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https://www.readbyqxmd.com/read/28106144/electronic-and-atomic-structures-of-the-sr3ir4sn13-single-crystal-a-possible-charge-density-wave-material
#1
H-T Wang, M K Srivastava, C-C Wu, S-H Hsieh, Y-F Wang, Y-C Shao, Y-H Liang, C-H Du, J-W Chiou, C-M Cheng, J-L Chen, C-W Pao, J-F Lee, C N Kuo, C S Lue, M-K Wu, W-F Pong
X-ray scattering (XRS), x-ray absorption near-edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) spectroscopic techniques were used to study the electronic and atomic structures of the high-quality Sr3Ir4Sn13 (SIS) single crystal below and above the transition temperature (T(*) ≈ 147 K). The evolution of a series of modulated satellite peaks below the transition temperature in the XRS experiment indicated the formation of a possible charge density wave (CDW) in the (110) plane...
January 20, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28102315/methyl-cytosine-driven-structural-changes-enhance-adduction-kinetics-of-an-exon-7-fragment-of-the-p53-gene
#2
Spundana Malla, Karteek Kadimisetty, You-Jun Fu, Dharamainder Choudhary, John B Schenkman, James F Rusling
Methylation of cytosine (C) at C-phosphate-guanine (CpG) sites enhances reactivity of DNA towards electrophiles. Mutations at CpG sites on the p53 tumor suppressor gene that can result from these adductions are in turn correlated with specific cancers. Here we describe the first restriction-enzyme-assisted LC-MS/MS sequencing study of the influence of methyl cytosines (MeC) on kinetics of p53 gene adduction by model metabolite benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE), using methodology applicable to correlate gene damage sites for drug and pollutant metabolites with mutation sites...
January 19, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28094946/competing-e2-and-sn2-mechanisms-for-the-f-ch3ch2i-reaction
#3
Li Yang, Jiaxu Zhang, Jing Xie, Xinyou Ma, Linyao Zhang, Chenyang Zhao, William Louis Hase
Anti-, syn-E2 and inv-, ret-SN2 reaction channels for the gas-phase reaction of F- + CH3CH2I were characterized with a variety of electronic structure calculations. A geometrical analysis confirmed the synchronous E2-type transition states for the elimination of current reaction, instead of nonconcerted processes through E1cb-like and E1-like mechanisms. Importantly, the controversy concerning reactant complex for anti-E2 and inv-SN2 paths have been clarified in the present work. A positive barrier of + 19...
January 17, 2017: Journal of Physical Chemistry. A
https://www.readbyqxmd.com/read/28094460/n-heterocyclic-carbene-catalyzed-intramolecular-nucleophilic-substitution-reaction-enantioselective-construction-of-all-carbon-quaternary-stereocenters
#4
Ming Zhao, Jie Chen, Hui Yang, Ling Zhou
An efficient enantioselective N-heterocyclic carbene (NHC) catalyzed intramolecular SN2' nucleophilic substitution reaction of aldehyde with (E/Z)-trisubstituted allylic bromides has been accomplished. A range of enantioenriched chromanones bearing an all-carbon quaternary stereocenter at the C3 position were prepared with up to 97% yield and 98% ee. The resulting vinyl and carbonyl groups in these products can be transformed to a variety of synthetically important building blocks.
January 17, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28075601/nitrogen-doped-mesoporous-carbons-as-counter-electrodes-in-quantum-dot-sensitized-solar-cells-with-a-conversion-efficiency-exceeding-12
#5
Shuang Jiao, Jun Du, Zhonglin Du, Donghui Long, Wuyou Jiang, Zhenxiao Pan, Yan Li, Xinhua Zhong
The exploration of catalyst materials for counter electrode (CE) in quantum dot sensitized solar cells (QDSCs) that have both high electrocatalytic activity and low charge transfer resistance is always significant yet challenging. In this work, we report the incorporation of nitrogen heteroatoms into carbon lattices leading to nitrogen doped mesoporous carbon (N-MC) materials with superior catalytic activity when used as CE in Zn-Cu-In-Se QDSCs. A series of N-MC materials with different nitrogen contents were synthesized by colloidal silica nanocasting method...
January 11, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28075138/control-of-chemo-regio-and-enantioselectivity-in-copper-hydride-reductions-of-morita-baylis-hillman-adducts
#6
Roscoe T H Linstadt, Carl A Peterson, Carina I Jette, Zarko V Boskovic, Bruce H Lipshutz
Nonracemically ligated copper hydride can be used to effect tandem SN2'/1,2-reductions of racemic Morita-Baylis-Hillman (MBH) acetates to access enantioenriched chiral allylic alcohols with defined olefin geometry. MBH esters, including those with β-substitution, can be transformed to stereodefined enoates by taking advantage of a bulky, oligomeric, in situ generated trialkoxysiloxane leaving group. Finally, an atypical conversion of easily arrived at MBH alcohol derivatives to nonracemic allylic alcohols is disclosed...
January 11, 2017: Organic Letters
https://www.readbyqxmd.com/read/28071915/variational-flooding-study-of-a-sn2-reaction
#7
GiovanniMaria Piccini, James McCarty, Omar Valsson, Michele Parrinello
We have studied the reaction dynamics of a prototypical organic reaction using a variationally optimized truncated bias to accelerate transitions between educts and products reactant states. The asymmetric SN2nucleophilic substitution reaction of fluoromethane and chloromethane CH3F + Cl- <=> CH3Cl + F- is considered and many independent biased molecular dynamics simulations have been performed at 600, 900, and 1200 K collecting several hundred transitions at each temperature. The transition times and relative rate constants have been obtained for both reaction directions...
January 10, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28071904/new-insight-into-the-formation-mechanism-of-imidazolium-based-ionic-liquids-from-n-alkyl-imidazoles-and-halogenated-hydrocarbons-a-polar-microenvironment-induced-and-auto-promoted-process
#8
Xueli Mu, Nan Jiang, Chengbu Liu, Dongju Zhang
To illustrate the formation mechanism of imidazolium-based ionic liquids (ILs) from N-alkyl imidazoles and halogenated hydrocarbons, density functional theory calculations have been carried out on a representative system, the reaction of N-methyl imidazole with chloroethane to form 1-ethyl-3-methyl imidazolium chloride ([Emim]Cl) IL. The reaction is shown to proceed via a SN2 transition state with a free energy barrier of 34.4 kcal/mol in gas phase and 27.6 kcal/mol in toluene solvent. The reaction can be remarkably promoted by the presence of ionic products and water molecules...
January 10, 2017: Journal of Physical Chemistry. A
https://www.readbyqxmd.com/read/28051314/mapping-the-reactivity-and-selectivity-of-2-azidofucosyl-donors-for-the-assembly-of-n-acetylfucosamine-containing-bacterial-oligosaccharides
#9
Bas Hagen, Sara Ali, Herman S Overkleeft, Gijsbert A van der Marel, Jeroen D C Codée
The synthesis of complex oligosaccharides is often hindered by a lack of knowledge on the reactivity and selectivity of their constituent building blocks. We investigated the reactivity and selectivity of 2-azidofucosyl (FucN3) donors, valuable synthons in the synthesis of 2-acetamido-2-deoxyfucose (FucNAc) containing oligosaccharides. Six FucN3 donors, bearing benzyl, benzoyl, or tert-butyldimethylsilyl protecting groups at the C3-O and C4-O positions, were synthesized, and their reactivity was assessed in a series of glycosylations using acceptors of varying nucleophilicity and size...
January 10, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28045531/activation-strain-analysis-of-sn2-reactions-at-c-n-o-and-f-centers
#10
Jan Kubelka, F Matthias Bickelhaupt
Fundamental principles that determine chemical reactivity and reaction mechanisms are the very foundation of chemistry and many related fields of science. Bimolecular nucleophilic substitutions (SN2) are among the most common and therefore most important reaction types. In this report, we examine the trends in the SN2 reactions with respect to increasing electronegativity of the reaction center by comparing the well-studied backside SN2 Cl- + CH3Cl with similar C- substitutions on the isoelectronic series with the second period elements N, O and F in place of C...
January 3, 2017: Journal of Physical Chemistry. A
https://www.readbyqxmd.com/read/28042341/anti-angiogenic-nanotherapy-inhibits-airway-remodeling-and-hyper-responsiveness-of-dust-mite-triggered-asthma-in-the-brown-norway-rat
#11
Gregory M Lanza, John Jenkins, Anne H Schmieder, Aigul Moldobaeva, Grace Cui, Huiying Zhang, Xiaoxia Yang, Qiong Zhong, Jochen Keupp, Ismail Sergin, Krishna S Paranandi, Lindsey Eldridge, John S Allen, Todd Williams, Michael J Scott, Babak Razani, Elizabeth M Wagner
Although angiogenesis is a hallmark feature of asthmatic inflammatory responses, therapeutic anti-angiogenesis interventions have received little attention. Objective: Assess the effectiveness of anti-angiogenic Sn2 lipase-labile prodrugs delivered via αvβ3-micellar nanotherapy to suppress microvascular expansion, bronchial remodeling, and airway hyper-responsiveness in Brown Norway rats exposed to serial house dust mite (HDM) inhalation challenges. Results: Anti-neovascular effectiveness of αvβ3-mixed micelles incorporating docetaxel-prodrug (Dxtl-PD) or fumagillin-prodrug (Fum-PD) were shown to robustly suppress neovascular expansion (p<0...
2017: Theranostics
https://www.readbyqxmd.com/read/28041800/synthesis-of-seleno-fucose-compounds-and-their-application-to-the-x-ray-structural-determination-of-carbohydrate-lectin-complexes-using-single-multi-wavelength-anomalous-dispersion-phasing
#12
Junpei Shimabukuro, Hisayoshi Makyio, Tatsuya Suzuki, Yosuke Nishikawa, Masato Kawasaki, Akihiro Imamura, Hideharu Ishida, Hiromune Ando, Ryuichi Kato, Makoto Kiso
Selenium-incorporated fucoses (seleno-fucoses) differing in the position of the seleno-substituent were synthesized and applied to the X-ray structural determination of a carbohydrate-lectin complex using single/multi-wavelength anomalous dispersion (SAD/MAD) phasing. The hydroxyl groups at the C-1, -2, -3 and -4 position of fucose were individually substituted with a methylseleno group via a transacetalization reaction using MeSeCH2OBn or by an SN2 reaction with TolSe(-) equivalents to afford the corresponding MeSe-fucose...
December 19, 2016: Bioorganic & Medicinal Chemistry
https://www.readbyqxmd.com/read/27997103/kinetic-isotope-effects-and-transition-state-structure-for-human-phenylethanolamine-n-methyltransferase
#13
Christopher F Stratton, Myles B Poulin, Quan Du, Vern L Schramm
Phenylethanolamine N-methyltransferase (PNMT) catalyzes the S-adenosyl-l-methionine (SAM)-dependent conversion of norepinephrine to epinephrine. Epinephrine has been associated with critical processes in humans including the control of respiration and blood pressure. Additionally, PNMT activity has been suggested to play a role in hypertension and Alzheimer's disease. In the current study, labeled SAM substrates were used to measure primary methyl-(14)C and (36)S and secondary methyl-(3)H, 5'-(3)H, and 5'-(14)C intrinsic kinetic isotope effects for human PNMT...
December 28, 2016: ACS Chemical Biology
https://www.readbyqxmd.com/read/27993008/spinning-around-in-transition-metal-chemistry
#14
Marcel Swart, Maja Gruden
The great diversity and richness of transition metal chemistry, such as the features of an open d-shell, opened a way to numerous areas of scientific research and technological applications. Depending on the nature of the metal and its environment, there are often several energetically accessible spin states, and the progress in accurate theoretical treatment of this complicated phenomenon is presented in this Account. The spin state energetics of a transition metal complex can be predicted theoretically on the basis of density functional theory (DFT) or wave function based methodology, where DFT has advantages since it can be applied routinely to medium-to-large-sized molecules and spin-state consistent density functionals are now available...
December 20, 2016: Accounts of Chemical Research
https://www.readbyqxmd.com/read/27992868/do-abrasives-play-a-role-in-toothpaste-efficacy-against-erosion-abrasion
#15
Carolina Ganss, Maike Möllers, Nadine Schlueter
Abrasives may counteract the efficacy of anti-erosion toothpastes either due to physical effects or due to interaction with active agents. This study aimed to investigate whether the amount of abrasives is a determinant for the efficacy of Sn2+-containing toothpastes with or without chitosan additive. Enamel samples were eroded (0.50 wt% citric acid, pH 2.5; 6 × 2 min/day) on a shaking desk - 30/min in experiment 1 (E1) and 35/min in experiments 2 (E2) and 3 (E3) - and immersed in toothpaste slurries (2 × 2 min)...
December 20, 2016: Caries Research
https://www.readbyqxmd.com/read/27984914/tetrel-bond-of-pseudohalide-anions-with-xh3f-x-c-si-ge-and-sn-and-its-role-in-sn2-reaction
#16
Mingxiu Liu, Qingzhong Li, Jianbo Cheng, Wenzuo Li, Hai-Bei Li
The complexes of XH3F⋯N3(-)/OCN(-)/SCN(-) (X = C, Si, Ge, and Sn) have been investigated at the MP2/aug-cc-pVTZ(PP) level. The σ-hole of X atom in XH3F acts as a Lewis acid forming a tetrel bond with pseudohalide anions. Interaction energies of these complexes vary from -8 to -50 kcal/mol, mainly depending on the nature of X and pseudohalide anions. Charge transfer from N/O/S lone pair to X-F and X-H σ(*) orbitals results in the stabilization of these complexes, and the former orbital interaction is responsible for the large elongation of X-F bond length and the remarkable red shift of its stretch vibration...
December 14, 2016: Journal of Chemical Physics
https://www.readbyqxmd.com/read/27978641/controllable-o-nucleometalation-cyclization-strategy-access-to-divergent-ring-functionalized-molecules
#17
Jia Zheng, Zun Li, Wanqing Wu, Huanfeng Jiang
The vinyl moiety-assisted selective O-nucleopalladation is reported, which offers rapid constructions of cycloolefins and cyclopropanes via oxidant-induced cyclization of enynes. O2 resulted in the unexpected 6-endo-Heck cyclization, while CuCl2 led to a 5-exo-trig pathway and synergetic SN2-type C-C bond formation. Amide works as an O-transferred nucleophilic group to activate the alkyne moiety, which induced divergent annulation processes. Moreover, the regenerated amides could be used for further modifications...
December 16, 2016: Organic Letters
https://www.readbyqxmd.com/read/27973833/cmirs-solvation-model-for-methanol-parametrization-testing-and-comparison-with-smd-sm8-and-cosmo-rs
#18
Natalia M Silva, Peter Deglmann, Josefredo R Pliego
The new continuum solvation model, composite method for implicit representation of solvent (CMIRS), proposed by Pomogaeva and Chipman and implemented in GAMESS was parametrized for methanol solvent, with the aim of using it for ionic reactions in solution. The model was tested for predicting single-ion solvation free energy, pKa of acids and protonated bases, and the activation free-energy barriers of SN2 and SNAr reactions in methanol. A comparison was performed with other continuum models, such as SMD, SM8, and COSMO-RS...
December 15, 2016: Journal of Physical Chemistry. B
https://www.readbyqxmd.com/read/27973829/understanding-the-effect-of-solvent-structure-on-organic-reaction-outcomes-when-using-ionic-liquid-acetonitrile-mixtures
#19
Sinead T Keaveney, Tamar L Greaves, Danielle F Kennedy, Jason B Harper
The rate constant for the reaction between hexan-1-amine and 4-methoxybenzaldehyde was determined in ionic liquids containing an imidazolium cation. The effect on the rate constant of increasing the length of the alkyl substituent on the cation was examined in a number of ionic liquid/acetonitrile mixtures. In general it was found that there was no significant effect of changing the alkyl substituent on the rate constant of this process, suggesting that any nanodomains in these mixtures do not have a significant effect on the outcome of this process...
December 15, 2016: Journal of Physical Chemistry. B
https://www.readbyqxmd.com/read/27940912/kinetic-isotope-effects-reveal-early-transition-state-of-protein-lysine-methyltransferase-set8
#20
Joshua A Linscott, Kanishk Kapilashrami, Zhen Wang, Chamara Senevirathne, Ian R Bothwell, Gil Blum, Minkui Luo
Protein lysine methyltransferases (PKMTs) catalyze the methylation of protein substrates, and their dysregulation has been linked to many diseases, including cancer. Accumulated evidence suggests that the reaction path of PKMT-catalyzed methylation consists of the formation of a cofactor(cosubstrate)-PKMT-substrate complex, lysine deprotonation through dynamic water channels, and a nucleophilic substitution (SN2) transition state for transmethylation. However, the molecular characters of the proposed process remain to be elucidated experimentally...
December 27, 2016: Proceedings of the National Academy of Sciences of the United States of America
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