No description available.

No description available.

Group-III-nitrides have been intensively investigated for optoelectronics and power electronics and are uniquely suitable for energy-related applications, such as solar hydrogen generation and nanogenerators. Compared to planar group-III-nitrides, their nanostructures offer a high surface-to-volume ratio, increased light absorption cross-section, and improved carrier transportation behavior. This thesis focuses on molecular-beam-epitaxy-grown group-III-nitrides, specifically nanowires and membranes, and applications in renewable energy harvesting and conversion. A Mo2C-decorated (In,Ga)N nanowire-based photocathode was demonstrated for nitrogen fixation. The conventional Haber-Bosch method demands high reaction pressure and temperature while releasing a considerable amount of greenhouse gas. The proposed photoelectrocatalytic method can utilize solar energy to generate ammonia without carbon emissions. The proposed photocathodes can achieve maximum faradaic efficiency of 12 %, ammonia yield of 8.9 µg/h/cm2, and excellent stability for over 12 hrs. Moreover, group-III-nitrides were fabricated into a freestanding membrane through a novel method combining electrochemical porosification and controlled spalling. The novel method is reproducible and scalable, which can significantly reduce the consumption of sacrificial substrates compared to existing nitride membrane exfoliation techniques, thus promising a scalable platform. The as-fabricated GaN membranes were demonstrated for photoelectrocatalytic methylene blue degradation. Through laboratory tests and rooftop field tests, we proved the feasibility of our wafer-scale GaN membranes in achieving a dye degradation efficiency of 92%, a total organic carbon removal rate of 50.2%, and extraordinary stability for ~ 50 hours under solar illumination. The membrane can also degrade ~87% of MB under visible-light illumination. Furthermore, the (Al,Ga)N membranes were fabricated into flexible transparent piezoelectric devices. The devices can sense compression pressure and bending strain while giving a comparable compression sensitivity to other thin film piezotronics devices of ~ 2.41 mV/kPa and 42.36 pA/kPa, a maximum bending gauge factor of ~ 1271, and an output power density of ~ 5.38 nW/cm2. The sensors can withstand over 35000 cycles of operation and can be utilized for sensing and harvesting mechanical energies from human motions and environmental signals. This research utilized nanowires and membrane-based group-III-nitrides for different photoelectrocatalytic reactions and piezotronics devices, from material preparation and characterizations, and demonstrated practical devices for clean energy-related applications.

Contamination of natural waters due to nitrogenous wastes has become a crucial environmental problem due to deterioration of water quality and eutrophication in aquatic eco-systems. Thus, the reduction of nitrogen accumulation in the natural environment is vital to maintain a healthy eco-system. Bipolar membrane electrodialysis (BMED) is a promising technology for selective ammonia separation from high-strength wastewater, such as liquid digestates of food waste or wastewater sludge. This technology was recently studied for reducing membrane scaling problems associated with conventional electrodialysis (ED) systems due to the water splitting mechanism in the BPM interface. A bench-scale BMED stack was built using 5 pairs of cation exchange membranes (CEMs) and bipolar membranes (BPMs). Using the BMED stack, a simulated food liquid digestate solution was examined to separate ammonia with different voltage applications and inter-membrane distances. The highest ammonia recovery was obtained at a cell pair voltage of 5.83 V (81% separation). Experiments on investigation of optimal inter-membrane distance of BMED operation suggested that the inter-membrane distance could be increased up to 2.46 mm without a significant decrease in nitrogen recovery. The residual Ca2+ and Mg2+ in the CIP (clean-in-place) solution which explains the degree of the scaling problem in the BMED was observed consistently below 2% of the initial mass introduced to the system, indicating that BMED design and regular CIP were effective in scaling control. The ammonia loss through CEMs to the feed cell by back diffusion was minimized due to high pH in the base cell since uncharged free ammonia was dominant over ammonium cation in the base cell. The energy required for BMED operation was comparatively low; 1.93-6.93 kWh/kg-N within 90 mins. Therefore, BMED can be considered as a sustainable candidate for selective ammonia recovery at high energy efficiency with successful scaling control. / Thesis / Master of Civil Engineering (MCE)

This investigation is concerned with cell surface antigens present on murine AKR/J mice spleen and thymus cells which have been extracted with papain. Isolation of individual proteins was accomplished by granulated gel electrofocusing. Similar patterns recorded by both electrofocusing procedures identified several proteins limited to the AKR/J and C3Heb/FeJ spleen and thymus samples, which represent Murine Leukemia Virus-associated surface proteins.

Although cell membranes normally resist the hydrolysis of secretory phospholipase A2, a series of current investigations demonstrated that the changes in lipid order caused by increased calcium has a relationship with the susceptibility to phospholipase A2. To further explore this relationship, we setup ordinary differential equations models, statistic models and stochastic models to compare the response of human erythrocytes to the hydrolyzing action of secretory phospholipase A2 and the relationship between the susceptibility of hydrolysis and the physical properties of secretory phospholipase A2. Furthermore, we use models to determine the ability of calcium ionophore to increased membrane susceptibility.

Separation of the pigment-lipid esters of Xanthomonas juglandis (campestris) in a silica gel G:celite 545 column yielded 4 bands. Two of these bands, ester #1 and #2, make up over 95% of the mixture. Analysis of the four pigments indicate that three are phospholipids and that the phosphate accounts for about 3-4% of the weight of each of the two major esters.

The Amyloid Cascade hypothesis provides a molecular-level mechanism for the etiology of Alzheimer’s Disease (AD) and proposes a central role for the genesis and aggregation of Aβ protein. Aβ protein is the product of cleavage of the amyloid precursor protein (APP), a single pass transmembrane protein, by secretases and is found in a variety of isoforms, with longer isoforms being linked to the early onset of AD. The isoform distribution is dependent on membrane environment, mutations, and post-translational modifications. Lipid rafts are characterized by lipids induced into the liquid ordered phase by cholesterol, enhancing membrane thickness and lateral lipid density. Protein preference for rafts can control protein kinetics, and has been implicated in determining whether APP is processed by α– or β-secretase in the plasma membrane. In addition to inducing lipid rafts, cholesterol is hypothesized to directly modulate APP, the C-terminal fragment of APP (C99), and γ-secretase structure and function via direct interaction. To date, the molecular details involved in these fundamental events involved in Aβ genesis have yet to be resolved using experimental approaches, suggesting a critical role for computation. This thesis presents the results of investigations of lipid phase separation and cholesterol and their effects on C99 using molecular dynamics simulation. To gain insight into the nature of lipid rafts, studies characterizing the simulation system sizes required for observation of phase separation, exploring the effect of cholesterol concentration on phase separation and lipid phases, and examining the applicability of different lipid and cholesterol models for the simulation of lipid phases and protein structure were performed. To gain insight into the fundamental properties of C99, studies exploring the structure of full-length C99, the interaction of cholesterol with C99 in various mutational states, the effect of membrane thickness on the C99 extramembrane domains, and the structure of C99 monomer and dimer were performed. Taken together these studies advance our molecular-level understanding of the nature of cholesterol, the role of cholesterol in lipid phase separation, the effect of cholesterol on C99, and the structure of the full-sequence C99 monomer and dimer that play a critical role in the evolution of AD.

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Ionized calcium (Ca2+) is a signaling messenger that controls numerous cellular processes essential for life. The fidelity of Ca2+ signaling depends on the mechanisms that dynamically regulate its cytosolic concentration and maintain it at a low level in a resting cell. Plasma Membrane Ca2+ ATPase (PMCA) is a high affinity Ca2+ extrusion pathway involved in Ca2+ homeostasis and signal transduction. PMCA are encoded by 4 genes (PMCA1-4), which are expressed in a tissue dependent manner. The diversity of PMCA isoforms is further increased by alternative splicing. Changes in PMCA activity occur in heart failure and hypertension. Specific inhibitors of other ion transporters such as thapsigargin and digoxin, have made their mark in cell biology, but the currently used inhibitors of PMCA (vanadate and eosin) are non-specific. Thus, selective inhibitors of PMCA are needed to discern its role in Ca2+ signaling in physiology and pathophysiology. We introduced the concept of caloxins - peptides that specifically inhibit the activity of PMCA by binding to one of its five extracellular domains (exdoms) 1 to 5. The earlier caloxins including 2a1 and 3a1 were obtained by screening a phage display random 12-amino acid peptide (Ph.D-12) library for binding to synthetic peptides based on the exdom sequences. However, they all had low affinity. The objective of this research was to develop caloxins with high affinity and PMCA4 isoform selectivity. A two-step screening method was developed to screen the Ph.D-12 library to first bind to the synthetic exdom of PMCA4, followed by affinity chromatography using PMCA protein purified from human erythrocyte ghosts (mainly PMCA4). This method was used to obtain caloxins 1b1 and 1b2 to bind to the N and C-terminal halves of the exdom 1 of PMCA4, respectively. Both caloxins 1b1 and 1b2 had a 10-fold higher affinity than the prototype caloxin 2a1 and showed slight PMCA4 isoform preference. To engineer inhibitors with greater affinity and PMCA4 isoform selectivity, Ph.D caloxin 1b1 like peptide library was constructed. Most of the peptides expressed in this library differed from caloxin 1b1 in 0, 1, 2 or 3 amino acid residues at random. The library was screened to obtain several peptides one of which was caloxin 1c2. Caloxin 1c2 had 200-fold higher affinity than caloxin 2a1 and was isoform selective, with greater than 10-fold affinity for PMCA4 than for PMCA isoforms 1, 2 or 3. Thus, caloxin 1c2 is the first high affinity PMCA inhibitor that also is selective for an individual PMCA isoform. The second aim of this research was to establish that caloxin 1c2 binds to PMCA protein in erythrocyte ghosts. Two photoreactive caloxin 1c2-derivatives containing the photoactivable residue benzoylphenylalanine (Bpa) and a C-terminal biotin tag were used. Bpa substituted tryptophan at position 3 (3Bpa1c2-biotin) and serine at position 16 (16Bpa1c2-biotin) in caloxin 1c2. Both the derivatives inhibited PMCA activity in the erythrocyte ghosts. The intensity of the biotin label in the photolabeled erythrocyte ghosts was much stronger with 3Bpa1c2-biotin, which was then used in the subsequent experiments. The photolabeled proteins in erythrocyte ghosts were detected as a 250-270 kDa doublet in Western blots using streptavidin and the PMCA specific antibody. The degree of photolabeling depended on the UV-crosslinking time, and on the concentrations of 3Bpa1c2-biotin and the ghost protein. The selectivity of the photolabeling site was confirmed by decreased photolabel incorporation at 250-270 kDa doublet in the presence of excess caloxin 1c2 and the synthetic exdom 1X peptide of PMCA4. The photolabeled erythrocyte ghosts were solubilized and analyzed by immunoprecipitation with the PMCA specific antibody. The immunoprecipitate showed a 250-270 kDa doublet in Western blots using streptavidin. This confirmed that PMCA protein was photolabeled by the photoreactive derivatives of caloxin 1c2. Thus, caloxin 1c2 inhibits PMCA activity by binding to the exdom 1X of PMCA4. My work in M.Sc. initiated the concept of caloxins in the literature. This research has taken it to the stage where we can obtain caloxins selective for individual PMCA isoforms. This contrasts with the relative paucity of inhibitors specific for individual isoforms of other ion pumps. The high affinity isoform selective caloxin 1c2 and previous caloxins are being used to study PMCA physiology in our lab and by other researchers. Since caloxins act when added extracellularly and it is possible to obtain PMCA isoform selective caloxins, it is anticipated that they will aid in understanding the role of PMCA in signal transduction and homeostasis in health and disease. / Thesis / Doctor of Philosophy (PhD)