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In this contribution, we report a straightforwardly and easily one-step synthesis of a small family of composites based in polyaniline grafted on HB2 graphite (PANI@UG) and their copper-doped derivatives (Cu50PANI@UG5-6). The PANI@UG composites were synthesized through electrochemical polymerization using cyclic voltammetry (CV) in three different acidic media: i) acetic acid (AcOH) at high and low concentration (12 and 1â M, using KCl as electrolytic support); ii) a mixture of AcOH and sulfuric acid (H2SO4, which have two roles: as electrolytic support and proton source) and iii) a mixture of acetonitrile (NCCH3) and H2SO4, under atmospheric conditions. Once the best conditions were achieved, our next step was focused on obtaining the Cu50PANI@UG5-6 composites using a solution of aniline and CuSO4 (50â mM) in AcOH:H2SO4 and NCCH3:H2SO4 solutions, respectively. All composites were characterized by CV, FT-IR, SEM and MALDI-TOF experiments. So, the current value was enhanced for the Cu50PANI@UG6 composite, which have three potential catalytical applications in: i) HClO4 acid sensing, ii) click chemistry and iii) sunlight drive photo-activation of H2O2.
RESUMO
RATIONALE: Quantification of small molecules by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) is challenging yet attractive, due to micro-scale procedural simplicity, high throughput and lack of memory effects. Since these features are important while analyzing trace elements in quality control schemes, MALDI-TOFMS was used for the determination of copper (Cu) and lead (Pb) in tequila with quantification carried out by partial least squares regression (PLS2) and by univariate calibration (UC). METHODS: In the proposed procedure, Bi(III) was added as internal standard (IS), diethyldithiocarbamate complexes were formed (pH 7.4) and extracted into chloroform; after solvent evaporation and re-constitution in acetonitrile, the sample was co-crystallized with α-cyano-4-hydroxycinnamic acid on a steel target. From the acquired mass spectra, UC was performed using IS-normalized signals of the monoisotopic ions of analytes, and the m/z range 350-513 was used for PLS2. Accuracy was tested by recovery experiments and by inductively coupled plasma (ICP)-MS analysis. RESULTS: When compared with direct analyte signal measurements, application of IS yielded enhanced analytical performance using either UC or PLS2; the method quantification limits were: 11.1 µg L-1 , 23.4 µg L-1 for Cu and 89.8 µg L-1 , 97.1 µg L-1 for Pb, respectively. In tequila, MALDI-TOFMS and ICP-MS provided consistent results for Cu (165-2599 µg L-1 ); Pb was not detected in any sample by MALDI-TOFMS, yet recoveries obtained after standard addition were indicative of acceptable accuracy (400 µg L-1 Pb added; recoveries: 91.2-108% for UC and 98.8-120% for PLS2). CONCLUSIONS: New experimental evidence has been provided supporting the inclusion of trace metals quantification within a range of MALDI-TOFMS applications. Slightly better results were obtained for UC as compared with PLS2 yet both methods can be recommended for testing the compliance of Cu and Pb levels with Official Mexican Norm. Of note, while using PLS2, there is no need for signal integration nor for IS normalization.
RESUMO
C-Br bond activation followed by a C-C coupling reaction of the 2-bromo-pyridyl unit of [1-phenyl-2-(6-bromopyridin-2-yl)-benzoimidazole] was performed by Pd(CH(2)CMe(2)-o-C(6)H(4))(η(4)-COD). Two new seven membered palladacycles were obtained. A combined experimental and theoretical DFT study elucidates the mechanism for this reaction.