds (chlorides and sulfates) were also identified in some samples. Single extraction procedures have put forward a strong dependence of the mobility with the concentration of chlorides and sulfates. Differences in efficiency of roasting furnaces from the three sites have been found.     

Ultrasonic study of wheat flour properties

In this work, the wheat flour properties are investigated using ultrasound techniques. Moreover, the flour samples were also characterized by means of well established techniques such as protein content, Alveograph and Mixolab®. A set of 35 dough samples, made of wheat flours with diverse physical and quality properties, were studied. The obtained results shown that ultrasound measurements can detect changes in the dough consistency induced by proteins and also by gelatinization of the starch. Furthermore, ultrasound measurements can be related to parameters indicative of the proteolytic degradation or softening of the dough due to protease activity. Thus, ultrasound can be considered a low cost and rapid tool, complementary to conventional test, for wheat flour characterization.     

How to work with one-dimensional quadratic maps

We analyse some identifiers which can univocally identify hyperbolic components and Misiurewicz points of one-dimensional quadratic maps. After seeing the equivalence among the different identifiers and how to go from one to another, we show which are the best for some specific tasks. Likewise, we present the analytic expressions, some of them shown for the first time in this paper, to calculate these identifiers. Some experimental considerations are taken into account.     

Structural changes induced by interactions between thyroid hormones and phospholipid membranes: a Raman Spectroscopy study

Previous reports from our laboratory have shown that thyroid hormones induce changes in the fluidity and permeability of phospholipid bilayers and modify the transmembrane dipolar organization according to their iodine content. The interactions of T2, T3, and T4 with a model membrane of dilauroylphosphatidylcholine in the liquid‐crystalline phase were analyzed by confocal Raman spectroscopy. Insights into the nature of the hormone effects on the membrane properties, as well as the structural adaptations of the hormones in response to the lipid environment were derived from the spectral changes. The series of progressive iodine substituents on the ring‐β allowed us to correlate the hormone effects according to the number and the orientation of the iodine atoms. T4 was responsible for producing the highest alteration in the hydrophobic region of the membrane. Copyright © 2012 John Wiley & Sons, Ltd.     

Experimental characterisation, optimisation and design of erbium-doped silica fibre lasers

A new characterisation method is described using the new theoretical model for erbium-doped silica fibre lasers (EDSFLs) based on the energy conservation principle. Using this method, we obtained absorption and emission coefficients for the lasing wavelength at lasing operating conditions. After that, an experimental procedure to deduce the spectral profiles of the absorption and emission coefficients is also presented. This procedure allows us to obtain the values of these parameters for the whole fluorescence spectrum through measurements of gain profiles under the lasing operation. Once the absorption and emission coefficients are known, the new model can be applied and a comparison with experimental results for two different laser configurations is shown. The theoretical model is proved to be accurate and in addition some equations are developed to allow the design and optimisation of EDSFLs. This revised version was published online in March 2005. In the previous version, the published online date was missing