Surface structure, bonding, and dynamics: The universality of zincblende (110) potential energy surfaces

Using a tight-binding, total energy (TBTE) model we examine the hypothesis that the potential energy surfaces (PES) describing the (110) cleavage faces of the tetrahedrally coordinated, zincblende-structure compound semiconductors exhibit a common universal'' form if expressed in terms of suitably scaled parameters. TBTE calculations on both III-V and II-VI compounds reveal a linear scaling with bulk lattice constant of the geometric parameters of the reconstructed surfaces. This scaling is analogous to that found using low-energy, electron-diffraction surface-structure determination. The surface atomic force constants (found from a TBTE calculation) also scale monotonically with the lattice constant. Using TBTE models proposed previously for GaP, GaAs, GaSb, InP, and ZnSe, we find that the force constants scale as the inverse square of the bulk lattice constant. These results suggest that if distances are measured in units of the bulk lattice constant, the PES may be a universal function for the cleavage surface of zincblende-structure compound semiconductors, on average, with small fluctuations from this average occurring in individual materials. 22 refs., 5 figs., 1 tab

Jahn-Teller stabilization of a "polar" metal oxide surface: Fe3O4(001)

Using ab initio thermodynamics we compile a phase diagram for the surface of Fe3O4(001) as a function of temperature and oxygen pressures. A hitherto ignored polar termination with octahedral iron and oxygen forming a wave-like structure along the [110]-direction is identified as the lowest energy configuration over a broad range of oxygen gas-phase conditions. This novel geometry is confirmed in a x-ray diffraction analysis. The stabilization of the Fe3O4(001)-surface goes together with dramatic changes in the electronic and magnetic properties, e.g., a halfmetal-to-metal transition.Comment: 4 pages, 4 figure

Surface electronic structure of the Fe3O4(100): Evidence of a half-metal to metal transition

In situ prepared Fe3O4(100) thin films were studied by means of scanning tunneling microscopy (STM) and spin-polarized photoelectron spectroscopy (SP-PES). The atomically resolved (2×2)R45°wavelike surface atomic structure observed by STM is explained based on density functional theory (DFT) and ab initio atomistic thermodynamics calculations as a laterally distorted surface layer containing octahedral iron and oxygen, referred to as a modified B layer. The work-function value of the Fe3O4(100) surface extracted from the cutoff of the photoelectron spectra is in good agreement with that predicted from DFT. On the Fe3O4(100) surface both the SP-PES measurements and the DFT results show a strong reduction of the spin polarization at the Fermi level (EF) compared to the bulk density of states. The nature of the states in the majority band gap of the Fe3O4 surface layer is analyzed

Changes in arginase isoforms in a murine model of neonatal brain hypoxia-ischemia.

BackgroundArginases (ARG isoforms, ARG-1/ARG-2) are key regulatory enzymes of inflammation and tissue repair; however, their role after neonatal brain hypoxia (H) and hypoxia-ischemia (HI) remains unknown.MethodsC57BL/6 mice subjected to the Vannucci procedure on postnatal day (P9) were sacrificed at different timepoints. The degree of brain damage was assessed histologically. ARG spatiotemporal localization was determined via immunohistochemistry. ARG expression was measured by Western blot and activity spectrophotometrically.ResultsARG isoform expression increased during neurodevelopment (P9-P17) in the cortex and hippocampus. This was suppressed with H and HI only in the hippocampus. In the cortex, both isoforms increased with H alone and only ARG-2 increased with HI at 3 days. ARG activity during neurodevelopment remained unchanged, but increased at 1 day with H and not HI. ARG-1 localized with microglia at the injury site as early as 4 h after injury, while ARG-2 localized with neurons.ConclusionsARG isoform expression increases with age from P9 to P17, but is suppressed by injury specifically in the hippocampus and not in the cortex. Both levels and activity of ARG isoforms increase with H, while ARG-1 immunolabelling is upregulated in the HI cortex. Evidently, ARG isoforms in the brain differ in spatiotemporal localization, expression, and activity during neurodevelopment and after injury.ImpactArginase isoforms change during neurodevelopment and after neonatal brain HI. This is the first study investigating the key enzymes of inflammation and tissue repair called arginases following murine neonatal brain HI. The highly region- and cell-specific expression suggests the possibility of specific functions of arginases. ARG-1 in microglia at the injury site may regulate neuroinflammation, while ARG-2 in neurons of developmental structures may impact neurodevelopment. While further studies are needed to describe the exact role of ARGs after neonatal brain HI, our study adds valuable data on anatomical localization and expression of ARGs in brain during development and after stroke

Genetic identification of cytomegaloviruses in a rural population of Côte d'Ivoire.

BACKGROUND: Cytomegaloviruses (CMVs) are herpesviruses that infect many mammalian species, including humans. Infection generally passes undetected, but the virus can cause serious disease in individuals with impaired immune function. Human CMV (HCMV) is circulating with high seroprevalence (60-100 %) on all continents. However, little information is available on HCMV genoprevalence and genetic diversity in subsaharan Africa, especially in rural areas of West Africa that are at high risk of human-to-human HCMV transmission. In addition, there is a potential for zoonotic spillover of pathogens through bushmeat hunting and handling in these areas as shown for various retroviruses. Although HCMV and nonhuman CMVs are regarded as species-specific, potential human infection with CMVs of non-human primate (NHP) origin, shown to circulate in the local NHP population, has not been studied. FINDINGS: Analysis of 657 human oral swabs and fecal samples collected from 518 individuals living in 8 villages of Côte d'Ivoire with generic PCR for identification of human and NHP CMVs revealed shedding of HCMV in 2.5 % of the individuals. Determination of glycoprotein B sequences showed identity with strains Towne, AD169 and Toledo, respectively. NHP CMV sequences were not detected. CONCLUSIONS: HCMV is actively circulating in a proportion of the rural Côte d'Ivoire human population with circulating strains being closely related to those previously identified in non-African countries. The lack of NHP CMVs in human populations in an environment conducive to cross-species infection supports zoonotic transmission of CMVs to humans being at most a rare event

Human Cytomegalovirus IE1 Protein Elicits a Type II Interferon-Like Host Cell Response That Depends on Activated STAT1 but Not Interferon-γ

Human cytomegalovirus (hCMV) is a highly prevalent pathogen that, upon primary infection, establishes life-long persistence in all infected individuals. Acute hCMV infections cause a variety of diseases in humans with developmental or acquired immune deficits. In addition, persistent hCMV infection may contribute to various chronic disease conditions even in immunologically normal people. The pathogenesis of hCMV disease has been frequently linked to inflammatory host immune responses triggered by virus-infected cells. Moreover, hCMV infection activates numerous host genes many of which encode pro-inflammatory proteins. However, little is known about the relative contributions of individual viral gene products to these changes in cellular transcription. We systematically analyzed the effects of the hCMV 72-kDa immediate-early 1 (IE1) protein, a major transcriptional activator and antagonist of type I interferon (IFN) signaling, on the human transcriptome. Following expression under conditions closely mimicking the situation during productive infection, IE1 elicits a global type II IFN-like host cell response. This response is dominated by the selective up-regulation of immune stimulatory genes normally controlled by IFN-γ and includes the synthesis and secretion of pro-inflammatory chemokines. IE1-mediated induction of IFN-stimulated genes strictly depends on tyrosine-phosphorylated signal transducer and activator of transcription 1 (STAT1) and correlates with the nuclear accumulation and sequence-specific binding of STAT1 to IFN-γ-responsive promoters. However, neither synthesis nor secretion of IFN-γ or other IFNs seems to be required for the IE1-dependent effects on cellular gene expression. Our results demonstrate that a single hCMV protein can trigger a pro-inflammatory host transcriptional response via an unexpected STAT1-dependent but IFN-independent mechanism and identify IE1 as a candidate determinant of hCMV pathogenicity

Human cytomegalovirus immediate-early 1 protein rewires upstream STAT3 to downstream STAT1 signaling switching an IL6-type to an IFNγ-like response

MN and CP were supported by the Wellcome Trust (www.wellcome.ac.uk) Institutional Strategic Support Fund and CP was supported by the Deutsche Forschungsgemeinschaft (PA 815/2-1; www.dfg.de).The human cytomegalovirus (hCMV) major immediate-early 1 protein (IE1) is best known for activating transcription to facilitate viral replication. Here we present transcriptome data indicating that IE1 is as significant a repressor as it is an activator of host gene expression. Human cells induced to express IE1 exhibit global repression of IL6- and oncostatin M-responsive STAT3 target genes. This repression is followed by STAT1 phosphorylation and activation of STAT1 target genes normally induced by IFNγ. The observed repression and subsequent activation are both mediated through the same region (amino acids 410 to 445) in the C-terminal domain of IE1, and this region serves as a binding site for STAT3. Depletion of STAT3 phenocopies the STAT1-dependent IFNγ-like response to IE1. In contrast, depletion of the IL6 receptor (IL6ST) or the STAT kinase JAK1 prevents this response. Accordingly, treatment with IL6 leads to prolonged STAT1 instead of STAT3 activation in wild-type IE1 expressing cells, but not in cells expressing a mutant protein (IE1dl410-420) deficient for STAT3 binding. A very similar STAT1-directed response to IL6 is also present in cells infected with a wild-type or revertant hCMV, but not an IE1dl410-420 mutant virus, and this response results in restricted viral replication. We conclude that IE1 is sufficient and necessary to rewire upstream IL6-type to downstream IFNγ-like signaling, two pathways linked to opposing actions, resulting in repressed STAT3- and activated STAT1-responsive genes. These findings relate transcriptional repressor and activator functions of IE1 and suggest unexpected outcomes relevant to viral pathogenesis in response to cytokines or growth factors that signal through the IL6ST-JAK1-STAT3 axis in hCMV-infected cells. Our results also reveal that IE1, a protein considered to be a key activator of the hCMV productive cycle, has an unanticipated role in tempering viral replication.Publisher PDFPeer reviewe

Surface structure, bonding, and dynamics: The universality of zincblende (110) potential energy surfaces

Using a tight-binding, total energy (TBTE) model we examine the hypothesis that the potential energy surfaces (PES) describing the (110) cleavage faces of the tetrahedrally coordinated, zincblende-structure compound semiconductors exhibit a common ``universal`` form if expressed in terms of suitably scaled parameters. TBTE calculations on both III-V and II-VI compounds reveal a linear scaling with bulk lattice constant of the geometric parameters of the reconstructed surfaces. This scaling is analogous to that found using low-energy, electron-diffraction surface-structure determination. The surface atomic force constants (found from a TBTE calculation) also scale monotonically with the lattice constant. Using TBTE models proposed previously for GaP, GaAs, GaSb, InP, and ZnSe, we find that the force constants scale as the inverse square of the bulk lattice constant. These results suggest that if distances are measured in units of the bulk lattice constant, the PES may be a universal function for the cleavage surface of zincblende-structure compound semiconductors, on average, with small fluctuations from this average occurring in individual materials. 22 refs., 5 figs., 1 tab

Semiconductor surface and interface dynamics from tight-binding molecular dynamics simulations

Tight-binding molecular dynamics simulations have bee performed to compute the bulk, (110) surface, and (110)-p(1 {times} 1)-Sb(1ML) interfacial atomic vibrational spectra for GaAs and InP. The same tight-binding total energy model which successfully described the static surface and interfacial atomic and electronic structure for these systems is utilized in the molecular dynamics simulations. The results for the bulk vibrational energies are in semi-quantitative agreement with experiments results, displaying approximately the same level of variance as other model computations. Moreover, these simulations are used to examine the effects of anharmonicity in the system by investigating the temperature dependence of the vibrational spectra. The (110) surface vibrational energies are in quantitative agreement with the scattering data, and a comparison of the results for GaAs(110) and InP(110) supports the existance of a surface vibrational mode which is characteristic of the relaxed (110) surface, and whose energy is similar for each zincblende (110) surface. Lastly, the computed vibrational energies for the 3-5(110)-p(1 {times} 1)-Sb(1ML) interface are in semi-quantitative agreement with Raman scattering data and illustrate the effects of the overlayer binding on the surface vibrational spectrum

Electronic structure and photophysical properties of polyimides

The quantum mechanical AM1 and CNDO/S3 models were used to examine the effect of isoelectronic substitutions on the conformation, electronic structure, and optical absorption spectra for a series of aromatic polyimides. An analysis of the geometric changes at the substitution site and its effect on the electronic structure allowed for the prediction of changes in the ICT band of the optical absorption spectra