| 1. |
- Xin, H., et al.
(författare)
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Strong Influence of Coadsorbate Interaction on CO Desorption Dynamics on Ru(0001) Probed by Ultrafast X-Ray Spectroscopy and Ab Initio Simulations
- 2015
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 114:15
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Tidskriftsartikel (refereegranskat)abstract
- We show that coadsorbed oxygen atoms have a dramatic influence on the CO desorption dynamics from Ru(0001). In contrast to the precursor-mediated desorption mechanism on Ru(0001), the presence of surface oxygen modifies the electronic structure of Ru atoms such that CO desorption occurs predominantly via the direct pathway. This phenomenon is directly observed in an ultrafast pump-probe experiment using a soft x-ray free-electron laser to monitor the dynamic evolution of the valence electronic structure of the surface species. This is supported with the potential of mean force along the CO desorption path obtained from density-functional theory calculations. Charge density distribution and frozen-orbital analysis suggest that the oxygen-induced reduction of the Pauli repulsion, and consequent increase of the dative interaction between the CO 5 sigma and the charged Ru atom, is the electronic origin of the distinct desorption dynamics. Ab initio molecular dynamics simulations of CO desorption from Ru(0001) and oxygen-coadsorbed Ru(0001) provide further insights into the surface bond-breaking process.
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| 2. |
- Östrom, Henrik, et al.
(författare)
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Probing the transition state region in catalytic CO oxidation on Ru
- 2015
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 347:6225, s. 978-982
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Tidskriftsartikel (refereegranskat)abstract
- Femtosecond x-ray laser pulses are used to probe the carbon monoxide (CO) oxidation reaction on ruthenium (Ru) initiated by an optical laser pulse. On a time scale of a few hundred femtoseconds, the optical laser pulse excites motions of CO and oxygen (O) on the surface, allowing the reactants to collide, and, with a transient close to a picosecond (ps), new electronic states appear in the OK-edge x-ray absorption spectrum. Density functional theory calculations indicate that these result from changes in the adsorption site and bond formation between CO and O with a distribution of OC-O bond lengths close to the transition state (TS). After 1 ps, 10% of the CO populate the TS region, which is consistent with predictions based on a quantum oscillator model.
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| 3. |
- Kanakis, G., et al.
(författare)
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Unusual Complication of a Pancreatic Neuroendocrine Tumor Presenting with Malignant Hypercalcemia
- 2012
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Ingår i: Journal of Clinical Endocrinology and Metabolism. - : The Endocrine Society. - 0021-972X .- 1945-7197. ; 97:4, s. E627-E631
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Tidskriftsartikel (refereegranskat)abstract
- Context: Hypersecretion of PTHrP is a relatively common cause of malignancy-related hypercalcemia but has only been described in a few cases of neuroendocrine tumors (NET). Objective: The aim of this case report is to describe the clinical syndrome, complex therapeutic interventions, and unusual complications caused by persistent PTHrP hypersecretion in a patient with a pancreatic NET. Case Illustration: A 58-yr-old male patient presented with nonspecific abdominal pain and was found to have severe hypercalcemia secondary to a well-differentiated NET of the pancreas associated with extensive liver metastases. Elevated ionized calcium levels accompanied by low serum PTH and remarkably elevated PTHrP concentrations were consistent with PTHrP-related hypercalcemia that proved to be resistant to various chemotherapeutic regimens and supportive therapy. Partial control of the humoral syndrome was obtained only after the application of cytoreductive interventions and the introduction of various molecular targeted therapies. Due to persistent PTHrP action, bone disease emerged in the form of brown tumors. Discussion: The manifestation of paraneoplastic syndrome due to PTHrP hypersecretion, despite its rareness in NET, should be considered in the differential diagnosis of hypercalcemia in such tumors. Moreover, the appearance of bone lesions in this setting may be in the context of metabolic bone disease and could be misdiagnosed as bone metastases.
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| 4. |
- LaRue, Jerry, et al.
(författare)
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Real-Time Elucidation of Catalytic Pathways in CO Hydrogenation on Ru
- 2017
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185 .- 1948-7185. ; 8:16, s. 3820-3825
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Tidskriftsartikel (refereegranskat)abstract
- The direct elucidation of the reaction pathways in heterogeneous catalysis has been challenging due to the short-lived nature of reaction intermediates. Here, we directly measured on ultrafast time scales the initial hydrogenation steps of adsorbed CO on a Ru catalyst surface, which is known as the bottleneck reaction in syngas and CO2 reforming processes. We initiated the hydrogenation of CO with an ultrafast laser temperature jump and probed transient changes in the electronic structure using real-time X-ray spectroscopy. In combination with theoretical simulations, we verified the formation of CHO during CO hydrogenation.
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| 5. |
- Miller, Daniel J., et al.
(författare)
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Low O-2 dissociation barrier on Pt(111) due to adsorbate-adsorbate interactions
- 2010
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics. - 0021-9606 .- 1089-7690. ; 133:22, s. 224701-
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Tidskriftsartikel (refereegranskat)abstract
- O2 dissociation on Pt(111) has been followed at low and saturation coverage using temperature-programmed x-ray photoelectron spectroscopy and simulated with mean-field kinetic modeling, yielding dissociation (Ea) and desorption (Ed) barriers of 0.32 and 0.36 eV, respectively. DFT calculations show that Ea is strongly influenced by the O–O interatomic potential in the atomic final state: of the supercells considered, that which maximizes attractive third-nearest-neighbor interactions in the atomic final state yields both the lowest computed dissociation barrier (0.24 eV) and the best agreement with experiment. It is proposed that the effect of adsorbate-adsorbate interactions must be considered when modeling catalytic processes involving dissociative steps.
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| 6. |
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| 7. |
- Beye, Martin, et al.
(författare)
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Chemical Bond Activation Observed with an X-ray Laser
- 2016
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185 .- 1948-7185. ; 7:18, s. 3647-3651
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Tidskriftsartikel (refereegranskat)abstract
- The concept of bonding and antibonding orbitals is fundamental in chemistry. The population of those orbitals and the energetic difference between the two reflect the strength of the bonding interaction. Weakening the bond is expected to reduce this energetic splitting, but the transient character of bond-activation has so far prohibited direct experimental access. Here we apply time-resolved soft X-ray spectroscopy at a free electron laser to directly observe the decreased bonding antibonding splitting following bond-activation using an ultrashort optical laser pulse.
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| 8. |
- Beye, M., et al.
(författare)
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Selective Ultrafast Probing of Transient Hot Chemisorbed and Precursor States of CO on Ru(0001)
- 2013
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 110:18
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the femtosecond dynamics following optical laser excitation of CO adsorbed on a Ru surface by monitoring changes in the occupied and unoccupied electronic structure using ultrafast soft x-ray absorption and emission. We recently reported [M. Dell'Angela et al. Science 339, 1302 (2013)] a phonon-mediated transition into a weakly adsorbed precursor state occurring on a time scale of >2 ps prior to desorption. Here we focus on processes within the first picosecond after laser excitation and show that the metal-adsorbate coordination is initially increased due to hot-electron-driven vibrational excitations. This process is faster than, but occurs in parallel with, the transition into the precursor state. With resonant x-ray emission spectroscopy, we probe each of these states selectively and determine the respective transient populations depending on optical laser fluence. Ab initio molecular dynamics simulations of CO adsorbed on Ru(0001) were performed at 1500 and 3000 K providing insight into the desorption process.
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| 9. |
- Dell'Angela, M., et al.
(författare)
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Real-Time Observation of Surface Bond Breaking with an X-ray Laser
- 2013
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 339:6125, s. 1302-1305
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Tidskriftsartikel (refereegranskat)abstract
- We used the Linac Coherent Light Source free-electron x-ray laser to probe the electronic structure of CO molecules as their chemisorption state on Ru(0001) changes upon exciting the substrate by using a femtosecond optical laser pulse. We observed electronic structure changes that are consistent with a weakening of the CO interaction with the substrate but without notable desorption. A large fraction of the molecules (30%) was trapped in a transient precursor state that would precede desorption. We calculated the free energy of the molecule as a function of the desorption reaction coordinate using density functional theory, including van der Waals interactions. Two distinct adsorption wells-chemisorbed and precursor state separated by an entropy barrier-explain the anomalously high prefactors often observed in desorption of molecules from metals.
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| 10. |
- Eriksson, B. K., et al.
(författare)
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Liver embolizations of patients with malignant neuroendocrine gastrointestinal tumors
- 1998
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Ingår i: Cancer. - 0008-543X .- 1097-0142. ; 83:11, s. 2293-2301
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND Patients with neuroendocrine gastrointestinal tumors usually present with inoperable metastatic disease and severe hormonal symptoms. Specific chemotherapy, interferon-alpha (IFN), and somatostatin analogs are established therapies for these patients, but all of them eventually fail. Hepatic arterial embolization can provide reduction of both hormonal symptoms and tumor burden in these patients. METHODS Between 1981 and 1995, a total of 55 liver embolizations with gel foam powder were performed on 41 patients with histopathologically verified neuroendocrine tumors; 29 had carcinoid tumors and 12 had endocrine pancreatic tumors (EPTs). All patients had received medical treatment, including chemotherapy (n = 18), IFN (n = 31), and octreotide (n = 19), and were experiencing treatment failure when liver embolization was performed at a median of 37 months after diagnosis of liver metastases. Medical treatment was continued after embolization. RESULTS An overall objective response was noted in 15 of 29 patients with carcinoid tumors (52%). The median duration of effect was 12 months in patients with midgut carcinoid tumors. An overall objective response was observed in 6 of 12 patients with EPTs (50%), with a median duration of effect of 10 months. Adverse events were observed, and, in agreement with earlier reports, the rate of serious complications was 10%. Survival analyses showed a median survival of 80 months and a 5-year survival rate of 60% from the performance of embolization on patients with midgut carcinoid tumors, whereas for patients with EPTs the median survival from embolization was only 20 months. CONCLUSIONS Liver embolizations performed relatively late in the clinical course in our series appeared to be as effective as "early" embolizations in other series of patients with carcinoid tumors. The results for those with EPTs were poorer, and earlier embolizations may result in better outcomes for these patients. Considering the morbidity associated with the procedure, it is imperative to select patients according to extent of liver involvement, severity of carcinoid heart disease, and somatostatin receptor status.
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