Employing theoretical methods for chemical prediction: a ticket into copolymerization, metal-organic catalysis and antioxidants.

The thesis shows how ab initio and DFT quantum chemical methods can be useful toward the interpretation and the prediction of chemical properties and reactivities. Well know post-Hartree-Fock quantum chemical methods and stochastic simulation approaches are intermixed, the synergy between them providing all the tools needed to evaluate the impact and validity of reaction mechanisms, for instance helping to rationalize radical and homogeneously catalyzed copolymerizations. The potentially positive impact that theoretical chemistry can have in those contexts was exploited to put the basis of new theoretical protocols able to predict the chemical features, that is still an attractive goal in academic and industrial field. The first study regards an example of how theoretical chemistry can provide information otherwise not achievable from experimental measurement. Specifically, by means of ab initio perturbation theory, we study novel anion receptors acting via hydrogen-bonding and halogen-bonding: UV-Vis and 1H-NMR titrations show that Iodine on the target receptor enhance the anion binding tendencies and X-ray structures evidenc the formation of halogen-bonding. The geometries in solution computed via MP2, however, reveal few possible conformers of the proposed molecules: theoretical energies allow the calculation of the ion pair dissociation energy (IPDE) as a way to evaluate the affinity between the molecules and an anion. IPDE values gave the same trend of experimental affinity constants, confirming the experimental constant affinities; moreover, computed chemical shifts of conformers help the interpretation of 1H-NMR titrations, giving the right importance at the HB and XB conformers in solution. The second topic is the prediction of the antioxidant activity through a theoretical approach, that led to the benchmark of DFT methods. The in depth study of two prototype molecules, edaravone and quercetin, carries out the bond dissociation enthalpy (BDE), the ionization potential (IP) and the proton dissociation enthalpy (PDE); the examination of the cumulative mean absolute error on the three parameters, compared to CBS-Q3 reference values, indicates the most suitable methods (LC-!PDE, M05-2X and M06-2X). Once the method was defined, we have studied 15 antioxidant belonging to the flavonols family, computating BDE, IP, PDE, proton affinity (PA) and electron transfer enthalpy (ETE) in vacuum and in water; these theoretical parameters are then correlated individually to several experimental data set. Among all attempts, the best correlation was found with ETE in vacuum (showing a R2=0.93 on 6 data set), that allows us to suppose that ETE is the theoretical parameter determining for prediction of antioxidant activity. After the analysis about the properties of a single molecule, DFT is employed to rationalize the products of a chemical reaction. In particular, we study the alkoxyhalogenation of alkynyl ureas and carbamates catalyzed by CuCl2, with the final aim of defining the reactive step that influence the selectivity. First, we propos a mechanism coherent with experimental product, characterizing all the minima and the transition states via DFT vibrational analysis. Studying in depth the equilibria involved at the beginning of the reaction, we characterize the two tautomers and two coordination site of CuCl2, the C-C triple bond and the heteroatom; moreover, we describe the formation of dimers between two urea and the catalyst. Dimers\u2019 stabilization plus the comparison of the energy paths lead to expect the production of the 5-exo-O product, in total accord with experiments. Successively, we attempt to apply the same mechanism on two carbamates, following the same approach than before. The results however rationalize only partially the experiments, in fact, for the phenyl-N-carbamate we observe a strong kinetic competition between two paths, at the same time the experiments carry out a mixture of products; instead, the reaction on tosyl-N-carbamate experimentally leads to a single product, while the theoretical investigation is not able to discriminate between two different products. In the last Chapter we aim higher, trying to predict the copolymer features boosting the DFT method with stochastic simulations; the ability to predict the microstructure of a copolymer would be a great help during the design process and the set up of a catalyzed copolymerization. In this regards, we decided to study the copolymerization of methyl methacrylate (MMA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) obtained via atomic-transfer radical-polymerization (ATRP), since the macroscopic properties used in biological fields are strictly related to the microscopic structure. Here we propose a synergistic DFT/kinetic Monte Carlo approach: by means of DFT, we compute the energies of monomers, dimers and transition states, thanks to which e calculate the reactivity ratios r1 and r2; employing the DFT data, we wrote a kMC code that, treating the copolymerization as a Markov chain, carries out the chains\u2019 microstructure, the distributions of monomers, diads and triads along the chains. The results give indication about the presence of a preferential partitioning of one of the two monomers close to each one of the two radicals, known as bootstrap effect. Moreover, the triad distributions along the chain reveal the gradient nature of the copolymer, suggesting different features of the chains at the proximity of the core of PEG and at the end, influencing directly the behavior of the materials in solution. Then, our attention moves on the homogeneous-catalyzed copolymerization. The aim of the investigation pointed the attention on the characterization of copolymerization mechanism and on the effect of penultimate monomers and the counter ion on the reactivity. The synergistic DFT-kMC approach is applied on the ethene/propene copolymerization catalyzed by two C2-symmetric catalyst, carrying out several interesting results; among all simulated systems, we reproduce the experimental data only taking into account specific features. In order to obtain results close to the experiments, the model has to include: the presence of two coordination sites, both giving active paths for the insertion, the coordination preequilibrium as well-defined step, the influence of the counter ion on the coordination barriers. These claim underline the importance of several aspect generally overlooked during the copolymerization; moreover, the ability to reproduce the experimental results can open the way to a theoretical model able to predict the product of a homogeneous catalyzed copolymerization

Use of HFC fluids as suitable replacements in low-temperature refrigeration plants

An experimental investigation of the performance of a low-temperature refrigerating unit working with R22 and a comparison of its performance when operating with replacement HFC fluids in accordance with the European Regulation CE-1005/2009 are presented in this paper. Plant working efficiency was tested with R22, as baseline, and then compared with four different HFC fluids: R413A, R417A, R422A and R422D. The refrigerating unit was a vapour-compression plant equipped with a reciprocating double-cylinder compressor able to keep the cold room at -20ºC. Lower values of the temperature at the end of compression and polytrophic exponent can be achieved with the HFC tested. Substituting the R22 led to refrigerating plant to underperform. The COP was lower for all the replacement fluids showing inferior energy efficiency and higher energy consumption. The TEWI parameter was also evaluated and compared for all the fluids tested in the present investigation, suggesting TEWI increments substituting the original fluid

Employing theoretical methods for chemical prediction: a ticket into copolymerization, metal-organic catalysis and antioxidants.

The thesis shows how ab initio and DFT quantum chemical methods can be useful toward the interpretation and the prediction of chemical properties and reactivities. Well know post-Hartree-Fock quantum chemical methods and stochastic simulation approaches are intermixed, the synergy between them providing all the tools needed to evaluate the impact and validity of reaction mechanisms, for instance helping to rationalize radical and homogeneously catalyzed copolymerizations. The potentially positive impact that theoretical chemistry can have in those contexts was exploited to put the basis of new theoretical protocols able to predict the chemical features, that is still an attractive goal in academic and industrial field. The first study regards an example of how theoretical chemistry can provide information otherwise not achievable from experimental measurement. Specifically, by means of ab initio perturbation theory, we study novel anion receptors acting via hydrogen-bonding and halogen-bonding: UV-Vis and 1H-NMR titrations show that Iodine on the target receptor enhance the anion binding tendencies and X-ray structures evidenc the formation of halogen-bonding. The geometries in solution computed via MP2, however, reveal few possible conformers of the proposed molecules: theoretical energies allow the calculation of the ion pair dissociation energy (IPDE) as a way to evaluate the affinity between the molecules and an anion. IPDE values gave the same trend of experimental affinity constants, confirming the experimental constant affinities; moreover, computed chemical shifts of conformers help the interpretation of 1H-NMR titrations, giving the right importance at the HB and XB conformers in solution. The second topic is the prediction of the antioxidant activity through a theoretical approach, that led to the benchmark of DFT methods. The in depth study of two prototype molecules, edaravone and quercetin, carries out the bond dissociation enthalpy (BDE), the ionization potential (IP) and the proton dissociation enthalpy (PDE); the examination of the cumulative mean absolute error on the three parameters, compared to CBS-Q3 reference values, indicates the most suitable methods (LC-!PDE, M05-2X and M06-2X). Once the method was defined, we have studied 15 antioxidant belonging to the flavonols family, computating BDE, IP, PDE, proton affinity (PA) and electron transfer enthalpy (ETE) in vacuum and in water; these theoretical parameters are then correlated individually to several experimental data set. Among all attempts, the best correlation was found with ETE in vacuum (showing a R2=0.93 on 6 data set), that allows us to suppose that ETE is the theoretical parameter determining for prediction of antioxidant activity. After the analysis about the properties of a single molecule, DFT is employed to rationalize the products of a chemical reaction. In particular, we study the alkoxyhalogenation of alkynyl ureas and carbamates catalyzed by CuCl2, with the final aim of defining the reactive step that influence the selectivity. First, we propos a mechanism coherent with experimental product, characterizing all the minima and the transition states via DFT vibrational analysis. Studying in depth the equilibria involved at the beginning of the reaction, we characterize the two tautomers and two coordination site of CuCl2, the C-C triple bond and the heteroatom; moreover, we describe the formation of dimers between two urea and the catalyst. Dimers’ stabilization plus the comparison of the energy paths lead to expect the production of the 5-exo-O product, in total accord with experiments. Successively, we attempt to apply the same mechanism on two carbamates, following the same approach than before. The results however rationalize only partially the experiments, in fact, for the phenyl-N-carbamate we observe a strong kinetic competition between two paths, at the same time the experiments carry out a mixture of products; instead, the reaction on tosyl-N-carbamate experimentally leads to a single product, while the theoretical investigation is not able to discriminate between two different products. In the last Chapter we aim higher, trying to predict the copolymer features boosting the DFT method with stochastic simulations; the ability to predict the microstructure of a copolymer would be a great help during the design process and the set up of a catalyzed copolymerization. In this regards, we decided to study the copolymerization of methyl methacrylate (MMA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) obtained via atomic-transfer radical-polymerization (ATRP), since the macroscopic properties used in biological fields are strictly related to the microscopic structure. Here we propose a synergistic DFT/kinetic Monte Carlo approach: by means of DFT, we compute the energies of monomers, dimers and transition states, thanks to which e calculate the reactivity ratios r1 and r2; employing the DFT data, we wrote a kMC code that, treating the copolymerization as a Markov chain, carries out the chains’ microstructure, the distributions of monomers, diads and triads along the chains. The results give indication about the presence of a preferential partitioning of one of the two monomers close to each one of the two radicals, known as bootstrap effect. Moreover, the triad distributions along the chain reveal the gradient nature of the copolymer, suggesting different features of the chains at the proximity of the core of PEG and at the end, influencing directly the behavior of the materials in solution. Then, our attention moves on the homogeneous-catalyzed copolymerization. The aim of the investigation pointed the attention on the characterization of copolymerization mechanism and on the effect of penultimate monomers and the counter ion on the reactivity. The synergistic DFT-kMC approach is applied on the ethene/propene copolymerization catalyzed by two C2-symmetric catalyst, carrying out several interesting results; among all simulated systems, we reproduce the experimental data only taking into account specific features. In order to obtain results close to the experiments, the model has to include: the presence of two coordination sites, both giving active paths for the insertion, the coordination preequilibrium as well-defined step, the influence of the counter ion on the coordination barriers. These claim underline the importance of several aspect generally overlooked during the copolymerization; moreover, the ability to reproduce the experimental results can open the way to a theoretical model able to predict the product of a homogeneous catalyzed copolymerization

Modelling heat transfer-controlled cooling and freezing times: A comparison between computational values and experimental results

Modelling of heat transfer-controlled cooling and freezing time predictions are very important for a good preservation of foodstuffs. In that regard, we used a computer code based on the finite-element method that allowed us to analyse the phase-change of various foodstuffs during their freezing. The model was exercised to predict process times. The results can be used to design high efficiency plants. In this work, the results predicted by the FEM program are compared with the experimental values given in technical literature

An experimental study of a refrigerating plant when replacing R22 with HFCs refrigerants

This paper presents the results of an experimental analysis comparing the performance of a vapour compression refrigerating unit operating with R22, and its performance in comparison to some HFCs fluids, substituting the former according to reg. n. 2037/2000. In particular, the plant working efficiency was first tested with R22 and then with three HFC fluids: R417A, R407C and R404A. The investigation verified that the performance with HFCs refrigerants did not result as efficient as when using R22. An environmental analysis also was performed

On-site Experimental Study of HCFC-22 Substitution with HFCs Refrigerants

Abstract The European Regulation no 2037/2000 has banned manufacturing HCFC refrigerants from January 1st 2010, although its use is allowed up to 2015 if the fluids come from a recycling process. This situation creates the need for developing new working fluids to replace the HCFC in the refrigeration plants now in operation. Among all the HCFCs the R22 is the most widely used in a wide range of applications, especially in air conditioning. This paper presents the results of an experimental analysis comparing the performance of a vapour compression refrigerating unit operating with R22, and its performance in comparison to some HFCs fluids, substituting the former. In particular, the plant working efficiency was first tested with R22 and then with three HFC fluids: R417A, R407C and R404A. The investigation verified that the performance with HFCs refrigerants did not result as efficient as when using R2

Dynamic Preisach hystersis model for magnetostrictive materials for energy application

Recently Magnetostrictive materials have been proposed as active materials to be used in several energy harvesting technology [1]. In this kind of application, the working condition of the material is highly dynamic and non linear. As a result static models of magnetostrictive materials are usually not very accurate and can be not reliable to develop a sufficiently accurate designof the energy harvesting devices. The presence of hysteresis requires accurate mathematical modeling in order to correctly foresee the behavior of real materials (ferromagnetic or magnetostrictive) used in control systems or in electrical machines and thus simplifying the design of such controllers or predicting with acceptable accuracy electromagnetic fields in such devices[2]. In order to overcome this problem, this paper addresses the development of Dynamic Preisach hysteresis model (DPM) for magnetostrictive materials for energy application operating in hysteretic and time varying nonlinear regimes. DPM is a development of classical Preisach Model which is able to include dynamical features in the mathematical model of hysteresis. In this paper the magnetostrictive material considered is Terfenol-D. Its hysteresis is modeled by applying the DPM whose identification procedure is performed by using a neural network procedure previously publised [3]. The neural network used is a multiplayer perceptron trained with the Levenberg-Marquadt training algorithm. This allows to obtain both Everett integrals and the Preisach distribution function, without any special conditioning of the measured data, owing to the filtering capabilities of the neural network interpolators. The model is able to reconstruct both the magnetization relation and the Field-strain relation. The model is validated through comparison and prediction of data collected from a typical Terfenol-D transducer

Caratterizzazione degli edifici non residenziali ad uso scolastico della PA siciliana

La presente relazione finale descrive le ricerche svolte, in seno all’accordo di collaborazione tra l’ENEA e il Dipartimento dell’Energia, ingegneria dell’Informazione e modelli Matematici (DEIM) dell’Università di Palermo. L’accordo di collaborazione è titolato “Caratterizzazione degli edifici scolastici nella Regione Sicilia”. La relazione è suddivisa in due sezioni: la prima, Parte A, illustra lo studio condotto per la caratterizzazione degli edifici non residenziali ad uso scolastico della PA siciliana; la seconda, Parte B, descrive lo stato dell’arte del “Ventilative Cooling” con riferimento particolare ad alcuni casi-studio reali, nel contesto della partecipazione del DEIM alle attività dell’IEA EBC ANNEX 62”. Nel corso dell’annualità precedente è stata effettuata un’analisi della consistenza, dello stato, e delle tipologie di involucro più significative del patrimonio edilizio scolastico siciliano, utilizzando dati statistici disponibili in letteratura e indagini di campo. Nel corso di questa annualità si è identificato un ristretto campione di edifici scolastici rappresentativo del patrimonio edilizio siciliano. Si tratta di tre edifici adibiti a strutture scolastiche relative a differenti gradi di istruzione: una scuola elementare, una media ed una superiore. In particolare, l’edificio che ospita la scuola elementare ha subito negli ultimi anni estesi interventi di ristrutturazione e riqualificazione energetica; il confronto tra le prestazioni energetiche dell’edificio riqualificato con quelle relative agli altri due edifici campione ha permesso di valutare i risparmi energetici indotti dall’introduzione di nuove normative di settore sugli edifici scolastici. Gli edifici analizzati sono sufficientemente rappresentativi della eterogeneità del patrimonio edilizio scolastico siciliano poiché si tratta di: - edifici differenti posti nelle zone climatiche B e C, che caratterizzano più del 65% dei Comuni siciliani, - edifici dalle caratteristiche termofisiche differenti: trasmittanze (U) tipiche delle costruzioni degli anni ’70 (Usuperfici_verticali>1 W/(m2 K)) ed edifici recentemente ristrutturati (U conforme al DPR n. 59/2009), - edifici che ospitano scuole di differente ordine e grado. Lo studio è stato sviluppato a partire da un approccio preliminare di raccolta ed analisi dei dati per ciascun edificio. L’analisi sistematica dei casi-studio ha consentito di desumere le caratteristiche fondamentali per la modellizzazione: stratigrafia, spessori e qualità termofisica dell’involucro edilizio, apporti termici interni causati da apparecchiature elettroniche ed illuminanti, livelli di occupazione in ogni zona dell’edificio e relativi apporti termici interni, caratteristiche degli impianti termici e modalità di funzionamento. L’analisi non ha tralasciato di esaminare “abitudini” e “pratiche comuni” utilizzate nella gestione degli immobili, come ad esempio la tendenza degli occupanti ad aprire le finestre o a utilizzare schermature solari in alcune fasce orarie nel corso dell’anno. Il passaggio seguente ha riguardato la suddivisione di ognuno dei tre edifici in opportune zone termiche, secondo logiche di uguale destinazione d’uso, di assimilabilità geometrica e di gestione comune di diversi locali da parte dello stesso impianto termico con le stesse regolazioni. Il software di calcolo prescelto per l’implementazione dei modelli è stato TRNSYS 17.01. La struttura geometrica di ogni edificio è stata dettagliatamente modellizzata in 3D tramite il software Google Sketchup; tali modelli sono successivamente stati importati in ambiente TRNSYS. Ogni modello è stato costruito implementando accuratamente le informazioni raccolte nella fase preliminare, integrandolo con le informazioni relative agli occupanti e alla descrizione dei carichi interni dell’edificio. Le logiche di funzionamento, di regolazione e d’uso degli impianti termici sono state implementate in ognuno dei modelli. L’analisi delle prestazioni energetiche dei tre edifici è stata effettuata tramite un set di indicatori sintetici, al fine di ottenere dei valori di riferimento e di benchmark per il patrimonio edilizio scolastico della Regione Sicilia; tra di essi il fabbisogno energetico per riscaldamento annuo, il fabbisogno energetico per riscaldamento annuo riferito alla superficie in pianta o al numero di studenti. La seconda parte del lavoro illustra lo stato dell’arte del “Ventilative Cooling” (raffrescamento per ventilazione) e tratta le tecniche di controllo passive e attive della movimentazione dei flussi d’aria all’interno degli ambienti confinati. L’importanza dello studio di tali tecniche è generata da un crescente interesse nell’uso della ventilazione quale strategia per garantire anche il comfort ambientale nel periodo estivo e nelle stagioni intermedie, limitando il ricorso ai sistemi di refrigerazione in un’ottica di risparmio energetico. Il lavoro è stato sviluppato nel novero delle attività dell’ “International Energy Agency – Energy in buildings and communities Annex 62, Ventilative Cooling”. Il DEIM partecipa ai lavori della Subtask A dell’Annex 62 suddetto, che focalizza il suo interesse sulla simulazione termofisica e sull’analisi del contesto legislativo a scala internazionale. Il gruppo di lavoro del DEIM ha partecipato al primo meeting dell’Annex 62, svoltosi all’Ecole Polytechnique Federale de Lausanne (EPFL) in Svizzera in qualità di “observer”; i lavori sono stati focalizzati principalmente sul completamento del report interno sullo stato dell’arte nelle pratiche di “Ventilative Cooling”. Il contributo del DEIM ai lavori dell’Annex 62 è relativo: - all’analisi dello stato dell’arte del “Ventilative Cooling” e alle potenziali applicazioni e implementazioni di tali contributi nella legislazione locale italiana; - alla modellizzazione del “Ventilative Cooling”

Ruolo della timectomia nel trattamento della miastenia gravis: considerazioni e casistica personale

L’effetto terapeutico della timectomia sul decorso clinico della miastemia gravis è ancora quanto mai controverso. Infatti, mentre la chirurgia è ormai universalmente accettata per i timomi, il suo ruolo è ancora discutibile in pazienti con miastenia gravis. La via chirurgica di elezione per la timectomia totale è rappre - sentata dalla sternotomia mediana. Altre metodologie chirurgiche includono l’accesso cervicale e la sternotomia parziale. Queste tecni - che, seppure con alterne fortune, hanno mostrato risultati eccellenti nella exeresi del timo. Più recentemente la timectomia toracoscopica video-assistita è stata proposta come una tecnica meno invasiva e parimenti efficace per l’asportazione di quest’organo ed il trattamento della miastenia gravis. Scopo del presente lavoro è quello di riferire l’esperienza degli Autori in tema di timectomia, analizzando i dati riportati dalla lette - ratura internazionale sulla mortalità operatoria, le eventuali compli - canze e i risultati estetici delle diverse tipologie di accesso chirurgico