Graphene, often known as a wonder material due to its remarkable properties, is the thinnest membrane available to us. In this project we have synthesised and characterised different types of graphene membranes and graphene-based membranes. Firstly, we have developed a simple fabrication technique to produce pressurised single-layer graphene membranes that can hold up to reversible strain of ~2%. The graphene balloons were investigated by Raman Spectroscopy: red shift of Raman peaks was observed with increasing strain, in good agreement with theoretical calculation. [2] Also, a characteristic broadening of the Raman peaks is observed beyond 1% strain, which has been attributed to nanoscale strain variations in the membranes. Another type of graphene-based membrane is prepared by assembling millions of tiny graphene flakes together into a laminate. Liquid-phase exfoliation is used to disperse graphene nanoflakes in a solution [3]; the dispersion is then deposited as a laminate by simple fabrication techniques such as drop casting. Because the properties of a graphene laminate strongly depend on the flake size and thickness distribution in the dispersion, it is important to be able to characterise LPE graphene. Here, we have developed a simple qualitative protocol based on Raman spectroscopy to characterise this materials. This protocol was first validated in two works, aimed at studying the enhancement of the yield of LPE graphene using two different stabilisers, n-octylbenzene and perchlorocoronene. We then applied our method to graphene/PIM-1 composite membrane. PIMs are a new class of polymers showing great potential in separation applications. An improvement in the performance of the membrane (e.g. permeability) is expected by adding graphene as a nanofiller. However, little is experimentally known about how the material disperses in PIM. Our results show that Raman spectroscopy is able to identify the presence of re-aggregated graphene-based materials in the composite. This is expected to produce strong changes in the mechanical properties and the physical ageing of the membrane. Lastly, we demonstrated fabrication of self-catalytic reactor membrane composed of graphitic carbon nitride (g-C3N4). Simple LPE and vacuum filtration techniques are employed, maximising the surface area and exposure of the active sites. The g-C3N4 membrane showed significantly enhanced catalytic performance compared to the bulk g-C3N4, achieving ~100% conversion efficiency for photo-degradation of several organic dyes. In conclusion, we investigated different types of graphene-based membranes, showing that LPE is simple technique with high versatility for different applications and Raman spectroscopy is a powerful technique for characterisation of graphene in all cases.

Dry/CO2 reforming is one the hydrocarbon processes that recently has been interesting due to it is ability of producing a lower synthesis gas ratio (H2/CO). This synthesis gas is a highly significant product since it costs more than 50% of the total capital cost of gas to liquid (GTL) process. However, since this reaction is thermodynamically limited, higher temperature or lower pressure is required to achieve higher conversion. Typically, reaction temperatures between 1073 and 1173 K are used for catalytic dry reforming reactions. Consequently, these extreme temperatures lead to a severe carbon deposition causing a catalyst deactivation which is the major difficulty related to CO2 reforming reaction. This has pushed the efforts to be focused mainly on the development of new catalysts. In fact, dry reforming of propane is an equilibrium-limited reaction which can be shifted to the product side by removing one of the products out of the system which can be achieved using a selective membrane reactor. This research is dedicated to investigate and study the catalytic performance of dry reforming of propane over cobalt-nickel catalyst under the temperature range of 773-973 K. This bimetallic catalyst supported on ??-Al2O3 has been utilized in this research since it exhibits better activity, selectivity, and deactivation resistance than monometallic catalysts. Based on this, the primary aims of this thesis are to examine this catalyst and to study the impact of using membrane reactor. In addition, the reaction mechanism and kinetic are investigated using a fixed-bed reactor. Experimental observations have exposed that the catalyst is offering good results under this reaction. The catalysts analysis has confirmed the presence of metal oxides in the catalyst. However, only at a lower carbon dioxide to propane ratio, i.e. lower than 3.5, a carbon signal has been reported. The activation energy study indicates that the process is unlimited by diffusion. The reaction order for propane and carbon dioxide has been found to be zero and 1.17 respectively. This in turn has indicated that C3H8 activation reaction is taking place rapidly and carbon dioxide is suggested to be involved in the rate determining step. In membrane reactor operation, the production rates for H2 and CO have been reported to increase as the sweep gas flow rate increases. The co-current mode offers higher production rate and more stability than counter-current mode over the range of feed ratio. On the other hand, fixed bed reactor shows stable performance and produces more CO and H2 for both modes.

Thesis (Ph. D.)--Ohio State University, 2006. / Full text release at OhioLINK's ETD Center delayed at author's request

Le lysosome est un organite acide qui contient de nombreuses hydrolases responsables de la dégradation d’une grande variété de molécules issues majoritairement des voies d’endocytose et d’autophagie. La membrane de l’organite contient, elle aussi, un certain nombre de protéines qui assurent diverses fonctions telles que la génération d’un gradient de pH intralysosomal, la translocation de produits de dégradation vers le cytosol, la régulation des contacts membranaires, etc. Cependant, au vu de la grande diversité des produits générés par l’hydrolyse intralysosomale et susceptibles d’être transportés vers le cytosol, et de la complexité des mécanismes de contact/fusion/fission qui impliquent la membrane lysosomale, il est hautement probable que de nombreuses protéines membranaires restent à être identifiées. Nous avons mis en évidence un nouveau candidat membranaire lysosomal au cours d’une analyse protéomique réalisée sur des fractions enrichies en membranes de lysosomes. Cette protéine de 372 acides aminés, que nous avons dénommée p40, présente de nombreux segments transmembranaires prédits, quatre motifs potentiels d’adressage aux lysosomes et une homologie de séquence partielle avec des transporteurs de sucres nucléotidylés. Nous avons recherché la localisation de p40 dans la cellule par des techniques de fractionnement subcellulaire, appliquées sur le foie de souris. Nous avons comparé la distribution de cette protéine au sein des fractions obtenues par centrifugation différentielle et par centrifugation isopycnique sur un gradient continu de saccharose (avec et sans traitement préalable de la souris avec du Triton WR-1339) à celles de protéines marqueurs des organites. Nous avons combiné cette approche à une analyse morphologique par microscopie à fluorescence confocale de la localisation de p40 dans des cellules eucaryotes transfectées. Nos résultats nous ont permis de démontrer la localisation lysosomale de p40. D’autre part, nous avons mis en évidence que le temps de demi-vie de p40 est d’environ 10 heures et que p40 est une protéine dépourvue de chaînes oligosaccharidiques, fortement associée aux membranes. Nous avons ensuite entrepris de rechercher une possible activité de transport pour p40, suggérée par l’homologie de séquence détectée avec des transporteurs connus. Pour cela, nous avons utilisé une technique d’électrophysiologie perfectionnée, bien adaptée à la réalisation d’un large criblage de substrats potentiels d’une hypothétique activité de transport. Bien que nous ayons testé près de 70 composés au total, nous n’avons pas mis en évidence la fonction de p40 par cette approche. Dans un troisième temps, nous nous sommes intéressés à la façon dont la protéine p40 néosynthétisée est spécifiquement ciblée vers les lysosomes. Nous avons muté les quatre motifs potentiels d’adressage aux lysosomes présents dans la séquence de p40 et nous avons observé l’impact de ces mutations sur sa localisation subcellulaire. Ces travaux ont révélé que l’envoi de p40 vers les lysosomes est assuré par un signal de type « dileucine » situé 11 résidus en amont de l’extrémité C-terminale de la protéine : le motif EQERL360L361. En effet, la substitution des deux résidus leucine critiques par d’autres acides aminés abolit le transport de la protéine p40 vers les lysosomes et induisait son envoi vers la membrane plasmique. En conclusion, notre recherche visant à caractériser p40 montre que cette protéine nouvellement identifiée est une protéine membranaire lysosomale non glycosylée, ciblée vers les lysosomes à partir du TGN par un signal d’adressage EQERL360L361 localisé dans sa queue C-terminale. Des études complémentaires sont nécessaires afin de cerner la fonction assurée par p40 au sein de la membrane des lysosomes.

In warm and humid climates, a primary source of building energy consumption is dehumidification of conditioned air supplied to the building spaces. The proposed system utilizes a selective membrane to remove water vapor from ambient air as opposed to a vapor compression cycle or a desiccant. This work provides an analysis of the membrane dehumidification system with a focus on the energy performance of the system. A system performance goal was set at the beginning for a given inlet and outlet ambient air condition and a total cooling load of one ton. The target COP of the combined sensible and latent cooling is 3.58 with a target value for only the latent system of 3.34. Two different simulations were developed including an initial simulation which uses a basic mass transfer model and a simpler condenser model. The initial model was used to develop the system, analyze operating parameters and provide initial performance results. The initial simulations indicate that the system requires two optimizations to meet the target performance: condenser pressure optimization and the use of multiple membrane segments operating at different pressures. The latent only COP including the optimizations was a maximum of 4.23. A second model was then developed which uses a more detailed mass transfer model and a more detailed condenser model based on the operating conditions. This simulation yielded a maximum latent only COP of 4.37 including the optimizations. The work also analyzes two different combined systems capable of providing both sensible and latent cooling. The first utilizes a conventional vapor compression cycle for sensible cooling and has a maximum COP of 3.93. The second uses multiple evaporative coolers in between multiple membrane dehumidification steps and was found to have a maximum COP of 3.73. Second law analysis of the systems was also conducted and found that the greatest reduction in latent system exergy loss can be obtained by improving the selectivity of the membrane. Apart from improving the membrane selectivity, the results show the greatest improvement can be found in improving the operation of the gas compression devices.

The Major Intrinsic Proteins are represented in all forms of life; plants, animals, bacteria and recently archaebacteria have all been shown to express at least one member of this superfamily of integral membrane proteins. We have overexpressed the E. coli aquaglyceroporin, glycerol facilitator (GlpF), to use as a model for studying membrane protein structure, folding and stability. Understanding membrane protein folding, stability, and dynamics is required for a molecular explanation of membrane protein function and for the development of interventions for the hundreds of membrane protein folding diseases. X-ray analysis of GlpF crystals shows that the protein exits as a tetramer in the crystallized state [1]. However, preparations of stable aqueous detergent solutions of GlpF in its native oligomeric state have been difficult to make; the protein readily unfolds and forms non-specific aggregates in many detergents. Here, I report the study of the structure and stability of the glycerol facilitator in several detergent solutions by blue native and sodium dodecyl sulphate polyacrylamide gel electrophoresis, circular dichroism, and fluorescence. For the first time, stable protein tetramers were prepared in two different detergent solutions (dodecyl maltoside (DDM) and lyso-myristoyl phosphatidylcholine (LMPC)) at neutral pH. Thermal unfolding experiments show that the protein is slightly more stable in LMPC than in DDM and that the thermal stability of the helical core at 95oC is slightly greater in the former detergent. In addition, tertiary structure unfolds before quaternary and secondary structures in LMPC whereas unfolding is more cooperative in DDM. The high stability of the protein is also evident from the unfolding half-life of 8 days in 8 M urea suggesting that hydrophobic interactions contribute to the stability. The GlpF tetramers are less resistant to acidic conditions; LMPC-solubilized GlpF shows loss of tertiary and quaternary structure by pH 6, while in DDM the tertiary structure is lost by pH 5, however the tetramer remains mostly intact at pH 4. The implications of thermal and chemical stress on the stability of the detergent-solubilized protein and its in vivo folding are discussed. / October 2008

Starch and chitosan films are both known to be effective barriers to gas permeation. Being naturally abundant, renewable, and biodegradable, starch and chitosan films have the potential to replace petroleum-based materials for food packaging applications. However, the gas permeability of starch-chitosan blend films has not been studied extensively. In order to characterize starch-chitosan blend films for food packaging application, the permeabilities of N2, O2 and CO2 in the blend films were studied at different operating conditions (e.g., relative humidity, chitosan content in the films, cross membrane pressure, and temperature). The gas permeation was measured using the traditional volumetric technique. Gas permeation through films containing different amounts of chitosan was measured at ambient temperature and at a cross membrane pressure of 60psi. In addition, pure chitosan was also tested at a high relative humidity where the gas was saturated with water vapor. The effects of temperature and cross membrane pressure on the gas permeability were studied with starch-chitosan blend films and pure chitosan films as well. It was found that an increase in pressure and/or temperature increased the permeability, and the temperature dependence of permeability followed the Arrhenius relation, from which activation energy of permeation was evaluated. The starch-chitosan blend films with approximately 60wt% chitosan showed the best gas barrier property and the highest activation energy for permeation.

Membranes provide a barrier to cells and organelles, and allow the selective transport of molecules between compartments. Membrane fusion is essential for organelle biogenesis as well as trafficking of molecules between cellular compartments. Membrane fusion is also required for the formation of the branched network of tubules that make up the Endoplasmic Reticulum (ER). One protein implicated in ER fusion is Atlastin, a dynamin like GTPase. Mutations in Atlastin-1, among others, cause Hereditary Spastic Paraplegias (HSP), a group of neurological disorders that cause progressive weakness of lower extremities. We have shown that the C-terminal tail of atlastin is necessary for membrane fusion. The requirement of the C-terminal tail can be partially abrogated in an unstable lipid environment. This implies that the C-terminal tail of Atlastin plays a role in perturbing the lipid bilayer to allow membrane fusion. Understanding the molecular details of how Atlastin drives membrane fusion may help elucidate the pathogenesis of HSP. Intracellular fusion at the plasma membrane is SNARE mediated and regulated by Sec1p/Munc18 (SM) proteins. Increased rate of glucose transport into fat and muscles cells by translocation of glucose transporter GLUT4 in response to insulin is a SNARE regulated fusion process. Recent reports have linked Munc18c and Syntaxin4 with obesity and Type 2 diabetes. We characterized the function of Munc18c, an SM protein, in regulating GLUT-4 containing vesicle fusion with the plasma membrane. We have shown that Munc18c directly inhibits membrane fusion by interacting with its cognate SNARE complexes. Characterization of membrane fusion in a minimal system as the in vitro liposome fusion assay offers a powerful tool with which to finely dissect the mechanistic basis of SM protein function.

Starch and chitosan films are both known to be effective barriers to gas permeation. Being naturally abundant, renewable, and biodegradable, starch and chitosan films have the potential to replace petroleum-based materials for food packaging applications. However, the gas permeability of starch-chitosan blend films has not been studied extensively. In order to characterize starch-chitosan blend films for food packaging application, the permeabilities of N2, O2 and CO2 in the blend films were studied at different operating conditions (e.g., relative humidity, chitosan content in the films, cross membrane pressure, and temperature). The gas permeation was measured using the traditional volumetric technique. Gas permeation through films containing different amounts of chitosan was measured at ambient temperature and at a cross membrane pressure of 60psi. In addition, pure chitosan was also tested at a high relative humidity where the gas was saturated with water vapor. The effects of temperature and cross membrane pressure on the gas permeability were studied with starch-chitosan blend films and pure chitosan films as well. It was found that an increase in pressure and/or temperature increased the permeability, and the temperature dependence of permeability followed the Arrhenius relation, from which activation energy of permeation was evaluated. The starch-chitosan blend films with approximately 60wt% chitosan showed the best gas barrier property and the highest activation energy for permeation.

Most membrane proteins in eukaryotic cells are co-translationally integrated into the endoplasmic reticulum (ER) membrane at aqueous pores termed translocons. During multi-spanning membrane protein (MSMP) integration, the nascent polypeptide is threaded into the translocon pore where each successive transmembrane segment (TMS) is moved laterally through the translocon into the bilayer. The hydrophilic polypeptide segments on each side of the TMS are alternately directed into either the aqueous cytosol or the aqueous ER lumen. How is the ER membrane permeability barrier maintained during this process? For a single-spanning signal-cleaved membrane protein, nascent chain movement into the lumen occurs while an ion-tight ribosome-translocon junction prevents ion flow through the translocon pore. Prior to opening this junction to allow nascent chain movement into the cytosol, BiP (Hsp70 binding protein) effects closure at the lumenal end of the pore to maintain the membrane permeability barrier. To determine whether the ribosome and BiP alternately mediate pore closure during the integration of a MSMP, integration intermediates with nascent chains of different lengths were prepared with a fluorescent probe positioned in the nascent chain far inside the ribosomal tunnel. Nascent chain exposure to the cytosol or lumen was then detected by the collisional quenching of the probe by iodide ions located on either the cytosolic or lumenal side of the membrane. While the first TMS through the tunnel caused the ribosome-translocon junction to open, the second TMS elicited both the closure of this junction and the opening of the lumenal end of the pore. Movement of a third TMS through the tunnel caused the ribosome-translocon junction to re-open after closure of the lumenal end. Pore opening and closing occurred after each TMS was 4-7 residues from the peptidyltransferase center, irrespective of TMS location in the nascent chain. The ribosome treated all TMSs in the same manner, regardless of their individual sequence or their native orientation. The ER membrane permeability barrier is maintained by ribosome-translocon interactions during cotranslational MSMP integration.