Investigating the role of undercoordinated Pt sites at the surface of layered PtTe2 for methanol decomposition.

Transition metal dichalcogenides, by virtue of their two-dimensional structures, could provide the largest active surface for reactions with minimal materials consumed, which has long been pursued in the design of ideal catalysts. Nevertheless, their structurally perfect basal planes are typically inert; their surface defects, such as under-coordinated atoms at the surfaces or edges, can instead serve as catalytically active centers. Here we show a reaction probability > 90 % for adsorbed methanol (CH3OH) on under-coordinated Pt sites at surface Te vacancies, produced with Ar+ bombardment, on layered PtTe2 - approximately 60 % of the methanol decompose to surface intermediates CHxO (x = 2, 3) and 35 % to CHx (x = 1, 2), and an ultimate production of gaseous molecular hydrogen, methane, water and formaldehyde. The characteristic reactivity is attributed to both the triangular positioning and varied degrees of oxidation of the under-coordinated Pt at Te vacancies.

Simultaneous ambient pressure x-ray photoelectron spectroscopy and grazing incidence x-ray scattering in gas environments.

We have developed an experimental system to simultaneously measure surface structure, morphology, composition, chemical state, and chemical activity for samples in gas phase environments. This is accomplished by simultaneously measuring x-ray photoelectron spectroscopy (XPS) and grazing incidence x-ray scattering in gas pressures as high as the multi-Torr regime while also recording mass spectrometry. Scattering patterns reflect near-surface sample structures from the nano-scale to the meso-scale, and the grazing incidence geometry provides tunable depth sensitivity of structural measurements. Scattered x rays are detected across a broad range of angles using a newly designed pivoting-UHV-manipulator for detector positioning. At the same time, XPS and mass spectrometry can be measured, all from the same sample spot and under ambient conditions. To demonstrate the capabilities of this system, we measured the chemical state, composition, and structure of Ag-behenate on a Si(001) wafer in vacuum and in O2 atmosphere at various temperatures. These simultaneous structural, chemical, and gas phase product probes enable detailed insights into the interplay between the structure and chemical state for samples in gas phase environments. The compact size of our pivoting-UHV-manipulator makes it possible to retrofit this technique into existing spectroscopic instruments installed at synchrotron beamlines. Because many synchrotron facilities are planning or undergoing upgrades to diffraction limited storage rings with transversely coherent beams, a newly emerging set of coherent x-ray scattering experiments can greatly benefit from the concepts we present here.

Impairment of mitochondrial unfolded protein response contribute to resistance declination of H2 O2 -induced injury in senescent MRC-5 cell model.

Accumulation of oxidative proteins within mitochondria leads to loss of mitochondrial function, which may lead to age-related degenerative diseases. Mitochondrial antioxidant defense capacity reflects the expression of mitochondrial unfolded protein response (mtUPR)-related proteins. Senescent cells are considered to be less resistant to cellular stress stimuli than exponentially growing cells. In this study, we aimed to investigate the ability of mitochondrial stress response in senescent cells to cope with the accumulation of mitochondrial unfolded proteins induced by hydrogen peroxide (H2 O2 ) and to understand the relevant molecular mechanisms. We report here that senescence-associated ß-galactosidase (SA-ß-gal) and senescence marker protein-30 (SMP-30), commonly used replicative senescence biomarkers, changed remarkably between population doubling (PD) 25 (exponentially growing cells) and PD50 (senescent cells) of MRC-5 fibroblasts. Mitochondrial unfolded proteins were significantly accumulated in H2 O2 -treated senescent cells, whereas mtUPR-related molecular chaperones (heat shock protein Hsp60 and Hsp10) and proteases (caseinolytic Clp protease) were not concomitantly elevated in senescent cells. In addition, decreased expression of stromal interacting molecule 1-Orai1-mediated store-operated Ca2+ entry following an declined intracellular calcium level after 2 mM calcium treatment together with H2 O2 addition, implying impairment of calcium influx in senescent MRC-5 during H2 O2 -induced injury. These findings suggest that senescent fibroblasts expressed higher vulnerability to H2 O2 -induced injury involving the imbalance of calcium homeostasis and impaired mitochondrial nuclear communication. This may provide useful information for the future development of therapeutic agents to prevent the adverse effects of aging on cells and the potential for treatment of proteinopathies in the elderly.

A meta-analysis of the relationship between foot local characteristics and major lower extremity amputation in diabetic foot patients.

OBJECTIVE: To clarify and quantify risk factors among local characteristics of the foot for major amputation in diabetic foot patients. METHODS: Articles published before January 2018 on PubMed and Embase were conducted observational studies about risk factors for major amputation in patients with diabetic foot were retrieved and systematically reviewed by using Stata 12.0 statistical software. RESULTS: A total of 4668 major amputees and 65 831 controls were reported in 18 observational studies. Across the studies, the overall odds ratios (ORs) and 95% confidence intervals (CIs) of significant risk factors are ulcer reaching bone (OR, 11.796; 95% CI, 6.905-20.152), gangrene (OR, 6.487; 95% CI, 4.088-10.293), hindfoot position (OR, 3.913; 95% CI, 2.254-6.795), decreased ankle-brachial index (ABI) (OR, 2.522; 95% CI, 1.805-3.523), infection (OR, 2.516; 95% CI, 1.708-3.706), peripheral arterial disease (PAD) (OR, 2.114; 95% CI, 1.326-3.372). While there is no significant difference in the size of the ulcer, neuropathy, Charcot foot, osteomyelitis and intermittent claudication (OR, 1.15; 95% CI, 0.85-1.54). CONCLUSION: Factors among local characteristics of the foot associated with major amputation in patients with diabetic foot are the ulcer reaching bone, gangrene, hindfoot position, decreased ABI, infection, and PAD, a negative risk factor for the risk of amputation. Further studies are required to provide more details of foot local characteristics.

Analysis of initial reactions of MALDI based on chemical properties of matrixes and excitation condition.

This investigation concerns the initial chemical reactions that affect the ionization of matrixes in matrix-assisted laser desorption/ionization (MALDI). The study focuses on the relaxations of photon energy that occur on a comparable time scale to that of ionization, in which the available laser energy is shared and the ionization condition is changed. The relaxations include fluorescence, fragmentation, and nonradiative relaxation from the excited state to the ground state. With high absorption cross section and long excited-state lifetime, photoionization of matrix plays an important role if sufficient laser energy is used. Under other conditions, thermal ionization of the molecule in the ground state is predicted to be one of the important reactions. Evidence of change in the branching ratio of initial reactions with the matrix and the excitation wavelength was obtained with α-cyano-4-hydroxycinnamic acid, sinapinic acid, 2,5-dihydroxybenzoic acid, and 2,4,6-trihydroxyacetophenone. These matrixes are studied by obtaining their mixed crystal absorption spectra, fluorescence properties, laser-induced infrared emission, and product ions. The exact ionization pathway depends on the chemical properties of matrixes and the excitation conditions. This concept may explain the diversity of experimental results observed in MALDI experiments, which provides an insight into the ensemble of chemical reactions that govern the generation of ions.

Comprehensive molecular imaging of photolabile surface samples with synchronized dual-polarity time-of-flight mass spectrometry.

This work presents the unique features of a novel configuration of a synchronized dual-polarity time-of-flight mass spectrometer for comprehensive surface imaging. Mass spectrometry imaging of surface samples covering positive and negative ion modes is difficult due to rapid signal depletion. This limitation is overcome here by dual-polarity time-of-flight mass spectrometry (DP-TOFMS) via two separate TOF mass analyzers that are installed above a sample surface. The new instrument eliminates the polarity bias characteristic of most mass spectrometers, which is important for the analysis of samples with diverse physical and chemical properties. The experimental results show for the first time that the spatial distribution of positive and negative ions of various photolabile samples can be distinguished, including pigments and conventional matrix-assisted laser desorption/ionization samples. The different positive and negative ion distributions suggest that accurate quantitative information can only be obtained when the entire sample region is examined by DP-TOFMS, which was unfeasible in the past. Such a comprehensive diagnostic method is essential for the molecular imaging of trace compositions in delicate biological tissues, as demonstrated here with a Phyllanthus urinaria leaf that only produced ion signals in the first examination and not in the subsequent measurements.

Initial ionization reaction in matrix-assisted laser desorption/ionization.

The initial ionization reaction in matrix-assisted laser desorption/ionization (MALDI) was examined on the basis of the appearance of photoelectrons. The threshold laser fluence for the ejection of photoelectrons from 2,5-dihydroxybenzoic acid (DHB), sinapinic acid (SA), and trihydroxyacetopheone (THAP) on stainless steel (SS) substrates was 0.05, 0.41, and 8.39 mJ/cm(2), respectively. These values are considerably lower than those for MALDI ions, indicating that the electron detachment likely precedes other ionization reactions. The SS substrate played an insignificant role in the production of photoelectrons because suspended DHB produced a photoelectron signal similar to DHB on the SS surface, and decreasing the DHB thickness on the SS reduced the photoelectron intensity. For crystalline DHB and SA, the photoelectron intensity increased with the laser (337 nm) fluence in a relationship of less than second order, suggesting considerable reductions of ionization potentials in comparison with free molecules. According to ab initio calculations, the ionization potential of DHB clusters reduces as the cluster size increases from monomer to octamer. The impact of these abundant electrons on the ion production in MALDI is discussed.

Incoherent production reactions of positive and negative ions in matrix-assisted laser desorption/ionization.

Utilizing synchronized dual-polarity matrix-assisted laser desorption/ionization (MALDI) mass spectrometry, we found good evidence of the incoherent production of positive and negative matrix ions. Using thin, homogeneous 2,5-dehydroxybenzoic acid (DHB) matrix films, positive and negative matrix ions were found to appear at different threshold laser fluences. The presence of molecular matrix ions of single charge polarity suggests that the existence of DHB ion-pairs may not be a prerequisite in MALDI. Photoelectrons induced by the laser excitation may assist the production of negative DHB ions, as shown in experiments conducted with stainless steel and glass substrates. At high laser fluences, the relative yield of positive and negative matrix ions remained constant when homogeneous matrix films were used, but it fluctuated significantly with inhomogeneous crystal morphology. This result is also inconsistent with the hypothesis that matrix ion-pairs are essential primary ions. Evidence from both low and high laser fluences suggests that the productions of positive and negative matrix ions in MALDI may occur via independent pathways.