Dissertations / Theses on the topic 'Photochemical processes'

El treball descrit en aquesta dissertació es centra en la implementació d’estratègies organocatalítiques per superar les limitacions de processos fotoquímics establerts. Específicament, dues transformacions impulsades per la llum han estat estudiades: (i) la fotoenolizació de 2-alquilbenzofenones per accedir a intermedis enòlics transitoris (fotoenols), i (ii) la ruptura homolítica fotoinduïda de derivats ditiocarbonílics per produir radicals. Per un costat, el procés de fotoenolizació acoblat amb la reactivitat de tipus Diels-Alder (seqüència fotoenolizació/ Diels-Alder) és una reacció fotoquímica històrica amb aplicacions conegudes en síntesi total. Malgrat això, una variant asimètrica d’aquest procés no ha estat encara reportada. Els Capítols II i III demostren com l’organocatàlisi asimètrica proporciona eines simples i efectives per fer participar a les espècies fotoenòliques en processos de tipus Diels-Alder i aldòlics altament estereoselectius. Per un altre costat, la ruptura fotolítica de espècies ditiocarboníliques capaces d’absorbir la llum visible, és un mètode conegut per la generació de radicals sota condicions suaus de reacció. Aquesta tecnologia fa ús de quantitats estequiomètriques de compostos ditiocarbonílics fàcilment accessibles. Encara que aquesta estratègia ha millorat considerablement les condicions per accedir a la reactivitat de tipus radicalària, aquesta requereix la síntesi prèvia de compostos que continguin la funcionalitat ditiocarbonílica. El Capítol IV detalla com aquest mètode de generació de radicals pot ser realitzat catalíticament, mitjançant el disseny d’un catalitzador
El trabajo descrito en esta disertación se centra en la implementación de estrategias organocatalíticas para superar las limitaciones de procesos fotoquímicos establecidos. Específicamente, dos transformaciones promovidas por la luz han sido estudiadas: (i) la fotoenolización de 2-alquilbenzofenonas para acceder intermedios enólicos transitorios (fotoenoles), y (ii) la ruptura homolítica fotoinducida de derivados ditiocarbonílicos para producir radicales. Por un lado, el proceso de fotoenolización acoplado con la reactividad de tipo Diels-Alder (secuencia fotoenolización/ Diels-Alder) es una histórica reacción fotoquímica con aplicaciones conocidas en síntesis total. Sin embargo, una variante asimétrica de este proceso no ha sido reportada. Los Capítulos II y III demuestran cómo la organocatálisis asimétrica proporciona herramientas simples y efectivas para hacer participar a las especies fotoenólicas en procesos de tipo Diels-Alder y aldólicos altamente esteroselectivos. Por otro lado, la ruptura fotolítica de especies ditiocarbonílicas capaces de absorber luz visible, es un conocido método para la generación de radicales bajo condiciones suaves de reacción. Esta tecnología hace uso de cantidades estequiométricas de compuestos ditiocarbonílicos fácilmente accesibles. Aunque esta estrategia ha mejorado considerablemente las condiciones para acceder a la reactividad de tipo radicalaria, ésta requiere la síntesis previa de compuestos que contentan la funcionalidad ditiocarbonílica.
The work described in this dissertation focuses on the implementation of organocatalytic strategies to overcome limitations of established photochemical processes. Specifically, two known light-driven transformations have been studied: (i) the photoenolization of 2-alkyl-benzophenones to access transient enol-intermediates (photoenols), and (ii) the photoinduced homolytic cleavage of stoichiometric dithiocarbonyl derivatives to produce radicals. On the one hand, the photoenolization process coupled with classical Diels-Alder chemistry (photoenolization/Diels- Alder sequence) is an historical photochemical reaction with known applications in total synthesis. However, an asymmetric catalytic variant of this light-driven transformation has remained elusive over the years. Chapter II and Chapter III demonstrate how asymmetric organocatalysis provides simple but effective catalytic tools to engage photoenols in highly stereoselective Diels-Alder and Aldol-type processes, respectively. On the other hand, the photolytic cleavage of visible-light-absorbing dithiocarbonyl-based compounds is a known effective method for the mild generation of radicals. This technology uses stoichiometric amounts of easy-to make dithiocarbonyl-based substrates, capable of triggering the formation of open-shell intermediates upon direct light-excitation. Although this strategy has greatly enhanced the conditions to access radical-type reactivity, it still relies on purposely designed stoichiometric reagents.

La capacitat de generar intermedis radicalaris, sota condicions suaus, ha portat a l'emergent camp de la catàlisi fotoredox al desenvolupament de noves transformacions. Tradicionalment, aquesta es basa en l'ús d'un fotocatalitzador, que absorbeix eficientment llum i indueix una transferència simple d'electrons (SET). No obstant això, la reactivitat química de les molècules excitades electrònicament difereix fonamentalment de les que es troben en el seu estat fonamental. Una molècula en estat excitat és alhora una millor donant i acceptora d'electrons que en el seu estat fonamental i es comporta respectivament com una millor reductora i una millor oxidant. El principal objectiu científic d'aquesta tesi doctoral ha estat investigar i comprendre la reactivitat de l'estat excitat d'algunes molècules orgàniques per desenvolupar nous processos fotoquímics de formació d'enllaços C-C. Per aconseguir aquest objectiu, s'ha combinat diferents eines de la química orgànica. En els primers projectes (discutits en els capítols III i IV), la fusió de la organocatàlisi i la fotoquímica han permès la funcionalització asimètrica directa en la posició β d’enals, desencadenada per l'excitació amb llum visible de sals de Imini quirals formades in situ. A la segona part d'aquests estudis doctorals (discutit en el capítol V), s'ha explotat les propietats de l'estat excitat de 4-alquil-1,4-dihidropiridines (alquil-DHP) en combinació amb la catàlisi de metalls de transició pel desenvolupament de catalitzadors de níquel en reaccions radicalàries d'acoblament creuat.
La capacidad de generar intermedios radicalarios, bajo condiciones suaves, ha llevado al emergente campo de la catálisis fotoredox al desarrollo de nuevas transformaciones. Tradicionalmente, esta se basa en el uso de un fotocatalizador, que absorbe eficientemente luz e induce una transferencia simple de electrones (SET). Sin embargo, la reactividad química de las moléculas excitadas electrónicamente difiere fundamentalmente de las que se encuentran en su estado fundamental. Una molécula en estado excitado es a la vez una mejor donante y aceptora de electrones que en su estado fundamental y se comporta respectivamente como una mejor reductora y una mejor oxidante. El principal objetivo científico de esta tesis doctoral ha sido investigar y comprender la reactividad del estado excitado de algunas moléculas orgánicas para desarrollar nuevos procesos fotoquímicos de formación de enlaces C-C. Para lograr este objetivo, se han combinado diferentes herramientas de la química orgánica. En los primeros proyectos (discutidos en los Capítulos III y IV), la fusión de la organocatálisis y la fotoquímica han permitido la funcionalización asimétrica directa en la posición β de enales, desencadenada por la excitación con luz visible de sales de iminio quirales formadas in situ. En la segunda parte de estos estudios doctorales (discutido en el Capítulo V), se ha explotado las propiedades del estado excitado de 4-alquil-1,4-dihidropiridinas (alquil-DHP) en combinación con la catálisis de metales de transición para el desarrollo de catalizadores de níquel en reacciones radicalarias de acoplamiento cruzado.
The emerging field of photoredox catalysis has led to the development of new transformations due to the ability to generate radical intermediates under mild conditions. Traditionally, this relies on the use of a photocatalyst, which efficiently absorbs light and induces a single electron transfer (SET). However, the chemical reactivity of electronically excited molecules differs fundamentally from that in the ground state. An excited-state molecule is both a better electron donor and a better electron acceptor than in the ground state and behaves respectively as a better reductant and a better oxidant. The main scientific objective of this doctoral research was to investigate and understand the excited-state reactivity of some organic molecules to develop novel photochemical C–C bond-forming processes. In order to achieve this goal, different tools of organic chemistry were combined. In the first projects (discussed in Chapter III and IV), the merger of organocatalysis and photochemistry enabled the direct asymmetric β-functionalization of enals triggered by the visible-light excitation of in situ formed chiral iminium salts. In the second part of the PhD studies (discussed in Chapter V), the excited-state properties of 4-alkyl-1,4-dihydropyridines (alkyl-DHP) were exploited in combination with transition metal catalysis for the development of nickel-catalyzed radical cross-couplings.

Les transformacions fotoquímiques es basen en la capacitat de molècules o catalitzadors orgànics d’absorbir llum i arribar als estats electrònicament excitats. Atès que les propietats físiques i químiques de les molècules en estat excitat difereixen significativament de l'estat fonamental, la química intervinguda per la llum pot oferir nous patrons interessants de reactivitat que no estan disponibles amb l'activació tèrmica. L’objectiu principal d’aquests estudis de doctorat va ser implementar estratègies fotoquímiques adequades per desenvolupar transformacions sintètiques útils no assolibles mitjançant processos tèrmics ja coneguts. En particular, he pogut investigar i explotar la capacitat única de les 4-substit-1,4-dihidropiridines (DHPs) per formar radicals de carboni centrats en condicions suaus. En el primer projecte (capítol III), es van utilitzar 4-alquil-1,4-dihidropiridines (alquil-DHPs) com a precursors del radical alquil en l'alquilació enantioselectiva d’enals desencadenada per l'excitació amb llum visible de sals d’iminium quirals generades in situ. En la segona part d’aquests estudis de doctorat (analitzats al capítol IV), es van emprar 4-carbamoil-1,4-dihidropiridines (carbamoil-DHP) com a font de radicals de carbamoil i es van aplicar en reaccions d’acoblament creuat de radicals catalitzats amb níquel per a la síntesi d’una àmplia gamma de (hetero) aril amides.
Las reacciones fotoquímicas se basan en la capacidad de moléculas orgánicas o catalizadores para absorber luz y alcanzar a un estado electrónicamente excitado. Dado que tanto las propiedades químicas como físicas de las moléculas en su estado excitado se diferencian de aquellas en su estado fundamental, la fotoquímica puede ofrecer acceso a interesante nueva reactividad no disponible por la vía térmica. El principal objetivo de esta tesis doctoral fue la implementación de estrategias fotoquímicas para el desarrollo de reacciones sintéticamente útiles no accesibles mediante el empleo de métodos térmicos ya establecidos. En particular, la investigación y explotación de la capacidad única de las 1,4-dihidropiridinas-4-substituidas (DHPs) para formar radicales de tipo carbono usando condiciones suaves. En el primer proyecto, 1,4-dihidropiridinas-4-alquilo (DHP-alquilo) se emplearon como precursores de radicales para la alquilación enantioselectiva de enales desencadenada por excitación mediante luz visible de una sal de iminio quiral formada in situ. En la segunda parte de la tesis doctoral (desarrollada en el capítulo 4), 1,4-dihidropiridinas-4-carbamoil (DHP-carbamoil) fueron empleadas como fuente de radicales de tipo carbamoil y aplicadas en reacciones de acoplamiento de radicales catalizadas por niquel para la síntesis de un amplio rango de (hetero)aril amidas.
Photochemical transformations rely on the ability of organic molecules or catalysts to absorb light and reach the electronically excited states. Since the chemical and physical properties of excited-state molecules significantly differ from the ground state, light-mediated chemistry can offer interesting new reactivity patterns that are unavailable under thermal activation. The main objective of this doctoral studies was to implement photochemical strategies suitable for developing useful synthetic transformations not achievable using established thermal approaches. In particular, I investigated and exploited the unique ability of 4-substituted-1,4-dihydropyridines (DHPs) to form carbon-centered radicals under mild conditions. In the first project (Chapter III), 4-alkyl-1,4-dihydropyridines (alkyl-DHPs) were employed as alkyl radical precursors in the enantioselective alkylation of enals triggered by the visible-light excitation of in situ generated chiral iminium salts. In the second part of the doctoral studies (discussed in Chapter IV), 4-carbamoyl-1,4-dihydropyridines (carbamoyl-DHP) were employed as carbamoyl radical sources and applied in nickel-catalyzed radical cross-coupling reactions for the synthesis of a wide range of (hetero)aryl amides.

La química desenvolupada durant la meva tesi doctoral ha estat impulsada per la capacitat d'intermedis rics en electrons (anions fenolat i enamines quirals), generats transitòriament a partir de precursors fotoquímicament inactius (fenols i aldèhids), per arribar directament a un estat electrònicament excitat després de l'absorció de llum i, posteriorment, promovent la formació d'espècies radicalàries reactives a partir dels iodurs d'alquil adequats. En les transformacions estudiades, la formació dels radicals és a través de l'escissió reductora de l'enllaç carboni-iode del precursor de iodur d'alquil mitjançant mecanismes de transferència d'un sol electró (SET). Inicialment, he desenvolupat un nou enfocament per a la perfluoroalquilació fotoquímica directa de fenols substituïts. L'ús de llum visible simple, sense la necessitat de cap fotocatalitzador o iniciador de radicals, pot promoure la perfluoroalquilació o trifluorometilació aromàtica de fenols a temperatura ambient. En un segon projecte, he desenvolupat una nova metodologia per a la metilació o bencilació en α d'aldèhids mitjançant la fotoorganocatálisi. En aquest cas, la reacció es produeix en absència de catalitzadors fotoredox externs, i els compostos desitjats s'obtenen amb bons rendiments aïllats i elevada enantioselectivitat.
La química desarrollada durante mi tesis doctoral ha sido impulsada por la capacidad de intermedios ricos en electrones (aniones fenolato y enaminas quirales), generados transitoriamente a partir de precursores fotoquímicamente inactivos (fenoles y aldehídos), para alcanzar directamente un estado electrónicamente excitado tras la absorción de luz y, posteriormente, promover la formación de especies radicalarias reactivas a partir de los yoduros de alquilo adecuados. En las transformaciones estudiadas, la formación de los radicales es a través de la escisión reductora del enlace carbono-yodo del precursor de yoduro de alquilo mediante mecanismos de transferencia de un solo electrón (SET). Inicialmente, he desarrollado un nuevo enfoque para la perfluoroalquilación fotoquímica directa de fenoles sustituidos. El uso de luz visible simple, sin necesidad de ningún fotocatalizador o iniciador de radicales, puede promover la perfluoroalquilación o trifluorometilación aromática de fenoles a temperatura ambiente. En un segundo proyecto, he desarrollado una nueva metodología para la metilación o bencilación en α de aldehídos mediante fotoorganocatálisis. En este caso, la reacción se produce en ausencia de catalizadores fotoredox externos, y los compuestos deseados se obtienen con buenos rendimientos aislados y elevada enantioselectividad.
The chemistry developed during my doctoral thesis was driven by the ability of electron rich intermediates (phenolate anions and chiral enamines), transiently generated from photochemically inactive precursors (phenols and aldehydes), to directly reach an electronically excited state upon light absorption and subsequently promoting the formation of reactive radical species from suitable alkyl iodides. In the studied transformations, the radicals are formed through the reductive cleavage of the carbon-iodine bond within the alkyl iodide precursor via single-electron transfer (SET) mechanisms. Initially, I developed a new approach for the photochemical direct perfluoroalkylation of substituted phenols. The use of simple visible light, without the need of any photocatalyst or radical initiator, can promote an aromatic perfluoroalkylation or trifluoromethylation of phenols at ambient temperature. In a second project, I developed a new methodology for the enantioselective formal α-methylation and α-benzylation of aldehydes by means of photo-organocatalysis. The reaction occurs in the absence of external photoredox catalysts, and the desired compounds were obtained in good isolated yields with high enantioselectivity.

Halogen-driven ozone and nonmethane hydrocarbon losses in springtime Arctic boundary layer are investigated using a regional chemical transport model (CTM). Surface observation of O3 at Alert and Barrow and aircraft observations of O3 and hydrocarbons during the TOPSE experiment from February to May in 2000 are analyzed. We prescribe halogen radical distributions based on GOME BrO observations and calculated or observed other halogen radical to BrO ratios. GOME BrO shows an apparent anti-correlation with surface temperature over high BrO regions. At its peak, area of simulated near-surface O3 depletions (O3 LT 20ppbv) covers GT 50% of the north high latitudes. Model simulated O3 losses are in agreement with surface and aircraft O3 observations. Simulation of halogen distributions are constrained using aircraft hydrocarbon measurements. We find the currently chemical mechanism overestimate the Cl/BrO ratios. The model can reproduce the observed halogen loss of NMHCs using the empirical Cl/BrO ratios. We find that the hydrocarbon loss is not as sensitive to the prescribed boundary layer height of halogen as that of O3, therefore producing a more robust measure for evaluating satellite column measurement. Tropospheric tracer transport and chemical oxidation processes are examined on the basis of the observations at northern mid-high latitudes and over the tropical Pacific and the corresponding global 3D CTM (GEOS-CHEM) simulations. The correlation between propane and ethane/propane ratio is employed using a finite mixing model to examine the mixing in addition to the OH oxidations. At northern mid-high latitudes the model agrees with the observations before March. The model appears to overestimate the transport from lower to middle latitudes and the horizontal transport and mixing at high latitudes in May. Over the tropical Pacific the model reproduces the observed two-branch slope values reflecting an underestimate of continental convective transport at northern mid-latitudes and an overestimate of latitudinal transport into the tropics. Inverse modeling using the subsets of observed and simulated data is more reliable by reducing (systematic) biases introduced by systematic model transport model transport errors. On the basis of this subset we find the model underestimates the emissions of ethane and propane by 14 5%.

A major source of radical species in the atmosphere is through the oxidation reactions of biogenic volatile organic compounds that are emitted from vegetation. Tropical rainforests are responsible for over half of such biogenic species that are emitted into the atmosphere and the local, regional and global impacts of their subsequent oxidation mechanisms are currently not well understood. Further, with tropical forests being removed to make way for new land uses (such as oil palm plantations), the subsequent change in the quantity and type of biogenic emissions into the atmosphere could have far-reaching impacts. The Oxidant, Particle and Photochemical Processes (OP3) field campaign conducted at Bukit Atur in Malaysian Borneo in 2008, aimed to address some of the uncertainties that currently exist surrounding the impact of forested regions on atmospheric chemistry. In particular, this project aims to predict the concentrations of OH, HO2 and RO2 radicals at Bukit Atur in Borneo during April and July of 2008, using a near-explicit photochemical box model with 15,000 reactions and 7,200 species. The model is constrained using observations made during the two experimental campaigns, and used to compare with radical measurements. In agreement with previous studies involving tropical forests, it was found that the standard model based on the Master Chemical Mechanism (MCM v3.1) underestimates the observed concentrations of OH by a factor of 0.5 on average and overestimates HO2 concentrations by a factor of 2. The results for RO2 were mixed with some days over-predicted and some under-predicted. The implementation of some new theoretically derived reaction pathways without the isoprene degradation scheme improved the predicted OH concentration (modelled:measured ratio improved to 0.3), but did not improve the HO2 estimation (modelled: measured ratio changed to 2.5). It was found that the modelled: measured discrepancy was better on days when the VOC:NOX ratio was lower, suggesting that even with the updated isoprene scheme, days with high biogenic concentrations are not well represented in the model. A rate of production analysis also confirmed that days where modelled OH agreed best with measurements were dominated more by NOX reactions, and less by for instance, Criegee biradical reactions, the latter an indication of biogenic influence. It seems likely from the results from this study (and others) that the suggested alterations to the isoprene chemistry scheme are incomplete, as they do not completely remove the model discrepancy in the predicted OH and HO2 concentrations. This work provides a useful contribution to the understanding of radical species production in tropical forests and provides more data in this area of research. However, this project also identifies that more research is required, particularly in the elucidation of isoprene degradation in the atmosphere, but also with issues such as the dry deposition rates of key intermediates in the model mechanism.

This work investigates the elimination of new and emerging microcontaminants (EMs) from water by means of photochemical oxidation processes, namely heterogeneous and homogeneous photocatalysis. Representative compounds of artificial sweeteners (saccharin, SAC), endocrine disruptors (bisphenol-A, BPA), and pharmaceutica ls (antipyrine, AP) of high environmental persistence and widespread occurrence in the water cycle are used as case studies. Novel concepts that can make photochemica l oxidation a more cost-effective and environmentally benign technology are tested. In Chapter 4, the photocatalytic treatment of SAC and BPA is investigated. Novel submicronic anatase-rutile nanocomposite particles with tuned phase ratio are used as catalysts to increase the photocatalytic performance under UVA irradiation. At the best-assayed conditions (C0 = 3 mg/L, catalyst = 400 mg/L), SAC and BPA are completely degraded within 90 and 150 min of photocatalytic treatment, respectively. [variables: anatase-rutile ratio; initial substrate concentration; catalyst concentration; catalyst reuse; sonication during catalyst recovery] In Chapter 5, a UVA light-emitting diode (UVA-LED) and sunlight are used as irradiation sources to reduce energy requirements and environmental impacts of photocatalytic processes. The photocatalytic degradation of SAC and BPA is studied under UVA irradiation provided by either a UVA-LED or a conventional fluoresce nt blacklight UVA lamp (UVA-BL) and solar irradiation. At the best-assayed conditions (C0 = 2.5 mg/L, TiO2 = 250 mg/L), BPA is completely degraded within 20, 30, and 120 min under UVA-LED, solar, and UVA-BL irradiation, respectively. The treatment time required for the complete elimination of SAC is 20 min under UVA-LED and 90 min under UVA-BL irradiation. [variables: initial substrate concentration; catalyst concentration; water matrix; light source; reactor configuration] In Chapter 6, a comparative study is carried out among the photocatalytic systems of Chapters 4 and 5 in terms of EMs removal, photonic and energy efficiencies. Technica l and economic aspects of all the processes are assessed. LED-driven photocatalysis achieves the highest efficiency in terms of organic removal with the minimum energy consumption, rendering it the most sustainable technology for the treatment of EMs. In Chapter 7, olive mill wastewater (OMW) is used as an iron-chelating agent in the photo-Fenton reaction to obviate the need for water acidification at pH 2.8. Conventional, OMW- and EDDS-assisted photo-Fenton treatment is applied for SAC degradation in a solar compound parabolic collector (CPC). It was found that OMW forms iron complexes able to catalyse H2O2 decomposition and generate hydroxyl radicals. At the optimal OMW dilution (1:800), 90% of SAC is degraded within 75 min. [variables: pH; iron-chelating agent; initial SAC concentration; OMW dilution] In Chapter 8, other complexing and oxidising agents, namely oxalate and persulfate, are used for the intensification of AP degradation during UVA-LED photo-Fenton treatment. Neural networks are applied for process modelling and optimisation. At the optimal conditions (hydrogen peroxide = 100 mg/L, ferrous iron = 20 mg/L, oxalic acid = 100 mg/L), complete degradation of AP and 93% mineralisation is achieved within 2.5 and 60 min, respectively. [variables: initial concentration of hydrogen peroxide, ferrous iron, oxalic acid, persulfate] It is concluded that LED-driven photocatalysis is a sustainable technology for the elimination of EMs from water. Results from this work highlight the need for development and optimisation of engineering proper LED reactors. Furthermore, this work introduces a new concept towards the sustainable operation of photo-Fenton that is based on the use of wastewaters rich in polyphenols instead of pricey and hazardous chemicals for iron chelation. The addition of ferrioxalate complexes is proposed for the intensification of EMs mineralisation during UVA-LED photo-Fenton treatment. Finally, the findings of this work encourage the use of chemometric tools as predictive and optimisation tools.

Thesis (Ph. D.)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2006.
Wang, Yuhang, Committee Chair ; Black, Robert, Committee Member ; Curry, Judith, Committee Member ; Huey, Greg, Committee Member ; Russell, Armistead G, Committee Member. Includes bibliographical references.

The purpose of this study was to simulate the liquid flow rate distribution in the etching modules and find the optimal setup in order to achieve a distribution as homogenous as possible. The commercial software Matlab 2015a has been employed for all the numerical simulations. The optimization has been carried out varying several parameters, i.e. spray cross sections of the nozzles, the oscillation parameters, the rotating angle of the nozzles within etching module 1 and the nozzle arrangement inside the modules. Furthermore, the optimization has been carried out separately along the two directions of the modules. The results achieved computationally have been validated via experimental procedures. During this study a specific experimental setup has been developed in order to be able to compare experimental and computational results. The validation process has shown that the computational method matches the experimental results to a good extent. The experimental liquid distribution in etching module 2 widely matches the simulations to a quantitative extent, while the one in etching module 1 provides the same qualitative but different quantitative results.

While Aluminium has lots of unique properties and is seen as a material of the future, its production and manufacturing has significant environmental impacts. For complex and dimensional shapes casting remains the main manufacturing method and in this study the environmental pressure of different casting techniques is compared. A screening LCA is conducted to determine the environmental impacts of plaster mould castings in a case study at the Ventana Hackås AB foundry in Mid Sweden. The findings are compared to models of sand, pressure die and lost wax castings, based on literature datasets. The most relevant factors for the environmental performance are identified as the production of the aluminium alloy and the amount and source of energy. For plaster mould castings additionally the plaster consumption is significant, while lost wax castings are dominated by the mould production and general processes. Under similar circumstances a relatively similar performance was found for all casting techniques except the lost wax process, which is at least 3 times more emission intensive. Of the remaining techniques pressure die castings performed the best and plaster mould castings the worst, but different sources of uncertainties have been identified in this comparison. In addition a carbon footprint interface is created based on these findings, to enable specific comparisons of different casting method setups. Customizable variables allow the adaptation of three scenarios to real world conditions. As the main influencing factors the aluminium alloy, source of electricity and casting technique have been identified.

2018-10-10

Advanced Oxidation Processes (AOPs) are suitable for achieving the complete mineralization of organic pollutants in wastewaters, since they are based on the generation of a powerful non-selective chemical oxidant. A major drawback of AOPs is that they involve high operating costs if high levels of mineralization are endeavoured. Integration of an AOP with a biological treatment has demonstrated to be a suitable alternative, since it combines the capacity of the AOP, in this case Photo-Fenton, to enhance biodegradability, with a biological treatment such as a Sequencing Batch Biofilter Reactor (SBBR), which operating costs are lower.

Photo-Fenton (Ph-F) process is carried out by irradiating the system with ultraviolet (UV) and/or visible (Vis) light. In Fenton processes, by combination of hydrogen peroxide (H2O2) as a reagent and iron ions (Fe2+ for example) as catalyst in acid medium, highly oxidant species are generated.

According to the results, most of the studied parameters may be written as a function of [H2O2]0, which means that temperature and [Fe2+]0 do not affect significantly the results. Moreover, a subsequent scale-up of the process shows that degradation follow very similar tendencies and shows similar results.

It has been observed that the efficiency of oxidation follows a tendency directly related to the amount of H2O2 applied. An innovative description of the process is their modelling regarding the evolution of COD and BOD5 over the oxidation process or depending on the amount of H2O2 applied. The models show good fitting properties, and they appear to be a good basis for more precise modelling of the system.

Regarding the integration of both processes, the best operating conditions consists of first treating the solution by Ph-F with 500 mg.L-1 of [H2O2]0 and 10 mg.L-1 of [Fe2+]0 at 27 ºC. The resulting product is then treated in the SBBR for 8 hours of time. More than 90 % of mineralization is achieved. The bioreactor show high resistance when is exposed to toxic shock load. Concerning control possibilities, monitoring the Oxygen Uptake Rate (OUR) by in-situ respirometry is suggested to be a good parameter, since it is a direct measurement of bacterial activity.

O dímero de pirimidina ciclobutano é uma lesão no DNA fotoinduzida por radiação ultravioleta que pode evoluir para um tipo de câncer de pele. Uma das formas de reparar essa lesão usada por alguns organismos é através do processo enzimático de fotoreativação, induzido por radiação UV na região do visível. Crucial neste processo é a transferência de um elétron primária do cofator enzimático FADH POT.- para o dímero após a qual ocorre separação do dímero em monômeros. Vários compostos indólicos forma estudados no passado com o objetivo de mimetizar o sistema enzimático, entre eles o complexo não-enzimático covalentemente ligado indol-dímero. No entanto, não foi possível até o presente obter um sistema substitutivo que opere tão eficientemente quanto o enzimático. Nesta tese, fizemos um estudo teórico e fenomenológico da eficiência de reparo dos dímeros de pirimidina quando efetuado tanto pelo complexo enzimático como pelo complexo covalentemente ligado (indol-dímero). Tentativamente, buscamos determinar os elementos físicos e químicos que são influentes para a eficiência do processo de reparo, concentrando os esforços na compreensão do papel de processos competitivos à reação intrínseca de separação dos dímeros o que inclui a possibilidade de transferência de elétrons de volta para o doador original. Para isso, formulamos uma expressão para a eficiência de reparo em termos das quantidades que regulam as taxas das etapas intermediárias, incluindo tanto o processo direto de transferência de elétrons, como o de volta. O elemento de transição eletrônica que toma parte nesta expressão é calculado explicitamente na aproximação do modelo \"ligação firme\", usando o método da Expansão Perturbativa Renormalizada, para levar em conta a natureza de longo-alcance do processo de transferência de elétrons neste caso. Estimamos também os parâmetros nucleares que incorporam as expressões para as taxas de transferência de elétrons, como prescrito pela teoria de Marcus. Análise subsequente do processo de reparo usando esta fórmula permitiu-nos interpretar a natureza do compromisso entre as duas reações de transferência de elétrons e do controle exercido por estas sobre a eficiência do reparo. Pudemos então propor uma forma para estudar este compromisso em termos de grandezas mensuráveis, quais sejam, a polaridade do solvente e o seu grau de especularidade do cromóforo. Isto permitiu sugerir maneiras práticas de combinar estes efeitos para obter compostos artificiais com eficiências mais altas.
The ultraviolet photo induced cyclobutane pyrimidine dimer is a lesion to DNA that can evolve to a type of skin cancer. One of the mechanisms to repair the lesion is through the enrymatic photoreactivation process induced by solar radiation in the visible region. A crucial step in this process is a primary electron transfer reaction from the photolyase enzyme cofactor FADH to the dimer, after which dimer cleavage occurs. Several indolic compounds, as for instance the simple covalently linked indole-dimer, have been designed in the past years in order to mimic the actions of enzymatic complex. Nevertheless, up to the present it was not possible to find a substitute that operates as efficiently as the enzyme. In the present thesis, we perform a theoretical and phenomenological study of the efficiency of dimer repair by both enzymatic and indolic complexes. We attempt to find physical and chemical elements that are influential to the efficiency of the repair process focusing on the role of competitive reactions to the cleavage, including explicitly the possibility of quenching by back-electron transfer. For this, we formulate an expression for the efficiency of repair in terms of the quantities that regulate the rates for intermediate reactions, including primary and back electron transfers. The electronic transition element entering this expression is calculated in the tight-binding approximation using the Renormalized Perturbation Expansion method to account for the long-range nature of the electron transfer process in this case. We also estimate the nuclear parameters that enter the rate expression as prescribed by Marcus theory. A subsequent phenomenological analysis of the repair process using this formula and applied to both enzymatic and indolic systems, allowed us to understand the nature of the compromise established between the primary and back electron to control the efficiency of repair. We could then propose a way to study this compromise in terms of measurable quantities, namely the solvent polarity and another that depends on the degree of spectral specularity of the chromophore. This allowed us to suggest practical ways to combine these effects in order to increase the efficiency of designed artificial compounds.

Agrotóxicos são frequentemente relatados na literatura em contaminações de ambientes aquáticos, sendo provenientes do lixiviamento de solos, do descarte inadequado de embalagens agrícolas, dentre outros. Nesse contexto, os processos oxidativos avançados (POA) têm sido estudados como alternativa para o tratamento desses compostos em meio aquoso. Os POA consistem na oxidação de compostos orgânicos pela formação de radicais livres com alto poder oxidante. Diante desses aspectos, o presente trabalho teve como proposta o estudo da degradação dos herbicidas hexazinona e diuron, aliada ao planejamento experimental do tipo composto central, a fim de otimizar o processo de degradação. Para tanto, realizaram-se as degradações através dos processos H2O2/UV e foto-Fenton em concentrações iniciais próximas a 7 e 20 mg L-1 para a hexazinona e diuron, respectivamente. Os experimentos foram conduzidos em um reator fotoquímico (200 mL a 25 °C) com aplicação de irradiação UV, proveniente de uma lâmpada de Hg (degradação H2O2/UV) e de luz negra (degradação foto-Fenton). No processo via H2O2/UV foram avaliadas a concentração de H2O2 (0,65 a 13,34 mmol L-1) e pH (2,77 a 11,23), e para o processo foto-Feton avaliou-se a concentração de H2O2 (0,09 a 29,1 mmol L-1) e Fe (II) (0,01 a 0,92 mmol L-1). Como variável independente, utilizou-se a remoção de Carbono Orgânico Total (COT) nos dois casos. A eficiência na degradação dos herbicidas foi determinada através das técnicas de Espectroscopia UV-Vis, Cromatografia Líquida de Alta Eficiência (HPLC/UV), remoção de Carbono Orgânico Total e Cromatografia de Íons. A análise dos modelos matemáticos, obtidos a partir dos planejamentos, possibilitou a avaliação da influência das variáveis, determinando as melhores condições. No processo H2O2/UV observou-se que a influência da variável H2O2 é maior comparada ao pH. A melhor condição de degradação apresentou concentrações de H2O2 iguais a 7 mmol L-1 e valores de pH de 2,8. Como resultado, obteve-se 96 % de remoção do COT e a não detecção de ambos os herbicidas após 2 minutos de reação. No processo foto-Fenton, a realização de três planejamentos foi necessária para a otimização do sistema. Primeiro e segundo planejamentos indicaram a melhor condição, enquanto que o terceiro planejamento revelou que concentrações elevadas de H2O2 e Fe2+ não garantem maior eficiência. As condições ideais encontradas foram iguais a 0,291 mmol L-1 para o Fe2+ e 2,91 mmol L-1 para o H2O2, obtendo-se 76 % de remoção do COT e não detecção dos herbicidas nos primeiros minutos de degradação. Em ambas as degradações não foi possível observar diferenças em relação a cinética de degradação para os herbicidas. A degradação via H2O2/UV mostrou melhor desempenho, pois apresentou maior taxa de mineralização além de não necessitar o emprego do íon Fe(II).
Pesticides are often reported in the literature on aquatic environments contamination, being a result of soil leaching, improper disposal of agricultural packages, among others. In this context, advanced oxidation processes (AOP) have been studied as an alternative to treat these compounds in aqueous medium. The AOP consist in the oxidation of organic compounds through the formation of free radicals with a high oxidizing power. Considering these aspects, the present work aimed to study degradation of the herbicides diuron and hexazinone, coupled with an experimental setup as central compost, in order to optimize the degradation process. For this purpose, the degradation was carried out by H2O2/UV and photo-Fenton processes at initial concentrations close to 7 and 20 mg L-1 to hexazinone and diuron, respectively. The experiments were conducted in a photochemical reactor (200 mL at 25 ° C) with application of UV irradiation from Hg lamp (H2O2/UV degradation) and black-light (photo-Fenton degradation). In the H2O2/UV process, the concentrations of H2O2 (0.65 to 13.34 mmol L-1) and pH (2.77 to 11.23) were evaluated, and in the photo-Fenton process, the concentrations of H2O2 (0.09 to 29.1 mmol L-1) and Fe (II) (0.01 to 0.92 mmol L-1) were analyzed. In both processes, the removal of Total Organic Carbon (TOC) was used as an independent variable. The efficiency of the herbicide degradation was determined by UV/Vis spectroscopy, high performance liquid chromatography (HPLC/UV), removal of the Total Organic Carbon and ion chromatography. The analysis of the mathematical models obtained from the experimental setup allowed the evaluation of the variables influence ,determining the best conditions. The H2O2/UV process showed that the influence of the H2O2 is higher compared to that of the pH. The best degradation condition presented H2O2 concentrations of 7 mmol L-1 and a pH value of 2.8. As a result, 96% TOC removal was observed, and none of the herbicides were detected after 2 minutes of reaction. In the photo-Fenton process, the conduction of three setups was necessary to confirm the best condition. The first and second setups indicated the best condition, while the third one showed that high concentrations of H2O2 and Fe2+ do not guarantee a greater degradation efficiency. Ideal conditions were equal to 0.291 mmol L-1 for Fe2+ and 2.91 mmol L-1 for H2O2, where 76% of TOC removal was obtained and also no herbicides detection was seen in the early minutes of degradation. In both processes, it was not possible to observe differences in the degradation kinetics of the herbicides. The H2O2/UV degradation showed better performance because of a greater mineralization rate besides not requiring the ion Fe (II) use.

Efluentes contendo resíduos perigosos ou substâncias orgânicas recalcitrantes são geradas em uma ampla variedade de processos industriais. O manejo inadequado destes efluentes pode causar contaminação das águas superficiais e subterrâneas. O seu tratamento por processos convencionais muitas vezes não é eficiente, por vezes impedindo o despejo ou reutilização de águas em unidades industriais. Os processos oxidativos avançados têm sido o foco de vários estudos em busca de alternativas viáveis para o tratamento de águas residuais contendo contaminantes orgânicos tóxicos, ou recalcitrantes. No presente estudo, o processo foto-Fenton é abordado, com a utilização de luz solar como fonte de fótons. O estudo consistiu de uma etapa de experimentos em um reator solar provido de coletores parabólicos compostos (CPC), ligados a um tanque agitado equipado com lâmpadas elétricas. Este sistema de operação foi utilizado em diferentes configurações, como operação em batelada ou contínuo, com variação de área irradiada por luz solar e com variação da potência total das lâmpadas no tanque. Na maior parte dos experimentos, com o reator operando em regime batelada, mais de 90% do carbono orgânico dissolvido (COD) foi removido em menos de 3 horas de irradiação solar, um desempenho equivalente ao de reatores baseados em fontes de luz artificial. Os dados experimentais foram usados no ajuste de modelos matemáticos empíricos baseados em redes neurais para simulação da taxa de remoção de COD em função das condições experimentais. Este modelo foi combinado com balanços de massa, que permite simular o desempenho do reator para diferentes valores das variáveis operacionais e de projeto. Os resultados das simulações do modelo mostraram boa concordância com os dados experimentais para a maioria dos casos. Além de evidenciar a relação entre as variáveis de processo, os resultados obtidos possibilitam identificar aspectos importantes no projeto de reatores baseados em radiação solar para tratamento de efluentes.
Wastewaters containing hazardous, or recalcitrant organic substances are generated in a wide variety of industrial processes. The inadequate management of these effluents can cause contamination of underground and surface water. Their treatment by conventional processes may not be technically efficient, and usually prevents effluents from being discarded or reused in industrial processing units. Photochemical advanced oxidation technologies can be a feasible alternative for wastewater treatment. In this study the photo-irradiated Fenton process is considered, with the aim of utilizing solar radiation as a photon source to the process. The study comprised experiments carried out in a solar reactor based on compound parabolic collectors (CPC) connected to a stirred tank equipped with electric lamps. This reaction system operated under different conditions, and different configurations (continuous and batch operation, different solar irradiated area, different electric power for the light sources in the stirred tank). In general, the performance of the solar reactor was similar to the performance of reactors based on electric light sources (for instance, in batch operation more than 90% of the dissolved organic carbon in solution (DOC) was removed in less than 3 hours). The experimental results were used to fit a neural network-based mathematical model to simulate the DOC removal rate as a function of the experimental conditions. This model was combined with mass balances, enabling to simulate the reactor performance for different values of the operating and design variables. The model results showed good agreement with most of the experiments. The simulation results enabled to evaluate the effect of the variables included in the study, and to identify important aspects related to reactor performance under different conditions of solar radiation and electric energy sources.

Background. Platelets (thrombocytes) are the smallest cells in the blood. Platelet fulfils functions as formation of blood clots when bleeding. Low levels leads to bleeding while high levels increase the risk of thrombosis (obstruction of the circulatory flow system). Platelet transfusions may be required for patients with systemic bleeding and for patients at higher risk of bleeding because of coagulation defects, sepsis (presence of bacteria in the bloodstream), or platelet dysfunction related to medication or disease. A pathogen-reduction system for platelet components would be a useful method since it reduces the risk of bacterial, protozoa, viral and white blood cell contamination. The Intercept Blood System method (IBS) for platelets, destroys DNA and RNA and was validated against the routine method in order to reduce pathogen transmission risk during transfusion. The validation of IBS, the trombocyte count for100 buffy coat concentrates from 2007 were compared to values for 100 buffy coat concentrates from 2006 that had been treated with gamma-radiation. Akademiska sjukhuset in Uppsala has a requirement that 75% of the platelet concentrates contain at least 300*10 9 platelets per unit. IBS fulfilled to 94% compared to 98% for the routine method.

Thus, the IBS-method was well above the required value and is now used at

Akademiska sjukhuset in Uppsala.

A racionalização dos recursos hídricos tem sido uma das metas das indústrias em vários setores. Tais metas exigem inovações tecnológicas tanto para novos processos produtivos quanto para novas técnicas de tratamento e reutilização de água na cadeia de produção. Os custos elevados de água industrial no Brasil, particularmente nas regiões metropolitanas, têm estimulado as indústrias nacionais a avaliar as possibilidades de reúso. O objetivo deste trabalho é a aplicação do tratamento de águas de processo contendo polipropileno utilizando radiação ultravioleta e peróxido de hidrogênio, isto é, o sistema UV/H2O2, visando adequá-las para reúso no próprio processo, reduzindo a necessidade de captação de água pré-tratada e de descarte de efluente. A primeira parte do estudo consistiu na realização de experimentos em um sistema fotoquímico de batelada, empregando quatro diferentes correntes efluentes de processo, para a avaliação da viabilidade técnico-econômica do tratamento fotoquímico, bem como para a obtenção de dados referentes à cinética das reações fotoquímicas. Com base nas informações obtidas, na segunda parte do estudo foram realizados experimentos em um sistema fotoquímico contínuo, a fim de obter dados para o aumento de escala para aplicação industrial do processo de tratamento contínuo. Os resultados experimentais indicaram a viabilidade técnica de aplicação do sistema UV/H2O2 utilizando fonte de luz artificial para todas as correntes de processo estudadas, tendo sido alcançados níveis de remoção de matéria orgânica acima de 90%. No entanto, sob o ponto de vista econômico, apenas as correntes com baixo teor de carbono orgânico total dissolvido (COT), entre 6 e 12 mgC L-1, mostraram-se adequadas ao reúso, após o tratamento.
Rationalization of water use has been one of the goals in many industrial activities, and, in particular, in the petrochemical industry. Such goals demand technological innovations in the productive processes and in techniques for treatment and reuse of water in the production chain. The high costs of industrial water, particularly in some metropolitan regions, have stimulated the industries to evaluate the possibilities of water reuse. The objective of this work is to evaluate the feasibility of the UV/H2O2 photochemical process applied to the treatment of process waste water containing polypropylene, aiming at the reuse of the waste water in the as process water in the industrial complex, thus reducing the need for tap water supply and waste water generation rate. The first part of this study consisted of laboratory-scale experiments in a batch photochemical reactor with four different waste water streams to perform the technical and economical feasibility of the photochemical treatment, as well to obtain data on the degradation rate. Based on the results of the first part, the second part of this study consisted of experiments in a continuous photochemical reactor, aimed at obtaining experimental data for reactor scale-up. Experimental results indicate that the UV/H2O2 photodegradation process is able to remove more than 90% of the organic compounds contained in the waste water. However, only waste waters containing relatively low contaminant levels (between 6 and 12 mgC L-1) can be treated at economically favourable costs.

Since their discovery, organic electronic materials have been of great interest as an alternative active layer material for active area materials in electronic applications. Initially studied as probes or lasing material the field has progressed to the point where both conjugated polymers and small organics have become fashionable objects of current device oriented solid state research. Organic electronic materials are liquid crystalline materials, packing into well-ordered domains when annealed thermally or via solvent annealing. The macromolecular orientation of the molecules in the solid state causes a shift in the electronic properties due to coupling of the dipoles. The amount of interaction between molecules can be correlated to different nanoscale morphologies. Such morphologies can be measured using microscopy techniques and compared to the spectroscopic results. This can then be extrapolated out to infer how the charges move within a film. Cyanine dyes represent an interesting form class of dyes as the molecular packing is strongly affected by hydrophilic and hydrophobic pendent groups, which cause the dye to arrange into a tubular bilayer. Spectroelectrochemistry is used to monitor and controllably oxidize the samples. Using singular value decomposition (SVD) it is possible to extract each electronic species formed during electrochemical oxidation and model the proposed species using semi empirical quantum mechanical calculations. Polyfluorene is a blue luminescent polymer of interest for its high quantum yield. The solution and solid-state conformation has shown two distinct phases. The formation of the secondary phase shows a dependence on the molecular weight. In a poor solvent, as the molecular weight increases, the secondary phase forms easier. In the solid state, the highly efficient blue emission from polyfluorene is degraded by ketone defects. The energy transfer to preexisting ketone defects is increased as the filmed is thermally ordered. Glass transitions of block copolymers are studied using synthetically novel polymers where an environmentally sensitive fluorescent reporter is placed within various regions of a self-assembled film. Different dynamics are observed within the block of the film then specifically at the interface of two blocks.
text

Part I:

This thesis consists of two chapters concerning photochemical processes in the atmospheres of earth and Mars. The first chapter is a comprehensive study of the photochemistry of the martian atmosphere. Classical models of the Mars atmosphere have neglected an important property of carbon dioxide, namely that the photoabsorption cross section decreases with lower temperature. Accounting for this effect yields a smaller photolysis rate for CO_2 and more importantly, an enhanced photolysis rate for water vapor. Both effects combine to yield carbon monoxide mixing ratios smaller by a factor of four than observations indicate. We propose modifications in the rate coefficients for two key reactions, CO + OH and OH + HO_2, in order to resolve this discrepancy. We note that similar revisions have been proposed to reconcile models and observations of ozone in the terrestrial mesosphere. Other investigators have proposed a heterogeneous sink of odd hydrogen radicals on aerosols; we find that such a sink is unnecessary. Finally, we have performed the first time dependent calculation to examine the mechanism by which the escape of atomic oxygen controls the escape flux of hydrogen from the atmosphere. We show that this coupling operates over a time scale of 10^5 years.

In chapter two we investigate the formation and evolution of low ozone anomalies in the northern winter stratosphere using a Lagrangian photochemical model. The UARS spacecraft has observed pockets of low ozone in the 6 to 10 millibar altitude range, where the effects of dynamics and chemistry on the ozone budget are comparable. We employ the Lagrangian model to compute the ozone loss rate within an isolated parcel of air as it travels along a specified trajectory. Since we have decoupled the dynamics and chemistry, disagreement between the model and observations should reflect deficiencies in the chemistry. We find that the model consistently overestimates the ozone loss rate above about 7 millibars altitude, which is a common feature of most current photochemical models. Below 10 millibars altitude, the model is in good agreement with the observations, indicating that the description of chemistry is valid in the low to mid stratosphere.

Part II:

Photochemical models have historically overestimated ozone loss rates in the upper stratosphere and lower mesosphere, where ozone is photochemically controlled. Thus it is evident that there is some missing chemistry in current models. Current understanding of the factors controlling ozone in the low to mid stratosphere is that dynamical influences play a large role in determining the ozone abundance. It is difficult to test the chemistry in the models at these altitudes since the contributions from transport and chemistry must be separated.

The Microwave Limb Sounder (MLS) aboard the Upper Atmosphere Research Satellite (UARS) has observed pockets of low ozone in the winter polar stratosphere outside the polar vortex. These pockets occur in the 6 to 10 millibar altitude range, where the effects of dynamics and chemistry on the ozone budget are comparable. The formation and evolution of these anomalies are investigated using a Lagrangian photochemical model, where the chemistry within an isolated parcel of air is simulated as it travels along a specified trajectory. Since we have decoupled the dynamics and chemistry, disagreement between the model and observations should reflect deficiencies in the chemistry.

We find that the model consistently overestimates the ozone loss rate above about 7 millibars, where the ozone deficit tends to manifest itself. Below 10 millibars altitude, the model is in good agreement with the observations, indicating that the description of chemistry is valid in the low to mid stratosphere. Individual trajectories have many uncertainties associated with them; in order to present more quantitative conclusions the results computed along many trajectories should be taken together to minimize errors.

Tese de doutoramento em Química, na especialidade de Espectroscopia Molecular, apresentada à Fac. de Ciências e Tecnologia de Coimbra
In the first part of this Thesis, the detailed characterization of the molecular structure, photochemistry and spectroscopic properties of a series of heterocyclic molecules containing nitrogen or/and their precursors and photoproducts was undertaken by matrix isolation infrared spectroscopy and high-level quantum chemical calculations. The characterization of the low energy conformers was made by undertaking a systematic investigation of the DFT(B3LYP)/6-311++G(d,p) potential energy surface of the molecules. In the case of the azide representative (methyl (Z)-2-azido-3-chloro-3-benzoylpropenoate, MACBP) and its photoproducts, systematic preliminary explorations of the potential energy surfaces were performed using the semi-empirical PM3 method. The studied five-membered ring derivatives (methyl 4-chloro-5-phenyl-1,3-oxazole-2-carboxylate and methyl 4-chloro-5-phenylisoxazole-3-carboxylate) and MACBP represent interesting systems where conformational cooling takes place during deposition of the matrices and partial conversion of higher energy isomers into the more stable forms during matrix annealing were found to be relevant. The photochemical transformations resulting from in situ irradiation of the matrix-isolated compounds were studied using broadband ultraviolet light (UV) for all compounds, and narrowband UV laser irradiation for methyl aziridine-2-carboxylate. In the second part of this Thesis, formic and acetic acids were studied in solid nitrogen. The low-energy trans and high-energy cis conformers of monomeric forms of formic and acetic acids, have been identified and their IR spectra assigned. The higher-energy cis conformers of these molecules were produced by vibrational excitation of the more stable trans conformers. The decay of the cis forms into the trans forms was observed and explained by tunneling of hydrogen atom through the cis–to–trans torsional barrier, similarly to what has been previously observed for these species in rare-gas matrices. Three trans-trans and two trans-cis dimers of acetic acid were produced in solid nitrogen and structurally and vibrationally characterized. One trans-trans dimer and both observed trans-cis dimers were reported for the first time. On the whole, the studies reported in this Thesis address some of the most important chemical phenomena and processes taking place for criteriously chosen molecules isolated in matrices: thermally induced reactions (conformational cooling; thermally induced-conformational isomerization upon annealing of the matrices; thermal mobilization of monomers to produce dimers); photochemical reactions (UV-induced conformational isomerizations, tautomerizations and other rearrangements, including complex bond breaking – bond forming processes); infrared-induced conformational conversions; and reactions occurring by tunneling mechanism.
Na primeira parte desta Tese, a caracterização detalhada da estrutura molecular, fotoquímica e propriedades espectroscópicas numa série de moléculas heterocíclicas contendo um átomo de nitrogénio e/ou seus precursores e seus fotoprodutos foi efectuado através da espectroscopia de infravermelho com isolamento em matrizes e recorrendo a métodos teóricos de química quântica. A caracterização dos confórmeros de menor energia foi realizado através de um varrimento da superfície de energia potencial das diferentes moléculas ao nível DFT(B3LYP)/6-311++G(d,p). No caso do representante da azida ((Z)-2-azido-3-cloro-3-benzoilpropenoato de metilo, “MACBP”) e dos seus fotoprodutos, foi realizado um varrimento do espaço conformacional preliminar usando o método semi-empírico PM3. Os derivados com anéis de cinco membros (4-cloro-5-fenil-1,3-oxazole-2-carboxilato de metilo e 4-cloro-5-fenil-isoxazole-2-carboxilato de metilo) e “MACBP” representam casos de sistemas interessantes em que ocorre arrefecimento conformacional durante a deposição das matrizes e conversão parcial dos isómeros mais energéticos nas formas mais estáveis em experiências de variação de temperatura da matriz (“annealing”). As transformações fotoquímicas resultantes da irradiação in situ dos monómeros das moléculas isoladas em matrizes de árgon e xénon foram estudadas usando irradiação na região do ultravioleta (UV) de banda larga, e com irradiação na região do ultravioleta (UV) de banda estreita no caso da aziridina-2-carboxilato de metilo. Na segunda parte desta Tese, os ácidos fórmico e acético foram estudados em matrizes de nitrogénio. O confórmero menos energético trans e o mais energético cis das formas monoméricas dos ácidos fórmico e acético, foram identificados e os espectros vibracionais atribuídos. Os confórmeros mais energéticos cis destas moléculas foram produzidos por excitação vibracional dos confórmeros mais estáveis trans. O decaimento das formas cis nas formas trans foi observado e explicado recorrendo ao mecanismo do efeito de túnel do átomo de hidrogénio através da barreira torsional cis trans, que ocorre de um modo similar ao observado anteriormente para estas espécies em outras matrizes criogénicas. Três dimeros trans-trans e dois dimeros trans-cis do ácido acético, foram produzidos em nitrogénio sólido e estrutural e vibracionalmente caracterizados. Um dos dímeros trans-trans e ambos os dímeros trans-cis foram observados pela primeira vez. No seu todo, os estudos referidos nesta Tese relatam alguns dos fenómenos e processos químicos mais importantes que ocorrem para moléculas criteriosamente escolhidas isoladas em matrizes: reacções termicamente induzidas (arrefecimento conformacional; isomerizações conformacionais termicamente induzidas; mobilização térmica dos monómeros para produzir dímeros); reacções fotoquímicas (isomerizações conformacionais induzidas por radiação UV, tautomerizações, e outros rearranjos, incluindo processos complexos envolvendo quebra de ligações – formação de novas ligações); conversões conformacionais induzidas por radiação na região do infravermelho e reacções que ocorrem através do mecanismo do efeito de túnel.

The present thesis reports about vibrational and quantum chemical investigations on model systems undergoing photochemical processes and pharmaceutically active compounds, respectively. Infrared (IR) and Raman spectroscopy were applied for the characterization of the ground state molecular structure. Moreover, resonance Raman (RR) spectra contain additional information about the resonantly enhanced excited state molecular structure. A quantitative resonance Raman intensity analysis in conjunction with the simultaneous simulation of the absorption spectra by means of time-dependent propagation methods was accomplished in order to extract valuable information about the excited state molecular structures of the investigated systems. Surface enhanced Raman scattering (SERS) allows one to determine the interaction and adsorption site of active agents on a metal substrate. Furthermore, density functional theory (DFT) and potential energy distribution (PED) calculations were carried out for an exact assignment of the vibrational spectra. Complete active space self consistent field (CASSCF) and configuration interaction (CI) calculations for some model systems were also performed to assess the experimental results on the excited state potential surfaces. The fundamentals of resonance Raman spectroscopy are treated in detail, describing the physical processes and emphasizing the theoretical methodologies which allow one to obtain the information about the resonantly excited state via an RR intensity analysis. The Brownian oscillator model to determine the solvent reorganization energy is briefly presented. Furthermore, the SERS enhancement mechanisms and selection rules to determine the orientation of the molecules adsorbed on the metal substrate are discussed. The Hartree-Fock approach to calculate the ground state geometry is expatiated, and the basic characteristics of the CI and CASSCF calculations are specified. The chapter ends with a short description of the DFT calculations. Chapter 4 deals with the investigation of the excited state intramolecular proton transfer of the model system, 1-hydroxy-2-acetonaphthone (HAN). The vibrations showing the highest displacement parameters correspond to stretching and in-plane deformation modes of the naphthalene ring and the conjugated carbonyl group, while the OH stretching mode exhibits no observable enhancement. The cooperative effect of the skeletal vibrations reduces the distance between the carbonyl and hydroxyl oxygen atoms in accordance with a general electron density redistribution. Hence, the leading force in the proton transfer process is the increase in electron density on the carbonyl group and the decrease of the negative charge on the hydroxyl oxygen. In chapter 5 the structural and vibrational characteristics of the organic mixed valence system N,N,N’,N’-tetraphenylphenylenediamine radical cation (1+) are discussed. The resonance Raman measurements showed that at least eight vibrational modes are strongly coupled to the optical charge transfer process in (1+). These Franck-Condon active modes were assigned to symmetric vibrations. The most enhanced band corresponds to the symmetric stretching mode along the N-phenylene-N unit and exhibits the largest vibrational reorganization energy. Nevertheless, symmetric stretching modes of the phenylene and phenyl units as well as deformation modes are also coupled to the electronic process. The total vibrational reorganization energy of these symmetrical modes is dominant, while the solvent induced broadening and reorganization energy are found to be small. Hence, (1+) adopts a symmetrical delocalized Robin-Day Class III structure in the ground state. Chapter 6 reports about a vibrational spectroscopic investigation of a model organic photorefractive thiophene derivative, 2-(N,N-diethylamino)-5-(2’,2’-dicyanovinyl)-thiophene. The geometry of the first excited state were optimized and the FC parameters were calculated using the configuration interaction with single excitations method. These calculations show that the contribution of the zwitterionic structure to the excited state is significantly higher than in the ground state. The resonance Raman spectra indicate that several stretching modes along the bonds connecting the donor and acceptor moieties as well as the S-C stretching vibrations are enhanced. Chapter 7 presents the vibrational analysis of an aziridinyl tripeptide, a cysteine protease inhibitor active drug. The vibrational analysis reveals stronger H-bonding of the aziridine NH unit in the solid state of the aziridinyl tripeptide than in the liquid electrophilic building block, indicating medium strong intermolecular H-bond interactions in the crystal unit. The amide hydrogen atoms of the aziridinyl tripeptide are involved in weaker H-bonds than in an epoxide analogon. Furthermore, the characteristic vibrational modes of the peptide backbone were discussed. Chapter 8 reports on the adsorption mechanism of two related anti-leukemia active agents, 6-mercaptopurine (6MP) and 6-mercaptopurine-ribose (6MPR) on a silver colloid. Both molecules adsorb through the N1 and possibly S atom on the metal surface under basic conditions. The SERS spectra recorded for acidic pH values showed that the ribose derivative exhibits a different adsorption behavior compared to the free base. 6MP probably adsorbs on the silver sol through the N9 and N3 atoms, while 6MPR interacts with the surface via the N7 and probably S atoms. Around critical biological concentrations and pH values i.e. at low concentrations and almost neutral condition (pH 7-9), 6MPR interacts with the substrate through both N7 and N1 atoms, possibly forming two differently adsorbed species, while for 6MP only the species adsorbed via N1 was evidenced
In der vorliegenden Arbeit wurden schwingungsspektroskopische und quanten-chemische Untersuchungen an unterschiedlichen Modellsystemen, die an photochemischen Prozessen beteiligt sind, und an verschiedenen Pharmazeutika durchgeführt. Die Methoden der Infrarot- (IR) und Raman-Spektroskopie wurden für die Charakterisierung der Grund-zustandsgeometrie verwendet. Darüber hinaus konnten aus Resonanz-Raman- (RR) Spektren zusätzliche Informationen über den elektronisch angeregten Zustand erhalten werden. Diese aufschlussreichen Aussagen über die elektronisch angeregten Zustände der untersuchten Systeme wurden durch die simultane quantitative Analyse der Resonanz-Raman-Spektren und des Absorptionsspektrums gewonnen. Die Anregungsprofile für die Resonanz-Raman-Streuung und die Absorptionsquerschnitte wurden mittels zeitabhängiger Propagationsmethoden berechnet. Oberflächen-verstärkte Raman-Streu- (SERS) Experimente ermöglichten die Charakterisierung der Wechselwirkungen und Adsorptionsbindungsstellen von Wirkstoffen an Metalloberflächen. Des Weiteren wurden Dichtefunktionaltheorie- (DFT) und PED-Rechnungen durchgeführt, um eine genaue Zuordnung der Schwingungsspektren zu gestatten. CASSCF- und CI-Rechnungen wurden in einzelnen Fällen durchgeführt, um sie mit den experimentellen Ergebnissen für die Potenzialhyperfläche des angeregten Zustands vergleichen zu können. Die Grundlagen der Resonanz-Raman-Spekroskopie wurden ausführlich diskutiert. Dabei wurden die physikalischen Prozesse beschrieben und die mathematischen Techniken, die die Bestimmung der Parameter des angeregten Zustands durch die RR-Intensitätsanalyse ermöglichen, hervorgehoben. Das Modell des Brownian-Oszillators für die Ermittlung der Lösungsmittel-Reorganisations-energie wurde kurz beschrieben. Weiterhin wurden die SERS Verstärkungsmechanismen und Auswahlregeln diskutiert. Der Hartree-Fock-Ansatz zur Berechnung des Grundzustandes sowie die CI- und CASSCF-Methoden wurde erläutert. Das Kapitel endete mit einer kurzen Beschreibung der Grundlagen von DFT-Rechnungen. Im vierten Kapitel wurden die Untersuchungen an einem Modell-Systems (1-hydroxy-2-acetonaphthone HAN), das einen Protonentransferprozess im angeregten Zustand zeigt, dargestellt. Die Streck- und Deformationsmoden des Naphthalinrings und der konjugierten Carbonylgruppe weisen die größten Displacement-Parameter auf, während die O-H-Streckschwingung keine Resonanz-Verstärkung erfährt. Diese Gerüst-schwingungsmoden verringern den Abstand zwischen den Carbonyl- und Hydroxyl-Sauerstoffatomen, was mit einer generellen Umverteilung der Elektronendichte einhergeht. Daher wird der Protonentransferprozess durch die Zunahme der Elektronendichte auf dem Carbonylsauerstoffatom und der gleichzeitigen Abnahme der negativen Ladung auf dem Hydroxylsauerstoffatom gesteuert. Im fünften Kapitel wurden die strukturellen und vibronischen Eigenschaften eines organischen gemischtvalenten Systems, des N,N,N’,N’-tetraphenylphenylenediamine Radikalkations (1+), untersucht. Die Resonanz-Raman-Experimente zeigten, dass mindestens acht Schwingungsmoden stark an den optischen Ladungstransferprozess gekoppelt sind. Diese Franck-Condon aktiven Moden wurden vornehmlich symmetrischen Moden zugeordnet. Die am meisten verstärkte Mode entspricht der symmetrischen Streckschwingung entlang der N-Ar-N-Achse. Jedoch sind auch symmetrische Streckschwingungsmoden der Phenyl- und Phyenylen-Gruppen und Deformationsmoden an dem elektronischen Prozess beteiligt. Der Beitrag dieser symmetrischen Moden zur Reorganisationsenergie dominiert, während die Lösungsmittelreorganisationsenergie nur sehr gering ist. Die erhaltenen Ergebnisse beweisen, dass es sich hier um ein symmetrisches delokalisiertes Robin-Day-Class-III-System handelt. Das sechste Kapitel beschäftigt sich mit einer schwingungsspektroskopischen Analyse eines photorefraktiven Thiophen-Derivat-Modellsystems, 2-(N,N-diethylamino)-5(2’,2’-dicyanovinyl)-thiophen. Die Geometrien des Grund- und ersten angeregten Zustands wurden optimiert und die FC Parameter unter Anwendung der CIS Methode berechnet. Diese Rechnungen ergaben, dass der Anteil der zwitterionischen Struktur im angeregten Zustand dominiert. Die Resonanz-Raman-Spektren zeigten, dass mehrere Streckschwingungsmoden entlang der Bindungen, die die Donor- und Akzeptor-Einheiten verknüpfen, und die S-C Streckschwingungsmoden verstärkt wurden. Das siebte Kapitel behandelt die Analyse eines Aziridinyl-Tripeptids, ein Wirkstoff gegen Cystein-Proteasen. Die Schwingungsanalyse ergab eine stärkere Wasserstoffbrückenbindung der Aziridin NH-Gruppe des Aziridinyl-Tripeptids im festen Zustand als in der flüssigen Baueinheit. Die Wasserstoffatome der Amidgruppen des Tripeptids sind an schwächeren Wasserstoffbrückenbindungen als die des Epoxid-Analogons beteiligt. Darüber hinaus wurden die charakteristischen Gerüstschwingungsmoden des Tripeptids diskutiert. Im vorletzten Kapitel wurde der Adsorptionsmechanismus von zwei Anti-Leukämie-Wirkstoffen, 6-Mercaptopurin (6MP) und 6-Mercaptopurin-ribose (6MPR) diskutiert. Unter basischen Bedingungen adsorbieren beide Moleküle über die N1- und S-Atome an der Metalloberfläche. Für biologisch kritischen Konzentrationen und pH-Werten, d.h. für nahezu neutrale Bedingungen (pH-Wert 7-9) und eine geringe Konzentration, wurde festgestellt, dass das 6MPR-Molekül mit dem Substrat sowohl über das N7- als auch N1-Atom wechselwirkt, wobei wahrscheinlich zwei unterschiedlich adsorbierte Spezies vorhanden sind. Im Gegensatz dazu weist das 6MP-Molekül nur eine über das N1-Atom adsorbierte Spezies auf

Yes
The peripheral nervous system has a limited innate capacity for self-repair following injury, and surgical intervention is often required. For injuries greater than a few millimeters autografting is standard practice although it is associated with donor site morbidity and is limited in its availability. Because of this, nerve guidance conduits (NGCs) can be viewed as an advantageous alternative, but currently have limited efficacy for short and large injury gaps in comparison to autograft. Current commercially available NGC designs rely on existing regulatory approved materials and traditional production methods, limiting improvement of their design. The aim of this study was to establish a novel method for NGC manufacture using a custom built laser-based microstereolithography (muSL) setup that incorporated a 405 nm laser source to produce 3D constructs with approximately 50 mum resolution from a photocurable poly(ethylene glycol) resin. These were evaluated by SEM, in vitro neuronal, Schwann and dorsal root ganglion culture and in vivo using a thy-1-YFP-H mouse common fibular nerve injury model. NGCs with dimensions of 1 mm internal diameter x 5 mm length with a wall thickness of 250 mum were fabricated and capable of supporting re-innervation across a 3 mm injury gap after 21 days, with results close to that of an autograft control. The study provides a technology platform for the rapid microfabrication of biocompatible materials, a novel method for in vivo evaluation, and a benchmark for future development in more advanced NGC designs, biodegradable and larger device sizes, and longer-term implantation studies.