Die Radiomarkierung biologisch relevanter Verbindungen mit dem Radionuklid 18F erlaubt Untersuchungen mit Hilfe der Positronen-Emissions-Tomographie (PET). Mit Hilfe der PET werden quantitative Informationen über die räumliche und zeitliche Verteilung von Radiotracern im lebenden Organismus erhalten. Diese Radiotracer sind Grundlage für die in vivo-Erforschung der Physiologie des menschlichen Organismus, sowie zur Aufklärung und Nachverfolgung pathologischer Prozesse. Neben bekannten Ansätzen der Acylierung, Thioetherbildung und Hydrazonbildung ist es notwendig neue Markierungsmethoden zu entwickeln, um Probleme bei Markierungsreaktionen, wie niedrige Ausbeuten und Denaturierung empfindlicher biologisch relevanter Moleküle, zu umgehen. Die vorliegende Arbeit beschäftigt sich mit der Evaluation der Click-Chemie, speziell der 1,3 dipolaren [3+2]Cycloaddition von Alkin- und Azid-Derivaten als neue, alternative Reaktion zur Markierung von biologisch relevanten Molekülen. Ziel der Arbeit war es einen 18F markierten, bifunktionellen Markierungsbaustein, versehen mit einer Alkinfunktion durch eine vollautomatisierte Synthese (Modulsynthese) herzustellen. Ein Peptid, ein Protein und ein Oligonukleotid als biologisch relevante Moleküle, sollten mit einer Azidfunktionalität versehen werden. Mit Hilfe eines geeigneten Katalysator-Ligandsystems sollten ein bifunktioneller Markierungsbaustein, sowie ein azidfunktionalisiertes biologisch relevantes Molekül miteinander gekuppelt werden unter Verwendung der 1,3-dipolaren [3+2]Cycloaddition. Die untersuchte Methode sollte mit anderen Markierungsmethoden verglichen werden. Es wurde eine Modulsynthese zur einfachen, schnellen und vollautomatisierten Herstellung eines alkinfunktionalisierten Synthesebausteins, 4-[18F]Fluor-N-methyl-N-(prop-2-inyl)benzolsulfonamid, p[18F]F SA, entwickelt. Dieser basiert auf einem Sulfonamid-Derivat und ist mit dem Positronenstrahler 18F gekuppelt. Ausgehend von einer Trimethylammonium-Markierungsvorstufe kann das p[18F]F SA mit einer radiochemischen Ausbeute von 27-40% und einer radiochemischen Reinheit >99% innerhalb von 80 min hergestellt werden. Die Reaktion läuft in Sulfolan bei 80°C innerhalb von 10 min ab. Das Produkt liegt aufgrund der HPLC-Reinigung mit einem hohen Reinheitsgrad (RCR >99%) vor und weist eine spezifische Aktivität von 120 570 GBq/µmol auf. p[18F]F SA eignet sich zur Markierung von biologisch relevanten Molekülen, da es unter den Markierungsbedingungen der Cycloaddition stabil ist und eine für das Arbeiten im wässrigen Milieu günstige Lipophilie (logP = 1,7) aufweist. Die verschiedenen Beispiele der drei Verbindungsklassen werden mit einer Azidfunktion versehen. Ein Phosphopeptid (H-MQSpTPL-OH), HSA und ein Aminohexylspacer tragendes Oligonukleotid (NH2 (CH2)6 pCCG CAC CGC ACA GCC GC) werden mit Succinimidyl-5-azidvalerat umgesetzt, wodurch eine Funktionalisierung an den Aminogruppen erfolgt. Während das Phosphopeptid und das Oligonukleotid einfach azidfunktionalisiert vorliegen, werden durch diese Methode 27 Azidreste an das HSA angebracht. Damit stehen Alkin- und Azid-Derivat für die Cycloaddition zur Verfügung. Das Phosphopeptid konnte mit einer Ausbeute von 29% innerhalb von 45 min hergestellt werden. Als Katalysator-Ligandsystem wird ein Gemisch aus Kupfersulfat und Natriumascorbat in Boratpuffer (pH = 8,4) eingesetzt. Man geht von 0,3-0,4 mg der peptidischen Markierungsvorstufe aus. Die Methode wurde mit der [18F]SFB-Markierung des Phosphopeptids verglichen. Man erhält ähnliche Ausbeuten und Reinheiten bei ähnlichen Reaktionsbedingungen. Ein wesentlicher Vorteil ist die Höhe der spezifischen Aktivität des eingesetzten p[18F]F SA, die bis zu zehnfach höher ist, als die des [18F]SFB. Das führt vermutlich zu einem ähnlichen Unterschied der spezifischen Aktivitäten der markierten Peptide, die jedoch nicht genau bestimmt wurden. Auch sind die Reaktionszeiten zur Peptidmarkierung bei Nutzung von p[18F]F SA um ein Drittel geringer. Das führt zur Verminderung der gesamten Synthesezeit. Die Markierung von azidfunktionalisiertem HSA (Beispielprotein) erfolgt mit einer radiochemischen Ausbeute von 57% innerhalb von ca. 45 min. Als Katalysator-Ligandsystem wird ein Komplex aus TBTA und Kupfer(I)-Ionen in Phosphatpuffer (pH = 7,4) / Dimethylsulfoxid verwendet. Die Masse der eingesetzten Markierungsvorstufe beträgt 0,3 mg. Ein Vergleich der Markierungsmethode erfolgte mit der Markierung mit den bifunktionellen Markierungsbausteinen [18F]SFB und [18F]FBA. Bei gleicher Proteinkonzentration ist der Umsatz von p[18F]F SA mit 94% am höchsten. Die Reaktion des hydrazinfunktionalisierten HSA mit [18F]FBA erfordert Temperaturen von 50-60°C, um einen Umsatz des Markierungsbausteins in ähnlicher Höhe wie bei Markierungen mit p[18F]F SA und [18F]SFB zu erreichen. Die Bedingungen für die Markierung mit [18F]SFB weicht dahingehend ab, dass ein pH Wert von 8,4 angewandt wird um eine Markierung zu erreichen. Grund ist die Notwendigkeit der Deprotonierung der im HSA vorhandenen, bei niedrigeren pH Werten protonierten Aminogruppen. Das limitiert die Reaktion auf einen Bereich um diesen pH-Wert. Die Untersuchung der Markierung von Oligonukleotiden ergab, dass ebenfalls ein Komplex aus TBTA und Kupfer(I)-Ionen notwendig ist. Als Lösungsmittel dient ein Gemisch aus 1 M Natriumhydrogencarbonat-Lösung, Acetonitril und Dimethylsulfoxid (14:5:1). Nach 20 min Reaktionszeit bei 10°C kann das Produkt mit einem Anteil von 30% im Reaktionsgemisch nachgewiesen werden. Damit ist nachgewiesen, dass auch die Markierung von Oligonukleotiden unter milden Bedingungen mit dieser Reaktion möglich ist. Zusammenfassend kann man feststellen, dass sich die Click-Reaktion hervorragend für die schonende Markierung der biologisch relevanten Moleküle Phosphopeptid, HSA und Oligonukleotid eignet. TBTA wirkt während der Reaktion als Chelatbildner für die Kupfer(I)-Ionen und verhindert somit eine Bindung an die zu markierenden Moleküle oder deren Zersetzung. Damit wird die Stabilität der biologisch relevanten Moleküle gewährleistet und bei in vivo-Anwendung, das Einbringen cytotoxischen Kupfers verhindert. Im Zuge der Untersuchungen wurde ein Vergleich der Markierungsreaktionen Acylierung, Thioetherbildung, sowie Hydrazon- und Oximbildung durchgeführt. Die bifunktionellen Markierungsbausteine [18F]SFB, [18F]FBAM und [18F]FBA wurden dafür herangezogen. Die 1,3-dipolare [3+2]Cycloaddition unterscheidet sich von den zum Vergleich herangezogenen Reaktionen. Sie vereint die positiven Eigenschaften der anderen Markierungsreaktionen in sich: • Die Reaktion läuft unter milden Reaktionsbedingungen ab. • Der verwendete Markierungsbaustein p[18F]F SA ist unter den Markierungsbedingungen stabil und lässt sich in einer Einschrittsynthese mit Hilfe eines vollautomatisierten Synthesemoduls einfach in hohen Ausbeuten und Reinheiten, sowie mit einer hohen spezifischen Aktivität herstellen. Damit erweitert die 1,3 dipolare [3+2]Cycloaddition das Spektrum der Markierungsreaktionen und bietet das Potential zur Markierung verschiedenster biologisch relevanter Moleküle.

Organofluorine compounds constitute a large part of all the drugs, crop protection agents and advanced materials produced nowadays. Therefore, there is a great interest in developing the new methods of synthesis of organofluorine compounds. In this thesis we report a novel method of synthesis of monofluorinated cyclopropanes based on the Michael-initiating ring closure (MIRC) reaction. Our method allows obtaining polysubstituted monofluorinated cyclopropanes from ethyl dibromofluoroacetate and various Michael acceptors. We have also implemented the asymetric version of cyclopropanation using a novel oxazolodinone-derived chiral fluorinated reagent. In the final part of this thesis we report the synthesis of a fluorinated analog of L-FAP4, a potent agonist of group II metabotropic glutamate receptors (mGluR II). Incorporation of a fluorine atom is expected to increase the biological activity and bioavailabiblity of this compound.

A new route to a well-defined block copolymer with alternating PEO-solubilising groups and fluorinated distyrylbenzene units was established. The Horner Wittig reaction was used as the polycondensation reaction. The non-fluorinated analogue of this block copolymer was prepared via the Wittig reaction. Both polymers were soluble in chloroform and free-standing films could be cast from solution. The position of the HOMO and LUMO energy levels of these two materials were determined by a combination of cyclic voltammetry, UV photoelectron spectroscopy and UV/Vis absorption spectroscopy. The presence of fluorine substituents on the distyrylbenzene unit had no influence on the HOMO-LUMO band-gap (3.0 eV). However, the position of these two energy levels relative to the vacuum level was shifted to higher energies (0.85 eV shift) in the case of the fluorinated block copolymer. The photoluminescence quantum efficiency of the fluorinated block copolymer was 17%, that of the non-fluorinated block copolymer was 34%. The former was used as the electron conducting layer in a light emitting diode with poly(p-phenylene vinylene) as the emissive layer. The latter was used as the emissive layer in light emitting diodes. Luminances over 2000 cd/m(^2) were observed for devices based on the non-fluorinated block copolymer using indium tin oxide as the anode and aluminium as the cathode. The luminescence efficiency of such devices was as high as 0.5 cd/A, corresponding to an internal quantum efficiency of 1.1%.Furthermore, an oligo(p-phenylene vinylene) was synthesised that contained two terminal fluorinated benzene rings and two central non-fluorinated benzene rings, all connected by vinylene bridges. This material aggregated in a 'brickwall' motif, where each molecule overlaps with two halves of molecules in the row above and below. The structure of this J aggregate is due to aryl-fluoroaryl-interactions and was demonstrated by X-ray crystal structure analysis.

Made available in DSpace on 2014-10-09T12:43:29Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:58:02Z (GMT). No. of bitstreams: 1 06527.pdf: 4630361 bytes, checksum: 63a6de51ce3a3389c54c25a8dc2ff557 (MD5) / Mestrado (Dissertacao) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Many countries including Sweden are planning to replace fossil fuel-based vehicles with electric vehicles. This is one of the main reasons that companies all over the world are investing more and more money in the development of lithium-ion batteries, for electric vehicles. There are several different risks with the conventional lithium-ion batteries including the high flammability of the electrolytes, which can lead to high heat release rate, risk of explosion and high toxicity in the form of hydrogen fluoride gas. The hydrogen fluoride is lethal even at low concentration. These potential risks are based on the structure of the flammable electrolytes inside the lithium-ion batteries. Because of that, there is a big interest in finding an electrolyte with similar battery performance and better fire properties as compared with the conventional electrolytes commercially available on the market.   The intent with this work is to investigate the fire properties of different halogen-free electrolytes. The two newly developed salts Li[MEA] & Li[MEEA] as well as the available salt Li[BOB] will be compared with the commercially used halogen-containing electrolyte based on lithium hexafluorophosphate (LiPF6) salt.   Physical and electrochemical properties of these electrolytes such as solubility in different organic solvents, density, viscosity, ionic conductivity and electrochemical window will be studied in the first step. The electrolytes showing the most promising electrochemical properties will then be further investigated regarding fire properties, heat release rate, flash point and toxicity. The electrolytes will be compared with the conventional electrolyte containing LiPF6.   Li[BOB] was not dissolved in the solvents with the strongest dissolving properties, therefore it was not further tested. The electrolytes that were tested regarding fire properties were Li[MEA] and Li[MEEA] with the organic solvents of ethylene carbonate and dimethyl carbonate. Ionic liquid was also added to Li[MEEA] to investigate how it affected the fire properties for the electrolyte.   When examine the heat release rate for the newly developed salts, as well as LiPF6, it was observed that the highest peaks were similar to each other. The combustion time for the electrolyte containing LiPF6 was noticeable shorter than for the other three electrolytes. This is likely due to the fluorine content in LiPF6. The electrolytes undergoing the cone calorimeter test in this work was not charged so therefore the peaks of the heat release rate may look different. For further studies, it could be of interest to construct a complete lithium-ion battery using these electrolytes to see how the battery cells and the electrolytes behave in different set of charges.   Another essential point, is the ignition time that showed varied times for the tests containing Li[MEEA] together with the organic solvents and with the added ionic liquid. This is an interesting result that probably can be explained by the homogeneity of the electrolyte. The homogeneity was only verified with the help of the human eye and therefore it may not be fully dissolved.   The flashpoint for the different mixtures of electrolytes showed values of interest where the electrolyte containing ionic liquid that showed the lowest flashpoint. This was unexpected concerning that these types of additives are common for improving the fire resistance capacity.   The key aspect discussed when analyzing the result from the FTIR spectroscopy was how the Li[MEA], Li[MEEA] and LiPF6 salts varied. The ones that did not have any fluorine in its structure resulted in production of carbon dioxide. However, the electrolyte containing fluorine resulted, as expected, in values of hydrogen fluorine and carbon dioxide but also other combustion products that was hard to determine.   These salts and electrolytes need to be further studied and tested to see if it is possible to use them in an actual lithium-ion battery. Besides further tests of the salts and ionic liquid tested in this work, it is important that the work with conventional and newly developed electrolytes aims for improvements in fire resistance as well as toxicity. / Många länder inklusive Sverige planerar att byta ut fordon som använder fossila bränslen mot elfordon. Detta är en av huvudanledningarna till att företag runt om i världen satsar mer och mer pengar på att utveckla litiumjonbatterier för elfordon. Litiumjonbatterier medför en del risker såsom hög värmeutveckling, brandfarliga vätskor, risk för explosion och toxiska gaser samt produceringen av vätefluorid. Redan vid låga koncentrationer är vätefluoriden dödlig. Riskerna baseras på strukturen av elektrolyten som finns i litiumjonbatteriet. På grund av dessa risker så är det intressant att utveckla en elektrolyt som har liknande batteriegenskaper men bättre brandegenskaper än de elektrolyter som finns och används idag.   I detta arbete har brandegenskaper för olika halogenfria elektrolyter testats. De två nyutvecklade salterna Li[MEA] & Li[MEEA] har tillsammans med det existerande saltet Li[BOB] jämförts med det kommersiella saltet litium hexafluorfosfat (LiPF6) som används till många elektrolyter i dagens litiumjonbatterier.   De fysiska och elektrokemiska egenskaperna såsom löslighet i organiska lösningsmedel, densitet, viskositet, jonkonduktiviet och elektrokemiskt fönster har testats för elektrolyterna i den första delen av arbetet. Elektrolyterna som uppvisade de mest lovande elektrokemiska egenskaper har även testats med avseende på brandegenskaperna, så som värmeutveckling, flampunkt och toxicitet. Elektrolyterna jämfördes mot den vanligt förekommande elektrolyten som innehåller litium hexafluorfosfat.   Saltet Li[BOB] löstes inte i lösningsmedel med bra lösningsegenskaper, vilket var anledningen till att det inte genomfördes ytterligare tester på den. Elektrolyterna som det genomfördes tester på avseende på brandegenskaper innehöll Li[MEA] och Li[MEEA] tillsammans med de organiska lösningsmedlen etylenekarbonat och dimetylkarbonat. För Li[MEEA] tillsattes det även jonvätska för att undersöka hur jonvätskan påverkar brandegenskaperna för elektrolyten.   När värmeutveckling för det nyutvecklade salterna och LiPF6 undersöktes, så uppvisade de liknande värden. Anmärkningsvärt var dock att förbränningstiden för LiPF6 varade under en kortare period i jämförelse med de tre andra elektrolyterna. En trolig orsak till detta är att LiPF6 innehåller fluor. Elektrolyterna som provades i konkalorimeter i detta arbete var ej laddade, vilket kan medföra att värmeutvecklingen kan se annorlunda ut vid ett laddat tillstånd. För framtida studier kan det vara intressant att konstruera ett komplett litiumjonbatteri, för att se hur elektrolyterna fungerar och påverkas, beroende på laddningsnivå.   Antändningstiden för Li[MEEA] blandat med de organiska lösningsmedlen tillsammans med jonvätska varierade mycket. Detta är ett intressant resultat, som förmodligen kan förklaras av homogeniteten på elektrolyten. Homogeniteten verifierades enbart okulärt, vilket inte säkerställer att jonvätskan har löst sig fullständigt i elektrolyten.   Resultat för flampunkten för det olika elektrolyterna var intressant, då elektrolyten som innehöll jonvätska visade på lägst flampunkt. Detta var oväntat då tillsatser som jonvätska brukar förbättra brandmotståndet.   Resultatet för FTIR-spektroskopin analyserades för att se hur Li[MEA], Li[MEEA] och LiPF6 skiljde sig åt. De elektrolyter som inte innehöll fluor, producerade bara koldioxid. Medans elektrolyten som innehöll fluor producerade, som väntat, vätefluorid och koldioxid, men även andra gaser som var svåranalyserade.   De framtagna elektrolyterna i detta arbete behöver studeras vidare och fler tester bör genomföras för att se om det finns en möjlighet att använda dem i faktiska litiumjonbatterier. Förutom att testa elektrolyterna i just detta arbete är det viktigt att forskningen kring brandegenskaper och toxiska egenskaper för elektrolyter fortsätter i framtiden.

Made available in DSpace on 2014-06-11T19:33:01Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-03-31Bitstream added on 2014-06-13T20:24:34Z : No. of bitstreams: 1 hirata_e_dr_araca.pdf: 850512 bytes, checksum: 5316dd8869bf9d969ea45d0d0ce44f57 (MD5) / A descoberta do efeito preventivo do flúor transformou esse material, ao longo do século XX, no principal agente responsável pela queda de prevalência de cárie, em vários países. Existem fortes evidências de que produtos fluoretados são os principais responsáveis pelo declínio observado na prevalência da cárie, e também pelo aumento na incidência de fluorose dental. Se pudéssemos diminuir sua concentração, sem perder efeito cariostático, sua margem de segurança seria maior ainda. O cálcio e fosfato fazem parte, juntamente com o flúor, do processo de equilíbrio mineral entre esmalte e saliva. A busca dos efeitos anticárie do cálcio e fosfato datam da década de 1960, quando alimentos foram enriquecidos com estes elementos. Experimentos com compostos contendo cálcio e/ou fosfato vêm sendo estudados, com o objetivo de compreendermos melhor os efeitos do cálcio e fosfato e a possibilidade do aumento de seu uso em produtos fluoretados. Na primeira parte do trabalho, realizamos uma revisão com tópicos relevantes para a compreensão de seu potencial anticariogênico. Na segunda parte, realizamos experimento in vitro para avaliar o potencial de remineralização de um dentifrício de baixa concentração de flúor suplementado com cálcio e fosfato. Pode-se concluir que a suplementação de dentifrícios fluoretados, com cálcio e fosfato, é mais um recurso na prevenção da cárie. / The use of fluoride was largely responsible for the drop in caries prevalence over the last few years, however, a great part of the population still suffers from its consequences and sequelae. The search for an ally to combat caries has impelled research in several directions, including the use of antimicrobial agents, sugar substitutes, food supplements and remineralizing agents. The effects of food supplements (bread, cereals, jellies, chewing gums, milk, honey) and other products, such as fluoridated dentifrices, with combinations of calcium and phosphates have been studied with the object of reducing caries incidence in animals and humans. With the object of having a better understanding of the effects of calcium and phosphate and the possibility of increasing their use in fluoridated products, a review was made of relevant topics to understand their anticariogenic potential. It was found that the use of calcium and phosphate, together with fluoride, forms part of the mineral balance process: enamel X saliva and/or biofilm; theoretical considerations indicate that calcium and phosphate, in adequate amounts in the biofilm, may diminish enamel dissolution; experiments with calcium- and/or phosphate-containing compounds have been studying supersaturation of these elements in saliva and biofilm, with the object of increasing enamel protection. It may be concluded that calcium and phosphate are of great importance in tooth enamel demineralization and remineralization events, and the possibility of applying the preventive action of these two elements, has made it possible to develop new products, both food and for use in dentistry, providing more treatment and caries prevention options.

Orientador: Carlos Rocha Gomes Torres / Coorientadora: Alessandra Bühler Borges / Banca: Taciana Marco Ferraz Caneppele / Banca: Eduardo Bresciani / Banca: Carlos Eduardo Francci / Banca: Ricardo Amore / Resumo: O objetivo deste estudo foi avaliar o efeito da aplicação de agentes remineralizantes contendo silicato de cálcio / fosfato e flúor ou fluoreto de sódio somente, sobre a redução da microdureza do esmalte causada pelo clareamento dental, cor dos dentes e perda de estrutura resultante da abrasão. Duzentos e quarenta amostras circulares de esmalte bovino foram preparadas, embutidas e polidas. Em seguida foram realizados testes iniciais de cor, microdureza e perfilometria. As amostras foram distribuídas aleatoriamente em 6 grupos (n=40): Grupo C -(controle negativo) - nenhum tratamento; Grupo CL (controle positivo)- Aplicação do agente clareador a base de peróxido de hidrogênio a 40% (Opalescence boost, Ultradent); Grupo CL/Rs - Aplicação do agente clareador seguido da aplicação do gel remineralizante a base de silicato de cálcio/fosfato (Regenerate Boosting serum- Unilever); Grupo Rs/CL - Aplicação do gel de silicato de cálcio/fosfato seguido da aplicação do agente clareador; Grupo Rs/CL/Rs - Aplicação do gel de silicato de cálcio/fosfato seguida da aplicação do agente clareador e aplicação novamente do gel de silicato de cálcio/fosfato; Grupo CL/F - Aplicação do agente clareador seguida da aplicação do gel de fluoreto de sódio a 2%. Após a etapa de clareamento (3 aplicações de 20 min) foram novamente realizadas as leituras de cor e microdureza. Em seguida os espécimes foram submetidos a 100.000 ciclos abrasivos em máquina de escovação. Cada grupo foi dividido em dois subgrupos... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: This study aimed to evaluate the effect of the application of remineralizing agents containing calcium/phosphate silicate and fluoride or only sodium fluoride on the reduction of enamel microhardness caused by tooth bleaching, tooth color and loss of structure resulting from abrasion. Two hundred and forty circular bovine enamel samples were prepared, embedded and polished. After that, initial tests of color, microhardness and profile were performed. Samples were randomized into six groups (n=40): Group C - (negative control) - no treatment; Group CL (positive control) - application of 40% hydrogen peroxide bleaching agent (Opalescence boost, Ultradent); Group CL/Rs - Application of bleaching agent followed by remineralizing gel based on calcium/phosphate silicate (Regenerate Boosting serumUnilever); Group Rs/CL - Application of calcium/phosphate silicate gel followed by bleaching agent; Group Rs/CL/Rs - Application of calcium/phosphate silicate gel followed by bleaching agent and new application of calcium/phosphate silicate gel; Group CL/F - Application of bleaching agent followed by 2% sodium fluoride gel. After bleaching stage (3 applications/20 min), color and microhardness readings were performed. Then, the specimens were subjected to 100.000 abrasive cycles in a brushing machine. Each group was divided into two subgroups according to the dentifrice used (n=20): Subgroup Cp -Close Up bioactive protection toothpaste (Unilever); Subgroup Rp- Regenerate toothpaste (Unilever). Final profiles of enamel surface were evaluated and the wear was calculated. Data were analyzed using ANOVA and Tukey variance analysis. Significant differences were observed for color variation (∆E) (p=0.000). Tukey test results were: C (1.31±0.58)a, Rs/CL/Rs (3.72±1.28)b, CL (3.75±1.04)b, CL/Rs (3.87±0.91)b, Rs/CL (3.88±0.94)b, CL/F (4.03±1.22)b. Statistically significant differences were ...(Resumo completo, clicar acesso eletrônico abaixo) / Doutor

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / In this work we perform a theoretical study about fluorine adsorption in BC2N nanostructures. The fluorine interaction with the BC2N nanostructures was studied using only atomic fluorine on two nanotubos with different chiralities (zigzag(5,0) and armchair(3,3)) and a monolayer. We used first principles calculations based on the density functional theory (DFT) taking account the effects of the spin polarization. For the exchange and correlation term, we use the generalized gradient approximation (GGA) and to describe the electron-ion interaction we use the pseudopotential approximation. The charge density is obtained solving the selfconsistent Kohn-Sham equations and to represent the Kohn-Sham wave functions a linear combination of atomic orbital is used. Our results show that when a single fluorine atom is adsorbed, the most stable configuration occurs when the fluorine atom is adsorbed on the boron atom (FB). The configurations with the fluorine adsorbed on carbon atom (FCI and FCII) are less stable than the FB configuration and the FN reaction is unstable. When the fluorine atom is adsorbed in BC2N nanostructure the local configuration is modified. It is observed that the atom bonded to the fluorine atom moves outward from the surface of the nanotubes and the monolayer. The electronic properties present similar characteristics in both nanotubes and also in the monolayer. The FCII configuration introduce acceptors properties in a BC2N nanostructures and the FCI configuration introduce donor properties. The fluorine adsorption in the most stable configuration gives rise to electronic levels in the band gap. When we investigated the BC2N monolayer with different fluorine coverage, the most stable configuration is obtained when the fluorine atoms are adsorbed on the boron atoms, forming a line. Defects levels are observed near to the top of the valence band and the system exhibit a p-type semiconductor character to low fluorine density and metallic character to the high fluorine density. We observe that the fluorine adsorption induces spin polarization effects in BC2N nanostructures leaving the system to present a spin magnetic moment. The absolute value of the spin magnetic moment depends on the density of fluorine adsorbed. / Nesse trabalho realizamos o estudo teórico da adsorção de flúor em nanoestruturas de BC2N. A interação de flúor com as nanoestruturas de BC2N foi estudada a partir da adsorção de flúor atômico em nanotubos de diferentes quiralidades, zigzag (5,0) e armchair (3,3), além da monocamada. Usamos cálculos de primeiros princípios dentro do formalismo da teoria do funcional da densidade (DFT), levando em consideração os efeitos de polarização de spin. Para o termo de troca e correlação, utilizamos a aproximação do gradiente generalizado (GGA) e para descrever a interação elétron-caro¸co utilizamos a aproximação do pseudopotencial. A densidade de carga é obtida resolvendo-se as equações de Kohn-Sham de maneira autoconsistente, com as funções de onda de Kohn-Sham expandidas em uma combinação linear de orbitais atômicos. Nossos resultados mostram que para a adsorção de um átomo de flúor, a configuração mais estável ocorre quando o átomo de flúor é adsorvido sobre o átomo de boro (FB). As configurações com adsorção de flúor em carbono (FCI e FCII) são menos favoráveis do que a adsorção ao FB, enquanto que a reação FN é instável. Quando o átomo de flúor é adsorvido nas nanoestruturas de BC2N a configuração local é modificada. Observa-se que o átomo ligado ao átomo de flúor desloca-se para fora da superfície dos nanotubos e em relação à monocamada temos um deslocamento deste átomo para fora da sua superfície. As propriedades eletrônicas apresentam características semelhantes em ambos os nanotubos e também para a monocamada. A configuração FCII faz com que as nanoestruturas de BC2N apresentem características aceitadoras e a configuração FCI faz com que essa estrutura apresente características doadoras. Para a adsorção de flóuor na configuração mais estável temos níveis rasos presentes na estrutura de bandas. Quando é feita a variação da densidade de flúor em uma monocamada de BC2N, a configuração mais estável é obtida quando os átomos de flúor são adsorvidos sobre átomos de boro formando uma linha, e na região do topo da banda de valência níveis de defeito podem ser observados. Em relação às propriedades eletrônicas é possível observar que em todas as estruturas ocorre uma perturbação no fundo da banda de condução. Na região do topo da banda de valência níveis de defeitos podem ser observados. Onde podemos obsevar que essas estruturas apresentam características de semicondutor do tipo-p para baixas densidades de flúor e metálicas para altas densidades. Temos que a adsorção de flúor provoca uma quebra de degenerescência de spin o que faz com que o sistema apresente um momento magnético de spin. O valor absoluto desse momento magn´etico de spin depende da densidade de flúor adsorvido.

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