keyword
MENU ▼
Read by QxMD icon Read
search

proton density

keyword
https://www.readbyqxmd.com/read/28323432/electronic-structures-and-oh-induced-atmospheric-degradation-of-cf3nsf2-a-potential-green-dielectric-replacement-for-sf6
#1
Lin Cheng, Xiaojuan Yu, Kun Zhao, Hua Hou, Baoshan Wang
Electronic structures of Trifluoromethyl imionosulfur difluoride (CF3NSF2) and degradation mechanisms by hydroxyl radical have been investigated using density functional theory (M06-2X), the complete basis set quadratic CBS-Q, and the explicitly correlated coupled-cluster methods [CCSD(T)-F12]. The d-function augmented Correlation-consistent basis sets including triple- and quadruple- were employed for the sulfur-containing species. It was found that CF3NSF2 exists as two conformations connected by the internal rotation of CF3 around the central NS bond...
March 21, 2017: Journal of Physical Chemistry. A
https://www.readbyqxmd.com/read/28319377/mechanism-and-origins-of-stereoselectivity-in-the-cinchona-thiourea-and-squaramide-catalyzed-asymmetric-michael-addition-of-nitroalkanes-to-enones
#2
Matthew N Grayson
We report density functional theory calculations which examine the mechanism and origins of stereoselectivity of Soós' landmark discovery from 2005 that cinchona thioureas catalyze the asymmetric Michael addition of nitroalkanes to enones. We show that the electrophile is activated by the catalyst's protonated amine and that the nucleophile binds to the thiourea moiety by hydrogen bonding. These results lead to the correction of published mechanistic work which did not consider this activation mode. We have also investigated the corresponding cinchona squaramide-catalyzed reaction and found that it proceeds by the same mechanism, despite the differences in the geometry of the two catalysts' hydrogen bond donating groups, which demonstrates the generality of this mechanistic model...
March 20, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28318741/neonatal-magnetic-resonance-imaging-without-sedation-correlates-with-injury-severity-in-brachial-plexus-birth-palsy
#3
Andrea S Bauer, Peter Y Shen, Anna E Nidecker, Paul S Lee, Michelle A James
PURPOSE: Which infants with brachial plexus birth palsy (BPBP) should undergo microsurgical plexus reconstruction remains controversial. The current gold standard for the decision for plexus reconstruction is serial clinical examinations, but this approach obviates the possibility of early surgical treatment. We hypothesize that a new technique using 3-dimensional volumetric proton density magnetic resonance imaging (MRI) without sedation can evaluate the severity of BPBP injury earlier than serial clinical examinations...
March 16, 2017: Journal of Hand Surgery
https://www.readbyqxmd.com/read/28314204/stability-speciation-and-spectral-properties-of-npo2-complexes-with-pyridine-monocarboxylates-in-aqueous-solution
#4
Rama Mohana Rao Dumpala, Neetika Rawat, B S Tomar
Neptunyl ion as NpO2(+) is the least reacting and most mobile radioactive species among all the actinides. The picolinic acid used for decontamination is co-disposed along with the radioactive waste. Thus, in long term storage of HLW, there is high possibility of interaction of actinides and long lived fission products with the picolinate and can cause migration. The complexation of NpO2(+) with the three structural isomers of pyridine monocarboxylates provides an insight to explore the role of hetero atom (nitrogen) with respect to key binding moiety (carboxylate)...
March 6, 2017: Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy
https://www.readbyqxmd.com/read/28306556/metal-artifact-reduction-in-mri-based-cervical-cancer-intracavitary-brachytherapy
#5
Yuan James Rao, Jacqueline E Zoberi, Mo Kadbi, Perry W Grigsby, Jochen Cammin, Stacie L Mackey, Jose Garcia-Ramirez, S Murty Goddu, Julie K Schwarz, H Michael Gach
Magnetic resonance imaging (MRI) plays an increasingly important role in brachytherapy planning for cervical cancer. Yet, metal tandem, ovoid intracavitary applicators, and fiducial markers used in brachytherapy cause magnetic susceptibility artifacts in standard MRI. These artifacts may impact the accuracy of brachytherapy treatment and the evaluation of tumor response by misrepresenting the size and location of the metal implant, and distorting the surrounding anatomy and tissue. Metal artifact reduction sequences (MARS) with high bandwidth RF selective excitations and turbo spin-echo readouts were developed for MRI of orthopedic implants...
March 17, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28304068/high-velocity-proton-collision-with-liquid-lithium-a-time-dependent-density-functional-theory-study
#6
Gang Bi, Jun Kang, Lin-Wang Wang
Liquid lithium is often used as a coating material in fusion reaction chambers, where it is under constant bombardment from high speed neutrons and protons. However, numerous fundamental questions are unanswered, for example whether a single proton impact can cause Li atom sputtering, and what is the electron excitation energy profile after a collision particularly for extremely high energy projectiles. Herein, we use a real-time dependent density functional method to study these questions for proton energies in the range of 30 eV to 1 MeV...
March 17, 2017: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/28304035/nuclear-dynamics-and-phase-polymorphism-in-solid-formic-acid
#7
Maciej Krzystyniak, Kacper Drużbicki, Giovanni Romanelli, Matthias J Gutmann, Svemir Rudić, Silvia Imberti, Felix Fernandez-Alonso
We apply a unique sequence of structural and dynamical neutron-scattering techniques, augmented with density-functional electronic-structure calculations, to establish the degree of polymorphism in an archetypal hydrogen-bonded system - crystalline formic acid. Using this combination of experimental and theoretical techniques, the hypothesis by Zelsmann on the coexistence of the β1 and β2 phases above 220 K is tested. Contrary to the postulated scenario of proton-transfer-driven phase coexistence, the emerging picture is one of a quantitatively different structural change over this temperature range, whereby the loosening of crystal packing promotes temperature-induced shearing of the hydrogen-bonded chains...
March 17, 2017: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/28300265/catalytic-routes-to-fuels-from-c1-and-oxygenate-molecules
#8
Shuai Wang, Iker Agirrezabal-Telleria, Aditya Bhan, Dante Simonetti, Kazuhiro Takanabe, Enrique Iglesia
This account illustrates concepts in chemical kinetics underpinned by the formalism of transition state theory using catalytic processes that enable the synthesis of molecules suitable as fuels from C1 and oxygenate reactants. Such feedstocks provide an essential bridge towards a carbon-free energy future, but their volatility and low energy density require the formation of new C-C bonds and the removal of oxygen. These transformations are described here through recent advances in our understanding of the mechanisms and site requirements in catalysis by surfaces, with emphasis on enabling concepts that tackle ubiquitous reactivity and selectivity challenges...
March 16, 2017: Faraday Discussions
https://www.readbyqxmd.com/read/28297858/quantitative-shadowgraphy-and-proton-radiography-for-large-intensity-modulations
#9
Muhammad Firmansyah Kasim, Luke Ceurvorst, Naren Ratan, James Sadler, Nicholas Chen, Alexander Sävert, Raoul Trines, Robert Bingham, Philip N Burrows, Malte C Kaluza, Peter Norreys
Shadowgraphy is a technique widely used to diagnose objects or systems in various fields in physics and engineering. In shadowgraphy, an optical beam is deflected by the object and then the intensity modulation is captured on a screen placed some distance away. However, retrieving quantitative information from the shadowgrams themselves is a challenging task because of the nonlinear nature of the process. Here, we present a method to retrieve quantitative information from shadowgrams, based on computational geometry...
February 2017: Physical Review. E
https://www.readbyqxmd.com/read/28296979/feasibility-of-assessing-bone-matrix-and-mineral-properties-in-vivo-by-combined-solid-state-1h-and-31p-mri
#10
Xia Zhao, Hee Kwon Song, Alan C Seifert, Cheng Li, Felix W Wehrli
PURPOSE: To develop and evaluate an integrated imaging protocol for bone water and phosphorus quantification in vivo by solid-state 1H and 31P MRI. MATERIALS AND METHODS: All studies were HIPAA-compliant and were performed with institutional review board approval and written informed consent. Proton (1H) ultra-short echo-time (UTE) and phosphorus (31P) zero echo-time (ZTE) sequences were designed and implemented on a 3 T clinical MR scanner to quantify bone water and mineral in vivo...
2017: PloS One
https://www.readbyqxmd.com/read/28296415/proton-transfer-mechanisms-at-the-water-zno-interface-the-role-of-presolvation
#11
Vanessa Quaranta, Matti Hellström, Jörg Behler
The dissociation of water is an important step in many chemical processes at solid surfaces. In particular, water often spontaneously dissociates near metal oxide surfaces, resulting in a mixture of H2O, H(+), and OH(-) at the interface. Ubiquitous proton-transfer (PT) reactions cause these species to dynamically interconvert, but the underlying mechanisms are poorly understood. Here, we develop and use a reactive high-dimensional neural-network potential based on density functional theory data to elucidate the structural and dynamical properties of the interfacial species at the liquid-water-metal-oxide interface, using the nonpolar ZnO(101̅0) surface as a prototypical case...
March 20, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28291350/quantum-mechanical-study-of-n-heterocyclic-carbene-adsorption-on-au-surfaces
#12
Kuan Chang, Jingguang G Chen, Qi Lu, Mu-Jeng Cheng
There is an increasing interest in using N-heterocyclic carbenes (NHCs) as surface ligands to stabilize transition metal nanoparticles (NPs) and to replace thiols for the preparation of self-assembled monolayers (SAMs) on gold surfaces. This type of surface decoration is advantageous, since it leads to improved catalytic activity of NPs and increased stability of SAM, as shown by recent experiments. In this work, we used quantum mechanics combined with periodic surface models to study the adsorption of NHCs on the Au(111) surface...
March 14, 2017: Journal of Physical Chemistry. A
https://www.readbyqxmd.com/read/28291336/direct-observation-of-an-iron-bound-terminal-hydride-in-fefe-hydrogenase-by-nuclear-resonance-vibrational-spectroscopy
#13
Edward J Reijerse, Cindy C Pham, Vladimir Pelmenschikov, Ryan Gilbert-Wilson, Agnieszka Adamska-Venkatesh, Judith F Siebel, Leland B Gee, Yoshitaka Yoda, Kenji Tamasaku, Wolfgang Lubitz, Thomas B Rauchfuss, Stephen P Cramer
[FeFe]-hydrogenases catalyse the reversible reduction of protons to molecular hydrogen with extremely high efficiency. The active site ("H-cluster") consists of a [4Fe-4S]H cluster linked through a bridging cysteine to a [2Fe]H subsite coordinated by CN(-) and CO ligands featuring a dithiol-amine moiety which serves as proton shuttle between the protein proton channel and the catalytic distal iron site (Fed). Although there is broad consensus that an iron bound terminal hydride species must occur in the catalytic mechanism, such a species has never been directly observed experimentally...
March 14, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28288458/gastric-acid-suppression-is-associated-with-an-increased-risk-of-adverse-outcomes-in-inflammatory-bowel-disease
#14
Rajesh Shah, Peter Richardson, Hong Yu, Jennifer Kramer, Jason Ken Hou
BACKGROUND: The intestinal microbiota may influence inflammatory bowel disease (IBD) activity. Histamine 2 receptor antagonists (H2RAs) and proton pump inhibitors (PPIs) can alter the intestinal microbiota. The aim of this study was to assess the relationship between H2RAs, PPIs, and IBD-related outcomes. METHODS: We conducted a case-control study of IBD patients using the Veterans Health Affairs databases. Cases were defined by their first instance of an IBD-related hospitalization or surgery and the exposure of interest was H2RA or PPI use 30 days prior to the outcome...
March 14, 2017: Digestion
https://www.readbyqxmd.com/read/28286210/using-a-3-proton-density-fat-fraction-as-a-cut-off-value-increases-sensitivity-of-detection-of-hepatic-steatosis-based-on-results-from-histopathology-analysis
#15
Patrik Nasr, Mikael F Forsgren, Simone Ignatova, Nils Dahlström, Gunnar Cedersund, Olof Dahlqvist Leinhard, Bengt Norén, Mattias Ekstedt, Peter Lundberg, Stergios Kechagias
It is possible to estimate hepatic triglyceride content by calculating the proton density fat fraction (PDFF), using proton magnetic resonance spectroscopy ((1)H-MRS), instead of collecting and analyzing liver biopsies to detect steatosis. However, the current PDFF cut-off value (5%) used to define steatosis by magnetic resonance was derived from studies that did not use histopathology as the reference standard. We performed a prospective study to determine the accuracy of (1)H-MRS PDFF in measurement of steatosis using histopathology analysis as the standard...
March 9, 2017: Gastroenterology
https://www.readbyqxmd.com/read/28285444/the-interaction-strengths-and-spectroscopy-parameters-of-the-c2h2%C3%A2-%C3%A2-%C3%A2-hx-and-hcn%C3%A2-%C3%A2-%C3%A2-hx-complexes-x-f-cl-cn-and-cch-and-related-ternary-systems-valued-by-fluxes-of-charge-densities-qtaim-ccfo-and-nbo-calculations
#16
Marco A A Viana, Regiane C M U Araújo, José A Maia Neto, Henrique C Chame, Arquimedes M Pereira, Boaz G Oliveira
This theoretical work exhibits a new systematic study of structural parameters, electronic properties, infrared vibration modes, and molecular topography of hydrogen complexes, namely linear-type HCN⋯HX and T-type C2H2⋯HX (X = F, Cl, CN, and CCH). Ideally, the knowledge of the ternary systems of C2H2⋯HCN⋯HF and HCN⋯HCN⋯HF whose subparts integrate the linear and T-shaped complexes were used to give support in this current research. By means of computational calculations carried out in both levels B3LYP and MP2, the variations of the HX bond lengths are clearly overestimated in the HCN⋯HX linear complexes...
April 2017: Journal of Molecular Modeling
https://www.readbyqxmd.com/read/28285049/adsorption-and-release-of-ampicillin-antibiotic-from-ordered-mesoporous-silica
#17
Valentina Nairi, Luca Medda, Maura Monduzzi, Andrea Salis
In this work the adsorption and the release of ampicillin - a β-lactam penicillin-like antibiotic - from MCM-41, SBA-15, and (amino functionalized) SBA-15-NH2 ordered mesoporous silica (OMS) materials were investigated. The silica matrices differ for their pore size (SBA-15 vs. MCM-41) mainly, and also for surface charge (SBA-15 and MCM-41, vs. SBA-15-NH2). OMS samples were characterized through small-angle X-rays scattering (SAXS), transmission electron microscopy (TEM), N2 adsorption-desorption isotherms, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and potentiometric titrations...
March 6, 2017: Journal of Colloid and Interface Science
https://www.readbyqxmd.com/read/28283687/impact-of-gain-of-function-mutations-in-the-low-density-lipoprotein-receptor-related-protein-5-lrp5-on-glucose-and-lipid-homeostasis
#18
D Foer, M Zhu, R L Cardone, C Simpson, R Sullivan, S Nemiroff, G Lee, R G Kibbey, K F Petersen, K L Insogna
LRP5 loss-of-function mutations have been shown to cause profound osteoporosis and have been associated with impaired insulin sensitivity and dysregulated lipid metabolism. We hypothesized that gain-of-function mutations in LRP5 would also affect these parameters. We therefore studied individuals with LRP5 gain-of-function mutations exhibiting high bone mass (HBM) phenotypes and found that while there was no detected change in insulin sensitivity, there was a significant reduction in serum LDL. INTRODUCTION: Wnt signaling through LRP5 represents a newly appreciated metabolic pathway, which potentially represents a target for drug discovery in type 2 diabetes and hyperlipidemia...
March 10, 2017: Osteoporosis International
https://www.readbyqxmd.com/read/28283532/molecular-architecture-of-the-n-type-atpase-rotor-ring-from-burkholderia-pseudomallei
#19
Sarah Schulz, Martin Wilkes, Deryck J Mills, Werner Kühlbrandt, Thomas Meier
The genome of the highly infectious bacterium Burkholderia pseudomallei harbors an atp operon that encodes an N-type rotary ATPase, in addition to an operon for a regular F-type rotary ATPase. The molecular architecture of N-type ATPases is unknown and their biochemical properties and cellular functions are largely unexplored. We studied the B. pseudomallei N1No-type ATPase and investigated the structure and ion specificity of its membrane-embedded c-ring rotor by single-particle electron cryo-microscopy. Of several amphiphilic compounds tested for solubilizing the complex, the choice of the low-density, low-CMC detergent LDAO was optimal in terms of map quality and resolution...
March 10, 2017: EMBO Reports
https://www.readbyqxmd.com/read/28282807/radiological-pathological-correlation-in-alzheimer-s-disease-systematic-review-of-antemortem-magnetic-resonance-imaging-findings
#20
Caroline Dallaire-Théroux, Brandy L Callahan, Olivier Potvin, Stephan Saikali, Simon Duchesne
BACKGROUND: The standard method of ascertaining Alzheimer's disease (AD) remains postmortem assessment of amyloid plaques and neurofibrillary degeneration. Vascular pathology, Lewy bodies, TDP-43, and hippocampal sclerosis are frequent comorbidities. There is therefore a need for biomarkers that can assess these etiologies and provide a diagnosis in vivo. OBJECTIVE: We conducted a systematic review of published radiological-pathological correlation studies to determine the relationship between antemortem magnetic resonance imaging (MRI) and neuropathological findings in AD...
March 6, 2017: Journal of Alzheimer's Disease: JAD
keyword
keyword
84238
1
2
Fetch more papers »
Fetching more papers... Fetching...
Read by QxMD. Sign in or create an account to discover new knowledge that matter to you.
Remove bar
Read by QxMD icon Read
×

Search Tips

Use Boolean operators: AND/OR

diabetic AND foot
diabetes OR diabetic

Exclude a word using the 'minus' sign

Virchow -triad

Use Parentheses

water AND (cup OR glass)

Add an asterisk (*) at end of a word to include word stems

Neuro* will search for Neurology, Neuroscientist, Neurological, and so on

Use quotes to search for an exact phrase

"primary prevention of cancer"
(heart or cardiac or cardio*) AND arrest -"American Heart Association"