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https://www.readbyqxmd.com/read/28440624/acid-base-catalysis-in-glycosidations-a-nature-derived-alternative-to-the-generally-employed-methodology
#1
Peng Peng, Richard R Schmidt
Inverting glycosyltransferases enforce in the active site an intramolecular, acid-base catalyzed glycosidation that, due to proximity of the donor anomeric carbon and the acceptor hydroxyl group, follows an SN2-type reaction. Spacers, tethering donor and acceptor via nonreacting functional groups, led in intramolecular glycosidations to excellent yields and, independent of the donor anomeric configuration, to either the α- or the β-anomer. The requirement of a demanding protecting group pattern confines the application of this efficient method...
April 25, 2017: Accounts of Chemical Research
https://www.readbyqxmd.com/read/28440317/live-cell-imaging-of-mitochondria-following-targeted-irradiation-in-situ-reveals-rapid-and-highly-localized-loss-of-membrane-potential
#2
Dietrich W M Walsh, Christian Siebenwirth, Christoph Greubel, Katarina Ilicic, Judith Reindl, Stefanie Girst, Giovanna Muggiolu, Marina Simon, Philippe Barberet, Hervé Seznec, Hans Zischka, Gabriele Multhoff, Thomas E Schmid, Guenther Dollinger
The reliance of all cell types on the mitochondrial function for survival makes mitochondria an interesting target when trying to understand their role in the cellular response to ionizing radiation. By harnessing highly focused carbon ions and protons using microbeams, we have performed in situ live cell imaging of the targeted irradiation of individual mitochondria stained with Tetramethyl rhodamine ethyl ester (TMRE), a cationic fluorophore which accumulates electrophoretically in polarized mitochondria...
April 25, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28437697/catalytic-polymer-clay-composite-for-enhanced-removal-and-degradation-of-diazinon
#3
Itamar A Shabtai, Yael G Mishael
It is well established that organophosphate pesticides, such as diazinon, pose environmental and health risks. Diazinon is prone to rapid acidic hydrolysis, forming the less toxic compound 2-isopropyl-6-methyl-4-pyrimidinol (IMP). In this study, diazinon surface catalyzed hydrolysis was achieved by its adsorption to a composite, based on protonated poly (4-vinyl-pyridine-co-styrene) (HPVPcoS) and montmorillonite (MMT) clay. The adsorption affinity and kinetics of diazinon to HPVPcoS-MMT were significantly higher than those obtained to the deprotonated PVPcoS-MMT, emphasizing the importance of hydrogen bonding...
April 6, 2017: Journal of Hazardous Materials
https://www.readbyqxmd.com/read/28436218/the-ptr3-a-novel-instrument-for-studying-the-lifecycle-of-reactive-organic-carbon-in-the-atmosphere
#4
Martin Breitenlechner, Lukas Fischer, Markus Hainer, Martin Heinritzi, Joachim Curtius, Armin Hansel
We have developed and characterized the novel PTR3, a Proton Transfer Reaction Time-of-Flight mass spectrometer (PTR-ToF) using a new gas inlet and an innovative reaction chamber design. The reaction chamber consists of a tripole operated with RF voltages generating an electric field only in radial direction. An elevated electrical field is necessary to reduce clustering of primary hydronium (H3O(+)) and product ions with water molecules present in the sample gas. The axial movement of the ions is achieved by the sample gas flow only...
April 24, 2017: Analytical Chemistry
https://www.readbyqxmd.com/read/28435780/highly-active-and-stable-pt-pd-alloy-catalysts-synthesized-by-room-temperature-electron-reduction-for-oxygen-reduction-reaction
#5
Wei Wang, Zongyuan Wang, Jiajun Wang, Chuan-Jian Zhong, Chang-Jun Liu
Carbon-supported platinum (Pt) and palladium (Pd) alloy catalyst has become a promising alternative electrocatalyst for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells. In this work, the synthesis of highly active and stable carbon-supported Pt-Pd alloy catalysts is reported with a room-temperature electron reduction method. The alloy nanoparticles thus prepared show a particle size around 2.6 nm and a core-shell structure with Pt as the shell. With this structure, the breaking of O-O bands and desorption of OH are both promoted in electrocatalysis of ORR...
April 2017: Advanced Science (Weinheim, Baden-Wurttemberg, Germany)
https://www.readbyqxmd.com/read/28433034/direct-1-h-nmr-evidence-of-spin-rotation-coupling-as-a-source-of-para-%C3%A2-ortho-h2-conversion-in-diamagnetic-solvents
#6
Camilla Terenzi, Sabine Bouguet-Bonnet, Daniel Canet
At ambient temperature, conversion from 100% enriched para-hydrogen (p-H2; singlet state) to ortho-hydrogen (o-H2; triplet state) leads necessarily to the thermodynamic equilibrium proportions: 75% of o-H2 and 25% of p-H2. When p-H2 is dissolved in a diamagnetic organic solvent, conversion is very slow and can be considered as arising from nuclear spin relaxation phenomena. A first relaxation mechanism, specific to the singlet state and involving a combination of auto-correlation and cross correlation spectral densities, can be retained: randomly fluctuating magnetic fields due to inter-molecular dipolar interactions...
April 21, 2017: Journal of Chemical Physics
https://www.readbyqxmd.com/read/28432983/improved-resolution-and-simplification-of-the-spin-diffusion-based-nmr-method-for-the-structural-analysis-of-mixed-linker-mofs
#7
Andraž Krajnc, Bart Bueken, Dirk De Vos, Gregor Mali
Nuclear magnetic resonance spectroscopy combined with modeling represents a powerful tool for the structural analysis of heterogeneous materials. In this contribution we describe an upgraded method, particularly suited for the structural analysis of mixed-linker metal-organic framework materials, which is based on the measurement and modeling of proton spin diffusion among constituents. We tested the method on a UiO-66-type metal-organic material, in which the organic building units were 1,4-benzenedicarboxylate and trans-1,4-cyclohexanedicarboxylate anions distributed within the framework in an unknown manner...
April 12, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28431207/syntheses-of-chroman-2-ones-and-%C3%AE-amino-acids-through-a-diastereoselective-domino-reaction
#8
D Balaji Chandrasekhar, Shwu-Chen Tsay, Tapan K Pradhan, Jih Ru Hwu
Many 3-aminochroman-2-ones and β,β-diarylalanines exhibit significant biological activities. A new method was thus developed for the syntheses of these compounds with high efficiency and diastereoselectivity. First, treatment of various phenols with Erlenmeyer-Plochl (Z)-azlactones and AlCl3 in toluene produced the desired cis-3-aminochroman-2-ones in 65-90% yields under kinetic control. This coupling reaction involved a domino process of Friedel-Crafts alkylation, 1,4-AlCl3 shift, transesterification, and protodealumination in a "single-flask...
April 21, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28429299/participation-of-c-h-protons-in-the-dissociation-of-a-proton-deficient-dipeptide
#9
Damodar Koirala, Sabyasachy Mistry, Paul G Wenthold
The dissociation of anionic dipeptides Phe*Gly and GlyPhe*, where Phe* refers to sulfonated phenyl alanine, has been investigated by using ion trap mass spectrometry. The dipeptides undergo collision-induced dissociation (CID) to give the same products, indicating that they rearrange to a common structure before dissociation. The rearrangement does not occur with the dipeptide methyl esters. The structures of the b2 ions were investigated to determine the effect that having a remote, anionic site has on product formation...
April 20, 2017: Journal of the American Society for Mass Spectrometry
https://www.readbyqxmd.com/read/28426168/walking-a-fine-line-with-sucrose-phosphorylase-efficient-single-step-biocatalytic-production-of-l-ascorbic-acid-2-glucoside-from-sucrose
#10
Rama Krishna Gudiminchi, Bernd Nidetzky
The 2-O-α-D-glucoside of L-ascorbic acid (AA-2G) is a highly stabilized form of vitamin C, with important applications in cosmetics, foods and pharmaceuticals. Sucrose would be an ideal substrate for AA-2G synthesis, but it cannot be used lacking a suitable transglycosidase. We show that in a narrow pH window with sharp optimum at pH 5.2, select sucrose phosphorylases catalyzed 2-O-α-glucosylation of L-ascorbic acid from sucrose with high efficiency and perfect site-selectivity. Optimized synthesis with the enzyme from Bifidobacterium longum at 40°C gave a concentrated product solution (155 g/L; 460 mM) from which pure AA-2G was recovered in ∼50% overall yield, so providing the basis for an advanced production process...
April 20, 2017: Chembiochem: a European Journal of Chemical Biology
https://www.readbyqxmd.com/read/28422490/redox-tagged-carbon-monoxide-releasing-molecules-corms-ferrocene-containing-mn-c-n-co-4-complexes-as-a-promising-new-corm-class
#11
Benjamin J Aucott, Jonathan S Ward, Samuel G Andrew, Jessica Milani, Adrian C Whitwood, Jason M Lynam, Alison Parkin, Ian J S Fairlamb
This study describes the synthesis and characterization of a new class of ferrocene-containing carbon monoxide-releasing molecules (CORMs, 1-3). The ferrocenyl group is both a recognized therapeutically viable coligand and a handle for informative infrared spectroelectrochemistry. Deoxymyoglobin CO-release assays and in situ infrared spectroscopy confirm compounds 2 and 3 as photoCORMs and 1 as a thermal CORM, attributed to the increased sensitivity of the Mn-ferrocenyl bond to protonation in 1. Electrochemical and infrared spectroelectrochemical experiments confirm a single reversible redox couple associated with the ferrocenyl moiety with the Mn tetracarbonyl center showing no redox activity up to +590 mV vs Fc/Fc(+), though no concomitant CO release was observed in association with the redox activity...
April 19, 2017: Inorganic Chemistry
https://www.readbyqxmd.com/read/28421764/total-synthesis-of-the-claimed-structure-of-%C3%A2-hyptinin-and-structural-revision-of-natural-hyptinin
#12
Kazuto Maeda, Toshiyuki Hamada, Satoaki Onitsuka, Hiroaki Okamura
A total synthesis of (±)-hyptinin was achieved via a convergent route using the key phosphonate, cyclic ketone, and aryl Grignard components. The (1)H and (13)C NMR spectra of natural hyptinin did not agree with those of the synthesized compound. In particular, there were considerable differences between the signals assigned to the protons and carbons surrounding the lactone carbonyl group for the natural and synthesized compounds. The NMR data strongly suggested that the naturally occurring compound, hyptinin, was a structural isomer of the synthesized compound...
April 19, 2017: Journal of Natural Products
https://www.readbyqxmd.com/read/28420165/impact-of-acetazolamide-a-carbonic-anhydrase-inhibitor-on-the-development-of-intestinal-polyps-in-min-mice
#13
Nobuharu Noma, Gen Fujii, Shingo Miyamoto, Masami Komiya, Ruri Nakanishi, Misato Shimura, Sei-Ichi Tanuma, Michihiro Mutoh
Colorectal cancer is a common cancer worldwide. Carbonic anhydrase (CA) catalyzes the reversible conversion of carbon dioxide to bicarbonate ion and a proton, and its inhibitor is reported to reduce cancer cell proliferation and induce apoptosis. Therefore, we asked whether acetazolamide, a CA inhibitor, could inhibit intestinal carcinogenesis. Five-week-old male Apc-mutant mice, Min mice, were fed a AIN-76A diet containing 200 or 400 ppm acetazolamide. As a result, acetazolamide treatment reduced the total number of intestinal polyps by up to 50% compared to the control group...
April 17, 2017: International Journal of Molecular Sciences
https://www.readbyqxmd.com/read/28416085/delamination-mechanism-study-of-large-size-waste-printed-circuit-boards-by-using-dimethylacetamide
#14
Himanshu Ranjan Verma, Kamalesh K Singh, Tilak Raj Mankhand
Present work investigates the recycling of waste printed circuit boards (PCBs) by cracking of its multi-layered structure by using dimethylacetamide (DMA). The study shows that cracking and separation of layers of PCBs increases as the temperature increases; and decreases as the surface area of PCBs increases. After separation of layers, the used solvent was analyzed by proton and carbon nuclear magnetic resonance spectroscopy (NMR) to understand the dissolution phenomenon of resin. Further, NMR and Fourier transform infrared spectroscopy analysis of DMA sample after 1h, 2h, 3h, 4h and 8h of reaction with PCBs at 433K and PCB:DMA ratio (wt/vol) of 3:10 has been carried out to investigate the mechanism of dissolution of resin...
April 13, 2017: Waste Management
https://www.readbyqxmd.com/read/28412811/two-dimensional-metal-free-organic-multiferroic-material-for-design-of-multifunctional-integrated-circuits
#15
Zhengyuan Tu, Menghao Wu, Xiao Cheng Zeng
Coexistence of ferromagnetism and ferroelectricity in a single 2D material is highly desirable for integration of multi-functional units in 2D material-based circuits. Herein, we report theoretical evidence of C6N8H organic network as being the first 2D organic multiferroic material with coexisting FM and FE properties. The ferroelectricity stems from multi-mode proton-transfer within the 2D C6N8H network, in which a long-range proton-transfer mode is enabled by the facilitation of oxygen molecule when the network is exposed to the air...
April 15, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28409860/hydrogenation-of-carbon-dioxide-to-methanol-catalyzed-by-iron-cobalt-and-manganese-cyclopentadienone-complexes-mechanistic-insights-and-computational-design
#16
Hongyu Ge, Xiangyang Chen, Xinzheng Yang
Density functional theory study of the hydrogenation of carbon dioxide to methanol catalyzed by iron, cobalt, and manganese cyclopentadienone complexes reveals a self-promoted mechanism which features a methanol or water molecule assisted proton transfer for the cleavage of H2. The total free energy barrier of the formation of methanol from CO2 and H2 catalyzed by Knölker's iron cyclopentadienone complex, [2,5-(SiMe3)2-3,4-(CH2)4(η5-C4COH)]Fe(CO)2H, is 26.0 kcal/mol in the methanol solvent. We also evaluated the catalytic activities of other 9 experimentally reported iron cyclopentadienone complexes and 37 iron, cobalt and manganese cyclopentadienone complexes proposed in this study...
April 13, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28409642/protic-ionic-liquids-for-the-belousov-zhabotinsky-reaction-aspects-of-the-bz-reaction-in-protic-ionic-liquids-and-its-use-for-the-autonomous-coil-globule-oscillation-of-a-linear-polymer
#17
Takeshi Ueki, Ko Matsukawa, Tsukuru Masuda, Ryo Yoshida
Herein, we describe the physicochemical aspects of the Belousov-Zhabotinsky (BZ) reaction in hydrated protic ionic liquids (PILs) combined with different cations with a hydrogen sulfate ([HSO4(-)]) anion. PILs were prepared from the neutralization reactions of sulfuric acid with 13 different aliphatic amines. The amine structure was selected to investigate the effect of the number of active protons, alkyl chain length (hydrophilicity), and cationic linearity on the mechanism of the BZ reaction. The pKa values of PILs were significantly higher (pKa = 1...
April 25, 2017: Journal of Physical Chemistry. B
https://www.readbyqxmd.com/read/28406796/experimental-dosimetric-comparison-of-1-h-4-he-12-c-and-16-o-scanned-ion-beams
#18
T Tessonnier, A Mairani, S Brons, T Haberer, J Debus, K Parodi
At the Heidelberg Ion Beam Therapy Center, scanned helium and oxygen ion beams are available in addition to the clinically used protons and carbon ions for physical and biological experiments. In this work, a study of the basic dosimetric features of the different ions is performed in the entire therapeutic energy range. Depth dose distributions are investigated for pencil-like beam irradiation, with and without a modulating ripple filter, focusing on the extraction of key Bragg curve parameters, such as the range, the peak-width and the distal 80%-20% fall-off...
April 13, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28402662/dominant-carbons-in-trans-and-cis-resveratrol-isomerization
#19
Feng Wang, Subhojyoti Chatterjee
A comprehensive analysis for isomerization of geometric isomers in the case of resveratrol (R) has been presented. As an important red wine molecule, only one geometric isomer of resveratrol, i.e., trans-R rather than cis-R, is primarily associated with health benefit. In the present study, density function theory (DFT) provides accurate descriptions of isomerization of resveratrol. The nearly planar trans-R forms a relatively rigid and less flexible conjugate network, but the nonplanar cis-R favors a more flexible structure with steric through space interaction...
April 26, 2017: Journal of Physical Chemistry. B
https://www.readbyqxmd.com/read/28402376/effect-of-low-water-content-in-protic-ionic-liquid-on-ions-electrosorption-in-porous-carbon-application-to-electrochemical-capacitors
#20
B Gorska, L Timperman, M Anouti, F Béguin
The effect of low water content (<20, 150, 1000, 10 000 ppm) in triethylammonium bis[(trifluoromethyl)sulfonyl]imide - [(C2H5)3N(+)H][TFSI(-)] - protic ionic liquid (PIL) on the performance of activated carbon (AC) electrodes as well as AC/AC electrochemical capacitors (ECs) is reported. Under negative polarization, hydrogen electrosorption onto carbon is enhanced along with the increase of water content in PIL, whereas the resulting desorption peaks are shifted to lower potential values, evidencing lower sorption energy when hydrogen is stored from moisture containing PIL...
April 12, 2017: Physical Chemistry Chemical Physics: PCCP
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