Doenças cardiovasculares (DCVs) são uma das maiores causas de morte ao redor do mundo, de acordo com a Organização Mundial da Saúde (OMS). Sabe-se que, alterações do nível das lipoproteínas plasmáticas, que são responsáveis pelo transporte do colesterol pela corrente sanguínea, estão relacionadas com o desenvolvimento de doenças cardiovasculares. Por essa razão conhecer os parâmetros biocinéticos das lipoproteínas plasmáticas e quantificá-los é importante para corrigir e aprofundar estudos relacionados às doenças associadas a alterações no nível das lipoproteínas. O objetivo principal deste trabalho é fornecer um modelo biocinético e estimar as doses radiométricas para o 3H-Colesterol, um traçador radioativo empregado em estudos fisiológicos e metabólicos. O modelo utilizado neste trabalho foi baseado em [SCHWARTZ e col., 2004] quanto à distribuição do colesterol pelas lipoproteínas e no modelo gastrointestinal do [ICRP 30, 1979]. As doses distribuídas nos compartimentos do modelo e nos órgãos e tecidos de um adulto padrão descritos no [ICRP 106, 2008] foram calculadas utilizando a metodologia MIRD (Medical Internal Radiation Dose) e a análise compartimental realizada pelo programa computacional Matlab®. Os coeficientes de doses foram estimados para um phantom de um homem padrão (73 kg) descrito no [ICRP 60, 1991]. As doses estimadas tanto para o modelo quanto as estimadas para outros órgãos foram baixas e não ultrapassaram a maior dose obtida que foi no intestino grosso superior, como sendo 46,8 μGy. Esses parâmetros poderão ser utilizados como auxilio em trabalhos que necessitem de pareceres dos comitês de ética, quanto ao uso do 3H-Colesterol como traçador radioativo. / Cardiovascular diseases (CVDs) are one of the major reasons of death around the world according to the World Health Organization (WHO). It is well known that changes in levels of plasma lipoproteins, which are responsible for the transport of cholesterol into the bloodstream, are associated with cardiovascular diseases. For this reason to know the biokinetic parameters of plasma lipoproteins and quantifies them is important to correct and deep understanding about the diseases associated with these disorders. The main aim of this study is to provide a biokinetic model and estimate the radiometric doses for 3H-Cholesterol, a radioactive tracer widely used in physiological and metabolic studies. The model was based on [Schwartz et al. 2004] about the distribution of cholesterol by the lipoprotein and gastrointestinal model [ICRP 30, 1979]. The doses distribution in compartments of the model and other organs and tissues of a standard adult described in [ICRP 106, 2008] was calculated using MIRD method (Medical Internal Radiation Dose) and compartmental analysis using the computer program Matlab®. The dose coefficients were estimated for a standard phantom man (73 kg) described in [ICRP 60, 1991]. The estimated doses for both model and for other organs were low and did not exceed the highest dose obtained that was in the upper large intestine, as 46.8 μGy these parameters will assist in ethics committees opinions on the use of works that use the 3H-cholesterol which radioactive tracer.

Foram desenvolvidos métodos de determinação de urina e trítio em urina. Para o urânio foi adaptada a técnica de análise por fluorimetria em meio sólido. O limite de sensibilidade foi de 5. 10-4µg U/0,1 ml e o erro foi de cerca de 10% para concentrações em torno de 0,05 µg U/0,1 ml. Foi padronizado para o trítio o método de análise por cintilação em meio líquido. O método determina quantidades de trítio até pelo menos 8,10-3µCi/ml e o erro foi de cerca de 4% para concentrações de trítio em torno de 0,34 µCi/l. Depois de adaptadas, as técnicas foram aplicadas a amostras de urinas de trabalhadores expostos a compostos de urânio ou trítio com a finalidade de verificar possível contaminação interna por estes radioisótopos. / Abstract not available.

Les interactions protéine–protéine jouent un rôle essentiel dans le fonctionnement cellulaire et sont impliquées dans diverses pathologies. L'étude de ces interactions est donc primordiale. Nous avons entrepris de développer une méthode de « footprinting » basée sur la différence d'accessibilité à l'eau des acides aminés d'une protéine selon qu'elle est seule ou en interaction. Le principe de cette méthode de caractérisation des zones d'interactions protéine–ligand, est basé sur une étape de génération de radicaux carbo-centrés sur les chaînes latérales des acides aminés de la protéine, et sur une étape de réparation de ces radicaux par un atome de tritium.<br /> <br />La première étape a été de déterminer la réactivité des 20 acides aminés communs vis-à-vis de notre méthode : <br />Lys>Leu>Arg>Ile>Trp>Phe>Val>Cys>Met>His>Tyr>Glu>Thr>Asp><br />Gln>Pro>Ala>Asn> Ser>Gly. Notre méthode ensuite appliquée à l'étude du complexe entre la protéine hAsf11-156 et un fragment de l'histone H3 a permis de caractériser sans ambiguïté les trois résidus principaux de H3 (L126, R129 et I130) impliqués dans cette interaction. De plus, nous avons mis en évidence que notre méthode de caractérisation des interactions protéique est à la fois sensible aux phénomènes d'interaction et de repliement.

Lors de la dégradation du peroxyde d'hydrogène en eau et dioxygène catalysée par les hémoenzymes à fer de type catalase et peroxydase, il se forme à l'échelle de la milliseconde un intermédiaire réactionnel radicalaire porté par la porphyrine. Dans le cas de l'enzyme modèle utilisée, la catalase de foie de bœuf, il a été montré par des études de spectroscopie RPE que ce radical est ensuite délocalisé sur un résidu tyrosyle de la chaîne polypeptidique. A ce jour, on ne connaît pas l'exacte localisation du résidu impliqué, donc le rôle de ce site d'oxydation alternatif. <br />Par ailleurs, il a été montré au laboratoire que l'identification et la quantification des radicaux formés sur les acides aminés d'une protéine par l'attaque de radicaux hydroxyle sont possibles. Cette méthode est basée sur le marquage au tritium des résidus acides aminés. Notre approche est basée sur la génération de radicaux hydroxyle par radiolyse de l'eau. Les radicaux hydroxyle formés arrachent un hydrogène sur la chaîne latérale des acides aminés et génèrent ainsi un radical carboné. Il est ensuite “réparé” in situ par un composé, le sel sodique de l'acide phénylphosphinique tritié, qui permet d'introduire un atome de tritium à la place de l'hydrogène précédemment arraché. Cet atome de tritium sert de marqueur pour détecter les sites de formation des radicaux. <br />Nous avons donc utilisé les propriétés de réparation du vecteur tritié pour identifier quelle est la tyrosine impliquée dans les transferts d'électrons de la BLC. Même s'il a été montré par RPE que la disparition du radical porté par la tyrosine est effective en présence de l'agent de réparation, les études de marquage n'ont pas abouti à déterminer l'exacte localisation du radical. Une des raisons invoquées est le manque d'efficacité de l'agent de réparation pour transférer son atome d'hydrogène. C'est pourquoi d'autres composés capables eux aussi de fournir un atome d'hydrogène par voie radicalaire ont été synthétisés puis testés sur ce système enzymatique par une étude de spectroscopie RPE.<br />En parallèle, nous avons voulu comprendre les mécanismes d'action des ces mêmes composés sur un système modèle en générant des radicaux sur la tyrosine en solution par radiolyse de l'eau. La méthode consiste à produire dans une solution aqueuse de tyrosine des radicaux hydroxyle, qui vont former les radicaux tyrosyle. Les radicaux ainsi générés peuvent être ensuite réparés par un atome de deutérium fourni par un donneur. L'incorporation en deutérium et la régiosélectivité de l'attaque sont ensuite analysées par spectrométrie de masse et RMN 2H. L'irradiation de solution de tyrosine en présence des différents composés choisis s'est révélée difficile à analyser, en raison notamment de la difficulté à déterminer la proportion de radicaux hydroxyle réagissant avec l'agent réparateur au lieu de la tyrosine, mais surtout en raison de l'incorporation inattendue de deutérium dans la tyrosine en l'absence de tout agent de transfert. Ce phénomène jusqu'alors inconnu a, dès lors, retenu toute notre attention. Nous avons alors focalisé nos travaux sur la compréhension des processus intervenant dans l'autoréparation de la tyrosine et ainsi proposé un mécanisme pour expliquer nos observations.

Current protection of the marine environment from radiation is based largely on measuring, estimating and modelling accumulation and impact(s) of radionuclides in a few marine species. Using a relevant marine organism, this thesis focusses on investigating some poorly described phenomena that could cause deviations from predicted measurements. Paper I investigated the biological transformation of tritium (radioactive hydrogen) into an organic compound. The resulting organically bound tritium (OBT) showed increased accumulation in mussels, unique incorporation into a key biological molecule (DNA), extended persistence in tissues, and greater toxicity than the inorganic form. Paper II demonstrated significant disparity in OBT accumulation between functionally similar microalgae species and that OBT in algae is readily transferred to a consumer. Highly radioactive particles are a complex issue in radioecology due to their concentrated dose geometry, potentially inducing very different impacts in organisms, compared to external irradiation. Paper III developed a method to introduce radioactive particles that would facilitate their recovery, improve dose-calculation, and aid the measurement of toxicological endpoints. It also showed that such particles can be incorporated into mussel tissues, causing significant effects. In Paper IV, hypoxia – another major ecological hazard in the marine environment – was expected to reduce radiosensitivity. The minimal observable effect from radiation prevented identification of such an interaction, and indicates drawbacks in the (otherwise sensitive) endpoints used. It appears that stressors like hypoxia may be more of a health hazard to marine organisms than environmental levels of ionising radiation. By understanding such causes of variation in accumulation and impact, it is possible to improve risk assessment, providing more justification for regulations chosen and minimising conservatism in setting environmental standards. / <p>At the time of doctoral defense, the following papers were not published and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.</p>

Utilisation des isotopes et du tritium dans les études limnologiques.

The accumulation of helium atoms in metals or metal tritides is known to result in the formation of helium bubbles in the lattice and to cause degradation of the material. Helium is introduced either through neutron transmutation reaction or via the radioactive decay of tritium. We have performed first-principles calculations of interstitial helium inside Pd and Pd tritide using density functional theory (DFT) and the projector augmented-wave (PAW) method within the generalized gradient approximation (GGA). We model the growth process of an interstitial helium cluster and find that when the size of the cluster reaches to five atoms, the cluster can induce an energetically favorable vacancy with a self-trapping mechanism. The cluster growth mechanism of interstitial helium is addressed by investigating the associated energetics, cluster configurations, and electronic structural properties. In addition, we study the diffusion properties of helium in palladium-based compounds by performing the nudged elastic band (NEB) calculations. Our computational models propose that by loading the lattice with hydrogen atoms at certain concentration, or substituting with alloying metals can modify the diffusivity by increasing its migration barrier, which may impede the cluster formation in the beginning stage.

M. Tech. Polymer Technology. / The gas permeability of composite epoxy resins formulated with graphene platelets and glass flakes was investigated. The purpose of researching the gas permeability of the composite resins was to develop a possible coating system that could prevent or limit the release of radioactive gases like tritium from irradiated graphite waste which may accumulate in underground repositories. Helium was used as a substitute gas to simulate the diffusive properties of tritium gas.

To assess the long-term performance of soil-cement materials used in source-control remediation methods (i.e. cement-based solidification/stabilization), procedures to measure or estimate contaminant migration parameters are essential. Previous research indicates that diffusion may be an important mechanism in contaminant transport through soil-cement materials. However, there is a paucity of information regarding the diffusion of contaminants through these materials. The development of a single-reservoir diffusion apparatus and methodology to assess the effective diffusion coefficient (De) and effective porosity (ne) of dissolved, conservative, inorganic chemicals for saturated, cured, monolithic soil-cement specimens is discussed. This is the only study known to investigate these parameters for these materials. The results of tritiated water diffusion tests on 14 different soil-cement mixtures are presented and the influence of curing time and mixture properties such as water-to-cement ratio, cement content, and grain-size distribution are examined. Results suggest that, to determine reasonable assessments of the longer-term parameters, soil-cement samples should be cured for a minimum of 70 days before commencing diffusion testing. Values of ne (0.21 to 0.41) and De (2.50×10-10 m2/s to 7.0×10-10 m2/s) determined are similar to those previously determined for a number other low-hydraulic conductivity materials (i.e. saturated inactive clays). The water content of the initial mixture is shown to have a substantial effect on the diffusive properties as the results indicate that both the total porosity (n) and the effective porosity, ne, generally increase with increasing initial water content. For the range of soils used in this investigation, grain-size distribution did not have a substantial effect on the values of ne or De determined from diffusion testing. The adaptation of a double-reservoir diffusion testing apparatus and methodology to evaluate the distribution coefficient (Kd) and De of organic contaminants is also presented. This apparatus is used to evaluate Kd and De of benzene, ethylbenzene, naphthalene, and trichloroethylene for three soil-cement mixtures. Values of Kd (0 to 2.5 cm3/g depending on the compound and soil-cement mixture tested) determined from diffusion testing, batch testing, and theoretical estimates from the literature were in general agreement. Values of De for the organic compounds ranged from 1.50×10-10 to 3.0×10-10 m2/s.

Šiame darbe eksperimentiniais ir modeliavimo metodais buvo nagrinėjami skirtingose hidrogeologinėse sąlygose esančių branduolinių objektų aikštelių aeracijos zonos gruntuose vystantys drėgmės (ir priemaišų) pernašos procesai. Aeracijos zonos profiliai buvo palyginti atlikus eksperimentinius tyrimus ir apibendrinus duomenis apie gruntų hidraulines savybes, drėgnį ir izotopinę sudėtį. Krituliuose ir aeracijos zonos grunto profilių drėgmėje buvo nustatyti globaliai paplitusio radionuklido tričio bei vandens molekulės izotopinių traserių pasiskirstymo ypatumai. Nustatyta, kad krituliuose pasireiškiančios stabiliųjų izotopų sezoninės variacijos aeracijos zonoje ir ypač gruntiniame vandenyje beveik išnyksta, tačiau išlieka nežymūs sezoninių smailių pėdsakai, kurie Maišiagalos aikštelėje yra šiek tiek kontrastiškesni nei Stabatiškės aikštelėje, kadangi Maišiagalos aikštelėje drėgmės tranzito aeracijos zonoje laikas trumpesnis. Priėmus hipotetines žemės paviršiaus užtvindymo sąlygas esant žemam, vidutiniškam ir aukštam slėgiui, momentiniam ir pastoviam priemaišų įvedimui, palyginimui buvo išnagrinėti šeši scenarijai. Sudarytas tričio pernašos aeracijos zonoje modelis parodė, kad paros įvesties parametrų suvidurkinimas atskiram mėnesiui gali riboti tričio koncentracijos aeracijos zonos profilyje ir vandens balanso elementų pasiskirstymo atkūrimą. / Two nuclear waste disposal sites (Maišiagala radioactive waste storage facility site and Stabatiškė near surface repository site) were compared in terms of the contaminant movement through the unsaturated zone. Extensive data sets of the hydraulic properties, water content and isotope composition have been collected and summarized. Distribution features of globally widespread radionuclide tritium and the water molecule tracer isotopes in precipitation, unsaturated zone soil moisture profiles and groundwater were determined. Stable isotopes seasonal variation occurring in precipitation almost disappears in the unsaturated zone soil moisture and especially in shallow groundwater, but in both sites slight seasonal peak traces remain, which at the Maišiagala site are a bit more contrasting in comparison with the Stabatiškė site. Both sites were modelled by using unsaturated flow and transport models. Six scenarios have been developed to simulate the water and solute movement under low, moderate, and high water input, and instantaneous and continuous solute input conditions. In order to validate the representativeness of the hydraulic parameters, the model has been used to estimate the tritium distribution in the unsaturated zone, which properly represents the dynamics of the unsaturated zone. The uniformity of the daily input in each month should be kept in mind in the evaluation of the smooth changes of the tritium profile and water budget elements.