The Experts below are selected from a list of 47079 Experts worldwide ranked by ideXlab platform
Massimo Boninsegni - One of the best experts on this subject based on the ideXlab platform.
-
Disorder and the elusive superfluid phase of Para-Hydrogen
Physical Review B, 2008Co-Authors: Joseph Turnbull, Massimo BoninsegniAbstract:The possibility that disorder may stabilize a superfluid phase of Para-Hydrogen in two dimensions is investigated theoretically by means of Quantum Monte Carlo simulations. We model disorder using a random distribution of scatterers, and study the thermodynamic behavior of the system as a function of the scatterer density. Disorder gives rise to equilibrium glassy phases with no superfluid properties. Indeed, the propensity for quantum exchanges of Hydrogen molecules is reduced even with respect to what is observed if the scatterers are arranged as a regular crystal, a physical setting that also yields no superfluidity.
-
CAN INCOMMENSURATION STABILIZE A SUPERFLUID PHASE OF Para-Hydrogen?
International Journal of Modern Physics B, 2006Co-Authors: Massimo BoninsegniAbstract:Extensive Path Integral Monte Carlo simulations of two-dimensional Para-Hydrogen embedded in a crystalline matrix of Alkali atoms, show no evidence of superfluid behavior at low temperature. Rather, the system is observed to form a commensurate (non superfluid) crystal.
-
Adsorption of Para-Hydrogen on krypton pre-plated graphite
Journal of Low Temperature Physics, 2005Co-Authors: Joseph Turnbull, Massimo BoninsegniAbstract:Adsorption of Para-Hydrogen on the surface of graphite pre-plated with a single atomic layer of krypton, is studied theoretically by means of path integral ground state Monte Carlo simulations. We compute energetics and density profiles of Para-Hydrogen, and determine the structure of the adsorbed film for various coverages. Results show that there are two thermodynamically stable monolayer phases of p-H_2, both solid; one is commensurate with the krypton layer, and has coverage θ ≈ 0.0636 Å^−2; the other is incommensurate, has coverage θ ≈ 0.0716 Å^−2, and is compressible up to θ ≈ 0.0769 Å^−2. No evidence is observed of a liquid phase at T:0 for intermediate coverages. These results are qualitatively similar to what is seen for p-H_2 on bare graphite. Quantum exchanges of Hydrogen molecules are suppressed in this system.
-
Adsorption of Para-Hydrogen on krypton pre-plated graphite
Journal of Low Temperature Physics, 2005Co-Authors: Joseph Turnbull, Massimo BoninsegniAbstract:Adsorption of Para-Hydrogen on the surface of graphite pre-plated with a single layer of atomic krypton is studied thoretically by means of Path Integral Ground State Monte Carlo simulations. We compute energetics and density profiles of Para-Hydrogen, and determine the structure of the adsorbed film for various coverages. Results show that there are two thermodynamically stable monolayer phases of Para-Hydrogen, both solid. One is commensurate with the krypton layer, the other is incommensurate. No evidence is seen of a thermodynamically stable liquid phase, at zero temperature. These results are qualitatively similar to what is seen for for Para-Hydrogen on bare graphite. Quantum exchanges of Hydrogen molecules are suppressed in this system.Comment: 12 pages, 6 figures, to appear in the proceedings of "Advances in Computational Many-Body Physics", Banff, Alberta (Canada), January 13-16 200
-
Adsorption of Para-Hydrogen on fullerenes
Physical Review B, 2005Co-Authors: Joseph Turnbull, Massimo BoninsegniAbstract:Adsorption of Para-Hydrogen on the outer surface of a single fullerene is studied theoretically, by means of ground state quantum Monte Carlo simulations. We compute energetics and radial density profiles of Para-Hydrogen for various coverages on a variety of small fullerenes. The equilibrium adsorbed solid monolayer is commensurate with the surface of the fullerene; as the chemical potential is increased, a discontinuous change is generally observed, to an incommensurate, compressible layer. Quantum exchanges of Hydrogen molecules are absent in these systems.
Stefan Glöggler - One of the best experts on this subject based on the ideXlab platform.
-
over 50 1h and 13c polarization for generating hyperpolarized metabolites a Para Hydrogen approach
ChemistryOpen, 2018Co-Authors: Sergey Korchak, Salvatore Mamone, Stefan GlögglerAbstract:Para-Hydrogen-induced polarization (PHIP) is a method to rapidly generate hyperpolarized compounds, enhancing the signal of nuclear magnetic resonance (NMR) experiments by several thousand-fold. The hyperpolarization of metabolites and their use as contrast agents in vivo is an emerging diagnostic technique. High degrees of polarization and extended polarization lifetime are necessary requirements for the detection of metabolites in vivo. Here, we present pulsed NMR methods for obtaining hyperpolarized magnetization in two metabolites. We demonstrate that the Hydrogenation with Para-Hydrogen of perdeuterated vinyl acetate allows us to create hyperpolarized ethyl acetate with close to 60 % 1H two-spin order. With nearly 100 % efficiency, this order can either be transferred to 1H in-phase magnetization or 13C magnetization of the carbonyl function. Close to 60 % polarization is experimentally verified for both nuclei. Cleavage of the ethyl acetate precursor in a 20 s reaction yields ethanol with approximately 27 % 1H polarization and acetate with around 20 % 13C polarization. This development will open new opportunities to generate metabolic contrast agents in less than one minute.
-
Pulsed Magnetic Resonance to Signal‐Enhance Metabolites within Seconds by utilizing Para‐Hydrogen
ChemistryOpen, 2018Co-Authors: Sergey Korchak, Shengjun Yang, Salvatore Mamone, Stefan GlögglerAbstract:Diseases such as Alzheimer's and cancer have been linked to metabolic dysfunctions, and further understanding of metabolic pathways raises hope to develop cures for such diseases. To broaden the knowledge of metabolisms in vitro and in vivo, methods are desirable for direct probing of metabolic function. Here, we are introducing a pulsed nuclear magnetic resonance (NMR) approach to generate hyperpolarized metabolites within seconds, which act as metabolism probes. Hyperpolarization represents a magnetic resonance technique to enhance signals by over 10 000-fold. We accomplished an efficient metabolite hyperpolarization by developing an isotopic labeling strategy for generating precursors containing a favorable nuclear spin system to add Para-Hydrogen and convert its two-spin longitudinal order into enhanced metabolite signals. The transfer is performed by an invented NMR experiment and 20 000-fold signal enhancements are achieved. Our technique provides a fast way of generating hyperpolarized metabolites by using Para-Hydrogen directly in a high magnetic field without the need for field cycling.
-
pulsed magnetic resonance to signal enhance metabolites within seconds by utilizing Para Hydrogen
ChemistryOpen, 2018Co-Authors: Sergey Korchak, Shengjun Yang, Salvatore Mamone, Stefan GlögglerAbstract:Diseases such as Alzheimer's and cancer have been linked to metabolic dysfunctions, and further understanding of metabolic pathways raises hope to develop cures for such diseases. To broaden the knowledge of metabolisms in vitro and in vivo, methods are desirable for direct probing of metabolic function. Here, we are introducing a pulsed nuclear magnetic resonance (NMR) approach to generate hyperpolarized metabolites within seconds, which act as metabolism probes. Hyperpolarization represents a magnetic resonance technique to enhance signals by over 10 000-fold. We accomplished an efficient metabolite hyperpolarization by developing an isotopic labeling strategy for generating precursors containing a favorable nuclear spin system to add Para-Hydrogen and convert its two-spin longitudinal order into enhanced metabolite signals. The transfer is performed by an invented NMR experiment and 20 000-fold signal enhancements are achieved. Our technique provides a fast way of generating hyperpolarized metabolites by using Para-Hydrogen directly in a high magnetic field without the need for field cycling.
-
a nanoparticle catalyst for heterogeneous phase Para Hydrogen induced polarization in water
Angewandte Chemie, 2015Co-Authors: Stefan Glöggler, Shawn Wagner, Alexander Grunfeld, Yavuz N. Ertas, Jeffrey Mccormick, P. Philipp M. Schleker, Louis-s. BouchardAbstract:Para-Hydrogen-induced polarization (PHIP) is a technique capable of producing spin polarization at a magnitude far greater than state-of-the-art magnets. A significant application of PHIP is to generate contrast agents for biomedical imaging. Clinically viable and effective contrast agents not only require high levels of polarization but heterogeneous catalysts that can be used in water to eliminate the toxicity impact. Herein, we demonstrate the use of Pt nanoparticles capped with glutathione to induce heterogeneous PHIP in water. The ligand-inhibited surface diffusion on the nanoparticles resulted in a 1H polarization of P=0.25 % for hydroxyethyl propionate, a known contrast agent for magnetic resonance angiography. Transferring the 1H polarization to a 13C nucleus using a Para-Hydrogen polarizer yielded a polarization of 0.013 %. The nuclear-spin polarizations achieved in these experiments are the first reported to date involving heterogeneous reactions in water.
-
A Nanoparticle Catalyst for Heterogeneous Phase Para‐Hydrogen‐Induced Polarization in Water
Angewandte Chemie (International ed. in English), 2015Co-Authors: Stefan Glöggler, Shawn Wagner, Alexander Grunfeld, Yavuz N. Ertas, Jeffrey Mccormick, P. Philipp M. Schleker, Louis-s. BouchardAbstract:Para-Hydrogen-induced polarization (PHIP) is a technique capable of producing spin polarization at a magnitude far greater than state-of-the-art magnets. A significant application of PHIP is to generate contrast agents for biomedical imaging. Clinically viable and effective contrast agents not only require high levels of polarization but heterogeneous catalysts that can be used in water to eliminate the toxicity impact. Herein, we demonstrate the use of Pt nanoparticles capped with glutathione to induce heterogeneous PHIP in water. The ligand-inhibited surface diffusion on the nanoparticles resulted in a 1H polarization of P=0.25 % for hydroxyethyl propionate, a known contrast agent for magnetic resonance angiography. Transferring the 1H polarization to a 13C nucleus using a Para-Hydrogen polarizer yielded a polarization of 0.013 %. The nuclear-spin polarizations achieved in these experiments are the first reported to date involving heterogeneous reactions in water.
Shawn Wagner - One of the best experts on this subject based on the ideXlab platform.
-
a nanoparticle catalyst for heterogeneous phase Para Hydrogen induced polarization in water
Angewandte Chemie, 2015Co-Authors: Stefan Glöggler, Shawn Wagner, Alexander Grunfeld, Yavuz N. Ertas, Jeffrey Mccormick, P. Philipp M. Schleker, Louis-s. BouchardAbstract:Para-Hydrogen-induced polarization (PHIP) is a technique capable of producing spin polarization at a magnitude far greater than state-of-the-art magnets. A significant application of PHIP is to generate contrast agents for biomedical imaging. Clinically viable and effective contrast agents not only require high levels of polarization but heterogeneous catalysts that can be used in water to eliminate the toxicity impact. Herein, we demonstrate the use of Pt nanoparticles capped with glutathione to induce heterogeneous PHIP in water. The ligand-inhibited surface diffusion on the nanoparticles resulted in a 1H polarization of P=0.25 % for hydroxyethyl propionate, a known contrast agent for magnetic resonance angiography. Transferring the 1H polarization to a 13C nucleus using a Para-Hydrogen polarizer yielded a polarization of 0.013 %. The nuclear-spin polarizations achieved in these experiments are the first reported to date involving heterogeneous reactions in water.
-
A Nanoparticle Catalyst for Heterogeneous Phase Para‐Hydrogen‐Induced Polarization in Water
Angewandte Chemie (International ed. in English), 2015Co-Authors: Stefan Glöggler, Shawn Wagner, Alexander Grunfeld, Yavuz N. Ertas, Jeffrey Mccormick, P. Philipp M. Schleker, Louis-s. BouchardAbstract:Para-Hydrogen-induced polarization (PHIP) is a technique capable of producing spin polarization at a magnitude far greater than state-of-the-art magnets. A significant application of PHIP is to generate contrast agents for biomedical imaging. Clinically viable and effective contrast agents not only require high levels of polarization but heterogeneous catalysts that can be used in water to eliminate the toxicity impact. Herein, we demonstrate the use of Pt nanoparticles capped with glutathione to induce heterogeneous PHIP in water. The ligand-inhibited surface diffusion on the nanoparticles resulted in a 1H polarization of P=0.25 % for hydroxyethyl propionate, a known contrast agent for magnetic resonance angiography. Transferring the 1H polarization to a 13C nucleus using a Para-Hydrogen polarizer yielded a polarization of 0.013 %. The nuclear-spin polarizations achieved in these experiments are the first reported to date involving heterogeneous reactions in water.
-
Conversion rate of Para-Hydrogen to ortho-Hydrogen by oxygen: implications for PHIP gas storage and utilization
Magnetic Resonance Materials in Physics Biology and Medicine, 2014Co-Authors: Shawn WagnerAbstract:Object To determine the storability of Para -Hydrogen before reestablishment of the room temperature thermal equilibrium mixture. Materials and methods Para -Hydrogen was produced at near 100 % purity and mixed with different oxygen quantities to determine the rate of conversion to the thermal equilibrium mixture of 75: 25 % ( ortho : Para ) by detecting the ortho -Hydrogen ^1H nuclear magnetic resonance using a 9.4 T imager. Results The Para -Hydrogen to ortho -Hydrogen velocity constant, k , near room temperature (292 K) was determined to be 8.27 ± 1.30 L/mol·min^−1. This value was calculated utilizing four different oxygen fractions. Conclusions Para -Hydrogen conversion to ortho -Hydrogen by oxygen can be minimized for long term storage with judicious removal of oxygen contamination. Prior calculated velocity rates were confirmed demonstrating a dependence on only the oxygen concentration.
-
conversion rate of Para Hydrogen to ortho Hydrogen by oxygen implications for phip gas storage and utilization
Magnetic Resonance Materials in Physics Biology and Medicine, 2014Co-Authors: Shawn WagnerAbstract:Object To determine the storability of Para-Hydrogen before reestablishment of the room temperature thermal equilibrium mixture.
-
Conversion rate of Para-Hydrogen to ortho-Hydrogen by oxygen: implications for PHIP gas storage and utilization
Magma (New York N.Y.), 2013Co-Authors: Shawn WagnerAbstract:To determine the storability of Para-Hydrogen before reestablishment of the room temperature thermal equilibrium mixture. Para-Hydrogen was produced at near 100 % purity and mixed with different oxygen quantities to determine the rate of conversion to the thermal equilibrium mixture of 75: 25 % (ortho: Para) by detecting the ortho-Hydrogen 1H nuclear magnetic resonance using a 9.4 T imager. The Para-Hydrogen to ortho-Hydrogen velocity constant, k, near room temperature (292 K) was determined to be 8.27 ± 1.30 L/mol·min−1. This value was calculated utilizing four different oxygen fractions. Para-Hydrogen conversion to ortho-Hydrogen by oxygen can be minimized for long term storage with judicious removal of oxygen contamination. Prior calculated velocity rates were confirmed demonstrating a dependence on only the oxygen concentration.
Yuan-pern Lee - One of the best experts on this subject based on the ideXlab platform.
-
Infrared spectroscopy of H+(CO)2 in the gas phase and in Para-Hydrogen matrices.
The Journal of chemical physics, 2020Co-Authors: Daniel Leicht, Brandon Rittgers, Gary E. Douberly, J. Philipp Wagner, David C. Mcdonald, D T Mauney, Masashi Tsuge, Yuan-pern Lee, Michael A. DuncanAbstract:The H+(CO)2 and D+(CO)2 molecular ions were investigated by infrared spectroscopy in the gas phase and in Para-Hydrogen matrices. In the gas phase, ions were generated in a supersonic molecular beam by a pulsed electrical discharge. After extraction into a time-of-flight mass spectrometer, the ions were mass selected and probed by infrared laser photodissociation spectroscopy in the 700 cm-1-3500 cm-1 region. Spectra were measured using either argon or neon tagging, as well as tagging with an excess CO molecule. In solid Para-Hydrogen, ions were generated by electron bombardment of a mixture of CO and Hydrogen, and absorption spectra were recorded in the 400 cm-1-4000 cm-1 region with a Fourier-transform infrared spectrometer. A comparison of the measured spectra with the predictions of anharmonic theory at the CCSD(T)/ANO1 level suggests that the predominant isomers formed by either argon tagging or Para-Hydrogen isolation are higher lying (+7.8 kcal mol-1), less symmetric isomers, and not the global minimum proton-bound dimer. Changing the formation environment or tagging strategy produces other non-centrosymmetric structures, but there is no spectroscopic evidence for the centrosymmetric proton-bound dimer. The formation of higher energy isomers may be caused by a kinetic effect, such as the binding of X (=Ar, Ne, or H2) to H+(CO) prior to the formation of X H+(CO)2. Regardless, there is a strong tendency to produce non-centrosymmetric structures in which HCO+ remains an intact core ion.
-
Site-Selective Reaction of Cl + Propene in Solid Para-Hydrogen: Formation of 2-Chloropropyl Radicals
The Journal of Physical Chemistry Letters, 2010Co-Authors: Jay C. Amicangelo, Yuan-pern LeeAbstract:The reaction of chlorine atoms with propene in a solid Para-Hydrogen matrix has been studied using infrared spectroscopy. For the Cl atom addition reaction, we find that the only observed isomer of the chloropropyl radical is the 2-chloropropyl and not the 1-chloropropyl radical, indicating that the addition of the Cl atom to the carbon−carbon double bond of propene occurs primarily at the central carbon atom. This is in sharp contrast to the generally accepted mechanism in organic chemistry and in gas-phase reactions in which the addition to the terminal carbon atom is greatly favored. This unique selectivity is possibly due to steric effects in solid Para-Hydrogen, in which the complex of Cl2 and propene are positioned so that the reacting Cl atom is closer to the central versus the terminal carbon atom of propene. One might be able to make use of this unique property to perform selective chemistry.
-
site selective reaction of cl propene in solid Para Hydrogen formation of 2 chloropropyl radicals
Journal of Physical Chemistry Letters, 2010Co-Authors: Jay C. Amicangelo, Yuan-pern LeeAbstract:The reaction of chlorine atoms with propene in a solid Para-Hydrogen matrix has been studied using infrared spectroscopy. For the Cl atom addition reaction, we find that the only observed isomer of the chloropropyl radical is the 2-chloropropyl and not the 1-chloropropyl radical, indicating that the addition of the Cl atom to the carbon−carbon double bond of propene occurs primarily at the central carbon atom. This is in sharp contrast to the generally accepted mechanism in organic chemistry and in gas-phase reactions in which the addition to the terminal carbon atom is greatly favored. This unique selectivity is possibly due to steric effects in solid Para-Hydrogen, in which the complex of Cl2 and propene are positioned so that the reacting Cl atom is closer to the central versus the terminal carbon atom of propene. One might be able to make use of this unique property to perform selective chemistry.
Joseph Turnbull - One of the best experts on this subject based on the ideXlab platform.
-
Disorder and the elusive superfluid phase of Para-Hydrogen
Physical Review B, 2008Co-Authors: Joseph Turnbull, Massimo BoninsegniAbstract:The possibility that disorder may stabilize a superfluid phase of Para-Hydrogen in two dimensions is investigated theoretically by means of Quantum Monte Carlo simulations. We model disorder using a random distribution of scatterers, and study the thermodynamic behavior of the system as a function of the scatterer density. Disorder gives rise to equilibrium glassy phases with no superfluid properties. Indeed, the propensity for quantum exchanges of Hydrogen molecules is reduced even with respect to what is observed if the scatterers are arranged as a regular crystal, a physical setting that also yields no superfluidity.
-
Adsorption of Para-Hydrogen on krypton pre-plated graphite
Journal of Low Temperature Physics, 2005Co-Authors: Joseph Turnbull, Massimo BoninsegniAbstract:Adsorption of Para-Hydrogen on the surface of graphite pre-plated with a single atomic layer of krypton, is studied theoretically by means of path integral ground state Monte Carlo simulations. We compute energetics and density profiles of Para-Hydrogen, and determine the structure of the adsorbed film for various coverages. Results show that there are two thermodynamically stable monolayer phases of p-H_2, both solid; one is commensurate with the krypton layer, and has coverage θ ≈ 0.0636 Å^−2; the other is incommensurate, has coverage θ ≈ 0.0716 Å^−2, and is compressible up to θ ≈ 0.0769 Å^−2. No evidence is observed of a liquid phase at T:0 for intermediate coverages. These results are qualitatively similar to what is seen for p-H_2 on bare graphite. Quantum exchanges of Hydrogen molecules are suppressed in this system.
-
Adsorption of Para-Hydrogen on krypton pre-plated graphite
Journal of Low Temperature Physics, 2005Co-Authors: Joseph Turnbull, Massimo BoninsegniAbstract:Adsorption of Para-Hydrogen on the surface of graphite pre-plated with a single layer of atomic krypton is studied thoretically by means of Path Integral Ground State Monte Carlo simulations. We compute energetics and density profiles of Para-Hydrogen, and determine the structure of the adsorbed film for various coverages. Results show that there are two thermodynamically stable monolayer phases of Para-Hydrogen, both solid. One is commensurate with the krypton layer, the other is incommensurate. No evidence is seen of a thermodynamically stable liquid phase, at zero temperature. These results are qualitatively similar to what is seen for for Para-Hydrogen on bare graphite. Quantum exchanges of Hydrogen molecules are suppressed in this system.Comment: 12 pages, 6 figures, to appear in the proceedings of "Advances in Computational Many-Body Physics", Banff, Alberta (Canada), January 13-16 200
-
Adsorption of Para-Hydrogen on fullerenes
Physical Review B, 2005Co-Authors: Joseph Turnbull, Massimo BoninsegniAbstract:Adsorption of Para-Hydrogen on the outer surface of a single fullerene is studied theoretically, by means of ground state quantum Monte Carlo simulations. We compute energetics and radial density profiles of Para-Hydrogen for various coverages on a variety of small fullerenes. The equilibrium adsorbed solid monolayer is commensurate with the surface of the fullerene; as the chemical potential is increased, a discontinuous change is generally observed, to an incommensurate, compressible layer. Quantum exchanges of Hydrogen molecules are absent in these systems.
