Global and local expression of chirality in serine on the Cu{110} surface

Establishing a molecular-level understanding of enantioselectivity and chiral resolution at the organic−inorganic interfaces is a key challenge in the field of heterogeneous catalysis. As a model system, we investigate the adsorption geometry of serine on Cu{110} using a combination of low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The chirality of enantiopure chemisorbed layers, where serine is in its deprotonated (anionic) state, is expressed at three levels: (i) the molecules form dimers whose orientation with respect to the substrate depends on the molecular chirality, (ii) dimers of l- and d-enantiomers aggregate into superstructures with chiral (−1 2; 4 0) lattices, respectively, which are mirror images of each other, and (iii) small islands have elongated shapes with the dominant direction depending on the chirality of the molecules. Dimer and superlattice formation can be explained in terms of intra- and interdimer bonds involving carboxylate, amino, and β−OH groups. The stability of the layers increases with the size of ordered islands. In racemic mixtures, we observe chiral resolution into small ordered enantiopure islands, which appears to be driven by the formation of homochiral dimer subunits and the directionality of interdimer hydrogen bonds. These islands show the same enantiospecific elongated shapes those as in low-coverage enantiopure layers

Enhanced oxidation resistance of active nanostructures via dynamic size effect.

A major challenge limiting the practical applications of nanomaterials is that the activities of nanostructures (NSs) increase with reduced size, often sacrificing their stability in the chemical environment. Under oxidative conditions, NSs with smaller sizes and higher defect densities are commonly expected to oxidize more easily, since high-concentration defects can facilitate oxidation by enhancing the reactivity with O2 and providing a fast channel for oxygen incorporation. Here, using FeO NSs as an example, we show to the contrary, that reducing the size of active NSs can drastically increase their oxidation resistance. A maximum oxidation resistance is found for FeO NSs with dimensions below 3.2 nm. Rather than being determined by the structure or electronic properties of active sites, the enhanced oxidation resistance originates from the size-dependent structural dynamics of FeO NSs in O2. We find this dynamic size effect to govern the chemical properties of active NSs

Loss of p53 Attenuates the Contribution of IL-6 Deletion on Suppressed Tumor Progression and Extended Survival in Kras-Driven Murine Lung Cancer

Interleukin-6 (IL-6) is involved in lung cancer tumorigenesis, tumor progression, metastasis, and drug resistance. Previous studies show that blockade of IL-6 signaling can inhibit tumor growth and increase drug sensitivity in mouse models. Clinical trials in non-small cell lung cancer (NSCLC) reveal that IL-6 targeted therapy relieves NSCLC-related anemia and cachexia, although other clinical effects require further study. We crossed IL-6-/- mice with KrasG12D mutant mice, which develop lung tumors after activation of mutant KrasG12D, to investigate whether IL-6 inhibition contributes to tumor progression and survival time in vivo. KrasG12D; IL-6-/- mice exhibited increased tumorigenesis, but slower tumor growth and longer survival, than KrasG12D mice. Further, in order to investigate whether IL-6 deletion contributes to suppression of lung cancer metastasis, we generated KrasG12D; p53flox/flox; IL-6-/- mice, which developed lung cancer with a trend for reduced metastases and longer survival than KrasG12D; p53flox/flox mice. Tumors from KrasG12D; IL-6-/- mice showed increased expression of TNFα and decreased expression of CCL-19, CCL-20 and phosphorylated STAT3 (pSTAT3) than KrasG12D mice; however, these changes were not present between tumors from KrasG12D; p53flox/flox; IL-6-/- and KrasG12D; p53flox/flox mice. Upregulation of pSTAT3 and phosphorylated AKT (pAKT) were observed in KrasG12D tumors with p53 deletion. Taken together, these results indicate that IL-6 deletion accelerates tumorigenesis but delays tumor progression and prolongs survival time in a Kras-driven mouse model of lung cancer. However, these effects can be attenuated by p53 deletion

Studies of Isolated and Non-isolated Photospheric Bright Points in an Active Region Observed by the New Vacuum Solar Telescope

Properties of photospheric bright points (BPs) near an active region have been studied in TiO λ 7058 Å images observed by the New Vacuum Solar Telescope of the Yunnan Observatories. We developed a novel recognition method that was used to identify and track 2010 BPs. The observed evolving BPs are classified into isolated (individual) and non-isolated (where multiple BPs are observed to display splitting and merging behaviors) sets. About 35.1% of BPs are non-isolated. For both isolated and non-isolated BPs, the brightness varies from 0.8 to 1.3 times the average background intensity and follows a Gaussian distribution. The lifetimes of BPs follow a log-normal distribution, with characteristic lifetimes of (267 ± 140) s and (421 ± 255) s, respectively. Their size also follows log-normal distribution, with an average size of about (2.15 ± 0.74) × 104 km2 and (3.00 ± 1.31) × 104 km2 for area, and (163 ± 27) km and (191 ± 40) km for diameter, respectively. Our results indicate that regions with strong background magnetic field have higher BP number density and higher BP area coverage than regions with weak background field. Apparently, the brightness/size of BPs does not depend on the background field. Lifetimes in regions with strong background magnetic field are shorter than those in regions with weak background field, on average

Polarimetric SAR Image Supervised Classification Method Integrating Eigenvalues

Since classification methods based on H/α space have the drawback of yielding poor classification results for terrains with similar scattering features, in this study, we propose a polarimetric Synthetic Aperture Radar (SAR) image classification method based on eigenvalues. First, we extract eigenvalues and fit their distribution with an adaptive Gaussian mixture model. Then, using the naive Bayesian classifier, we obtain preliminary classification results. The distribution of eigenvalues in two kinds of terrains may be similar, leading to incorrect classification in the preliminary step. So, we calculate the similarity of every terrain pair, and add them to the similarity table if their similarity is greater than a given threshold. We then apply the Wishart distance-based KNN classifier to these similar pairs to obtain further classification results. We used the proposed method on both airborne and spaceborne SAR datasets, and the results show that our method can overcome the shortcoming of the H/α-based unsupervised classification method for eigenvalues usage, and produces comparable results with the Support Vector Machine (SVM)-based classification method

Structural Transformation of Supported, Intercalated, and Doped Cu Nanostructures on FeO/Pt(111) under Oxidizing and Reducing Conditions

The structural evolution of supported metal catalysts often happens during reaction and can strongly influence their catalytic performance. Thus, understanding the structural transformation of metal catalysts under different conditions is critical to modulating their activity and stability. Here, Cu nanostructures on monolayer FeO film on Pt(111) have been constructed, which are used as model systems to study the structural changes of Cu under different treatment conditions by using scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). Supported Cu nanostructures on FeO (Cu/FeO/Pt(111)) can be prepared by deposition of Cu at 100 K, and they can transform into intercalated Cu structures (FeO/Cu/Pt(111)) by annealing at 300 K in ultrahigh vacuum and further change to PtCu alloy (FeO/Pt/PtCu) at 700 K. Annealing the supported and intercalated Cu structures in O2 atmosphere induces the formation of Cu dopants in the FeO film (CuxFeyOz/Pt(111)). Furthermore, intercalated and doped Cu nanostructures can be reversibly transformed into each other under redox treatments. The atomic identification of Cu structural evolution and the coordination environments of Cu dopants provide a deep understanding of Cu catalysts under reaction conditions

Origin of the Thickness-Dependent Oxidation of Ultrathin Cu Films on Au(111)

Ultrathin Cu films deposited on a metal substrate have been used as a model system to understand the structure function relationship in electro-catalysis, heterogeneous catalysis, and microelectronics. The stability of ultrathin Cu films against oxidation has been of particular interest, but there is a lack of microscopic understanding. We report here an atomic-level study on the thickness dependent oxidation kinetics of Cu layers on Au(111), from ultrahigh vacuum to near ambient conditions. Ultrathin Cu films on Au(111) were found to exhibit a superior oxidation resistance over Cu(111), and their oxidation resistances increase in the order of Cu(111) < 2.4 ML Cu < 0.4 ML Cu. For 0.4 ML Cu, the spontaneous subsurface diffusion of Cu at 300 K and the formation of a Au-rich surface alloy inhibit the formation of copper oxides at the O-2 pressure below 10(-4) mbar. However, at near ambient conditions, 0.4 ML Cu would be partially oxidized to the CuO phase directly. In contrast, multilayer Cu or bulk Cu(111), though oxidized more rapidly, forms only Cu2O surface layers under the same oxidation conditions. We analyzed further the atomic process of alloying at elevated temperatures. An intermediate Au3Cu alloy phase was suggested at the subsurface at 400 K. The diffusion of Cu into bulk Au(111) at 600 K prevents the formation of copper oxides at 300 K even under near-ambient conditions. Our study could thus provide insight for the rational design of a highly efficient Cu-based oxidation catalyst

CO adsorption on a Pt(111) surface partially covered with FeOx nanostructures

The adsorption of CO on Pt group metals, as a most fundamental elementary reaction step, has been widely studied in catalysis and electrocatalysis. Particularly, the structures of CO on Pt(111) have been extensively investigated, owing to its importance to both fundamental and applied catalysis. Yet, much less is known regarding CO adsorption on a Pt(111) surface modulated by supported oxide nanostructures, which is of more relevance to technical catalysis. We thus investigated the coverage-dependent adsorption of CO on a Pt(111) surface partially covered by FeOx nanostructures, which has been demonstrated as a remarkable catalyst for low-temperature CO oxidation. We found that, due to its strong chemisorption, the coverage-dependent structure of CO on bare Pt is not influenced by the presence of FeOx. But, oxygen-terminated FeOx nanostructures could modulate the diffusivity of CO at their vicinity, and thus affect the formation of ordered CO superstructures at low temperatures. Using scanning tunneling microscopy (STM), we inspected the diffusivity of CO, followed the phase transitions of CO domains, and resolved the molecular details of the coverage-dependent CO structures. Our results provide a full picture for CO adsorption on a Pt(111) surface modulated by oxide nanostructures and shed lights on the inter-adsorbate interaction on metal surfaces. (C) 2017 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved

coadsorptiononapt111surfacepartiallycoveredwithfeoxnanostructures

The adsorption of co on pt group metals, as a most fundamental elementary reaction step, has been widely studied in catalysis and electrocatalysis. particularly, the structures of co on pt(111) have been extensively investigated, owing to its importance to both fundamental and applied catalysis. yet, much less is known regarding co adsorption on a pt(111) surface modulated by supported oxide nanostructures, which is of more relevance to technical catalysis. we thus investigated the coverage-dependent adsorption of co on a pt(111) surface partially covered by feox nanostructures, which has been demonstrated as a remarkable catalyst for low-temperature co oxidation. we found that, due to its strong chemisorption, the coverage-dependent structure of co on bare pt is not influenced by the presence of feox. but, oxygen-terminated feox nanostructures could modulate the diffusivity of co at their vicinity, and thus affect the formation of ordered co superstructures at low temperatures. using scanning tunneling microscopy (stm), we inspected the diffusivity of co, followed the phase transitions of co domains, and resolved the molecular details of the coverage-dependent co structures. our results provide a full picture for co adsorption on a pt(111) surface modulated by oxide nanostructures and shed lights on the inter-adsorbate interaction on metal surfaces. (c) 2017 science press and dalian institute of chemical physics, chinese academy of sciences. published by elsevier b.v. and science press. all rights reserved