Phosphine-free Suzuki cross-coupling reaction: a mild and selective method for the carbon–carbon bond formation in aqueous tea extract

A mild and selective protocol has been developed for the palladium-catalyzed phosphine-free Suzuki cross-coupling reaction of aryl bromides with arylboronic acids in aqueous tea extract at room temperature. It is noteworthy that the aqueous tea extract plays an important role in the reaction, and various functional groups are tolerated under the optimized conditions. The reactions proceeded with very good chemoselectivity in favor of the bromo instead of the chloro group even at higher temperatures. Furthermore, this protocol could be applied to the cross-coupling of 4-bromoindole without protecting the base sensitive amine group with arylboronic acids in moderate to excellent yields.     

Effect of Gd3+ doping on structural,optical and frequency-dependent dielectric response properties of pseudo-cubic BaTiO3 nanostructures

We report on the structural, optical and dielectric characterization of solid state derived, pseudo-cubic nanoscale barium titanates (BTs) with gadolinium (Gd³⁺) as substitutional dopant. Referring to X-ray diffractograms, apart from the BT peaks related to perovskite structure, the non-existence of any additional peaks due to byproducts has revealed that Gd³⁺ has undergone substitutional doping into the BT host lattice. The well-separated BT nanoparticles of typical size ～10–15 nm were observed through electron microscopy studies. Following a direct, allowed type carrier transition (n=1/2), a reduction in the optical band gap value (from 3.28 to 3.255 eV) was observed when the Gd-doping level was varied within 0–7 %. Conversely, the Urbach energy followed an increasing trend, from a value of 0.741 to 1.879 eV. Furthermore, the dielectric constant showed a decreasing tendency with doping content and with increasing frequency. However, in the low-frequency region, the loss tangent (tanδ), which is the combined result of orientational polarization and electrical conduction, was found to be quite high in the doped samples as compared to their un-doped counterpart. The frequency-dependent electrical data were also analyzed in the framework of conductivity and impedance formalisms. In particular, the ac conductivity which varies as ～ω ^s approaches ideal Debye behavior (s→1) for a low Gd level and a higher doping concentration did not show improved dielectric feature of the host. The incorporation of rare-earth (Gd³⁺) ions into the BT host system could greatly manifest dielectric relaxation and carrier conduction mechanisms, in a given frequency range, and thus can find immense scope in miniaturized nanoelectronic elements including ceramic capacitors and transducers.     

The cytidinium—cytidine complex: infrared and Raman spectroscopic studies

Using IR and Raman spectra, it is shown that the sytidinium cation hydrogen bonds to cytidine to form a stable 1:1 complex, in both aqueous solution (pH ~ 3.3) and as a solid. The spectra indicate that the proton is located asymmetrically in the NH?N bond of the complex, on the vibrational time scale, in both solution and the solid. The perdeuterated systems were also examined; their spectra support these conclusions.     

Intersalation Reactions of Trisdiimine Metal Complexes with Montmorillonite Clay: A New Approach

Intersalation reactions of the complexes [Ni(L-L)(3)]SO(4) and [Ni(L-L)(3)]Cl(2) (L-L=1,10-phenanthroline (phen), 2,2'-bipyridyl (bpy)), with Na-montmorillonite carried out under different dynamic conditions such as ultrasonic irradiation, refluxing, autoclaving, and vigorous stirring showed that under ultrasonic irradiation, maximum adsorption of the metal complexes occurred within a period of 30 min. Metal complexes containing the phen ligand showed higher adsorption than those containing bpy. Maximum adsorption up to about three times the cation exchange capacity (CEC) of the clay was observed. Aggregated (basal spacing d(001) 12.5 ?) Na-montmorillonite, in treatment with a higher amount (>CEC) of metal complexes, formed monolayered (basal spacing d(001) 17.6 ?) species, while with predispersed clay, bilayered (basal spacing d(001)>28 ?) or pseudo-trilayer (basal spacing d(001)>32 ?) species were formed. The bilayered species were thermally stable up to 250 degrees C and above this temperature monolayered species were formed. The thermal stability of the intersalated species was higher than that of the intercalated ones. X-ray diffraction, UV-visible, IR-spectroscopy, thermal analyses, and surface area measurements were used for characterization of the products. Copyright 2001 Academic Press.     

On the Single-machine Scheduling Problem with Tardiness Penalties

The n-job, single-machine total tardiness problem is considered in this paper. A branching algorithm based on three theorems is proposed to generate a reduced set of candidate sequences. The computational results indicate that the proposed algorithm provides a smaller set of candidate sequences than the DP algorithm of Schrage and Baker.     

Thermal dependency of RAG1 self-association properties

Background  

Functional immunoglobulin and T cell receptor genes are produced in developing lymphocytes by V(D)J recombination. The initial site-specific DNA cleavage steps in this process are catalyzed by the V(D)J recombinase, consisting of RAG1 and RAG2, which is directed to appropriate DNA cleavage sites by recognition of the conserved recombination signal sequence (RSS). RAG1 contains both the active site and the RSS binding domains, although RAG2 is also required for DNA cleavage activity. An understanding of the physicochemical properties of the RAG proteins, their association, and their interaction with the RSS is not yet well developed.     

Adsorption and surface complexation of trimesic acid at the alpha-alumina-electrolyte interface

Adsorption kinetics, adsorption isotherms and surface complexation of trimesic acid onto alpha-alumina surfaces were investigated. Adsorption kinetics of trimesic acid with an initial concentration of 0.5 mM onto alpha-alumina surfaces were carried out in batch method in presence of 0.05 mM NaCl (aq) at pH 6 and 298.15, 303.15 and 313.15 K. Adsorption isotherms were carried out at 298.15 K, pH 5-9, and 0.05 mM NaCl (aq) by varying trimesic acid concentration from 0.01 to 0.6 mM. Three kinetics equations such as pseudo-first-order, pseudo-second-order and Ho equations were used to estimate the kinetics parameters of the adsorption of trimesic acid on the alpha-alumina surfaces. Ho equation fits the experimental kinetics data significantly better and the estimated equilibrium concentration is in excellent agreement with the experimental value. The adsorption data were fitted to Freundlich and Langmuir adsorption model and the later best fits the adsorption isotherms. Comparison of adsorption density of trimesic acid with that of benzoic and phthalic acids follows the sequence: benzoic acid < trimesic acid < phthalic acid. The negative activation energy and the Gibbs free energy for adsorption indicate that the adsorption of trimesic acid onto alpha-alumina is spontaneous and facile. DRIFT spectroscopic studies reveal that trimesate forms outer-sphere complexes with the surface hydroxyl groups that are generated onto alpha-alumina surfaces in the pH range of the study.     

Bromamine-T as an efficient amine source for Sharpless asymmetric aminohydroxylation of olefins

Asymmetric aminohydroxylation of various olefins was carried out using bromamine-T as nitrogen source in the presence of (DHQ)₂PHAL ligand. The new nitrogen source has been found to be effective in terms of yield and reaction time. The optical purities of the products could be obtained with up to 99% ee.