No description available.

No description available.

No description available.

<p> Under 248 nm laser flash photolysis, the photodecomposition of 1,3,4-trimethyl-1-phenyl-1-germacyclopent-3-ene (28) in dry, deoxygenated hexane solution at 23 °C leads to the prompt formation of two transient species: phenylmethylgermylene (29) and its Ge=Ge doubly bonded dimer, 1,2-dimethyl-1 ,2-diphenyldigemene (30). The formation of 29 proceeds in high chemical yield as shown by the results of steady state trapping experiments with methanol and isoprene. The transient assigned to 29 exhibits λmax = 490 nm and decays with second-order kinetics (τ ~ 2 μs). The second transient, which is formed from the latter, is assigned to digermene 30 and exhibits λmax = 420 nm and a lifetime, τ ~ 8 μs. The assignments are based on comparisons to the spectra of other simple germylenes, such as dimethyl-, diphenyl and dimesitylgermylene as well as on the pattern of reactivity with trapping reagents in solution at room temperature.</p> <p> Reactions studied include N-H, O-H and Sn-H insertion reactions, the [1+2] addition to isoprene and t-butylacetylene, and halogen atom abstraction from carbon tetrachloride.</p> <p> Absolute rate constants for quenching of 29 with the above mentioned scavengers were obtained by direct measurement of the germylene decay kinetics, over the concentration range where the formation of the digermene was more than 70% quenched. This ensures that the decay of 29 was dominated by the reaction with the trapping reagent.</p> <p> Absolute rate constants for reaction of the same reagents with 30 have also been determined for most of the scavengers studied. However, the digermene was found to be considerably less reactive than phenylmethylgermylene in all cases.</p> <p> The trends in spectroscopic properties and reactivity of simple germylenes in solution are discussed.</p> / Thesis / Master of Science (MSc)

O presente trabalho tem por objetivo o estudo da fotólise de uma série de brometos de benzila orto-substituídos em solventes apoIares, visando contribuir para a elucidação, tanto dos mecanismos operativos após a homólise de ligações carbono., halogênio em sistemas benzílicos, como das espécies intermediárias envolvidas no processo. Assim sendo, irradiaram-se soluções benzênicas dos compostos &#945;-bromo-o-xileno (MBX), &#945, &#945;-dibromo-o-xileno (GBX), &#945, &#945;-dibromo-o-xileno (DBX), &#945, &#945; &#945;\'tribromo-o-xileno (TRBX) e &#945, &#945; &#945, &#945;-tetrabromo-o-xileno (TBX) e soluções de MBX e DBX em iso-octano, utilizando-se uma lâmpada de vapor de mercúrio de baixa pressão ( &#955;emissão=254nm). Os produtos foram analisados e identificados por cromatografia gasosa acoplada a espectrometria de massas e confirmados por co-injeção de amostras autênticas, sintetizadas por via térmica. Os rendimentos quânticos dos produtos foram calculados, utilizando-se o leucocianeto de verde-malaquita como actinômetro. A análise dos produtos revelou que a homólise da ligação C-Br é seguida de uma série de reações de abstração de hidrogênio e recombinação de radicais resultando sempre em xilenos menos e mais bromados que o xileno de partida. Benzaldeídos, resultantes da hidrólise dos dibrometos geminais, também são formados, devido à presença de traços de água. Quando o solvente é iso-octano, o produto menos bromado aparece com maior rendimento quântico relativo, devido à abstração de hidrogênio do solvente pelo fotoproduto primário, um radical benzila; além disso, observa-se a formação de um novo produto: o 2-bromo-2,4,4-trimetil-pentano. Os rendimentos quânticos de desaparecimento de substrato observados na fotólise de soluções benzênicas de MBX (0,33) e DBX (0,52) foram superiores àqueles encontrados ao se utilizar iso-octano como solvente: 0,22 e 0,32, respectivamente. Isto sugere que o benzeno excitado esteja intermediando o processo (i.e., agindo como sensibilizador), transferindo energia de excitação para o brometo de benzila. Um intermediário bi-radicalar do tipo orto-quinodimetano (o-xilileno) era esperado em caso de: (i) fotólise do radical benzila formado (processo bifotônico) ou (ii) abstração de hidrogênio intramolecular. Entretanto, não se observaram produtos derivados de adição de Diels-Alder, quando ciclo-hexeno foi adicionado ao sistema. Também não se observou formação perceptível de brometo de hidrogênio, em nenhum dos sistemas investigados. Foram feitos, também, estudos de fotólise por pulso de laser, em iso-octano, para os compostos MBX, DBX, GBX e TBX utilizando-se o 4&ordm; harmônico de um laser de Nd:YAG (&#955; =266nm). As soluções de trabalho foram desaeradas por, pelo menos, três ciclos de congelamento-degaseamento-descongelamento até 10-5mmHg. A cinética de decaimento das absorções observadas foi analisada como sendo devida a duas espécies, isto é, os resultados são compatíveis com um decaimento duplo-exponencial, cujos tempos de vida seriam da ordem de &#181;s e ms, para as espécies de tempos de vida curto e longo, respectivamente. Além disso, as distribuições espectrais observadas a 0,1 e 10&#181;s mostraram-se diferentes, indicando a presença de dois transientes. A análise da cinética de decaimento das absorções transientes de MBX e DBX, além das distribuições espectrais obtidas para as transições Dn&#8592;Do (&#955;.=320nrn e 338nm, respectivamente) mostram que, na fotólise destes dois compostos, forma-se, inicialmente, um radical, de tempo de vida da ordem de microssegundos, por cisão homolítica da ligação C-Br: o-metil-benzila, no caso de MBX e o-(bromo-metil)benzila para DBX. Além destas espécies, formam-se cátions (detectáveis para todos os compostos estudados) que apresentam uma banda de absorção larga e desestruturada (de 330 a 360nrn;&#955; .max = 347nrn) e com tempo de vida da ordem de milissegundos nas condições de trabalho, a partir de um radical excitado, pela perda de um segundo elétron (Tokumura et a/ii 1989; 1991). Resultados análogos foram obtidos para a fotólise de DBX e TBX, em solução benzênica, empregando-se um laser de exímero de XeCI (308nrn), tendo sido nestes experimentos que se detectou o radical gerado de TBX, o qual não é observável em iso-octano. Em benzeno observou-se, também, a formação do complexo Br./benzeno (&#955;..max = 550nrn), fato este que vem a reforçar a proposição de estarem-se gerando radicais nestes sistemas. / In the present work, the photolyses, in apoIar soIvents, of a series of bromoderivatives of o-xylene is investigated, aiming at attaining an improved understanding of the reaction mechanism and at the identification of the transient species formed after homolysis ofthe carbon-halogen bond. &#945;-Bromo-o-xylene (MBX), &#945;, &#945; -dibromo-o-xylene (GBX), &#945;, &#945;\' -dibromo-o-xylene (DBX), &#945;, &#945;, &#945; \' -tribromo-o-xylene and &#945;, &#945;, &#945;,&#945;\' -tetrabromo-o-xylene (TBX) were subjected to steady-state 254nm irradiation in deaerated benzene and isooctane. The products were identified by GC-MS and also by co-injection of authentic samples. The analysis of the products formed revealed that homolysis of C-Br bond is followed by a series of hydrogen abstraction and radical recombination reactions, resulting in xylenes more and less brominated than the starting compound. Benzaldehydes are also formed from hydrolysis of the geminal dibromides, due to the presence of trace amounts of water. When isoöctane is the solvent, the less brominated products are formed with higher relative quantum yields, as the solvent undergoes hydrogen abstraction by the primary photoproduct, the o-methylbenzyI radical, a process also leading to the formation of 2-bromo-2,4,4-trimethylpentane. This notwithstanding, no trace of HBr was detected. The photolysis of MBX and DBX presented higher absolute quantum yields in benzene than in isoöctane, indicating sensitization by the solvent in the former case. A biradical intermediate, belonging to the orto-quinodimethane c1ass, was expected on the occurrence of either (a) photolysis of the o-methylbenzyl radical formed (a biphotonic process) or (b) intramolecular hydrogen abstraction. However, in the presence of cyclohexene no Diels-AIder adduct was observed. Laser flash-photolysis studies at 266nm (quadrupled Nd:YAG) have been performed for MBX, DBX, GBX and TBX, using degassed isoöctane as solvent. The observed transient spectral and kinetic data indicates initial formation of a radical and of a cation, which present micro and millisecond lifetimes, respectively. Moreover, the spectral distributions were different at 0.1 and 10&#181;s, as expected for two different transients. Similar results were obtained from DBX, on 308nm laser irradiation (XeCl eximer). For TBX, however, on1y in these latter conditions we were able to detect the &#945;-bromo-o-(dibromomethyl)benzyl radical (which half-life is toa short in isoöctane to be detected by our apparatus). Both substracts also gave rise to the Br/benzene complex (&#955;max = 550nm), in the 308nm photolyses, thus confirming the presence ofBro in the system under study.

Resumo O presente trabalho teve como objetivo sintetizar e caracterizar um novo complexo trinuclear de rutênio, [Ru3O(CH3OO)6(3-pic)2(NO)]+, através de rotas sintéticas previamente descritas na literatura para complexos análogos. Para a obtenção deste complexo, foram necessárias cinco etapas de síntese, cada qual gerando o precursor da etapa seguinte. Os complexos precursores [Ru3O(CH3OO)6(3-pic)3]+, [Ru3O(CH3OO)6(3-pic)2(CO)] e [Ru3O(CH3OO)6(3-pic)2(H2O)]+, foram caracterizados por técnicas espectroscópicas e voltamétricas. Para o complexo de interesse, [Ru3O(CH3OO)6(3-pic)2(NO)]+, além da caracterização por técnicas espectroscópicas e voltamétricas, foram realizados estudos de fotólise e de interação com albumina de soro humano (HSA). Pelas técnicas espectroscópicas, pudemos ratificar as estruturas propostas tanto para o nitrosilo quanto para os precursores estudados. Para a caracterização do complexo [Ru3O(CH3OO)6(3-pic)2(NO)]+, utilizando a técnica de espectroscopia de infravermelho verificamos a coordenação do ligante NO ao centro metálico [Ru3O], devido ao estiramento característico deste ligante. Os espectros de absorção UV-vis e RMN mostraram que existe uma forte interação entre o elétron desemparelhado do centro metálico e o elétron do ligante NO. Pelos estudos de voltametria cíclica, observamos que os processos redox envolvendo o ligante NO, são compartilhados com o centro metálico. A fotólise do complexo [Ru3O(CH3OO)6(3-pic)2(NO)]+, mostrou-se eficiente, uma vez que a liberação fotoinduzida do NO ocorreu na região do visível e em pH fisiológico. Pelos estudos de supressão de fluorescência, observamos que o complexo realmente interage com a HSA na proporção de 1:1, na região em que se encontra o resíduo de triptofano. / The aim of the present study was synthesize and characterize a new trinuclear ruthenium complex, [Ru3O(CH3OO)6(3-pic)2(NO)]+, via synthetic routes previously described in the literature for analogous complexes. To obtain this complex, it took five synthetic steps, each one yielding a precursor for the next step. The precursor complexes [Ru3O(CH3OO)6(3-pic)3]+, [Ru3O(CH3OO)6(3-pic)2(CO)] and [Ru3O(CH3OO)6(3-pic)2(H2O)]+, were characterized by spectroscopic and voltammetric techniques. For the complex of interest, [Ru3O(CH3OO)6(3-pic)2(NO)]+, in addition to characterization by spectroscopic and voltammetric studies, it was carried out photolysis and interaction with human serum albumin. By spectroscopic techniques, we could confirm the proposed structures for both the nitrosyl and precursors. For characterization of the complex [Ru3O(CH3OO)6(3-pic)2(NO)]+, infrared spectroscopy allowed us to verify that the ligand coordination to the metal center [Ru3O], due to the characteristic stretching band of that ligand. The absorption spectra of UV-vis and NMR showed that there is a strong interaction between the unpaired electron of the metal center and the NO ligand. By cyclic voltammetry studies, we observed that the redox processes involving the NO ligand are shared with the metal center processes. The photolysis of the complex [Ru3O (CH3OO) 6 (3-pic) 2 (NO)] +, was efficient, since the photoinduced release of NO occurred in the visible region and at physiological pH. By fluorescence quenching studies, we observed that the complex actually interacts with the HSA in a 1:1 ratio, in the region which is the residue of tryptophan.

Radical reactions play central roles in regulating regional air quality and global climate. Some potentially important gas phase radical reactions are being investigated in this research project, including Cl reactions with acetone, butanone, 3-pentanone, pyridine, and dimethyl selenide (DMSe), HO2 complex formation and dissociation with formic and acetic acids, and reactive and non-reactive quenching of O(1D) by the potent greenhouse gases SO2F2, NF3, and SF5CF3. The involved radicals are generated by laser flash photolysis (LFP). Temporal profiles of either the radical reactant or a product are monitored in "real time" using atomic resonance fluorescence spectroscopy (RF), time-resolved UV-visible absorption spectroscopy (TRUVVAS), or tunable diode laser absorption spectroscopy (TDLAS), allowing kinetic and mechanistic information of these reactions to be obtained. These studies provide new knowledge of the investigated radical reactions and facilitate a better understanding of their significance in atmospheric chemistry.

No description available.

Heme-copper oxidases are transmembrane proteins that are found in aerobic and anaerobic respiratory chains. During aerobic respiration, these enzymes reduce dioxygen to water. The energy released in the reaction is used to transport protons across a biological membrane. Stored as proton electrochemical gradient, the energy can be used to regenerate ATP. It is known that aa3 oxidases, which are the most common oxidases, transport pumped protons and protons used for the catalytic reaction using two proton pathways. However, the molecular mechanism of pumping is still being debated. When oxygen is available in very small quantities, oxygen reductases with high affinity for oxygen are expressed by organisms like Thermus thermophilus. The proton pumping mechanism in the ba3 oxidase is slightly different from that of aa3 oxidases as this enzyme only uses a single proton uptake pathway. Here we analyzed the reaction mechanism of ba3 oxidase and found evidence that the first proton taken up by the four-electron reduced ba3 oxidase is transferred to a site distant from the catalytic site, the pump site, and that only every second proton taken up from solution is pumped. Data obtained from studies using site-directed mutagenesis and flow-flash spectroscopy suggest a probable location of the pump site. Under anaerobic conditions, some organisms are able to generate a proton- motive force using nitrate and nitrite as electron acceptors. In this process, the cytotoxic reaction intermediate nitric oxide is produced. Nitric oxide reductase (NOR), a deviant heme-copper oxidase that reduces NO to the rather harmless N2O, does not pump any protons. The catalytic mechanism of nitric oxide reduction by NOR is very poorly understood. Here we demonstrate that substrate inhibition, which occurs in NOR from Paracoccus denitrificans above 5 μM NO, can already be observed before the electrons from the low-spin hemes re-distribute to the active site. Furthermore, we found that a single specific proton pathway is used for proton-transfer leading from the periplasm to the active site.

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Includes bibliographical references (p. 164-174).