Iron and manganese in bottom sediments and interstitial waters sampled in the White Sea on August 21-30, 2003

Iron and manganese in bottom sediments studied along the sublatitudinal transect from Kandalaksha to Arkhangelsk are characterized by various contents and speciations depending on sedimentation environment, grain size of sediments, and diagenetic processes. The latter include redistribution of reactive forms leading to enrichment in Fe and Mn of surface sediments, formation of films, incrustations, and ferromanganese nodules. Variations in total Fe content (2-8%) are accompanied by changes in concentration of its reactive forms (acid extraction) and concentration of dissolved Fe in interstitial waters (1-14 µM). Variations in Mn content in bottom sediments (0.03-3.7%) and interstitial waters (up to 500 µM) correspond to high diagenetic mobility of this element. Changes in oxidation degree of chemical elements result in redox stratification of sediment strata with maximum concentrations of Fe, Mn, and sulfides. Organic matter of bottom sediments with considerable terrestrial constituent is oxidized by bottom water oxygen mainly at the sediment surface or in anaerobic conditions within the sediment strata. The role of inorganic components in organic matter oxidation changes from surface layer bottom sediments (where manganese oxyhydroxide dominates among oxidants) to deeper layers (where sulfate of interstitial water serves as the main oxidant). Differences in river runoff and hydrodynamics are responsible for geochemical asymmetry of the transect. The deep Kandalaksha Bay serves as a sediment trap for manganese (Mn content in sediments varies within 0.5-0.7%), whereas the sedimentary environment in the Dvina Bay promotes its removal from bottom sediments (Mn 0.05%).

Iron and carbon geochemistry of sediment core GeoB1401-4

Iron speciation was determined in hemiplegic sediments from a high productivity area to investigate systematically the early diagenetic reactivity of Fe. A combination of various leaching agents (1 M HCI, dithionite buffered in citrate/acetic acid, HF/H2SO4, acetic Cr(II)) was applied to sediment and extracted more than 80% of total Fe. Subsequent Fe species determination defined specific mineral fractions that are available for Fe reduction and fractions formed as products of Fe diagenesis. To determine the Fe speciation of (sheet) silicates we explored an extraction procedure (HF/H2SO4) and verified the procedure by application to standard rocks. Variations of Fe speciation of (sheet) silicates reflect the possible formation of Fe-bearing silicates in near surface sediments. The same fraction indicates a change in the primary input at greater depth, which is supported by other parameters. The Fe(II)/ Fe(III) -ratio of total sediment determined by extractions was compared with Mössbauer-spectroscopy ] at room temperature and showed agreement within 10%. M6ssbauer-spectroscopy indicates the occurrence of siderite in the presence of free sulfide and pyrite, supporting the importance of microenvironments during mineral formation. The occurrence of other Fe(II) bearing minerals such as ankerite (Ca-, Fe-, Mg-carbonate) can be presumed but remains speculative.

Iron chelates bind nitric oxide and decrease mortality in an experimental model of septic shock.

The hydroxamic acid siderophore ferrioxamine B [FeIII(HDFB)+] and the iron complex of diethylenetri-aminepentaacetic acid [FeIII(DTPA)2-] protected mice against death by septic shock induced by Corynebacterium parvum + lipopolysaccharide. Although FeIII(DTPA)2- was somewhat more effective than FeIII(HDFB)+, the iron-free ligand H4DFB+ was significantly more effective than DTPA. The hydroxamic acid chelator has a much higher iron affinity than the amine carboxylate, allowing for more efficient formation of the FeIII(HDFB)+ complex upon administration of the iron-free ligand. Electrochemical studies show that FeIII(DTPA)2- binds NO stoichiometrically upon reduction to iron(II) at biologically relevant potentials to form a stable NO adduct. In contrast, FeIII(HDFB)+ is a stable and efficient electrocatalyst for the reduction of NO to N2O at biologically relevant potentials. These results suggest that the mechanism of protection against death by septic shock involves NO scavenging and that particularly effective drugs that operate a low dosages may be designed based on the principle of redox catalysis. These complexes constitute a new family of drugs that rely on the special ability of transition metals to activate small molecules. In addition, the wealth of information available on siderophore chemistry and biology provides an intellectual platform for further development.

Propriedades fotoquímicas de alguns complexos de ferro(II) e rênio(I)

Neste trabalho, foram estudadas as propriedades fotoquímica e/ou fotofísica de alguns compostos de coordenação de rênio(l) e ferro(I I). A irradiação dos complexos fac-[Re(CO)3(NN)(trans-L)]+, NN= 4,7-difenil-1,10- fenantrolina (ph2phen) ou 5-cloro-1,10-fenantrolina (Clphen) e L = 1,2-bis(4-piridil)etileno (bpe) ou 4-estirilpiridina (stpy), em acetonitrila ou em filme de poli(metacrilato de metila) (PMMA) resulta em variações espectrais condizentes com a fotoisomerização trans-cis do ligante coordenado. A determinação dos rendimentos quânticos para a fotorreação pela variação espectral resultou em valores aparentes, uma vez que o reagente e o fotoproduto absorvem na mesma região. Para a determinação do rendimento quântico real, Φreal, utilizou-se a técnica de 1H RMN, na qual os sinais do fotoproduto e do reagente são observados em regiões distintas com diferentes constantes de acoplamento. Os valores de Φreal obtidos para fac-[Re(CO)3h(NN)(trans-bpe)]+ (ph2phen: Φ313= 0,43 ± 0,03; Φ365= 0,44 ± 0,02; Φ404= 0,43 ± 0,02; Clphen: Φ313= 0,56 ± 0,03; Φ365= 0,55 ± 0,04; Φ404= 0,57 ± 0,06) são independentes do comprimento de onda de irradiação, indicando a existência de um único canal para a população do estado excitado 3ILtrans-bpe. Por outro lado, para fac-[Re(CO)3(NN)(trans-stpy)]+, os valores de Φreal sob irradiação a 404 nm são menores que os determinados para os demais comprimentos de onda de irradiação (ph2phen: Φ313= 0,60 ± 0,05; Φ365= 0,64 ± 0,09; Φ404= 0,42 ± 0,03; Clphen: Φ313= 0,52 ± 0,05; Φ365= 0,58 ± 0,02; Φ404= 0,41 ± 0,06), indicando que, a energias maiores, em que o Iigante absorve significativamente, deve existir a contribuição de outro canal para a população do estado excitado 3ILtrans-stpy. A eficiência do fotoprocesso foi avaliada por meio da substituição dos ligantes NN e/ou L, e a diferença nos valores de Φreal entre os complexos deve estar relacionada principalmente com as distintas eficiências de cruzamento intersistemas. o fotoprocesso altera as propriedades fotofísicas desses complexos. Os isômeros trans apresentam fraca ou nenhuma emissão a 298 K, enquanto os fotoprodutos, fac-[Re(CO)3(NN)(cis-L)]+, apresentam intensa luminescência dominada pelo estado excitado 3MLCTRe→NN, que é sensivel à rigidez do meio. A reatividade fotoquímica dos pentacianoferratos(II) [Fe(CN)5 (NN)]3-, NN= 2aminobenzilamina (aba), 2-aminobenzamida (ab), 2-(dimetilaminometil)-3-hidroxipiridina (dmampy), 2-aminometilpiridina (ampy), 2-aminoetilpiridina (aepy) ou 2-(2metilaminoetil) piridina (maepy), também foi investigada. A irradiação desses complexos resulta na fotossubstituição do CN-, a qual só pode ser detectada quando o ligante possui um segundo grupo coordenante nas proximidades da esfera de coordenação. Os rendimentos quânticos da fotossubstituição são dependentes do comprimento de onda de irradiação (Φ313= 0,13 ± 0,01; Φ334= 0,091 ± 0,001; Φ365= 0,056 ± 0,002; Φ404= 0,022 ± 0,002; Φ436= 0,015 ± 0,001, por exemplo, para NN = aba) e indicam a existência de canais distintos pelos quais a fotorreação ocorre ou as diferentes eficiências de cruzamento intersistema para a população do estado excitado reativo. A eficiência do fotoprocesso também depende do Iigante utilizado (λirr= 365 nm: Φaba= 0,056, Φab= 0,14, Φampy= 0,046, Φaepy= 0,066, Φmaepy= 0,069 e Φdmampy= 0,12). Na série das diaminas, o rendimento quântico é maior para [Fe(CN)5(ab)]3-, que possui dois sítios para ocorrer o fechamento do anel. Na série das aminopiridinas, observa-se a influência do comprimento da cadeia na eficiência do fechamento do anel. A presença de metilas ligadas ao nitrogênio alifático deve ter pouca ou nenhuma influência na eficiência do fotoprocesso.

Inositol polyphosphate-mediated iron transport in Pseudomonas aeruginosa

It has previously been shown that myo-inositol hexakisphosphate (myo- InsP6) mediates iron transport into Pseudomonas aeruginosa and overcomes iron-dependent growth inhibition. In this study, the iron transport properties of myo-inositol trisphosphate and tetrakisphosphate regio-isomers were studied. Pseudomonas aeruginosa accumulated iron (III) at similar rates whether complexed with myo-Ins(1,2,3)P3 or myo-InsP6. Iron accumulation from other compounds, notably D/L myo-Ins(1,2,4,5)P4 and another inositol trisphosphate regio-isomer, D-myo-Ins(1,4,5)P3, was dramatically increased. Iron transport profiles from myo-InsP6 into mutants lacking the outer membrane porins oprF, oprD and oprP were similar to the wild-type, indicating that these porins are not involved in the transport process. The rates of reduction of iron (III) to iron (II) complexed to any of the compounds by a Ps. aeruginosa cell lysate were similar, suggesting that a reductive mechanism is not the rate-determining step.

Alquilação de tolueno com propeno, através de complexo ferro (II) ᵦ- diimina homogêneo e heterogeneizado em MCM-41, Al-MCM-41 e SBA-15

This work describes the synthesis and aplication of homogeneous and heterogenized iron catalysts in the alkylation reaction of toluene with propene, empolying experimental design. The homogenous complex was obtained trough the synthesis of the organic ligand folowed by the complexation of the iron(II) chloride. As to the heterogenized complexes, first were synthetized the inorganic supports (SBA-15, MCM-41 and Al-MCM-41). Then, it was synthetized the ligand again, that through funcionalization with chloropropyltrimethoxysilane (CPTMS), was anchored on the support previously calcinated. To these anchored ligands, was complexed the iron(II) chloride, previously solubilizated in tetrahydrofuran (THF). The organic ligand characterization was accomplished trough nuclear magnetic resonance (NMR) and Infrared spectroscopy (IV). The supports were characterized with x-ray diffraction (DRX), texture analysis with nitrogen adsorption/desorption (before and after the anchoring), termogravimetric analysis (TG) and infrared (IV). The metalic content was quantified trough the atomic absorption spectrophotometry (AAS). The complexes were tested in catalytic reactions emolying ethylaluminium sesquichloride (EASC) as co-catalyst in steel reactor, under mecanic stirring. The reaction conditions ranged from 4 to 36 ◦C, with many aluminum/iron ratios. The catalysts were actives in homogeneous and heterogenized ways. The homogenous catalytic complex showed a maximum turnover frequency (TOF) of 8.63 ×103 · h −1 , while, in some conditions, the anchored complexes showed better results, with TOF of until 8.08 ×103 · h −1 . Aditionally, it was possible to determine an equation, to the homogenous catalyst, that describes the product quantity in function of reacional temperature and aluminum/iron ratio.

The thermal decomposition of hydronium jarosite and ammoniojarosite

The thermal decomposition of hydronium jarosite and ammoniojarosite was studied using thermogravimetric analysis and mass spectrometry, in situ synchrotron X-ray diffraction and infrared emission spectroscopy. There was no evidence for the simultaneous loss of water and sulfur dioxide during the desulfonation stage as has previously been reported for hydronium jarosite. Conversely, all hydrogen atoms are lost during the dehydration and dehydroxylation stage from 270 to 400 °C and no water, hydroxyl groups or hydronium ions persist after 400 °C. The same can be said for ammoniojarosite. The first mass loss step during the decomposition of hydronium jarosite has been assigned to the loss of the hydronium ion via protonation of the surrounding hydroxyl groups to evolve two water molecules. For ammoniojarosite, this step corresponds to the protonation of a hydroxyl group by ammonium, so that ammonia and water are liberated simultaneously. Iron(II) sulfate was identified as a possible intermediate during the decomposition of ammoniojarosite (421–521 °C) due to a redox reaction between iron(III) and the liberated ammonia during decomposition. Iron(II) ions were also confirmed with the 1,10-phenanthroline test. Iron(III) sulfate and other commonly suggested intermediates for hydronium and ammoniojarosite decomposition are not major crystalline phases; if they are formed, then they most likely exist as an amorphous phase or a different low temperature phases than usual.

Late Transition Metal and Aluminum Complexes for the Polymerization of Ethene and Acrylates

Polyethene, polyacrylates and polymethyl acrylates are versatile materials that find wide variety of applications in several areas. Therefore, polymerization of ethene, acrylates and methacrylates has achieved a lot attention during past years. Numbers of metal catalysts have been introduced in order to control the polymerization and to produce tailored polymer structures. Herein an overview on the possible polymerization pathways for ethene, acrylates and methacrylates is presented. In this thesis iron(II) and cobalt(II) complexes bearing tri- and tetradentate nitrogen ligands were synthesized and studied in the polymerization of tertbutyl acrylate (tBA) and methyl methacrylate (MMA). Complexes are activated with methylaluminoxane (MAO) before they form active combinations for polymerization reactions. The effect of reaction conditions, i.e. monomer concentration, reaction time, temperature, MAO to metal ratio, on activity and polymer properties were investigated. The described polymerization system enables mild reaction conditions, the possibility to tailor molar mass of the produced polymers and provides good control over the polymerization. Moreover, the polymerization of MMA in the presence of iron(II) complex with tetradentate nitrogen ligands under conditions of atom transfer radical polymerization (ATRP) was studied. Several manganese(II) complexes were studied in the ethene polymerization with combinatorial methods and new active catalysts were found. These complexes were also studied in acrylate and methacrylate polymerizations after MAO activation and converted into the corresponding alkyl (methyl or benzyl) derivatives. Combinatorial methods were introduced to discover aluminum alkyl complexes for the polymerization of acrylates and methacrylates. Various combinations of aluminum alkyls and ligands, including phosphines, salicylaldimines and nitrogen donor ligands, were prepared in situ and utilized to initiate the polymerization of tBA. Phosphine ligands were found to be the most active and the polymerization MMA was studied with these active combinations. In addition, a plausible polymerization mechanism for MMA based on ESI-MS, 1H and 13C NMR is proposed.

Schiff Base Complexes and their Assemblies on Surfaces

Schiff bases and their transition metal complexes are of significant current interest even though they have been prepared for decades. They have been used in various applications such as catalysis, corrosion protection, and molecular sensors. In this study, N-aryl Schiff base ketimine ligands as well as numerous new, differently substituted salen and salophen-type ligands and their cobalt(II), copper(II), iron(II), manganese(II), and nickel(II) complexes were synthesised. New solid state structures of the above compounds and the dioxygen coordination properties of cobalt(II) complexes and catalytic properties of three synthesised binuclear complexes were examined. The prepared complexes were applied in the formation of self-assembled layers on a polycrystalline gold surface and liquid-graphite interface. The effect of metal ion and ligand structure on the as-formed patterns was studied. When studying gold surfaces, a unique thiol-assisted dissolution of elemental gold was observed and a new thin gold foil preparation method was introduced. In the summary, synthesis, structures, and properties of Schiff base ligands and their transition metal complexes are described in detail and the applications of these reviewed. Assemblies of other complexes on a liquid-graphite interface and on a gold surface are also presented, and the surface characterisation methods and surfaces employed are described.

A new method for the titrimetric determination of perchlorate

A new method for the titrimetric determination of perchlorate has been developed, based on its reduction to chloride by iron(II) in a strong sulphuric acid medium at high temperature. The effect of variables, such as the sulphuric acid concentration, the temperature and the period of heating, on the extent of reduction has been studied and the optimal conditions for analytical determination of perehlorate derived.