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Articles 1 - 30 of 39
Full-Text Articles in Physical Chemistry
Group 14 Metallocene Catalysts For Carbonyl Hydroboration And Cyanosilylation, Haley J. Robertson, Mallory N. Fujiwara, Allegra L. Liberman-Martin
Group 14 Metallocene Catalysts For Carbonyl Hydroboration And Cyanosilylation, Haley J. Robertson, Mallory N. Fujiwara, Allegra L. Liberman-Martin
Biology, Chemistry, and Environmental Sciences Faculty Articles and Research
A series of six Group 14 metallocene compounds (M = Ge, Sn, Pb) were studied as catalysts for carbonyl hydroboration and cyanosilylation reactions at room temperature. Both bis(pentamethylcyclopentadienyl) and tetramethyldisiloxa[3]metallocenophane compounds were compared. The tin and lead metallocenophanes exhibited the highest reactivity in hydroboration and cyanosilylation reactions. Hammett analysis of aldehyde hydroboration provided a ρ value of 0.73, suggesting a buildup of negative charge during the turnover-limiting step, consistent with the transition state for hydride transfer to the carbonyl center. NMR studies of Lewis acidity indicate that the Ge, Sn, and Pb tetramethyldisiloxa[3]metallocenophane compounds are weak Lewis acids.
Symmetry-Resolved Co Desorption And Oxidation Dynamics On O/Ru(0001) Probed At The C K-Edge By Ultrafast X-Ray Spectroscopy, Jerry Larue, Boyang Liu, Gabriel L. S. Rodrigues, Chang Liu, Jose Antonio Garrido Torres, Simon Schreck, Elias Diesen, Matthew Weston, Hirohito Ogasawara, Fivos Perakis, Martina Dell'angela, Flavio Capotondi, Devon Ball, Conner Carnahan, Gary Zeri, Luca Giannessi, Emanuele Pedersoli, Denys Naumenko, Peter Amann, Ivaylo Nikolov, Lorenzo Raimondi, Carlo Spezzani, Martin Beye, Johannes Voss, Hsin-Yi Wang, Filippo Cavalca, Jörgen Gladh, Sergey Koroidov, Frank Abild-Pedersen, Manuel Kolb, Piter S. Miedema, Roberto Costantini, Tony F. Heinz, Alan C. Luntz, Lars G. M. Pettersson, Anders Nilsson
Symmetry-Resolved Co Desorption And Oxidation Dynamics On O/Ru(0001) Probed At The C K-Edge By Ultrafast X-Ray Spectroscopy, Jerry Larue, Boyang Liu, Gabriel L. S. Rodrigues, Chang Liu, Jose Antonio Garrido Torres, Simon Schreck, Elias Diesen, Matthew Weston, Hirohito Ogasawara, Fivos Perakis, Martina Dell'angela, Flavio Capotondi, Devon Ball, Conner Carnahan, Gary Zeri, Luca Giannessi, Emanuele Pedersoli, Denys Naumenko, Peter Amann, Ivaylo Nikolov, Lorenzo Raimondi, Carlo Spezzani, Martin Beye, Johannes Voss, Hsin-Yi Wang, Filippo Cavalca, Jörgen Gladh, Sergey Koroidov, Frank Abild-Pedersen, Manuel Kolb, Piter S. Miedema, Roberto Costantini, Tony F. Heinz, Alan C. Luntz, Lars G. M. Pettersson, Anders Nilsson
Biology, Chemistry, and Environmental Sciences Faculty Articles and Research
We report on carbon monoxide desorption and oxidation induced by 400 nm femtosecond laser excitation on the O/Ru(0001) surface probed by time-resolved x-ray absorption spectroscopy (TR-XAS) at the carbon K-edge. The experiments were performed under constant background pressures of CO (6 × 10−8 Torr) and O2 (3 × 10−8 Torr). Under these conditions, we detect two transient CO species with narrow 2π* peaks, suggesting little 2π* interaction with the surface. Based on polarization measurements, we find that these two species have opposing orientations: (1) CO favoring a more perpendicular orientation and (2) CO favoring a more parallel orientation …
An Examination Of Factors Influencing Small Proton Chemical Shift Differences In Nitrogen-Substituted Monodeuterated Methyl Groups, Stuart J. Elliott, O. Maduka Ogba, Lynda J. Brown, Daniel J. O'Leary
An Examination Of Factors Influencing Small Proton Chemical Shift Differences In Nitrogen-Substituted Monodeuterated Methyl Groups, Stuart J. Elliott, O. Maduka Ogba, Lynda J. Brown, Daniel J. O'Leary
Biology, Chemistry, and Environmental Sciences Faculty Articles and Research
Monodeuterated methyl groups have previously been demonstrated to provide access to long-lived nuclear spin states. This is possible when the CH2 D rotamers have sufficiently different populations and the local environment is chiral, which foments a non-negligible isotropic chemical shift difference between the two CH2 D protons. In this article, the focus is on the N-CH2 D group of N-CH2 D-2-methylpiperidine and other suitable CH2 D piperidine derivatives. We used a combined experimental and computational approach to investigate how rotameric symmetry breaking leads to a 1H CH2 D chemical shift …
Crystal Structure Of 2-(2,6-Diisopropylphenyl)-N,Ndiethyl- 3,3-Dimethyl-2-Azaspiro[4.5]Decan-1- Amine: A Diethylamine Adduct Of A Cyclic(Alkyl)- (Amino)Carbene (Caac), Roxanne A. Naumann, Joseph W. Ziller, Allegra Liberman-Martin
Crystal Structure Of 2-(2,6-Diisopropylphenyl)-N,Ndiethyl- 3,3-Dimethyl-2-Azaspiro[4.5]Decan-1- Amine: A Diethylamine Adduct Of A Cyclic(Alkyl)- (Amino)Carbene (Caac), Roxanne A. Naumann, Joseph W. Ziller, Allegra Liberman-Martin
Biology, Chemistry, and Environmental Sciences Faculty Articles and Research
The structure of the title compound, C27H46N2, at 93 K has monoclinic (P21/n) symmetry. The title compound was prepared by treatment of 2-(2,6-diisopropylphenyl)-3,3-dimethyl-2-azaspiro[4.5]dec-1-en-2-ium hydrogen dichloride with two equivalents of lithium diethylamide. Characterization of the title compound by single-crystal X-ray diffraction and 1H and 13C NMR spectroscopy is presented. Formation of the diethylamine adduct of the cyclic(alkyl)(amino)carbene (CAAC) was unexpected, as deprotonation using lithium diisopropylamide results in free CAAC formation.
Ultrafast Adsorbate Excitation Probed With Subpicosecond-Resolution X-Ray Absorption Spectroscopy, Elias Diesen, Hsin-Yi Wang, Simon Schreck, Matthew Weston, Hirohito Ogasawara, Jerry Larue, Fivos Perakis, Martina Dell'angela, Flavio Capotondi, Luca Giannessi, Martin Beye, Filippo Cavalca, Boyang Liu, Jörgen Gladh, Sergey Koroidov, Piter S. Miedema, Roberto Costantini, Tony F. Heinz, Frank Abild-Pedersen, Johannes Voss, Alan C. Luntz, Anders Nilsson
Ultrafast Adsorbate Excitation Probed With Subpicosecond-Resolution X-Ray Absorption Spectroscopy, Elias Diesen, Hsin-Yi Wang, Simon Schreck, Matthew Weston, Hirohito Ogasawara, Jerry Larue, Fivos Perakis, Martina Dell'angela, Flavio Capotondi, Luca Giannessi, Martin Beye, Filippo Cavalca, Boyang Liu, Jörgen Gladh, Sergey Koroidov, Piter S. Miedema, Roberto Costantini, Tony F. Heinz, Frank Abild-Pedersen, Johannes Voss, Alan C. Luntz, Anders Nilsson
Biology, Chemistry, and Environmental Sciences Faculty Articles and Research
We use a pump-probe scheme to measure the time evolution of the C K-edge x-ray absorption spectrum from CO/Ru(0001) after excitation by an ultrashort high-intensity optical laser pulse. Because of the short duration of the x-ray probe pulse and precise control of the pulse delay, the excitation-induced dynamics during the first picosecond after the pump can be resolved with unprecedented time resolution. By comparing with density functional theory spectrum calculations, we find high excitation of the internal stretch and frustrated rotation modes occurring within 200 fs of laser excitation, as well as thermalization of the system in the picosecond …
Mechanism And Chemoselectivity For Hocl-Mediated Oxidation Of Zinc-Bound Thiolates, Lindsay Zumwalt, Arden Perkins, O. Maduka Ogba
Mechanism And Chemoselectivity For Hocl-Mediated Oxidation Of Zinc-Bound Thiolates, Lindsay Zumwalt, Arden Perkins, O. Maduka Ogba
Biology, Chemistry, and Environmental Sciences Faculty Articles and Research
Quantum mechanical calculations reveal the preferred mechanism and origins of chemoselectivity for HOCl‐mediated oxidation of zinc‐bound thiolates implicated in bacterial redox sensing. Distortion/interaction models show that minimizing geometric distortion at the zinc complex during the rate‐limiting nucleophilic substitution step controls the mechanistic preference for OH over Cl transfer with HOCl and the chemoselectivity for HOCl over H2O2.
Mechanism And Chemoselectivity For Hocl-Mediated Oxidation Of Zinc-Bound Thiolates, Lindsay Zumwalt, Arden Perkins, O. Maduka Ogba
Mechanism And Chemoselectivity For Hocl-Mediated Oxidation Of Zinc-Bound Thiolates, Lindsay Zumwalt, Arden Perkins, O. Maduka Ogba
Biology, Chemistry, and Environmental Sciences Faculty Articles and Research
Quantum mechanical calculations reveal the preferred mechanism and origins of chemoselectivity for HOCl‐mediated oxidation of zinc‐bound thiolates implicated in bacterial redox sensing. Distortion/interaction models show that minimizing geometric distortion at the zinc complex during the rate‐limiting nucleophilic substitution step controls the mechanistic preference for OH over Cl transfer with HOCl and the chemoselectivity for HOCl over H2O2.
Time-Resolved Observation Of Transient Precursor State Of Co On Ru(0001) Using Carbon K-Edge Spectroscopy, Hsin-Yi Wang, Simon Schreck, Matthew Weston, Hirohito Ogasawara, Jerry Larue, Fivos Perakis, Martina Dell'angela, Flavio Capotondi, Luca Giannessi, Emanuele Pedersoli, Denys Naumenko, Ivaylo Nikolov, Lorenzo Raimondi, Carlo Spezzani, Martin Beye, Filippo Cavalca, Boyang Liu, Jörgen Gladh, Sergey Koroidov, Piter S. Miedema, Roberto Costantini, Lars G. M. Pettersson, Anders Nilsson
Time-Resolved Observation Of Transient Precursor State Of Co On Ru(0001) Using Carbon K-Edge Spectroscopy, Hsin-Yi Wang, Simon Schreck, Matthew Weston, Hirohito Ogasawara, Jerry Larue, Fivos Perakis, Martina Dell'angela, Flavio Capotondi, Luca Giannessi, Emanuele Pedersoli, Denys Naumenko, Ivaylo Nikolov, Lorenzo Raimondi, Carlo Spezzani, Martin Beye, Filippo Cavalca, Boyang Liu, Jörgen Gladh, Sergey Koroidov, Piter S. Miedema, Roberto Costantini, Lars G. M. Pettersson, Anders Nilsson
Biology, Chemistry, and Environmental Sciences Faculty Articles and Research
The transient dynamics of carbon monoxide (CO) molecules on a Ru(0001) surface following femtosecond optical laser pump excitation has been studied by monitoring changes in the unoccupied electronic structure using an ultrafast X-ray free-electron laser (FEL) probe. The particular symmetry of perpendicularly chemisorbed CO on the surface is exploited to investigate how the molecular orientation changes with time by varying the polarization of the FEL pulses. The time evolution of spectral features corresponding to the desorption precursor state was well distinguished due to the narrow line-width of the C K-edge in the X-ray absorption (XA) spectrum, illustrating that CO molecules …
Atom-Specific Activation In Co Oxidation, Simon Schreck, Elias Diesen, Jerry Larue, Hirohito Ogasawara, Kess Marks, Dennis Nordlund, Matthew Weston, Martin Beye, Filippo Cavalca, Fivos Perakis, Jonas Sellberg, André Eilert, Kyung Hwan Kim, Giacomo Coslovich, Ryan Coffee, Jacek Krzywinski, Alex Reid, Stefan Moeller, Alberto Lutman, Henrik Öström, Lars G. M. Pettersson, Anders Nilsson
Atom-Specific Activation In Co Oxidation, Simon Schreck, Elias Diesen, Jerry Larue, Hirohito Ogasawara, Kess Marks, Dennis Nordlund, Matthew Weston, Martin Beye, Filippo Cavalca, Fivos Perakis, Jonas Sellberg, André Eilert, Kyung Hwan Kim, Giacomo Coslovich, Ryan Coffee, Jacek Krzywinski, Alex Reid, Stefan Moeller, Alberto Lutman, Henrik Öström, Lars G. M. Pettersson, Anders Nilsson
Biology, Chemistry, and Environmental Sciences Faculty Articles and Research
We report on atom-specific activation of CO oxidation on Ru(0001) via resonant X-ray excitation. We show that resonant 1s core-level excitation of atomically adsorbed oxygen in the co-adsorbed phase of CO and oxygen directly drives CO oxidation. We separate this direct resonant channel from indirectly driven oxidation via X-ray induced substrate heating. Based on density functional theory calculations, we identify the valence-excited state created by the Auger decay as the driving electronic state for direct CO oxidation. We utilized the fresh-slice multi-pulse mode at the Linac Coherent Light Source that provided time-overlapped and 30 fs delayed pairs of soft …
Phase Behavior Of Binary And Polydisperse Suspensions Of Compressible Microgels Controlled By Selective Particle Deswelling, A. Scotti, U. Gasser, E. S. Herman, Jun Han, A. Menzel, L. Andrew Lyon, A. Fernandez-Nieves
Phase Behavior Of Binary And Polydisperse Suspensions Of Compressible Microgels Controlled By Selective Particle Deswelling, A. Scotti, U. Gasser, E. S. Herman, Jun Han, A. Menzel, L. Andrew Lyon, A. Fernandez-Nieves
Biology, Chemistry, and Environmental Sciences Faculty Articles and Research
We investigate the phase behavior of suspensions of poly(N-isopropylacrylamide) (pNIPAM) microgels with either bimodal or polydisperse size distribution. We observe a shift of the fluid-crystal transition to higher concentrations depending on the polydispersity or the fraction of large particles in suspension. Crystallization is observed up to polydispersities as high as 18.5%, and up to a number fraction of large particles of 29% in bidisperse suspensions. The crystal structure is random hexagonal close-packed as in monodisperse pNIPAM microgel suspensions.We explain our experimental results by considering the effect of bound counterions. Above a critical particle concentration, these cause deswelling of the largest …
Application Of Bottlebrush Block Copolymers As Photonic Crystals, Allegra L. Liberman-Martin, Crystal K. Chu, Robert H. Grubbs
Application Of Bottlebrush Block Copolymers As Photonic Crystals, Allegra L. Liberman-Martin, Crystal K. Chu, Robert H. Grubbs
Biology, Chemistry, and Environmental Sciences Faculty Articles and Research
Brush block copolymers are a class of comb polymers that feature polymeric side chains densely grafted to a linear backbone. These polymers display interesting properties due to their dense functionality, low entanglement, and ability to rapidly self-assemble to highly ordered nanostructures. The ability to prepare brush polymers with precise structures has been enabled by advancements in controlled polymerization techniques. This Feature Article highlights the development of brush block copolymers as photonic crystals that can reflect visible to near-infrared wavelengths of light. Fabrication of these materials relies on polymer self-assembly processes to achieve nanoscale ordering, which allows for the rapid preparation …
Catalysis In Real Time Using X-Ray Lasers, A. Nilsson, Jerry L. Larue, H. Öberg, H. Ogasawara, M. Dell’Angela, M. Beye, H. Öström, J. Gladh, J. K. Nørskov, W. Wurth, F. Abild-Pedersen, L. G. M. Pettersson
Catalysis In Real Time Using X-Ray Lasers, A. Nilsson, Jerry L. Larue, H. Öberg, H. Ogasawara, M. Dell’Angela, M. Beye, H. Öström, J. Gladh, J. K. Nørskov, W. Wurth, F. Abild-Pedersen, L. G. M. Pettersson
Biology, Chemistry, and Environmental Sciences Faculty Articles and Research
We describe how the unique temporal and spectral characteristics of X-ray free-electron lasers (XFEL) can be utilized to follow chemical transformations in heterogeneous catalysis in real time. We highlight the systematic study of CO oxidation on Ru(0001), which we initiate either using a femtosecond pulse from an optical laser or by activating only the oxygen atoms using a THz pulse. We find that CO is promoted into an entropy-controlled precursor state prior to desorbing when the surface is heated in the absence of oxygen, whereas in the presence of oxygen, CO desorbs directly into the gas phase. We monitor the …
Electrophilic Activation Of Silicon–Hydrogen Bonds In Catalytic Hydrosilations, Mark C. Lipke, Allegra L. Liberman-Martin, T. Don Tilley
Electrophilic Activation Of Silicon–Hydrogen Bonds In Catalytic Hydrosilations, Mark C. Lipke, Allegra L. Liberman-Martin, T. Don Tilley
Biology, Chemistry, and Environmental Sciences Faculty Articles and Research
Hydrosilation reactions represent an important class of chemical transformations and there has been considerable recent interest in expanding the scope of these reactions by developing new catalysts. A major theme to emerge from these investigations is the development of catalysts with electrophilic character that transfer electrophilicity to silicon by Si-H activation. This type of mechanism has been proposed for catalysts ranging from Group 4 transition metals to Group 15 main group species. Additionally, other electrophilic silicon species, such as silylene complexes and η3-H2SiRR′ complexes, have been identified as intermediates in hydrosilation reactions. In this Review, different types of catalysts are …
Thz-Pulse-Induced Selective Catalytic Co Oxidation On Ru, Jerry L. Larue, Tetsuo Katayama, Aaron Lindenberg, Alan S. Fisher, Henrik Öström, Anders Nilsson, Hirohito Ogasawara
Thz-Pulse-Induced Selective Catalytic Co Oxidation On Ru, Jerry L. Larue, Tetsuo Katayama, Aaron Lindenberg, Alan S. Fisher, Henrik Öström, Anders Nilsson, Hirohito Ogasawara
Biology, Chemistry, and Environmental Sciences Faculty Articles and Research
We demonstrate the use of intense, quasi-half-cycle THz pulses, with an associated electric field component comparable to intramolecular electric fields, to direct the reaction coordinate of a chemical reaction by stimulating the nuclear motions of the reactants. Using a strong electric field from a THz pulse generated via coherent transition radiation from an ultrashort electron bunch, we present evidence that CO oxidation on Ru(0001) is selectively induced, while not promoting the thermally induced CO desorption process. The reaction is initiated by the motion of the O atoms on the surface driven by the electric field component of the THz pulse, …
Strong Influence Of Coadsorbate Interaction On Co Desorption Dynamics On Ru(0001) Probed By Ultrafast X-Ray Spectroscopy And Ab Initio Simulations, H. Xin, Jerry L. Larue, H. Öberg, M. Beye, M. Dell'angela, J. J. Turner, J. Gladh, M. L. Ng, J. A. Sellberg, S. Kaya, G. Mercurio, F. Hieke, D. Nordlund, W. F. Schlotter, G. L. Dakovski, M. P. Minitti, A. Föhlisch, M. Wolf, W. Wurth, H. Ogasawara, J. K. Nørskov, H. Öström, L. G. M. Pettersson, A. Nilsson, F. Abild-Pedersen
Strong Influence Of Coadsorbate Interaction On Co Desorption Dynamics On Ru(0001) Probed By Ultrafast X-Ray Spectroscopy And Ab Initio Simulations, H. Xin, Jerry L. Larue, H. Öberg, M. Beye, M. Dell'angela, J. J. Turner, J. Gladh, M. L. Ng, J. A. Sellberg, S. Kaya, G. Mercurio, F. Hieke, D. Nordlund, W. F. Schlotter, G. L. Dakovski, M. P. Minitti, A. Föhlisch, M. Wolf, W. Wurth, H. Ogasawara, J. K. Nørskov, H. Öström, L. G. M. Pettersson, A. Nilsson, F. Abild-Pedersen
Biology, Chemistry, and Environmental Sciences Faculty Articles and Research
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 …
Optical Laser-Induced Co Desorption From Ru(0001) Monitored With A Free-Electron X-Ray Laser: Dft Prediction And X-Ray Confirmation Of A Precursor State, H. Öberg, J. Gladh, M. Dell'angela, T. Anniyev, M. Beye, R. Coffee, A. Föhlisch, T. Katayama, S. Kaya, Jerry L. Larue, A. Møgelhøj, D. Nordlund, H. Ogasawara, W. F. Schlotter, J. A. Sellberg, F. Sorgenfrei, J. J. Turner, M. Wolf, W. Wurth, H. Öström, A. Nilsson, J. K. Nørskov, L. G. M. Pettersson
Optical Laser-Induced Co Desorption From Ru(0001) Monitored With A Free-Electron X-Ray Laser: Dft Prediction And X-Ray Confirmation Of A Precursor State, H. Öberg, J. Gladh, M. Dell'angela, T. Anniyev, M. Beye, R. Coffee, A. Föhlisch, T. Katayama, S. Kaya, Jerry L. Larue, A. Møgelhøj, D. Nordlund, H. Ogasawara, W. F. Schlotter, J. A. Sellberg, F. Sorgenfrei, J. J. Turner, M. Wolf, W. Wurth, H. Öström, A. Nilsson, J. K. Nørskov, L. G. M. Pettersson
Biology, Chemistry, and Environmental Sciences Faculty Articles and Research
We present density functional theory modeling of time-resolved optical pump/X-ray spectroscopic probe data of CO desorption from Ru(0001). The BEEF van der Waals functional predicts a weakly bound state as a precursor to desorption. The optical pump leads to a near-instantaneous (< 100 fs) increase of the electronic temperature to nearly 7000 K. The temperature evolution and energy transfer between electrons, substrate phonons and adsorbate is described by the two-temperature model and found to equilibrate on a timescale of a few picoseconds to an elevated local temperature of ~ 2000 K. Estimating the free energy based on the computed potential of mean force along the desorption path, we find an entropic barrier to desorption (and by time-reversal also to adsorption). This entropic barrier separates the chemisorbed and precursor states, and becomes significant at the elevated temperature of the experiment (~ 1.4 eV at 2000 K). Experimental pump-probe X-ray absorption/X-ray emission spectroscopy indicates population of a precursor state to desorption upon laser-excitation of the system (Dell'Angela et al., 2013). Computing spectra along the desorption path confirms the picture of a weakly bound transient state arising from ultrafast heating of the metal substrate.
"Probing The Transition State Region In Catalytic Co Oxidation On Ru" Data Files, H. Öström, H. Öberg, H. Xin, Jerry L. Larue, M. Beye, M. Dell'angela, J. Gladh, M. L. Ng, J. A. Sellberg, S. Kaya, G. Mercurio, D. Nordlund, W. F. Schlotter, A. Föhlisch, M. Wolf, W. Wurth, M. Persson, J. K. Nørskov, F. Abild-Pedersen, H. Ogasawara, L. G. M. Pettersson, A. Nilsson
"Probing The Transition State Region In Catalytic Co Oxidation On Ru" Data Files, H. Öström, H. Öberg, H. Xin, Jerry L. Larue, M. Beye, M. Dell'angela, J. Gladh, M. L. Ng, J. A. Sellberg, S. Kaya, G. Mercurio, D. Nordlund, W. F. Schlotter, A. Föhlisch, M. Wolf, W. Wurth, M. Persson, J. K. Nørskov, F. Abild-Pedersen, H. Ogasawara, L. G. M. Pettersson, A. Nilsson
Biology, Chemistry, and Environmental Sciences Faculty Data Sets
Femtosecond x-ray laser pulses are used to probe the CO oxidation reaction on Ru initiated by an optical laser pulse. On a timescale of a few hundred femtoseconds, the optical laser pulse excites motions of CO and O on the surface allowing the reactants to collide and, with a transient close to a picosecond (ps), new electronic states appear in the O K-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 …
Probing The Transition State Region In Catalytic Co Oxidation On Ru, H. Öström, H. Öberg, H. Xin, Jerry L. Larue, M. Beye, M. Dell'angela, J. Gladh, M. L. Ng, J. A. Sellberg, S. Kaya, G. Mercurio, D. Nordlund, M. Hantschmann, F. Hieke, D. Kühn, W. F. Schlotter, G. L. Dakovski, J. J. Turner, M. P. Minitti, A. Mitra, S. P. Moeller, A. Föhlisch, M. Wolf, W. Wurth, M. Persson, J. K. Nørskov, F. Abild-Pedersen, H. Ogasawara, L. G. M. Pettersson, A. Nilsson
Probing The Transition State Region In Catalytic Co Oxidation On Ru, H. Öström, H. Öberg, H. Xin, Jerry L. Larue, M. Beye, M. Dell'angela, J. Gladh, M. L. Ng, J. A. Sellberg, S. Kaya, G. Mercurio, D. Nordlund, M. Hantschmann, F. Hieke, D. Kühn, W. F. Schlotter, G. L. Dakovski, J. J. Turner, M. P. Minitti, A. Mitra, S. P. Moeller, A. Föhlisch, M. Wolf, W. Wurth, M. Persson, J. K. Nørskov, F. Abild-Pedersen, H. Ogasawara, L. G. M. Pettersson, A. Nilsson
Biology, Chemistry, and Environmental Sciences Faculty Articles and Research
Femtosecond x-ray laser pulses are used to probe the CO oxidation reaction on Ru initiated by an optical laser pulse. On a timescale of a few hundred femtoseconds, the optical laser pulse excites motions of CO and O on the surface allowing the reactants to collide and, with a transient close to a picosecond (ps), new electronic states appear in the O K-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 …
The Role Of Hydroxyl Channel In Defining Selected Physicochemical Peculiarities Exhibited By Hydroxyapatite, Vuk Uskoković
The Role Of Hydroxyl Channel In Defining Selected Physicochemical Peculiarities Exhibited By Hydroxyapatite, Vuk Uskoković
Pharmacy Faculty Articles and Research
Mysteries surrounding the most important mineral for the vertebrate biology, hydroxyapatite, are many. Perhaps the Greek root of its name, απαταo, meaning ‘to deceive’ and given to its mineral form by the early gem collectors who confused it with more precious stones, is still applicable today, though in a different connotation, descriptive of a number of physicochemical peculiarities exhibited by it. Comparable to water as the epitome of peculiarities in the realm of liquids, hydroxyapatite can serve as a paradigm for peculiarities in the world of solids. Ten of the peculiar properties of hydroxyapatite are sketched in this review piece, …
A New, Simple, Green And One-Pot Four-Component Synthesis Of Bare And Poly(Α, Γ, L-Glutamic Acid) Capped Silver Nanoparticles, Magdalena Stevanović, Igor Savanović, Vuk Uskoković, Srečo D. Škapin, Ines Bračko, Uroš Jovanović, Dragan Uskoković
A New, Simple, Green And One-Pot Four-Component Synthesis Of Bare And Poly(Α, Γ, L-Glutamic Acid) Capped Silver Nanoparticles, Magdalena Stevanović, Igor Savanović, Vuk Uskoković, Srečo D. Škapin, Ines Bračko, Uroš Jovanović, Dragan Uskoković
Pharmacy Faculty Articles and Research
A simple and green chemical method has been developed to synthesize stable bare and capped silver nanoparticles based on the reduction of silver ions by glucose and capping by poly(α,γ,Lglutamic acid) (PGA). The use of ammonia during synthesis was avoided. PGA has had a dual role in the synthesis and was used as a capping agent to make the silver nanoparticle more biocompatible and to protect the nanoparticles from agglomerating in the liquid medium. The synthesized PGA-capped silver nanoparticles in the size range 5–45 nm were stable over long periods of time, without signs of precipitation. Morphological examination has shown …
Pegylated Silicon Nanowire Coated Silica Microparticles For Drug Delivery Across Intestinal Epithelium, Vuk Uskoković, Phin-Peng Lee, Laura Walsh, Kathleen Fischer, Tejal Dasai
Pegylated Silicon Nanowire Coated Silica Microparticles For Drug Delivery Across Intestinal Epithelium, Vuk Uskoković, Phin-Peng Lee, Laura Walsh, Kathleen Fischer, Tejal Dasai
Pharmacy Faculty Articles and Research
Composite particles made by growing nanoscopic silicon wires from the surface of monodispersed, microsized silica beads were tested in this study for their ability to affect the integrity and permeability of an epithelial cell layer. Polyethylene glycol (PEG) is known to sterically stabilize particles and prevent protein binding; as such, it is a routine way to impart in vivo longevity to drug carriers. The effect of the silica beads, both with and without silicon nanowires and PEG, on the disruption of the tight junctions in Caco-2 cells was evaluated by means of: (a) analysis of the localization of zonula occludens-1 …
Dynamic Light Scattering And Microelectrophoresis: Main Prospects And Limitations, Vuk Uskoković
Dynamic Light Scattering And Microelectrophoresis: Main Prospects And Limitations, Vuk Uskoković
Pharmacy Faculty Articles and Research
Microelectrophoresis based on the dynamic light scattering (DLS) effect has been a major tool for assessing and controlling the conditions for stability of colloidal systems. However, both the DLS methods for characterization of the hydrodynamic size of dispersed submicron particles and the theory behind the electrokinetic phenomena are associated with fundamental and practical approximations that limit their sensitivity and information output. Some of these fundamental limitations, including the spherical approximation of DLS measurements and an inability of microelectrophoretic analyses of colloidal systems to detect discrete charges and differ between differently charged particle surfaces due to rotational diffusion and particle orientation …
Communication: Bubbles, Crystals, And Laser-Induced Nucleation, Brandon C. Knott, Jerry L. Larue, Alec M. Wodtke, Michael F. Doherty, Baron Peters
Communication: Bubbles, Crystals, And Laser-Induced Nucleation, Brandon C. Knott, Jerry L. Larue, Alec M. Wodtke, Michael F. Doherty, Baron Peters
Biology, Chemistry, and Environmental Sciences Faculty Articles and Research
Short intense laser pulses of visible and infrared light can dramatically accelerate crystal nucleation from transparent solutions; previous studies invoke mechanisms that are only applicable for nucleation of ordered phases or high dielectric phases. However, we show that similar laser pulses induce CO2bubblenucleation in carbonated water. Additionally, in water that is cosupersaturated with argon and glycine, argon bubbles escaping from the water can induce crystal nucleation without a laser. Our findings suggest a possible link between laser-induced nucleation of bubbles and crystals.
Dynamic Light Scattering And Zeta Potential Of Colloidal Mixtures Of Amelogenin And Hydroxyapatite In Calcium And Phosphate Rich Ionic Milieus, Vuk Uskoković, Roselyn Odsinada, Sonia Djordjevic, Stefan Habelitz
Dynamic Light Scattering And Zeta Potential Of Colloidal Mixtures Of Amelogenin And Hydroxyapatite In Calcium And Phosphate Rich Ionic Milieus, Vuk Uskoković, Roselyn Odsinada, Sonia Djordjevic, Stefan Habelitz
Pharmacy Faculty Articles and Research
The concept of zeta-potential has been used for more than a century as a basic parameter in controlling the stability of colloidal suspensions, irrespective of the nature of their particulate ingredients – organic or inorganic. There are prospects that self-assembly of peptide species and the protein-mineral interactions related to biomineralization may be controlled using this fundamental physicochemical parameter. In this study, we have analyzed the particle size and zeta-potential of the full-length recombinant human amelogenin (rH174), the main protein of the developing enamel matrix, in the presence of calcium and phosphate ions and hydroxyapatite (HAP) particles. As calcium and phosphate …
Vibrationally Promoted Electron Emission At A Metal Surface: Electron Kinetic Energy Distributions, Jerry L. Larue, Tim Schäfer, Daniel Matsiev, Luis Velarde, N. Hendrick Nahler, Daniel J. Auerbach, Alec M. Wodtke
Vibrationally Promoted Electron Emission At A Metal Surface: Electron Kinetic Energy Distributions, Jerry L. Larue, Tim Schäfer, Daniel Matsiev, Luis Velarde, N. Hendrick Nahler, Daniel J. Auerbach, Alec M. Wodtke
Biology, Chemistry, and Environmental Sciences Faculty Articles and Research
We report the first direct measurement of the kinetic energy of exoelectrons produced by collisions of vibrationally excited molecules with a low work function metal surface exhibiting electron excitations of 64% (most probable) and 95% (maximum) of the initial vibrational energy. This remarkable efficiency for vibrational-to-electronic energy transfer is in good agreement with previous results suggesting the coupling of multiple vibrational quanta to a single electron.
Site-Specific Photocatalytic Splitting Of Methanol On Tio2(110), Chuanyao Zhou, Zefeng Ren, Shijing Tan, Zhibo Ma, Xinchun Mao, Dongxu Dai, Hongjun Fan, Xueming Yang, Jerry L. Larue, Russell Cooper, Alec M. Wodtke, Zhou Wang, Zhenyu Li, Bing Wang, Jinlong Yang, Jianguo Hou
Site-Specific Photocatalytic Splitting Of Methanol On Tio2(110), Chuanyao Zhou, Zefeng Ren, Shijing Tan, Zhibo Ma, Xinchun Mao, Dongxu Dai, Hongjun Fan, Xueming Yang, Jerry L. Larue, Russell Cooper, Alec M. Wodtke, Zhou Wang, Zhenyu Li, Bing Wang, Jinlong Yang, Jianguo Hou
Biology, Chemistry, and Environmental Sciences Faculty Articles and Research
Clean hydrogen production is highly desirable for future energy needs, making the understanding of molecular-level phenomena underlying photocatalytic hydrogen production both fundamentally and practically important. Water splitting on pure TiO2 is inefficient, however, adding sacrificial methanol could significantly enhance the photocatalyzed H2 production. Therefore, understanding the photochemistry of methanol on TiO2 at the molecular level could provide important insights to its photocatalytic activity. Here, we report the first clear evidence of photocatalyzed splitting of methanol on TiO2 derived from time-dependent two-photon photoemission (TD-2PPE) results in combination with scanning tunneling microscopy (STM). STM tip induced molecular manipulation …
A Surface Femtosecond Two-Photon Photoemission Spectrometer For Excited Electron Dynamics And Time-Dependent Photochemical Kinetics, Zefeng Ren, Chuanyao Zhou, Zhibo Ma, Chun-Lei Xhao, Xinchun Mao, Dongxu Dai, Jerry L. Larue, Russell Cooper, Alec M. Wodtke, Xueming Yang
A Surface Femtosecond Two-Photon Photoemission Spectrometer For Excited Electron Dynamics And Time-Dependent Photochemical Kinetics, Zefeng Ren, Chuanyao Zhou, Zhibo Ma, Chun-Lei Xhao, Xinchun Mao, Dongxu Dai, Jerry L. Larue, Russell Cooper, Alec M. Wodtke, Xueming Yang
Biology, Chemistry, and Environmental Sciences Faculty Articles and Research
A surface femtosecond two-photon photoemission (2PPE) spectrometer devoted to the study of ultrafast excited electron dynamics and photochemical kinetics on metal and metal oxide surfaces has been constructed. Low energy photoelectrons are measured using a hemispheri- cal electron energy analyzer with an imaging detector that allows us to detect the energy and the angular distributions of the photoelectrons simultaneously. A Mach-Zehnder interferom- eter was built for the time-resolved 2PPE (TR-2PPE) measurement to study ultrafast surface excited electron dynamics, which was demonstrated on the Cu(111) surface. A scheme for measuring time-dependent 2PPE (TD-2PPE) spectra has also been developed for studies of …
Inverse Velocity Dependence Of Vibrationally Promoted Electron Emission From A Metal Surface, N. H. Nahler, J. D. White, Jerry L. Larue, Daniel J. Auerbach, Alec M. Wodtke
Inverse Velocity Dependence Of Vibrationally Promoted Electron Emission From A Metal Surface, N. H. Nahler, J. D. White, Jerry L. Larue, Daniel J. Auerbach, Alec M. Wodtke
Biology, Chemistry, and Environmental Sciences Faculty Articles and Research
All previous experimental and theoretical studies of molecular interactions at metal surfaces show that electronically nonadiabatic influences increase with molecular velocity. We report the observation of a nonadiabatic electronic effect that follows the opposite trend: The probability of electron emission from a low–work function surface—Au(111) capped by half a monolayer of Cs—increases as the velocity of the incident NO molecule decreases during collisions with highly vibrationally excited NO(X2π½, V = 18; V is the vibrational quantum number of NO), reaching 0.1 at the lowest velocity studied. We show that these results are consistent with a vibrational …
The Work Function Of Submonolayer Cesium-Covered Gold: A Photoelectron Spectroscopy Study, Jerry L. Larue, J. D. White, N. H. Nahler, Z. Liu, Y. Sun, P. A. Pianetta, Daniel J. Auerbach, Alec M. Wodtke
The Work Function Of Submonolayer Cesium-Covered Gold: A Photoelectron Spectroscopy Study, Jerry L. Larue, J. D. White, N. H. Nahler, Z. Liu, Y. Sun, P. A. Pianetta, Daniel J. Auerbach, Alec M. Wodtke
Biology, Chemistry, and Environmental Sciences Faculty Articles and Research
Using visible and x-ray photoelectron spectroscopy, we measured the work function of a Au(111) surface at a well-defined submonolayer coverage of Cs. For a Cs coverage producing a photoemission maximum with a He–Ne laser, the work function is , consistent with previous assumptions used to analyze vibrationally promoted electron emission. A discussion of possible Cs layer structures is also presented.
Silica-Coated Lanthanum-Strontium Manganites For Hyperthermia Treatments, Vuk Uskoković, Aljoša Košak, Miha Drofenik
Silica-Coated Lanthanum-Strontium Manganites For Hyperthermia Treatments, Vuk Uskoković, Aljoša Košak, Miha Drofenik
Pharmacy Faculty Articles and Research
La0.76Sr0.24MnO3 + δ particles, prepared by performing a traditional, solid-state method of synthesis, were coated by uniform layers of silica via initiating hydrolysis and condensation of TEOS in aqueous–alcoholic alkali environment. The eventually obtained samples exhibited Curie temperature at ∼40 °C, and comprised core-shell particles of ∼250 nm in diameter. By varying stoichiometric ratio of cations within manganite cores of the particles, Curie point of the resulting material can be varied too, thus opening a way for the simple design of biocompatible, temperature-self-regulating particles for application in hyperthermia treatments, with Curie point thereof adjusted to …