Synthesis and characterization of copper(II) and nickel(II) complexes of the Schiff base derived from 2-(2-aminophenyl)benzimidazole and salicylaldehyde

Summary Copper(II) and nickel(II) complexes with the Schiff base derived from 2-(2-aminophenyl)benzimidazole and salicylaldehyde, L, have been prepared. They are of the general types ML₂X₂ (M = Ni or Cu and X = Cl, Br, NO₃ or ClO₄) and NiL(NCS)₂.The compounds have been characterized by elemental analyses, magnetic measurements, e.s.r., electronic and i.r. spectra studies. The i.r. spectra suggest that the molecule, and not the anion, of the Schiff base is coordinated as a bidentate ligand with the metal ion. Possible structures for the complexes have been proposed.     

Studies on diastereoselective reduction of cyclic β-ketoesters with boron hydrides. Part 4: The reductive profile of functionalized cyclohexanone derivatives

Reduction of 2-allyl-2-carboalkoxycyclohexanones (3d-f), 2-propyl-2-carboethoxycyclohexanone (3g) and 2-benzyl-2-carboethoxycyclohexanone (3h) with boron hydrides in the presence and absence of several chelating agents were studied. Molecular modeling studies using semiempirical PM3 method were performed in order to find a suitable explanation of the diastereoselection of ketone carbonyl faces during the reductive process, which yielded trans-2-allyl-2-carboethoxycyclohexanol (6e) and cis-2-allyl-2-carboethoxycyclohexanol (7e) in good diastereomeric excess by using inexpensive sodium and tetrabutylammonium borohydrides.     

Selective determination of trimethylamine in air by liquid chromatography using solid phase extraction cartridges for sampling

The selective determination of trimethylamine (TMA) in air by liquid chromatography is reported. Sampling is effected by flushing air through C18-packed solid-phase extraction (SPE) cartridges at a flow rate of 15 mL/min for 15 min. Next, TMA is desorbed from the cartridges and injected into the chromatographic system. The analyte is then selectively retained on a precolumn (20 mm x 2.1 mm i.d., packed with 30 microm, Hypersil C18 phase), and derivatized on-line by injecting 9-fluorenylmethyl chloroformate (FMOC). Finally, the TMA-FMOC derivative is transferred to the analytical column (125 mm x 4 mm i.d., LiChrospher 100 RP18, 5 microm), and monitored at 262 nm. The method was applied to the measurement of TMA in air in the 0.25-2.5 microg interval (equivalent to concentrations of TMA of 1.1-11 mg/m3), providing good linearity, reproducibility and accuracy. The mean recovery of TMA was (96 +/- 7%) (n = 12), and the limit of detection was 0.05 microg. The proposed procedure allows the selective determination of TMA in the presence of other primary and secondary short-chain aliphatic amines.     

Synthesis,Structure and Reactivity of [1, 2‐Bis(diphenylphosphinite)ethane]bromotricarbonylmanganese(I) with Reactions of Phosphites,Phosphonites. and Phosphinites

The manganese carbonyl complex [MnBr(CO)₃ L ] ( 1 ), where L = Ph₂POCH₂CH₂OPPh₂, was prepared by reacting [MnBr(CO)₅] with the bidentate ligand 1, 2‐Bis(diphenylphosphinite)ethane. From this compound and the appropriate phosphite, phosphinite or phosphonite ligands were synthesized the complexes [MnBr(CO)₂ LL ′], where L ′ = P(OMe)₃ ( 2 ) or P(OEt)₃ ( 3 ) and [MnBr(CO)₃ L ′₂], where L ′ =PPh(OEt)₂ ( 4 ) or PPh₂(OEt) ( 5 ). The obtained compounds have been characterized by elemental analysis, mass spectrometry, IR and NMR (¹H, ¹³C and ³¹P) spectroscopies and X‐ray diffractometry for the complexes 1 , 4 and 5 .     

Determination of cadmium,aluminium, and copper in beer and products used in its manufacture by electrothermal atomic absorption spectrometry

Procedures were developed for determining cadmium, aluminium, and copper in beer and the products used in its manufacture by electrothermal atomic absorption spectrometry. Beer samples were injected into the furnace and solid samples were introduced as suspensions after preparation in a medium containing hydrogen peroxide, nitric acid, and ammonium dihydrogen phosphate for cadmium atomization. Calibration was performed with aqueous standards, and characteristic masses and detection limits were, respectively, 1 and 0.3 pg for cadmium, 18 and 5.4 pg for aluminium, and 5.6 and 6.8 pg for copper. Different samples of beer, wort, brewer's yeast, malt, raw grain, and hops were analyzed by the proposed procedures. Cadmium was found in low concentrations (0.001-0.08 microg/g and 0-1.3 ng/mL); copper (3-13 microg/g and 25-137 ng/mL) and aluminium (0.6-9 microg/g and 0.1-2 microg/mL) were found at higher levels. The reliability of the procedure was confirmed by comparing the results obtained with others based on microwave oven sample digestion, and by analyzing several certified reference materials.     

Fluorescence lifetimes of some Harmala and Rauwolfia alkaloids

Quantum yields and lifetimes of several derivatives of the Peganum Harmala and Rauwolfia alkaloids have been measured. The natural lifetimes of these alkaloids have been calculated from a modified form of the Strickler—Berg equation and the results are compared with the observed lifetimes.     

Early-late heterobimetallic alkoxides as model systems for late-transition-metal catalysts supported on titania

Titanium complexes with chelating alkoxide ligands [TiCp*(O(2)Bz)(OBzOH)] (1) and [TiCp*(Me)((OCH(2))(2)Py)] (2) were synthesised by reaction of [TiCp*Me(3)] (Cp*=eta(5)-C(5)Me(5)) with 2-hydroxybenzyl alcohol ((HO)(2)Bz) and 2,6-pyridinedimethanol ((HOCH(2))(2)Py), respectively. Complex 1 reacts with [(M(mu-OH)(cod))(2)] (M=Rh, Ir) to yield the early-late heterobimetallic complexes [TiCp*(O(2)Bz)(2)M(cod)] [M=Rh (3), Ir (4)]. Carbon monoxide readily replaces the COD ligand in 3 to give the rhodium dicarbonyl derivative [TiCp*(O(2)Bz)(2)Rh(CO)(2)] (5). Compound 2 reacts with [(M(mu-OH)(cod))(2)] (M=Rh, Ir) with protonolysis of a Tibond;Me bond to give [TiCp*((OCH(2))(2)Py)(mu-O)M(cod)] [M=Rh (6), Ir (7)]. The molecular structures of complexes 3, 5 and 7 were established by single-crystal X-ray diffraction studies.     

Complete 1H and 13C NMR assignments of aurasperone A and fonsecinone A, two bis-naphthopyrones produced by Aspergillus aculeatus

Complete assignments of 1H and 13C NMR chemical shifts of the polyketides aurasperone A and fonsecinone A were made by means of nuclear Overhauser enhancement and heteronuclear NMR correlation experiments. These compounds were isolated for the first time from Aspergillus aculeatus, an endophytic fungus obtained from leaves of Melia azedarach(Meliaceae).     

Improved coupled-column liquid chromatographic method for the determination of glyphosate and aminomethylphosphonic acid residues in environmental waters

An existing method for the determination of glyphosate and its main metabolite aminomethylphosphonic acid (AMPA) in water has been improved. It is based on precolumn derivatization with the fluorescent reagent 9-fluorenylmethylcloroformate (FMOC) followed by large-volume injection in a coupled-column LC system using fluorescence detection (LC-LC-FD). The derivatization step was slightly modified by changing parameters such as volume and/or concentration of sample and reagents to decrease the limits of quantification (LOQ) of glyphosate and AMPA to 0.1 microg/l. Additionally, the use of Amberlite IRA-900 for preconcentration of glyphosate, prior to the derivatization step, was investigated; the LOQ of glyphosate was lowered to 0.02 microg/l. Drinking, surface and ground water spiked with glyphosate and AMPA at 0.1-10 microg/l concentrations were analysed by the improved LC-LC-FD method. Recoveries were 87-106% with relative standard deviations lower than 8%. Drinking and ground water spiked with glyphosate at 0.02 and 0.1 microg/l were analysed after preconcentration on the anion-exchange resin with satisfactory recoveries (94-105%) and precision (better than 8%).