<p>NR 20140805</p>

A espectroscopia de ressonância ciclotrônica de íons foi usada para estudar reações de íons alcóxido, hidróxido, fluoreto, íon-radical óxido, acetileto e amideto com formiatos de alquila; o último íon reage também com N,N-dimetilformamida. Em todos os casos ocorre uma reação de descarbonilação, dando origem a um íon solvatado, que as evidências experimentais indicam ser unido por ponte de hidrogênio. Deslocamentos nucleófilos de grupos ligados ao esqueleto formílico podem ocorrer em casos adequados e em casos especiais ocorre ainda a formação de íons formiato. Os íons solvatados formados a partir de íons fluoreto e alcóxido com formiatos de alquila reagem com álcoois, podendo-se desta meneira estabelecer uma ordem de capacidade de solvatação para os álcoois alifáticos simples. A ordem estabelecida foi: CH3OH < C2H5OH < iso-C3H7OH < tert-C4H9OH. Foram determinadas constantes relativas de velocidade para as reações de vários íons negativos com formiatos de alquila, em sistemas onde se forma mais de um produto. Nos casos mais favoráveis (reações de íons fluoreto) foram calculadas constantes de velocidade absolutas para os vários canais de reação. / Ion-cyclotron resonance spectroscopy has been used to study the reactions between alkoxide, hydroxide, fluoride, O-, acetylide and amide ions with alkyl formates; the last ion reacts also with N,N-dimethylformamide. In all systems a decarbonylation occurs, giving rise to a solvated product ion, held by a hydrogen bond, as evidenced experimentally. Nucleophilic displacement of the formyl group substituents may occur in favorable cases and in a few particular systems the formation of formate ion is observed. The solvated ions formed through the reaction of fluoride or alkoxide ions with alkyl formates can react further with alcohols to establish the intrinsic clustering ability of simple aliphatic alcohols. The order of solvating ability is shown to follow the order CH3OH < C2H5OH < iso-C3H7OH < tert-C4H9OH. In systems where parallel reactions occur, relative rate constants were determined; in the most favorable cases (reactions of fluoride ions), absolute rate constants for the various reaction channels were calculated.

A espectroscopia de ressonância ciclotrônica de íons foi usada para estudar reações de íons alcóxido, hidróxido, fluoreto, íon-radical óxido, acetileto e amideto com formiatos de alquila; o último íon reage também com N,N-dimetilformamida. Em todos os casos ocorre uma reação de descarbonilação, dando origem a um íon solvatado, que as evidências experimentais indicam ser unido por ponte de hidrogênio. Deslocamentos nucleófilos de grupos ligados ao esqueleto formílico podem ocorrer em casos adequados e em casos especiais ocorre ainda a formação de íons formiato. Os íons solvatados formados a partir de íons fluoreto e alcóxido com formiatos de alquila reagem com álcoois, podendo-se desta meneira estabelecer uma ordem de capacidade de solvatação para os álcoois alifáticos simples. A ordem estabelecida foi: CH3OH < C2H5OH < iso-C3H7OH < tert-C4H9OH. Foram determinadas constantes relativas de velocidade para as reações de vários íons negativos com formiatos de alquila, em sistemas onde se forma mais de um produto. Nos casos mais favoráveis (reações de íons fluoreto) foram calculadas constantes de velocidade absolutas para os vários canais de reação. / Ion-cyclotron resonance spectroscopy has been used to study the reactions between alkoxide, hydroxide, fluoride, O-, acetylide and amide ions with alkyl formates; the last ion reacts also with N,N-dimethylformamide. In all systems a decarbonylation occurs, giving rise to a solvated product ion, held by a hydrogen bond, as evidenced experimentally. Nucleophilic displacement of the formyl group substituents may occur in favorable cases and in a few particular systems the formation of formate ion is observed. The solvated ions formed through the reaction of fluoride or alkoxide ions with alkyl formates can react further with alcohols to establish the intrinsic clustering ability of simple aliphatic alcohols. The order of solvating ability is shown to follow the order CH3OH < C2H5OH < iso-C3H7OH < tert-C4H9OH. In systems where parallel reactions occur, relative rate constants were determined; in the most favorable cases (reactions of fluoride ions), absolute rate constants for the various reaction channels were calculated.

No description available.

Advances in science and technology during the past decade have greatly enhanced the level of the structural investigation of macromolecules – peptides and proteins. Biological mass spectrometry has become one of the most precise and sensitive techniques in peptide and protein analysis. However, increasing demands of biotechnological applications require further progress to be made. In the present thesis the development and improvement of peptide and protein characterization methods and techniques based on ion-electron and ion-photon reactions in electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry are described. The focus is on the development of the electron capture dissociation method, recently discovered by the group of professor McLafferty, into a high rate, efficient tandem mass spectrometrical technique. The rate and reliability of the electron capture dissociation technique were greatly increased by implementation of low-energy pencil electron beam injection systems based on indirectly heated dispenser cathodes. Further implementation of a hollow electron beam injection system combined, in a single experimental configuration, two rapid fragmentation techniques, high rate electron capture dissociation and infrared multiphoton dissociation. Simultaneous and consecutive irradiations of trapped ions with electrons and photons extended the possibilities for ion activation/dissociation reaction schemes and lead to improved peptide and protein characterization. Using these improvements, high rate electron capture dissociation was employed in time-limited experiments, such as liquid chromatography–tandem mass spectrometry and capillary electrophoresis-tandem mass spectrometry. The analytical applications of the developed techniques have been demonstrated in top-down sequencing of peptides and proteins up to 29 kDa, improved sequencing of peptides with multiple disulfide bridges and secondary fragmentation (w-ion formation), as well as extended characterization of peptide mixtures separated by liquid chromatography and capillary electrophoresis. For instance, the dissociation of peptides resulting from enzymatic digestion of proteins provided complementary structural information on peptides and proteins, as well as their post-translational modifications.

No description available.

Black carbon (BC) is a complex mixture of polycondensed aromatic compounds produced by the incomplete combustion of biomass during events such as wildfires and the burning of fossil fuels. Black carbon was initially considered to be a refractory form of organic matter. However, recent studies have shown that BC can be quite mobile and reactive in the terrestrial environment. Black carbon can be translocated from soils and sediments in the form of dissolved BC (DBC). A global correlation between DBC and bulk dissolved organic carbon (DOC) has been established for fluvial systems where DBC comprises approximately 10% of the total DOC pool, which suggests that DBC may be a significant contributor to the global carbon cycle. The primary objective of this thesis was to further characterize DBC and elucidate some of the specific physical and chemical processes that promote its transfer to the aqueous phase and drive the DBC-DOC relationship. The molecular composition and qualitative distribution of DBC was assessed using Fourier transform ion cyclotron resonance mass spectrometry. Black carbon in both dissolved and particulate (PBC) phases was quantified by the benzenepolycarboxylic acid method. Dissolved BC was found to contain considerable amounts of nitrogen and the export of this dissolved black nitrogen was linked to watershed land use in global rivers. The riverine flux of PBC, a previously unstudied BC removal mechanism, was significantly increased by local wildfire activity. However in-stream DBC did not appear to be affected by short-term fire events. Once translocated to surface waters, DBC is susceptible to photodegradative processes. Dissolved BC in high molecular weight DOC fractions was more photoreactive than DBC associated with lower molecular weight fractions. In the coming decades, wildfire frequency is expected to increase with climate change and natural lands will continue to be altered for anthropogenic use. These processes have already been shown to significantly impact the composition of DOC and associated DBC exported to inland waters. The quality of DBC influences its stability in soil and resistance to degradation. Therefore, it is essential that we aim to fully understand DBC dynamics in natural systems in order to assess its contribution to global carbon cycling.

Many Best Management Practices (BMPs) have been developed to reduce excessive nutrients in stormwater runoff and mitigate harmful algal blooms in downstream receiving water bodies. This study demonstrates a new BMP by comparing two green sorption media (i.e., specialty adsorbents) for nutrient removal in cascade upflow biofiltration systems operated in parallel. The proposed filtration technology can control hydraulic gradients, prevent clogging and settlements, and increase hydraulic loading while removing more nutrients in an integrated physicochemical and microbiological treatment process. The two green sorption media being tested in this study include zero-valent-iron and perlite-based green sorption media (ZIPGEM) and biochar, iron, and perlite-integrated green sorption media (BIPGEM). BIPGEM or ZIPGEM was installed in two identical upflow bioreactors operated in sequence within each biofiltration system compared mainly for nitrate removal at three influent conditions for process reliability assessment. In addition, kinetics studies were conducted and analyzed to improve the understanding of reactor design. Dissolved organic nitrogen was monitored by using FT-ICR MS (Fourier transform ion cyclotron resonance mass spectrometer) whereas population dynamics of nitrifiers and denitrifiers were quantified by using RT-PCR (real time polymerase chain reaction). The process reliability was compared and confirmed based on the nitrate removal efficiencies, microbial population, and oxidation-reduction potential variations across the two biofiltration systems with different green sorption media. Results indicated that ZIPGEM performed slightly better than BIPGEM and the two identical upflow bioreactors operated in sequence within each biofiltration system exhibited steady operation with higher hydraulic loading relative to the downflow settings in the literature.

No description available.

Íons polihalogenados de Si, X3Si+ (X = F, Cl), são fragmentos facilmente gerados em espectrometria de massas por ionização eletrônica de compostos de silício polihalogenados. Estes cátions possuem um elevado caráter eletrofílico e desempenham um papel importante como intermediários em processos de corrosão auxiliados por plasma utilizados na fabricação de dispositivos em microeletrônica. Esta dissertação apresenta um estudo sobre a reatividade dos íons +SiCl3, em fase gasosa, perante uma série de substratos neutros simples como água, alcoóis, amônia, aminas e algumas bases doadoras de elétrons &pi;. As reações íon-molécula em fase gasosa foram caracterizadas do ponto de vista experimental por espectrometria de massas de ressonância ciclotrônica de íons por transformada de Fourier (FTICR) a pressões da ordem de 10-8 Torr. As reações foram acompanhadas em função do tempo de reação na cela do espectrômetro, o que permitiu a elucidação de uma série de reações sequenciais. O perfil de energia das reações e as estruturas dos íons silicênios formados nestas reações foram também caracterizados por métodos de química computacional, usando métodos ab initio e métodos baseados na teoria do funcional da densidade, a fim de elucidar o mecanismo das reações. Observou-se que o cátion +SiCl3 reage rapidamente em fase gasosa com os diversos substratos neutros através de processos semelhantes a reações de solvólise que resultam na adição do neutro seguida de eliminação de HCl. Em vários dos casos, foi possível observar a solvólise total do cátion com substituição dos três átomos de cloro. Os cálculos revelam que estas reações se processam inicialmente pela adição do eletrófilo aos centros ricos em densidade eletrônica dos substratos neutros e que estes adutos são mais estáveis que os reagentes isolados. O estado de transição destas reações envolve uma migração 1,3 de um hidrogênio e a energia calculada para o estado de transição é consideravelmente menor que a energia dos reagentes, fato este comum para reações rápidas íon/molécula em fase gasosa. Os cálculos para a espécie correspondente +CCl3 revelam que este tipo de reação não é favorável para os cátions metílicos substituídos e experimentalmente reações semelhantes não são observadas para +CCl3. No caso dos íons ClnSi(OH)3-n+ (n=1, 2 e 3), oriundos das reações de hidrólise do íon +SiCl3, observou-se reações secundárias de condensação com SiCl4 que levam a formação de espécies iônicas com ligações tipo siloxanas (-Si-O-Si-). Os cálculos teóricos sugerem que estas reações se processam inicialmente através de um intermediário tipo clorônio, R1-Cl+-R2 seguida de uma transferência formal de um átomo de Cl e rearranjo para uma estrutura tipo siloxana. / Polyhalogenated silicenium ions, X3Si+ (X = F, Cl), are common fragment ions in the mass spectra of polyhalogenated silanes obtained by electron ionization. These ions are powerful electrophiles and are believed to play a role in plasma enhanced corrosion processes and plasma enhanced chemical vapour deposition processes. In this dissertation, we present some new results on the gas-phase reactivity of the +SiCl3 ion with a number of simple n electron donor bases such as water, alcohols, ammonia, amines and some &pi; electron donor bases. Ion-molecule reactions were characterized experimentally by Fourier transform ion cyclotron resonance mass spectrometry (FTICR) at pressures in the 10-8 Torr range. Reactions were followed as a function of trapping time of the ions in the cell of the spectrometer and this allowed for the identification of subsequent reactions of the primary product ions. The energy diagram and structure of the different silicenium ions were also characterized by computational chemistry using both ab initio and density functional theory methods in order to understand the mechanism of these reactions. +SiCl3 reacts rapidly in gas phase with various neutral substrates through processes similar to solvolysis in which the neutral substrate adds onto the silicenium ion followed by elimination of HCl. In some cases, complete solvolysis is observed with substitution of all three chlorine atoms. The calculations show that reactions proceed by initial addition of the electrophile onto the electron center of the neutral substrates giving rise to stable adducts. The transition state for these reactions involve a 1,3 hydrogen migration and the calculated energy for these transition states is less than the energy of the isolated reactants, a fact that is common to fast gas-phase ion-molecule reactions. Similar calculations for +CCl3 reveal similar solvolysis reactions to be energetically unfavourable, and in fact these reactions are not observed experimentally. Secondary reactions have been observed for the product ions ClnSi(OH)3-n+ (n = 1, 2 and 3), obtained from successive hydrolysis of +SiCl3, with the parent SiCl4 neutral. These secondary condensation reactions yield ionic species containing a siloxane type linkage (-Si-O-Si-). The theoretical calculations suggest that is that these secondary condensation reactions initially proceed via chloronium ion intermediate, R1-Cl+-R2 , followed by formal Cl transfer and rearrangement to a siloxane type structure.