Correlations between the interfacial chemistry and current-voltage behavior of n-GaAs/liquid junctions

Correlations between the surface chemistry of etched, (100) oriented n-GaAs electrodes and their subsequent photoelectrochemical behavior have been probed by high-resolution x-ray photoelectron spectroscopy. GaAs photoanodes were chemically treated to prepare either an oxide-free near stoichiometric surface, a surface enriched in zero-valent arsenic (As0), or a substrate-oxide terminated surface. The current-voltage (I-V) behavior of each surface type was subsequently monitored in contact with several electrolytes

Photoelectrochemical Behavior of n-GaAs and n-Al_xGa_(1-x)As in CH_3CN

Current density vs potential, open-circuit voltage vs temperature, and differential capacitance vs potential measurements have been used to show that n-GaAs and n-Al_xGa_(1-x)As electrodes exhibit partial Fermi level pinning in contact with CH_3CN over a wide range of redox potentials. Despite a change of over 1.2 V in redox potential of the solution, the open-circuit voltage only changed by ∼300 mV. The slope of the open-circuit voltage vs redox potential of the solution was typically 0.33−0.44. Differential capacitance vs potential data also yielded a barrier height change of less than 300 mV for over 1.2 V change in the redox potential of the solution. The dependence of the current density vs potential behavior of n-GaAs/CH_3CN−ferricenium−ferrocene^(+/0) on variables such as the illumination intensity, dopant density of the semiconductor, concentration of redox acceptor in the solution, crystal face, electrolyte, and cell temperature was evaluated. The resultant kinetic data indicate that surface-state recombination is the dominant recombination mechanism at these interfaces, which are capable of producing an open-circuit voltage of 0.83 V at a short-circuit current density of 20 mA cm^(-2), as well as energy conversion efficiencies of > 10%. X-ray photoelectron spectroscopy investigation of n-GaAs confirmed surface changes were induced by electrochemical operation of n-GaAs electrodes in CH_3CN−cobaltocenium−cobaltocene^(+/)0 electrolyte. The presence of Fermi level pinning and the existence of changes in n-GaAs and n-Al_xGa_(1-x)As electrode surfaces when these electrodes are in contact with CH3CN−cobaltocenium−cobaltocene^(+/0) electrolyte complicates the extraction of k_(et) values from the steady-state current density vs potential behavior of n-GaAs or n-Al_xGa_(1-x)As/CH_3CN contacts

CD4+ T cell vaccination overcomes defective cross-presentation of fungal antigens in a mouse model of chronic granulomatous disease

Aspergillus fumigatus is a model fungal pathogen and a common cause of infection in individuals with the primary immunodeficiency chronic granulomatous disease (CGD). Although primarily considered a deficiency of innate immunity, CGD is also linked to dysfunctional T cell reactivity. Both CD4+ and CD8+ T cells mediate vaccine-induced protection from experimental aspergillosis, but the molecular mechanisms leading to the generation of protective immunity and whether these mechanisms are dysregulated in individuals with CGD have not been determined. Here, we show that activation of either T cell subset in a mouse model of CGD is contingent upon the nature of the fungal vaccine, the involvement of distinct innate receptor signaling pathways, and the mode of antigen routing and presentation in DCs. Aspergillus conidia activated CD8+ T cells upon sorting to the Rab14+ endosomal compartment required for alternative MHC class I presentation. Cross-priming of CD8+ T cells failed to occur in mice with CGD due to defective DC endosomal alkalinization and autophagy. However, long-lasting antifungal protection and disease control were successfully achieved upon vaccination with purified fungal antigens that activated CD4+ T cells through the endosome/lysosome pathway. Our study thus indicates that distinct intracellular pathways are exploited for the priming of CD4+ and CD8+ T cells to A. fumigatus and suggests that CD4+ T cell vaccination may be able to overcome defective antifungal CD8+ T cell memory in individuals with CGD

The Unfolded Protein Response Is Induced by the Cell Wall Integrity Mitogen-activated Protein Kinase Signaling Cascade and Is Required for Cell Wall Integrity in Saccharomyces cerevisiae

The yeast cell wall is an extracellular structure that is dependent on secretory and membrane proteins for its construction. We investigated the role of protein quality control mechanisms in cell wall integrity and found that the unfolded protein response (UPR) and, to a lesser extent, endoplasmic reticulum (ER)-associated degradation (ERAD) pathways are required for proper cell wall construction. Null mutation of IRE1, double mutation of ERAD components (hrd1Δ and ubc7Δ) and ire1Δ, or expression of misfolded proteins show phenotypes similar to mutation of cell wall proteins, including hypersensitivity to cell wall-targeted molecules, alterations to cell wall protein layer, decreased cell wall thickness by electron microscopy, and increased cellular aggregation. Consistent with its important role in cell wall integrity, UPR is activated by signaling through the cell wall integrity mitogen-activated protein (MAP) kinase pathway during cell wall stress and unstressed vegetative growth. Both cell wall stress and basal UPR activity is mediated by Swi6p, a regulator of cell cycle and cell wall stress gene transcription, in a manner that is independent of its known coregulatory molecules. We propose that the cellular responses to ER and cell wall stress are coordinated to buffer the cell against these two related cellular stresses