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https://www.readbyqxmd.com/read/29676410/newly-proposed-proton-abstraction-roundabout-with-backside-attack-mechanism-for-the-s-n-2-reaction-at-the-nitrogen-center-in-f-nh-2-cl
#1
Yongfang Li, Dunyou Wang
Recent studies have improved our understanding of the mechanism and dynamics of the bimolecular nucleophilic substitution (SN2) reaction at the carbon center. Nonetheless, the SN2 reaction at the nitrogen center has received scarce attention and is less understood. Herein, we propose a new reaction mechanism for the SN2 reaction at the nitrogen center in the F- + NH2Cl reaction using ab initio molecular dynamics calculations. The newly proposed mechanism involves the rotation of NHCl with one proton of NH2Cl abstracted by the nucleophile, followed by the classical backside-attack process...
April 20, 2018: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/29676056/pseudocapacitive-sodium-storage-by-ferroelectric-sn-2-p-2-s-6-with-layered-nanostructure
#2
Sheng Huang, Chao Meng, Min Xiao, Shan Ren, Shuanjin Wang, Dongmei Han, Yuning Li, Yuezhong Meng
Sodium ion batteries (SIB) are considered promising alternative candidates for lithium ion batteries (LIB) because of the wide availability and low cost of sodium, therefore the development of alternative sodium storage materials with comparable performance to LIB is urgently desired. The sodium ions with larger sizes resist intercalation or alloying because of slow reaction kinetics. Most pseudocapacitive sodium storage materials are based on subtle nanomaterial engineering, which is difficult for large-scale production...
April 19, 2018: Small
https://www.readbyqxmd.com/read/29664105/facile-access-to-2-acyloxy-aryloxy-and-alkenyloxy-2h-azirines-via-an-s-n-2-s-n-2-cascade-in-2-halo-2h-azirines
#3
Nikolai V Rostovskii, Ilia A Smetanin, Anastasiya V Agafonova, Pavel A Sakharov, Julia O Ruvinskaya, Alexander F Khlebnikov, Mikhail S Novikov
Various 2-oxygen-substituted 2H-azirine-2-carboxylic acid derivatives were synthesized in high yields under mild conditions from readily available precursors, 2-halo-2H-azirines and OH-reagents having pKa values in the range of 3-10. This reaction is the first example of substitution at the azirine carbon atom for which an unusual SN2'-SN2' cascade mechanism was revealed.
April 17, 2018: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/29660706/evaluation-of-sno-2-for-sunlight-photocatalytic-decontamination-of-water
#4
M Aslam, M Tariq Qamar, Shahid Ali, Ateeq Ur Rehman, M T Soomro, Ikram Ahmed, I M I Ismail, A Hameed
The broad bandgap tin (IV) oxide (SnO2 ) is the least investigated semiconductor material for photocatalytic water decontamination in sunlight exposure. A detailed study covering the synthesis, characterization and the evaluation of photocatalytic activity of SnO2 , in the natural sunlight exposure, is presented. The structural characterization by XRD revealed the formation of phase pure tetragonal SnO2 with the average crystallite size of ∼41.5 nm whereas minor Sn2+ states in the material were identified by XPS analysis...
April 13, 2018: Journal of Environmental Management
https://www.readbyqxmd.com/read/29645401/phosphine-catalyzed-activation-of-vinylcyclopropanes-rearrangement-of-vinylcyclopropylketones-to-cycloheptenones
#5
Jun Wu, Yuhai Tang, Wen Wei, Yong Wu, Yang Li, Junjie Zhang, Yuansuo Zheng, Silong Xu
We report a phosphine-catalyzed activation of electron-deficient vinylcyclopropanes (VCPs) to generate an ambident C5 synthon that is poised to undergo consecutive reactions. The utility of the activation is demonstrated in a phosphine-catalyzed rearrangement of vinylcyclopropylketones to cycloheptenones in good yields with a broad substrate scope. Mechanistic investigations support a stepwise process comprising homoconjugate addition, water-involved hydrogen transfer, and 7-endo-trig SN2' ring closure.
April 12, 2018: Angewandte Chemie
https://www.readbyqxmd.com/read/29608046/cornucopia-of-structures-in-the-pseudobinary-system-snse-x-bi-2-se-3-a-crystal-chemical-copycat
#6
Frank Heinke, Philipp Urban, Anton Werwein, Christina Fraunhofer, Tobias Rosenthal, Stefan Schwarzmüller, Daniel Souchay, Felix Fahrnbauer, Vadim Dyadkin, Gerald Wagner, Oliver Oeckler
Pseudobinary phases (SnSe)x Bi2 Se3 exhibit a very diverse structural chemistry characterized by different building blocks, all of which are cutouts of the NaCl type. For SnSe contents between x = 5 and x = 0.5, several new phases were discovered. Next to, for example, Sn4 Bi2 Se7 ( x = 4) in the NaCl structure type and SnBi4 Se7 ( x = 0.5) in the layered defect GeSb2 Te4 structure type, there are at least four compounds (0.8 ≤ x ≤ 3) with lillianite-like structures built up from distorted NaCl-type slabs (L4,4-type Sn2...
April 2, 2018: Inorganic Chemistry
https://www.readbyqxmd.com/read/29604859/sn-2-stabilization-in-masni-3-perovskites-by-superhalide-incorporation
#7
Junxiang Xiang, Kan Wang, Bin Xiang, Xudong Cui
Sn-based hybrid halide perovskites are a potential solution to replace Pb and thereby reduce Pb toxicity in MAPbI3 perovskite-based solar cells. However, the instability of Sn2+ in air atmosphere causes a poor reproducibility of MASnI3 , hindering steps towards this goal. In this paper, we propose a new type of organic metal-superhalide perovskite of MASnI2 BH4 and MASnI2 AlH4 . Through first-principles calculations, our results reveal that the incorporation of BH4 and AlH4 superhalides can realize an impressive enhancement of oxidation resistance of Sn2+ in MASnI3 perovskites because of the large electron transfer between Sn2+ and [BH4 ]- /[AlH4 ]- ...
March 28, 2018: Journal of Chemical Physics
https://www.readbyqxmd.com/read/29604356/effect-of-metal-ions-on-the-enzymatic-hydrolysis-of-hemp-seed-oil-by-lipase-candida-sp-99-125
#8
Jike Lu, Pei Wang, Zhaodi Ke, Xin Liu, Qiaozhen Kang, Limin Hao
In order to study the effect of metal ions on the enzymatic hydrolysis of hemp seed oil by Candida sp. 99-125, the spectroscopy, stability and hydrolytic activity of the biocatalyst were investigated in presence of Ca2+ , Mg2+ , Fe2+ , Fe3+ , Cu2+ , Sn2+ , Pb2+ , Zn2+ and Ba2+ metal ions, respectively. The UV spectroscopy showed that all the metal ions enhanced the absorbance but the decrease of fluorescence intensity was observed. All the metal ions could improve the lipase thermal stability except Cu2+ and Ba2+ ...
March 28, 2018: International Journal of Biological Macromolecules
https://www.readbyqxmd.com/read/29603445/pb-sn-cu-ternary-organometallic-halide-perovskite-solar-cells
#9
Meng Li, Zhao-Kui Wang, Ming-Peng Zhuo, Yun Hu, Ke-Hao Hu, Qing-Qing Ye, Sagar M Jain, Ying-Guo Yang, Xing-Yu Gao, Liang-Sheng Liao
Exploiting organic/inorganic hybrid perovskite solar cells (PSCs) with reduced Pb content is very important for developing environment-friendly photovoltaics. Utilizing of Pb-Sn alloying perovskite is considered as an efficient route to reduce the risk of ecosystem pollution. However, the trade-off between device performance and Sn substitution ratio due to the instability of Sn2+ is a current dilemma. Here, for the first time, the highly efficient Pb-Sn-Cu ternary PSCs are reported by partial replacing of PbI2 with SnI2 and CuBr2 ...
March 30, 2018: Advanced Materials
https://www.readbyqxmd.com/read/29568839/potassium-fluoride-activation-for-the-nucleophilic-fluorination-reaction-using-18-crown-6-2-2-2-cryptand-pentaethylene-glycol-and-comparison-with-the-new-hydro-crown-scaffold-a-theoretical-analysis
#10
Josefredo R Pliego
Activation of potassium fluoride salt for selective and fast nucleophilic fluorination requires its solubilization and stabilization of the respective transition state. This goal can be achieved through control of the nano-environment around the reactants via cation or ion-pair binding catalysis. In this work, six different species were theoretically investigated as promoters and catalysts for nucleophilic fluorination: tri-tert-butanolamine, 18-crown-6, pentaethylene glycol, [2.2.2]-cryptand, and two new hydroxylated crown ethers (hydro-crowns)...
March 23, 2018: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/29568509/-17-o-solid-state-nmr-spectroscopy-of-a-2-b-2-o-7-oxides-quantitative-isotopic-enrichment-and-spectral-acquisition
#11
Arantxa Fernandes, Robert F Moran, Scott Sneddon, Daniel M Dawson, David McKay, Giulia P M Bignami, Frédéric Blanc, Karl R Whittle, Sharon E Ashbrook
The potential of17 O NMR spectroscopy for the investigation of A2 B2 O7 ceramic oxides important in the encapsulation of radioactive waste is demonstrated, with post-synthetic enrichment by exchange with17 O2 gas. For Y2 Sn2 O7 , Y2 Ti2 O7 and La2 Sn2 O7 pyrochlores, enrichment of the two distinct O species is clearly non quantitative at lower temperatures (∼700 °C and below) and at shorter times, despite these being used in prior work, with preferential enrichment of OA2 B2 favoured over that of OA4 . At higher temperatures, the17 O NMR spectra suggest that quantitative enrichment has been achieved, but the integrated signal intensities do not reflect the crystallographic 1 : 6 (O1 : O2) ratio until corrected for differences in T 1 relaxation rates and, more importantly, the contribution of the satellite transitions...
February 13, 2018: RSC Advances
https://www.readbyqxmd.com/read/29555992/massive-dirac-fermions-in-a-ferromagnetic-kagome-metal
#12
Linda Ye, Mingu Kang, Junwei Liu, Felix von Cube, Christina R Wicker, Takehito Suzuki, Chris Jozwiak, Aaron Bostwick, Eli Rotenberg, David C Bell, Liang Fu, Riccardo Comin, Joseph G Checkelsky
The kagome lattice is a two-dimensional network of corner-sharing triangles that is known to host exotic quantum magnetic states. Theoretical work has predicted that kagome lattices may also host Dirac electronic states that could lead to topological and Chern insulating phases, but these states have so far not been detected in experiments. Here we study the d-electron kagome metal Fe3 Sn2 , which is designed to support bulk massive Dirac fermions in the presence of ferromagnetic order. We observe a temperature-independent intrinsic anomalous Hall conductivity that persists above room temperature, which is suggestive of prominent Berry curvature from the time-reversal-symmetry-breaking electronic bands of the kagome plane...
March 19, 2018: Nature
https://www.readbyqxmd.com/read/29555289/ultrasound-assisted-dispersion-of-bi-2-sn-2-o-7-c-3-n-4-nanophotocatalyst-over-various-amount-of-zeolite-y-for-enhanced-solar-light-photocatalytic-degradation-of-tetracycline-in-aqueous-solution
#13
Shirin Heidari, Mohammad Haghighi, Maryam Shabani
Bi2 Sn2 O7 -C3 N4 /Y nanophotocatalyst with various ratios of zeolite and high activity under simulated solar light irradiation were successfully synthesized using ultrasound-assisted dispersion method. The effect of different amounts of zeolite (10, 20 and 30 wt%) on the photocatalytic degradation of antibiotic tetracycline was investigated. The as-prepared nanophotocatalysts were characterized by XRD, FESEM, EDX, BET, FTIR, DRS and pHpzc techniques. The degradation results demonstrated that, Bi2 Sn2 O7 -C3 N4 /Y(10) nanophotocatalyst with a degradation efficiency of about 80...
May 2018: Ultrasonics Sonochemistry
https://www.readbyqxmd.com/read/29543154/acyl-chain-asymmetry-and-polyunsaturation-of-brain-phospholipids-facilitate-membrane-vesiculation-without-leakage
#14
Marco M Manni, Marion L Tiberti, Sophie Pagnotta, Hélène Barelli, Romain Gautier, Bruno Antonny
Phospholipid membranes form cellular barriers but need to be flexible enough to divide by fission. Phospholipids generally contain a saturated fatty acid (FA) at position sn1 whereas the sn2 -FA is saturated, monounsaturated or polyunsaturated. Our understanding of the impact of phospholipid unsaturation on membrane flexibility and fission is fragmentary. Here, we provide a comprehensive view of the effects of the FA profile of phospholipids on membrane vesiculation by dynamin and endophilin. Coupled to simulations, this analysis indicates that: (i) phospholipids with two polyunsaturated FAs make membranes prone to vesiculation but highly permeable; (ii) asymmetric sn1 -saturated- sn2 -polyunsaturated phospholipids provide a tradeoff between efficient membrane vesiculation and low membrane permeability; (iii) When incorporated into phospholipids, docosahexaenoic acid (DHA; omega-3) makes membranes more deformable than arachidonic acid (omega-6)...
March 15, 2018: ELife
https://www.readbyqxmd.com/read/29542853/nucleophilic-substitution-sn2-dependence-on-nucleophile-leaving-group-central-atom-substituents-and-solvent
#15
Trevor A Hamlin, Marcel Swart, F Matthias Bickelhaupt
The reaction potential energy surface (PES) and, thus, the mechanism of bimolecular nucleophilic substitution (SN2) depend profoundly on the nature of the nucleophile and leaving group, but also on the central, electrophilic atom, its substituents, as well as on the medium in which the reaction takes place. Here, we provide an overview of recent studies and demonstrate how changes in any one of the aforementioned factors affect the SN2 mechanism. One of the most striking effects is the transition from a double-well to a single-well PES when the central atom is changed from a second-period (e...
March 15, 2018: Chemphyschem: a European Journal of Chemical Physics and Physical Chemistry
https://www.readbyqxmd.com/read/29511393/one-step-growth-of-thin-film-sns-with-large-grains-using-mocvd
#16
Andrew J Clayton, Cecile M E Charbonneau, Wing C Tsoi, Peter J Siderfin, Stuart J C Irvine
Thin film tin sulphide (SnS) films were produced with grain sizes greater than 1 μm using a one-step metal organic chemical vapour deposition process. Tin-doped indium oxide (ITO) was used as the substrate, having a similar work function to molybdenum typically used as the back contact, but with potential use of its transparency for bifacial illumination. Tetraethyltin and ditertiarybutylsulphide were used as precursors with process temperatures 430-470 °C to promote film growth with large grains. The film stoichiometry was controlled by varying the precursor partial pressure ratios and characterised with energy dispersive X-ray spectroscopy to optimise the SnS composition...
2018: Science and Technology of Advanced Materials
https://www.readbyqxmd.com/read/29508466/a-general-catalytic-method-for-nucleophilic-substitutions-in-high-cost-and-atom-efficiency
#17
Peter Huy, Isabel Filbrich
Herein, a general formamide catalyzed protocol for the efficient transformation of alcohols into alkyl chlorides, which is promoted by substoichiometric amounts (down to 34 mol%) of inexpensive trichlorotriazine (TCT), is introduced. Importantly, the present work is the first example of a TCT mediated dehydroxychlorination of an OH-group containing substrate (e. g. alcohols and carboxylic acid), in which all three chlorine atoms of TCT are transferred onto the starting material. The consequently enhanced atom-economy facilitates a significantly improved waste balance (E-factors down to 4), cost-efficiency and scalability (>50 g)...
March 5, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29498521/theoretical-investigation-of-the-gas-phase-s-n-2-reactions-of-anionic-and-neutral-nucleophiles-with-chloramines
#18
Jieqing Liu, Meng Dong, Shuo Zhang, Yongdong Liu, Rugang Zhong
The SN2 reactions at nitrogen center (SN2@N) play a significant role in organic synthesis, carcinogenesis, and the formation of some environmentally toxic compounds. However, the SN2@N reactions especially for the neutral compounds as nucleophiles are less known. In this work, reactions of dimethylamine (DMA) and F- with NH2Cl were investigated as model reactions to validate an accurate functional from 24 DFT functionals by comparing with the CCSD(T) reference data. M06-2X functional was found to perform best and applied to systematically explore the trends in reactivity for halides (F- and Cl-) and simple amines towards the substrates NH2Cl and NHCl2 (SN2@N) as well as CH3Cl and CH2Cl2 (SN2@C)...
March 2, 2018: Journal of Physical Chemistry. A
https://www.readbyqxmd.com/read/29484790/inversion-of-configuration-at-the-phosphorus-nucleophile-in-diastereoselective-and-enantioselective-synthesis-of-p-stereogenic-syn-phosphiranes-from-chiral-epoxides
#19
Jake Muldoon, Balazs Varga, Meaghan Deegan, Timothy Chapp, Adam Eordogh, Russell Hughes, David S Glueck, Curtis Moore, Arnold Rheingold
Nucleophilic substitution results in inversion of configuration at the electrophilic carbon (SN2) or racemization (SN1). Stereochemistry at the nucleophile is rarely considered, but phosphines, which have a high barrier to pyramidal inversion, attack electrophiles with retention of configuration at P. Surprisingly, cyclization of bifunctional secondary phosphine alkyl tosylates proceeded under mild conditions with inversion of configuration at the nucleophile to yield P-stereogenic syn-phosphiranes. DFT studies suggested that the novel stereochemistry results from acid-promoted tosylate dissociation to yield an intermediate phosphenium-bridged cation, which undergoes syn-selective cyclization...
February 26, 2018: Angewandte Chemie
https://www.readbyqxmd.com/read/29460630/insights-on-the-origin-of-catalysis-on-glycine-n-methyltransferase-from-computational-modelling
#20
Katarzyna Świderek, Iñaki Tuñón, Ian H Williams, Vicent Moliner
The origin of enzyme catalysis remains a question of debate despite much intense study. We report a QM/MM theoretical study of the SN2 methyl transfer reaction catalyzed by a glycine N-methyltransferase (GNMT) and three mutants to test whether recent experimental observations of rate-constant reductions and variations in inverse secondary α-3H kinetic isotope effects (KIEs) should be attributed to changes in the methyl donor-acceptor distance (DAD): is catalysis due to a compression effect? Semiempirical (AM1) and DFT (M06-2X) methods were used to describe the QM subset of atoms, while OPLS-AA and TIP3P classical force fields were used for the protein and water molecules, respectively...
February 20, 2018: Journal of the American Chemical Society
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