PTSA catalyzed simple and green synthesis of benzothiazole derivatives in water

Abstract  

p-Toluenesulfonic acid (10 mol%) was found to be an effective and efficient catalyst for the synthesis of 2-substituted benzothiazoles from aromatic aldehydes and 2-aminothiophenol in moderate to excellent yields in water. This method provides a simple and efficient protocol in terms of mild reaction conditions, clean reaction profiles, small quantity of catalyst, and simple workup procedure.     

Synthesis and characterization of nickel(II) complexes with three potentially hexadentate Schiff-base ligands and polyamines: X-ray crystal structure determination of one nickel(II) complex

Three new potentially hexadentate N₄O₂ Schiff-base ligands (H₂L¹, H₂L² and H₂L³) were prepared from the reaction of the polyamines N,N′-bis(2-aminophenyl)-1,2-ethanediamine (L¹), N,N′-bis(2-aminophenyl)-1,3-propanediamine (L²) and N,N′-bis(2-aminophenyl)-1,4-butanediamine (L³), respectively with salicylaldehyde. Reaction of the Schiff bases with Ni(II) salts in the presence of N(Et)₃ gave the neutral complexes [NiL⁴], [NiL⁵] and [NiL⁶]. Ni(II) complexes of the polyamines were also prepared. One of complexes [Ni(L¹)(MeCN)₂](ClO₄)₂·MeCN has been characterized through X-ray diffraction methods.     

Parallel vector analysis based soft resolution of spectral data from pH‐metric titration using symmetry constraint

In this study, a soft method is proposed to calculate concentration and spectral profiles for the two‐way spectral data from dissociation equilibria of polyprotic acids (H_nA). This method has four main distinct steps: (i) a fixed size moving window evolving factor analysis (FSMWEFA) was used to identify the local rank map, (ii) WFA was applied to calculate the concentration profiles of H_nA and Aⁿ⁻ (selection of the window for application of WFA was performed using EFA), (iii) PVA was used to calculate H_{n − 1}A to HA spectral profiles, and (iv) a symmetry constraint, in addition to the non‐negativity constraint, was utilized to obtain the unique concentration and spectral profiles from different acceptable sets of profiles. In the absence of any selective region in the spectral data, the proposed soft method resulted in unique solution without rotational ambiguity. This study is the first application of symmetry constraint on concentration profiles. The rotational ambiguity drastically decreased on considering the constraint of symmetry of the H_{n − 1}A and HA concentration profiles, in addition to non‐negativity of profiles. Simulated examples were used to confirm these approaches. Effect of closeness of dissociation constants on the estimated values of constants was investigated. The results showed that when the difference between pK_a values is more than 1.2, the obtained errors in the estimation of pK_a values are less than about 6.5%. The considered real data were from pH‐metric titration of fluorescein. The obtained spectral and concentration profiles and the estimated pK_a values for fluorescein were in good agreement with the previously reported data. Copyright © 2009 John Wiley & Sons, Ltd.     

Prediction of sound velocity and compressibility via molecular simulation at fixed entropy

A molecular-level simulation route is proposed to compute the isentropic thermodynamic properties in a fluid system by Monte Carlo simulation at fixed entropy. The method involves computation of the pressure response of a system to an infinitesimal change in system density by introduction of a single molecule, while retaining the system volume as well as the absolute molar entropy. The probability for accepting a change in temperature during the Monte Carlo moves was weighted against the argument proposed by Smith et al. [W.R. Smith, M. Lísal, I. Nezbeda, Chem. Phys. Lett. 426 (2006) 436–440]. Application to fluid argon has confirmed superior accuracy for the technique within the gas state to yield results within 1.2% of the measured values for the range of thermodynamic conditions investigated.     

Preparation and biological evaluation of radiogallium labeled glucagon for SPECT imaging

In this work, recently prepared ⁶⁷Ga-labeled glucagon (⁶⁷Ga-DTPA-GCG) for imaging studies (radiochemical purity >94%; HPLC, S.A. 296–370 GBq/mM) was used in biological studies. The wild-type rat biodistribution results, 2 h post injection, demonstrated high tissue:muscle ratios for target tissues (liver, kidney, heart, spleen, fat intestine stomach and pancreas), 234, 18.45, 7.12, 1.75, 128.7, 4.9, 6.3 and 1.11, respectively. The tracer binding capacity using freshly prepared rat brain homogenate demonstrated significant specific binding of the tracer to neuronal GCG receptors (⁶⁷Ga-DTPA-GCG/⁶⁷Ga:3 and ⁶⁷Ga-DTPA-GCG/⁶⁷GaDTPA:2.2 at 90 min). SPECT images also demonstrated target specific binding of the tracer at 4 h. The data suggests the tracer is accumulated in GCGR rich tissues 2–4 h post injection, suggesting potentials of the tracer for future imaging studies in glocagonoma models.     

Characterization of a peptide family from the skin secretion of the Middle East Tree Frog Hyla savignyi by composition‐based de novo sequencing

A new tryptophyllin‐like peptide family was found in the skin secretion of the tree frog Hyla savignyi. Peptides were characterized by database‐independent sequencing strategies and specific ion fragmentation features were investigated. Skin secretions from specimens of Hyla savignyi were collected by mild electrical stimulation. Peptides were separated by reversed‐phase nano‐high‐performance liquid chromatography (nanoHPLC) and mass spectra were acquired online by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FTICR‐MS). Peptides were characterized by manual de novo sequencing and by composition‐based sequencing (CBS), appearing mostly as C‐terminal free acids and as their acid amide analogs. Amide peptides yielded lower intensities of y‐type ions after collision‐induced dissociation (CID) than their acid analogs. A mechanism of internal b‐ion formation (positive ion mode) and of CO₂ elimination (negative ion mode) is proposed. We also exemplified phenomena such as the proline effect and formation of non‐direct sequence ions after sequence rearrangements. The occurrence of rearrangement products, of internal ions and of the proline effect made the CID spectra highly complex. CBS analysis nevertheless resulted in successful and highly reliable sequence analysis. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthetic and computational studies of the palladium(iv) system Pd(alkyl)(aryl)(alkynyl)(bidentate)(triflate) exhibiting selectivity in C-C reductive elimination

Synthetic routes to methyl(aryl)alkynylpalladium(iv) motifs are presented, together with studies of selectivity in carbon-carbon coupling by reductive elimination from Pd(IV) centres. The iodonium reagents IPh(C[triple bond, length as m-dash]CR)(OTf) (R = SiMe(3), Bu(t), OTf = O(3)SCF(3)) oxidise Pd(II)Me(p-Tol)(L(2)) (1-3) [L(2) = 1,2-bis(dimethylphosphino)ethane (dmpe) (1), 2,2'-bipyridine (bpy) (2), 1,10-phenanthroline (phen) (3)] in acetone-d(6) or toluene-d(9) at -80 °C to form complexes Pd(IV)(OTf)Me(p-Tol)(C[triple bond, length as m-dash]CR)(L(2)) [R = SiMe(3), L(2) = dmpe (4), bpy (5), phen (6); R = Bu(t), L(2) = dmpe (7), bpy (8), phen (9)] which reductively eliminate predominantly (>90%) p-Tol-C[triple bond, length as m-dash]CR above ～-50 °C. NMR spectra show that isomeric mixtures are present for the Pd(IV) complexes: three for dmpe complexes (4, 7), and two for bpy and phen complexes (5, 6, 8, 9), with reversible reduction in the number of isomers to two occurring between -80 °C and -60 °C observed for the dmpe complex 4 in toluene-d(8). Kinetic data for reductive elimination from Pd(IV)(OTf)Me(p-Tol)(C[triple bond, length as m-dash]CSiMe(3))(dmpe) (4) yield similar activation parameters in acetone-d(6) (66 ± 2 kJ mol(-1), ΔH(?) 64 ± 2 kJ mol(-1), ΔS(?)-67 ± 2 J K(-1) mol(-1)) and toluene-d(8) (E(a) 68 ± 3 kJ mol(-1), ΔH(?) 66 ± 3 kJ mol(-1), ΔS(?)-74 ± 3 J K(-1) mol(-1)). The reaction rate in acetone-d(6) is unaffected by addition of sodium triflate, indicative of reductive elimination without prior dissociation of triflate. DFT computational studies at the B97-D level show that the energy difference between the three isomers of 4 is small (12.6 kJ mol(-1)), and is similar to the energy difference encompassing the six potential transition state structures from these isomers leading to three feasible C-C coupling products (13.0 kJ mol(-1)). The calculations are supportive of reductive elimination occurring directly from two of the three NMR observed isomers of 4, involving lower activation energies to form p-TolC[triple bond, length as m-dash]CSiMe(3) and earlier transition states than for other products, and involving coupling of carbon atoms with higher s character of σ-bonds (sp(2) for p-Tol, sp for C[triple bond, length as m-dash]C-SiMe(3)) to form the product with the strongest C-C bond energy of the potential coupling products. Reductive elimination occurs predominantly from the isomer with Me(3)SiC[triple bond, length as m-dash]C trans to OTf. Crystal structure analyses are presented for Pd(II)Me(p-Tol)(dmpe) (1), Pd(II)Me(p-Tol)(bpy) (2), and the acetonyl complex Pd(II)Me(CH(2)COMe)(bpy) (11).     

Effect of ZnO nanoparticles on kinetics of thermal degradation and final properties of ethylene–propylene–diene rubber systems

The morphology, thermal degradation behavior in addition to static and dynamic mechanical properties of various ethylene?Cpropylene?Cdiene (EPDM) rubber compounds containing nano-zinc oxide (NZnO) were investigated compared to those of EPDM with ordinary-sized ZnO (OSZnO). The field-emission scanning electron microscopy studies showed that unlike the conventional system, the formation of large size ZnO agglomerates was discouraged for NZnO filled systems. Thermogravimetric analysis (TG) revealed that the thermal degradation of EPDM system was delayed upon the inclusion of NZnO instead of OSZnO in the compound. The kinetic analysis of TG data based on Friedman and Kissinger methods showed that the nanocomposite samples exhibited higher activation energy (E _a ) and lower order of reaction (n) over the conventional system, suggesting the enhancement of thermal stability upon decreasing ZnO particle size. The results obtained from dynamic mechanical analysis and static mechanical characterizations in terms of hardness, resilience, and abrasion tests interestingly indicated that NZnO not merely could act as a thermal insulator, but also could perform as a nano-filler to improve the final performance of EPDM elastomers.     

Tetrafluorobenzyne thermochemistry: experiment and theory

Gas-phase thermodynamic properties of 1,2,3,4-tetrafluorobenzyne (1 H-(2)) were determined by Fourier transform mass spectrometry and ab initio and density functional theory methods. 1,2,3,4-Tetrafluorobenzyne radical anion was generated by abstraction of a proton and a hydrogen atom upon reaction of 1,2,3,4-tetrafluorobenzene (1) with O(-.). The resulting structure was confirmed by converting it to a species which could be independently prepared. Bracketing results provided the proton affinity of 1,2,3,4-tetrafluorobenzyne radical anion and the electron affinities of 1,2,3,4-tetrafluorobenzyne and 1,2,3,4-tetrafluorophenyl radical. These measured values were combined in a thermodynamic cycle to provide the heat of hydrogenation of 1 H(2) (DeltaH degree (hyd) = 367 +/- 18 kJ mol(-1)) and the first and second CH bond dissociation energies of 1 (481 +/- 11 and 321 +/- 13 kJ mol(-1)). The same approach failed for the meta and para isomers, but their energetics were examined using B3LYP and CCSD(T) computations.     

Optimization of the extraction of paclitaxel from Taxus baccata L. by the use of microwave energy

A simple and rapid microwave-assisted extraction (MAE) procedure was developed and optimized for the extraction of paclitaxel (Taxol) from the needles of yew trees Taxus baccata L. grown in Iranian habitats. The samples, immersed in a methanol-water mixture, were irradiated with microwaves in a closed-vessel system. The method was evaluated using a factorial design approach based on parameters such as extraction time, temperature, methanol concentration in water (v/v), and the ratio of grams of sample to 10 mL of solvent. Statistical treatment of the results revealed that the selected parameters were all significant except the extraction time. Optimum conditions would be 1.5 g samples in 10 mL solvent (90% methanol), an extraction temperature of 95 degrees C, and an extraction time of 7 min. The extracts has been analyzed by reverse-phase high-performance liquid chromatography with UV detection (LC/UV) at 227 nm for quantification. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used for confirmation. The main advantage of the proposed MAE method versus conventional solvent extraction (CSE) are the considerable reductions in time (7 min versus 16 h) and in solvent consumption (20 mL versus 150 mL). The MAE procedure yielded extracts that could be analyzed directly without any preliminary clean-up or solvent exchange steps. Both extraction methods show RSDs lower than 10% and lead to comparable recoveries of paclitaxel (87-92%).