New catalytic processes for the synthesis of adipic acid

The aim of my Ph.D. research was to study the new synthetic ways for the production of adipic acid. Three different pathways were studied: i) oxidation of cyclohexanone with molecular oxygen using Keggin – heteropolycompounds as the catalyst, ii) Baeyer – Villiger oxidation of cyclohexanone with hydrogen peroxide in the presence of two different heterogeneous catalysts, titanium silicalite and silica grafted decatungstate, iii) two step synthesis of adipic acid starting from cyclohexene via 1,2-cyclohexanediol. The first step was catalyzed by H2WO4 in the presence of the phase transfer catalyst, the oxidant was hydrogen peroxide. The second step, oxidation of 1,2 – cyclohexanediol was performed in the presence of oxygen and the heterogeneous catalyst – ruthenium on alumina. The results of my research showed that: i) Oxidation of cyclohexanone with molecular oxygen using Keggin heteropolycompounds is possible, anyway the conversion of ketone is low and the selectivity to adipic acid is lowered by the consecutive reaction to from lower diacids. Moreover it was found out, that there are two mechanisms involved: redox type and radicalic chain-reaction autoxidation. The presence of the different mechanism is influenced by the reaction condition. ii) It is possible to perform thermally activated oxidation of cyclohexanone and obtain non negligible amount of the products (caprolactone and adipic acid). Performing the catalyzed reaction it was demonstrated that the choice of the reaction condition and of the catalyst plays a crucial role in the product selectivity, explaining the discrepancies between the literature and our research. iii) Interesting results can be obtained performing the two step oxidation of cyclohexene via 1,2-cyclohexanediol. In the presence of phase transfer catalyst it is possible to obtain high selectivity to alcohol with stoichiometric amount of oxidant. In the second step of the synthesis, the conversion of alcohol is rather low with modest selectivity to adipic acid

ROS generate dalle NAD(P)H ossidasi nella segnalazione redox in linee cellulari leucemiche

Discovery of the Nox family has led to the concept that ROS are “intentionally” generated and are biologically functional in various cell types. Over the last decades, ROS have been shown to be involved in several physiological and pathological processes and ROS producing enzymes have been suggested as a target for drug development. The mechanism involved in the prosurvival effect of cytokines on the human acute myeloid leukaemia cell lines M07e and B1647 is investigated. A decrease in intracellular reactive oxygen species (ROS) content, glucose transport activity and cell survival was observed in the presence of inhibitors of plasma membrane ROS sources, such as DPI and apocynin, and by small interference RNA for NOX2 in M07e cells. Furthermore, Nox generated ROS are required to sustain B1647 cell viability and proliferation; in fact, antioxidants such as EUK-134 or Nox inhibitors and siRNA direct cells to apoptotic cell death, suggesting that manipulation of cellular NOX2 and NOX4 could affect survival of leukemic cells. Moreover, hydrogen peroxide has been long thought to be freely diffusible but recent evidence suggest that specific mammalian aquaporin homologues (AQP8) possess the capacity to channel H2O2 across membrane. In this thesis is shown that inhibition of aquaporins diminishes intracellular ROS accumulation either when H2O2 is produced by Nox enzymes or when is added exogenously to the medium. These data suggest that specific inhibition of Nox enzymes and AQP8 could be an interesting novel anti-leukemic strategy.

Elektrochemisch gesteuerte zeitaufgelöste Infrarotspektroskopie an Redox-Membranproteinen in einer biomimetischen Membran-Architektur

Das Protein Cytochrom c Oxidase (CcO) ist ein Enzym der mitochondrialen Atmungskette. Als letzter Komplex (Komplex IV) einer Elektronentransportkette katalysiert sie die Reduktion von molekularem Sauerstoff zu Wasser. Hierbei werden Elektronen von Cytochrom c (Cc) in das Enzym geleitet. Die durch den Redoxprozess freiwerdende freie Enthalpie wird dazu genutzt, einen Protonengradienten über die innere Mitochondrien-Membran aufzubauen. Die zurückwandernden Protonen treiben in der ATP-Synthase die Produktion von Adenosintriphosphat (ATP) an, dem universellen Energieträger in lebenden Organismen. Gegenstand dieser Dissertation sind zeitaufgelöste ATR-FTIR-Messungen des direkten Elektronentransfers in die CcO. Das Protein wird hierzu orientiert auf einer Goldelektrode immobilisiert und in eine künstliche Membran rekonstituiert (Protein-tethered Bilayer Lipid Membrane, ptBLM). Das ptBLM-System wird hinsichtlich einer möglichst hohen Protein-Aktivität optimiert. Elektronen werden durch elektrochemische Anregung von der Elektrode in die CcO injiziert. Die Goldoberfläche wird auf die reflektierende Oberfläche eines Silizium-ATR-Kristalls aufgebracht. Durch die Präparation einer rauen Oberfläche (RMS-Rauigkeit ca. 5 nm) wird eine Verstärkung der IR-Absorption erreicht. Die mit den Ladungstransferprozessen einhergehenden Konformationsänderungen der die Redoxzentren umgebenden Gruppen (CONH-Gerüst und Aminosäure-Seitenketten) können durch Infrarot-Spektroskopie nachgewiesen werden. Phasensensitive Detektion (PSD) wird zur Rauschminderung eingesetzt, um Geschwindigkeitskonstanten für die Redox-Übergänge zu bestimmen. Im Bereich der Amid-I-Bande werden etliche Peaks identifiziert, die sich mit dem Redoxzustand des Proteins ändern. Für das CuA-Zentrum, welches als erstes der vier Redoxzentren der CcO reduziert wird, wird die schnellste Geschwindigkeitskonstante ks=4870/s ermittelt. Für das Häm a3-Zentrum wird eine Geschwindigkeitskonstante von ks=13,8/s ermittelt. Die Ergebnisse sind konsistent zu elektrochemischen und Raman-Spektroskopie-Experimenten, welche ebenfalls in unserer Gruppe durchgeführt wurden. Weitere Themen dieser Dissertation sind der Nachweis der Anwendbarkeit des ptBLM-Systems für andere Membranproteine (Beispiel: bakterielles photosynthetisches Reaktionszentrum) und der Einsatz des ATR-FTIR-Setups für verschiedene künstliche Membransysteme (Aktivitätsnachweis des OR5-Geruchsrezeptors in einer peptidgestützten Membran, Eigenschaften eines Oligoethylenglycol-Spacers).

Catalysts and processes for next-generation H2 production

The present study is focused on the development of new VIII group metal on CeO2 – ZrO2 (CZO) catalyst to be used in reforming reaction for syngas production. The catalyst are tested in the oxyreforming process, extensively studied by Barbera [44] in a new multistep process configuration, with intermediate H2 membrane separation, that can be carried out at lower temperature (750°C) with respect the reforming processes (900 – 1000°C). In spite of the milder temperatures, the oxy-reforming conditions (S/C = 0.7; O2/C = 0.21) remain critical regarding the deactivation problems mainly deriving from thermal sintering and carbon formation phenomena. The combination of the high thermal stability characterizing the ZrO2, with the CeO2 redox properties, allows the formation of stable mixed oxide system with high oxygen mobility. This feature can be exploited in order to contrast the carbon deposition on the active metal surface through the oxidation of the carbon by means of the mobile oxygen atoms available at the surface of the CZO support. Ce0.5Zr0.5O2 is the phase claimed to have the highest oxygen mobility but its formation is difficult through classical synthesis (co-precipitation), hence a water-in-oil microemulsion method is, widely studied and characterized. Two methods (IWI and bulk) for the insertion of the active metal (Rh, Ru, Ni) are followed and their effects, mainly related to the metal stability and dispersion on the support, are discussed, correlating the characterization with the catalytic activity. Different parameters (calcination and reduction temperatures) are tuned to obtain the best catalytic system both in terms of activity and stability. Interesting results are obtained with impregnated and bulk catalysts, the latter representing a new class of catalysts. The best catalysts are also tested in a low temperature (350 – 500°C) steam reforming process and preliminary tests with H2 membrane separation have been also carried out.

Structural aspects of redox-mediated electron tunneling (Dedicated to the memory of professor Alexander M. Kuznetsov)

We investigated structural aspects of electron transfer (ET) in tunneling junctions (Au(1 1 1)vertical bar FcN vertical bar solution gap vertical bar Au STM tip) with four different redox-active N-thioalk(ano)ylferrocenes (FcN) embedded. The investigated molecules consist of a redox-active ferrocene (Fc) moiety connected via alkyl spacers with N = 4, 6, 8 and 11 carbon atoms to a thiol anchoring group. We found that for short FcNs (N = 4, 6,8) the redox-mediated ET response increases with the increase of the alkyl chain length, while no enhancement of the ET was observed for Fc1 1. The model of two-step ET with partial vibrational relaxation by Kuznetsov and Ulstrup was used to rationalize these results. The theoretical ET steps were assigned to two processes: (1) electron tunneling from the Fc group to the Au tip through the electrolyte layer and (2) electron transport from the Au(1 1 1) substrate to the Fc group through the organic adlayer. We argue that for the three short FcNs, the first process represents the rate-limiting step. The increase of the length of the alkyl chain leads to an approach of the Fc group to the STM tip, and consequently accelerates the first El' step. In case of the Fcl 1 junctions the rather high thickness of the organic layer leads to a decrease of the rate of the second ET step. In consequence, the contribution of the redox-mediated current enhancement to the total tunneling current appears to be insignificant. Our work demonstrates the importance of combined structural and transport approaches for the understanding of Er processes in electrochemical nanosystems. (C) 2010 Elsevier B.V. All rights reserved.

Exploratory studies on coordination chemistry of a redox-active bridging ligand: synthesis, properties and solid state structures of the complexes

The explorative coordination chemistry of the bridging ligand TTF-PPB is presented. Its strong binding ability to Co(II) and then to Ni(II) or Cu(II) in the presence of hexafluoroacetylacetonate (hfac(-)), forming new mono-and dinuclear complexes 1-3, is described. X-ray crystallographic studies have been conducted in the case of the free ligand TTF-PPB as well as its complexes [Co(TTF-PPB)(hfac)(2)] (1) and [Co(hfac)(2)(mu-TTF-PPB)Ni(hfac)(2)] (2). Each metal ion is bonded to two bidentate hfac-anions through their oxygen atoms and two nitrogen atoms of the PPB moiety with a distorted octahedral coordination geometry. Specifically, nitrogen donor atoms of TTF-PPB adopt a cis-coordination but not in the equatorial plane, which is quite rare. Electronic absorption, photoinduced intraligand charge transfer ((1)ILCT), and electrochemical behaviour of 1-3 have been investigated. UV-Vis spectroscopy shows very strong bands in the UV region consistent with ligand centred pi-pi* transitions and an intense broad band in the visible region corresponding to a spin-allowed pi-pi* (1)ILCT transition. Upon coordination, the (1)ILCT band is bathochromically shifted by 3100, 6100 and 5900 cm(-1) on going from 1 to 3. The electrochemical studies reveal that all of them undergo two reversible oxidation and one reversible reduction processes, ascribed to the successive oxidations of the TTF moiety and the reduction of the PPB unit, respectively.

Biogeochemical processes in a clay formation in situ experiment: Part F - Reactive transport modelling

Reactive transport modelling was used to simulate solute transport, thermodynamic reactions, ion exchange and biodegradation in the Porewater Chemistry (PC) experiment at the Mont Terri Rock Laboratory. Simulations show that the most important chemical processes controlling the fluid composition within the borehole and the surrounding formation during the experiment are ion exchange, biodegradation and dissolution/precipitation reactions involving pyrite and carbonate minerals. In contrast, thermodynamic mineral dissolution/precipitation reactions involving alumo-silicate minerals have little impact on the fluid composition on the time-scale of the experiment. With the accurate description of the initial chemical condition in the formation in combination with kinetic formulations describing the different stages of bacterial activities, it has been possible to reproduce the evolution of important system parameters, such as the pH, redox potential, total organic C. dissolved inorganic C and SO(4) concentration. Leaching of glycerol from the pH-electrode may be the primary source of organic material that initiated bacterial growth, which caused the chemical perturbation in the borehole. Results from these simulations are consistent with data from the over-coring and demonstrate that the Opalinus Clay has a high buffering capacity in terms of chemical perturbations caused by bacterial activity. This buffering capacity can be attributed to the carbonate system as well as to the reactivity of clay surfaces.

Methane and microbiological processes in the Barents Sea

Biogeochemical cycle of methane in the Barents Sea was studied using isotope geochemistry to determine rates of microbial methane oxidation. It was established that microbiological processes (glucose consumption, 14CO2 assimilation, sulfate reduction, and slow methane oxidation) in oxidized surface and weakly reduced sediments are marked by only insignificant change in SO4 concentration and absence of notable increase of total alkalinity and N/NH4 downward sediment cores. Microbial methane productivity was 0.111x10**6 mol/day. Taking into account volume of the water column, microbial methane consumption therein can be as much as 1.8x10**6 mol/day.

Sulfur and carbon in mIcrobial processes in waters and sediments of the Kara Sea in September 2007

Results of microbiological, biogeochemical and isotope geochemical studies in the Kara Sea are described. Samples for these studies were obtained during Cruise 54 of R/V Akademik Mstislav Keldysh in September 2007. The studied area covered the northern, central, and southwestern parts of the Kara Sea and the Obskaya Guba (Ob River estuary). Quantitative characteristics of total bacterial population and activity of microbial processes in the water column and bottom sediments were obtained. Total abundance of bacterioplankton (BP) varied from 250000 cells/ml in the northern Kara Sea to 3000000 cells/ml in the Obskaya Guba. BP abundance depended on concentration of suspensded matter. Net BP production was minimal in the central Kara Sea (up to 0.15-0.2 µg C/l/day) and maximal (0.5-0.75 µg C/l/day) in the Obskaya Guba. Organic material at the majority of stations at the Ob transect predominantly contained light carbon isotopes (-28.0 to -30.18 per mil) of terrigenous origin. Methane concentration in the surface water layer varied from 0.18 to 2.0 µl CH4/l, and methane oxidation rate varied from 0.1 to 100 nl CH4/l/day. Methane concentration in the upper sediment layer varied from 30 to 300 µl CH4/dm**3; rate of methane formation was varied from 44 to 500 nl CH4/dm**3/day and rate of methane oxidation - from 30 to 2000 nl CH4/dm**3/day. Rate of sulfate reduction varied from 4 to 184 µg S/dm**3/day.

Major, trace element and XRF data for sediments and fish tooth samples, from a shallow marine setting with varying redox conditions (Site U1356, Wilkes Land Margin, E.Antarctica)

Fossil fish teeth from pelagic open ocean settings are considered a robust archive for preserving the neodymium (Nd) isotopic composition of ancient seawater. However, using fossil fish teeth as an archive to reconstruct seawater Nd isotopic compositions in different sedimentary redox environments and in terrigenous-dominated, shallow marine settings is less proven. To address these uncertainties, fish tooth and sediment samples from a middle Eocene section deposited proximal to the East Antarctic margin at Integrated Ocean Drilling Program Site U1356 were analyzed for major and trace element geochemistry, and Nd isotopes. Major and trace element analyses of the sediments reveal changing redox conditions throughout deposition in a shallow marine environment. However, variations in the Nd isotopic composition and rare earth element (REE) patterns of the associated fish teeth do not correspond to redox changes in the sediments. REE patterns in fish teeth at Site U1356 carry a typical mid-REE-enriched signature. However, a consistently positive Ce anomaly marks a deviation from a pure authigenic origin of REEs to the fish tooth. Neodymium isotopic compositions of cleaned and uncleaned fish teeth fall between modern seawater and local sediments and hence could be authigenic in nature, but could also be influenced by sedimentary fluxes. We conclude that the fossil fish tooth Nd isotope proxy is not sensitive to moderate changes in pore water oxygenation. However, combined studies on sediments, pore waters, fish teeth and seawater are needed to fully understand processes driving the reconstructed signature from shallow marine sections in proximity to continental sources. This article is protected by copyright. All rights reserved.

(Table 1) Redox potential and chemical element contents in CaCO3 and amorphous silica free matter in surface layer bottom sediments of the Pacific Ocean from Hawaiian Islands to Mexico coast

Distribution of Fe, Mn, P, Ti, Cu, Ni, Co, V, Cr, W, Mo, and As in the surface sediment layer on the section from the Hawaiian Islands to the coast of Mexico (Mexico section) is studied. Contents of all studied elements increase from biogenic-terrigenous sediments off the coast of Mexico to pelagic red clays of the Northeast Basin, and more sharply for mobile elements - Mn, Mo, Cu, Ni, Co, and As. In near Hawaii sediments rich in coarsely fragmented volcanic-terrigenous and pyroclastic material of basaltic composition with high contents of Ti, Fe, V, Cr, W, and P, contents of these elements increase sharply, and contents of Mn, Mo, Ni, Co, and Cu for the same reason decrease sharply in comparison with red clay. Abnormally high contents of Mn, Mo, Cu, Ni, Co, and As in the upper layer of hemipelagic and transition sediments of the Mexico section result from diagenetic redistribution and their accumulation on the surface. Processes of diagenetic redistribution in hemipelagic and transition sediment mass of the Mexico section are more rapid than in similar sediments of the Japan section due lower sedimentation rates and higher initial concentrations of Mn. Basic similarity of element distribution regularities in sediments of Japan and Mexico sections is shown.

Ocean Acidification Affects Redox-Balance and Ion-Homeostasis in the Life-Cycle Stages of Emiliania huxleyi

Ocean Acidification (OA) has been shown to affect photosynthesis and calcification in the coccolithophore Emiliania huxleyi, a cosmopolitan calcifier that significantly contributes to the regulation of the biological carbon pumps. Its non-calcifying, haploid life-cycle stage was found to be relatively unaffected by OA with respect to biomass production. Deeper insights into physiological key processes and their dependence on environmental factors are lacking, but are required to understand and possibly estimate the dynamics of carbon cycling in present and future oceans. Therefore, calcifying diploid and non-calcifying haploid cells were acclimated to present and future CO2 partial pressures (pCO2; 38.5 Pa vs. 101.3 Pa CO2) under low and high light (50 vs. 300 µmol photons/m**2 /s). Comparative microarray-based transcriptome profiling was used to screen for the underlying cellular processes and allowed to follow up interpretations derived from physiological data. In the diplont, the observed increases in biomass production under OA are likely caused by stimulated production of glycoconjugates and lipids. The observed lowered calcification under OA can be attributed to impaired signal-transduction and ion-transport. The haplont utilizes distinct genes and metabolic pathways, reflecting the stage-specific usage of certain portions of the genome. With respect to functionality and energy-dependence, however, the transcriptomic OA-responses resemble those of the diplont. In both life-cycle stages, OA affects the cellular redox-state as a master regulator and thereby causes a metabolic shift from oxidative towards reductive pathways, which involves a reconstellation of carbon flux networks within and across compartments. Whereas signal transduction and ion-homeostasis appear equally OA-sensitive under both light intensities, the effects on carbon metabolism and light physiology are clearly modulated by light availability. These interactive effects can be attributed to the influence of OA and light on the redox equilibria of NAD and NADP, which function as major sensors for energization and stress. This generic mode of action of OA may therefore provoke similar cell-physiological responses in other protists.

Urinary 8-oxo-2′-deoxyguanosine:Redox regulation of DNA repair in vivo?

DNA is susceptible to damage by reactive oxygen species (ROS). ROS are produced during normal and pathophysiological processes in addition to ionizing radiation, environmental mutagens, and carcinogens. 8-oxo-2′-deoxyguanosine (8-oxodG) is probably one of the most abundant DNA lesion formed during oxidative stress. This potentially mutagenic lesion causes G → T transversions and is therefore an important candidate lesion for repair, particularly in mammalian cells. Several pathways exist for the removal, or repair, of this lesion from mammalian DNA. The most established is via the base excision repair enzyme, human 8-oxoguanine glycosylase (hOgg1), which acts in combination with the human apurinic endonuclease (hApe). The latter is known to respond to regulation by redox reactions and may act in combination with hOgg1. We discuss evidence in this review article concerning alternative pathways in humans, such as nucleotide excision repair (NER), which could possibly remove the 8-oxodG lesion. We also propose that redox-active components of the diet, such as vitamin C, may promote such repair, affecting NER specifically. © 2002 Elsevier Science Inc.

Redox signalling and detection of protein oxidation by mass spectrometry

It is now recognised that redox control of proteins plays an important role in many signalling pathways both in health and disease. Proteins can undergo a wide variety of oxidative post-translational modifications (oxPTM); while the reversible modifications are thought to be most important in physiological processes, non-reversible oxPTM may contribute to pathological situations and disease. The oxidant is also important in determining the type of oxPTM (chlorination, nitration, etc.), and the susceptibilities of residues vary depending on their structural location. The best characterized oxPTMs involved in signalling modulation are partial oxidations of cysteine to the disulfide, glutathionylated or sulfenic acid forms, but there is increasing evidence that specific oxidations of methionine and tyrosine may have some biological roles. Well understood examples of oxidative regulation include protein tyrosine phosphatases, e.g. PTP1B/C, and members of the MAPK pathways such as MEKK1 and ASK1. Transcription factors such as NFkB and Nrf-2 are also regulated by redox-active cysteines. Improved methods for analysing specific oxPTMs in biological samples are critical for understanding the physiological and pathological roles of these changes, and tandem or MS3 mass spectrometry techniques interfaced with nano-LC separation are being now used. MS3 fragmentation markers for a variety of oxidized residues including tyrosine, tryptophan and proline have been identified, and a precursor ion scanning method that allows the selective identification of these oxPTMs in complex samples has been developed. Such advances in technology offer potential for biomarker development, disease diagnosis and understanding pathology.