The effect of pH and ionic strength on the equilibrium adsorptive behavior of β-lactoglobulin onto hydrophobic and hydrophilic silicon surfaces was studied using ellipsometry. Plots of amount adsorbed (μg protein/cm²) as a function of protein concentration (mg/ml) exhibited attainment of plateau values beyond a protein concentration of 0.250 mg/ml. At a given pH and ionic strength, plateau values associated with hydrophobic surfaces were observed to be greater than those associated with hydrophilic surfaces. The Langmuir adsorption isotherm was chosen as the most appropriate model to represent the data and was used to compare results obtained under different experimental conditions. Effects of pH and ionic strength on protein adsorption at hydrophilic surfaces indicate that electrostatics played a major role, while pH and ionic strength effects on adsorption to hydrophobic surfaces reflect a greater importance of nonelectrostatic interactions. / Graduation date: 1991

While assessment of folate requirements has been based only on dietary intakes, folate produced by the colonic microflora can exceed amounts consumed in food. Bacterially synthesized folate is absorbed across the rat and piglet colon. In vitro studies suggest, but direct evidence is lacking that folate is absorbed across the intact human colon. If indeed folate is absorbed, the amount synthesized may be susceptible to manipulation by fibre and prebiotics intake. We therefore performed two studies to investigate folate absorption across the colon. To confirm absorption across the intact human colon, in our first study, 684 nmol (320 µg) 13C5-glutamyl-[6S]-5-formyltetrahydrofolate was infused into the cecum of six adults and blood samples were collected. Tandem mass spectrometry confirmed folate absorption across the colon by appearance in plasma of 13C5-[6S]-5-methyltetrahydrofolate, at a rate of 0.6±0.2 nmol/h versus 7±1.2 nmol/h after intravenous injection of 172 nmol 13C5-5-formyltetrahydrofolate. Since bifidobacteria are potent folate producers, in our second study we evaluated the influence of bifidogenic oligosaccharides on colonic folate production and host folate status, using a piglet animal model. Piglets (n=12) were randomly assigned a milk-based formula with 5g/L inulin + 5g/L galactooligosaccharides, or 5g/L maltodextrin (control). After 28 days, the weights of colon contents (178 %) and colon tissue (37.9 %) of piglets fed oligosaccharides were greater than controls (P=0.0003, P=0.0044, respectively). The bacterial load and folate contents in the colons of piglets fed oligosaccharides were greater than controls (P=0.0022, P=0.0218, respectively). Body weights, blood folate status and liver and kidney folate concentrations did not differ. In conclusion, folate is absorbed across the human colon. Supplementation of the piglet diet with 5g/L inulin and 5g/L galactooligosaccharides increased the amounts of microbial folate, and the weights of colon tissue and contents, but folate concentrations in colon contents, blood and organs were not affected.

Fundamental questions related to the locations of Cerebrospinal Spinal Fluid (CSF) absorption deficit and causes of the pressure gradients that expand the ventricles with hydrocephalus remain largely unanswered. Work in the Johnston lab over a 15 year period has demonstrated that CSF moves through the cribriform plate foramina in association with the olfactory nerves and is absorbed by a network of lymphatic vessels located within the olfactory turbinates. A kaolin-based rat model of communicating hydrocephalus was developed as a collaborative effort with Drs. McAllister, Wagshul and Li. After developing a method to quantify lymphatic CSF uptake in rats, we examined and observed that the movement of a radioactive tracer into the nasal turbinates was significantly reduced in the kaolin-injected animals compared to saline injected controls. However, it was possible that while lymphatic CSF uptake was compromised, other CSF absorption pathways may have compensated. To answer this, we measured the CSF outflow resistance (Rout) and observed it to be significantly greater in the kaolin group compared with animals receiving saline and there was a significant positive correlation between CSF Rout and ventricular volume. Nonetheless, it is not clear how impaired CSF clearance could lead to a dilation of the ventricles since the ventricular and subarachnoid compartments are in communication with one another and pressure would likely increase equally in both. At this point, we came across a theoretical paper that postulated that a drop in periventricular interstitial fluid pressure might provide an intraparenchymal pressure gradient favouring ventricular expansion. In addition, studies in non-CNS tissues indicated that a disruption of beta-1 (β1) integrin-matrix interactions could lower tissue pressure. Based on these suppositions and data, we examined if these concepts had relevance to the brain. For this, we measured pressure in the brain and observed a decline in periventricular pressures to values significantly below those monitored in the ventricular system following the injection of the anti integrin antibodies. Many of the animals developed hydrocephalus over 2 weeks post antibody injection. These data provide a novel mechanism for the generation of intraparenchymal pressure gradients that is likely contributing to ventricular expansion.

Chronic arsenic poisoning due to arsenic contamination of groundwater is a serious public health problem in Bangladesh and neighboring countries. Severe health effects associated with chronic exposure to arsenic include melanosis and several kinds of cancer. It is now generally agreed that the arsenic contamination of groundwater in Bangladesh is of geological origin. Arsenic naturally present in aquifers may be mobilized into drinking water by microbial action.<p> The formation of a novel arsenic-selenium compound: seleno-bis (S-glutathionyl) arsinium ion, [(GS)2AsSe]-, and its subsequent excretion in rabbit bile has been demonstrated previously. This molecular basis for the in vivo antagonism between arsenic and selenium was discovered using X-ray absorption spectroscopy. There is growing evidence that, in Bangladeshi people who are suffering long term chronic lowlevel arsenic poisoning, this antagonism is causing a selenium deficiency. Administering selenium supplements might provide a simple but highly effective treatment of the Bangladeshi arsenic poisoning.<p> In order to examine the disposition of [(GS)2AsSe]-, a set of rabbits were intravenously injected with selenite, arsenite or both. Whole blood, red blood cell and plasma samples were collected at different time intervals within 2hrs after injection and cecotrope samples 24hr after injection. Samples were examined using X-ray absorption spectroscopy and both arsenic and selenium K-near edge spectra were recorded.<p> iii Speciation of arsenic and selenium will be discussed in this thesis. Results indicate that [(GS)2AsSe]- is formed in blood very rapidly after injection of both arsenite and selenite, and then is removed from blood stream within 2hrs post injection. Results also show that [(GS)2AsSe]- is assembled in red blood cells, with no [(GS)2AsSe]- detected in plasma samples. [(GS)2AsSe]- is also found in cecotrope samples after injection of both arsenite and selenite.<p> The results of this study in rabbits will contribute to the understanding of chronic arsenic poisoning in humans.

The desire for low cost electronics has led to a huge increase in research focused on organic materials. These materials are appealing due to their unique electrical and material-processing properties and are rapidly being adopted in old and new electronic applications. To create practical devices requires a further understanding of the charge transport properties of the unique anisotropic molecular crystal structures. This work looks at how doping with the transition-metal element manganese can alter the electronic structure of the organic material pentacene. It has been found that using manganese as a dopant provides novel physical characteristics previously not encountered in organic field effect transistors based on pentacene. These organic thin films were characterized using X-ray absorption spectroscopy and the results compared to computational density functional theory analysis.

While assessment of folate requirements has been based only on dietary intakes, folate produced by the colonic microflora can exceed amounts consumed in food. Bacterially synthesized folate is absorbed across the rat and piglet colon. In vitro studies suggest, but direct evidence is lacking that folate is absorbed across the intact human colon. If indeed folate is absorbed, the amount synthesized may be susceptible to manipulation by fibre and prebiotics intake. We therefore performed two studies to investigate folate absorption across the colon. To confirm absorption across the intact human colon, in our first study, 684 nmol (320 µg) 13C5-glutamyl-[6S]-5-formyltetrahydrofolate was infused into the cecum of six adults and blood samples were collected. Tandem mass spectrometry confirmed folate absorption across the colon by appearance in plasma of 13C5-[6S]-5-methyltetrahydrofolate, at a rate of 0.6±0.2 nmol/h versus 7±1.2 nmol/h after intravenous injection of 172 nmol 13C5-5-formyltetrahydrofolate. Since bifidobacteria are potent folate producers, in our second study we evaluated the influence of bifidogenic oligosaccharides on colonic folate production and host folate status, using a piglet animal model. Piglets (n=12) were randomly assigned a milk-based formula with 5g/L inulin + 5g/L galactooligosaccharides, or 5g/L maltodextrin (control). After 28 days, the weights of colon contents (178 %) and colon tissue (37.9 %) of piglets fed oligosaccharides were greater than controls (P=0.0003, P=0.0044, respectively). The bacterial load and folate contents in the colons of piglets fed oligosaccharides were greater than controls (P=0.0022, P=0.0218, respectively). Body weights, blood folate status and liver and kidney folate concentrations did not differ. In conclusion, folate is absorbed across the human colon. Supplementation of the piglet diet with 5g/L inulin and 5g/L galactooligosaccharides increased the amounts of microbial folate, and the weights of colon tissue and contents, but folate concentrations in colon contents, blood and organs were not affected.

Fundamental questions related to the locations of Cerebrospinal Spinal Fluid (CSF) absorption deficit and causes of the pressure gradients that expand the ventricles with hydrocephalus remain largely unanswered. Work in the Johnston lab over a 15 year period has demonstrated that CSF moves through the cribriform plate foramina in association with the olfactory nerves and is absorbed by a network of lymphatic vessels located within the olfactory turbinates. A kaolin-based rat model of communicating hydrocephalus was developed as a collaborative effort with Drs. McAllister, Wagshul and Li. After developing a method to quantify lymphatic CSF uptake in rats, we examined and observed that the movement of a radioactive tracer into the nasal turbinates was significantly reduced in the kaolin-injected animals compared to saline injected controls. However, it was possible that while lymphatic CSF uptake was compromised, other CSF absorption pathways may have compensated. To answer this, we measured the CSF outflow resistance (Rout) and observed it to be significantly greater in the kaolin group compared with animals receiving saline and there was a significant positive correlation between CSF Rout and ventricular volume. Nonetheless, it is not clear how impaired CSF clearance could lead to a dilation of the ventricles since the ventricular and subarachnoid compartments are in communication with one another and pressure would likely increase equally in both. At this point, we came across a theoretical paper that postulated that a drop in periventricular interstitial fluid pressure might provide an intraparenchymal pressure gradient favouring ventricular expansion. In addition, studies in non-CNS tissues indicated that a disruption of beta-1 (β1) integrin-matrix interactions could lower tissue pressure. Based on these suppositions and data, we examined if these concepts had relevance to the brain. For this, we measured pressure in the brain and observed a decline in periventricular pressures to values significantly below those monitored in the ventricular system following the injection of the anti integrin antibodies. Many of the animals developed hydrocephalus over 2 weeks post antibody injection. These data provide a novel mechanism for the generation of intraparenchymal pressure gradients that is likely contributing to ventricular expansion.

En esta tesis se analiza de manera detallada los sistemas de refrigeración solar con equipos de absorción de doble efecto con captadores solares de concentración en términos de energía primaria consumida. El análisis de estos sistemas permite compararlos con sistemas de refrigeración por absorción de simple efecto accionados con energía solar térmica de baja temperatura y con sistemas convencionales de compresión. Estos tres tipos de sistemas han sido modelizados mediante el software de simulación TRNSYS para cubrir la demanda frigorífica de un edificio genérico de oficinas localizado en Sevilla (España). Un aspecto importante en esta tesis es la modelización de las enfriadoras de absorción de simple y doble efecto mediante el método de la ecuación característica. Este método permite modelizar las prestaciones térmicas del equipo de absorción de manera sencilla y robusta, además que debido a su estructura puede ser aplicado a cualquier sistema de refrigeración por absorción. / This thesis presents a detailed analysis of solar cooling systems, with double-effect absorption chillers activated by concentrating solar collectors, in terms of primary energy savings. This analysis allows comparing this type of systems with solar assisted air-conditioning installations composed by single-effect absorption chillers and flat plate solar collectors, and conventional compression systems. These three types of systems have been modeled in a TRNSYS simulation environment and applied to a generic building located in the city of Seville (Spain) to cover its cooling demand. An important aspect of this thesis is the modeling of single and double-effect absorption chillers by means of the characteristic equation method (ChEM). This method permits modeling of thermal performance of the absorption machine in a simple and robust manner, and due to its structure, the method can be applied to any absorption refrigeration system.

The desire for low cost electronics has led to a huge increase in research focused on organic materials. These materials are appealing due to their unique electrical and material-processing properties and are rapidly being adopted in old and new electronic applications. To create practical devices requires a further understanding of the charge transport properties of the unique anisotropic molecular crystal structures. This work looks at how doping with the transition-metal element manganese can alter the electronic structure of the organic material pentacene. It has been found that using manganese as a dopant provides novel physical characteristics previously not encountered in organic field effect transistors based on pentacene. These organic thin films were characterized using X-ray absorption spectroscopy and the results compared to computational density functional theory analysis.

Chronic arsenic poisoning due to arsenic contamination of groundwater is a serious public health problem in Bangladesh and neighboring countries. Severe health effects associated with chronic exposure to arsenic include melanosis and several kinds of cancer. It is now generally agreed that the arsenic contamination of groundwater in Bangladesh is of geological origin. Arsenic naturally present in aquifers may be mobilized into drinking water by microbial action.<p> The formation of a novel arsenic-selenium compound: seleno-bis (S-glutathionyl) arsinium ion, [(GS)2AsSe]-, and its subsequent excretion in rabbit bile has been demonstrated previously. This molecular basis for the in vivo antagonism between arsenic and selenium was discovered using X-ray absorption spectroscopy. There is growing evidence that, in Bangladeshi people who are suffering long term chronic lowlevel arsenic poisoning, this antagonism is causing a selenium deficiency. Administering selenium supplements might provide a simple but highly effective treatment of the Bangladeshi arsenic poisoning.<p> In order to examine the disposition of [(GS)2AsSe]-, a set of rabbits were intravenously injected with selenite, arsenite or both. Whole blood, red blood cell and plasma samples were collected at different time intervals within 2hrs after injection and cecotrope samples 24hr after injection. Samples were examined using X-ray absorption spectroscopy and both arsenic and selenium K-near edge spectra were recorded.<p> iii Speciation of arsenic and selenium will be discussed in this thesis. Results indicate that [(GS)2AsSe]- is formed in blood very rapidly after injection of both arsenite and selenite, and then is removed from blood stream within 2hrs post injection. Results also show that [(GS)2AsSe]- is assembled in red blood cells, with no [(GS)2AsSe]- detected in plasma samples. [(GS)2AsSe]- is also found in cecotrope samples after injection of both arsenite and selenite.<p> The results of this study in rabbits will contribute to the understanding of chronic arsenic poisoning in humans.