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https://www.readbyqxmd.com/read/29676661/atomistic-mechanisms-of-the-double-proton-transfer-in-the-h-bonded-nucleobase-pairs-qm-qtaim-computational-lessons
#1
Ol'ha O Brovarets', Dmytro M Hovorun
In this Review we have summarized and generalized the results of the investigation of the microstructural mechanisms of the tautomerisation by the counter movement of the protons along the neighboring intermolecular H-bonds in 22 biologically important pairs of nucleotide bases in the framework of the original method, which allows to trace the evolution of the physico-chemical parameters, that characterize these processes along the intrinsic reaction coordinate (IRC). It was demonstrated the performance of the introduction of the conception of the key points (KPs) (from nine to five, depending on the symmetry and nature of system), which exhaustively characterize the flow of the tautomerisation processes...
April 20, 2018: Journal of Biomolecular Structure & Dynamics
https://www.readbyqxmd.com/read/29675207/a-practical-organic-mediated-hybrid-electrolyser-that-decouples-hydrogen-production-at-high-current-densities
#2
Niall Kirkaldy, Greig Chisholm, Jia-Jia Chen, Leroy Cronin
Hydrogen is seen as a sustainable fuel of the future, yet the vast majority of global hydrogen production comes from the reformation of fossil fuels. Electrolytic water splitting using proton exchange membrane electrolysers (PEMEs) provides a pathway to sustainable hydrogen production through coupling to renewable energy sources, but can suffer from gas crossover at low current densities and high operating pressures, causing explosive gas mixtures and decreasing cell lifetimes. Here we demonstrate the application of a highly stable, organic electron-coupled proton buffer (ECPB) which allows the decoupling of hydrogen and oxygen production during water splitting...
February 14, 2018: Chemical Science
https://www.readbyqxmd.com/read/29674667/a-mixed-periodic-paralysis-myotonia-mutant-p1158s-imparts-ph-sensitivity-in-skeletal-muscle-voltage-gated-sodium-channels
#3
Mohammad-Reza Ghovanloo, Mena Abdelsayed, Colin H Peters, Peter C Ruben
Skeletal muscle channelopathies, many of which are inherited as autosomal dominant mutations, include myotonia and periodic paralysis. Myotonia is defined by a delayed relaxation after muscular contraction, whereas periodic paralysis is defined by episodic attacks of weakness. One sub-type of periodic paralysis, known as hypokalemic periodic paralysis (hypoPP), is associated with low potassium levels. Interestingly, the P1158S missense mutant, located in the third domain S4-S5 linker of the "skeletal muscle", Nav1...
April 19, 2018: Scientific Reports
https://www.readbyqxmd.com/read/29671924/effects-of-syn1-q555x-mutation-on-cortical-gray-matter-microstructure
#4
Jean-François Cabana, Guillaume Gilbert, Laurent Létourneau-Guillon, Dima Safi, Isabelle Rouleau, Patrick Cossette, Dang Khoa Nguyen
A new Q555X mutation on the SYN1 gene was recently found in several members of a family segregating dyslexia, epilepsy, and autism spectrum disorder. To describe the effects of this mutation on cortical gray matter microstructure, we performed a surface-based group study using novel diffusion and quantitative multiparametric imaging on 13 SYN1Q555X mutation carriers and 13 age- and sex-matched controls. Specifically, diffusion kurtosis imaging (DKI) and neurite orientation and dispersion and density imaging (NODDI) were used to analyze multi-shell diffusion data and obtain parametric maps sensitive to tissue structure, while quantitative metrics sensitive to tissue composition (T1, T2* and relative proton density [PD]) were obtained from a multi-echo variable flip angle FLASH acquisition...
April 19, 2018: Human Brain Mapping
https://www.readbyqxmd.com/read/29670577/anatomical-variation-of-age-related-changes-in-vertebral-bone-marrow-composition-using-chemical-shift-encoding-based-water-fat-magnetic-resonance-imaging
#5
Thomas Baum, Alexander Rohrmeier, Jan Syväri, Maximilian N Diefenbach, Daniela Franz, Michael Dieckmeyer, Andreas Scharr, Hans Hauner, Stefan Ruschke, Jan S Kirschke, Dimitrios C Karampinos
Assessment of vertebral bone marrow composition has been proposed as imaging biomarker for osteoporosis, hematopoietic, and metabolic disorders. We investigated the anatomical variation of age-related changes of vertebral proton density fat fraction (PDFF) using chemical shift encoding-based water-fat magnetic resonance imaging (MRI). 156 healthy subjects were recruited (age range 20-29 years: 12/30 males/females; 30-39: 15/9; 40-49: 4/14; 50-59: 9/27; 60-69: 5/19; 70-79: 4/8). An eight-echo 3D spoiled gradient-echo sequence at 3T MRI was used for chemical shift-encoding based water-fat separation at the lumbar spine...
2018: Frontiers in Endocrinology
https://www.readbyqxmd.com/read/29667337/insights-into-the-n-heterocyclic-carbene-nhc-catalyzed-intramolecular-cyclization-of-aldimines-general-mechanism-and-role-of-catalyst
#6
Xue Li, Mingsheng Tang, Yanyan Wang, Yang Wang, Zhongjun Li, Ling-Bo Qu, Donghui Wei
One of the most challenging questions in the Lewis base organocatalyst field is how to predict the most electrophilic carbon for the complexation of N-heterocyclic carbene (NHC) and reactant. This study provides a valuable case for this issue. Multiple mechanisms (A, B, C, D and E) for the intramolecular cyclization of aldimine catalyzed by NHC were investigated using density functional theory (DFT). The computed results reveal that NHC energetically prefers attacking the iminyl carbon (AIC mode, which is associated with mechanisms A and C) rather than attacking the olefin carbon (AOC mode, which is associated with mechanisms B and D) or attacking the carbonyl carbon (ACC mode, which is associated with mechanism E) of aldimine...
April 17, 2018: Chemistry, An Asian Journal
https://www.readbyqxmd.com/read/29665193/validation-of-a-motion-robust-2d-sequential-technique-for-quantification-of-hepatic-proton-density-fat-fraction-during-free-breathing
#7
B Dustin Pooler, Diego Hernando, Jeannine A Ruby, Hiroshi Ishii, Ann Shimakawa, Scott B Reeder
BACKGROUND: Current chemical-shift-encoded (CSE) MRI techniques for measuring hepatic proton density fat fraction (PDFF) are sensitive to motion artifacts. PURPOSE: Initial validation of a motion-robust 2D-sequential CSE-MRI technique for quantification of hepatic PDFF. STUDY TYPE: Phantom study and prospective in vivo cohort. POPULATION: Fifty adult patients (27 women, 23 men, mean age 57.2 years). FIELD STRENGTH/SEQUENCE: 3D, 2D-interleaved, and 2D-sequential CSE-MRI acquisitions at 1...
April 17, 2018: Journal of Magnetic Resonance Imaging: JMRI
https://www.readbyqxmd.com/read/29664095/dft-studies-on-the-distinct-mechanisms-of-c-h-activation-and-oxidation-reactions-mediated-by-mononuclear-and-binuclear-palladium
#8
Lu-Lu Zhang, Lei Zhang, Shi-Jun Li, De-Cai Fang
A series of density functional theory calculations have been carried out to investigate the detailed mechanisms of C-H activation and oxidation reactions, and further to disclose the distinct effects of mononuclear- and binuclear-palladium on these reaction pathways. The results of calculations demonstrated that the C-H activation of 2-phenylpyridine with mononuclear Pd(OAc)2 prefers the inner-shell proton-abstraction mechanism, while that with binuclear Pd2(μ-OAc)4 is biased to the outer-shell proton-abstraction mechanism...
April 17, 2018: Dalton Transactions: An International Journal of Inorganic Chemistry
https://www.readbyqxmd.com/read/29663545/detecting-proton-transfer-in-co2-species-chemisorbed-on-amine-modified-mesoporous-silicas-using-13c-nmr-chemical-shift-anisotropy-and-smart-control-of-amine-surface-density
#9
Tomaz Cendak, Lisa Sequeira, Mariana Sardo, Anabela Valente, Moisés Pinto, Luís Mafra
The wealth of site-selective structural information on CO2 speciation, obtained by spectroscopic techniques, is often hampered by the lack of easy-to-control synthetic routes. Herein, an alternative experimental protocol that relies on the high sensitivity of 13C chemical shift anisotropy (CSA) tensors to proton-transfer, is presented to unambiguously distinguish between ionic/charged and neutral CO2 species, formed upon adsorption of 13CO2 in amine-modified porous materials. Control of the surface amine spacing was achieved through the use of amine protecting groups during functionalization prior to CO2 adsorption...
April 16, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29661684/trabecular-bone-score-and-hip-structural-analysis-in-patients-with-atypical-femur-fractures
#10
Sanne K C Buitendijk, Denise M van de Laarschot, Alexandra A A Smits, Fjorda Koromani, Fernando Rivadeneira, Thomas J Beck, M Carola Zillikens
Bisphosphonate use has declined dramatically in recent years, partly because of fear of rare side effects like atypical femur fractures (AFFs). It is therefore desirable to have a diagnostic method to identify those at risk of AFF to prevent this serious complication. We compared trabecular microarchitecture and hip geometry between 30 patients with AFF and 141 controls of similar age and sex, using bisphosphonates. Trabecular bone score (TBS) and hip structural analysis (HSA) were used to assess trabecular microarchitecture and macroscopic hip geometry from dual-energy X-ray absorptiometry images of the lumbar spine and hip, respectively...
March 22, 2018: Journal of Clinical Densitometry
https://www.readbyqxmd.com/read/29660530/assessing-patterns-of-t2-t1rho-change-in-grade-1-cartilage-lesions-of-the-distal-femur-using-an-angle-layer-dependent-approach
#11
Yasuhito Kaneko, Taiki Nozaki, Hon Yu, Ran Schwarzkopf, Takeshi Hara, Hiroshi Yoshioka
PURPOSE: To assess changes in the patterns of T2 and T1rho values within grade 1 cartilage lesions of osteoarthritis (OA) patients compared to healthy controls. MATERIALS AND METHODS: Twenty healthy knees and 25 OA knees were examined on a 3 T scanner. Areas of signal heterogeneity within the cartilage of the distal femur were identified using fat suppressed proton density-weighted imagines. T2 and T1rho values in each OA patient with grade 1 lesions were compared to average T2 and T1rho values of the corresponding areas in healthy subjects...
April 7, 2018: Clinical Imaging
https://www.readbyqxmd.com/read/29660324/magnetic-resonance-imaging-proton-density-fat-fraction-associates-with-progression-of-fibrosis-in-patients-with-nonalcoholic-fatty-liver-disease
#12
Veeral Ajmera, Charlie C Park, Cyrielle Caussy, Seema Singh, Carolyn Hernandez, Ricki Bettencourt, Jonathan Hooker, Ethan Sy, Cynthia Behling, Ronghui Xu, Michael S Middleton, Mark A Valasek, Claire Faulkner, Emily Rizo, Lisa Richards, Claude B Sirlin, Rohit Loomba
Markers are needed to predict progression of nonalcoholic fatty liver disease (NAFLD). The proton density fat fraction, measured by magnetic resonance imaging (MRI-PDFF), provides an accurate, validated marker of hepatic steatosis. However, it is not clear whether the proton density fat fraction identifies patients at risk for NAFLD progression. We performed a follow-up study of 95 well-characterized patients with biopsy-proven NAFLD and examined the association between liver fat content and fibrosis progression...
April 13, 2018: Gastroenterology
https://www.readbyqxmd.com/read/29659278/mechanism-of-photoinduced-triplet-intermolecular-hydrogen-transfer-between-cycloxydim-and-chlorothalonil
#13
Qi Yuan, Dimitrios Toroz, Nathan Kidley, Ian R Gould
The possible reaction mechanisms for the experimentally observed hydrogen transfer between herbicide Cycloxydim (CD) and triplet fungicide Chlorothalonil (CT) were identified with density functional theory (DFT) and time dependent density function theory (TDDFT) computations. Excited energy transfer (EET) calculations indicate that reactants for intermolecular hydrogen transfer were formed via energy transfer from triplet CT to ground state CD. Three possible reaction pathways after EET were identified, and hydrogen transfer from the hydroxyl group on the cyclohexane ring of CD to CT exhibited the lowest energy barrier...
April 16, 2018: Journal of Physical Chemistry. A
https://www.readbyqxmd.com/read/29659264/kinetics-and-mechanism-of-oxirane-formation-by-darzens-condensation-of-ketones-quantification-of-the-electrophilicities-of-ketones
#14
Zhen Li, Harish Jangra, Quan Chen, Peter Mayer, Armin R Ofial, Hendrik Zipse, Herbert Mayr
The kinetics of epoxide formation by Darzens condensation of aliphatic ketones 1 with arylsulfonyl-substituted chloromethyl anions 2 (ArSO2 CHCl- ) have been determined photometrically in DMSO solution at 20 °C. The reactions proceed via nucleophilic attack of the carbanions at the carbonyl group to give intermediate halohydrin anions 4, which subsequently cyclize with formation of the oxiranes 3. Protonation of the reaction mixture obtained in THF solution at low temperature allowed the intermediates to be trapped and the corresponding halohydrins 4-H to be isolated...
April 16, 2018: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29658780/inter-and-intraobserver-variability-of-an-anatomical-landmark-based-manual-segmentation-method-by-mri-for-the-assessment-of-skeletal-muscle-fat-content-and-area-in-subjects-from-the-general-population
#15
Lena Sophie Kiefer, Jana Fabian, Roberto Lorbeer, Jürgen Machann, Corinna Storz, Mareen Sarah Kraus, Elke Wintermeyer, Christopher L Schlett, Frank Roemer, Konstantin Nikolaou, Annette Peters, Fabian Bamberg
OBJECTIVES: Changes in skeletal muscle composition, such as fat content and mass, may exert unique metabolic and musculoskeletal risks; however, the reproducibility of their assessment is unknown. We determined the variability of the assessment of skeletal muscle fat content and area by magnetic resonance imaging (MRI) in a population-based sample. METHODS: A random sample from a prospective, community-based cohort study (KORA-FF4) was included. Skeletal muscle fat content was quantified as proton-density fat-fraction (PDFF) and area as cross-sectional area (CSA) in multi-echo Dixon sequences (TR 8...
April 16, 2018: British Journal of Radiology
https://www.readbyqxmd.com/read/29652141/insights-into-2-and-4-5-nitroimidazole-decomposition-into-relevant-ions-and-molecules-induced-by-vuv-ionization
#16
A Cartoni, A R Casavola, P Bolognesi, M C Castrovilli, D Catone, J Chiarinelli, R Richter, L Avaldi
Nitromidazoles are relevant compounds of multidisciplinary interest, and knowledge of their physical-chemical parameters as well as their decomposition under photon irradiation is needed. Here we report an experimental and theoretical study of the mechanisms of VUV photofragmentation of 2- and 4(5)-nitromidazoles, compounds used as radiosensitizers in conjunction with radiotherapy as well as high-energy density materials. Photoelectron-photoion coincidence experiments, measurements of the appearance energies of the most important ionic fragments, density functional theory, and single-point coupled cluster calculations have been used to provide an overall insight into the energetics and structure of the different ionic/neutral products of the fragmentation processes...
April 13, 2018: Journal of Physical Chemistry. A
https://www.readbyqxmd.com/read/29649874/structural-dynamics-of-the-oxygen-evolving-complex-of-photosystem-ii-in-water-splitting-action
#17
Andrew J Wilson, Prashant K Jain
Oxygenic photosynthesis in nature occurs via water splitting catalyzed by the oxygen evolving complex (OEC) of photo-system II. To split water, the OEC cycles through a sequence of oxidation states (Si , i = 0-4), the structural mechanism of which is not fully understood under physiological conditions. We monitored the OEC in visible light-driven water-splitting action by using in-situ, aqueous-environment surface-enhanced Raman scattering (SERS). In the unexplored low-frequency region of SERS, we found dynamic vibrational signatures of water binding and splitting...
April 12, 2018: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29645033/ion-pairing-in-1-butyl-3-methylpyridinium-halide-ionic-liquids-studied-using-nmr-and-dft-calculations
#18
Vincent P Swamy, Hirekodathakallu V Thulasiram, Federico Rastrelli, Giacomo Saielli
We present the 1H, 13C and 15N NMR chemical shifts of bulk ionic liquids based on 1-butyl-3-methylimidazolium (the cation also known as 1-butyl-3-picolinium) halides (Cl-, Br- and I-) and tribromide (Br3-) salts. A characterization in solution of the analogous ICl2- and I3- salts is also reported. A series of DFT calculations has been run to predict the features of the NMR spectra of the pure ILs based on a few selected supramolecular ionic aggregates. To test the effect of temperature, and vibrational and conformational motions, only for the chloride salt, we also run first-principles molecular dynamics simulations of the ion pair in the gas phase, using the ADMP scheme (Atom Centered Density Matrix Propagation molecular dynamics model)...
April 12, 2018: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/29644729/hydration-of-concrete-the-first-steps
#19
Peter Thissen, Carsten Natzeck, Nicolas Giraudo, Peter Weidler, Christof Wöll
Concrete is the most important construction material used by mankind and, at the same time, one of the most complex substances known in materials science. Since this mineral compound is highly porous, a better understanding of its surface chemistry, and in particular the reaction with water, is urgently required to understand and avoid corrosion of infrastructure like buildings and bridges. We have gained insight into proton transfer from concrete upon contact with water by applying the so-called Surface Science approach to a well-defined mineral, Wollastonite...
April 12, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29629807/clinical-feasibility-of-mr-elastography-in-patients-with-biliary-obstruction
#20
Dong Kyu Kim, Jin Young Choi, Mi-Suk Park, Myeong-Jin Kim, Yong Eun Chung
OBJECTIVE: The purpose of this study is to evaluate the clinical effect of liver stiffness measured using MR elastography (MRE) in patients with cholestasis due to biliary obstruction. MATERIALS AND METHODS: In this retrospective study, 69 consecutive patients with no history of diffuse liver disease who underwent pancreaticobiliary imaging with MRE were included. Quantitative MRI parameters (i.e., liver stiffness, apparent diffusion coefficient, R2*, and proton density fat fraction) and laboratory results (i...
April 9, 2018: AJR. American Journal of Roentgenology
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