A practical method,NaOCl-mediated,to prepare thiabendazoles via intramolecular amination reaction

A series of new chlorinated thiabendazoles (6a–m) have been synthesized from readily available anilines and 4-cyanothiazole in moderate to good yields. All synthesized compounds were fully characterized using ¹H NMR, ¹³C NMR, IR, and mass spectrometry. Additionally, the structure of the compound (6f) was confirmed by single-crystal X-ray diffraction. In addition, synthesis of 2-substituted benzimidazoles and 2-phenyl benzothiazole was investigated using our optimized conditions and the outcome is presented herein.     

Single and double A3-coupling (aldehyde-amine-alkyne) reaction catalyzed by an air stable copper(I)-phosphole complex

An air stable copper(I)-phosphole complex, [CuCl{2,5-bis(2-thienyl)-1-phenylphosphole}₂] (1), was utilized as a catalyst in single and double A³-coupling reactions for preparing mono- and bi-propargylamines. A variety of aldehydes, amines and terminal alkynes were tested. Most of these reactions led to formation of the expected propargylamines in good yields using low amounts catalyst and obviating both the use of purified reagents as employ of a glovebox.     

Immobilization and Stabilization of Beta-Xylosidases from Penicillium janczewskii

β-Xylosidases are critical for complete degradation of xylan, the second main constituent of plant cell walls. A minor β-xylosidase (BXYL II) from Penicillium janczewskii was purified by ammonium sulfate precipitation (30% saturation) followed by DEAE-Sephadex chromatography in pH 6.5 and elution with KCl. The enzyme presented molecular weight (MW) of 301 kDa estimated by size exclusion chromatography. Optimal activity was observed in pH 3.0 and 70–75 °C, with higher stability in pH 3.0–4.5 and half-lives of 11, 5, and 2 min at 65, 70, and 75 °C, respectively. Inhibition was moderate with Pb⁺² and citrate and total with Cu⁺², Hg⁺², and Co⁺². Partially purified BXYL II and BXYL I (the main β-xylosidase from this fungus) were individually immobilized and stabilized in glyoxyl agarose gels. At 65 °C, immobilized BXYL I and BXYL II presented half-lives of 4.9 and 23.1 h, respectively, therefore being 12.3-fold and 33-fold more stable than their unipuntual CNBr derivatives (reference mimicking soluble enzyme behaviors). During long-term incubation in pH 5.0 at 50 °C, BXYL I and BXYL II glyoxyl derivatives preserved 85 and 35% activity after 25 and 7 days, respectively. Immobilized BXYL I retained 70% activity after 10 reuse cycles of p-nitrophenyl-β-D-xylopyranoside hydrolysis.

     

A New Synthesis of Charge‐Neutral Tris‐Pyrazolyl and ‐Methimazolyl Borate Ligands

The dimethylamine in the adducts [(HNMe₂)B(azolyl)₃] (azolyl=methimazolyl, pyrazolyl), obtained by reaction of the azole with B(NMe₂)₃, can readily be substituted with a range of nitrogen donors to provide new charge‐neutral, tripodal ligands in high yield. This observation has led to a revision of an earlier interpretation of the mechanism of the formation of these species. The donor properties of the ligands [(nmi)B(azolyl)₃] (nmi=N‐methylimidazole) have been compared with their anionic analogues [HB(azolyl)₃]^? by synthesis of their manganese(I)–tricarbonyl complexes and comparison of their infrared ν_CO energies. This comparison indicates that the new neutral ligands are only marginally weaker donors than the corresponding anionic hydrotris(azolyl)borate ligands. This may be explained by the ability of the attached nmi ring to stabilize a positive charge remotely from the coordinated metal, which may also account for the fact that the [(nmi)B(pyrazolyl)₃] ligand is a substantially stronger donor than the similarly neutral tris(pyrazolyl)methane ligand.     

Simultaneous determination of angiotensins II and 1-7 by capillary zone electrophoresis in plasma and urine from hypertensive rats

We describe the procedure developed for the simultaneous detection and quantification of angiotensin II and angiotensin-(1-7), by capillary zone electrophoresis with UV detection by photodiode-array, at a wavelength of 200 nm, in the plasma and urine from hypertensive rats. Optimal separation was achieved with a 100 mM boric acid + 3 mM tartaric acid + 10 fM gold (III) chloride electrolyte solution at pH 9.80. The applied voltage was 30 kV and the capillary temperature was kept constant at 20 °C. The method was over the concentration range of 0.01-500 pmol/mL. All determination coefficients were higher or equal to 0.9985. Limits of detection and quantification for angiotensin II were 0.0110 pmol/mL (S/N = 3) and 0.0195 pmol/mL (S/N = 5), respectively. While for angiotensin-(1-7), the limits were 0.0112 pmol/mL (S/N = 3) and 0.0193 pmol/mL (S/N = 5), respectively. The present method offers a time-saving way to simultaneous determination of angiotensin II and angiotensin-(1-7), since it can be completed in 10 min, compared to other methodologies reported in the literature for capillary electrophoresis and liquid chromatography, which require more than 1 h for analysis of complex matrices, such as plasma and urine. The procedure is illustrated by experiments that quantify simultaneously angiotensin II and angiotensin-(1-7) in plasma and urine from hypertensive and normotensive rats, with and without antihypertensive treatment. The levels of angiotensin II and angiotensin-(1-7) detected in the experimental model, resulted in a recovery of 99.00-106.01% and a reproducibility of less than 10%. The proposed analytical method is a use full tool for the simultaneous detection of angiotensin II and angiotensin-(1-7) implicated in vascular remodeling in pathologies such as hypertension.     

Flow injection system for the on-line preconcentration of Pb by cloud point extraction coupled to USN–ICP OES

A novel method for the determination of Pb by on-line cloud point extraction coupled to inductively coupled plasma optical emission spectrometry with ultrasonic nebulization (USN–ICP OES) is presented. The cloud point system was formed in the presence of non-ionic micelles of polyethyleneglycolmono-p-nonylphenylether (PONPE 7.5) and was retained in a minicolumn filled with particles of PTFE. Since the micelles of PONPE were able to extract Pb from the solutions, the use of a complexing reagent was not necessary. Afterwards, the surfactant-rich phase containing the analyte was removed from the minicolumn with nitric acid and introduced into the ultrasonic nebulizer. A total enhancement factor of 150 was obtained for a preconcentration time of 3.3 min, with respect to the direct determination of Pb by conventional ICP OES. The values of the detection (3σ) and quantification (10σ) limits for the preconcentration of 10 mL of sample solution were 0.09 µg L^{− 1} and 0.2 µg L^{− 1} respectively. The precision, expressed as the relative standard deviation (RSD), for 10 replicate determinations at 5.0 µg L^{− 1} Pb level was 6.0%. Verification of the accuracy was carried out by analysis of two certified reference materials (NIST SRM 1640e and VKI QC Metal LL1). The method was successfully applied to the determination of Pb in drinking water samples.     

Co(II), Cu(II) and Zn(II) dinuclear complexes of a polypodal ligand containing phenolate and pyridyl donor groups

Acetate and perchlorate dinuclear metal complexes of Co(II), Cu(II) and Zn(II) with the cresolate polypodal ligand having mixed phenolate and pyridyl pendant functionalities, H₃L, have been synthesized. The complexes were characterized by microanalysis, LSI mass spectrometry, IR, UV–Vis spectroscopy, magnetic studies and conductivity measurements. Crystal structures of H₃L, [Cu₂(HL)(OAc)(H₂O)₂](OAc)·1.5H₂O and [Zn₂L(CH₃OH)₃](ClO₄)CH₃OH·2H₂O complexes, have been also determined.     

Internal standard in flow injection analysis with amperometric detection

In this work, we describe for the first time the use of the internal standard method in flow injection analysis (FIA) with amperometric detection. The method is based on the application of sequential potential pulses to the working electrode in an electrochemical flow cell. The sequence of potential pulses is selected in such a way that the analyte and internal standard compound are detected and monitored individually and independently at the same working electrode. This approach compensates for random errors associated with variations of flow rate, injection volume, ionic strength difference between standards and samples, and accidental insertion or formation of air bubbles in the carrier stream. In addition, this method can overcome the major drawback of amperometric detection using solid electrodes, which is gradual electrode passivation. To illustrate the potential of this method, the flow-injection amperometric detection of uric acid using [Fe(CN)₆]^3? as an internal standard (IS) is presented as an example.     

The lithium–thiophene interaction: a critical study using highly correlated electronic structure approaches of quantum chemistry

The fundamental multicentric interaction of a lithium atom with a single thiophene ring is addressed. A systematic study of the interaction energy (IE) and geometry for the Li–T charge-transfer complex is done at the MP2 and CCSD(T) levels using increasingly large basis sets up to aug-cc-pVQZ (AVQZ). Basis set superposition errors (BSSE) are evaluated and shown to have a major impact on the value of the IE. The Fixed-Node Diffusion Monte Carlo (FN-DMC) method is used as an alternative basis-set-free approach to obtain what is likely to be the most accurate estimate of the IE obtained so far. While counterpoise-corrected MP2/AVQZ and CCSD(T)/AVTZ interaction energies are found to be ?3.8 and ?7.5 kcal/mol, the FN-DMC method yields +1.3 ± 1.7 kcal/mol. The slow convergence of the ab initio IE (and some key structural parameters) with respect to basis set quality and the discrepancy with the FN-DMC result is discussed. A visualization of the electron pairing using the electron pair localization function (EPLF) for the Li-doped versus undoped thiophene is also presented.