Sviluppo di un metodo elettrochimico per la determinazione della capacità antiossidante

The aim of the present thesis, carried out at the Analytical Group of the Faculty of Industrial Chemistry in Bologna, is to develop a new electrochemical method for the determination of the Antioxidant Capacity (AOC). The approach is based on the deposition of a non-conducting polymeric film on the working electrode surface and the following exposition to the radicals OH· produced by H2O2 photolysis. The strongly oxidant action of hydroxyl radicals degrades, causing an increase of the Faradic current, relevant to the redox couple [Ru(NH3)6]2+/3+ monitored by cyclic voltammetry(CV); the presence of an antioxidant compound in solution slows down the radical action, thus protecting the polymeric film and blocking the charge transfer. The parameter adopted for the quantification of the AOC, was the induction time, called also lag phase, which is the time when the degradation of the film starts. Five pure compounds, among most commonly antioxidant, were investigated : Trolox®(an analogue water-soluble of vitamin E), (L)-ascorbic acid, gallic acid, pyrogallol and (-)- epicatechin. The AOC of each antioxidant was expressed by TEAC index (Trolox® Equivalent Antioxidant Capacity), calculated from the ratio between the slope of the calibration curve of the target compound and the slope of the calibration curve of Trolox®. The results from the electrochemical method, have been compared with those obtained from some other standardized methods, widely employed. The assays used for the comparison, have been: ORAC, a spectrofluorimetric method based on the decrease of fluorescein emission after the attack of alkylperoxide radicals, ABTS and DPPH that exploit the decoloration of stable nitrogen radicals when they are reduced in presence of an antioxidant compound and, finally, a potentiometric method based on the response of the redox couple [Fe(CN)6]3-/ [Fe(CN)6]4-. From the results obtained from pure compounds, it has been found that ORAC is the methodology showing the best correlation with the developed electrochemical method, maybe since similar radical species are involved. The comparison between the considered assays, was also extended to the analysis of a real sample of fruit juice. In such a case the TEAC value resulting from the electrochemical method is higher than those from standardized assays.

Deposizione elettrochimica di film polimerici foto-attivi per la realizzazione di celle solari

Plastic solar cells bear the potential for large-scale power generation based on flexible, lightweight, inexpensive materials. Since the discovery of the photo-induced electron transfer from a conjugated polymer (electron-donor) to fullerene or its derivatives molecules (electron-acceptors), followed by the introduction of the bulk heterojunction concept which means donors and acceptors blended together to realize the fotoactive layer, materials and deposition techniques have been extensively studied. In this work, electrochemical-deposition methods of polymeric conductive films were studied in order to realize bulk heterojunction solar cells. Indium Tin Oxide (ITO) glass electrodes modified with a thin layer of poly(3,4-ethylenedioxythiophene) (PEDOT) were electrochemically prepared under potentiodynamic and potentiostatic conditions; then those techniques were applied for the electrochemical co-deposition of donor and acceptor on modified ITO electrode to produce the active layer (blend). For the deposition of the electron-donor polymer the electropolymerization of many functionalized thiophene monomers was investigated while, as regards acceptors, fullerene was used first, then the study was focused on its derivative PCBM ([6,6]-phenyl-C61-butyric acid methyl ester). The polymeric films obtained (PEDOT and blend) were electrochemically and spectrophotometrically characterized and the film thicknesses were evaluated by atomic force microscopy (AFM). Finally, to check the performances and the efficiency of the realized solar cells, tests were carried out under standard conditions. Nowadays bulk heterojunction solar cells are still poorly efficient to be competitively commercialized. A challenge will be to find new materials and better deposition techniques in order to obtain better performances. The research has led to several breakthroughs in efficiency, with a power conversion efficiency approaching 5 %. The efficiency of the solar cells produced in this work is even lower (lower than 1 %). Despite all, solar cells of this type are interesting and may represent a cheaper and easier alternative to traditional silicon-based solar panels.

Stabilizzazione del Blu di Prussia con film politiofenici depositati per via elettrochimica

Hydrogen peroxide (H2O2) is a powerful oxidant which is commonly used in a wide range of applications in the industrial field. Several methods for the quantification of H2O2 have been developed. Among them, electrochemical methods exploit the ability of some hexacyanoferrates (such as Prussian Blue) to detect H2O2 at potentials close to 0.0 V (vs. SCE) avoiding the occurrence of secondary reactions, which are likely to run at large overpotentials. This electrocatalytic behaviour makes hexacyanoferrates excellent redox mediators. When deposited in the form of thin films on the electrode surfaces, they can be employed in the fabrication of sensors and biosensors, normally operated in solutions at pH values close to physiological ones. As hexacyanoferrates show limited stability in not strongly acidic solutions, it is necessary to improve the configuration of the modified electrodes to increase the stability of the films. In this thesis work, organic conducting polymers were used to fabricate composite films with Prussian Blue (PB) to be electro-deposited on Pt surfaces, in order to increase their pH stability. Different electrode configurations and different methods of synthesis of both components were tested, and for each one the achievement of a possible increase in the operational stability of Prussian Blue was verified. Good results were obtained for the polymer 3,3''-didodecyl-2,2':5',2''-terthiophene (poly(3,3''-DDTT)), whose presence created a favourable microenvironment for the electrodeposition of Prussian Blue. The electrochemical behaviour of the modified electrodes was studied in both aqueous and organic solutions. Poly(3,3''-DDTT) showed no response in aqueous solution in the potential range where PB is electroactive, thus in buffered aqueous solution is was possible to characterize the composite material, focusing only on the redox behaviour of PB. A combined effect of anion and cation of the supporting electrolyte was noticed. The response of Pt electrodes modified with films of the PB /poly(3,3''-DDTT) composite was evaluated for the determination of H2O2. The performance of such films was found better than that of the PB alone. It can be concluded that poly(3,3''-DDTT) plays a key role in the stabilization of Prussian Blue causing also a wider linearity range for the electrocatalytic response to H2O2.

Valutazione della qualità di oli extravergini di oliva chiarificati mediante gas inerte

Diversi studi presenti in letteratura hanno messo in evidenza come il sistema di filtrazione di un olio extravergine di oliva rivesta un ruolo importante per una corretta conservazione del prodotto nel tempo; contestualmente, l’applicazione di metodi tradizionali di trattamento comporta la diminuzione di alcuni componenti minori: oltre all’allontanamento dei composti in sospensione, che concorrono a fornire l’aspetto torbido all’olio non trattato, viene allontanata acqua micro dispersa, che ha l’importante compito di solubilizzare molecole dotate di una certa polarità, principalmente fenoliche che, come noto, risultano indispensabili per la stabilità ossidativa e giocano un ruolo chiave nell’impartire all’olio extravergine di oliva alcune note sensoriali peculiari, quali l’amaro ed il piccante, percepibili in fase gustativa. Lo scopo di questo progetto sperimentale è stato di valutare la qualità chimica e sensoriale di tre oli extra vergini di oliva sottoposti ad un sistema brevettato di illimpidimento, basato sul passaggio di un flusso di gas inerte, quale l’argon, nella massa di olio d'oliva. Questo metodo può rappresentare una valida alternativa ai trattamenti tradizionali e per questo è indispensabile valutarne i punti di forza e di debolezza in relazione all’effettiva possibilità di impiego nella produzione industriale. Per questa finalità, il sistema brevettato dall'Università di Bologna e dalla Sapio (una società privata che fornisce il gas per i settori industriali e della ricerca) è stato applicato a un lotto di 50 L di ciascun olio dopo la sua produzione mediante mini-frantoio. I campioni, sia trattati che controllo, sono stati imbottigliati e conservati a temperatura ambiente e mantenuti al buio prima dell'analisi. Dopo quattro mesi di conservazione, sono stati valutati gli indici di qualità di base, tra cui acidità libera, numero di perossidi, assorbimento specifico nella zona dei dieni e trieni coniugati e il profilo sensoriale. Inoltre è stata valutata la stabilità ossidativa in condizioni forzate, il profilo dei composti maggioritari (acidi grassi) e dei composti minori (tocoferoli, fenoli, volatili, acqua). I risultati sono stati utilizzati per la comparazione della qualità complessiva degli oli extravergini di oliva sottoposti a chiarifica con sistema brevettato rispetto a quelli non trattati, permettendo una valutazione dell’effetto del nuovo sistema sulle caratteristiche chimiche e sensoriali del prodotto.

Development of Organocatalytic stereoselective SN1 type reactions

The proposal in my thesis has been the study of Stereoselective α-alkylation through SN1 type reaction. SN1 type reaction involves a stabilized and reactive carbocation intermediate By taking advantages of stability of particular carbocations, the use of carbocations in selective reactions has been important. In this work has been necessary to know the stability and reactivity of carbocations. And the work of Mayr group has helped to rationalize the behaviour and reactivity between the carbocations and nucleophiles by the use of Mayr’s scale of reactivity. The use of alcohols to performed the stable and reactive carbocations have been the key in my thesis. The direct nucleophilic substitution of alcohols has been a crucial scope in the field of organic synthesis, because offer a wide range of intermediates for the synthesis of natural products and pharmaceutics synthesis. In particular the catalytic nucleophilic direct substitution of alcohols represents a novel methodology for the preparation of a variety of derivatives, and water only as the sub-product in the reaction. The stereochemical control of the transformation C-H bond into stereogenic C-C bond adjacent to carbonyl functionalized has been studied for asymmetric catalysis. And the field of organocatalysis has introduced the use of small organic molecule as catalyst for stereoselective transformations. Merging these two concepts Organocatalysis and Mayr’s scale, my thesis has developed a new approach for the α-alkylation of aldehydes and ketones through SN1 type reaction.

Thiophene- Based Materials for Photovoltaic Applications

Thiophene oligomers (OTs) and polymers (PTs) are currently attracting remarkable attention as organic materials showing semiconducting, fluorescent, nonlinear optical and liquid crystalline properties. All these properties can be fine-tuned through minor structural modifications. As a consequence, thiophene oligomers and polymers are among the most investigated compounds for applications in organic electronics, optoelectronics and thin film devices such as field effect transistors (FETs), light emitting diodes (LEDs) and photovoltaic devices (PVDs). Our research aims to explore the self-assembly features and the optical, electrical and photovoltaic properties of a class of thiophene based materials so far scarcely investigated, namely that of oligo- and polythiophenes head-to-head substituted with alkyl or S-alkyl chains. In particular, we synthesized these compounds in short reaction times, high yields, high purity and environmentally friendly procedures taking advantage of ultrasound (US) and microwave (MW) enabling technologies in Suzuki-Miyaura cross-couplings.

Synthesis and Supramolecular Architectures of Lipophilic Derivatives of Guanine

Self-assembly relies on the association of pre-programmed building blocks through non-covalent interactions to give complex supramolecular architectures. Previous studies provided evidence for the unique self-assembly properties of semi-synthetic lipophilic guanosine derivatives which can sequestrate ions from an aqueous phase, carry them into an organic phase where they promote the generation of well-defined supramolecular assemblies. In the presence of cations lipophilic guanosines form columnar aggregates while in their absence they generate supramolecular ribbons. The aim of this thesis has been the synthesis of guanine derivatives, in particular N9-alkylated guanines and a guanosine functionalized as a perchlorotriphenylmetil moiety (Gace-a-HPTM) in order to observe their supramolecular behaviour in the absence of sugar (ribose or deoxyribose) and in the presence of a bulky and chiral substituent respectively. By using guanine instead of guanosine, while maintaining all the hydrogen bond acceptor and donor groups required for supramolecular aggregation, the steric hindrance to supramolecular aggregation is notably reduced because (i.e. guanines with groups in N9 different from sugar are expected to have a greatest conformational freedom even in presence of bulky groups in C8). Supramolecular self-assembly of these derivatives has been accomplished in solutions by NMR and CD spectroscopy and on surface by STM technique. In analogy with other guanosine derivatives, also N9-substituted guanines and GAceHPTM form either ribbon-like aggregates or cation-templated G-quartet based columnar structures.

Sulfanyl Radical Addition to Alkynes: Revisiting an Old Reaction to Enter the Novel Realms of Green Chemistry, Bioconjugation, and Material Chemistry

In the last decade considerable attention has been devoted to the rewarding use of Green Chemistry in various synthetic processes and applications. Green Chemistry is of special interest in the synthesis of expensive pharmaceutical products, where suitable adoption of “green” reagents and conditions is highly desirable. Our project especially focused in a search for new green radical processes which might also find useful applications in the industry. In particular, we have explored the possible adoption of green solvents in radical Thiol-Ene and Thiol-Yne coupling reactions, which to date have been normally performed in “ordinary” organic solvents such as benzene and toluene, with the primary aim of applying those coupling reactions to the construction of biological substrates. We have additionally tuned adequate reaction conditions which might enable achievement of highly functionalised materials and/or complex bioconjugation via homo/heterosequence. Furthermore, we have performed suitable theoretical studies to gain useful chemical information concerning mechanistic implications of the use of green solvents in the radical Thiol-Yne coupling reactions.

Pyrolysis-Gas Chromatography-Mass Spectometry and Chemometric Analysis for the Characterization of Complex Matrices

The present PhD thesis was focused on the development and application of chemical methodology (Py-GC-MS) and data-processing method by multivariate data analysis (chemometrics). The chromatographic and mass spectrometric data obtained with this technique are particularly suitable to be interpreted by chemometric methods such as PCA (Principal Component Analysis) as regards data exploration and SIMCA (Soft Independent Models of Class Analogy) for the classification. As a first approach, some issues related to the field of cultural heritage were discussed with a particular attention to the differentiation of binders used in pictorial field. A marker of egg tempera the phosphoric acid esterified, a pyrolysis product of lecithin, was determined using HMDS (hexamethyldisilazane) rather than the TMAH (tetramethylammonium hydroxide) as a derivatizing reagent. The validity of analytical pyrolysis as tool to characterize and classify different types of bacteria was verified. The FAMEs chromatographic profiles represent an important tool for the bacterial identification. Because of the complexity of the chromatograms, it was possible to characterize the bacteria only according to their genus, while the differentiation at the species level has been achieved by means of chemometric analysis. To perform this study, normalized areas peaks relevant to fatty acids were taken into account. Chemometric methods were applied to experimental datasets. The obtained results demonstrate the effectiveness of analytical pyrolysis and chemometric analysis for the rapid characterization of bacterial species. Application to a samples of bacterial (Pseudomonas Mendocina), fungal (Pleorotus ostreatus) and mixed- biofilms was also performed. A comparison with the chromatographic profiles established the possibility to: • Differentiate the bacterial and fungal biofilms according to the (FAMEs) profile. • Characterize the fungal biofilm by means the typical pattern of pyrolytic fragments derived from saccharides present in the cell wall. • Individuate the markers of bacterial and fungal biofilm in the same mixed-biofilm sample.

Analisi del ciclo di vita di processi chimici industriali: applicazione alla sintesi di acrilonitrile mediante reazione di ammonossidazione

La green chemistry può essere definita come “l’utilizzo di una serie di principi che riducono o eliminano l’uso o la formazione di sostanze pericolose nella progettazione, produzione e applicazione di prodotti chimici”. . È in questo contesto che si inserisce la metodologia LCA (Life Cycle Assessment), come strumento di analisi e di valutazione. Lo scopo del presente lavoro di tesi è l’analisi degli impatti ambientali associati a processi chimici, ambito ancora poco sviluppato nella letteratura degli studi di LCA. Viene studiato e modellato il ciclo di vita (dall’ottenimento delle materie prime fino alla produzione del prodotto) della reazione di ammonossidazione per la produzione di acrilonitrile, valutando e comparando due alternative di processo: quella tradizionale, che utilizza propilene ( processo SOHIO), e le vie sintetiche che utilizzano propano, ad oggi poco sviluppate industrialmente. Sono stati pertanto creati sei scenari: due da propene (SOHIO FCC, con propene prodotto mediante Fluid Catalytic Cracking, e SOHIO Steam), e quattro da propano (ASAHI, MITSUBISHI, BP povero e ricco in propano). Nonostante la produzione dell’alcano abbia un impatto inferiore rispetto all’olefina, dovuto ai minori stadi di processo, dai risultati emerge che l’ammonossidazione di propano ha un impatto maggiore rispetto a quella del propene. Ciò è dovuto ai processi catalitici che utilizzano propano, che differiscono per composizione e prestazioni, rispetto a quelli da propene: essi risultano meno efficienti rispetto ai tradizionali, comportando maggiori consumi di reattivi in input . Dai risultati emerge che gli scenari da propano presentano maggiori impatti globali di quelli da propene per le categorie Cambiamento climatico, Formazione di materiale e Consumo di combustibili fossili. Invece per la categoria Consumo di metalli un impatto maggiore viene attribuito ai processi che utilizzano propene, per la maggior percentuale di metalli impiegata nel sistema catalitico, rispetto al supporto. L’analisi di contributo, eseguita per valutare quali sono le fasi più impattanti, conferma i risultati. Il maggior contributo per la categoria Consumo di combustibili fossili è ascrivibile ai processi di produzione del propano, dell’ammoniaca e del solfato di ammonio ( legato all’ammoniaca non reagita ). Stessi risultati si hanno per la categoria Cambiamento climatico, mentre per la categoria Formazione di materiale particolato, gli impatti maggiori sono dati dai processi di produzione del solfato di ammonio, del propano e dell’acido solforico (necessario per neutralizzare l’ammoniaca non reagita). Per la categoria Consumo di metalli, il contributo maggiore è dato dalla presenza del catalizzatore. È stata infine eseguita un’analisi di incertezza tramite il metodo Monte Carlo, verificando la riproducibilità dei risultati.

Design e sintesi di nuove sonde luminescenti per il "targeting" dell'avidina

Recent studies on the use of bio-conjugating organometallic probes report on the possibility to use biotinylated-derivatives to selectively coordinate to a specific protein, avidin. In the present thesis, the synthesis of four new bifunctional ligands is described. The ligands contain both a pyridine triazolic unit able to coordinate a transition metal, and a biotin fragment able to bond avidin: the two functionalities are linked together by an appropriate aromatic linker (amide or ester). The obtained ligands were then employed to form luminescent Ir(III) complexes, that have been fully characterized also by a photophysical point of view both in organic and in aqueous solvent. Therefore, titrations of solutions of avidin with aqueous solutions of Ir(III)-complexes have been performed in order to estimate the luminescence variations of the complexes in the presence or in the absence of bio-conjugation.

Idrossiamminazione asimmetrica di nitroolefine catalizzata da derivati degli alcaloidi della cinchona

Questo lavoro di tesi ha riguardato lo studio della reazione di addizione coniugata enantioselettiva di idrossilammine N-Cbz-protette a nitroolefine, attraverso l’utilizzo di una serie di catalizzatori organici bi-funzionali in grado di attivare contemporaneamente la nucleofilicità dell’idrossilammina, per mezzo di una reazione acido-base, e il trans-β-nitrostirene, attraverso interazione via legame a idrogeno.

Studio e sviluppo di tecniche per la produzione di nanocompositi a matrice di alluminio

Foundry aluminum alloys play a fundamental role in several industrial fields, as they are employed in the production of several components in a wide range of applications. Moreover, these alloys can be employed as matrix for the development of Metal Matrix Composites (MMC), whose reinforcing phases may have different composition, shape and dimension. Ceramic particle reinforced MMCs are particular interesting due to their isotropic properties and their high temperature resistance. For this kind of composites, usually, decreasing the size of the reinforcing phase leads to the increase of mechanical properties. For this reason, in the last 30 years, the research has developed micro-reinforced composites at first, characterized by low ductility, and more recently nano-reinforced ones (the so called metal matrix nanocomposite, MMNCs). The nanocomposites can be obtained through several production routes: they can be divided in in-situ techniques, where the reinforcing phase is generated during the composite production through appropriate chemical reactions, and ex situ techniques, where ceramic dispersoids are added to the matrix once already formed. The enhancement in mechanical properties of MMNCs is proved by several studies; nevertheless, it is necessary to address some issues related to each processing route, as the control of process parameters and the effort to obtain an effective dispersion of the nanoparticles in the matrix, which sometimes actually restrict the use of these materials at industrial level. In this work of thesis, a feasibility study and implementation of production processes for Aluminum and AlSi7Mg based-MMNCs was conducted. The attention was focused on the in-situ process of gas bubbling, with the aim to obtain an aluminum oxide reinforcing phase, generated by the chemical reaction between the molten matrix and industrial dry air injected in the melt. Moreover, for what concerns the ex-situ techniques, stir casting process was studied and applied to introduce alumina nanoparticles in the same matrix alloys. The obtained samples were characterized through optical and electronic microscopy, then by micro-hardness tests, in order to evaluate possible improvements in mechanical properties of the materials.

Studio di un nuovo processo per la sintesi di anidride maleica mediante ossidazione di 1-butanolo

La sintesi industriale di anidride maleica (AM) è realizzata industrialmente mediante ossidazione selettiva di n-butano in aria ad opera di un catalizzatore a base di ossidi misti di vanadio e fosforo, avente formula chimica (VO)2P2O7 ed indicato con la sigla VPP (pirofosfato di vanadile). Vi è attualmente un notevole interesse per lo sviluppo di nuove vie sintetiche che utilizzino come reagenti molecole ottenute da materie prime rinnovabili; un’alternativa è costituita dall’utilizzo di 1-butanolo, un bio-alcool ottenuto mediante un processo fermentativo da biomasse; la sua disponibilità e il prezzo competitivo con quello delle materie prime tradizionali lo rendono una molecola interessante per la produzione di building blocks. Per studiare la reazione di ossidazione selettiva di 1-butanolo ad AM, sono state condotte prove di reattività su un catalizzatore industriale a base di VPP al variare di diversi parametri: configurazione del reattore, temperatura, tempo di contatto e frazione molare di ossigeno in alimentazione. Le prove hanno portato a risultati interessanti di selettività in AM, tali da confermare l’effettiva validità di 1-butanolo come reagente alternativo per questo tipo di sintesi.