Estudos do mecanismo de reações unimoleculares, das moléculas de acetato de metila e etila, induzidas por absorção multifotônica e de reações bimoleculares com os radicais OH e Cl, usando cálculos ab initio e de funcional de densidade foram realizados neste trabalho. A análise dos cálculos das barreiras de energia e das constantes de velocidade microcanônicas das reações unimoleculares com o formalismo da teoria RRKM, permitiu prever algumas reações cujos produtos não foram determinados experimentalmente. Além disso, semelhanças das geometrias e dos valores de energia de algumas estruturas entre diferentes superfícies de energia, analisadas com cálculos de IRC, permitiram a explicação da viabilidade de determinada via de reação em detrimento de outra. Em outro método, relatado por Forst(1), na determinação das constantes de velocidade variacionais, comparadas com a variação da energia de Gibbs, verificou-se constantes de velocidade microcanônicas menores e a localização dos estados de transição em comprimentos de ligação, também, menores. Nas reações com o radical OH e Cl, a via predominante de reação é o ataque aos hidrogênios do grupo ligado diretamente ao oxigênio da molécula, responsável pelo valor da constante final de mais de 93% nas reações com OH e 99% nas reações com Cl, a 298K, em concordância com os resultados experimentais, em detrimento do ataque ao grupo CH3 da porção carboxilato da molécula. Nas reações com OH, os valores de constante de velocidade calculados mais próximos dos valores experimentais foram obtidos a partir dos resultados com os funcionais mPW1B95-41, para o acetato de metila, e mPW1B95-44, para o acetato de etila, enquanto que nas reações com Cl foram obtidos com o os métodos CCSD(T)//B3LYP para o acetato de metila e CCSD(T)//MP2 para o acetato de etila. Os valores de constante de velocidade da reação com cloro são cerca de dez vezes maiores que aquelas para as reações com radicais OH. As reações com OH e Cl ocorrem em uma única etapa, sem estabilização do intermediário e sem efeito de tunelamento significante. Por sua vez, cálculos da constante de velocidade, pelo método da relação estrutura reatividade (SAR), sobreestimam a reatividade dos hidrogênios dos grupos CH3 na porção carboxilato, em ambos os acetatos, e na porção etóxido do acetato de etila. Este método falha ao descrever a participação de cada grupo na reação com Cl, pois prevê que a reação no grupo CH3 da porção alcóxido passa a ser predominante sobre a reação ao grupo CH2 nas reações do acetato de etila, oposto aos nossos cálculos onde a reação com o grupo CH2 é a predominante. Outra falha do método é na previsão de mesma reatividade para ambos os grupos CH3 no acetato de metila, pois por nossos cálculos a reação ocorre predominantemente no grupo CH3 na porção alcóxido da molécula. / Computational studies on methyl and ethyl acetates molecules using ab initio and density functional calculations exploring the unimolecular mechanism, induced by multiphoton absorption, and the bimolecular reactions with OH and Cl radicals, have been performed in this work. Analysis of the calculated energy barriers and rate constants of unimolecular reactions with the RRKM microcanonical theory, predicts the occurrence of some reactions whose products were not determined experimentally. Furthermore, similarities on geometrical and energetic of some structures between different energy surfaces, analyzed with IRC calculations, allowed the explanation of the viability of a particular reaction pathway over another. Forst\'s method, used to determine variational rate constants, when compared with the variation of Gibbs energy, generates microcanonical rate constants with smaller values and location of transition states in smaller bond lengths. With OH and Cl, the predominant reaction route is the attack on the hydrogens of the group bonded directly to oxygen in the molecule, responsible for more than 93% of the final constant value in reactions with OH and 99% in reactions with Cl , at 298 K, in agreement with the experimental results, while the attack to the CH3 group in the carboxylate portion of the molecule is the less likely to occur. In reactions with OH, the values of the rate constant calculated closer to the experimental values were obtained from the results with functional mPW1B95-41, for methyl acetate, and mPW1B95-44 for ethyl acetate, whereas in reactions with Cl, were obtained with the CCSD(T)//B3LYP method for the methyl acetate and the CCSD(T)//MP2 method for ethyl acetate. The rate constant for the reaction with chlorine are about ten times larger than those for reactions with OH radicals. Reactions with OH and Cl occur in a single step, without stabilization of the intermediary and without significant tunneling effect. The rate constant obtained by the structure-reactivity relationship (SAR) overestimates the reactivity of the hydrogens of the CH3 groups at the carboxylate portion, in both acetates, and at the ethoxide portion of ethyl acetate. This method fails to describe the participation of each group in the reaction with Cl, predicting that the reaction on the CH3 portion of the alkoxide becomes predominant over the reaction on the CH2 group of ethyl acetate, relative to our calculations where the reaction with the CH2 group is predominant. Another flaw by providing the same reactivity for both the CH3 in methyl acetate, is in disagreement with our calculations which indicate that the reaction occurs predominantly in the CH3 group at the alkoxide portion of the molecule.

<p>Studies of binding reactions are of highest importance in a vast number of areas of biomedicine and biotechnology. A demand for fast and accurate small-volume measurements grows stronger, partly due to the development of therapeutic antibodies. In this report, a novel method for studies of binding reactions of antibodies is described. The use of a microfluidic platform shows promising results in determination of affinity binding constants.</p><p>Affinities between 1E-09 and 1E-11 M have been determined for four TSH antibodies. Reproducibility tests give a CV below 10%, using different Gyrolab instruments and microfluidic CD:s. The method carries the advantages of using solution-based measurements of unmodified molecules. Also an initial proof-of-concept for measurement of binding reaction rate constants shows further usage of the method. The kinetic association rate constant has been determined to 2E+06 M-1s-1 for one antibody. The possibility of using this method for screening of antibody libraries is also discussed.</p>

Studies of binding reactions are of highest importance in a vast number of areas of biomedicine and biotechnology. A demand for fast and accurate small-volume measurements grows stronger, partly due to the development of therapeutic antibodies. In this report, a novel method for studies of binding reactions of antibodies is described. The use of a microfluidic platform shows promising results in determination of affinity binding constants. Affinities between 1E-09 and 1E-11 M have been determined for four TSH antibodies. Reproducibility tests give a CV below 10%, using different Gyrolab instruments and microfluidic CD:s. The method carries the advantages of using solution-based measurements of unmodified molecules. Also an initial proof-of-concept for measurement of binding reaction rate constants shows further usage of the method. The kinetic association rate constant has been determined to 2E+06 M-1s-1 for one antibody. The possibility of using this method for screening of antibody libraries is also discussed.

Permafrost soils in the Arctic store large quantities of organic matter, roughly twice the amount of carbon that was present in the atmosphere before the industrial revolution. This freeze-locked carbon pool is susceptible to thawing caused by amplified global warming at high latitudes. The remobilization of old permafrost carbon facilitates its degradation to carbon dioxide and methane, thereby providing a positive feedback to climate change. Accelerating coastal erosion in addition to projected rising river discharge with enhancing sediment loads are anticipated to transport increasing amounts of land-derived organic carbon (OC) to the Arctic Ocean. On its shallow continental shelves, this material may be remineralized in the water column or in the sediments, transported without being altered off shelf towards the deep sea of the Arctic Interior or buried in marine sediments and hence sequestered from the contemporary carbon cycle. The fate of terrigenous material in the marine environment, though offering potentially important mechanisms to either strengthen or attenuate the permafrost-carbon climate feedback, is so far insufficiently understood. In this doctoral thesis, sediments from the wide East Siberian Arctic Shelf, the world’s largest shelf-sea system, were used to investigate some of the key processes for OC cycling. A range of bulk sediment properties, carbon isotopes and molecular markers were employed to elucidate the relative importance of different organic matter sources, the role of cross-shelf transport and the relevance of degradation during transport and after burial. Overall, OC released from thawing permafrost constitutes a significant proportion of the sedimentary organic matter on the East Siberian Arctic Shelf. Two sediment cores from the inner and outer East Siberian Sea recorded no substantial changes in source material or clear trends in degradation status for the last century. With increasing distance from the coast, however, strong gradients were detected towards lower concentrations of increasingly reworked land-derived OC. The time spent during cross-shelf transport was consequently found to exert first-order control on degradation. Compound-specific radiocarbon dating on terrigenous biomarkers revealed a net transport time of ~4 000 years across the 600 km wide Laptev Sea shelf, yielding degradation rate constants for bulk terrigenous OC and specific biomarkers on the order of 2-4 kyr-1. From these results, the carbon flux released by degradation of terrigenous OC in surface sediments was estimated to be ~1.7 Gg yr-1, several orders of magnitude lower than what had been quantified earlier for dissolved and particulate OC in the water column. Lower oxygen availability and close associations with the mineral matrix may protect sedimentary OC from remineralization and thereby weaken the permafrost-carbon feedback to present climate change. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 4: Manuscript.</p>

Saxitoxins were extracted from a bloom of toxic Anabaena circinalis and used to spike treated water from Hope Valley Reservoir (HVTW) and Milli-Q water. The waters were treated with ozone using the batch method and saxitoxin levels were measured in the samples using HPLC. The results for oxidation of saxitoxins in Milli-Q water versus HVTW show that despite the presence of natural organic matter(NOM) and the production of vastly different ozone residuals, there was a similar removal of all saxitoxins in both waters. The results show that high concentrations of saxitoxins were present in solution after ozonation with doses and contact times typically used in water treatment. Relating the toxin destruction to ozone residual showed that even with a residual ozone concentration of 0.8 mg/L after 10 minutes contact in HVTW, over 60% of the initial saxitoxin content was still present in the samples. The presence of an ozone residual in the water could not be related to saxitoxin destruction and it appeared that saxitoxin removal occurred more rapidly when ozone was consumed rather than stabilised in solution. The results indicate that the mechanism for toxin removal is probably based on the reaction with a hydroxyl radical species as the oxidant rather than molecular ozone. The results obtained during these experiments indicate that ozone is not an effective oxidant for this class of compound. A range of ozone doses were applied to two different treated reservoir waters that had been spiked with microcystins LA (mLA) and LR (mLR). At the ozone dose where a residual was first measured in the sample after 5 minutes exposure time, no microcystins were detected by HPLC in either water. The removal of mLA and mLR was identical in all samples. The absence of mLA and mLR by HPLC was supported by a loss of toxicity using a highly sensitive and specific bioassay (PP2A) and by in vivo studies in mice. In both waters microcystins were removed with an ozone dose typical of that used in drinking water treatment. The results indicate that conventional ozone treatment was effective in removing hepatotoxicity at microcystin levels greater than those likely to be found in drinking water. Two waters were sampled from reservoirs in South Australia. One was collected directly from Happy Valley Reservoir (HVRW) and the other from Myponga Reservoir after treatment but before chlorination (MFCW). They were spiked with mLA and mLR and chlorinated to measure toxin removal and chlorine consumption using the CT concept. In MFCW at pH 7 there was a better removal of both mLA and mLR than in HVRW at pH 8.1. There was also a lesser effect from water temperature upon toxin removal in MFCW. Microcystin LA was less easily removed than mLR at both temperatures in both waters. For HVRW, at the higher pH, this required an initial dose of 7 mg/L of chlorine which corresponded to a CT of around 70 min.mg/L. If the water temperature was reduced to 6??C then under these conditions there would still be 40% of the initial concentration of mLA and mLR present in this water. At this temperature a final chlorine residual of 3.5 mg/L after 30 minutes, requiring a chlorine dose of 8mg/L and corresponding to a CT of about 95 min.mg/L, was required to reduce microcystin levels below the WHO guidelines. This implies that in colder climates the application of chlorine for microcystin removal may require elevated chlorine doses and CT values. Arrhenius activation energies were calculated for mLA and mLR in both waters, revealing different Ea values for both toxins. Due to the complexity of the reactions and the possible effects of pH in solution, this system was considered too complicated to be described by the Arrhenius equation. NOM was collected from Myponga Reservoir in South Australia using magnetic ion exchange (MIEX??) resin. The collected NOM was desorbed and separated into fractions of different molecular weight and character using ultrafiltration and mixed resin ion exchange. At approximately 5 mg/L dissolved organic carbon (DOC) the measured apparent second order rate constant (kapp) for mLA and mLR removal was fairly similar in both the high molecular weight fraction (designated F3), and the intermediate high molecular weight fraction (designated F2). The low molecular weight fraction (designated EN) had slightly higher kapp values as would be expected due to the less reactive nature of the NOM in this fraction. This meant more chlorine was available to react with microcystins in this fraction. Fractions F3 and F2 produced similar kapp values to those from the parent water source following treatment, indicating the similar reactivity of these NOM fractions at comparable DOC levels. Increasing the DOC concentration in the F2 fraction increased kapp for both mLA and mLR due to the additional chlorine needed to react with the additional NOM present. The results showed that pH, temperature and DOC concentration have a higher impact upon chlorination rates, and the efficiency of toxin removal, than NOM character alone. In general it is assumed that chlorine will be more effective at removing toxins in water with a low SUVA and low specific colour as these indicate less 'reactive' NOM in the water. The results of this study show that toxin removal was more effective in the EN fraction as indicated by the higher kapp. This fraction also had the lowest SUVA and lowest specific colour which supports the generally held view in water treatment. Relating the toxin removal to chlorine residual in these reconstituted fractionated NOM samples, indicated that a residual of around 1.5 mg/L after 30 minutes contact was generally adequate to remove all toxins in water with a DOC level of around 5 mg/L. This is consistent with the results obtained in real waters, where at 20??C a chlorine residual of 2 mg/L was found to be sufficient for removal of both mLA and mLR.

La maitrise de la qualité des produits carnés transformés (conservés, marinés, cuits, salés, digérés...) nécessite une meilleure compréhension des mécanismes responsables des phénomènes oxydatifs et des lois cinétiques qui les régissent. Au cours des processus oxydatifs, la phase d’initiation des oxydations est capitale. Cette phase se caractérise par la vitesse à laquelle l’oxygène et le peroxyde d’hydrogène réagissent avec le fer dont la viande est plus ou moins riche selon l’espèce. Les radicaux libres, principalement superoxyde (O2°-) et hydroxyle (OH°) conduisent à l’oxydation des lipides et des protéines de la viande. Ce travail s’appuie en alternance sur des expérimentations avec un milieu modèle bien contrôlé et des sondes spécifiques permettant de caractériser la production radicalaire, et sur des simulations de calculs avec un modèle stœchio-cinétique basé sur un ensemble de réactions élémentaires et de réactions bilans permettant d’évaluer l’incidence i) de chacun des paramètres du système réactionnel (constante réactionnelle k, énergie d’activation Ea, réactivité du fer P) ii) de la concentration en réactants (Fer, H2O2, chlorure et antioxydants iii) des conditions environnementales (température, pH et force ionique) sur les cinétiques de production des radicaux libres. Les résultats expérimentaux montrent : (1) un effet synergique des oxydants et de la température sur les oxydations (2) une incidence importante des contres ions et du pH sur les complexes du fer et les niveaux d’oxydation (3) un important effet de la nature des oxydants et des antioxydants sur l'oxydation. Les constantes de vitesse controversées et les énergies d'activation de certaines réactions ainsi que les coefficients de réactivité du fer ont été ajustés localement un par un. Les prédictions du modèle stoechio-cinétique reproduisent des tendances expérimentales, exceptés pour des concentrations élevées en réactants, pour des températures extrêmes et certains antioxydants. Une optimisation globale des valeurs des k, des Ea et de la réactivité du fer pourrait améliorer les résultats prédictifs. / Control of meat quality during meat processes (storage, cooking, curing, digestion) requires a better understanding of the mechanisms responsible of the oxidative phenomena and of the kinetic laws that govern them. The initiation stage of oxidation is crucial and characterized by the rate of reaction of oxygen and hydrogen peroxide with iron; this latter compound is more or less rich depending on muscles, animals and species. Superoxide radical (O2°- ) and hydroxyl radical (OH°) are produced and initiate the cascade of reactions implicated in protein and lipid oxidations. To investigate the impact of the physicochemical parameters on the free radicals production our trials were carried out with a mimetic model of meat using two specific probes (nitroblue tetrazolium and terephthalate) and a stoichio-kinetic mathematical model composed of interactive chemical reactions. This approach enables to measure many production kinetics of O2°- and OH° and to assess unknown kinetic parameters (rate constant and activation energy and iron reactivity) by comparison of calculations to measurements. The experimental results show: (1) a synergistic effect of oxidants and temperature on oxidations (2) a significant effect of counter ions and pH on iron complexes and oxidation levels (3) a significant effect of oxidants and antioxidants on oxidation. Controversial rate constants and activation energies of some reactions as well as iron reactivity coefficients were adjusted. The predictions of the stoechio-kinetic model reproduce experimental trends except for high reactants concentrations, for extreme temperatures and for some antioxidants. A global optimization of k, Ea and iron reactivities values could improve predictive results.

Nous avons étudié les collisions réactives O(1D) + CH4 et O(1D) + H2O d’intérêt atmosphérique et astrophysique à l’aide de méthodes de chimie quantique et de dynamique réactionnelle. Pour la première réaction, des calculs de dynamique quantique à l’aide d’une méthode indépendante du temps ont été entrepris sur une surface d’énergie potentielle existante en considérant CH3 comme un pseudo-atome. Cette approche à dimensionnalité réduite, qualifiée ici de modèle pseudo-triatomique, a permis d’obtenir les probabilités de réaction à un moment angulaire total nul (J=0), puis de calculer les sections efficaces et les taux de réaction par une méthode approchée de type J-shifting. Nos résultats quantiques ont été comparés aux résultats obtenus par une méthode quasi-classique de trajectoires et aux prédictions expérimentales. Ces comparaisons ont, entre autre, validé le fait que la voie de sortie OH + CH3 était la voie principale pour cette réaction. La seconde réaction O(1D) + H2O a été abordée d’un point de vue structure électronique. Nous avons caractérisé les grandes lignes de la surface d’énergie potentielle de H2O2 en tenant compte de tous les degrés de liberté avec une méthode de calcul de haut niveau (MRCI : Multi Reference Configuration Interaction). Ainsi, nous avons pu déterminer avec une grande précision les géométries, les fréquences et les énergies des isomères du système H2O2 ainsi que son diagramme énergétique. A l’avenir, il faudra construire une surface d’énergie potentielle qui sera utilisée pour décrire la dynamique de cette réaction. / We have studied the reactive collisions, O (1D) + CH4 and O (1D) + H2O, of atmospheric and astrophysical interest, using different quantum chemistry methods and reaction dynamics approaches. For the first reaction, quantum dynamical calculations using a time-independent method were carried out on an existing potential energy surface by considering CH3 as a pseudo-atom. This reduced dimensionality approach, i.e. a pseudo triatomic model, yielded the calculation of the reaction probabilities at zero total angular momentum (J = 0). The cross sections and reaction rates have been computed by the approximate J-shifting method. Our quantum results were compared with results obtained by a quasi-classical trajectory method and experimental predictions. These comparisons, among others, have enabled the fact that the channel CH3 + OH was the main exit channel for this reaction. The second reaction O(1D) + H2O has been studied at the level of electronic structure. We have characterized the outline of the potential energy surface of H2O2 , taking into account all the degrees of freedom at a high level calculation (MRCI: Multi Reference Configuration Interaction). Thus, we were able to determine with great accuracy the geometries, frequencies and energies of isomers of the H2O2 system and its energy diagram. In the future, a potential energy surface has to be built to be used in the dynamical calculations for this reaction.

This thesis describes the measurement of rate constants for gas phase reactions as a function of temperature (285 ≤ T/K ≤ 850) and pressure (48 ≤ P/Torr ≤ 700). One or both reactants was monitored directly in real time, using time–resolved resonance fluorescence (for atoms) and u.v. absorption (for radicals). Reactants were produced by exciplex laser flash photolysis. The technique was used to measure rate constants to high precision for the following reactions under the stated conditions: • H+O2+He->HO2+He and H+O2−→OH+O, for 800 ≤ T/K ≤ 850 and 100 ≤ P/Torr ≤ 259. A time–resolved study was performed at conditions close to criticality in the H2–O2 system. The competition between the two reactions affected the behaviour of the system after photolysis, and the rate constants were inferred from this behaviour. • H+C2H4+He<-->C2H5+He (T = 800 K, 97 ≤ P/Torr ≤ 600). The reactions were well into the fall–off region at all conditions studied. At 800 K, the system was studied under equilibrating conditions. The study provided values of the forward and reverse rate constants at high temperatures and enabled a test of a new theory of reversible unimolecular reactions. The controversial standard enthalpy of formation of ethyl, DH0f,298 (C2H5), was determined to be 120.2±0.8 kJ mol−1. Master Equation calculations showed that reversible and irreversible treatments of an equilibrating system should yield the same value for both thermal rate constants. • H+C3H5+He->C3H6+He (T = 291 K, 98 ≤ P/Torr ≤ 600) and O+C3H5 −→ products (286 ≤ T/K ≤ 500, 48 ≤ P/Torr ≤ 348). Both reactions were pressure–independent, and the latter was also independent of temperature with a value of (2.0±0.2) ×10−10 cm3 molecule−1 s−1. • H+C2H2+He<-->C2H3+He (298 ≤ T/K ≤ 845, 50 ≤ P/Torr ≤ 600). At 845 K, both reactions were in the fall–off region; rate constants were used to determine the standard enthalpy of formation of vinyl, ¢H0f,298 (C2H3), as 293±7 kJ mol−1. The value of this quantity has until recently been very controversial. • H+CH4 <--> CH3+H2. The standard enthalpy of formation of methyl, DH0 f,298 (CH3), was determined by re–analysing existing kinetic data at T = 825 K and 875 K. A value of 144.7±1.1 kJ mol−1 was determined. Preliminary models were examined to describe the loss of reactants from the observation region by diffusion and pump–out. Such models, including diffusion and drift, should prove useful in describing the loss of reactive species in many slow–flow systems, enabling more accurate rate constants to be determined.

The deprotonation characteristics of fluorescent probes -naphthol and 8-hydroxypyrene-1,3,6-trisulphonic acid (HPTS) were studied in this diploma thesis, using steady-state and time-resolved fluorescence spectroscopy. Two cationic surfactants, Septonex and cetyltrimethylammonium bromide (CTAB), were studied. These surfactants were measured in the complex with hyaluronan (1.75 MDa, 1 MDa and 300 kDa). Steady-state fluorescence was used for determination of critical aggregation concentration of each surfactant and pKa*. Time-resolved fluorescence decays were used to calculate the average lifetimes and the deprotonation constants of naphthol and HPTS. The measurement with hyaluronan were compared with the polystyrenesulfonate (PSS) – surfactant system. The effect of hydration shell of hyaluronan on hyaluronan – surfactant complex formation results from the comparison of above mentioned systems. Large differences were found in the deprotonation characteristic between surfactants and even between individual molecular weights of hyaluronan. The measurement shows that the hydration shell is located near to the dissociated carboxyl groups of hyaluronan chain, where the interaction with the positively charged surfactants occurs. Furthermore, the aggregation number of Septonex was determined by quenching of pyrene using cetylpyridinium chloride (CPC) as a quencher. The aggregation number for 20 mM Septonex solution was determined as a value of 104 molecules. CPC was used for confirmation of the localization of -naphthol in the micelles of CTAB and polymer – CTAB, respectively.

No description available.