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CO Molecule (co + molecule)
Selected AbstractsTheory of tip-dependent imaging of adsorbates in the STM: CO on Cu(111)INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 6 2006D. Drakova Abstract The processes of local electron injection or extraction in the scanning tunneling microscopy (STM) and spectroscopy (STS) lead to the creation of short-lived excited states localized at the electrode surfaces. The dynamic relaxation of the transient negative or positive ion resonances, due to both local and long-range interactions, is the clue to the understanding of numerous phenomena in STM/STS ranging from the "anomalously" large tip height corrugation amplitudes on clean metal surfaces to the observation of quantum mirages and features in the STS, which are not observed with the help of other surface spectroscopies. Quantum nanodynamics theory (QND) has been applied to calculate the interaction potential of a single CO molecule with the Cu(111) surface, with a transient negative ion resonance formed when an electron is injected from the tip, and the tunneling conductance on the clean and CO covered Cu(111) surface using a clean metal tip Al/Al(111) and a Pt(111) tip with an adsorbed CO molecule at the apex. Within QND and three-dimensional scattering theory, regarding the tunneling as an excited-state problem, we provide the explanation of the tip-dependent STM image of a single CO molecule on Cu(111). The appearance of the CO molecule as an indentation, using a clean metal tip and as a protrusion with a tip terminated by a CO molecule, is understood as a result of tunneling through two competing channels. Tunneling via adsorbate-induced ion resonances enhances the tunneling conductance. In contrast, tunneling via metal ion resonances only leads to attenuation of the conductance in the presence of the adsorbate. The current in the vicinity of the adsorbed CO molecule is reduced when a clean metal tip is used; i.e., CO appears dark in the STM image, because metal ion resonances on Cu(111) derive from the surface states with image state components coupling to plasmons and are therefore very diffuse. With a CO-terminated tip, the major current channel is, for symmetry reasons, from the 2,-derived orbital of the tip CO molecule, via the diffuse 2,-derived orbital of the CO molecule on the sample, hence adsorbed CO appears bright. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source] Refinement of modulated structures against X-ray powder diffraction data with JANA2000JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2001M. Du JANA is a computer program for the refinement and analysis of periodic and aperiodic (incommensurately modulated structures and composite crystals) crystal structures. Here a new module is introduced that allows Rietveld refinements against powder diffraction data. It is shown that JANA2000 provides a state-of-the-art description of the peak profiles. A re-analysis of the low-temperature structure of (CO)xC60 showed that the application of icosahedral symmetry restrictions to the C60 molecule leads to a better description of the electron density and to a corrected position of the CO molecule as compared with a rigid-body refinement. The incommensurately modulated structure of NbTe4 has been successfully refined against X-ray powder diffraction data. The structural parameters are equal to, but less accurate, than the parameters obtained from a single-crystal study. [source] First-principle calculations on CO oxidation catalyzed by a gold nanoparticleJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 2 2010Hsin-Tsung Chen Abstract We have elucidated the mechanism of CO oxidation catalyzed by gold nanoparticles through first-principle density-functional theory (DFT) calculations. Calculations on selected model show that the low-coordinated Au atoms of the Au29 nanoparticle carry slightly negative charges, which enhance the O2 binding energy compared with the corresponding bulk surfaces. Two reaction pathways of the CO oxidation were considered: the Eley,Rideal (ER) and Langmuir,Hinshelwood (LH). The overall LH reaction O2(ads) + CO(gas) , O2(ads) + CO(ads) , OOCO(ads) , O(ads) + CO2(gas) is calculated to be exothermic by 3.72 eV; the potential energies of the two transition states (TSLH1 and TSLH2) are smaller than the reactants, indicating that no net activation energy is required for this process. The CO oxidation via ER reaction Au29 + O2(gas) + CO(gas) , Au29,O2(ads) + CO(gas) , Au29,CO3(ads) , Au29,O(ads) + CO2(gas) requires an overall activation barrier of 0.19 eV, and the formation of Au29,CO3(ads) intermediate possesses high exothermicity of 4.33 eV, indicating that this process may compete with the LH mechanism. Thereafter, a second CO molecule can react with the remaining O atom via the ER mechanism with a very small barrier (0.03 eV). Our calculations suggest that the CO oxidation catalyzed by the Au29 nanoparticle is likely to occur at or even below room temperature. To gain insights into high-catalytic activity of the gold nanoparticles, the interaction nature between adsorbate and substrate is also analyzed by the detailed electronic analysis. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 [source] Tracking ligand-migration pathways of carbonmonoxy myoglobin in crystals at cryogenic temperaturesACTA CRYSTALLOGRAPHICA SECTION A, Issue 2 2010Ayana Tomita In order to explore the ligand-migration dynamics in myoglobin induced by photodissociation, cryogenic X-ray crystallographic investigations of carbonmonoxy myoglobin crystals illuminated by continuous wave and pulsed lasers at 1,15,kHz repetition rate have been carried out. Here it is shown that this novel method, extended pulsed-laser pumping of carbonmonoxy myoglobin, promotes ligand migration in the protein matrix by crossing the glass transition temperature repeatedly, and enables the visualization of the migration pathway of the photodissociated ligands in native Mb at cryogenic temperatures. It has revealed that the migration of the CO molecule into each cavity induces structural changes of the amino-acid residues around the cavity which result in the expansion of the cavity. The sequential motion of the ligand and the cavity suggests a self-opening mechanism of the ligand-migration channel arising by induced fit. [source] Flame-Synthesized Copper Dimers: Flame-Synthesized Ceria-Supported Copper Dimers for Preferential Oxidation of CO (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 3 2009Mater. On page 369, R. Kydd et al. describe the creation of highly dispersed copper dimers (violet areas) on Ceria nanoparticles (green areas) via rapid flame-spray pyrolysis. These as-prepared copper dimers, in synergism with the oxygen vacancies in ceria, exhibit favourable electronic and catalytic interactions with incident CO molecules. Consequently, CO can be preferentially oxidised in H2 streams at low temperatures. [source] Interaction of CO and NO with the spinel CuCr2O4 (100) surface: A DFT studyINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 9 2008Xiang-Lan Xu Abstract The characteristics of CO and NO molecules at Cu2+ and Cr3+ ion sites on the CuCr2O4 (100) surface have been studied by first principles calculations based on spin-polarized density functional theory (DFT). The calculated results show that adsorption energies for X-down(C, N) adsorption vary in the order: Cu2+ -CO>Cr3+ -NO,Cr3+ -CO>Cu2+ -NO. CO molecules are preferentially adsorbed at Cu sites, whereas NO molecules adsorb favorably at Cu2+ and Cr3+ ion sites. The C-O and N-O stretching frequencies are red-shifted upon adsorption. Combining the analysis of frontier molecular orbitals and Mulliken charge, for CO and NO X-down adsorption systems, the 5, orbitals donate electrons and the 2,* orbitals obtain back-donated electrons. Although for NO with O-down adsorption systems, the NO-2,* orbitals obtain back-donated electrons from substrates without 5,-donation. Coadsorption calculations show the CO/NO mixture adsorb selectively at the Cu2+ion site but simultaneously at the Cr3+ ion site, respectively. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] Fragmentation of star-forming clouds enriched with the first dustMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2006Raffaella Schneider ABSTRACT The thermal and fragmentation properties of star forming clouds have important consequences on the corresponding characteristic stellar mass. The initial composition of the gas within these clouds is a record of the nucleosynthetic products of previous stellar generations. In this paper, we present a model for the evolution of star forming clouds enriched by metals and dust from the first supernovae (SNe), resulting from the explosions of metal-free progenitors with masses in the range 12,30 M, and 140,260 M,. Using a self-consistent approach, we show that: (i) metals depleted on to dust grains play a fundamental role, enabling fragmentation to solar or subsolar mass scales already at metallicities Zcr= 10,6 Z,; (ii) even at metallicities as high as 10,2 Z,, metals diffused in the gas phase lead to fragment mass scales which are ,100 M,; (iii) C atoms are strongly depleted on to amorphous carbon grains and CO molecules so that C ii plays a minor role in gas cooling, leaving O i as the main gas-phase cooling agent in low-metallicity clouds. These conclusions hold independently of the assumed SN progenitors and suggest that the onset of low-mass star formation is conditioned to the presence of dust in the parent clouds. [source] Electrospray ionization tandem mass spectrometry fragmentation of protonated flavone and flavonol aglycones: a re-examinationRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 2 2009Gonçalo C. Justino Flavonoids are important phytochemicals which have been intensively studied in the last decades in view of their antioxidant activity, which is of particular importance in the case of flavones and flavonols, that differ in a single 3-OH group. Mass spectrometry has been used to elucidate the structures of many types of flavonoids and their metabolites. The work we present here is focused on the electrospray ionization tandem mass spectrometry (ESI-MS/MS) analysis of flavone and flavonols aglycones. Their fragmentation mechanisms in the positive ion mode are described and compared with previously reported mechanisms. We analyzed flavonoid derivatives produced by reaction of the flavonoids with chemically synthesized hypohalous acids (HOCl, HOBr and HOI) and peroxynitrite, reactive species involved in the inflammatory response. All the proposed pathways have been analyzed using computational chemistry methods in order to seek for possible variations and establish the most plausible ones. We observed that the losses of one and two CO molecules can be useful in terms of antioxidant activity prediction. Losses of one and two C2H2O groups are also informative in terms of structure and activity predictions. The retro-Diels-Alder fragmentations, and subsequent neutral losses, were reviewed and, according to our calculations, the most plausible structures for the product ions were established. These fingerprints will be of great value for differentiating flavonoids from other compounds in complex biological mixtures and for a thorough structural identification of flavonoid aglycones and their invivo metabolites. Copyright © 2008 John Wiley & Sons, Ltd. [source] Analysis of bufadienolides in the Chinese drug ChanSu by high-performance liquid chromatography with atmospheric pressure chemical ionization tandem mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 13 2005Min Ye The qualitative analysis of bufadienolides in the Chinese drug ChanSu was performed using high-performance liquid chromatography with atmospheric pressure chemical ionization tandem mass spectrometry (APCI-MS/MS). Bufadienolides are the major bioactive constituents of ChanSu, which is used to treat heart failure and cancer in traditional Chinese medicine. The APCI-MS fragmentation behavior of bufadienolides was studied. For bufadienolides with only hydroxyl substituents, the fragmentation was characterized by successive eliminations of H2O and CO molecules, and the profile of MS/MS product ions was correlated with the number of hydroxyl groups. If a C-16 acetoxyl group was present, the fragmentation of [M+H]+ ions was triggered by initial loss of 60,Da (HOAc). The elimination of CO was significant for bufadienolides with a 19-formyl group, and the 19-hydroxyl group could be characterized by the loss of 30,Da (HCHO). These fragmentation rules were applied to the identification of bufadienolides in a methanolic extract of ChanSu, which was separated on a C18 column with gradient elution. A total of 35 bufadienolides were identified, including four new constituents. The method established here facilitated the convenient and rapid quality control of ChanSu crude drug and its pharmaceutical preparations. Copyright © 2005 John Wiley & Sons, Ltd. [source] | ||||||||||