264 research outputs found

    Vegetable oils epoxidation : from batch to continuous process

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    Epoxides are a class of compounds characterized by the oxirane functional group, a polar three-terms strain ring composed by two carbon atoms and an oxygen atom. These two properties make the oxirane ring a highly reactive moiety. For this reason, epoxides are important and valuable industrial building blocks for the synthesis of several organic compounds, e.g., di- or polyalcohols, lactones, ÎČ-hydroxesters, carbonates etc. In this scenario, Epoxidized Vegetable Oils (EVOs), which are obtained from renewable feedstock, represent noteworthy green platforms to produce chemicals and biomaterials. Epoxides originating from vegetable oils, as well as from derivates of vegetable oils, have already been successfully applied, among others, as plasticizers in the poly(vinyl-chloride) resins, partially replacing phthalates, as intermediates to produce polyurethane, representing an environmentally friendly route compared to the toxic isocyanate process, and as bio-lubricants. Thus, it is possible to understand the ongoing interest, in both academic and industrial research, to this class of value-added chemical compounds. Nevertheless, the industrial synthesis still relies on a semibatch technology, limiting the productivity and selectivity to this platform chemical. The epoxidation via the Prilezhaev reaction method is the synthesis pathway studied in the present work to produce of epoxides from vegetable oils, both edible and not. The choice of studying this synthesis path is because it is the only one with relevant current industrial application in the epoxidation of this promising feedstock and, more importantly, it belongs to the category of green chemistry and green process technology. The reaction system is composed of two immiscible liquid phases and consecutive reactions take place in the two phases and at the interphase between them. The work was mainly focused in the study of the different reaction steps of the Prilezhaev reaction method in order to efficiently shift to a continuous operation. A new and fast analytical method based on protonic nuclear magnetic resonance (1H-NMR) was developed in alternative to the traditional volumetric analytical methods to evaluate the double bond conversion and the selectivity to the target product. At first, the system was studied in semibatch operation in the presence of linseed oil to evaluate the reactivity of this highly unsaturated organic substrate. The aim was to develop a biphasic kinetic model able to predict the behavior of organic substrates with different amounts of double bonds, in a backmixed reactor, in terms of conversion, selectivity and, more importantly, thermal profile. Next, the research was focused on the kinetic study of the percarboxylic acid formation and its decomposition. The former reaction, indeed, is the preliminary reaction step before the epoxidation reaction. An important aspect of the reaction system, because of the immiscibility of the two phases, is the partition of the species, especially the oxygen donor. For this reason, the partition coefficients of formic acid, the precursor of the oxygen donor, were experimentally determined. Finally, the epoxidation reaction via the Prilezhaev concept was successfully carried out in a continuous device obtaining satisfactory results in terms of conversion and selectivity adopting milder conditions than the semibatch process.Epoxider Ă€r kemiska komponenter som karakteriseras av funktionella oxirangrupper, Oxiran Ă€r en triangulĂ€r ring, som bestĂ„r av tvĂ„ kolatomer och en syreatom. Denna struktur innebĂ€r att oxiranringen Ă€r synnerligen reaktiv. PĂ„ grund av den höga reaktiviteten Ă€r epoxiderna viktiga och vĂ€rdefulla byggstenar i industriell syntes av flera organiska komponenter, t.ex. di- och polyalkoholer, ÎČ-hydroxiestrar och karbonater. I detta scenario representerar epoxiderade vĂ€xtoljor, som erhĂ„lls frĂ„n förnyelsebar rĂ„vara, en betydelsefull grön plattform för produktion av kemikalier och biomaterial. Epoxider som hĂ€rstammar frĂ„n vĂ€xtoljor samt oljederivat har redan tillĂ€mpats bl.a. som biosmörjmedel, som mjukgörare i polyvinylkloridhartser, som ersĂ€ttare av ftalater, och som intermediĂ€rer för framstĂ€llning av polyuretan, dĂ€r anvĂ€ndning av epoxider möjliggör en miljövĂ€nlig reaktionsrutt jĂ€mfört med den giftiga isocyanatreaktionen. PĂ„ grund av detta Ă€r det lĂ€tt att förstĂ„ det intensiva akademiska och industriella forskningsintresset för dessa mycket vĂ€rdefulla kemiska komponenter. Beklagligtvis baserar sig den industriella syntesmetoden av epoxiderade vĂ€xtoljor fortfarande pĂ„ halvkontinuerlig teknologi, vilket begrĂ€nsar bĂ„de produktiviteten och selektiviteten av dessa eftertraktade plattformkemikalier. Epoxidering av vĂ€xtoljor enligt Prilezhaevmetoden Ă€r den syntesrutt som studerades i detta doktorsarbete för produktion av epoxider utgĂ„ende frĂ„n Ă€tbara och icke-Ă€tbara vĂ€xtoljor. Valet av syntesmetoden baserade sig pĂ„ det faktum att Prilezhaevmetoden Ă€r hittills den enda industriellt relevanta tillĂ€mpningen för epoxidering av den miljövĂ€nliga rĂ„varan och metoden hör definitivt till kategorierna grön kemi och grön processteknologi. Reaktionssystemet bestĂ„r av tvĂ„ icke-blandbara vĂ€tskefaser, dĂ€r konsekutiva perhydrolys-, epoxiderings- och ringöppningsreaktioner pĂ„gĂ„r inne i dessa faser och vid fasgrĂ€nsytan. Arbetet fokuserades huvudsakligen pĂ„ studier av de olika reaktionsstegen i Prilezhaevmetoden för att effektivt kunna övergĂ„ frĂ„n den nuvarande prekĂ€ra halvkontinuerliga produktionsprocessen till en kontinuerlig process, som skulle innebĂ€ra en snabbare syntes och förbĂ€ttad processĂ€kerhet. En ny och snabb analysmetod baserad pĂ„ kĂ€rnmagnetisk resonansspektroskopi (1H-NMR) utvecklades som alternativ till traditionella volymetriska metoder för att bestĂ€mma dubbelbindningarnas omsĂ€ttning och produktselektivitet. Först studerades den halvkontinuerliga reaktorteknologin i nĂ€rvaro av linfröolja för att evaluera reaktiviteten av denna i högsta grad omĂ€ttade organiska rĂ„vara. MĂ„let var att utveckla en kinetisk modell för reaktionshastigheterna i tvĂ„fassystemet sĂ„ att beteendet av organiska molekyler med olika antal dubbelbindningar kan kartlĂ€ggas i avseende pĂ„ rĂ„varans omsĂ€ttning, produktens selektivitet och vĂ€rmeeffekter. I följande steget fokuserades forskningen pĂ„ kinetiska studier av bildningen och sönderfallet av perkarboxylsyror. Bildningen av perkarboxylsyra ur tillsatt karboxylsyra, t.ex. myrsyra och vĂ€teperoxid Ă€r de facto det första reaktionssteget före sjĂ€lva epoxideringsreaktionen. En speciellt viktig aspekt betrĂ€ffande sjĂ€lva reaktionssystemet Ă€r att vatten- och oljefaserna Ă€r icke-blandbara, vilket innebĂ€r att komponenternas fördelning mellan faserna Ă€r av oerhört stor betydelse. DĂ€rför bestĂ€mdes fördelningskoefficienten av syrekĂ€llan, myrsyra experimentellt. I sista skedet kulminerade arbetet i utvecklingen av en helt ny kontinuerlig reaktorteknologi för att uppnĂ„ tillfreds-stĂ€llande resultat för reaktantomsĂ€ttningen och produktselektiviten. Den kontinuerliga teknologin som baserar sig pĂ„ en eller flera seriekopplade kolonnreaktorer visade sig vara överlĂ€gsen jĂ€mfört med det existerande halvkontinuerliga förfarandet: en klart högre reaktantomsĂ€ttning och produktselektivitet uppnĂ„ddes i den kontinuerliga reaktoranlĂ€ggningen som ocksĂ„ modellerades matematiskt.Gli epossidi sono una classe di composti caratterizzati da un gruppo funzionale ossiranico, un anello a tre termini rigido e polare, composto da due atomi di carbonio ed un atomo di ossigeno. Tali caratteristiche fanno dell’anello ossiranico un gruppo altamente reattivo. Per questa ragione, gli epossidi sono importanti e preziosi intermedi industriali per la sintesi di un’ampia gamma di composti organici, i.e. di- o polialcoli, lattoni, ÎČ-idrossiesteri, carbonati etc. A tal proposito, gli oli vegetali epossidati, ottenuti a partire da fonti rinnovabili, rappresentano materiali di partenza notevoli e sostenibili per la produzione di agenti chimici e biomateriali. Gli epossidi ottenuti da oli vegetali, cosĂŹ come dai derivati degli oli vegetali, sono giĂ  stati ampiamente utilizzati come plasticizzanti nelle resine poliviniliche, sostituendo parzialmente gli ftalati, come intermedi per la produzione di poliuretano, rappresentando una via di sintesi ecosostenibile rispetto il processo via isocianato, e come biolubrificanti. Quindi, Ăš possibile capire l’attuale interesse, sia da un punto di vista accademico che industriale, verso questa classe di composti chimici. Ciononostante, la sintesi industriale fa ancora affidamento su un processo semicontinuo, limitandone produttivitĂ  e selettivitĂ . Nel presente lavoro di tesi Ăš stata studiata nel dettaglio la reazione di epossidazione, condotta secondo il metodo Prilezhaev, attualmente considerata la via piĂč comune di sintesi per la produzione di epossidi a partire da oli vegetali, edibili e non. La scelta nello studiare tale processo risiede nel fatto che quest’ultimo Ăš l’unico metodo con ampia applicazione nell’attuale pratica industriale per la produzione di epossidi a partire da materiali di partenza promettenti quali gli oli e, molto piĂč importante, tale sintesi appartiene alla categoria della chimica verde e dei processi ecosostenibili. Il sistema di reazione si compone di due liquidi immiscibili e alcune reazioni consecutive che avvengono sia nelle due fasi che all’interfaccia tra le stesse. Il lavoro Ăš stato prevalentemente focalizzato sullo studio dei differenti passaggi nella reazione secondo il metodo Prilezhaev, con lo scopo di trasferire efficientemente il processo in continuo. Un metodo di analisi nuovo e rapido incentrato sulla risonanza magnetica protonica (1H-NMR) Ăš stato sviluppato come alternativa ai tradizionali metodi volumetrici per la valutazione della conversione dei doppi legami e selettivitĂ  del prodotto desiderato. Inizialmente, il sistema reattivo Ăš stato studiato in presenza di olio di lino in un reattore semicontinuo per valutare la reattivitĂ  di un substrato organico ad alto contenuto di doppi legami. Lo sviluppo di un modello reattoristico in grado di predire il comportamento di substrati organici a diverso contenuto di doppi legami in un reattore miscelato, in termini di conversione, selettivitĂ  e, molto piĂč importante, profilo termico, ero lo scopo principale dell’investigazione. Successivamente, la ricerca si Ăš focalizzata sullo studio della cinetica della reazione di formazione e decomposizione dell’acido percarbossilico. La prima reazione infatti Ăš propedeutica all’epossidazione. Un aspetto importante del sistema reattivo, a causa dell’immiscibilitĂ  delle due fasi, Ăš la ripartizione delle specie, specialmente la specie ossidante. Per questa ragione, il coefficiente di partizione dell’acido formico, precursore della specie ossidante, Ăš stato determinato sperimentalmente. Infine, il processo di epossidazione secondo il metodo Prilezhaev Ăš stato condotto con successo in un’apparecchiatura operante in continuo, ottenendo eccellenti valori di conversione e selettivitĂ  in condizioni meno severe rispetto al processo semicontinuo

    The OpenMolcas Web: A Community-Driven Approach to Advancing Computational Chemistry

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    The developments of the open-source OpenMolcas chemistry software environment since spring 2020 are described, with a focus on novel functionalities accessible in the stable branch of the package or via interfaces with other packages. These developments span a wide range of topics in computational chemistry and are presented in thematic sections: electronic structure theory, electronic spectroscopy simulations, analytic gradients and molecular structure optimizations, ab initio molecular dynamics, and other new features. This report offers an overview of the chemical phenomena and processes OpenMolcas can address, while showing that OpenMolcas is an attractive platform for state-of-the-art atomistic computer simulations

    NEGATIVE ION PHOTOELECTRON SPECTROSCOPY: ANTIOXIDANTS, ACTINIDE CLUSTERS, MOLECULAR ACTIVATION, AND SUPERATOMS

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    Negative ion photoelectron spectroscopy (PES) utilizes photons to examine the electronic and geometric properties of negative ions and their corresponding neutrals. A diverse range of topics spanning biology, chemistry, physics, and material science were investigated, including antioxidation abilities of antioxidants, electronic structure of actinide-containing clusters, mechanism of activation reactions, design of superatoms, multiple Rydberg anions, and electron induced proton transfer. The insight acquired from anion photoelectron spectroscopy has provided understanding into the above-mentioned topics at a molecular level. After briefly introducing the PES technique, Chapters II to VI present these studies in detail. In Chapter II, the antioxidation abilities of two famous antioxidants in the body and food, ascorbic acid and gallic acid, were measured spectroscopically and compared to computations. In Chapter III, we studied the interactions of hydrogen, oxygen, or gold atoms with thorium or uranium atoms; chemical bonding between thorium and thorium atoms in clusters; and electron affinity of the uranium atom. Chapter IV discusses the small molecule activation, such as water, carbon dioxide, methane, or hydroxylamine, by single metal anions or metal hydride anions. With the help of high-level quantum chemistry calculations, reaction mechanisms were revealed at a molecular level. Finally, Chapter V shows that the electronic spectra in cobalt sulfide superatomic clusters are tunable via ligand substitution, shedding light on novel material designs

    Advanced 1,2,3-triazolate-based coordination compounds: from carbonic anhydrase mimics, molecular building blocks, and catalyst supports to electrically conducting spin-crossover MOFs

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    Kuratowski complexes and related metal-organic frameworks (MOF), especially of the MFU-4-type, built from 1,2,3-triazolate-based ligands gained increasing interest in the last years due to their variable side ligands and metal sites. Such materials and their post-synthetic modifications have shown an outstanding potential for applications such as adsorption, capture, separation and kinetic trapping of gases, drug delivery, atmospheric water harvesting, sensing, H2/D2 quantum sieving, investigation of fundamental magnetic phenomena, and in particular catalysis. In this respect, MFU-4-type MOF catalysts were shown to outperform other heterogeneous catalysts for the dimerization and polymerization of olefins with some applications already advancing toward commercial applicability. This thesis mainly aims to extend the functionality of 1,2,3-triazolate-based coordination materials via advanced linker designs, novel framework assembly strategies, and post-synthetic modifications, as well as through a better understanding of the underlying material properties. During this project, several new organic and complex building blocks, as well as advanced framework structures were prepared and characterized. Furthermore, additional emphasis was directed to the investigation and interpretation of resulting physical phenomena like phase transitions, magnetism, and electrical conductivity. The Zn-MFU-4l ([Zn5IICl4(BTDD)3]; H2-BTDD = bis(1H-1,2,3-triazolo[4,5-b][4â€Č,5â€Č-i])dibenzo[1,4]dioxin) and Co-MFU-4l ([Zn1.3IICo3.7IICl4(BTDD)3]) metal-organic frameworks were prepared according to the literature procedures and modified by a post-synthetic side ligand exchange of the chloride anions, which led to MFU-4-type structures featuring organometallic metal-carbon bonds. Overall, five new Zn-MFU-4l structures of the general formula [Zn5IILxCl4–x(BTDD)3] (4 ≄ x > 3; L = methanido, ethanido, n-butanido, tert-butanido, 3,3-dimethyl-1-butyn-1-ido; Zn-MFU-4l-Me, -Et, -n-Bu, -t-Bu, -Butyne) and two new Co-MFU-4l structures, Co-MFU-4l-Me ([Zn1.5IICo3.5IIMe3.1Cl0.9(BTDD)3]) and Co-MFU-4l-OH ([Zn1.4IICo3.6II (OH)3.1Cl0.9(BTDD)3]), were obtained. Such side ligands were not characterized for MFU-4-type MOFs before, although they are presumed responsible for the metal site activation during olefin catalysis reactions, which require organometallic co-catalysts. For this purpose, a combination of simulated and measured IR spectra was developed as well-suited characterization technique for such insoluble materials, which preclude analytical methods like liquid state NMR and mass spectroscopy. A high stability of the organometallic Zn-MFU-4l derivatives was observed, whereas the Co-MFU-4l-Me was of a pyrophoric nature and reacted upon water contact to Co-MFU-4l-OH, which exhibited a CO2 binding mechanism comparable to that of carbonic anhydrase. Synthesis of Kuratowski complexes built from 1H-benzotriazole-5,6-diamine (H-btda) ligands and post-synthetic exchange of the chloride side ligands with Tp/Tp* (Tp= hydrotris(pyrazolyl)borate; Tp* = hydrotris(3,5-dimethyl-1-pyrazolyl)borate) provided us with a variety of six-fold diamine-functionalized molecular building blocks intended for the development of novel MOF construction pathways. Crystallization of those compounds have already led to the assembly of porous metal hydrogen-bonded frameworks (M-HOF), some of which have even exhibited permanent porosity. This is a rare property of this material class, which is still in its infancy with only a few structures reported so far. Overall, five new metal hydrogen-bonded framework assemblies (CFA-20-X ((2,6-lutidinium)+[Zn5X4(btda)6X]−· n(DMF); X= Cl−, Br−), CFA-20-Tp, CFA-20-Tp*, CFA-20-Tp*-DMSO ([Zn5Y4(btda)6]; Y = Tp, Tp*) could be characterized, thus representing a significant contribution to this field of study. Although no MOFs could be crystallized from reactions of these complexes with metal salts, preliminary results have shown that direct incorporation of metal sites is a suitable pathway to convert M-HOFs into more stable MOFs. Taking the functionality of MFU-4-type frameworks to the next level, the novel 1,1',5,5'-tetrahydro-6,6'-biimidazo[4,5-f]benzotriazole (H4-bibt) ligand was developed to potentiate the post-synthetic modification possibilities compared to other MFU-4-type frameworks via introduction of additional and easily accessible biimidazole coordination sites at the linker backbone. This gave rise to the five most sophisticated MFU-4-type structures prepared so far. Post-synthetic Tp ligand exchange in the resulting MFU-4-type CFA-19 ([Co5IICl4(H2-bibt)3]) provided the stable CFA-19-Tp ([Co5IICl0.4Tp3.6(H2-bibt)3]) framework, in which the additional coordination sites were saturated in a third modification step with MIBr(CO)3 (M= Re, Mn) moieties or deprotonated via introduction of ZnEt moieties. The resulting materials exhibit high metal site density single-crystal X-ray structures with over 1700 atoms per unit cell for the ReBr(CO)3@CFA-19-Tp ([Co5IICl0.4Tp3.6(H2-bibt)3·(ReIBr(CO)3)2.8]) and a thermally induced release of all CO ligands for the MnBr(CO)3@CFA-19-Tp ([Co5IICl0.4Tp3.6(H2-bibt)3(MnIBr(CO)3)3]·3.1(MnIBr(CO)X)). Preliminary results also indicate a facile incorporation of other coordination moieties such as MIICl2 (M= PdII, PtII). These proof-of-principle incorporations of coordination moieties and open metal sites render such CFA-19-type scaffolds promising supports for an even larger variety of active species intended for the binding and activation of small molecules in future investigations. Coincidental synthesis of the novel CFA-23 ((((propan-2-yl)oxidanium)+[Mn6IICl5(ta)8]−; H-ta= 1H-1,2,3-triazole) coordination framework provided the opportunity to investigate changes of the resulting magnetic properties in comparison to a similar structure built from 1H-1,2,3-benzotriazole, as well as the ultra-narrow character of the pore channels in CFA-23. High purity samples of the literature-known Fe(ta)2 (H-ta= 1H-1,2,3-triazole) framework were prepared and investigated in detail to unveil its record hysteresis spin-crossover phase transition. Aiming at the use of Fe(ta)2 in surface acoustic wave-based sensor applications, experimental and theoretical insights into the material’s electrical conductivity changes upon adsorption of inert gases were assisted with the measurement of adsorption isotherms and the determination of the resulting isosteric enthalpies of adsorption

    Theoretical studies on the Annexin A1-S100A11 Heterotetramer and Platinum-Mediated C-H Activation Pathways

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    Computational chemistry is a powerful tool for characterizing chemical phenomena when they are difficult to observe in laboratory settings or simply elusive. By employing the fundamental equations of nature, computational chemistry simulates a systemñ€ℱs behavior through efficient computer programs and algorithms. In this work, two computational approaches were used to investigate biologically important systems. In Chapter 3, molecular dynamics simulations were performed on the Annexin A1-S100A11 heterotetramer. Annexins are important calcium binding proteins which have implications in calcium-regulation and numerous pathologies including many types of cancer. Annexin-A1 is known to interact with S100A11 to form a heterotetramer which is involved in regulating EGFR and thus tumor growth. In this work, the Annexin A1-S100A11 heterotetramer was modeled for the first time and subjected to multiple MD simulations to characterize the complex on the atomic level. Principle component analysis revealed three conformations of the Annexin N-terminus stemming from a kink formed through W12ñ€ℱs interaction with M63. We identified a consistent, stable binding mode between the first 11 residues of A1 and S100A1 which was consistent to available crystal structures for A1-S100A11 and A2-S100A10. This work suggests that this stable binding mode is potentially a theme for other Annexin-S100 complexes and that the flexibility of the A1-ND affords multiple possible conformations of the A1t. In Chapters 4 and 5, quantum mechanics calculations were performed in conjunction with the Nudged Elastic Band method to investigate the mechanisms of platinum mediated C-H activation. Direct conversion of C-H bonds into other bond types is inherently difficult owing to the inertness of standard C-H bonds. In recent years, transition metal-catalyzed C-H functionalization has grown in popularity due to its numerous applications in pharmaceuticals and chemical industry. Due to their versatile electronic properties, platinum complexes have found applications ranging from OLED technology to medical imaging and anticancer treatments. In this work, computational approaches were employed on two pathways: 1) Pt-catalyzed C-H acylation of 2-(2-methylphenoxy)-pyridine and 2) solvent-controlled sp2/sp3 C-H activation of N-methyl-N-phenyl-6-(1H-pyrazol-1-yl)pyridine-2-amine. In the former, ligand exchange for cis isomers was found to be kinetically favored which was congruent with experimental observations. In the latter, several key intermediates were identified for solvent-controlled cycloplatination reactions. With a catalytic water molecule, a significant reduction in energy barrier was observed for sp2 reactions. Additionally, water was observed to facilitate a square pyramidal intermediate via oxidative addition to the platinum center in sp3 pathways

    Feature Papers in Compounds

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    This book represents a collection of contributions in the field of the synthesis and characterization of chemical compounds, natural products, chemical reactivity, and computational chemistry. Among its contents, the reader will find high-quality, peer-reviewed research and review articles that were published in the open access journal Compounds by members of the Editorial Board and the authors invited by the Editorial Office and Editor-in-Chief

    Computational study of electron-transfers and singlet oxygen in aprotic metal-O2 batteries

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    Aprotic metal-oxygen batteries (MOBs), based on the electroreduction of molecular oxygen at a porous cathode, have attracted a vast interest in research, owing to their potential upgrade in terms of energy density and costs over present lithium-ion batteries. Despite their highly promising features, aprotic MOBs based on alkali and alkaline-earth metals still suffer severe limitations in their practical applicability. One of the main unresolved issues, especially with Li-O2 batteries, is represented by the high degree of parasitic reactivity. Singlet oxygen (1O2) is today held responsible for a major contribution to such reactivity, and the disproportionation of the superoxide anion is considered as one of the most likely source of 1O2 in the cell environment. Experimental evidences for electrolyte degradation and evolution of 1O2 have been reported, but the fundamental chemical mechanisms underlying these phenomena are still poorly understood. A valid strategy for contrasting the arise of side-reactions and materials degradation is to use redox mediators (RMs), which allow to recharge the battery with greatly reduced overpotentials. Understanding the con- nection of RM-assisted charging with the production 1O2 is likely to play a key role in the design of fully reversible and efficient practical MOBs in the future. In this thesis, quantum chemical computational methods were used to investigate reactive processes of electron-transfer involving reduced oxygen species in aprotic MOBs. The possibility of reactive pathways leading to the release of 1O2 was addressed in particular. The aim of the thesis was to apply theoretical methods to the modeling of reactive systems, in order to unravel part of the mechanisms which underpin the parasitic chemistry of MOBs. Despite their apparent simplicity, the reaction governing the chemistry of the cells involve a complex interplay of radical species and electronic excited states. For this reason, our approach was to use mainly ab-initio correlated multiconfigurational methods for a high-level description of potential energy surfaces and reaction energies. Owing to the computational costs of the methods, such an approach necessarily entails the resort to simplified models, including the exclusive use of implicit solvent and the neglect of solid phases and interfacial effects

    Crossroads at the Origin of Prebiotic Chemical Complexity: Hydrogen Cyanide Product Diversification

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    Products of hydrogen cyanide (HCN) reactivity are suspected to play important roles in astrochemistry and, possibly, the origin of life. The composition, chemical structure, and mechanistic details for formation of products from HCN\u27s self-reactions have, however, proven elusive for decades. Here, we elucidate base-catalyzed reaction mechanisms for the formation of diaminomaleonitrile and polyimine in liquid HCN using ab initio molecular dynamics simulations. Both materials are proposed as key intermediates for driving further chemical evolution. The formation of these materials is predicted to proceed at similar rates, thereby offering an explanation of how HCN\u27s self-reactions can diversify quickly under kinetic control. Knowledge of these reaction routes provides a basis for rationalizing subsequent reactivity in astrochemical environments such as on Saturn\u27s moon Titan, in the subsurface of comets, in exoplanet atmospheres, and on the early Earth

    The Development of Energy Efficient Wastewater Treatment: Electrochemical Oxidation and PFACs liquid-liquid Extraction

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    EAOPs are new, and environmental-friendly techniques that can oxidize organic compounds by direct oxidation and indirect oxidation (hydroxyl radical HO‱) on the anode. The benefits of EAOPs are: 1) They are driven by electric power. The stoichiometric connection between power consumption and pollutant removal in EAOP is almost linear. Therefore, they are ease of control. 2) they can generate hydroxyl radical HO‱ without any chemical additive. However, EAOPs also face several problems for industrial applications. 1) Since the reaction mostly happens on the electrode surface, the mass transfer is the limiting factor in electric efficiency. 2) High operation potential is required for hydroxyl radical generation leading to high energy costs. 3) EAOPs did not have selectivity in terms of the organic compounds. For the third problem, we developed Liquid-liquid extraction to extract and separate specific refractory degradable: PFACs. To improve the EAOPs' energy efficiency, The EAOPs system was optimized at three levels: 1) System level: energy recovery system, and electric power mode; 2) Reactor level: flow-through wire mesh anode 3) Electrode level: electrode material modification. To be specific, a novel EAOP-fuel cell energy recovery system is proposed, and the system performance in varied conditions are summarized. A flow-through multiple layer wire mesh anode reactor is developed for improved mass transfer and PFACs treatment. The Mn2O3-TiO2 NTAs porous anode is developed for optimized electrode conductivity. The anode is tested by both electrochemical oxidation experiments and advanced characterization methods. A pulse potential instead of DC power is used to drive the EAOPs reaction to investigate the frequency and potential amplitude effect on the oxidation. In terms of liquid-liquid extraction, Ionic liquids were used as an extractant for liquid-liquid extraction of PFOA removal from the aqueous phase. The optimized extraction condition is investigated. COSMO-RS, a quantum chemistry-based equilibrium thermodynamics method, is used to screen the ILs for high extraction efficiency. In conclusion, the mass transfer is improved by using the porous anode and multiple-layer wire mesh anodes structure. The mass transfer impact on the overall oxidation is evaluated through the limiting current density analysis. Using the cathodic hydrogen gas for energy recovery reduces the high operation power caused by the operation voltage. The liquid-liquid extraction has the capability of PFACs extraction. In the future, it could be combined with PFACs degradation methodsPh.D

    Adsorption and migration of Cs and Na ions in geopolymers and zeolites

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    Geopolymers may provide a more sustainable alternative to Portland Cement for various possible applications. Geopolymers have attracted particular interest for the immobilization of pollutants, owing to their high adsorption capacity, high thermal and chemical resistance, and low leachability. However, practical implementation is currently hindered by a limited understanding of how adsorption processes occur in geopolymers, and how they can be engineered to optimize the incorporation of pollutants and avoid their release. In this work, Molecular Dynamics simulations provide insights into these processes at the atomic scale, studying the role of host material composition and structure in the immobilization of Na and Cs ions. The simulations reveal that the most stable configurations for these ions are near the center of 6- and 8-membered aluminosilicate rings, where the coordination with the geopolymer is maximum. Higher contents of Al and degrees of crystallinity are found to yield more stable configurations for Cs ions, with more favorable adsorption enthalpies and lower diffusion coefficients. The comparison of different crystalline zeolite structures reveals that the framework of sodalite, used as the baseline to develop model geopolymer structures, is the most suitable for the immobilization of Cs since there are no channels and it is formed by small 4- and 6-member, all preventing Cs ions from escaping the cavities
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