Indoor acids and bases.

Numerous acids and bases influence indoor air quality. The most abundant of these species are CO2 (acidic) and NH3 (basic), both emitted by building occupants. Other prominent inorganic acids are HNO3 , HONO, SO2 , H2 SO4 , HCl, and HOCl. Prominent organic acids include formic, acetic, and lactic; nicotine is a noteworthy organic base. Sources of N-, S-, and Cl-containing acids can include ventilation from outdoors, indoor combustion, consumer product use, and chemical reactions. Organic acids are commonly more abundant indoors than outdoors, with indoor sources including occupants, wood, and cooking. Beyond NH3 and nicotine, other noteworthy bases include inorganic and organic amines. Acids and bases partition indoors among the gas-phase, airborne particles, bulk water, and surfaces; relevant thermodynamic parameters governing the partitioning are the acid-dissociation constant (Ka ), Henry's law constant (KH ), and the octanol-air partition coefficient (Koa ). Condensed-phase water strongly influences the fate of indoor acids and bases and is also a medium for chemical interactions. Indoor surfaces can be large reservoirs of acids and bases. This extensive review of the state of knowledge establishes a foundation for future inquiry to better understand how acids and bases influence the suitability of indoor environments for occupants, cultural artifacts, and sensitive equipment

RNA packaging motor: From structure to quantum mechanical modelling and sequential-stochastic mechanism

The bacteriophages of the Cystoviridae family package their single stranded RNA genomic precursors into empty capsid (procapsids) using a hexameric packaging ATPase motor (P4). This molecular motor shares sequence and structural similarity with RecA-like hexameric helicases. A concerted structural, mutational and kinetic analysis helped to define the mechanical reaction coordinate, i.e. the conformational changes associated with RNA translocation. The results also allowed us to propose a possible scheme of coupling between ATP hydrolysis and translocation which requires the cooperative action of three consecutive subunits. Here, we first test this model by preparing hexamers with defined proportions of wild type and mutant subunits and measuring their activity. Then, we develop a stochastic kinetic model which accounts for the catalytic cooperativity of the P4 hexamer. Finally, we use the available structural information to construct a quantum-chemical model of the chemical reaction coordinate and obtain a detailed description of the electron density changes during ATP hydrolysis. The model explains the results of the mutational analyses and yields new insights into the role of several conserved residues within the ATP binding pocket. These hypotheses will guide future experimental work

Development of the SAFT-γ Mie equation of state for predicting the thermodynamic behaviour of strong and weak electrolyte solutions

The thermodynamic modelling of fluid mixtures containing electrolytes using the SAFT-γ Mie equation of state is addressed in detail in this thesis. The SAFT-γ Mie approach allows the implementation of heteronuclear molecules using a group-contribution formalism, and offers a versatile framework for developing models to describe molecules of varying chemical functionality for a broad range of physical properties. In the present work, the SAFT-γ Mie equation of state is extended to electrolyte mixtures with the incorporation of the primitive unrestricted mean spherical approximation (MSA-PM) for describing the Coulombic ion–ion interactions, and the Born solvation free energy to implicitly treat ion– solvent polar interactions. Novel reformulations of the MSA-PM and Born theories within a group-contribution framework are proposed in order to enable ionic species of any size and chemical structure to be modelled, from small inorganic ions to large non-spherical charged molecules. Taking carboxylate anions in linear alkyl chain molecules as an illustrative case study, the proposed theory is shown to effectively account for localised charge effects arising from the structural topology of the charged species. A holistic description of electrolyte solutions is employed in this work; in addition to the short-range dispersion forces and the long-range Coulombic interactions which are pertinent to such mixtures, the models developed here also account for the formation of hydrogen bonds, ion-pairing phenomena, and electrolyte dissociation equilibria. The proposed SAFT-γ Mie equation of state is used to model aqueous solutions of strong electrolytes including alkali halide salts, hydrogen halide acids, and alkali hydroxide bases. Aqueous solutions of sulphuric acid and nitric acid are studied in detail by modelling these as speciating weak electrolytes. Finally, the treatment of ion-pairing phenomena is investigated through a consideration of aqueous alkali nitrate salt solutions. This work presents a new theoretical formulation and SAFT-γ Mie group models for twenty species in total.Open Acces

Vegetable oils epoxidation : from batch to continuous process

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, β-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 är kemiska komponenter som karakteriseras av funktionella oxirangrupper, Oxiran är en triangulär ring, som består av två kolatomer och en syreatom. Denna struktur innebär att oxiranringen är synnerligen reaktiv. På grund av den höga reaktiviteten är epoxiderna viktiga och värdefulla byggstenar i industriell syntes av flera organiska komponenter, t.ex. di- och polyalkoholer, β-hydroxiestrar och karbonater. I detta scenario representerar epoxiderade växtoljor, som erhålls från förnyelsebar råvara, en betydelsefull grön plattform för produktion av kemikalier och biomaterial. Epoxider som härstammar från växtoljor samt oljederivat har redan tillämpats bl.a. som biosmörjmedel, som mjukgörare i polyvinylkloridhartser, som ersättare av ftalater, och som intermediärer för framställning av polyuretan, där användning av epoxider möjliggör en miljövänlig reaktionsrutt jämfört med den giftiga isocyanatreaktionen. På grund av detta är det lätt att förstå det intensiva akademiska och industriella forskningsintresset för dessa mycket värdefulla kemiska komponenter. Beklagligtvis baserar sig den industriella syntesmetoden av epoxiderade växtoljor fortfarande på halvkontinuerlig teknologi, vilket begränsar både produktiviteten och selektiviteten av dessa eftertraktade plattformkemikalier. Epoxidering av växtoljor enligt Prilezhaevmetoden är den syntesrutt som studerades i detta doktorsarbete för produktion av epoxider utgående från ätbara och icke-ätbara växtoljor. Valet av syntesmetoden baserade sig på det faktum att Prilezhaevmetoden är hittills den enda industriellt relevanta tillämpningen för epoxidering av den miljövänliga råvaran och metoden hör definitivt till kategorierna grön kemi och grön processteknologi. Reaktionssystemet består av två icke-blandbara vätskefaser, där konsekutiva perhydrolys-, epoxiderings- och ringöppningsreaktioner pågår inne i dessa faser och vid fasgränsytan. Arbetet fokuserades huvudsakligen på studier av de olika reaktionsstegen i Prilezhaevmetoden för att effektivt kunna övergå från den nuvarande prekära halvkontinuerliga produktionsprocessen till en kontinuerlig process, som skulle innebära en snabbare syntes och förbättad processäkerhet. En ny och snabb analysmetod baserad på kärnmagnetisk resonansspektroskopi (1H-NMR) utvecklades som alternativ till traditionella volymetriska metoder för att bestämma dubbelbindningarnas omsättning och produktselektivitet. Först studerades den halvkontinuerliga reaktorteknologin i närvaro av linfröolja för att evaluera reaktiviteten av denna i högsta grad omättade organiska råvara. Målet var att utveckla en kinetisk modell för reaktionshastigheterna i tvåfassystemet så att beteendet av organiska molekyler med olika antal dubbelbindningar kan kartläggas i avseende på råvarans omsättning, produktens selektivitet och värmeeffekter. I följande steget fokuserades forskningen på kinetiska studier av bildningen och sönderfallet av perkarboxylsyror. Bildningen av perkarboxylsyra ur tillsatt karboxylsyra, t.ex. myrsyra och väteperoxid är de facto det första reaktionssteget före själva epoxideringsreaktionen. En speciellt viktig aspekt beträffande själva reaktionssystemet är att vatten- och oljefaserna är icke-blandbara, vilket innebär att komponenternas fördelning mellan faserna är av oerhört stor betydelse. Därför bestämdes fördelningskoefficienten av syrekällan, myrsyra experimentellt. I sista skedet kulminerade arbetet i utvecklingen av en helt ny kontinuerlig reaktorteknologi för att uppnå tillfreds-ställande resultat för reaktantomsättningen och produktselektiviten. Den kontinuerliga teknologin som baserar sig på en eller flera seriekopplade kolonnreaktorer visade sig vara överlägsen jämfört med det existerande halvkontinuerliga förfarandet: en klart högre reaktantomsättning och produktselektivitet uppnåddes i den kontinuerliga reaktoranläggningen som också 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, β-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, così come dai derivati degli oli vegetali, sono già 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, è 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 produttività e selettività. Nel presente lavoro di tesi è stata studiata nel dettaglio la reazione di epossidazione, condotta secondo il metodo Prilezhaev, attualmente considerata la via più 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 è 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 più 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 è 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) è stato sviluppato come alternativa ai tradizionali metodi volumetrici per la valutazione della conversione dei doppi legami e selettività del prodotto desiderato. Inizialmente, il sistema reattivo è stato studiato in presenza di olio di lino in un reattore semicontinuo per valutare la reattività 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, selettività e, molto più importante, profilo termico, ero lo scopo principale dell’investigazione. Successivamente, la ricerca si è focalizzata sullo studio della cinetica della reazione di formazione e decomposizione dell’acido percarbossilico. La prima reazione infatti è propedeutica all’epossidazione. Un aspetto importante del sistema reattivo, a causa dell’immiscibilità delle due fasi, è la ripartizione delle specie, specialmente la specie ossidante. Per questa ragione, il coefficiente di partizione dell’acido formico, precursore della specie ossidante, è stato determinato sperimentalmente. Infine, il processo di epossidazione secondo il metodo Prilezhaev è stato condotto con successo in un’apparecchiatura operante in continuo, ottenendo eccellenti valori di conversione e selettività in condizioni meno severe rispetto al processo semicontinuo