Anyone who has eaten spicy foods has experienced the adverse effects of capsaicin, the pungent chemical found in hot chili that causes a burning sensation. The specific action of capsaicin occurs by the activation of receptors in sensory neurons. This thesis investigates the interaction of capsaicin with model cell membranes representing the structure of neurons. In particular, we are interested in the changes induced by capsaicin to the structure and dynamics of membranes. Molecular dynamics simulations are used to study the molecular interactions. The first part of this study evaluates different molecular representations for capsaicin in an 1-octanol/water system. This inhomogeneous system is commonly used to determine the partition of compounds between hydrophilic and hydrophobic environments, as that found in biological membranes. The results of these simulations validate the OPLS united-atom force field as a reasonable molecular representation of capsaicin, as it describes the behavior of capsaicin both quantitatively and qualitatively in 1-octanol/water mixtures. In the second part, simulations are performed for capsaicin and model cell membranes consisting of dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylethanolamine, two of the most commonly found lipids. Simulations investigated capsaicin in the aqueous and lipid phases. The results provide insight into the changes to the bilayers caused by capsaicin. Bilayers containing dipalmitoylphosphatidylethanolamine showed lower permeabilities to capsaicin than those composed of pure dipalmitoylphosphatidylcholine. Temperature is found to be an important factor in the permeability of capsaicin in the bilayer. Capsaicin in the bilayer concentrated in a region beneath the lipid/water interface, in which favorable hydrophilic and lipophilic interactions occur. The structure of the bilayer is not significantly changed at the concentrations of capsaicin considered. One important result from the simulations indicates that the interfacial density decreases with increasing capsaicin concentration in the bilayer, supporting the experimental observations of increased permeability in bilayers exposed to capsaicin. / Master of Science

A família Myrtaceae tem muitas espécies frutíferas, algumas são utilizadas comercialmente, entre elas o cambuci (Campomanesia phaea). Os objetivos deste trabalho foram descrever a fenologia reprodutiva, a biologia floral, o sistema reprodutivo e identificar os polinizadores do cambuci para gerar novos conhecimentos que possam contribuir com a produtividade desta espécie. O estudo de fenologia reprodutiva foi conduzido por dois anos, em área de ocorrência natural e área de cultivo comercial. As fenofases (floração e frutificação) foram monitoradas com duas métricas: Índice de atividade (sincronia) e Índice de intensidade (intensidade - Fournier) e correlacionadas com fatores abióticos (temperatura, pluviosidade e comprimento do dia). Os resultados mostraram que a floração e frutificação na área de ocorrência natural e cultivo foram diferentes, mesmo sob mesmas condições climáticas. A floração e frutificação foram mais intensas e sincrônicas na área de cultivo. Os fatores abióticos não explicaram estas diferenças nas fenofases entre as áreas de estudo, porém a adubação do solo e diversidade de polinizadores tiveram papel importante. No estudo de polinização de C. phaea foram observados a duração de antese, recursos florais, receptividade do estigma e viabilidade polínica. O sistema reprodutivo de C. phaea foi investigado baseado na razão P:O e pelos experimentos de polinização manual. Os visitantes florais foram capturados e os polinizadores mais eficientes foram determinados, conforme número de pólen depositado no estigma e número de frutos produzidos. As flores de C. phaea duram dois dias, são hermafroditas e têm o pólen como o único recurso disponível para os visitantes florais. A antese é noturna e começa em torno das 5 h. O sistema reprodutivo de C. phaea é o autoincompatível. Foram coletadas 52 espécies de visitantes florais e entre elas as mais eficientes na polinização foram as abelhas noturnas e crepusculares (Megalopta sodalis, Megommation insigne, Ptiloglossa latecalcarata e Zikanapis seabrai). Além destas abelhas, as flores de C. phaea também foram visitadas e polinizadas por Apis mellifera nos períodos crepusculares e diurnos. Para entender como as abelhas noturnas/crepusculares encontram as flores do cambuci no escuro foram coletadas amostras dos voláteis florais (a noite e durante o dia), pelo método de dynamic headspace e posteriormente analisados por GC-MS. Experimentos eletroantenográficos (GC-EAD) e biotestes foram realizados para testar se os compostos identificados das flores do cambuci são capazes de estimular respostas eletrofisiológicas e comportamentais nas abelhas noturnas/crepusculares. Foram encontrados 14 compostos voláteis nas flores de C. phaea, os mesmos nas amostras da noite e do dia, embora a composição relativa do odor tenha diferido entre os dois períodos. A emissão dos voláteis é maior a noite durante a atividade das abelhas noturnas/crepusculares, e alguns compostos são mais eminentes durante a noite (ex, 1-Octanol) e outros ao dia (ex, 2-Phenylethanol). As abelhas noturnas foram atraídas para os odores sintéticos da flor do cambuci. Apis mellifera também respondeu positivamente ao teste eletroantenográfico e biotestes. Os resultados mostraram que os voláteis emitidos a noite pelas flores de C. phaea tem função atrativa para as abelhas noturnas/crepusculares, e sugere que 1-Octanol possa ser o composto chave nesta atração. / The family Myrtaceae has many fruiting species, some are commercially explored. Among those species is the cambuci (Campomanesia phaea). The objectives this work were to describe the reproductive phenology, the floral biology, the reproductive system, and to identify the pollinators of cambuci in order to generate new knowledge that may help increase the productivity of this species. The study about reproductive phenology was conducted for two years, in an area of natural occurrence and in a commercial crop. The phenophases (flowering and fruit set) were monitored with Activity index (synchrony) and Intensity index (Fournier intensity) and correlated with abiotic factors (temperature, rainfall, and day length). The results showed that flowering and fruit set of C. phaea in natural area and crop were different even under same climatic conditions. The flowering and fruit set were more intense and synchrony in the crop. The abioctic factors do not explain these differences in the phenophases between the study areas, but other variables, such as soil fertilization and pollinator diversity, play an important role. In the pollination study of C. phaea were observed the anthesis duration, floral resources, stigma receptivity, and pollen viability. The reproductive system of C. phaea was investigated based on the P:O ratio and by carrying out manual pollination tests. The flower visitors were captured and determined the most efficient pollinators, according to effectiveness by number of pollen grains deposited in the stigma and number of fruit set. The flowers of C. phaea last two days, are hermaphrodite, and have pollen as the only resource offered to flower visitors. Its anthesis is nocturnal and begins around 5 h. The reproductive system of C. phaea is self-incompatible. Were collected 52 species of flower visitors and among them the most efficient in pollination were nocturnal and crepuscular bees (Megalopta sodalis, Megommation insigne, Ptiloglossa latecalcarata e Zikanapis seabrai). Besides these bees, the flowers of C. phaea flowers were also visited and pollinated by Apis mellifera in crepuscular and diurnal periods. In order to understand how the nocturnal/crepuscular bees find cambuci flowers in darkness flower volatiles were collected (at night and during the day) by dynamic headspace method and after analyzed by GC-MS. In addition, electroantennographic (GC-EAD) and behavioural experiments (bioassays) were performed to test if compounds identified from cambuci flowers are capable in eliciting electrophysiological and behavioural responses in nocturnal/crepuscular bees. In total 14 volatiles compounds were found in C. phaea flowers, the same in the night and day samples. Although, the relative scent composition differed between these two periods. The volatile emission is higher during the activity of nocturnal/crepuscular bees, and some compounds are more eminent during the night (e.g., 1-Octanol) and some during the day (e.g., 2-Phenylethanol). The nocturnal/crepuscular were attracted by synthetic scent of the cambuci flowers. Apis mellifera also showed positive responds towards for electroantennographic and behavioural bioassays. The results showed that volatiles emitted at night by C. phaea flowers have attractive function to nocturnal/crepuscular bees, and suggest that 1-Octanol can be the key compound for this attraction.

A família Myrtaceae tem muitas espécies frutíferas, algumas são utilizadas comercialmente, entre elas o cambuci (Campomanesia phaea). Os objetivos deste trabalho foram descrever a fenologia reprodutiva, a biologia floral, o sistema reprodutivo e identificar os polinizadores do cambuci para gerar novos conhecimentos que possam contribuir com a produtividade desta espécie. O estudo de fenologia reprodutiva foi conduzido por dois anos, em área de ocorrência natural e área de cultivo comercial. As fenofases (floração e frutificação) foram monitoradas com duas métricas: Índice de atividade (sincronia) e Índice de intensidade (intensidade - Fournier) e correlacionadas com fatores abióticos (temperatura, pluviosidade e comprimento do dia). Os resultados mostraram que a floração e frutificação na área de ocorrência natural e cultivo foram diferentes, mesmo sob mesmas condições climáticas. A floração e frutificação foram mais intensas e sincrônicas na área de cultivo. Os fatores abióticos não explicaram estas diferenças nas fenofases entre as áreas de estudo, porém a adubação do solo e diversidade de polinizadores tiveram papel importante. No estudo de polinização de C. phaea foram observados a duração de antese, recursos florais, receptividade do estigma e viabilidade polínica. O sistema reprodutivo de C. phaea foi investigado baseado na razão P:O e pelos experimentos de polinização manual. Os visitantes florais foram capturados e os polinizadores mais eficientes foram determinados, conforme número de pólen depositado no estigma e número de frutos produzidos. As flores de C. phaea duram dois dias, são hermafroditas e têm o pólen como o único recurso disponível para os visitantes florais. A antese é noturna e começa em torno das 5 h. O sistema reprodutivo de C. phaea é o autoincompatível. Foram coletadas 52 espécies de visitantes florais e entre elas as mais eficientes na polinização foram as abelhas noturnas e crepusculares (Megalopta sodalis, Megommation insigne, Ptiloglossa latecalcarata e Zikanapis seabrai). Além destas abelhas, as flores de C. phaea também foram visitadas e polinizadas por Apis mellifera nos períodos crepusculares e diurnos. Para entender como as abelhas noturnas/crepusculares encontram as flores do cambuci no escuro foram coletadas amostras dos voláteis florais (a noite e durante o dia), pelo método de dynamic headspace e posteriormente analisados por GC-MS. Experimentos eletroantenográficos (GC-EAD) e biotestes foram realizados para testar se os compostos identificados das flores do cambuci são capazes de estimular respostas eletrofisiológicas e comportamentais nas abelhas noturnas/crepusculares. Foram encontrados 14 compostos voláteis nas flores de C. phaea, os mesmos nas amostras da noite e do dia, embora a composição relativa do odor tenha diferido entre os dois períodos. A emissão dos voláteis é maior a noite durante a atividade das abelhas noturnas/crepusculares, e alguns compostos são mais eminentes durante a noite (ex, 1-Octanol) e outros ao dia (ex, 2-Phenylethanol). As abelhas noturnas foram atraídas para os odores sintéticos da flor do cambuci. Apis mellifera também respondeu positivamente ao teste eletroantenográfico e biotestes. Os resultados mostraram que os voláteis emitidos a noite pelas flores de C. phaea tem função atrativa para as abelhas noturnas/crepusculares, e sugere que 1-Octanol possa ser o composto chave nesta atração. / The family Myrtaceae has many fruiting species, some are commercially explored. Among those species is the cambuci (Campomanesia phaea). The objectives this work were to describe the reproductive phenology, the floral biology, the reproductive system, and to identify the pollinators of cambuci in order to generate new knowledge that may help increase the productivity of this species. The study about reproductive phenology was conducted for two years, in an area of natural occurrence and in a commercial crop. The phenophases (flowering and fruit set) were monitored with Activity index (synchrony) and Intensity index (Fournier intensity) and correlated with abiotic factors (temperature, rainfall, and day length). The results showed that flowering and fruit set of C. phaea in natural area and crop were different even under same climatic conditions. The flowering and fruit set were more intense and synchrony in the crop. The abioctic factors do not explain these differences in the phenophases between the study areas, but other variables, such as soil fertilization and pollinator diversity, play an important role. In the pollination study of C. phaea were observed the anthesis duration, floral resources, stigma receptivity, and pollen viability. The reproductive system of C. phaea was investigated based on the P:O ratio and by carrying out manual pollination tests. The flower visitors were captured and determined the most efficient pollinators, according to effectiveness by number of pollen grains deposited in the stigma and number of fruit set. The flowers of C. phaea last two days, are hermaphrodite, and have pollen as the only resource offered to flower visitors. Its anthesis is nocturnal and begins around 5 h. The reproductive system of C. phaea is self-incompatible. Were collected 52 species of flower visitors and among them the most efficient in pollination were nocturnal and crepuscular bees (Megalopta sodalis, Megommation insigne, Ptiloglossa latecalcarata e Zikanapis seabrai). Besides these bees, the flowers of C. phaea flowers were also visited and pollinated by Apis mellifera in crepuscular and diurnal periods. In order to understand how the nocturnal/crepuscular bees find cambuci flowers in darkness flower volatiles were collected (at night and during the day) by dynamic headspace method and after analyzed by GC-MS. In addition, electroantennographic (GC-EAD) and behavioural experiments (bioassays) were performed to test if compounds identified from cambuci flowers are capable in eliciting electrophysiological and behavioural responses in nocturnal/crepuscular bees. In total 14 volatiles compounds were found in C. phaea flowers, the same in the night and day samples. Although, the relative scent composition differed between these two periods. The volatile emission is higher during the activity of nocturnal/crepuscular bees, and some compounds are more eminent during the night (e.g., 1-Octanol) and some during the day (e.g., 2-Phenylethanol). The nocturnal/crepuscular were attracted by synthetic scent of the cambuci flowers. Apis mellifera also showed positive responds towards for electroantennographic and behavioural bioassays. The results showed that volatiles emitted at night by C. phaea flowers have attractive function to nocturnal/crepuscular bees, and suggest that 1-Octanol can be the key compound for this attraction.

Cette étude s’attache à la caractérisation physico-chimique des contaminants des emballages alimentaires organiques, précisément les phtalates et les alkylphénols, en terme de solubilité aqueuse, coefficient de partage octanol-eau et pression de vapeur. Cette caractérisation se situe dans le cadre des règlementations REACH concernant l’identification des substances chimiques toxiques. Les mesures expérimentales de solubilité aqueuse sont effectuées par la méthode dynamique de saturation dans un intervalle de température [298.15-328.15K], celles du coefficient de partage octanol-eau avec la méthode « shake-flask » à 298.15. Les mesures de pression de vapeur sont réalisées avec la méthode dynamique de saturation dans un intervalle de température [313.15-423.15K] et validées avec la méthode statique. A partir de ces mesures, les coefficients de partage air-eau et octanol-air sont déterminés. En addition des mesures expérimentales, une prédiction de ces propriétés est effectuée avec les modèles thermodynamiques : UNIFAC originale, UNIQUAC, NRTL et COSMO-sac-dsp. A l’issue de ces résultats, une évaluation quantitative et qualitative de chacun des modèles est effectuée. Cette évaluation facilitera l’optimisation des paramètres de chacun des modèles des deux familles dans le but de créer un modèle de prédiction du phénomène de migration de l’emballage vers l’aliment / The aim of this study is the physical-chemical characterization of the organic food packaging contaminants, particularly phthalates and alkyl phenols, in terms of aqueous solubility, octanol-water partition coefficient and vapor pressure. This characterization falls within the scope of REACH regulations for the identification of chemical substances. The aqueous solubility measurements are performed using the dynamic saturation method in a temperature range of [298.15 – 328.15K], those of octanol-water partition coefficient with the “shake-flask” method at 298.15K. The vapor pressure measurements are carried out with the “dynamic saturation method” in a temperature range between 313.15 and 423.15K, and validated with the static method. These measurements are used in the determination of air-water and octnol-air partition coefficients. Beside experimental measurements, these poperties are predicted using thermodynamic models: UNIFAC originale, UNIQUAC, NRTL and COSMO-sac-dsp. A qualitative and quantitative evaluation is performed for each model. This evaluation will facilitate the optimization of the models’ parameters concerning phthalates and alkyl phenols in order to generate a model for the contaminants migration process

A new approach for predicting octanol-water partition coefficients (Log P) of linear perfluorinated compounds, making use of the limited experimental data available, previous observations and the consistent similarities observed between the experimental and calculated (with electronic structure methods and using EPI suite) slopes of the linear plots of Log P values with the number of carbon atoms (N = 2 to 11) is described here. Eight families of linear organic compounds were investigated: carboxylic acids, perfluorinated carboxylic acids, sulfonic acids and perfluorinated sulfonic acids, together with their corresponding conjugate bases. To the best of our knowledge, this work reports the first application of density functional theory methods to the calculation of Log P values of perfluorinated compounds. A second part of the thesis, describes the study of the thermodynamic stability of the PFOA family of 39 structural isomers with the M06-2X, LC-ωPBE, B97D and B3LYP functionals and with the PM6 method. The PM6 results closely resemble the M06-2X results for neutral PFOAs, but greatly disagree regarding anions. The four functionals applied behave similarly from a qualitative point of view, but quantitatively speaking, the LC-ωPBE and B97D results are between the M06-2X and B3LYP stability results. M06-2X ranks highly substituted isomers as more stable than did B3LYP, and ranks less-branched isomers quite low in relative stability compared to B3LYP. Various similarities with a former PFOSs study applying the M06-2X and B3LYP functionals have been identified. The degree of branching within structural isomers cannot always be precisely determined, and is not the only aspect that determines thermodynamic stability; the pattern of substitution seems to also play a significant role. / Graduate

The proposed human intestinal absorption prediction model is applied to over 900 pharmaceuticals and has about 82.5% true prediction power. This study will provide a screening tool that can differentiate well absorbed and poorly absorbed drugs in the early stage of drug discovery and development. This model is based on fundamental physicochemical properties and can be applied to virtual compounds. The maximum well-absorbed dose (i.e., the maximum dose that will be more than 50 percent absorbed) calculated using this model can be utilized as a guideline for drug design, synthesis, and pre-clinical studies.

The principal aim of this research was to determine the optimum conditions of extraction and separation of niobium and tantalum with octanol as solvent, from Mozambican tantalite using ammonium bifluoride as an alternative to hydrofluoric acid. The extraction of niobium and tantalum from tantalite can be divided into three activities, viz., acid treatment of the ore to bring the niobium and tantalum values into solution, separation of niobium and tantalum by solvent extraction and preparation of pure niobium pentoxide and tantalum pentoxide by precipitation followed by calcination. An initial solution was prepared by melting a mixture of tantalite and ammonium bifluoride followed by leaching of the soluble component with water and separation of the solution by filtration. The solution filtered was successfully used after adjustment of the acidity for the extraction and separation of niobium and tantalum. After liquid-liquid extraction highly pure niobium pentoxide and tantalum pentoxide were obtained through precipitation with ammonium hydroxide and calcination. Comparative experiments were performed modifying the following variables: decomposition temperature; decomposition time of the digestion of niobium and tantalum; acid concentration of feed solution; solvent agent; and stripping agent. From the experimental results it was determined that the decomposition temperature, decomposition time of the digestion of niobium and tantalum, the acidity of the feed solution, the solvent agent, and stripping agent, all have an important effect on the extraction and separation of tantalum and niobium. The optimal conditions were determined to be: tantalite-to-ammonium bifluoride 1:30; decomposition temperature 250°C; decomposition time 3 hours; and a water leach period of 10 minutes. Under these conditions the leach recovery of niobium and tantalum was about 95.07% and 98.52%, respectively. For nearly complete extraction of tantalum and niobium with 2-octanol, two and three equilibrium stages, respectively, are required. The equilibrium data were obtained at an aqueous-to-organic ratio (A/O) of 1:1 using: 100% 2 octanol; 6 M H2SO4; 10 minutes contact time at room temperature for tantalum; and 100% 2 octanol, 9 M H2SO4, 10 minutes contact time at room temperature for niobium. Different stripping agents were used and water seems to give good result for both. For the nearly complete stripping process four equilibrium stages are required. From the results obtained an optimum stripping efficiency is achieved after 15 minutes for a 1:1 ratio. Niobium and tantalum were then neutralized using 28% ammonium hydroxide. The precipitate obtained was dried and placed in a muffle furnace for 4 hours at 900°C. After calcinations, pure tantalum pentoxide and niobium pentoxide were obtained and characterized using XRD and SEM. Tantalum pentoxide and niobium pentoxide synthesized contain trace impurities such as iron and titanium which can be removed by incorporating an appropriate intermediate treatment. / Dissertation (MSc)--University of Pretoria, 2012. / Chemical Engineering / unrestricted

No description available.

Solid-phase microextraction (SPME) coupled with gas chromatography/mass spectrometry (GC/MS) is routinely used to analyze polycyclic aromatic hydrocarbons (PAHs) in water. A common SPME-GC/MS approach quantifies target analytes using isotopically labeled standards (IISs); one IIS is needed for each target analyte. This approach is challenging, even prohibitive since IISs are often expensive; moreover, they are generally not available for each analyte of interest. This study developed a novel SPME-GC/MS approach for the quantification of PAHs in water. The new method, which employs only a small number of IISs, uses relative response factor (RRF) (i.e., analyte corresponding to IIS) to quantify PAHs in water. Possible matrix dependency of RRFs values was examined using water that was modified concerning different physical-chemical characteristics (i.e., ionic strength, pH, suspended solids, humic acid, and biological organic carbon represented by hemoglobin). The results revealed that RRFs are not noticeably affected by changing ionic strength and pH; the other three parameters did affect the RRFs. However, the results also showed that the effect is minimal when the solution is dilute (i.e., low concentrations of suspended solids, humic acid or hemoglobin). Relatively stable RRFs for dilute water solutions indicates that this approach can be used for routine quantification of water that does not contain prohibitive amounts of suspended solids, humic acid, and biological organic matter. The developed method was employed to quantify trace levels of PAHs in three different types of water, namely river water, well water, and bottled water. PAH levels in every kind of water were less than 100 ng/L level (i.e., 0.1 ppb). Analyses of spiked water samples containing 2 ng PAHs revealed correlations between calculated RRFs and the physical-chemical properties of the PAHs investigated (i.e., vapor pressure, boiling point, octanol/water partition coefficient, octanol/air partition coefficient, GC retention time). This implies that RRFs for PAHs not examined in this study can be predicted. Overall, the results presented herein constitute a meaningful contribution to the development of SPME-GC/MS methods for quantitative analysis of PAHs and other chemicals in dilute aqueous solutions. Moreover, the development of methods that alleviate the need for IISs corresponding to each target analyte.

El trabajo realizado en esta tesis doctoral tiene como objetivo mejorar las metodologías de la química teórica y computacional en la descripción de los efectos del entorno en sistemas químicos. La primera parte se centra en el efecto del solvente, en concreto en el desarrollo de modelos cuánticos continuos de solvatación, y en la derivación de modelos de solvatación fraccional obtenidos a partir de métodos continuos capaces de descomponer energías libres de solvatación y de transferencia entre solventes en contribuciones asociadas a fragmentos químicos de una molécula. Esto permite obtener el perfil tridimensional de las regiones hidrofóbicas/hidrofílicas de una molécula a partir de sus contribuciones fraccionales a la solvatación, siendo esta información muy útil en el establecimiento de relaciones cuantitativas estructura-actividad para el desarrollo de nuevos fármacos, o en la definiciones de índices de similaridad hidrofóbicos, basados en la similitud de este perfil tridimensional entre dos compuestos. Con este objetivo se ha parametrizado satisfactoriamente el modelo continuo MST para la predicción de coeficientes de partición octanol/agua y de energías libres de solvatación en agua, cloroformo, tetracloruro de carbono y octanol, tanto a nivel ab initio HF/6-31G(d) como a niveles semiempíricos AM1 y PM3. También se ha parametrizado el modelo MST para el estudio de especies iónicas en solución. Finalmente, se ha llevado a cabo una comparación entre la respuesta electrostática obtenida a partir de diferentes modelos continuos SCRF (MST, SM5.42R y MPE), ilustrando las grandes diferencias que se pueden encontrar entre las contribuciones electrostáticas y no electrostáticas según sea el modelo usado, y poniendo así de manifiesto la estrecha relación que hay que considerar entre estas contribuciones a la solvatación y la parametrización específica de cada modelo continuo. La metodología de solvatación fraccional usada ha permitido además ilustrar la dependencia de estas contribuciones fragmentales respecto a efectos electrónicos, estéricos o tautoméricos. La segunda parte de este trabajo se centra en el desarrollo de metodologías eficientes y precisas para la descripción de las fuerzas de polarización en campos de fuerzas clásicos. Se han estudiado dos metodologías, una basada en un tratamiento implícito de estas fuerzas a partir de un modelo de doble carga, que permite describir satisfactoriamente la distribución de carga de una molécula en un entorno aislado, y frente a la acción de un campo externo, respectivamente, permitiendo reproducir de forma adecuada las energías de polarización para una serie de complejos por puente de hidrógeno y catión-pi. También se ha estudiado la inclusión de los efectos de polarización mediante dipolos puntuales inducidos. En este sentido, se ha profundizado en una metodología capaz de obtener modelos distribuidos de polarizabilidades atómicas isotrópicas muy eficiente computacionalmente y que permite reproducir de forma precisa la polarizabilidad global de las moléculas para la serie de derivados bencénicos estudiados, así como la contribución de polarización en sus energías de interacción catión-pi con un catión de sodio. / The objective of this work is the improvement of the methodologies available in the field of theoretical and computacional chemistry for the description of the effects of environment in chemical systems.First, it is presented a set of studies on the effect of the solvent, in particular on the development of quantum continuum solvation models and the decomposition of free energies of solvation and transfer into contributions associated to chemical fragments of a molecule. In this way, it can be obtained a 3D picture of the hydrophobic/hydrophylic regions of a molecule, and this information is very valuable in the establishment of quantitative structure-activity relationships for the development of new drugs, and permits also the definition of a hydrophobic similarity index based on the the hydrophobic profile of two different compounds. The parametrization of the MST model presented is able to satisfactorily reproduce octanol/water partition coefficients and free energies of solvation in water, chloroform, carbon tetrachloride and octanol, both at the ab initio HF/6-31G(d) and semiempirical AM1 and PM3 levels of theory. The hydration of ionic species has also been revised in the framework of the MST model. Finally, a comparison of the electrostatic response obtained from different SCRF continuum models (MST, SM5.42R and MPE) is presented. A different balance between the electrostatic and nonelectrostatic contributions has been obtained from the different models, and show that it is necessary to mantain a close correspondece between each SCRF formalism and the specific details of its parametrization. Finally, the transferability of fragmental contributions to solvation has been explored. The second part of this work is aimed at the development of efficient methodologies for the description of polarization forces in classical force fields. Two methodologies has been explored. The first is based on an implicit treatment of these forces through a dual charge model, that represent the charge distribution of a molecule alone and in response to an external field, respectively. Finally, the explicit treatment of polarization effects through induced point dipoles has been studied. In particular, it has been explored an efficient methodology to obtain distributed models of atomic isotropic polarizabilities.