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https://www.readbyqxmd.com/read/29224357/investigation-of-the-nucleophilic-attack-of-dichlorvos-by-reduced-sulfur-species-using-1h-nmr
#1
Saumil Christian, Padmanava Pradhan, Urs Jans
The mechanism of the reaction of dichlorvos through hydrolysis reactions and through the reaction with polysulfide (Sn2-) and thiophenolate (PhS-) were investigated by proton nuclear magnetic resonance (1H NMR). The study confirmed product identities of an organophosphorus insecticide reacting with reduced sulfur species using 1H NMR in oxygen sensitive solutions. The experiments of dichlorvos with polysulfide led to the detection of a previously undetected product. The thiophenolate experiments were further advanced to investigate second-order rate kinetics using an internal standard...
December 9, 2017: Journal of Agricultural and Food Chemistry
https://www.readbyqxmd.com/read/29219848/embedded-tin-nanocrystals-in-silicon-an-electrical-characterization
#2
Leopold Scheffler, Mark Jonas Haastrup, Søren Roesgaard, John Lundsgaard Hansen, Arne Nylandsted Larsen, Brian Julsgaard
Tin nanocrystals embedded in a SiSn layer grown by molecular beam epitaxy on n-type Si are investigated by means of deep level transient spectroscopy. Two Sn related deep traps are observed, depending on the annealing temperature of the samples. A deep level at EC - 0.62 eV (Sn1) is observed for annealing temperatures up to 650 °C, whereas a level at EC - 0.53 eV (Sn2) appears for annealing temperatures above 600 °C. Scanning transmission electron microscopy shows the formation of Sn nanocrystals at 600 °C, which coincides with the appearance of Sn2...
December 8, 2017: Nanotechnology
https://www.readbyqxmd.com/read/29214274/radical-mechanism-of-a-nucleophilic-reaction-depending-on-a-two-dimensional-structure
#3
Wenchuan Lai, Yuehui Yuan, Xu Wang, Yang Liu, Yulong Li, Xiangyang Liu
The mechanism of nucleophilic substitution deserves more investigation to include more reaction systems such as two-dimensional (2D) materials. In this study, we used fluorinated graphene (FG) as a representative 2D material to reveal the in-depth mechanism of its defluorination and nucleophilic substitution reaction under attack of common nucleophiles to explore the chemistry of 2D materials and enrich the research on the nucleophilic substitution reaction. DFT calculations and electron paramagnetic resonance spectroscopy (EPR) demonstrated that defluorination of FG occurred via a radical mechanism after a single electron transfer (SET) reaction between the nucleophile and C-F bond, and a spin center was generated on the nanosheet and fluorine anion...
December 7, 2017: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/29209816/gas-phase-alkyl-and-n-alkylamino-cation-affinities-of-anionic-alpha-oxygen-nucleophiles-h-n-xo-x%C3%A2-%C3%A2-n-p-as-o-s-se-f-cl-br-n%C3%A2-%C3%A2-0-2-a-theoretical-g2-m-study
#4
Song Geng, Yun-Yun Liu, Ying Xue
In this work, we studied anionic alpha-oxygen nucleophiles in which there was an atom of with one or more unshared lone-pair electrons from groups 15-17 and periods 2-4 of the periodic table positioned adjacent to the negative attacking-oxygen (i.e., H n XO-; X = N, P, As, O, S, Se, F, Cl, Br; n = 0-2); these nucleophiles were termed "alpha-agents." Specifically, we investigated the gas-phase simple alkyl cation affinities (ACAs) and the simple N-alkylamino cation affinities (NAAMCAs) of these alpha-agents theoretically via the modified G2(+)M method...
December 5, 2017: Journal of Molecular Modeling
https://www.readbyqxmd.com/read/29208698/arginine-123-of-apolipoprotein-a-i-is-essential-for-lecithin-cholesterol-acyltransferase-activity
#5
Irina N Gorshkova, Xiaohu Mei, David Atkinson
ApoA-I activates LCAT that converts lipoprotein cholesterol to cholesteryl ester (CE). Molecular dynamic simulations suggested earlier that helices 5 of two antiparallel apoA-I molecules on discoidal HDL form an amphipathic tunnel for migration of acyl chains and unesterified cholesterol to the active sites of LCAT. Our recent crystal structure of Δ(185-243)apoA-I showed the tunnel formed by helices 5/5, with two positively charged residues Arg123 positioned at the edge of the hydrophobic tunnel. We hypothesized that these uniquely positioned Arg123 are poised for interaction with fatty acids produced by LCAT hydrolysis of the sn2-chains of phosphatidylcholine thus positioning the fatty acids for esterification to cholesterol...
December 5, 2017: Journal of Lipid Research
https://www.readbyqxmd.com/read/29200268/design-of-a-photoredox-catalyst-that-enables-the-direct-synthesis-of-carbamate-protected-primary-amines-via-photoinduced-copper-catalyzed-n-alkylation-reactions-of-unactivated-secondary-halides
#6
Jun Myun Ahn, Jonas C Peters, Gregory C Fu
Despite the long history of SN2 reactions between nitrogen nucleophiles and alkyl electrophiles, many such substitution reactions remain out of reach. In recent years, efforts to develop transition-metal catalysts to address this deficiency have begun to emerge. In this report, we address the challenge of coupling a carbamate nucleophile with an unactivated secondary alkyl electrophile to generate a substituted carbamate, a process that has not been achieved effectively in the absence of a catalyst; the product carbamates can serve as useful intermediates in organic synthesis as well as bioactive compounds in their own right...
December 4, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29194973/perovskite-quantum-dots-and-their-application-in-light-emitting-diodes
#7
REVIEW
Hung-Chia Wang, Zhen Bao, Hsin-Yu Tsai, An-Cih Tang, Ru-Shi Liu
Perovskite quantum dots (PQDs) attract significant interest in recent years because of their unique optical properties, such as tunable wavelength, narrow emission, and high photoluminescence quantum efficiency (PLQY). Recent studies report new types of formamidinium (FA) PbBr3 PQDs, PQDs with organic-inorganic mixed cations, divalent cation doped colloidal CsPb1-x Mx Br3 PQDs (M = Sn2+ , Cd2+ , Zn2+ , Mn2+ ) featuring partial cation exchange, and heterovalent cation doped into PQDs (Bi3+ ). These PQD analogs open new possibilities for optoelectronic devices...
November 30, 2017: Small
https://www.readbyqxmd.com/read/29178786/chemoselective-sn2-allylations-of-detrifluoroacetylatively-in-situ-generated-3-fluoroindolin-2-one-derived-tertiary-enolates-with-morita-baylis-hillman-carbonates
#8
Yi Zhu, Haibo Mei, Jianlin Han, Vadim Anatolievich Soloshonok, Jie Zhou, Yi Pan
The first example of SN2' reaction type of the detrifluoroacetylatively in situ generated tertiary fluoro-enolates in the uncatalyzed reactions with Morita-Baylis-Hillman derivatives has been described. The SN2' substitution takes place in highly chemoselective manner as no corresponding SN2 products were observed in the reaction mixtures. Due to the excellent stereochemical outcome, the reactions seem to have apparent synthetic value for preparation of structurally new fluorinated oxindoles.
November 27, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/29155598/total-synthesis-of-neodysiherbaine-a-via-1-3-dipolar-cycloaddition-of-a-chiral-nitrone-template
#9
Toshihiro Hirai, Kohki Shibata, Yohei Niwano, Masao Shiozaki, Yoshimitsu Hashimoto, Nobuyoshi Morita, Shintaro Ban, Osamu Tamura
The total synthesis of neodysiherbaine A was achieved via 1,3-dipolar cycloaddition of a chiral nitrone template with a sugar-derived allyl alcohol in the presence of MgBr2·OEt2. This cycloaddition constructed the C2 and C4 asymmetric centers in a single step. Then reductive cleavage, intramolecular SN2 reaction of the tertiary alcohol, and oxidation of the primary alcohol afforded neodysiherbaine A.
November 20, 2017: Organic Letters
https://www.readbyqxmd.com/read/29149539/dynamic-cross-exchange-in-halophosphonium-species-first-direct-observation-of-stereochemical-inversion-in-the-course-of-an-sn2-process
#10
Kirill Nikitin, Elizabeth V Jennings, Sulaiman Al Sulaimi, Yannick Ortin, Declan G Gilheany
The complex fluxional interconversions between, otherwise very similar, phosphonium bromides and chlorides R3PX+X- (R = Alk, Ar, X = Cl or Br) was studied by NMR techniques. Their energy barriers are typically ca. 11 kcal/mol but rise rapidly as bulky groups are attached to phosphorus, revealing the importance of steric factors. In contrast, electronic effects, as measured by Hammett analysis, are modest (rho 1.46) but still clearly indicate negative charge flow towards phosphorus in the transition state. Most significantly, detailed analysis of the exchange pathways unequivocally, and for the first time in any such process, shows that nucleophilic attack of the nucleophilic anion on the tetrahedral centre results in inversion of configuration...
November 17, 2017: Angewandte Chemie
https://www.readbyqxmd.com/read/29131453/mechanistic-insights-on-human-phosphoglucomutase-revealed-by-transition-path-sampling-and-molecular-dynamics-calculations
#11
Natercia Bras, Pedro Fernandes, Maria Ramos, Steven Schwartz
Human -phosphoglucomutase 1 (-PGM) catalyzes the isomerization of glucose-1-phosphate into glucose-6-phosphate (G6P) via two sequential phosphoryl transfer steps with a glucose-1,6-bisphosphate (G16P) intermediate. Given that the release of G6P in gluconeogenesis raises glucose output levels, -PGM represents a tempting pharmacological target for type 2 diabetes. Here, we provide the first theoretical study of the catalytic mechanism of human -PGM. We performed transition path sampling simulations to unveil the atomic details of the two catalytic chemical steps, which could be key for developing transition state (TS) analogue molecules with inhibitory properties...
November 12, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29105716/hydrogen-bonds-and-%C3%AF-hole-and-%C3%AF-hole-bonds-mechanisms-protecting-doublet-and-octet-electron-structures
#12
Sławomir J Grabowski
The hydrogen bond interaction and σ-hole and π-hole bonds are steered by the same mechanisms. There is electron charge transfer from the Lewis base to the Lewis acid unit, and further, for various interactions the same mechanisms try to protect the former electronic structure of the Lewis acid centre. The increase of the polarization of bonds to this centre seems to be the common effect. In the case of the A-HB hydrogen bond it is the increase of the polarization of the A-H bond connected with the outflow of the electron charge from the H-atom to the A-centre...
November 6, 2017: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/29091449/aerogels-from-chloromethyltrimethoxysilane-and-their-functionalizations
#13
Tomoki Kimura, Taiyo Shimizu, Kazuyoshi Kanamori, Ayaka Maeno, Hironori Kaji, Kazuki Nakanishi
Reactions of chloromethyltrimethoxysilane (CMTMS) and its derived colloidal network polychloromethylsilsesquioxane (PCMSQ) have been investigated to extend the material design strategy toward mechanically reinforced aerogels. In a carefully designed sol-gel system, CMTMS has afforded transparent aerogels under the presence of cationic surfactant. The surface chloromethyl groups with polarity and reactivity are shown to be useful for supporting nanostructures, photoluminescent carbon dots (C-dots) prepared from polyethyleneimine and citric acid as an example...
November 1, 2017: Langmuir: the ACS Journal of Surfaces and Colloids
https://www.readbyqxmd.com/read/29083162/evaluating-metabolite-related-dna-oxidation-and-adduct-damage-from-aryl-amines-using-a-microfluidic-ecl-array
#14
Itti Bist, Snehasis Bhakta, Di Jiang, Tia E Keyes, Aaron Martin, Robert J Forster, James F Rusling
Damage to DNA from the metabolites of drugs and pollutants constitutes a major human toxicity pathway known as genotoxicity. Metabolites can react with metal ions and NADPH to oxidize DNA or participate in SN2 reactions to form covalently linked adducts with DNA bases. Guanines are the main DNA oxidation sites, and 8-oxo-7,8-dihydro-2-deoxyguanosine (8-oxodG) is the initial product. Here we describe a novel electrochemiluminescent (ECL) microwell array that produces metabolites from test compounds and measures relative rates of DNA oxidation and DNA adduct damage...
November 9, 2017: Analytical Chemistry
https://www.readbyqxmd.com/read/29077421/copper-mediated-sn2-allyl-alkyl-and-allyl-boryl-couplings-of-vinyl-cyclic-carbonates
#15
Núria Miralles, José Enrique Gómez, Arjan W Kleij, Elena Fernández
A method for the copper-catalyzed borylmethylation and borylation of vinyl cyclic carbonates through an SN2' mechanism is reported. These singular reactions involve selective SN2' allylic substitutions with concomitant ring opening of the cyclic carbonate and with extrusion of CO2 and formation of a useful hydroxyl functionality in a single step. The stereoselectivity of the homoallylic borylation and allylic borylation processes can be controlled, and synthetically useful unsaturated (E)-pent-2-ene-1,5-diols and (E)-but-2-ene-1,4-diols are accessed...
November 17, 2017: Organic Letters
https://www.readbyqxmd.com/read/29072908/theoretical-studies-of-the-glycosidation-of-2-o-substituted-5-fluorouracil-n-regioselective-synthesis-with-the-phase-transfer-catalysis-method
#16
Yi-Gui Wang, Ericka C Barnes
The observed N-regioselective glycosidation of 2-O-substituted 5-fluorouracil (5-FU) via the phase-transfer-catalysis (PTC) method was investigated computationally. The Gibbs free energy reaction barrier of the N-reaction between the 5-FU anion and 1-bromo-1-deoxy-2,3,4,6-tetra-O-acetyl-α-d-glucopyranose was computed at the MP2/6-311++G(2d,p)//B3LYP/6-31+G* level. The calculated transition states were, in general, quite "loose", with the ambident reaction sites at the N3- or O4-positions on 5-FU located approximately 2...
November 9, 2017: Journal of Physical Chemistry. A
https://www.readbyqxmd.com/read/29064664/nitrogenase-cofactor-assembly-an-elemental-inventory
#17
Nathaniel S Sickerman, Markus W Ribbe, Yilin Hu
Nitrogenase is known for its remarkable ability to catalyze the reduction of N2 to NH3, and C1 substrates to short-chain hydrocarbon products, under ambient conditions. The best-studied Mo-nitrogenase utilizes a complex metallocofactor as the site of substrate binding and reduction. Designated the M-cluster, this [MoFe7S9C(R-homocitrate)] cluster can be viewed as [MoFe3S3] and [Fe4S3] subclusters bridged by three μ2-sulfides and one μ6-interstitial carbide, with its Mo end further coordinated by an R-homocitrate moiety...
October 24, 2017: Accounts of Chemical Research
https://www.readbyqxmd.com/read/29053182/mechanisms-of-oxidative-addition-to-ni-pme3-4-the-special-role-of-the-tris-phosphine-intermediate
#18
Feliu Maseras, Ignacio Funes, David Nelson
Density functional theory (DFT) calculations have been used to study the oxidative addition of aryl halides to [Ni(PMe3)4]. The formation of NiI versus NiII has been rationalised through the study of two different pathways, both of which proceed via [Ni(PMe3)3]. [NiX(PMe3)3] forms via an open-shell singlet transition state with concommitant formation of an aryl radical, while [Ni(Ar)X(PMe3)2] is produced via SN2-type oxidative addition followed by phosphine dissociation. A microkinetic model was used to show that these data are consistent with the experimentally-observed ratios of NiI and NiII...
October 20, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29052413/asymmetric-synthesis-of-functionalized-trans-cyclopropoxy-building-block-for-grazoprevir
#19
Feng Xu, Yong-Li Zhong, Hongming Li, Ji Qi, Richard Desmond, Zhiguo J Song, Jeonghan Park, Tao Wang, Matthew Truppo, Guy R Humphrey, Rebecca T Ruck
A practical and asymmetric synthesis of a functionalized trans-cyclopropoxy building block for the preparation of the HCV NS3/4a protease inhibitor grazoprevir is reported. Intramolecular SN2 displacement-ring closure, followed by a Baeyer-Villiger oxidation, yields the desired trans-cyclopropanol with full control of diastereoselectivity. A terminal alkyne is then effectively installed using LiNH(CH2)2NEt2. Starting from (S)-epichlorohydrin, the cyclopropoxy building block is prepared in 51% overall yield with >99...
October 20, 2017: Organic Letters
https://www.readbyqxmd.com/read/29045783/reinvestigation-of-the-substitutions-reaction-of-stereogenic-phosphoryl-compounds-stereochemistry-mechanism-and-applications
#20
Li-Juan Liu, Wei-Min Wang, Lan Yao, Fan-Jie Meng, Yong-Ming Sun, Hao Xu, Zhong-Yuan Xu, Qiang Li, Chang-Qiu Zhao, Li-Biao Han
Nucleophilic substitutions at P centers are of high importance in biological processes and asymmetric synthesis. However, detailed studies on this topic are rare. P-Stereogenic compounds containing P-Cl, P-O, and P-S bonds were diastereoselectively prepared and then used to study the substitution of Cl, O, and S at phosphorus centers with organometallic reagents. It was proposed that with alkynyl metallic reagents an SN2-like mechanism (route A1) and a Berry pseudorotation (BPR) of pentacoordinated phosphorus intermediates (route B1) were involved and afforded P-inverted and P-retained products, respectively...
November 1, 2017: Journal of Organic Chemistry
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