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https://www.readbyqxmd.com/read/29334461/enhanced-proton-loss-from-neutral-free-radicals-towards-carbon-centered-superacids
#1
John C Walton
Radical centers close to protons are known to enhance their dissociation. Investigation of the generality of this Radical Enhanced Deprotonation (RED-shift) phenomenon and the kinds of structures in which it operates are reported. The pKas for sulfinic, sulfonic, pentan-2,4-dione and Meldrum's acid species, with adjacent radicals centered on C-, N- and O-atoms, were computed by a DFT method from free energies of deprotonation. All series showed significant RED-shifts that increased with the electronegativity of the radical center...
January 15, 2018: Journal of Physical Chemistry. A
https://www.readbyqxmd.com/read/29334424/in-vivo-epr-characterization-of-semi-synthetic-fefe-hydrogenases
#2
Livia S Meszaros, Brigitta Nemeth, Charlene Esmieu, Pierre Ceccaldi, Gustav Berggren
EPR spectroscopy reveals the formation of two different semi-synthetic hydrogenases in vivo. [FeFe] hydrogenases are metalloenzymes that catalyse the interconversion of molecular hydrogen and protons. The reaction is catalyzed by the H-cluster, consisting of a canonical iron-sulfur cluster and an organometallic [2Fe] subsite. It was recently shown how the enzyme can be reconstituted with synthetic cofactors mimicking the composition of the [2Fe] subsite, resulting in semi-synthetic hydrogenases. Here we employ EPR spectroscopy to monitor the formation of two such semi-synthetic enzymes in whole cells...
January 15, 2018: Angewandte Chemie
https://www.readbyqxmd.com/read/29334407/chiral-separation-of-novel-iminonaringenin-derivatives
#3
Meriem Bouanini, Nasser Belboukhari, J Carlos Menéndez, Khaled Sekkoum, Abdelkarim Cheriti, Hassan Y Aboul-Enein
A series of 4-iminonaringenin derivatives 2-6 have been prepared in good overall yields from a condensation reaction between naringenin and primary amines. The structures of all products were confirmed by ultraviolet, infrared, proton nuclear magnetic resonance, and carbon-13 nuclear magnetic resonance spectroscopic techniques. These derivatives were analyzed by high-performance liquid chromatography using polysaccharide-based chiral stationary phases, namely, Chiralpak IB and Chiralcel OD, using various mobile phases...
January 15, 2018: Chirality
https://www.readbyqxmd.com/read/29334141/characterization-of-macromolecular-baseline-of-human-brain-using-metabolite-cycled-semi-laser-at-9-4t
#4
Ioannis-Angelos Giapitzakis, Nikolai Avdievich, Anke Henning
PURPOSE: Macromolecular resonances (MM) arise mainly from cytosolic proteins and overlap with metabolites, influencing metabolite quantification. Macromolecules can serve as valuable biomarkers for diseases and pathologies. The objectives of this study were to characterize MM at 9.4T in the human brain (occipital and left parietal lobe) and to describe the RF coil setup used for MM acquisition in the two regions. METHODS: An adiabatic inversion pulse was optimised for metabolite nulling at 9...
January 15, 2018: Magnetic Resonance in Medicine: Official Journal of the Society of Magnetic Resonance in Medicine
https://www.readbyqxmd.com/read/29334125/determination-of-isoorientin-levels-in-rat-plasma-after-oral-administration-of-vaccinum-bracteatum-thunb-methanol-extract-by-high-performance-liquid-chromatography-tandem-mass-spectrometry
#5
Min-Ji Kim, Seung-Hwan Kwon, Choon-Gon Jang, Han-Joo Maeng
A simple, sensitive and rapid liquid chromatography tandem mass spectrometry method (LC-MS/MS) was developed and validated for the determination of plasma isoorientin levels in rats. After simple protein precipitation using methanol, chromatographic analysis was performed using a Synergi 4μ polar-RP 80A column (150 mm × 2.0 mm, 4 μm) under isocratic conditions and a mobile phase consisting of 0.1% formic acid in water and methanol (80:20, v/v) at a flow rate of 0.2 mL/min. In positive electrospray ionization mode, the protonated precursor and product ion transitions of isoorientin (m/z 449...
January 15, 2018: Biomedical Chromatography: BMC
https://www.readbyqxmd.com/read/29334093/three-component-difluoroalkylation-and-trifluoromethylthiolation-trifluoromethylselenolation-of-%C3%AF-bonds
#6
Bo-Sheng Zhang, Lu-Yao Gao, Zhe Zhang, Yu-Hua Wen, Yong-Min Liang
This report describes a new method for three-component difluoroalkylation and trifluoromethylthiolation/trifluoromethylselenolation of π-bonds via air-stable SCF3 and SeCF3 reagents as free-radical initiators of ethyl iododifluoroacetate. β-Proton elimination can be overcome effectively in this reaction system, and a broad substrate scope, including alkenes and alkynes, makes this approach practical and attractive.
January 15, 2018: Chemical Communications: Chem Comm
https://www.readbyqxmd.com/read/29333555/a-mechanism-study-on-the-hydrogen-evolution-reaction-catalyzed-by-molybdenum-disulfide-complexes
#7
Ti-Long Yang, Shao-Fei Ni, Peng Qin, Li Dang
Density functional theory (DFT) calculations show that H2 evolution is attributed to active sulfur hydrides derived from MoS2 complexes via two- or three-electron reduction from the synthesized [(PY5Me2)MoS2]2+. Water acts as a bridge for H2 evolution from the intermolecular H+/H- coupling between sulfur hydride complexes and hydrated protons.
January 15, 2018: Chemical Communications: Chem Comm
https://www.readbyqxmd.com/read/29333550/cuwo4-as-a-photocatalyst-for-room-temperature-aerobic-benzylamine-oxidation
#8
Aaron D Proctor, Shobhana Panuganti, Bart M Bartlett
The aerobic photochemical oxidation of benzylamine was carried out on the ternary oxides CuWO4 and BiVO4 as a test proton-coupled-electron-transfer reaction in acetonitrile. Both oxides give the coupled imine product, N-benzylidenebenzylamine, in near quantitative (98-99%) yield, with rate constants of 0.34 h-1 g-1 and 0.70 h-1 g-1 for CuWO4 and BiVO4, respectively.
January 15, 2018: Chemical Communications: Chem Comm
https://www.readbyqxmd.com/read/29333061/critical-appraisal-of-rome-iv-criteria-hypersensitive-esophagus-does-belong-to-gastroesophageal-reflux-disease-spectrum
#9
REVIEW
Leonardo Frazzoni, Marzio Frazzoni, Nicola de Bortoli, Salvatore Tolone, Irene Martinucci, Lorenzo Fuccio, Vincenzo Savarino, Edoardo Savarino
The Rome IV Committee introduced a major change in the classification of functional gastrointestinal disorders, proposing a more restrictive definition of gastroesophageal reflux disease (GERD). It was suggested that hypersensitive esophagus (HE) may sit more firmly within the functional realm. It was suggested that GERD diagnosis should be based upon abnormal acid exposure time (AET) only, implying no advantage of impedance-pH over pH monitoring. Symptom association probability (SAP), symptom index (SI) and heartburn relief with proton pump inhibitor (PPI) therapy were regarded as unreliable, whereas a lack of response to PPI was considered as evidence of functional heartburn...
January 2018: Annals of Gastroenterology: Quarterly Publication of the Hellenic Society of Gastroenterology
https://www.readbyqxmd.com/read/29332843/intrinsic-electron-trapping-in-amorphous-oxide
#10
Jack Strand, Moloud Kaviani, Valeri V Afanas'ev, Judit Lisoni, Alexander L Shluger
We demonstrate that electron trapping at intrinsic precursor sites is endemic to non-glass-forming amorphous oxide films. The energy distributions of trapped electron states in ultra-pure prototype amorphous (a)-HfO<sub>2</sub> insulator obtained from exhaustive photo-depopulation experiments demonstrate the electron states in the energy range of 2-3 eV below the oxide conduction band. These energy distributions are compared to the results of density functional calculations of a-HfO<sub>2</sub> models of realistic density...
January 15, 2018: Nanotechnology
https://www.readbyqxmd.com/read/29332800/acidity-of-substituted-cathinones-studied-by-capillary-electrophoresis-using-the-standard-and-fast-alternative-approaches
#11
Michał Woźniakiewicz, Paweł Mateusz Nowak, Małgorzata Gołąb, Piotr Adamowicz, Maria Kała, Paweł Kościelniak
Cathinone derivatives are notorious but still weakly characterized molecules, known mainly as components of the designer and illicit drugs. The knowledge on their acidity is scarce and incomplete, therefore, we decided to determine the pKa values for six of them: 2-methylmethcathinone, 3-methylmethcathinone, 4-methylmethcathinone, α-pyrrolidinovalerophenone, methylenedioxypyrovalerone and ephedrone. For that purpose we employed capillary electrophoresis, which is known for its accurateness in comparison to other analytical techniques...
April 1, 2018: Talanta
https://www.readbyqxmd.com/read/29332400/multiscale-kinetic-modeling-reveals-ensemble-of-cl-h-exchange-pathways-in-clc-ec1-antiporter
#12
Heather B Mayes, Sangyun Lee, Andrew D White, Gregory A Voth, Jessica M J Swanson
Despite several years of research, the ion exchange mechanisms in chloride/proton antiporters and many other coupled transporters are not yet understood at the molecular level. Here, we present a novel approach to kinetic modeling and apply it to ion exchange in ClC-ec1. Our multiscale kinetic model (MKM) is developed by 1) calculating the state-to-state rate coefficients with reactive and polarizable molecular dynamics simulations, 2) optimizing these rates in a global kinetic network, and 3) predicting new electrophysiological results...
January 14, 2018: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29332399/endor-induced-epr-of-disordered-systems-application-to-x-irradiated-alanine
#13
Jevgenij Kusakovskij, Kwinten Maes, Freddy Callens, Henk Vrielinck
The electron paramagnetic resonance (EPR) spectra of radiation-induced radicals in organic solids are generally composed of multiple components that largely overlap due to their similar weak g anisotropy and a large number of hyperfine (HF) interactions. Such properties make these systems difficult to study using standard cw EPR spectroscopy even in single crystals. Electron-nuclear double resonance (ENDOR) spectroscopy is a powerful and widely used complementary technique. In particular, ENDOR-induced EPR (EIE) experiments are useful for separating the overlapping contributions...
January 14, 2018: Journal of Physical Chemistry. A
https://www.readbyqxmd.com/read/29332380/solvent-modulation-of-aromatic-substituent-effects-in-molecular-balances-controlled-by-ch-%C3%AF-interactions
#14
Bright U Emenike, Ronald A Spinelle, Ambar Rosario, David W Shinn, Barney Yoo
CH-π aromatic interactions are ubiquitous in nature and are capable of regulating important chemical and biochemical processes. Solvation and aromatic substituent effects are known to perturb the CH-π aromatic interactions. However, the nature by which the two factors influence one another is relatively unexplored. Here we demonstrate experimentally that there is a quantitative correlation between substituent effects in CH-π interactions and the hydrogen-bond acceptor constant of the solvating molecule. The CH-π interaction energies were measured by the conformational study of a series of aryl-substituted molecular balances in which the conformational preferences depended on the relative strengths of the methyl and aryl CH-π interactions in the folded and unfolded states, respectively...
January 15, 2018: Journal of Physical Chemistry. A
https://www.readbyqxmd.com/read/29332243/photosystem-i-with-benzoquinone-analogues-incorporated-into-the-a1-binding-site
#15
Hiroki Makita, Gary Hastings
Time-resolved FTIR difference spectroscopy has been used to study photosystem I (PSI) particles with three different benzoquinones [plastoquinone-9 (PQ), 2,6-dimethyl-1,4-benzoquinone (DMBQ), 2,3,5,6-tetrachloro-1,4-benzoquinone (Cl4BQ)] incorporated into the A1 binding site. If PSI samples are cooled in the dark to 77 K, the incorporated benzoquinones are shown to be functional, allowing the production of time-resolved (P700+A1--P700A1) FTIR difference spectra. If samples are subjected to repetitive flash illumination at room temperature prior to cooling, however, the time-resolved FTIR difference spectra at 77 K display contributions typical of the P700 triplet state (3P700), indicating a loss of functionality of the incorporated benzoquinones, that occurs because of double protonation of the incorporated benzoquinones...
January 13, 2018: Photosynthesis Research
https://www.readbyqxmd.com/read/29331301/marrow-adipose-tissue-imaging-in-humans
#16
Vibha Singhal, Miriam A Bredella
Bone strength is affected not only by bone mineral density (BMD) and bone microarchitecture but also its microenvironment. Recent studies have focused on the role of marrow adipose tissue (MAT) in the pathogenesis of bone loss. Osteoblasts and adipocytes arise from a common mesenchymal stem cell within bone marrow and many osteoporotic states, including aging, medication use, immobility, over - and undernutrition are associated with increased marrow adiposity. Advancements in imaging technology allow the non-invasive quantification of MAT...
January 10, 2018: Bone
https://www.readbyqxmd.com/read/29331136/zwitterionization-of-glycine-in-water-environment-stabilization-mechanism-and-nmr-spectral-signatures
#17
Danillo Valverde, Zélia Maria da Costa Ludwig, Célia Regina da Costa, Valdemir Ludwig, Herbert C Georg
At physiological conditions, myriads of biomolecules (e.g., amino acids, peptides, and proteins) exist predominantly in the zwitterionic structural form and their biological functions will result in these conditions. However these geometrical structures are inaccessible energetically in the gas phase, and at this point, stabilization of amino-acids in physiological conditions is still under debate. In this paper, the electronic properties of a glycine molecule in the liquid environment were studied by performing a relaxation of the glycine geometry in liquid water using the free energy gradient method combined with a sequential quantum mechanics/molecular mechanics approach...
January 14, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/29331134/coarse-grained-model-of-nanoscale-segregation-water-diffusion-and-proton-transport-in-nafion-membranes
#18
Aleksey Vishnyakov, Runfang Mao, Ming-Tsung Lee, Alexander V Neimark
We present a coarse-grained model of the acid form of Nafion membrane that explicitly includes proton transport. This model is based on a soft-core bead representation of the polymer implemented into the dissipative particle dynamics (DPD) simulation framework. The proton is introduced as a separate charged bead that forms dissociable Morse bonds with water beads. Morse bond formation and breakup artificially mimics the Grotthuss hopping mechanism of proton transport. The proposed DPD model is parameterized to account for the specifics of the conformations and flexibility of the Nafion backbone and sidechains; it treats electrostatic interactions in the smeared charge approximation...
January 14, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/29330619/mr-arthrography-of-the-hip-diagnostic-performance-and-image-quality-of-3d-steady-state-free-precession-versus-2d-turbo-spin-echo-sequences
#19
Mareen Sarah Kraus, Mike Notohamiprodjo, Sasan Partovi, Ahmed Sobieh, Andrea Baur-Melnyk, Joerg Hausdorf, Ulrich Grosse
OBJECTIVE: To retrospectively compare the diagnostic performance of isotropic 3D steady-state free precession (3D-SSFP) sequences with 2D turbo spin-echo proton density-weighted fat-saturated (2D-TSE-PD fs) images in hip magnetic resonance arthrography; arthroscopy was a standard of reference. METHODS: Eighty-one patients with suspected labral tears who underwent hip MR arthrography (3-T scanner) were included. 2D-TSE-PD fs sequences were acquired in three planes and a singular sagittal 3D-SSFP...
January 12, 2018: Skeletal Radiology
https://www.readbyqxmd.com/read/29330604/driving-forces-of-translocation-through-bacterial-translocon-secyeg
#20
Denis G Knyazev, Roland Kuttner, Mirjam Zimmermann, Ekaterina Sobakinskaya, Peter Pohl
This review focusses on the energetics of protein translocation via the Sec translocation machinery. First we complement structural data about SecYEG's conformational rearrangements by insight obtained from functional assays. These include measurements of SecYEG permeability that allow assessment of channel gating by ligand binding and membrane voltage. Second we will discuss the power stroke and Brownian ratcheting models of substrate translocation and the role that the two models assign to the putative driving forces: (i) ATP (SecA) and GTP (ribosome) hydrolysis, (ii) interaction with accessory proteins, (iii) membrane partitioning and folding, (iv) proton motive force (PMF), and (v) entropic contributions...
January 12, 2018: Journal of Membrane Biology
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