Electrochemistry of organometallic compounds. Part II. Oxidations of alkyl and aryl derivatives of bis(salicylaldehyde)ethylenediimine cobalt(III) in dimethylformamide

The influence of the axial organic ligand R on the electrochemical oxidation of the compounds [RCoIII(salen)DMF)], where salen is bis(salicylaldehyde)ethylenediimine, and R CH3, C2H5, n-C3H7, n-C4H9, s-C4H9, i-C4H9, CH2Cl, CF3CH2, c-C6H11CH2, c-C6H11, C6H5, C6H5CH2, p-CH3C6H4CH2, and p-NO2C6H4CH2, was studied by means of cyclic voltametry in dimethylformamide (DMF), 0.2 M in tetraethylammonium perchlorate (TEAP), at 25 and -20°C, with a platinum disc working electrode. The above-mentioned compounds can be classified according to their electrochemical behavior. (a) The complexes with R CH3, C2H5, n-C3H7, n-C4H9, c-C6H11CH2, and C6H5 undergo a reversible one-electron oxidation in the 10-50 V s-1 potential scan range. At slower scan rates, the oxidized product decomposes chemically. At -20°C, this chemical step is slow, and a reversible one-electron electrochemical oxidation is observed. (b) The compounds with R CH2Cl, C6H5CH2, p-CH3C6H4CH2 and p-NO2C6H4CH2 undergo a quasi-reversible one-electron oxidation at room temperaure. At -20°C, the electrochemical process becomes more complex. A following chemical reactions is coupled to the quasi-reversible one-electron transfer. Two reduction peaks are observed. (c) The compounds with R i-C4H9, s-C4H9, and c-C6H11 undergo a reversible one-electron oxidation at -20°C. At room temperature, the irreversible chemical reaction following the electron transfer step is too fast to allow the isolation of the electrochemical step. (d) At -20°C, the derivatives with R C2H5, c-C6H11 CH2 and c-C6H11 are adsorbed at the electrode surface. Evidence indicates that the reagent in these reactions is the pentacoordinated species [RCoIII(salen)]. A linear free-energy relationship between E1/2 (for reversible processes) and the Taft polar parameters o* was obtained with a slope of ρ* = 0.25 ± 0.03. As expected, the benzyl derivatives which present mesomeric effects do not fit this polar correlation. The rated of the electrochemical oxidation is also affected by the nature of the ligand R. For the ligands which are strong electron-withdrawing groups and for the benzyl derivatives, the rate of the electrochemical oxidation of the metal ion decreases at room temperature. At lower temperatures, it is suggested that the oxidation to the CoIV-R species is followed by a chemical reaction in which this complex is partly transformed into a CoIII(R*) species, which is reduced at a much more cathodic potential than the Co(IV) species. © 1979.

Kinetics of the reaction of alkylamines with 7,7,8,8-tetracyanoquinodimethane (TCNQ) in organic solvents

The following sequence of substitution reactions was studied spectrophotometrically in organic solvents: RNH2 + TCNQ →-HCN 7-substituted TCNQ →-HCN +RNH2 7.7-disubstituted TCNQ where R = butyl, octyl, dodecyl, and hexadecyl. The production of 7-(alkylamino)-7,7,8-tricyanoquinodimethanes proceeds via the formation of the anion radical of TCNQ (TCNQ-·) whose rate of appearance was found to be a function of the chain length of R, reaching a maximum for octylamine. The formation of TCNQ-· was sensitive to the solvent polarity and electron-donor power and was associated with a small enthalpy and a highly negative entropy of activation. Above a certain [C8H17NH2] the rate of disappearance of TCNQ-· was independent of the amine concentration, and the reaction had a much higher enthalpy and entropy of activation. The occurrence of tautomerism precluded an investigation of the conversion of 7-(octylamino)-7,8,8-tricyanoquinodimethane into 7,7-bis(octylamino)-8,8-dicyanoquinodimethane. A study of the reaction of octylamine with 7-morpholino-7,8,8-tricyanoquinodimethane (which does not exist in tautomeric forms) showed that the second substitution step proceeds with the same mechanism as the first one. The only difference between the two compounds (TCNQ and its monosubstituted morpholino derivative) is one of reactivity. © 1985 American Chemical Society.

Mercury(II) and thallium(III) organometallic derivatives of 2-Mercaptobenzoxazole

Some derivatives of 2-mercaptobenzoxazole (HL) of the type MRnL [M = Hg or Tl, R = Me or Ph and n = 1 (Hg) or 2 (Tl)] have been prepared. The structure of HgMeL has been determined by an X-ray diffraction study; in the crystal there are two independent planar molecules in each asymmetric unit, with the ligand in its thiolic form and an almost linear CHgS linkage. Weak intramolecular and intermolecular secondary interactions complement the mercurysulphur bond. The spectroscopic (IR, Raman, mass, 13C-NMR), conductimetric, and dipolar properties of this and the other compounds are discussed. © 1991.

Effect of organic synthetic food colours on mitochondrial respiration

Eleven organic synthetic dyes, currently or formerly used as food colours in Brazil, were tested to determine their effect on mitochondrial respiration in mitochondria isolated from rat liver and kidney. The compounds tested were: Erythrosine, Ponceau 4R, Allura Red, Sunset yellow, Tartrazine, Amaranth, Brilliant Blue, Indigotine Blue, Fast Red E, Orange GGN and Scarlet GN. All food colours tested inhibited mitochondrial respiration (State III respiration, uncoupled) supported either by α-ketoglutarate or succinate. this inhibition varied largely, e.g. from 100% to 16% for Erythrosine and Tartrazine respectively, at a concentration of 0.1 mg food colour per mitochondrial protein. Both rat liver and kidney mitochondria showed similar patterns of inhibition among the food colours tested. This effect was dose related and the concentration to give 50% inhibition was determined for some of the dyes. The xanthene dye Erythrosine, which showed the strongest effect, was selected for further investigation on mitochondria in vivo.

Phase analysis of seeded and doped PbMg1/3Nb2/3O3 prepared by organic solution of citrates

PbMg1/3Nb2/3O3 (PMN) prepared by organic solution of citrates was analyzed by the Rietveld method to determine the influence of seeds and dopants on the perovskite and pyrochlore phase formation. It was observed that pyrochlore phase formation increases with an increase in calcination time when no additives are included during the preparation. It was also observed that a greater amount of perovskite phase appeared in doped or seeded samples. The fraction of perovskite phase increased from 88 mol % in pure sample to ∼95 mol % in doped and seeded samples calcined at 800°C for 1 h. It is clear that the addition of dopants or seeds during PMN preparation can enhance the formation of perovskite phase.

Reduction of dissolved oxygen in water: Hydrazine and its organic substitutes

In industrial processes using aqueous solutions, corrosion of metal surfaces may occur at various locations. Much of the damage to steam generators and boilers is caused by corrosion. Dissolved oxygen in water is one of the most potent corrosion-causing factors, and therefore oxygen should be eliminated from steam-generating systems' feedwater. Chemical reduction, by reagents such as hydrazine or organic compounds, generally is used for the deoxygenation of water. This article reviews the major oxygen scavengers currently available.

Preparation of 9.5/65/35 PLZT powders by organic precursor method

In this study the preparation of 9.5/65/35 PLZT ceramic powders were investigated. The powders with the formula Pb0.905La0.095(Zr0.65 Ti0.35)0.976O3 + 3.5 w% PbO were prepared using Pechini process and partial oxalate method. The powder phase formation, powder morphology, and green density of PLZT were shown.

Room temperature visible/infrared emission and energy transfer in Nd3+-based organic/inorganic hybrids

The photoluminescence features and the energy transfer processes of Nd3+-based siloxanepoly(oxyethylene) hybrids are reported. The host matrix of these materials, classed as di-ureasils, is formed by a siloxane backbone covalently bonded to polyether chains of two molecular weights by means of urea cross-links. The room-temperature photoluminescence spectra of these xerogels show a wide broad purple-blue-green band (350-570 nm), associated with the emitting centres of the di-ureasil host, and the typical near infrared emission of Nd3+ (700-1400 nm), assigned to the 4F3/2 → 4I9/2,11/2,13/2 transitions. Self-absorptions in the visible range, resonant with intra-4f3 transitions, indicate the existence of an energy conversion mechanism of visible di-ureasil emission into near infrared Nd3+ luminescence. The existence of energy transfer between the di-ureasil's emitting centres and the Nd3+ ions is demonstrated calculating the lifetimes of these emitting centres. The efficiency of that energy transfer changes both with the polymer molecular weight and the Nd3+ concentration.

Thermal Behavior and Spectroscopic Study of Neutral and Cationic Mononuclear Cyclopalladated Compounds

The reactions of the precursor [Pd(N,C-dmba)(MeCN)2](NO 3) (1) (dmba = N,N-dimethylbenzylamine), with the proligands 3,5-dimethylpyrazole (Hdmpz), 2-quinolinethiol (qnSH) and 1,1′- bis(diphenylphosphine)ferrocene (dppf) afforded the compounds [Pd(N,C-dmba)(Hdmpz)(ONO2)]0.5CH2Cl2 (2), [Pd(N,C-dmba)(qnSH)(ONO2)] 0.5CH2Cl2 (3) and [Pd(N,C-dmba)(dppf)](NO3) (4), respectively. The mononuclear species 2,3 and 4 were characterized by elemental analysis, infrared spectroscopy, NMR and thermogravimetric analysis. The IR spectra show bands which are consistent with terminal monodentate nitrate group for 2-3 and ionic nitrate for 4. The 1H and 13C NMR data confirm that coordination of the organic ligands has occurred and the 31P{1H} NMR data for 4 clearly evidences the occurrence in solution of three cyclopalladated species with the dppf acting as a bridging ligand in two cases and as a chelate in one. The thermal behavior of compounds 1-4 suggests that complex 2 is the most stable. The X-ray diffractometry results show the formation of PdO from 1 and 2, Pd2OSO4 from 3, and of a mixture of PdO and Fe 2(PO4)3 from 4, as final decomposition products.

Waveguide features in self-patternable amine functionalized organic-inorganic hybrids

We report the use of organic-inorganic sol-gel derived poly(oxyehylene)/ siloxane hybrid doped with methacrylic acid modified zirconium (IV) n-propoxide for the fabrication of low cost waveguides trough direct UV laser writing. The organic-inorganic hybrids were processed as monoliths with size and shape control. The effective guiding region was identified and the number of modes was estimated via mode field analyses. A grating was successfully superimposed on the channel and the respective reflection spectrum was measured, enabling the determination of the guiding region dimension, the calculation of the effective refractive index of the guided mode. © 2007 IEEE.

Heterogeneous photocatalytic treatment of organic dyes in air and aqueous media

This review focuses on the heterogeneous photocatalytic treatment of organic dyes in air and water. Representative studies spanning approximately three decades are included in this review. These studies have mostly used titanium dioxide (TiO2) as the inorganic semiconductor photocatalyst of choice for decolorizing and decomposing the organic dye to mineralized products. Other semiconductors such as ZnO, CdS, WO3, and Fe2O3 have also been used, albeit to a much smaller extent. The topics covered include historical aspects, dark adsorption of the dye on the semiconductor surface and its role in the subsequent photoreaction, semiconductor preparation details, photoreactor configurations, photooxidation kinetics/mechanisms and comparison with other Advanced Oxidation Processes (e.g., UV/H2O2, ozonation, UV/O3, Fenton and photo-Fenton reactions), visible light-induced dye decomposition by sensitization mechanism, reaction intermediates and toxicity issues, and real-world process scenarios. © 2008 Elsevier B.V. All rights reserved.

Integrated analysis of halogenated organic pollutants in sub-millilitre volumes of venous and umbilical cord blood sera

A rapid, robust and economical method for the analysis of persistent halogenated organic compounds in small volumes of human serum and umbilical cord blood is described. The pollutants studied cover a broad range of molecules of contemporary epidemiological and legislative concern, including polychlorobiphenyls (PCBs), polychlorobenzenes (CBs), hexachlorocyclohexanes (HCHs), DDTs, polychlorostyrenes (PCSs) and polybromodiphenyl ethers (PBDEs). Extraction and clean-up with n-hexane and concentrated sulphuric acid was followed with analysis by gas chromatography coupled to electron capture (GC-ECD) and GC coupled to negative ion chemical ionisation mass spectrometry (GC-NICI-MS). The advantages of this method rest in the broad range of analytes and its simplicity and robustness, while the use of concentrated sulphuric acid extraction/clean-up destroys viruses that may be present in the samples. Small volumes of reference serum between 50 and 1000 μL were extracted and the limits of detection/quantification and repeatability were determined. Recoveries of spiked compounds for the extraction of small volumes (≥300 μL) of the spiked reference serum were between 90% and 120%. The coefficients of variation of repeatability ranged from 0.1-14%, depending on the compound. Samples of 4-year-old serum and umbilical cord blood (n = 73 and 40, respectively) from a population inhabiting a village near a chloro-alkali plant were screened for the above-mentioned halogenated pollutants using this method and the results are briefly described. © 2010 Springer-Verlag.

Influence of organic and mineral soil fertilization on essential oil of Spilanthes oleracea cv. Jambuarana

In the present study, the composition of essential oil of leaves and inflorescences of jambu (Spilanthes oleracea. Jambuarana), under organic manuring and mineral fertilization, was stuhed. Jambu plants show important chemical properties and their production has been addressed for the extraction of the essential oils for cosmetics industries, due to their pharmacolopcal properties. The experimental area of treatments contained urea as mineral fertilizer (120 g m2), applied twice and organic fertilizer (8 kg m2), applied at the planting. Jambu leaves and flowers were harvested twice: the first at 90 days after seedling transplantation and at the opening of the flower buds. Branches were cut at 7 cm from the soil, thus new branches can bud for the accomplishment of the second crop which happened 40 days after the re-budhng. The essential oil was analyzed by gas chromatography coupled with mass-spectrometry. According to our results the most representative compounds were trans-caryophyllene, germacrene-D, 1-dodecene, spathulenol and spilanthol (a compound presenting anesthetic properties) occurring in inflorescences. Fertilization procedure does not affect the content and the quality of the essential oil in Jambu plants. © 2012 Academic Journals Inc.

Cover crops and no-till effects on physical fractions of soil organic matter

Physical fractions (free light fraction, intra-aggregate light fraction and heavy fraction) of soil organic matter (SOM) are good indicators of soil quality for sustainable land use. The objective of this study was to evaluate the effect of cover crops on total organic carbon (TOC) and physical fractions of soil organic matter in soil under a no-tillage system (NTS) and a conventional tillage system (CTS, one plowing and two disking). A three-year field experiment was carried out as a cover crop-rice (Oryza sativa)-cover crop-rice rotation. Treatments included cover crops (Panicum maximum, Brachiaria ruziziensis, Brachiaria brizantha, and pearl millet (Pennisetum glaucum), fallow, till or no till. The SOM was physically fractionated in free light fraction (FLF), intra-aggregates light fraction (IALF) and heavy fraction (HF). The levels of C in whole soil were also evaluated, as well as C in the light fractions (FLF+IALF) and in the HF. Results indicated that concentrations of C in the FLF and IALF in surface soils (0-0.05m) were much higher (10.8 and 1.95gkg-1, respectively) than that in the 0.05-0.1m soil depth (7.68 and 1.54gkg-1, respectively) and in the 0.1-0.2m soil depth (4.98 and 1.24gkg-1, respectively). The NTS resulted in higher levels of FLF (12.2gkg-1) and IALF (2.19gkg-1) than with CTS (1.37-7.30gkg-1). Millet had the highest C (19.5gkg-1) and N (1.1gkg-1) concentrations in soil. There was an accumulation of TOC and total N in the surface soil with cover crops, and concentrations of TOC were higher in the HF (79.0%) than in the light fractions (21.0%). Although SOM changed little during the two years of this experiment, the various C fractions were significantly affected by the tillage treatments. We conclude that SOM physical fractionation allowed seeing significant differences caused by the soil management in the organic matter dynamics in a short period of time. © 2013 Elsevier B.V.

Determination of Total Nitrosamines in Vegetables Cultivated Organic and Conventional Using Diamond Electrode

Vegetables were analyzed for total N-nitrosamines (NAs) and the influence of disinfection processes was assessed. Differences in NAs found in cabbage, spinach, and broccoli were determined by square wave voltammetry using a boron-doped diamond electrode. Analysis of samples showed that all samples contained detectable levels of NAs but the results indicated that organic contained less than conventionally grown products. The sum of the total NAs was higher in the cabbage samples, ranging between 2.8-3.1 ppb and lower in broccoli samples at 0.2-1.1 ppb. The method described is simple, rapid, selective, and sensitive. The results suggested that the disinfection process affects the level of NAs, in this manner affecting the level of human exposure to NAs. © 2012 Springer Science+Business Media New York.