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PubMed2004

Water formation on Pd(111) by reaction of oxygen with atomic and molecular hydrogen.

In this work we have studied the steady-state reaction of molecular and atomic hydrogen with oxygen on a Pd(111) surface at a low total pressure (<10(-7) mbar) and at sample temperatures ranging from 100 to 1100 K. Characteristic features of the water formation rate Phi(pH2; pO2; TPd) are presented and discussed, including effects that are due to the use of gas-phase atomic hydrogen for exposure. Optimum impingement ratios (OIR) for hydrogen and oxygen for water formation and their dependence on the sample temperature have been determined. The occurring shift in the OIR could be ascribed to the temperature dependence of the sticking coefficients for hydrogen (SH2) and oxygen (SO2) on Pd(111). Using gas-phase atomic hydrogen for water formation leads to an increase of the OIR, suggesting that hydrogen abstraction via hot-atom reactions competes with H2O formation. The velocity distributions of the desorbing water molecules formed on the Pd(111) surface have been measured by time-of-flight spectroscopy under various conditions, using either gas-phase H atoms or molecular H2 as reactants. In all cases, the desorbing water flux could be represented by a Maxwellian distribution corresponding to the surface temperature, thus giving direct evidence for a Langmuir-Hinshelwood mechanism for water formation on Pd(111).

Journal Article↗
PubMed2005

A density functional study of NO adsorption and decomposition on Ni(211) and Pd(211) surfaces.

The adsorption and decomposition of NO have been investigated by using density functional theory method at the generalized gradient approximation level. We have performed calculations on adsorption energies and structures of NO on Ni(211) and Pd(211) surfaces with full-geometry optimization and compared them with the experimental data. The most favorite adsorption on both surfaces occurs at the bridge site parallel to step edge (sb), while the energy difference from the second favorite site of a threefold hollow site near step edge is less than 0.1 eV. Decomposition pathways have been investigated with transition state search. The decomposition pathway, where NO leans toward the step, is most probable for both surfaces. The overall activation energy for decomposition is 0.39 and 1.26 eV for Ni(211) and Pd(211), respectively. The present results clearly show that the NO molecules on Pd(211) are less activated than those on Ni(211). We have studied also reorganization of NO on Pd(211) at higher coverages up to 1/3 ML (monolayer) [three NO molecules in a (3 x 1) unit cell]. The site occupation is not in a sequential manner as the NO coverage is increased, and a reorganization of NO adsorbates occurs (the NO molecule at sb becomes tilting up at higher coverage), which can interpret the experimental data of Yates and co-workers very well.

Journal Article↗
PubMed2005

Growth and sintering of Pd clusters on alpha-Al2O3(0001).

The growth and sintering of Pd nanoparticles on alpha-Al(2)O(3)(0001) have been studied by noncontact atomic force microscopy (NC-AFM), low-energy ion scattering spectroscopy (LEIS), temperature-programmed desorption (TPD) and x-ray photoelectron spectroscopy (XPS). This is the first study of metal nanoparticles on a well-defined oxide surface where both NC-AFM and LEIS are used for characterization. These prove to be a powerful combination in assessing particle dimensions. The clean alumina surface showed atomically flat, 200-700 nm wide terraces. The sharp step edges are straight (within our resolution) for lengths of >300 nm and have heights in multiples of 0.2 nm. The Pd grows initially as two-dimensional (2D) islands at 300 K, with the transition to 3D particle growth at 0.25 ML (ML=monolayers). Upon heating at 1 K/s, the Pd starts to sinter below 400 K, and sinters at a nearly constant rate with increasing temperature, covering approximately 50% less of the alumina surface by approximately 1000 K, with a doubling in particle diameter and an eightfold decrease in particle number density. By approximately 1000 K, the number density was approximately 9 x 10(11)cm(2) for 0.8 ML of Pd, with an average diameter of 5 nm and an average thickness of 1 nm.

Journal Article↗
PubMed2005

Observation and manipulation of subsurface hydride in Pd[111] and its effect on surface chemical, physical, and electronic properties.

We report the observation and manipulation of hydrogen atoms beneath the surface of a Pd[111] crystal by using low-temperature scanning tunneling microscopy. These subsurface hydride sites have been postulated to have critical roles in hydrogen storage, metal embrittlement, fuel cells, and catalytic reactions, but they have been neither observed directly nor selectively populated previously. We demonstrate that the subsurface region of Pd can be populated with hydrogen atoms from the bulk by applying voltage pulses from a scanning tunneling microscope tip. This phenomenon is explained with an inelastic excitation mechanism, whereby hydrogen atoms in the bulk are excited by tunneling electrons and are promoted to more stable sites in the subsurface region. We show that this selectively placed subsurface hydride affects the electronic, geometric, and chemical properties of the surface. Specifically, we observed the effects of hydride formation on surface deformation and charge and on adsorbed hydrogen on the surface. Hydrogen segregation and overlayer vacancy ordering on the Pd[111] have been characterized and explained in terms of the surface changes attributable to selective hydrogen occupation of subsurface hydride sites in Pd[111].

Journal Article↗
PubMed1998

p53 transactivation of the HIV-1 long terminal repeat is blocked by PD 144795, a calcineurin-inhibitor with anti-HIV properties.

Previous reports have indicated that benzothiophenes exhibit broad anti-inflammatory properties and inhibit human immunodeficiency virus-type 1 (HIV-1) replication. We show that the immunosuppressant cyclosporin A (CsA) and benzothiophene-2-carboxamide, 5-methoxy-3-(1-methyl ethoxy)-1-oxide (PD 144795) block the induction of p53 and NF-kappaB binding to the HIV-1 long terminal repeat (LTR) by the T cell receptor activator phytohemagglutinin. CsA and PD 144795 also inhibit the induction by phytohemagglutinin of the transcription mediated by an HIV-1 LTR fragment containing the p53 and NF-kappaB sites. These effects of PD 144795 on HIV-1 transcription correlate with its ability to inhibit the phosphatase activity of calcineurin and are similar to those previously described for CsA. Moreover, a constitutive active form of calcineurin is able to induce expression from the HIV-1 LTR in a p53- and NF-kappaB-dependent manner and PD 144795 is able to block this induction. These results demonstrate that the DNA binding of p53 to the HIV-1 LTR can be modulated by calcineurin and provide a framework to understand the anti-HIV properties of benzothiophene derivatives.

Anti-HIV Agents↗
PubMed1998

Direct inhibition of cyclooxygenase-1 and -2 by the kinase inhibitors SB 203580 and PD 98059. SB 203580 also inhibits thromboxane synthase.

The kinase inhibitors SB 203580 and PD 98059 have been reported to be specific inhibitors of the 38- and 42/44-kDa mitogen-activated protein kinase (MAPK) pathways, respectively. In this study, the two inhibitors were found to decrease platelet aggregation induced by low concentrations of arachidonic acid, suggesting that they also interfere with the metabolism of arachidonic acid to thromboxane A2. In support of this, SB 203580 and PD 98059 inhibited the conversion of exogenous [3H]arachidonic acid to [3H]thromboxane in intact platelets. Measurement of platelet cyclooxygenase-1 activity following immunoprecipitation revealed that SB 203580 and PD 98059 are direct inhibitors of this enzyme. Both compounds were shown to inhibit purified cyclooxygenase-1 and -2 by a reversible mechanism. In addition, SB 203580 (but not PD 98059) inhibited platelet aggregation induced by prostaglandin H2 and the conversion of prostaglandin H2 to thromboxane A2 in intact platelets. SB 203580 also inhibited this pathway in platelet microsome preparations, suggesting a direct inhibitory effect on thromboxane synthase. These results demonstrate that direct effects of the two kinase inhibitors on active arachidonic acid metabolites have to be excluded before using these compounds for the investigation of MAPKs in signal transduction pathways. This is of particular relevance to studies on the regulation of cytosolic phospholipase A2 as these two MAPKs are capable of phosphorylating cytosolic phospholipase A2, thereby increasing its intrinsic activity.

Arachidonic Acid↗
PubMed2006

Interaction of some Pd(II) complexes with Na+ / K+-ATPase: inhibition, kinetics, prevention and recovery.

The aim of this work was to investigate the influence of [PdCl4]2-, [PdCl(dien)]+ and [PdCl(Me4dien)]+ complexes on Na+ / K+-ATPase activity. The dose-dependent inhibition curves were obtained in all cases. IC50 values determined by Hill analysis were 2.25 x 10(-5) M, 1.21 x 10(-4) M and 2.36 x 10(-4) M, respectively. Na+ / K+-ATPase exhibited typical Michelis-Menten kinetics in the presence of Pd(II) complexes. Kinetic parameters (Vmax, Km) derived using Eadie-Hofstee transformation indicated a noncompetitive type of Na+ / K+-ATPase inhibition. The inhibitor constants (Ki) were determined from Dixon plots. The order of complex affinity for binding with Na+ / K+-ATPase, deducted from Ki values, was [PdCl4]2- > [PdCl(dien)]+ > [PdCl(Me4dien)]+. The results indicated that the potency of Pd(II) complexes to inhibit Na+/ K +-ATPase activity depended strongly on ligands of the related compound. Furthermore, the ability of SH-donor ligands, L-cysteine and glutathione, to prevent and recover the Pd(II) complexes-induced inhibition of Na+ / K+-ATPase was examined. The addition of 1 mM L-cysteine or glutathione to the reaction mixture before exposure to Pd(II) complexes prevented the inhibition by increasing the IC50 values by one order of magnitude. Moreover, the inhibited enzymatic activity was recovered by addition of SH-donor ligands in a concentration-dependent manner.

Adenosine Triphosphatases↗
PubMed2003

B7DC/PDL2 promotes tumor immunity by a PD-1-independent mechanism.

B7H1 (PDL1) and B7DC (PDL2) are two new members of the B7 family that can interact with PD-1, a putative negative regulator for immune function. Recent studies have provided evidence for inhibitory functions of both members via PD-1. Meanwhile, compelling evidence exists for costimulatory function of both members. Here we demonstrate that expression of B7DC on the tumor cells promotes CD8 T cell-mediated rejection of tumor cells, at both the induction and effector phase of antitumor immunity. Moreover, B7DC binds to PD-1(-/-) cells and enhances T cell killing in a PD-1-independent mechanism. Our results demonstrate a novel pathway for B7DC to promote tumor immunity and may reconcile the apparently contradictory findings on the function of B7DC.

Adoptive Transfer↗
PubMed1989

In-vitro activity of PD 117558, a new quinolone against bacterial isolates from cancer patients.

The in-vitro activity of PD 117558, a new quinolone antimicrobial agent, was compared to that of four other quinolones, imipenem and ceftazidime against a variety of Gram-positive and Gram-negative isolates from cancer patients. PD 117558 was found to have a broad antimicrobial spectrum with excellent activity against all Gram-positive isolates (including methicillin-resistant Staphylococcus aureus, coagulase-negative staphylococci, Streptococcus faecalis and Group JK-corynebacteria). It was also extremely active against Gram-negative bacilli with the exception of Pseudomonas aeruginosa against which ciprofloxacin was more active. Fleroxacin was slightly less active and S-25930 and S-25932 considerably less active than PD 117558. PD 117558 also had lower minimal inhibitory concentrations for most organisms tested than either imipenem or ceftazidime.

4-Quinolones↗
PubMed1993

Methods for testing the susceptibility of anaerobic bacteria to two fluoroquinolone compounds, PD 131628 and clinafloxacin.

The susceptibility of anaerobic bacteria to two new fluoroquinolones, PD 131628 (the bioactive form of PD 131112 or CI-990) and clinafloxacin (CI-960 or PD 127391), was determined with the agar dilution procedures and two media, and one broth microdilution procedure. Sparfloxacin and ciprofloxacin were also tested by the broth microdilution method. One hundred anaerobic isolates and four control strains were tested by the three methods which gave minimum inhibitory concentrations (MICs) that were essentially comparable, but not identical. With the broth microdilution method, the relative potency of the four fluoroquinolones was: clinafloxacin > PD 131628 > sparfloxacin > ciprofloxacin. For the latter three drugs but not clinafloxacin, the MIC values were often near the proposed interpretive breakpoint concentrations, and thus minor methodological differences frequently influenced the interpretive categories. Replicate agar dilution tests in five laboratories established MIC control limits for each of four control strains: those MIC limits could also be used to define the expected performance of the two alternative methods.

Anti-Infective Agents↗
PubMed1996

Tentative interpretive criteria and quality control parameters for in-vitro susceptibility testing of Neisseria gonorrhoeae to two fluoroquinolones (PD 131628 and grepafloxacin (OPC 17116)).

The susceptibility of Neisseria gonorrhoeae to PD 131628 and grepafloxacin (OPC 17116) was evaluated by agar dilution and disc diffusion methods. A tentative susceptibility category for both fluoroquinolones included strains for which the MICs are < or = 0.06 mg/L and the zones of inhibition are > or = 38 mm for PD 131628 and > or = 37 mm for grepafloxacin. Quality control studies with N. gonorrhoeae ATCC 49226 suggested that agar dilution MIC limits were 0.002-0.008 mg/L and 0.004-0.03 mg/L for PD 131628 and grepafloxacin, respectively. The zone size limits were 50-58 mm for PD 131628 and 44-52 mm for grepafloxacin.

Anti-Infective Agents↗
PubMedDate not supplied

Photoreceptor dysplasia (pd) in miniature schnauzer dogs: evaluation of candidate genes by molecular genetic analysis.

Photoreceptor dysplasia (pd) is one of a group of at least six distinct autosomal and one X-linked retinal disorders identified in dogs which are collectively known as progressive retinal atrophy (PRA). It is an early onset retinal disease identified in miniature schnauzer dogs, and pedigree analysis and breeding studies have established autosomal recessive inheritance of the disease. Using a gene-based approach, a number of retina-expressed genes, including some members of the phototransduction pathway, have been causally implicated in retinal diseases of humans and other animals. Here we examined seven such potential candidate genes (opsin, RDS/peripherin, ROM1, rod cGMP-gated cation channel alpha-subunit, and three subunits of transducin) for their causal association with the pd locus by testing segregation of intragenic markers with the disease locus, or, in the absence of informative polymorphisms, sequencing of the coding regions of the genes. Based on these results, we have conclusively excluded four photoreceptor-specific genes as candidates for pd by linkage analysis. For three other photoreceptor-specific genes, we did not find any mutation in the coding sequences of the genes and have excluded them provisionally. Formal exclusion would require investigation of the levels of expression of the candidate genes in pd-affected dogs relative to age-matched controls. At present we are building suitable informative pedigrees for the disease locus with a sufficient number of meiosis to be useful for genomewide screening. This should identify markers linked to the disease locus and eventually permit progress toward the identification of the photoreceptor dysplasia gene and the disease-causing mutation.

Animals↗
PubMed2006

PD in the elderly--a challenge for the (pre)dialysis team.

Peritoneal dialysis in elderly patients is not widely applied, although data show that PD is often preferred by elderly patients. This paper describes current restrictions to the application of PD in elderly patients and their possible solutions. This includes (contra) indications to PD as well as data on patients' preference, quality of life specific for elderly patients and data on outcome of PD in older patients. The possibility of assisted peritoneal dialysis is offered as a challenge to the dialysis team.

Age Factors↗
PubMed2004

In vivo binding behavior of dopamine receptor agonist (+)-PD 128907 and implications for the "ceiling effect" in endogenous competition studies with [(11)C]raclopride-a positron emission tomography study in Macaca mulatta.

In in vivo positron emission tomography (PET) studies, dopamine that is released secondary to amphetamine administration appears unable to achieve a receptor occupancy that is significantly higher than 50% ("ceiling effect"). Also with exogenous agonists no studies have reported a higher than 50% occupancy. To investigate the feasibility of exceeding 50% occupancy in vivo with a dopamine receptor agonist we administered D2/D3 agonist (+)-PD 128907 over an extensive dose range. Two anesthetised Macaca mulatta males were used in a bolus-infusion protocol for [(11)C]raclopride. (+)-PD 128907 was administered as an intravenous challenge during separate PET scans in a dose range of 10 to 10000 nmol/kg. Occupancy by (+)-PD 128907 was estimated by comparing the binding before and after challenge. In a striatal region of interest, receptor occupancy by (+)-PD 128907 increased in an orderly dose-dependent manner to a maximum of at least 85%. This is the first indication that virtually all dopamine D2/D3 receptors in the striatum are in principle accessible to agonist binding. In the case of dopamine a number of protective mechanisms may be responsible for the ceiling effect.

Animals↗
PubMed1993

Vasoconstriction in the rat kidney induced by endothelin-1 is blocked by PD 145065.

We have previously shown that the receptors mediating the renal and systemic vasoconstrictor effects of endothelin-1 (ET-1) are of two distinct endothelin receptor subtypes. Here, we evaluate the effect of PD 145065, a nonselective endothelin receptor antagonist, on the renal vasoconstrictor effects of ET-1 in the rat kidney. ET-1 induced concentration-dependent increases in perfusion pressure in the isolated perfused kidney of the rat. The ETA receptor-selective antagonists BQ-123 (10 microM) and FR 139317 (10 microM) lowered the ET-1-induced rise in perfusion pressure by 57% and 61%, respectively, at 3 x 10(-10) M ET-1. By comparison, the ET-1-induced vasoconstriction was fully antagonized (96% inhibition) by PD 145065 (10 microM). In the anesthetized rat, ET-1 produced a dose-dependent increase in mean arterial pressure, which was attenuated by PD 145065. The initial depressor response to ET-1 was completely blocked by PD 145065, as were the reduction in renal blood flow and increase in renal vascular resistance induced by ET-1. These results suggest that both the ETA and a non-ETA receptor subtype play an important role in mediating the vasoconstrictor effects of ET-1 in the rat kidney.

Amino Acid Sequence↗
PubMed2000

Magnetic quantum critical point and superconductivity in UPt3 doped with Pd.

Transverse-field muon spin relaxation measurements have been carried out on the heavy-fermion superconductor UPt (3) doped with small amounts of Pd. We find that the critical Pd concentration for the emergence of the large-moment antiferromagnetic phase is approximately 0.6 at. %Pd. At the same Pd content, superconductivity is completely suppressed. The existence of a magnetic quantum critical point in the phase diagram, which coincides with the critical point for superconductivity, provides evidence for ferromagnetic spin-fluctuation mediated odd-parity superconductivity, which competes with antiferromagnetic order.

Journal Article↗
PubMed2002

Adsorbate-oxide interactions during the NO + CO reaction on MgO(100) supported Pd monolayer films.

The potential energy diagram for the NO+CO reaction on 1, 2, and 3 monolayer (ML) Pd films supported by MgO(100) is calculated using density functional theory. Thin Pd films are generally found to be more reactive than thick films, with a notable exception for nitrogen adsorption on 2 ML Pd/MgO(100). For this system an attractive through-the-metal adsorbate-oxide interaction of 0.5 eV is identified. Nitrogen adsorption is consequently estimated to provide a thermodynamic driving force for the reconstruction of MgO(100) supported 3 ML (or thicker) Pd clusters into thinner Pd clusters.

Journal Article↗
PubMed2002

Highly strained structure of a four-layer deposit of Pd on Ni(110): a coupled theoretical and experimental study.

The structure of a four monolayer deposit of Pd on Ni(110) has been determined by a combination of x-ray diffraction experiments and density-functional theory calculations. This Pd film presents, after annealing at 500 K, a (Nx2) reconstruction associated with a large enhancement of its catalytic activity. The N superstructure, along the dense [11;0] direction, comes from periodic edge dislocations initiated by a vacancy in the first Pd layer. In the perpendicular direction, the doubling of the period originates in a pairing-buckling displacement of the rows. This study evidences a new Pd atoms arrangement with quasi-four-fold hollow sites on the surface, which could play an important role in the exceptional catalytic activity.

Journal Article↗