Suzuki-Miyaura cross-coupling reactions of aryl tellurides with potassium aryltrifluoroborate salts

[reaction: see text] Palladium(0)-catalyzed cross-coupling between potassium aryltrifluoroborate salts and aryl tellurides proceeds readily to afford the desired biaryls in good to excellent yield. The reaction seems to be unaffected by the presence of electron-withdrawing or electron-donating substituents in both the potassium aryltrifluoroborate salts and aryl tellurides partners. Biaryls containing a variety of functional groups can be prepared. A chemoselectivity study was also carried out using aryl tellurides bearing halogen atoms in the same compound. In addition, this new version of the Suzuki-Miyaura cross-coupling reaction was monitored by electrospray ionization mass spectrometry where some reaction intermediates were detected and analyzed.     

Structure functions in nuclei: Quark clusters and size effects

Two of the most interesting ideas to explain the EMC effect, clusters of quarks and confinement size factors, are unable to fully explain the existing data. In this paper we argue that the existence of clusters with different numbers of quarks are in the origin of different size parameters controlling the lowQ ² limit in the QCD evolution and thus we combine the two ideas. As a result we obtain a model for structure functions with two basic effective parameters: the average numberi of nucleons per cluster and the corresponding size parameterR _i . We achieve good agreement with the existing data for a wide range ofQ ²(?2 GeV²) and for all values ofx. Simple parametrizations of the Sea, Gluon and Valence distributions, for pion, nucleon and nuclei, are given. Some applications of the model, in particular to Drell-Yan processes, are discussed.     

Lambda polarization in the K− fragmentation region

Results on Λ polarization in the inclusive reaction K^?p→Λ + X at 12 and 16 GeV/c for 0.6<x<1.0, are presented. These results, obtained with the CERN Omega Spectrometer, show that the polarization is important at large x and increases with p_t over the covered range 0<p_t<1.2 GeV/c. The average polarization for 31 857 lambdas with x>0.6 is P_Λ = 0.35 ± 0.02, along the direction $\text{K}{}^{\mathrm{?}}\text{×}\text{Λ}$. The polarization can be expressed as P(x, p_t) = (0.66±0.03)p_t independent of x in the range covered by the experiment.     

Synthesis and functionalization of N-sulfinyl imines: Sonogashira reaction and copper-catalyzed azide-alkyne cycloaddition

A small library of novel molecules was generated using a rapid and efficient methodology for the synthesis of N-sulfinyl imine triazole compounds. The process involves a coupling step from the Sonogashira cross-coupling reaction and then, in a one-step reaction, deprotection of the trimethylsilyl group and triazole heterocyclic ring formation using a microwave reactor.     

Moving pieces in a proteomic puzzle: mass fingerprinting of toxic fractions from the venom of Tityus serrulatus (Scorpiones, Buthidae).

Scorpion venoms are very complex mixtures of molecules, most of which are peptides that display different kinds of biological activity. These venoms have been studied in the light of their pharmacological targets and their constituents are able to bind specifically to a variety of ionic channels located in prey tissues, resulting in neurotoxic effects. Toxins that modulate Na(+), K(+), Ca(++) and Cl(-) currents have been described in scorpion venoms. Mass spectrometry was employed to analyze toxic fractions from the venom of the Brazilian scorpion Tityus serrulatus in order to shed light on the molecular composition of this venom and to facilitate the search for novel pharmacologically active compounds. T. serrulatus venom was first subjected to gel filtration to separate its constituents according to their molecular size. The resultant fractions II and III, which account for 90 and 10% respectively of the whole venom toxic effect, were further analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS), on-line liquid chromatography/electrospray mass spectrometry (LC/ESMS) and off-line LC/MALDI-TOFMS in order to establish their mass fingerprints. The molecular masses in fraction II were predominantly between 6500 and 7500 Da. This corresponds to long-chain toxins that mainly act on voltage-gated Na(+) channels. Fraction III is more complex and predominantly contained molecules with masses between 2500 and 5000 Da. This corresponds to the short-chain toxin family, most of which act on K(+) channels, and other unknown peptides. Finally, we were able to measure the molecular masses of 380 different compounds present in the two fractions investigated. To our knowledge, this is the largest number of components ever detected in the venom of a single animal species. Some of the toxins described previously from T. serrulatus venom could be detected by virtue of their molecular masses. The interpretation of this large set of data has provided us with useful proteomic information on the venom, and the implications of these findings are discussed.     

Structure elucidation and NMR assignments of two unusual monoterpene indole alkaloids from Psychotria stachyoides

Two unusual monoterpene indole alkaloids, stachyoside ( 1 ) and nor‐methyl‐23‐oxo‐correantoside ( 2 ), have been isolated from the aerial parts of Psychotria stachyoides. The structural elucidation of both compounds was performed by the aid of HRESIMS, FT‐IR, and 1D‐ and 2D‐NMR techniques including COSY, HSQC, HMBC, and NOESY. Copyright © 2010 John Wiley & Sons, Ltd.     

Rheology of viscoelastic mixed surfactant solutions: effect of scission on nonlinear flow and rheochaos

The linear and nonlinear rheology of viscoelastic mixed anionic-zwitterionic surfactant solutions has been systematically investigated. In the linear viscoelastic regime, these systems display nearly Maxwellian behavior with a unique relaxation time, tau0, and a characteristic elastic plateau modulus, G0. Linear rheological data were used to calculate the repitation and breaking times of the micelles, tau(rep) and tau(b), respectively. Surprisingly, the elastic modulus G0 significantly increases with salt concentration c(s), whereas tau(b) decreases by 1 order of magnitude. The strong effect of c(s) on the material parameters and microstructure of rodlike micelles allowed for the systematic investigation of the effect of these parameters on nonlinear flow. For samples with relatively long tau(b), the quasi-static flow diagram (stress vs shear rate) shows a stress peak followed by a metastable branch (a region of decreasing shear stress), whereas for samples with relatively short tau(b), this phenomenon is not observed. Transient flow responses corroborate quasi-static flow findings and further reveal the significance of microscopic dynamic parameters on flow behavior. Shear stress time series were recorded at constant shear rates, and above a critical shear rate, gamma(c2), stress fluctuations are observed. The amplitude of these stress fluctuations, Delta sigma, was found to scale as Delta sigma approximately equal to G0(tau(b)| gamma - gamma(c2)|)beta with beta approximately 0.5. This scaling is observed for micellar systems with tau(b) ranging from 0.12 to 0.01 s and G0 ranging from 1 x 10(3) to 7 x 10(3) dyn/cm2.