72 research outputs found

    A quantum chemistry description of carbon monoxide and water absorbates on single-crystal rhodium and platinum clusters

    Get PDF
    Extended Hückel molecular-orbital calculations of CO and HO adsorbed ensembles on single-crystal Pt and Rh clusters are presented. The energy ranges related to the stability of adsorbed ensembles of the type (Me)N(CO)n(OH)m, where Me stands for Rh(100), Rh(111), Pt(100) and Pt(111), were calculated for various coordination geometries and applied potential conditions. A stability inversion potential was found for each ensemble. A correlation was obtained between the stability inversion potentials resulting from the different adsorbed ensembles and the potentials of the current peaks related to the voltammetric oxidation of CO adsorbates on Pt and Rh resulting from comparable potential perturbation conditions.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

    A quantum chemistry approach to the electro-oxidation of CO adsorbed on Rh (111) cluster surfaces

    Get PDF
    A molecular-orbital interpretation of the electro-oxidation of CO adsorbed on Rh(111) single-crystal clusters in the presence of H2O is described. Calculations were based on the atom super-position and electron delocalization method. Different stabilization energies for ensembles of the type [Me]N(CO)n(OH)m for M = Rh or Pt are given. The stability of possible CO adsorbate configurations on Rh(111) surfaces depends on the applied electric potential in a way which is directly comparable with the one reported previously for CO adsorbates on Pt(111). Only linearly bonded CO adsorbates appear to be involved in the electrochemical CO oxidative interaction with H2O molecules on both Rh(111) and Pt(111).Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

    Semi-empirical calculations of the vibrational frequency of carbon monoxide adsorbed on noble metal single-crystal surfaces

    Get PDF
    In this work we perform a theoretical analysis of the shift of the observed IR reflection—absorption spectroscopy (IRRAS) band of CO adsorbed on Pt(111), Rh(111) and Pt(100) single crystals as a function of both the degree of CO surface coverage and the electric potential applied at either the metal—vacuum or the metal—solution interface. The wavefunctions obtained using a modified extended Hückel molecular orbital (EHMO) method are used to predict the vibrational frequency data. The Pt(110), Rh(111) and Pt(111) single crystals are modelled by bilayer clusters of 25 and 22 atoms respectively. A theoretical description of the observed IRRAS shift is analysed by means of a population analysis of CO molecular orbitals, which confirms the donation—back-donation model.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

    A quantum chemistry approach to the electro-oxidation of CO adsorbed on Rh (111) cluster surfaces

    Get PDF
    A molecular-orbital interpretation of the electro-oxidation of CO adsorbed on Rh(111) single-crystal clusters in the presence of H2O is described. Calculations were based on the atom super-position and electron delocalization method. Different stabilization energies for ensembles of the type [Me]N(CO)n(OH)m for M = Rh or Pt are given. The stability of possible CO adsorbate configurations on Rh(111) surfaces depends on the applied electric potential in a way which is directly comparable with the one reported previously for CO adsorbates on Pt(111). Only linearly bonded CO adsorbates appear to be involved in the electrochemical CO oxidative interaction with H2O molecules on both Rh(111) and Pt(111).Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

    A quantum chemistry description of carbon monoxide and water absorbates on single-crystal rhodium and platinum clusters

    Get PDF
    Extended Hückel molecular-orbital calculations of CO and HO adsorbed ensembles on single-crystal Pt and Rh clusters are presented. The energy ranges related to the stability of adsorbed ensembles of the type (Me)N(CO)n(OH)m, where Me stands for Rh(100), Rh(111), Pt(100) and Pt(111), were calculated for various coordination geometries and applied potential conditions. A stability inversion potential was found for each ensemble. A correlation was obtained between the stability inversion potentials resulting from the different adsorbed ensembles and the potentials of the current peaks related to the voltammetric oxidation of CO adsorbates on Pt and Rh resulting from comparable potential perturbation conditions.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

    Semi-empirical calculations of the vibrational frequency of carbon monoxide adsorbed on noble metal single-crystal surfaces

    Get PDF
    In this work we perform a theoretical analysis of the shift of the observed IR reflection—absorption spectroscopy (IRRAS) band of CO adsorbed on Pt(111), Rh(111) and Pt(100) single crystals as a function of both the degree of CO surface coverage and the electric potential applied at either the metal—vacuum or the metal—solution interface. The wavefunctions obtained using a modified extended Hückel molecular orbital (EHMO) method are used to predict the vibrational frequency data. The Pt(110), Rh(111) and Pt(111) single crystals are modelled by bilayer clusters of 25 and 22 atoms respectively. A theoretical description of the observed IRRAS shift is analysed by means of a population analysis of CO molecular orbitals, which confirms the donation—back-donation model.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

    Towards precision medicine: defining and characterizing adipose tissue dysfunction to identify early immunometabolic risk in symptom-free adults from the GEMM family study

    Get PDF
    Interactions between macrophages and adipocytes are early molecular factors influencing adipose tissue (AT) dysfunction, resulting in high leptin, low adiponectin circulating levels and low-grade metaflammation, leading to insulin resistance (IR) with increased cardiovascular risk. We report the characterization of AT dysfunction through measurements of the adiponectin/leptin ratio (ALR), the adipo-insulin resistance index (Adipo-IRi), fasting/postprandial (F/P) immunometabolic phenotyping and direct F/P differential gene expression in AT biopsies obtained from symptom-free adults from the GEMM family study. AT dysfunction was evaluated through associations of the ALR with F/P insulin-glucose axis, lipid-lipoprotein metabolism, and inflammatory markers. A relevant pattern of negative associations between decreased ALR and markers of systemic low-grade metaflammation, HOMA, and postprandial cardiovascular risk hyperinsulinemic, triglyceride and GLP-1 curves was found. We also analysed their plasma non-coding microRNAs and shotgun lipidomics profiles finding trends that may reflect a pattern of adipose tissue dysfunction in the fed and fasted state. Direct gene differential expression data showed initial patterns of AT molecular signatures of key immunometabolic genes involved in AT expansion, angiogenic remodelling and immune cell migration. These data reinforce the central, early role of AT dysfunction at the molecular and systemic level in the pathogenesis of IR and immunometabolic disorders

    Using enhanced number and brightness to measure protein oligomerization dynamics in live cells

    Get PDF
    Protein dimerization and oligomerization are essential to most cellular functions, yet measurement of the size of these oligomers in live cells, especially when their size changes over time and space, remains a challenge. A commonly used approach for studying protein aggregates in cells is number and brightness (N&B), a fluorescence microscopy method that is capable of measuring the apparent average number of molecules and their oligomerization (brightness) in each pixel from a series of fluorescence microscopy images. We have recently expanded this approach in order to allow resampling of the raw data to resolve the statistical weighting of coexisting species within each pixel. This feature makes enhanced N&B (eN&B) optimal for capturing the temporal aspects of protein oligomerization when a distribution of oligomers shifts toward a larger central size over time. In this protocol, we demonstrate the application of eN&B by quantifying receptor clustering dynamics using electron-multiplying charge-coupled device (EMCCD)-based total internal reflection microscopy (TIRF) imaging. TIRF provides a superior signal-to-noise ratio, but we also provide guidelines for implementing eN&B in confocal microscopes. For each time point, eN&B requires the acquisition of 200 frames, and it takes a few seconds up to 2 min to complete a single time point. We provide an eN&B (and standard N&B) MATLAB software package amenable to any standard confocal or TIRF microscope. The software requires a high-RAM computer (64 Gb) to run and includes a photobleaching detrending algorithm, which allows extension of the live imaging for more than an hour

    Southern African Large Telescope Spectroscopy of BL Lacs for the CTA project

    Get PDF
    In the last two decades, very-high-energy gamma-ray astronomy has reached maturity: over 200 sources have been detected, both Galactic and extragalactic, by ground-based experiments. At present, Active Galactic Nuclei (AGN) make up about 40% of the more than 200 sources detected at very high energies with ground-based telescopes, the majority of which are blazars, i.e. their jets are closely aligned with the line of sight to Earth and three quarters of which are classified as high-frequency peaked BL Lac objects. One challenge to studies of the cosmological evolution of BL Lacs is the difficulty of obtaining redshifts from their nearly featureless, continuum-dominated spectra. It is expected that a significant fraction of the AGN to be detected with the future Cherenkov Telescope Array (CTA) observatory will have no spectroscopic redshifts, compromising the reliability of BL Lac population studies, particularly of their cosmic evolution. We started an effort in 2019 to measure the redshifts of a large fraction of the AGN that are likely to be detected with CTA, using the Southern African Large Telescope (SALT). In this contribution, we present two results from an on-going SALT program focused on the determination of BL Lac object redshifts that will be relevant for the CTA observatory

    Dental Health and Mortality in People With End-Stage Kidney Disease Treated With Hemodialysis: A Multinational Cohort Study

    Get PDF
    Background Dental disease is more extensive in adults with chronic kidney disease, but whether dental health and behaviors are associated with survival in the setting of hemodialysis is unknown. Study Design Prospective multinational cohort. Setting & Participants 4,205 adults treated with long-term hemodialysis, 2010 to 2012 (Oral Diseases in Hemodialysis [ORAL-D] Study). Predictors Dental health as assessed by a standardized dental examination using World Health Organization guidelines and personal oral care, including edentulousness; decayed, missing, and filled teeth index; teeth brushing and flossing; and dental health consultation. Outcomes All-cause and cardiovascular mortality at 12 months after dental assessment. Measurements Multivariable-adjusted Cox proportional hazards regression models fitted with shared frailty to account for clustering of mortality risk within countries. Results During a mean follow-up of 22.1 months, 942 deaths occurred, including 477 cardiovascular deaths. Edentulousness (adjusted HR, 1.29; 95% CI, 1.10-1.51) and decayed, missing, or filled teeth score ≥ 14 (adjusted HR, 1.70; 95% CI, 1.33-2.17) were associated with early all-cause mortality, while dental flossing, using mouthwash, brushing teeth daily, spending at least 2 minutes on oral hygiene daily, changing a toothbrush at least every 3 months, and visiting a dentist within the past 6 months (adjusted HRs of 0.52 [95% CI, 0.32-0.85], 0.79 [95% CI, 0.64-0.97], 0.76 [95% CI, 0.58-0.99], 0.84 [95% CI, 0.71-0.99], 0.79 [95% CI, 0.65-0.95], and 0.79 [95% CI, 0.65-0.96], respectively) were associated with better survival. Results for cardiovascular mortality were similar. Limitations Convenience sample of clinics. Conclusions In adults treated with hemodialysis, poorer dental health was associated with early death, whereas preventive dental health practices were associated with longer survival
    corecore