Local Structure of Hydrogen-Bonded Liquids

Ordinary yet unique, water is the substance on which life is based. Water seems, at first sight, to be a very simple molecule, consisting of two hydrogen atoms attached to one oxygen. Its small size belies the complexity of its action and its numerous anomalies, central to a broad class of important phenomena, ranging from global current circulation, terrestrial water and CO2 cycles to corrosion and wetting. The explanation of this complex behavior comes from water's unique ability to form extensive three-dimensional networks of hydrogen-bonds, whose nature and structures, in spite of a great deal of efforts involving a plethora of experimental and theoretical techniques, still lacks a complete scientific understanding. This thesis is devoted to the study of the local structure of hydrogen-bonded liquids, with a particular emphasis on water, taking advantage of a combination of core-level spectroscopies and density functional theory spectra calculations. X-ray absorption, in particular, is found to be sensitive to the local hydrogen-bond environment, thus offering a very promising tool for spectroscopic identification of specific structural configurations in water, alcohols and aqueous solutions. More specifically, the characteristic spectroscopic signature of the broken hydrogen-bond at the hydrogen side is used to analyze the structure of bulk water, leading to the finding that most molecules are arranged in two hydrogen-bond configurations, in contrast to the picture provided by molecular dynamics simulations. At the liquid-vapor interface, an interplay of surface sensitive measurements and theoretical calculations enables us to distinguish a new interfacial species in equilibrium with the gas. In a similar approach the cluster form of the excess proton in highly concentrated acid solutions and the different coordination of methanol at the vacuum interface and in the bulk can also be clearly identified. Finally the ability of core-level spectroscopies, aided by sophisticated density functional theory calculations, to directly probe the valence electronic structure of a system is used to observe the nature of the interaction between water molecules and solvated ions in solution. Water around transition metal ions is found to interact with the solute via orbital mixing with the metal d-orbitals. The hydrogen-bond between water molecules is explained in terms of electrostatic interactions enhanced by charge rehybridization in which charge transfer between connecting molecules is shown to be fundamental.

Liquid-liquid equilibria in binary solutions formed by [Pyridinium-Derived][F4B] ionic liquids and alkanols:new experimental data and validation of a multiparametric model for correlating LLE data

[EN]Experimental solubility data are presented for a set of binary systems composed of ionic liquids (IL) derived from pyridium, with the tetrafluoroborate anion, and normal alcohols ranging from ethanol to decanol, in the temperature interval of 275 420 K, at atmospheric pressure. For each case, the miscibility curve and the upper critical solubility temperature (UCST) values are presented. The effects of the ILs on the behavior of solutions with alkanols are analyzed, paying special attention to the pyridine derivatives, and considering a series of structural characteristics of the compounds involved.

Conformation and Stereodynamic of Hindered Aromatic System

The preparation of conformationally hindered molecules and their study by DNMR and computational methods are my thesis’s core. In the first chapter, the conformations and the stereodynamics of symmetrically ortho-disubstituted aryl carbinols and aryl ethers are described. In the second chapter, the structures of axially chiral atropisomers of hindered biphenyl carbinols are studied. In the third chapter, the steric barriers and the -barrier of 1,8-di-aylbiphenylenes are determined. Interesting atropisomers are found in the cases of arylanthrones, arylanthraquinones and arylanthracenes and are reported in the fourth chapter. By the combined use of dynamic NMR, ECD spectroscopy and DFT computations, the conformations and the absolute configurations of 2-Naphthylalkylsulfoxides are studied in the fifth chapter. In the last chapter, a new synthetic route to ,’-arylated secondary or tertiary alcohols by lithiated O-benzyl-carbamates carrying an N-aryl substituent and DFT calculations to determinate the cyclic intermediate are reported. This work was done in the research group of Prof. Jonathan Clayden, at the University of Manchester.

Acqua: solvente elettivo in Organocatalisi e Biocatalisi

Water is a safe, harmless, and environmentally benign solvent. From an eco-sustainable chemistry perspective, the use of water instead of organic solvent is preferred to decrease environmental contamination. Moreover, water has unique physical and chemical properties, such as high dielectric constant and high cohesive energy density compared to most organic solvents. The different interactions between water and substrates, make water an interesting candidate as a solvent or co-solvent from an industrial and laboratory perspective. In this regard, organic reactions in aqueous media are of current interest. In addition, from practical and synthetic standpoints, a great advantage of using water is immediately evident, since it does not require any preliminary drying process. This thesis was found on this aspect of chemical research, with particular attention to the mechanisms which control organo and bio-catalysis outcome. The first part of the study was focused on the aldol reaction. In particular, for the first time it has been analyzed for the first time the stereoselectivity of the condensation reaction between 3-pyridincarbaldehyde and the cyclohexanone, catalyzed by morpholine and 4-tertbutyldimethylsiloxyproline, using water as sole solvent. This interest has resulted in countless works appeared in the literature concerning the use of proline derivatives as effective catalysts in organic aqueous environment. These studies showed good enantio and diastereoselectivities but they did not present an in depth study of the reaction mechanism. The analysis of the products diastereomeric ratios through the Eyring equation allowed to compare the activation parameters (ΔΔH≠ and ΔΔS≠) of the diastereomeric reaction paths, and to compare the different type of catalysis. While morpholine showed constant diasteromeric ratio at all temperatures, the O(TBS)-L-proline, showed a non-linear Eyring diagram, with two linear trends and the presence of an inversion temperature (Tinv) at 53 ° C, which denotes the presence of solvation effects by water. A pH-dependent study allowed to identify two different reaction mechanisms, and in the case of O(TBS)-L-proline, to ensure the formation of an enaminic species, as a keyelement in the stereoselective process. Moreover, it has been studied the possibility of using the 6- aminopenicillanic acid (6-APA) as amino acid-type catalyst for aldol condensation between cyclohexanone and aromatic aldehydes. A detailed analysis of the catalyst regarding its behavior in different organic solvents and pH, allowed to prove its potential as a candidate for green catalysis. Best results were obtained in neat conditions, where 6-APA proved to be an effective catalyst in terms of yields. The catalyst performance in terms of enantio- and diastereo-selectivity, was impaired by the competition between two different catalytic mechanisms: one via imine-enamine mechanism and one via a Bronsted-acid catalysis. The last part of the thesis was dedicated to the enzymatic catalysis, with particular attention to the use of an enzyme belonging to the class of alcohol dehydrogenase, the Horse Liver Alcohol Dehydrogenase (HLADH) which was selected and used in the enantioselective reduction of aldehydes to enantiopure arylpropylic alcohols. This enzyme has showed an excellent responsiveness to this type of aldehydes and a good tolerance toward organic solvents. Moreover, the fast keto-enolic equilibrium of this class of aldehydes that induce the stereocentre racemization, allows the dynamic-kinetic resolution (DKR) to give the enantiopure alcohol. By analyzing the different reaction parameters, especially the pH and the amount of enzyme, and adding a small percentage of organic solvent, it was possible to control all the parameters involved in the reaction. The excellent enatioselectivity of HLADH along with the DKR of arylpropionic aldehydes, allowed to obtain the corresponding alcohols in quantitative yields and with an optical purity ranging from 64% to >99%.

Archaeological Baltic amber: degradation mechanisms and conservation measures

The aim of this project was to achieve a deep understanding of the mechanisms by which Baltic amber degrades, in order to develop techniques for preventive conservation of archaeological amber objects belonging to the National Museum of Denmark’s collections. To examine deterioration of Baltic amber, a starting point was to identify and monitor surface and bulk properties which are affected during degradation. The way to operate consisted of the use of accelerated ageing to initiate degradation of raw Baltic amber samples in different conditions of relative humidity, oxygen exposure or pH and, successively, of the use of non/micro-destructive techniques to identify and quantify changes in visual, chemical and structural properties. A large piece of raw Baltic amber was used to prepare several test samples for two different kinds of accelerated ageing: thermal-ageing and photo-ageing. During the ageing, amber samples were regularly examined through several analytical techniques related to different information: appearance/colour change by visual examination, photography and colorimetry; chemical change by infrared spectroscopy, Raman spectroscopy and elemental analysis; rate of oxidation by oxygen measurement; qualitative analysis of released volatiles by gas chromatography – mass spectrometry. The obtained results were analysed through both critical evaluation and statistical study. After the interpretation of the achieved data, the main relations between amber and environmental factors during the degradation process became clearer and it was possible to identify the major pathways by which amber degrades, such as hydrolysis of esters into alcohols and carboxylic acids, thermal-oxidation and photo-oxidation of terpenoid components, depolymerisation and decomposition of the chemical structure. At the end it was possible to suggest a preventive conservation strategy based on the control of climatic, atmospheric and lighting parameters in the environment where Baltic amber objects are stored and displayed.

Stereoselective Catalytic Processes for the Synthesis of Polycyclic Aromatic Compounds

In this PhD-thesis, two methodologies for enantioselective intramolecular ring closing reaction on indole cores are presented. The first methodology represents a highly stereoselective alkylation of the indole N1-nitrogen, leading to 3,4-dihydro-pyrazinoindol-1-ones – a structural class which is known for its activity on the CNS and therefore of high pharmacological interest concerning related diseases. In this approach, N-benzyl cinchona-alkaloids were used for the efficient catalysis of intramolecular aza-Michael reactions. Furthermore, computational studies in collaboration with the research group Prof. Andrea Bottoni (Department of Chemistry “G. Ciamician”, Bologna) were accomplished in order to get insight into the key interactions between catalyst and substrate, leading to enantiomeric excesses up to 91%. The results of the calculations on a model system are in accordance with the experimental results and demonstrate the high sensibility of the system towards structural modifications. The second project deals with a metal catalyzed, intramolecular Friedel-Crafts (FC)-reaction on indolyl substrates, carrying a side chain which on its behalf is furnished with an allylic alcohol unit. Allylic alcohols are part of the structural class of “π-activated alcohols” – alcohols, which are more easily activated due to the proximity to a π-unit (allyl-, propargyl-, benzyl-). The enantioselective intramolecular cyclization event is catalyzed efficiently by employment of a chiral Au(I)-catalyst, leading to 1-vinyl- or 4-vinyl-tetrahydrocarbazoles (THCs) under the formation of water as byproduct. This striking and novel process concerning the direct activation of alcohols in catalytic FC-reactions was subsequently extended to similar precursors, leading to functionalized tetrahydro-β-carbolines. These two methodologies represent highly efficient approaches towards the synthesis of scaffolds, which are of enormous pharmaceutical interest and amplify the spectra of enantioselective catalytic functionalisations of indoles.

Selektive und duale COX-1-, COX-2-Inhibitoren aus der Reihe der Methanone

Zusammenfassung: Prostaglandine (PG) sind wichtige biologische Entzündungsmediatoren, die aus der Arachidonsäure (AA) durch das Enzym Cyclooxygenase (COX) entstehen. Trotz einiger unerwünschter Wirkungen, sind Cyclooxygenase-Hemmer Mittel der Wahl zur Unterdrückung entzündlicher Prozesse. Von der Cyclooxygenase existieren zwei Isoenzyme: COX-1 und COX-2. Eine selektive Hemmung der COX-2 bzw. eine duale Hemmung der COX-1 und COX-2 wird als erfolgversprechendes Prinzip zur Behandlung von entzündlichen Erkrankungen diskutiert.Ziel der Arbeit war die Synthese und in vitro Testung sowie die Erstellung von Struktur-Wirkungs-Beziehungen selektiver bzw. dualer Hemmstoffe der COX-1/-2. Zusätzlich wurden die Substanzen auf inhibitorische Aktivität gegenüber der 5- und 12-Lipoxygenase untersucht.Ausgehend von der Struktur selektiver Hemmstoffe der COX-2 bzw. von dualen COX-1/ COX-2-Inhibitoren sowie von marktüblichen nichtsteroidalen Antirheumatika (NSAR), wurde das Diarylmethanon-Element als Basis gewählt. An diesem Strukturelement wurden Modifikationen vorgenommen, um selektive Hemmstoffe der COX-2 bzw. duale COX-1/ COX-2-Hemmstoffe zu erhalten.Die synthetisierten Verbindungen lassen sich in [4-(Methylsulfanyl)phenyl]- und [4-(Methylsulfonyl)phenyl](aryl)methanone, N-(Aroylphenyl)sulfonamide und -amide sowie (Hydroxyphenyl)(2-thienyl)methanone unterteilen.In der Reihe der [4-(Methylsulfanyl)phenyl](aryl)methanone sind potente Hemmstoffe sowohl der COX-1 als auch der COX-2 erhalten worden. Im Gegensatz dazu zeigen die [4-(Methylsulfonyl)phenyl](aryl)methanone gegenüber COX-1 und COX-2 keine inhibitorische Aktivität. Mit dem 2-Thienylderivat wurde ein potenter, dualer Hemmstoff beider Cyclooxygenase-Isoenzyme identifiziert, dessen Wirkstärke (bezüglich der COX-2) auf den Austausch von Phenyl gegen 2-Thienyl zurückzuführen ist.Die N-(Aroylphenyl)sulfonamide und -amide bilden die umfangreichste Gruppe bei den durchgeführten Untersuchungen, wobei besonders die regioisomeren N-(2-Aroylphenyl)sulfonamide und -amide eingehender studiert wurden. Auf der Basis der (2-Aroylphenyl)sulfonamide läßt sich für die Hemmung der COX-1 eine Struktur-Wirkungs-Beziehungen formulieren, die anhand Hilfe geeigneter Verbindungen überprüft wurde. Die Untersuchungen wurden zum Teil auch auf die 3- und 4-Regioisomeren ausgedehnt, wobei sich die erhaltenen Struktur-Wirkungs-Beziehungen bestätigten. Die Arylsulfonamide inhibieren bevorzugt die COX-1. Auch (4-Aroylphenyl)sulfonamide wurden auf mögliche inhibitorische Aktivität untersucht. Die Einbindung des Amidstickstoffs in ein Indolin- bzw. Tetrahydrochinolin-Ringsystem oder des Sulfonamids in ein 1,3-Propansultam führte in jedem Falle zu wenig aktiven Verbindungen gegenüber der COX-1. N-(2-Aroylphenyl)amide zeigten in Übereinstimmung mit der Hypothese an der COX-1 eine gute inhibitorische Aktivität.Aus der Reihe der (Hydroxyphenyl)(2-thienyl)methanone wurden die freien Alkohole, die Methylether und verschiedene Ester dargestellt und auf COX-1-Aktivität untersucht. Acetate, aber auch Phenole sind die potentesten Inhibitoren der COX-1. Als günstigte Positionen für die 2-Thienylcarbonyl-Einheit am Hydroxyphenylrest erweist sich die ortho- bzw. para-Position.

Study of the components of quality in SO2-free wines obtained by innovative vinification protocols. Evaluation of the pre-fermentative addition of lysozyme and oenological tannins.

The research performed during the PhD candidature was intended to evaluate the quality of white wines, as a function of the reduction in SO2 use during the first steps of the winemaking process. In order to investigate the mechanism and intensity of interactions occurring between lysozyme and the principal macro-components of musts and wines, a series of experiments on model wine solutions were undertaken, focusing attention on the polyphenols, SO2, oenological tannins, pectines, ethanol, and sugar components. In the second part of this research program, a series of conventional sulphite added vinifications were compared to vinifications in which sulphur dioxide was replaced by lysozyme and consequently define potential winemaking protocols suitable for the production of SO2-free wines. To reach the final goal, the technological performance of two selected yeast strains with a low aptitude to produce SO2 during fermentation were also evaluated. The data obtained suggested that the addition of lysozyme and oenological tannins during the alcoholic fermentation could represent a promising alternative to the use of sulphur dioxide and a reliable starting point for the production of SO2-free wines. The different vinification protocols studied influenced the composition of the volatile profile in wines at the end of the alcoholic fermentation, especially with regards to alcohols and ethyl esters also a consequence of the yeast’s response to the presence or absence of sulphites during fermentation, contributing in different ways to the sensory profiles of wines. In fact, the aminoacids analysis showed that lysozyme can affect the consumption of nitrogen as a function of the yeast strain used in fermentation. During the bottle storage, the evolution of volatile compounds is affected by the presence of SO2 and oenological tannins, confirming their positive role in scaveging oxygen and maintaining the amounts of esters over certain levels, avoiding a decline in the wine’s quality. Even though a natural decrease was found on phenolic profiles due to oxidation effects caused by the presence of oxygen dissolved in the medium during the storage period, the presence of SO2 together with tannins contrasted the decay of phenolic content at the end of the fermentation. Tannins also showed a central role in preserving the polyphenolic profile of wines during the storage period, confirming their antioxidant property, acting as reductants. Our study focused on the fundamental chemistry relevant to the oxidative phenolic spoilage of white wines has demonstrated the suitability of glutathione to inhibit the production of yellow xanthylium cation pigments generated from flavanols and glyoxylic acid at the concentration that it typically exists in wine. The ability of glutathione to bind glyoxylic acid rather than acetaldehyde may enable glutathione to be used as a ‘switch’ for glyoxylic acid-induced polymerisation mechanisms, as opposed to the equivalent acetaldehyde polymerisation, in processes such as microoxidation. Further research is required to assess the ability of glutathione to prevent xanthylium cation production during the in-situ production of glyoxylic acid and in the presence of sulphur dioxide.

Ternäre polymerhaltige Lösungen - Phasenverhalten und Grenzflächenspannung

Im Rahmen dieser Arbeit wurden experimentelle und theoretische Untersuchungen zum Phasen- und Grenzflächenverhalten von ternären Systemen des Typs Lösungsmittel/Fällungsmittel/Polymer durchgeführt. Diese Art der Mischungen ist vor allem für die Planung und Durchführung der Membranherstellung von Bedeutung, bei der die genaue Kenntnis des Phasendiagramms und der Grenzflächenspannung unabdingbar ist. Als Polymere dienten Polystyrol sowie Polydimethylsiloxan. Im Fall des Polystyrols kam Butanon-2 als Lösungsmittel zum Einsatz, wobei drei niedrigmolekulare lineare Alkohole als Fällungsmittel verwendet wurden. Für Polydimethylsiloxan eignen sich Toluol als Lösungsmittel und Ethanol als Fällungsmittel. Durch Lichtstreumessungen, Dampfdruckbestimmungen mittels Headspace-Gaschromatographie (VLE-Gleichgewichte) sowie Quellungsgleichgewichten lassen sich die thermodynamischen Eigenschaften der binären Subsysteme charakterisieren. Auf Grundlage der Flory-Huggins-Theorie kann das experimentell bestimmte Phasenverhalten (LLE-Gleichgewichte) in guter Übereinstimmung nach der Methode der Direktminimierung der Gibbs'schen Energie modelliert werden. Zieht man die Ergebnisse der Aktivitätsbestimmung von Dreikomponenten-Mischungen mit in Betracht, so ergeben sich systematische Abweichungen zwischen Experiment und Theorie. Sie können auf die Notwendigkeit ternärer Wechselwirkungsparameter zurückgeführt werden, die ebenfalls durch Modellierung zugänglich sind.Durch die aus den VLE- und LLE-Untersuchungen gewonnenen Ergebnissen kann die sog. Hump-Energie berechnet werden, die ein Maß für die Entmischungstendenz darstellt. Diese Größe eignet sich gut zur Beschreibung von Grenzflächenphänomenen mittels Skalengesetzen. Die für binäre Systeme gefundenen theoretisch fundierten Skalenparameter gelten jedoch nur teilweise. Ein neues Skalengesetz lässt erstmals eine Beschreibung über die gesamte Mischungslücke zu, wobei ein Parameter durch eine gemessene Grenzflächenspannung (zwischen Fällungsmittel/Polymer) ersetzt werden kann.

Synthese und radioaktive Markierung potentieller PET- bzw. SPECT-Liganden zur Quantifizierung und Visualisierung der pankreatischen beta-Zell-Masse

Abstract Due to the ongoing efforts in transplanting b-cell mass there is also a great medical interest in specific b-cell imaging agents to quantify the acceptance of transplanted islets in humans in vivo. Additionally, in the context of type 1 diabetes mellitus the chronic and progressive loss of b-cells caused by autoimmune destruction has led to concerted efforts to prevent further loss of b-cells by autoantigen-specific immunotherapy of pre-diabetic patients. nateglinide and glibenclamide are SUR1 ligands used to stimulate insulin secretion in type 2 diabetic patients. They bind to a class of molecules known as the ATP-sensitive potassium channels, located on the insulin producing b-cells of the islets of Langerhans and are therefore excellent candidates as b-cell specific tracers. To obtain a precursor for a direct labelling of nateglinide with [18F]fluoride, the aromatic system of the phenylalanine structure element was derivatised to obtain a phenolic OH-group in 4-position which is capable of further derivatisation. The formed phenylether N-(trans-4-isopropylcyclohexanecarbonyl)-O-(2-hydroxyethyl)-D-tyrosin benzylester was tried to be tosylated according to several literature procedures but none of them was applicable. The catalytic influence of ytterbium(III)triflate in the reaction of toluenesulfonic acid anhydride and the alcohol was investigated. It was found that Yb(III) facilitates the tosylation of the alcohol under non-basic conditions and was extended to the tosylation of a great variety of different alcohols to prove its applicability in general. The radioactive labelling of N-(trans-4-isopropyl-cyclohexanecarbonyl)-O-(2-[18F]fluoroethyl)-D-tyrosine with [18F]F-/ Kryptofix® 222/ K2CO3-system was achieved in radiochemical yields (RCY) of 10 % after deprotection with Pd/ C and H2. In addition to the direct labelling approach, a labelling procedure applying 2[18F]fluoroethyltosylate and N-(trans-4-isopropyl-cyclohexanecarbonyl)-D-tyrosin was performed in 40 % RCY. Unfortunately the determination of the KD value of N-(trans-4-isopropylcyclohexanecarbonyl)-O-(2-fluoroethyl)-D-tyrosine revealed a significant decrease in affinity compared to original nateglinide. The in vivo evaluation of some 18F-labelled glibenclamide derivatives in humans and animals revealed that longer measuring times are warranted because a high liver uptake spoiles the data acquisition and the activity washout proceeds very slowly. Therefore glibenclamide was labelled with a radioisotope with a longer half life such as 99mTc (t1/2 = 6 h) to lengthen the possible time frame for image acquisition. The synthesis of a 99mTc labelled hydrophilic glibenclamide derivative was performed. It is hoped that gliben-clamide is internalised into the b-cell and there binds to the 95 % of intracellular SUR-1 receptors with eventual metablolisation and thus trapping in the cell. The KD-value of the corresponding Re-compound was determined to be 0.5 nM and the insulin secretion properties were similar to those of original glibenclamide. The labelling precursor N-{4-[N,N-bis-(carboxy-methyl)-aminoethyl)-5-chlorobenzene-carboxamido]-ethyl}-benzene-sulfonyl-N'-cyclohexyl urea tris sodium salt was reacted with [99mTc(I)(OH2)3(CO)3] Cl to yield the final N-{4-[99mTc(I)-tricarbonyl-N,N-bis-(carboxymethyl)-aminoethyl)-5-chloro-benzene-carboxamidoethyl]-benzene-sulfonyl}-N'-cyclo-hexyl-urea sodium salt in 70% RCY.

Emissions of volatile organic compounds from tropical savanna vegetation and biomass burning

This dissertation focuses on characterizing the emissions of volatile organic compounds (VOCs) from grasses and young trees, and the burning of biomass mainly from Africa and Indonesia. The measurements were performed with a proton-transfer-reaction mass spectrometer (PTR-MS). The biogenic emissions of tropical savanna vegetation were studied in Calabozo (Venezuela). Two field campaigns were carried out, the first during the wet season (1999) and the second during the dry season (2000). Three grass species were studied: T. plumosus, H. rufa and A. canescens, and the tree species B. crassifolia, C. americana and C. vitifolium. The emission rates were determined with a dynamic plant enclosure system. In general, the emissions increased exponentially with increasing temperature and solar radiation. Therefore, the emission rates showed high variability. Consequently, the data were normalized to a standard temperature of 30°C, and standard emission rates thus determined allowed for interspecific and seasonal comparisons. The range of average daytime (10:00-16:00) emission rates of total VOCs measured from green (mature and young) grasses was between 510-960 ngC/g/h. Methanol was the primary emission (140-360 ngC/g/h), followed by acetaldehyde, butene and butanol and acetone with emission rates between 70-200 ngC/g/h. The emissions of propene and methyl ethyl ketone (MEK) were <80 ngC/g/h, and those of isoprene and C5-alcohols were between 10-130 ngC/g/h. The oxygenated species represented 70-75% of the total. The emission of VOCs was found to vary by up to a factor of three between plants of the same species, and by up to a factor of two between the different species. The annual source of methanol from savanna grasses worldwide estimated in this work was 3 to 4.4 TgC, which could represent up to 12% of the current estimated global emission from terrestrial vegetation. Two of the studied tree species, were isoprene emitters, and isoprene was also their primary emission (which accounted for 70-94% of the total carbon emitted) followed by methanol and butene + butanol. The daytime average emission rate of isoprene measured in the wet season was 27 mgC/g/h for B. crassifolia, and 123 mgC/g/h for C. vitifolium. The daytime emissions of methanol and butene + butanol were between 0.3 and 2 mgC/g/h. The total sum of VOCs emission measured during the day in the wet season was between 30 and 130 mgC/g/h. In the dry season, in contrast, the methanol emissions from C. vitifolium saplings –whose leaves were still developing– were an order of magnitude higher than in the wet season (15 mgC/g/h). The isoprene emission from B. crassifolia in the dry season was comparable to the emission in the wet season, whereas isoprene emission from C. vitifolium was about a factor of three lower (~43 mgC/g/h). Biogenic emission inventories show that isoprenoids are the most prominent and best-studied compounds. The standard emission rates of isoprene and monoterpenes of the measured savanna trees were in the lower end of the range found in the literature. The emission of other biogenic VOCs has been sparsely investigated, but in general, the standard emissions from trees studied here were within the range observed in previous investigations. The biomass burning study comprised the measurement of VOCs and other trace-gas emissions of 44 fires from 15 different fuel types, primarily from Africa and Indonesia, in a combustion laboratory. The average sum of emissions (excluding CO2, CO and NO) from African fuels was ~18 g(VOC)/kg. Six of the ten most important emissions were oxygenated VOCs. Acetic acid was the major emission, followed by methanol and formaldehyde. The emission of methane was of the same order as the methanol emission (~5 g/kg), and that of nitrogen-containing compounds was ~1 g/kg. An estimate of the VOC source from biomass burning of savannas and grasslands worldwide suggests that the sum of emissions is about 56 Tg/yr, of which 34 Tg correspond to oxygenated VOCs, 14 Tg to unsaturated and aromatic compounds, 5 Tg to methane and 3 Tg to N-compounds. The estimated emissions of CO, CO2 and NO are 216, 5117 and 9.4 Tg/yr, respectively. The emission factors reported here for Indonesian fuels are the first results of laboratory fires using Indonesian fuels. Acetic acid was the highest organic emission, followed by acetol, a compound not previously reported in smoke, methane, mass 97 (tentatively identified as furfural, dimethylfuran and ethylfuran), and methanol. The sum of total emissions of Indonesian fuels was 91 g/kg, which is 5 times higher than the emissions from African fuels. The results of this study reinforces the importance of oxygenated compounds. Due to the vast area covered by tropical savannas worldwide, the biogenic and biomass burning emission of methanol and other oxygenated compounds may be important for the regional and even global tropospheric chemistry.

Anaerobic oxidation of ethanol over spinel mixed oxides: the first step in the steam-iron process for H2 production

The future hydrogen demand is expected to increase, both in existing industries (including upgrading of fossil fuels or ammonia production) and in new technologies, like fuel cells. Nowadays, hydrogen is obtained predominantly by steam reforming of methane, but it is well known that hydrocarbon based routes result in environmental problems and besides the market is dependent on the availability of this finite resource which is suffering of rapid depletion. Therefore, alternative processes using renewable sources like wind, solar energy and biomass, are now being considered for the production of hydrogen. One of those alternative methods is the so-called “steam-iron process” which consists in the reduction of a metal-oxide by hydrogen-containing feedstock, like ethanol for instance, and then the reduced material is reoxidized with water to produce “clean” hydrogen (water splitting). This kind of thermochemical cycles have been studied before but currently some important facts like the development of more active catalysts, the flexibility of the feedstock (including renewable bio-alcohols) and the fact that the purification of hydrogen could be avoided, have significantly increased the interest for this research topic. With the aim of increasing the understanding of the reactions that govern the steam-iron route to produce hydrogen, it is necessary to go into the molecular level. Spectroscopic methods are an important tool to extract information that could help in the development of more efficient materials and processes. In this research, ethanol was chosen as a reducing fuel and the main goal was to study its interaction with different catalysts having similar structure (spinels), to make a correlation with the composition and the mechanism of the anaerobic oxidation of the ethanol which is the first step of the steam-iron cycle. To accomplish this, diffuse reflectance spectroscopy (DRIFTS) was used to study the surface composition of the catalysts during the adsorption of ethanol and its transformation during the temperature program. Furthermore, mass spectrometry was used to monitor the desorbed products. The set of studied materials include Cu, Co and Ni ferrites which were also characterized by means of X-ray diffraction, surface area measurements, Raman spectroscopy, and temperature programmed reduction.

Oxylipins biosynthesis in Lactobacillus helveticus in the presence of oxidative stress

This PhD thesis is aimed at studying the possible pathways and the mechanisms that can trigger oxylipins biosynthesis, and particularly that of short chain aldehydes and alcohols, in Lactobacillus helveticus, also in the presence of oxidative stress, using a totally labelled linoleic acid as precursor. In plants and fungi these molecules, involved in defence mechanisms against pathogens and in communication systems, derive from the oxidation of cellular unsaturated fatty acids (UFAs) and their accumulation is associated with stress exposure. Since some oxylipins are produced also by lactobacilli, it is possible to hypothesize that a metabolic pathway from UFAs to oxylipins, similar to what happens in plants and fungi, is present also in lactic acid bacteria. The results obtained pointed out that some volatile molecules are the result of UFAs catabolism, since they appear only when cells are incubated in their presence. Labelled linoleic acid is integrated in the membrane and subsequently transformed into aldehydes and alcohols, whose extent and carbon atoms number depend on stress exposure. The enzymes responsible for this metabolic pathway in plants and fungi (e.g. lipoxygenase, dioxygenase) seem to be absent in Lactobacillus helveticus and in other lactobacilli. Proteomic analyses show the over expression of many proteins, including thioredoxin reductase (part of the bacterial oxidative defence system), mainly in cells grown with linoleic acid without oxidative stress exposure, confirming that linoleic acid itself induces oxidative stress. 6 general oxidoreductases (class including dioxygenases and peroxidase) were found and therefore a deeper investigation on them could be productive in elucidating all steps involved in oxylipins biosynthesis in bacteria. Due to the multiple role of oxylipins (flavouring agents, antimicrobial compounds and interspecific signalling molecules) the identification of genes involved and regulating factors should have an important biotechnological impact, also allowing the overproduction of selected bioactive molecules.

Nuovi processi catalitici per la sintesi di prodotti ad attività farmacologica

The transition metal-catalyzed allylic alkylation (Tsuji-Trost type reaction) is a powerful tool for C-C, C-N, and C-O bond formation, which has been widely applied to organic chemistry over the last decades. Typical substrates for this transformation are activated allylic compounds such as halides, esters, carbonates, carbamates, phosphates, and so on. However, use of these substrates is associated with the disadvantage of generating a stoichiometric amount of chemical waste. Furthermore, these starting materials have to be prepared in an extra step from the corresponding allylic alcohol. Thus, ideal substrates would be the allylic alcohols themselves, with water being the only byproduct in this case. However, the scarse propensity of the hydroxyl moiety to act as good leaving group has significantly limited their use so far. During the last decade significant efforts have been made in order to develop more atom-economical and environmentally-friendly allylic alkylation protocols by employing allylic alcohols directly. In this PhD dissertation two main projects addressing this topic are presented. “Project 1” deals with the development of new metal-catalyzed intramolecular Friedel-Crafts (FC) allylic alkylations of electron-rich (PAPER A), as well as challenging electron-poor arenes (PAPER B) with alcohols. In “Project 2”, gold(I)-catalyzed intramolecular and stereoselective allylic alkylation reactions are reported. In particular, a FC alkylation of indole-containing allylic alcohols is presented in PAPER C. While, an O-alkylation of aminol-containing allylic alcohols is reported in PAPER D. To the best of knowledge, these reports represent the first example of gold(I)-catalyzed stereoselective alkylations with alcohols.