Pt atoms adsorbed on TiO2(110)-(1 × 1) studied with noncontact atomic force microscopy and first-principles simulations

We have studied the local properties of single Pt atoms adsorbed on hydroxylated TiO2(110)-(1 × 1) by combining noncontact atomic force microscopy (nc-AFM) and first-principles calculations. Room-temperature high-resolution nc-AFM images for the most frequently observed contrast modes reveal bright and elongated protrusions that can be traced back to the Pt atoms, and that are centered on the fivefold coordinated titanium rows, confined between two bridging oxygen rows. These observations are in line with the theoretical results, as the lowest energy sites for the Pt atom on the TiO2(110) surface are in the neighborhood of the titanium rows, and high energy barriers have to be overcome to displace the Pt atom over the bridging oxygen rows. Single Pt atoms can be distinguished from H adsorbates (OH defects) due to their characteristic shape and binding site and, because they appear as the brightest surface features in all of the contrast modes. Force spectroscopy data over the protrusion and hole imaging modes and the corresponding tip-sample forces, simulated with O and OH terminated TiO2 nanoclusters, provide an explanation for this puzzling result in terms of the intrinsic strength of the interaction with the Pt adatom and the adatom and tip apex relaxations induced by the tip-sample interaction. These imaging mechanisms can be extended to other electropositive metal dopants and support the use of nc-AFM not only to characterize their adsorption structure but also to directly probe their chemical reactivityThis work was supported by Grants-in-Aid for Scientific Research (No. 22221006, No. 25106002, No. 24360016, No. 26600099, No. 2600015, No. 26110516, and No. 20760024) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan, Funding Program for Next Generation World-Leading Researchers and by the Ministerio de Economia y Competitividad (MINECO, Spain) uder Projects No. MAT2011-23627, No. CSD2010-00024, and No. PLE2009-006

Quantum degeneracy in atomic point contacts revealed by chemical force and conductance

Quantum degeneracy is an important concept in quantum mechanics with large implications to many processes in condensed matter. Here, we show the consequences of electron energy level degeneracy on the conductance and the chemical force between two bodies at the atomic scale. We propose a novel way in which a scanning probe microscope can detect the presence of degenerate states in atomic-sized contacts even at room temperature. The tunneling conductance G and chemical binding force F between two bodies both tend to decay exponentially with distance in a certain distance range, usually maintaining direct proportionality G∝F. However, we show that a square relation G∝F2 arises as a consequence of quantum degeneracy between the interacting frontier states of the scanning tip and a surface atom. We demonstrate this phenomenon on the Si(111)-(7×7) surface reconstruction where the Si adatom possesses a strongly localized dangling-bond state at the Fermi levelThis work was supported by Grants-in-Aid for Scientific Research (Grants No. 22221006, No. 24360016, No. 24651116, No. 22760028, and No. 25106002) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan (MEXT), Funding Program for Next Generation World-Leading Researchers. P. J. and M. O. acknowledge the financial support of GAAV M100101207. M.O. acknowledges the support provided by the Czech Science Foundation (GAČR) under Project No. P204/11/P578. R. P. and P. P. acknowledge Projects No. MAT2011-23627, No. CSD2010-00024, No. PLE2009-0061 (MINECO, Spain), and CAM S2009/ MAT-1467. P. P. was supported by the Ramón y Cajal Program (MINECO, Spain

Understanding image contrast formation in TiO 2 with force spectroscopy

Site-specific force measurements on a rutile TiO 2(110) surface are combined with first-principles calculations in order to clarify the origin of the force contrast and to characterize the tip structures responsible for the two most common imaging modes. Our force data, collected over a broad range of distances, are only consistent with a tip apex contaminated with clusters of surface material. A flexible model tip terminated with an oxygen explains the protrusion mode. For the hole mode we rule out previously proposed Ti-terminated tips, pointing instead to a chemically inert, OH-terminated apex. These two tips, just differing in the terminal H, provide a natural explanation for the frequent contrast changes found in the experiments. As tip-sample contact is difficult to avoid while imaging oxide surfaces, we expect our tip models to be relevant to interpret scanning probe studies of defects and adsorbates on TiO 2 and other technologically relevant metal oxidesWe thank the MEXT (19053006, 22221006, 21246010, 21656013, 20760024, and 22760028), JST, Handai FRC (Japan), and the spanish MICINN (MAT2008-1497, CSD2007-41, MAT2008-02929, MAT2008-02939-E, MAT2008-02953-E, PLE2009-0061, CSD2010-00024) for financial support. P.J. thanks ME10076. Y.S., C.G., and P.P. thank, respectively, Funding Program for Next Generation World-Leading Researchers, a CSIC JAE-Doc contract, and the Ramon y Cajal Program (MICINN

Protein C activity as a potential prognostic factor for nursing home-acquired pneumonia

[Introduction] Despite the poor prognosis for nursing home acquired pneumonia (NHAP), a useful prognostic factor is lacking. We evaluated protein C (PC) activity as a predictor of in-hospital death in patients with NHAP and community-acquired pneumonia (CAP). [Methods] This prospective, observational study included all patients hospitalized with pneumonia between July 2007 and December 2012 in a single hospital. We measured PC activity at admission and investigated whether it was different between survivors and non-survivors. We also examined whether PC activity 20 mg/dL, respiratory rate >30/min, and blood pressure 65). When it was a useful prognostic factor for pneumonia, we combined PC activity with the existing prognostic scores, the pneumonia severity index (PSI) and CURB-65, and analyzed its additional effect by comparing the areas under the receiver operating characteristic curves (AUCs) of the modified and original scores. [Results] Participants comprised 75 NHAP and 315 CAP patients. PC activity was lower among non-survivors than among survivors in NHAP and all-pneumonia (CAP+NHAP). PC activity <55% was a useful prognostic predictor for NHAP (Odds ratio 7.39 (95% CI; 1.59–34.38), and when PSI or CURB-65 was combined with PC activity, the AUC improved (from 0.712 to 0.820 for PSI, and 0.657 to 0.734 for CURB-65). [Conclusions] PC activity was useful for predicting in-hospital death of pneumonia, especially in NHAP, and became more useful when combined with the PSI or CURB-65

Force mapping on a partially H-covered Si(111)-(7×7) surface: Influence of tip and surface reactivity

We report force mapping experiments on Si(111)-(7×7) surfaces with adsorbed hydrogen, using atomic force microscopy at room temperature supported by density functional theory (DFT) simulations. On the basis of noncontact atomic force microscopy (NC-AFM) images as well as force versus distance curves measured over both hydrogen-passivated and bare Si adatoms, we identified two types of tip termination, which result in different modes of interaction with the surface. The statistics of the tip dependence of the measured forces, which are effectuated using various tip states with different cantilevers, reveal the typical values of the force and their distribution in the two characteristic interaction modes. The experimental results are corroborated by DFT calculations performed for different tip structures. As a reactive tip, the dimer-terminated Si tip yields results in satisfactory agreement with experimental force curves for hydrogen-passivated and nonpassivated Si adatom sites. An oxidized Si dimer tip that bears a hydroxyl group on its apex reproduces well the experimental force curves acquired by nonreactive tips. This tip model could thus be used to interpret the experimentally obtained weak image contrast for the Si(111)-(7×7) surface. The forces are thought to arise as a result of a weak electrostatic interaction involving a permanent dipole at the tip apex enhanced by the charge density redistribution due to the interaction with surface adatomsThis work was supported by Grants-in-Aid for Scientific Research (22221006, 24360016, 24651116, and 22760028) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan, Funding Program for Next Generation World-Leading Researchers. This work is also supported by MAT2011-23627, CSD2010-00024, PLE2009- 0061 (MINECO, Spain). P.P. was supported by the Ramón y Cajal program (MINECO, Spain).We further acknowledge the support provided by the Czech Science Foundation (GACR) under the projects P204/11/P578 and P204/10/0952, the GAAV project IAA100100905 and project M10010120

Alstiphyllanines E–H, picraline and ajmaline-type alkaloids from Alstonia macrophylla inhibiting sodium glucose cotransporter

Three new picraline-type alkaloids, alstiphyllanines E–G (1–3) and a new ajmaline-type alkaloid, alstiphyllanine H (4) were isolated from the leaves of Alstonia macrophylla together with 16 related alkaloids (5–20). Structures and stereochemistry of 1–4 were fully elucidated and characterized by 2D NMR analysis. Alstiphyllanines E and F (1 and 2) showed moderate Na+-glucose cotransporter (SGLT1 and SGLT2) inhibitory activity. A series of a hydroxy substituted derivatives 21–28 at C-17 of the picraline-type alkaloids have been derived as having potent SGLT inhibitory activity. 10-Methoxy-N(1)-methylburnamine-17-O-veratrate (6) exhibited potent inhibitory activity, suggesting that the presence of an ester side chain at C-17 may be important to show SGLT inhibitory activity. Structure activity relationship of alstiphyllanines on inhibitory activity of SGLT was discussed