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https://www.readbyqxmd.com/read/28938199/determination-of-lead-at-trace-levels-in-mussel-and-sea-water-samples-using-vortex-assisted-dispersive-liquid-liquid-microextraction-slotted-quartz-tube-flame-atomic-absorption-spectrometry
#1
Sezin Erarpat, Gözde Özzeybek, Dotse Selali Chormey, Sezgin Bakırdere
In this study, dispersive liquid-liquid microextraction (DLLME) and slotted quartz tube (SQT) were coupled to flame atomic absorption spectrometry (FAAS) to increase the sensitivity of lead. Conditions such as the formation of the lead-dithizone complex, efficiency of the DLLME method and the output of the SQT were systematically optimized to improve the detection limit for the analyte. The conventional FAAS system was improved upon by about 3.0 times with SQT-FAAS, 32 times with DLLME-FAAS and 142 times with DLLME-SQT-FAAS...
September 17, 2017: Chemosphere
https://www.readbyqxmd.com/read/28938170/aromatic-hydrazones-derived-from-nicotinic-acid-hydrazide-as-fluorimetric-ph-sensing-molecules-structural-analysis-by-computational-and-spectroscopic-methods-in-solid-phase-and-in-solution
#2
T Benković, A Kenđel, J Parlov-Vuković, D Kontrec, V Chiş, S Miljanić, N Galić
Structural analyses of aroylhydrazones were performed by computational and spectroscopic methods (solid state NMR, 1 and 2D NMR spectroscopy, FT-IR (ATR) spectroscopy, Raman spectroscopy, UV-Vis spectrometry and spectrofluorimetry) in solid state and in solution. The studied compounds were N'-(2,3-dihydroxyphenylmethylidene)-3-pyridinecarbohydrazide (1), N'-(2,5-dihydroxyphenylmethylidene)-3-pyridinecarbohydrazide (2), N'-(3-chloro-2-hydroxy-phenylmethylidene)-3-pyridinecarbohydrazide (3), and N'-(2-hydroxy-4-methoxyphenyl-methylidene)-3-pyridinecarbohydrazide (4)...
September 15, 2017: Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy
https://www.readbyqxmd.com/read/28938074/native-electron-capture-dissociation-maps-to-iron-binding-channels-in-horse-spleen-ferritin
#3
Owen S Skinner, Michael O McAnally, Richard P Van Duyne, George C Schatz, Kathrin Breuker, Philip D Compton, Neil L Kelleher
Native electron capture dissociation (NECD) is a process during which proteins undergo fragmentation similar to that from radical dissociation methods, but without the addition of exogenous electrons. However, after three initial reports of NECD from the cytochrome c dimer complex, no further evidence of the effect has been published. Here, we report NECD behavior from horse spleen ferritin, a ~490 kDa protein complex ~20-fold larger than the previously studied cytochrome c dimer. Application of front-end infrared excitation (FIRE) in conjunction with low- and high-m/z quadrupole isolation and collisionally activated dissociation (CAD) provides new insights into the NECD mechanism...
September 22, 2017: Analytical Chemistry
https://www.readbyqxmd.com/read/28938072/machine-learning-for-silver-nanoparticle-electron-transfer-property-prediction
#4
Baichuan Sun, Michael Fernandez, Amanda S Barnard
Nanoparticles exhibit diverse structural and morphological features that are often inter-connected, making the correlation of structure/property relationships challenging. In this study a multi-structure/single-property relationship of silver nanoparticles is developed for the energy of Fermi level, which can be tuned to improve the transfer of electrons in a variety of applications. By combining different machine learning analytical algorithms, including k-mean, logistic regression and random forest with electronic structure simulations, we find that the degree of twinning (characterised by the fraction of hexagonal closed packed atoms) and the population of {111} facet (characterized by a surface coordination number of 9) are strongly correlated to the Fermi energy of silver nanoparticles...
September 22, 2017: Journal of Chemical Information and Modeling
https://www.readbyqxmd.com/read/28937994/modeling-of-annexin-a2-membrane-interactions-by-molecular-dynamics-simulations
#5
Davit Hakobyan, Volker Gerke, Andreas Heuer
The annexins are a family of Ca2+-regulated phospholipid binding proteins that are involved in membrane domain organization and membrane trafficking. Although they are widely studied and crystal structures are available for several soluble annexins their mode of membrane association has never been studied at the molecular level. Here we obtained molecular information on the annexin-membrane interaction that could serve as paradigm for the peripheral membrane association of cytosolic proteins by Molecular Dynamics simulations...
2017: PloS One
https://www.readbyqxmd.com/read/28937970/spectroscopy-and-enhanced-frequency-upconversion-in-nd-3-yb-3-codoped-tpo-glasses-energy-transfer-and-nir-to-visible-upconverter
#6
Mohd Azam, Vineet Kumar Rai, Deepak Kumar Mohanty
TeO2-Pb3O4 (TPO) glasses codoped with Nd(3+) and Yb(3+) ions have been fabricated by conventional melting technique. The absorption, emission and excitation spectra of the samples have been recorded. The optical band gap in both the doped/codoped glasses is found to be ∼3.31 eV. Judd-Ofelt analysis has been carried out by using the absorption spectrum of 0.8 mol% Nd(3+) doped glass to determine the radiative properties viz radiative transition probabilities, branching ratios, radiative lifetimes, quality factor and emission cross sections of some emitting levels for Nd(3+) ions...
September 22, 2017: Methods and Applications in Fluorescence
https://www.readbyqxmd.com/read/28937856/detection-of-selected-trace-elements-in-yogurt-components
#7
Marcela Capcarova, Lubos Harangozo, Tomas Toth, Loretta Schwarczova, Alica Bobkova, Robert Stawarz, Alessandra Guidi, Peter Massanyi
The objective of this study was to determine the concentrations of Cu, Cd, Pb, Mn, Cr, Co, Ni, Zn, and Hg in the white and fruit parts of commercially available yogurts (n = 30) from Nitra markets (Slovak Republic). The results were correlated to determine their relationships. Three yogurt fruit flavors were chosen and tested, strawberry (n = 10), blueberry (n = 10), and cherry (n = 10). The elements were analyzed using atomic absorption spectrophotometry. Higher concentrations of toxic elements, such as Cd and Pb, were found in the fruit parts of the yogurt, and in some cases, the tolerable limit was exceeded...
September 22, 2017: Journal of Environmental Science and Health. Part. B, Pesticides, Food Contaminants, and Agricultural Wastes
https://www.readbyqxmd.com/read/28937775/operando-phonon-studies-of-the-protonation-mechanism-in-highly-active-hydrogen-evolution-reaction-pentlandite-catalysts
#8
Ioannis Zegkinoglou, Ali Zendegani, Ilya Sinev, Sebastian Kunze, Hemma Mistry, Hyo Sang Jeon, Jiyong Zhao, Michael Y Hu, E Ercan Alp, Stefan Piontek, Mathias Smialkowski, Ulf-Peter Apfel, Fritz Körmann, Jorg Neugebauer, Tilmann Hickel, Beatriz Roldan Cuenya
Synthetic pentlandite (Fe4.5Ni4.5S8) is a promising electrocatalyst for hydrogen evolution, demonstrating high current densities, low overpotential and remarkable stability in bulk form. The depletion of sulfur from the surface of this catalyst during the electrochemical reaction has been proposed to be beneficial for its catalytic performance, but the role of sulfur vacancies and the mechanism determining the reaction kinetics are still unknown. We have performed electrochemical operando studies of the vibrational dynamics of pentlandite under hydrogen evolution reaction conditions using 57Fe nuclear resonant inelastic X-ray scattering...
September 22, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28937764/is-vitamin-a-an-antioxidant-or-a-prooxidant
#9
Duy Quang Dao, Thi Chinh Ngo, Nguyen Minh Thong, Pham Cam Nam
Antioxidant efficiency of all-trans-retinol has been studied on the basis of characteristic thermochemical properties using density functional theory. The influence of the solvent polarity has also been evaluated. It is found that retinol may act in parallel as an effective antioxidant via H-atom donating as well as a prooxidant in yielding reactive hydroxyl radical. In fact, the lowest values of bond dissociation enthalpy were found at C18-H and C18-OH positions. Retinol was also determined as good electron donor but bad acceptor in the single electron transfer (ET) reaction with hydroperoxyl (HOO●) radical...
September 22, 2017: Journal of Physical Chemistry. B
https://www.readbyqxmd.com/read/28937761/helium-nanodroplet-isolation-of-the-cyclobutyl-1-methylallyl-and-allylcarbinyl-radicals-infrared-spectroscopy-and-ab-initio-computations
#10
Alaina Rachel Brown, Peter Roland Franke, Gary E Douberly
Gas phase cyclobutyl radical (∙C4H7) is produced via pyrolysis of cyclobutylmethyl nitrite (C4H7(CH2)ONO). Other ∙C4H7 radicals, such as 1-methylallyl and allylcarbinyl, are similarly produced from nitrite precursors. Nascent radicals are promptly solvated in liquid He droplets, allowing for the acquisition of infrared spectra in the CH stretching region. For the cyclobutyl and 1-methylallyl radicals, anharmonic frequencies are predicted by VPT2+K simulations based upon a hybrid CCSD(T) force field with quadratic (cubic and quartic) force constants computed using the ANO1 (ANO0) basis set...
September 22, 2017: Journal of Physical Chemistry. A
https://www.readbyqxmd.com/read/28937755/stability-and-superconductivity-of-k-p-compounds-under-pressure
#11
Yunxian Liu, Chao Wang, Xiangmu Kong, Defang Duan
We explore the phase diagram, structures, electron properties, and potential superconductivity of the K-P system at pressures of up to 200 GPa through unbiased structure searching techniques and first-principles calculations. Five stable chemical stoichiometries (K4P, K3P, K2P, KP, and KP2) have been theoretically predicted. In particular, P2 units or P-chains are uncovered in K2P, KP, and KP2 compounds with the existence of covalent bonds by analyzing the electron localization functions. And the Bader analysis demonstrates that charges transfer from K atoms to P atoms...
September 22, 2017: Inorganic Chemistry
https://www.readbyqxmd.com/read/28937747/photo-and-electrocatalytic-hydrogen-production-using-valence-isomers-of-n2s2-type-nickel-complexes
#12
Satoshi Inoue, Manabu Mitsuhashi, Takeshi Ono, Yin-Nan Yan, Yusuke Kataoka, Makoto Handa, Tatsuya Kawamoto
Three Schiff-base-type nickel(II) complexes (1a-3a) and the corresponding noninnocent-type complexes (1b-3b) were synthesized, and the equilibria between these valence isomers were observed in tetrahydrofuran (THF) at room temperature. The electronic state of the noninnocent-type nickel complex was also confirmed by isolation of the one-electron-reduced species. The catalytic ability for the photogeneration of hydrogen from water was examined about 1a-3a and 1b-3b in the presence of a photosensitizer and a sacrificial electron donor...
September 22, 2017: Inorganic Chemistry
https://www.readbyqxmd.com/read/28937740/ab-initio-study-of-the-atomic-level-structure-of-the-rutile-tio2-110-titanium-nitride-tin-interface
#13
Jose Julio Gutierrez Moreno, Michael Nolan
Titanium nitride (TiN) is widely used in industry as a protective coating due to its hardness and resistance to corrosion and can spontaneously form a thin oxide layer when it is exposed to air, which could modify the properties of the coating. With limited understanding of the TiO2 - TiN interfacial system at present, this work aims to describe the structural and electronic properties of oxidized TiN based on a density functional theory (DFT) study of the rutile TiO2 (110) - TiN (100) interface model system, also including Hubbard +U correction on Ti 3d states...
September 22, 2017: ACS Applied Materials & Interfaces
https://www.readbyqxmd.com/read/28937737/hollow-pd-ag-composite-nanowires-for-fast-responding-and-transparent-hydrogen-sensors
#14
Ji-Soo Jang, Shaopeng Qiao, Seon-Jin Choi, Gaurav Jha, Alana F Ogata, Won-Tae Koo, Dong-Ha Kim, Il-Doo Kim, Reginald M Penner
Pd based alloy materials with hollow nanostructures are ideal hydrogen (H2) sensor building blocks because of the ultra-high surface area afforded by this architecture. In this work, for the first time, we report a simple fabrication process for preparing hollow Pd-Ag alloy nanowires (Pd@Ag HNWs) by using the electrodeposition of lithographically patterned silver nanowires and followed galvanic replacement reaction (GRR) to form palladium. By controlling the GRR time of aligned Ag NWs within an aqueous Pd2+-containing solution, the compositional transition and morphological evolution from Ag NWs to Pd@Ag HNWs simultaneously occurred, and the relative atomic ratio between Pt and Ag was controlled...
September 22, 2017: ACS Applied Materials & Interfaces
https://www.readbyqxmd.com/read/28937701/theoretical-study-on-geometric-electronic-and-catalytic-performances-of-fe-dopant-pairs-in-graphene
#15
Yanan Tang, Huadou Chai, Weiguang Chen, Xiao Cui, Yaqiang Ma, Mingyu Zhao, Xianqi Dai
The formation geometries, electronic structures and catalytic properties of monovacancy and divacancy graphene sheets with two embedded Fe dopants (2Fe-MG and 2Fe-DG) have been systematically investigated using the first-principles calculations. It was found that the configuration of 2Fe-DG is slightly more stable than that of 2Fe-MG sheets and the two doped Fe atoms in graphene (2Fe-graphene) as active sites could regulate the stability of gas molecules. In addition, the adsorption of O2 and CO molecules could modulate the electronic and magnetic properties of 2Fe-graphene systems...
September 22, 2017: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/28937695/trinuclear-complexes-of-palladium-ii-with-chalcogenated-n-heterocyclic-carbenes-catalysis-of-selective-nitrile-primary-amide-interconversion-and-sonogashira-coupling
#16
Pooja Dubey, Sonu Gupta, Ajai K Singh
3-Methyl-1-(2-(phenylthio/seleno)ethyl)-1H-benzo[d]imidazol-3-ium iodide (L1/L2), a precursor of sulfated/selenated N-heterocyclic carbene, was synthesized by the reaction of benzimidazole with 1,2-dichloroethane followed by treatment with PhS/SeNa and MeI. The reaction of L1/L2 with Ag2O followed by treatment with [Pd(CH3CN)2Cl2] (metal to ligand ratio 3 : 2), i.e. transmetallation, resulted in trinuclear palladium(ii) complexes [Pd3(L1/L2-HI)2(CH3CN)Cl6] (1-2). The complexes were characterized with (1)H, (13)C{(1)H} and (77)Se{(1)H} NMR (2 only), elemental analyses, HR-MS and single-crystal X-ray diffraction...
September 22, 2017: Dalton Transactions: An International Journal of Inorganic Chemistry
https://www.readbyqxmd.com/read/28937678/anionic-silicate-organic-frameworks-constructed-from-hexacoordinate-silicon-centres
#17
Jérôme Roeser, Dragica Prill, Michael J Bojdys, Pierre Fayon, Abbie Trewin, Andrew N Fitch, Martin U Schmidt, Arne Thomas
Crystalline frameworks composed of hexacoordinate silicon species have thus far only been observed in a few high pressure silicate phases. By implementing reversible Si-O chemistry for the crystallization of covalent organic frameworks, we demonstrate the simple one-pot synthesis of silicate organic frameworks based on octahedral dianionic SiO6 building units. Clear evidence of the hexacoordinate environment around the silicon atoms is given by (29)Si nuclear magnetic resonance analysis. Characterization by high-resolution powder X-ray diffraction, density functional theory calculation and analysis of the pair-distribution function showed that those anionic frameworks-M2[Si(C16H10O4)1...
October 2017: Nature Chemistry
https://www.readbyqxmd.com/read/28937670/feshbach-resonances-in-the-exit-channel-of-the-f%C3%A2-%C3%A2-ch3oh%C3%A2-%C3%A2-%C3%A2-hf%C3%A2-%C3%A2-ch3o-reaction-observed-using-transition-state-spectroscopy
#18
Marissa L Weichman, Jessalyn A DeVine, Mark C Babin, Jun Li, Lifen Guo, Jianyi Ma, Hua Guo, Daniel M Neumark
The transition state governs how chemical bonds form and cleave during a chemical reaction and its direct characterization is a long-standing challenge in physical chemistry. Transition state spectroscopy experiments based on negative-ion photodetachment provide a direct probe of the vibrational structure and metastable resonances that are characteristic of the reactive surface. Dynamical resonances are extremely sensitive to the topography of the reactive surface and provide an exceptional point of comparison with theory...
October 2017: Nature Chemistry
https://www.readbyqxmd.com/read/28937668/complete-protein-protein-association-kinetics-in-atomic-detail-revealed-by-molecular-dynamics-simulations-and-markov-modelling
#19
Nuria Plattner, Stefan Doerr, Gianni De Fabritiis, Frank Noé
Protein-protein association is fundamental to many life processes. However, a microscopic model describing the structures and kinetics during association and dissociation is lacking on account of the long lifetimes of associated states, which have prevented efficient sampling by direct molecular dynamics (MD) simulations. Here we demonstrate protein-protein association and dissociation in atomistic resolution for the ribonuclease barnase and its inhibitor barstar by combining adaptive high-throughput MD simulations and hidden Markov modelling...
October 2017: Nature Chemistry
https://www.readbyqxmd.com/read/28937664/transition-metal-free-chemo-and-regioselective-vinylation-of-azaallyls
#20
Minyan Li, Osvaldo Gutierrez, Simon Berritt, Ana Pascual-Escudero, Ahmet Yeşilçimen, Xiaodong Yang, Javier Adrio, Georgia Huang, Eiko Nakamaru-Ogiso, Marisa C Kozlowski, Patrick J Walsh
Direct C(sp(3))-C(sp(2)) bond formation under transition-metal-free conditions offers an atom-economical, inexpensive and environmentally benign alternative to traditional transition-metal-catalysed cross-coupling reactions. A new chemo- and regioselective coupling protocol between 3-aryl-substituted-1,1-diphenyl-2-azaallyl derivatives and vinyl bromides has been developed. This is the first transition-metal-free cross-coupling of azaallyls with vinyl bromide electrophiles and delivers allylic amines in excellent yields (up to 99%)...
October 2017: Nature Chemistry
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