Molecular dynamics (MD) is a computer simulation of physical movements of atoms and molecules. MD has now been widely used in materials, biochemical and pharmaceutical research. In recent years, zirconium phosphate (ZrP) compounds developed a new type of multi-function mediated porous materials, which the crystalline £\-zirconium phosphate (£\-ZrP) is a cationic layered compounds, with a neat layer structure and easy to design. Cetyl trimethyl ammonium bromide (CTAB) is a cationic surfactant, it¡¦s one kind of ammonium salt of a long carbon chain as hydrophobic groups. Ion exchange can occur with other exchangeable cations. In this study, we first use CTAB inserted into £\-ZrP interlayer to prepare £\-ZrP-CTAB material. Second, we add phenol solution in the system, and use molecular dynamics simulations to observe the solution¡¦s penetration and adsorption. The result shows that pure water can permeate through £\-ZrP CTAB membrane, and pure phenol will be adsorbed by the £\-ZrP-CTAB membrane. If we add phenol solution, the water molecules can pass through the £\-ZrP-CTAB membrane but phenol molecule can¡¦t. It can achieve the effect of separation of the mixed solution. Last we simulate phenolate solution system. The result shows that the number of phenolate molecule enter the membrane is less than phenol molecule in phenol solution. This result is also consistent with the experiments mentioned in the literature.

Bacteriophage holins are a diverse group of proteins that are responsible for the spontaneous and specifically-timed triggering of host cell lysis. The best-studied holin, S105 of phage lambda, is known to form lesions, or “holes”, in the inner membrane of E. coli which are large enough to allow the endolysin through to the periplasm. S105 has been studied extensively by both genetic and biochemical approaches; however, little is known about the mechanism of hole formation or the structure of the lambda holin and its inner membrane lesion. An in vitro system for reconstituting hole formation by S105 was developed in which liposomes containing a self-quenched fluorophore served as artificial cell membranes (1-2). Upon delivery of solubilized S105 to the liposomes, an increase in fluorescence was observed, indicating that the fluorophore within the liposomes had escaped into the surrounding media via an S105-mediated hole in the membrane. This in vitro system, which has been optimized in this work, has been a valuable biochemical tool for analysis and reconstitution of the pathway to S105 hole formation in the cell membrane. Due to the difficulty associated with over-expression and purification of toxic membrane proteins, there are no solved structures of bacteriophage holins. Sample preparation and experimental conditions for NMR spectroscopy were optimized and structural information about a lambda holin mutant protein was obtained. Specifically, micellar contacts of transmembrane domain regions versus water contacts of the C-terminal region, secondary structure, and backbone dynamics were determined. Cryo-electron microscopy was used to visualize the inner membrane lesions formed by phage holins [lambda] S105, P2 Y, and T4 T. Therefore, the large holes initially seen in cells expressing S105 are not specific to the lambda holin, nor to class I holins. The S105 holes average ~340 nm (3), and are the largest membrane lesions ever observed in biology. They are stable at their original size, and are not localized to a specific region of the membrane. In addition, missense mutants of S105 were used to correlate hole size, protein accumulation, and lysis timing in a current model for the S105 hole formation pathway.

The experimental tests and analysis of a fuel cell unit and a 150 W fuel cell stack are performance in this research. The experimental items in this study are various the types of flow channels, fasten torque, inlet gas pressure, Pt loading density, oxidizers, electron collector type etc. Through above a series of the tests, we can understand the key factors which influence the performance of the PEMFC. The experimental results can also provide us references when one assemble a fuel cell stack in future. PEMFC can start quickly at low temperature and achieves stable output voltage. When the 8 N-M torque is applied to fasten the reaction chamber, the contact resistance between electrode and electron collector reaches a minimum value. By designing the flow channel properly, the membrane hydration can remain a good state so that the conductivity of the proton exchange membrane can not be hinder. We found that the optimum channel among three types of the test channels is the conventional channel with the rib width 2 mm. When the output power is largest. Our experiments display that the increase of Pt loading in cathode can improve PEMFC performance. At certain voltage, there is a critical value in Pt loading. PEMFC performance can not be improved when Pt loading increases over this value. When the inlet pressure in cathode side increase to 10~20 psi higher than the pressure in anode side, the output power can improve apparently. Keyword: Proton exchange membrane, Pt loading, electron collector.

The research of a hydrogen proton exchange membrane fuel cell is performed under certain designing and operational conditions. The water management technique is incorperated into the experimental work. The cell voltage vs. the current densities are studied by changing the stack reactive temperatures, the gas inlet temperatures and pressures, and the relative humidities in hydrogen stream. Eventually, we hope that these experimental results can provide the information about the optimizing conditions of fuel cells so that they can be used to design a high power multiple-cell fuel cell stack. A membrane and electrode assembly (called MEA) which contains a proton exchange membrane Nafion 112, anode catalyst Pt 0.4 mg/cm2, and cathode catalyst Pt 1.0 mg/cm2 is used in this experiment. The gas flowing area is about 58% of the total area. A proper heating and humidification equipment is applied in this experimental system. The experimental results show that the cell voltage at low current density is slightly influenced by the hydrogen inlet temperature; however, the cell voltage at high current density is strongly influenced by the humidity ratio of hydrogen stream. Raising the hydrogen pressure and the oxygen pressure at the same time can increases the cell voltage, but it is no obvious effects on the cell voltage when the gas pressure increases to more than 2 atm. When air is used as a oxidizer, increasing the inlet air temperature always reduces the cell voltage. With the hydrogen stream at saturated temperature 80¢XC, the assembly torque of the stack at 4 N-m, and the stack temperature at 80¢XC, the single fuel cell stack can always generate the best cell voltages at most of the current densities. At this time, the cell voltage at current density 1 A/cm2 already can reach a value higher than 0.6 V.

Abstract The characteristics of PEMFC stacks in different designs and operational conditions are studied and manufactured in this thesis. There are many factors that affect the PEMFC performance. They include the familiar humidity, the torque, the inlet pressure, the geometries of inlet ports and the flow channels in reaction regions, the cell numbers of the stacks, the type of the oxidizer and its flow rate. To understand the performance characteristics of stacks the voltage and current density will be measured as well as the interior temperature of stacks in this research. The membrane exchange assembly (MEA) with Nafion 112, anode Pt 0.4 mg/cm² and cathode Pt 1.0 mg/cm² is used in these experimental works. The experimental results display that increasing the applied torque will reduce the contact resistance between bipolar plate and diffusion layer but increase the difficulty of gas penetrating into the reaction region beneath the bipolar rib. So proper torque is necessary to obtain the best voltage output. The voltage vs. current density also increases as the inlet pressure increases, but its effect will reduce when the inlet pressure increases over 2atm. The geometry and size of inlet port to each cell for a multi-cell stack will influence the voltage output, especially in high current density, so that special attention is needed in designing inlet port. When the air is used as an oxidizer, the fan with a high rotation speed is helpful in an open circuit design. The high air volume flow rate can avoid that the voltage output decays greatly in high current density. Increasing the cell number may cause extra internal resistance due to assembling improperly and reduce the voltage output. So special attention is also needed in assembling. Keyword: Proton Exchange Membrane Fuel Cell Stacks

Nearly five million Americans are living with heart failure and 550,000 new cases are diagnosed each year in the US. Amongst the new approaches to develop a better solution for Congestive Heart Failure, Ventricular Recovery (VR) holds the most promise. A team, under the guidance of Dr. Criscione in the Cardiac Mechanics Lab at Texas A&M University, is currently developing an investigative device which aims to assist in VR by restoration of physiological strain patterns in the myocardial cells. The contribution of this thesis has been towards the development of a molding apparatus that yields a polymeric membrane whose shape, when inflated, is similar to the shape of the human heart. This membrane would surround the epicardial surface of the heart, when used for the device being discussed and in particular for the prototypes being developed. Contribution also includes a testing apparatus that measures the inflation of a membrane and simulation to predict the behavior of isotropic ellipsoids upon inflation. After unsuccessful implementations of two processing techniques, the successful design, fabrication implementation and attachment method meets the design criteria and is based on a thermoforming technique. Inflation profiles for membranes developed using this technique were studied at different pressures, with the axis length as variable. At 1kpa, which is the normal coronary arterial pressure, the membrane with an axis length of 140mm was found to show a shape which is similar to the shape of the human heart. In order to better understand and predict the shape an isotropic ellipsoidal membrane would take upon inflation without experimentation, simulations were carried out. Successful conversion of ellipsoidal geometry, with a few degrees of freedom as parameters, aided in simulation.

During co-translational integration, the transmembrane (TM) sequence of a nascent membrane protein moves laterally into the ER lipid bilayer upon reaching the translocon. Our lab has previously shown that this movement is a multistep process, but it was not clear whether the observed photocrosslinking of the TM segment to translocon proteins resulted from specific interactions or simply from TM-translocon proximity. If the latter, the TM α-helix will be oriented randomly with respect to translocon proteins, whereas, if the former, a specific TM helix surface would face TRAM and/or Sec61α. Integration intermediates were prepared by in vitro translation of truncated mRNAs in the presence of a Lys-tRNA analog with a photoreactive moiety attached to the lysine side-chain. When photoadduct formation was monitored as a function of probe location within the TM α-helix, we found that the extent of photocrosslinking to TRAM and Sec61α was non-random. Thus, the TM sequence occupies a distinct location within the translocon, a result that can only be achieved through protein-protein interactions that mediate the lateral movement, positioning, and integration of the TM sequence. In the case of multi-spanning membrane proteins, it was unknown how multiple hydrophobic regions integrated into the ER membrane. By placing photoprobes within each of several TM domains of a multi-spanning membrane protein, we were able to determine at what stage of integration each TM segment was no longer adjacent to translocon proteins. Using this approach we were able to establish a mechanism of integration for multi-spanning membrane proteins co-translationally inserted into the ER membrane.

Produced water is a major waste produced from oil and natural gas wells in the state of Texas. This water could be a possible source of new fresh water to meet the growing demands of the state after treatment and purification. This thesis describes a research project that evaluated the treatment of brine generated in oil fields (produced water) with ultrafiltration membranes. The characteristics of various ultrafiltration membranes for oil and suspended solids removal from produced water were studied to test whether they could be used in a pretreatment method. The research measured the effect of pressure and flow rate on performance of three commercially available membranes for treatment of oily produced water. Oil and suspended solids removal were measured by using turbidity and oil in water measurements taken periodically. The study also analyzed the flux through the membrane and any effect it had on membrane performance. The research showed that an ultrafiltration membrane provided turbidity removal of over 99% and oil removal of 78% for the produced water samples. The results indicated that the ultrafiltration membranes would be useful as one of the first steps in purifying the water. Membrane cleaning of produced water-fouled membranes by micellar solutions was investigated. A neutral pH and ambient temperature micelle solution for effective cleaning of oily water-fouled membranes was developed and studied. The performance of cleaning solutions on ultrafiltration membranes was investigated on laboratory size membrane testing equipment. Different micro emulsion solutions were studied to evaluate the effect of solution properties on cleaning performance. Three types of multiple membranes were studied, each having the same polyvinylidene fluoride (PVDF) material but with different nominal separation or flux characteristics. The data showed that the use of a micelle solution to clean the produced water-fouled membranes was a feasible and effective method. The study showed with further adjustment of the micelle solution the cleaning effectiveness could be optimized to provide double the effectiveness of current industry methods for membranes fouled by produced water.

Efficient separation of target protein from impurities is crucial in bioseparation for large scale production and purity of the target protein. Two separation process approaches were considered in this study. The first approach focused on identifying major impurity and optimization of solution properties for target protein purification. The second approach consisted of designing an adsorbent that interacted specifically with the target molecule. The first study included modification of protein solution properties (pH, ionic strength, buffer ions) in order to maximize lysozyme purification by a strong cation exchange resin. The interaction of phytic acid, a major impurity, present in transgenic rice extracts, that contributes to decreased lysozyme adsorption capacity on SP Sepharose was evaluated. The target protein was lysozyme, which is used in a purified form as a baby formula additive to reduce gastrointestinal tract infections. At constant ionic strength, lysozyme in pH 4.5 acetate buffer had a higher binding capacity and stronger binding strength than at pH 6.0. Lysozyme in sodium phosphate buffer of pH 6.0 exhibited lower adsorption capacity than in pH 6 Tris buffer. Binding capacity and strength were significantly affected by phytic acid in all studies buffers. The second study consisted of surface modification of microfiltration membranes for protein purification and separation and reduces fouling. This study describes adsorption and fouling of chemically modified microfiltration membranes with bovine serum albumin (BSA) and immunoglobulin G (IgG). Least fouling resulted with polyethylene glycol (PEG) membranes when BSA protein was used. Amine-functionalized membranes showed specific interaction with BSA. There was multi-layer deposition of IgG on amine-functionalized membrane. G3 membrane synthesized to selectively bind IgG seemed a noble option to separate IgG from a protein mixture.

Although a long standing convention maintained that G Protein Coupled Receptors (GPCRs) exist in the plasma membrane solely as monomers, substantial work over the last two decades has demonstrated that these ubiquitous receptors can and in many cases, preferentially, exist as homodimers, heterodimers, or higher order oligomers. Often, two GPCRs of the same class heterodimerize; it is less common for two GPCRs of different signaling pathways to interact. The work presented here studied the physical and functional interaction of two GPCRs from discrete classes, the Beta 2 Adrenergic Receptor (β2AR), a Gαs-coupled receptor, and Bradykinin type 2 Receptor (Bk2R), a Gαq coupled receptor. These data show that Bk2R and β2AR are physically coupled when heterologously expressed in Xenopus oocytes, and in pheochromocytoma (PC12) cells and in freshly isolated murine ventricular myocytes, two systems that endogenously express these receptors. This physical coupling led to functional consequences in heterologous and endogenous expression systems, as Bk2R was able to transactivate β2AR signaling via its direct interaction with the receptor. Furthermore, coexpression of Bk2R shifted the dose response curve of β2AR for its selective agonist rightward in Xenopus oocyte electrophysiology experiments, suggesting the presence of Bk2R negatively affected β2AR native pharmacology. Up to thirty minutes of either bradykinin (BK) or isoproterenol exposure did not change the relative amount of Bk2R/β2AR heterodimer in PC12 cells, a rat adrenal medulla tumor cell line that endogenously expresses these receptors. Despite the obvious signaling consequences, the Bk2R/β2AR heterodimer accounted for only 10% of the total β2AR protein detected and 20% of the total Bk2R protein detected. When other Bk2R-specific ligands were also tested to examine the extent of β2AR transactivation, our data showed that both Lys-des-Arg-Bradykinin, a Bk2R partial agonist and NPC 567, a Bk2R antagonist, transactivated β2AR to the same extent as BK. Taken together, our data provide a novel mode of receptor regulation and signaling via Bk2R/β2AR heterodimerization. Because a large percentage of therapeutics target GPCRs, a greater understanding of how a GPCR heterodimer functions could be beneficial for targeting new drugs and refining existing drugs. Understanding the Bk2R/β2AR heterodimer provides a new perspective on the myriad of fucntional consequences that occur when a GPCR is activated.