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https://www.readbyqxmd.com/read/29927239/qm-mm-studies-of-dph5-a-promiscuous-methyltransferase-in-the-eukaryotic-biosynthetic-pathway-of-diphthamide
#1
Johanna H Ouml Rberg, Patricia Saenz-Méndez, Leif A Eriksson
Eukaryotic Diphthine Synthase, Dph5, is a promiscuous methyltransferase that catalyzes an extraordinary N,O-tetramethylation of 2-(3-carboxy-3-aminopropyl)-L-histidine (ACP) to yield diphthine methyl ester (DTM). These are intermediates in the biosynthesis of the post-translationally modified histidine residue diphthamide, a unique and essential residue part of eukaryotic elongation factor 2 (eEF2). Herein, the promiscuity of Saccharomyces cerevisiae Dph5 has been studied with in silico approaches, including homology modeling to provide the structure of Dph5, protein-protein docking and molecular dynamics to construct the Dph5-eEF2 complex, and quantum mechanics/molecular mechanics (QM/MM) calculations to outline a plausible mechanism...
June 21, 2018: Journal of Chemical Information and Modeling
https://www.readbyqxmd.com/read/29915845/synthesis-of-multi-substituted-allenes-from-organoalane-reagents-and-propargyl-esters-by-using-a-nickel-catalyst
#2
Xue Bei Shao, Zhen Zhang, Qing Han Li, Zhi Gang Zhao
A highly efficient and simple route for the synthesis of multi-substituted allenes has been developed by a nickel catalyzed SN2' substitution reaction of propargyl esters with organic aluminium reagents under mild conditions, which gave the corresponding multi-substituted allenes in good to excellent yields (up to 92%) and high selectivities (up to 99%) at 60 °C for 6 h in THF. Aryls bearing electron-donating or electron-withdrawing groups in propargyl esters gave products in good yields. In addition, the multi-substituted allenes bearing a thienyl or a pyridyl group were obtained in 95-97% selectivities with isolated yields of 72-83%...
June 19, 2018: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/29904983/helicenes-as-molecular-tweezers-in-the-formation-of-cation-%C3%AF-complexes-bonding-and-circular-dichroism-properties-from-relativistic-dft-calculations
#3
Alvaro Rafael Muñoz-Castro, Alexandre Ortolan, Giovanni Caramori, Renato Parreira
Helicene ligands possess a unique helicoidal π-conjugated framework providing high optical rotation values, where a growing interest in helicene derivatives as building blocks has triggered the development of simple strategies to tune their properties. In this context, here we evaluated the formation of cation-π complexes derived from [6]- and [7]helicene, involving Sn2+, Cd2+ and In+, besides of Ag+, which appears as a plausible modification of such helicoidal structure. The nature of the cation-π interaction in the studied helicene complexes exhibits a covalent character, accounting for ligand π-donation to 5s and 5p empty orbitals of the involved cations...
June 14, 2018: Chemphyschem: a European Journal of Chemical Physics and Physical Chemistry
https://www.readbyqxmd.com/read/29894179/-guanidine-copper-complex-catalyzed-enantioselective-dynamic-kinetic-allylic-alkynylation-under-biphasic-condition
#4
Xi-Yang Cui, Yi-Cen Ge, Siu Min Tan, Huan Jiang, Davin Tan, Yunpeng Lu, Richmond Lee, Choon-Hong Tan
Highly enantioselective allylic alkynylation of racemic bromides under biphasic condition is furnished in this report. This approach employs functionalized terminal alkynes as pro-nucleophiles and provides 6- and 7-membered cyclic 1,4-enynes with high yields and excellent enantioselectivities (up to 96% ee) under mild conditions. Enantio-retentive derivatizations highlight the synthetic utility of this transformation. Cold-spray ionization mass spectrometry (CSI-MS) and X-ray crystallography were used to identify catalytic intermediates, which include guanidinium cuprate ion pairs and a copper-alkynide complex...
June 12, 2018: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/29882367/direct-amination-of-alcohols-catalyzed-by-aluminum-triflate-an-experimental-and-computational-study
#5
Pierre-Adrien Payard, Qingyi Gu, Wenping Guo, Qianran Wang, Matthieu Corbet, Carine Michel, Philippe Sautet, Laurence Grimaud, Raphael Wischert, Marc Pera-Titus
Among the best performing homogeneous catalysts for the direct amination of activated secondary alcohols using electron-poor amine derivatives, metal triflates, such as aluminum triflate, Al(OTf)3, stand out. Here we report the extension of this reaction to electron-rich amines and activated primary alcohols, and provide detailed insight into the structure and reactivity of the catalyst under working conditions in both nitromethane and toluene solvent, through experiment (cyclic voltammetry, conductimetry, NMR), and density functional theory (DFT) simulations...
June 7, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29878774/benchmark-ab-initio-characterization-of-the-inversion-and-retention-pathways-of-the-oh-ch-3-y-y-f-cl-br-i-s-n-2-reactions
#6
Domonkos A Tasi, Zita Fabian, Gabor Czako
We study the Walden-inversion, front-side attack retention, and double-inversion retention pathways of the OH- + CH3Y [Y = F, Cl, Br, I] SN2 reactions using high-level ab initio methods. Benchmark stationary-point structures and frequencies are computed at the CCSD(T)-F12b/aug-cc-pVTZ level of theory and the best technically feasible relative energies are determined based on CCSD(T)-F12b/aug-cc-pVQZ computations complemented with post-CCSD(T) correlation effects at the CCSDT(Q)/aug-cc-pVDZ level, core correlation corrections at the CCSD(T)/aug-cc-pwCVTZ level, scalar relativistic effects using effective core potentials for Br and I, and zero-point energy corrections at the CCSD(T)-F12b/aug-cc-pVTZ level...
June 7, 2018: Journal of Physical Chemistry. A
https://www.readbyqxmd.com/read/29863870/synthesis-of-nonracemic-1-4-benzoxazines-via-ring-opening-cyclization-of-activated-aziridines-with-2-halophenols-formal-synthesis-of-levofloxacin
#7
Abhijit Mal, Imtiyaz Ahmad Wani, Gaurav Goswami, Manas K Ghorai
An efficient and simple route to synthesize 3,4-dihydro-1,4-benzoxazine derivatives in excellent yields (up to 95%) with excellent enantio- and diastereospecificity (ee >99%, de >99%) via Lewis acid catalyzed SN2-type ring opening of activated aziridines with 2-halophenols followed by Cu(I) catalyzed intramolecular C-N cyclization in a stepwise fashion under one-pot condition has been developed. As an application of the strategy a short and efficient synthesis to (S)-3-methyl-1,4-benzoxazine (S)-3t, a late stage intermediate in the synthesis of levofloxacin has also been developed...
June 4, 2018: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/29850882/pyrophosphate-hydrolysis-is-an-intrinsic-and-critical-step-of-the-dna-synthesis-reaction
#8
Jithesh Kottur, Deepak T Nair
DNA synthesis by DNA polymerases (dPols) is central to duplication and maintenance of the genome in all living organisms. dPols catalyze the formation of a phosphodiester bond between the incoming deoxynucleoside triphosphate and the terminal primer nucleotide with the release of a pyrophosphate (PPi) group. It is believed that formation of the phosphodiester bond is an endergonic reaction and PPi has to be hydrolyzed by accompanying pyrophosphatase enzymes to ensure that the free energy change of the DNA synthesis reaction is negative and it can proceed in the forward direction...
May 30, 2018: Nucleic Acids Research
https://www.readbyqxmd.com/read/29806167/nucleophilic-influences-and-origin-of-the-sn2-allylic-effect
#9
Boris Galabov, Gergana Koleva, Henry F Schaefer, Wesley D Allen
The potential energy surfaces for the SN2 reactions of allyl and propyl chlorides with 21 anionic and neutral nucleophiles have been studied using ωB97X-D/6-311++G(3df,2pd) computations. The "allylic effect" on SN2 barriers is well manifested for all reactions and ranges between -0.2 and -4.5 kcal mol-1 in the gas phase. Strong correlations of the SN2 net activation barriers with cation affinities, proton affinities, and electrostatic potentials at nuclei (EPN) demonstrate the powerful influence of electrostatics on these reactions...
May 27, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29796920/steering-charge-kinetics-of-tin-niobate-photocatalysts-key-roles-of-phase-structure-and-electronic-structure
#10
Shushu Huang, Chunyan Wang, Hao Sun, Xiaojing Wang, Yiguo Su
Tin niobate photocatalysts with the phase structures of froodite (SnNb2 O6 ) and pyrochlore (Sn2 Nb2 O7 ) were obtained by a facile solvothermal method in order to explore the impact of phase structure and electronic structure on the charge kinetics and photocatalytic performance. By employing tin niobate as a model compound, the effects of phase structure over electronic structure, photocatalytic activity toward methyl orange solution and hydrogen evolution were systematically investigated. It is found that the variation of phase structure from SnNb2 O6 to Sn2 Nb2 O7 accompanied with modulation of particle size and band edge potentials that has great consequences on photocatalytic performance...
May 23, 2018: Nanoscale Research Letters
https://www.readbyqxmd.com/read/29792318/condensed-tannin-reacts-with-so2-during-wine-aging-yielding-flavan-3-ol-sulfonates
#11
Lingjun Ma, Aude Annie Watrelot, Bennett Addison, Andrew L Waterhouse
Numerous monomeric and oligomeric flavanol sulfonation products were observed in 10 wines. Levels of 0.85-20.06 mg/L and 0-14.72 mg/L were quantified for two monomeric sulfonated flavan-3-ols, and surprisingly, were generally higher than the well-known native flavan-3-ol monomers. Increasing SO2 levels during wine aging increased the sulfonate modified flavan-3-ol monomers and dimers along with higher concentrations of native monomers. The results indicate that >10% of SO2 is reacting with the C4 carbocation, formed from acid cleavage of the interflavan bond, perhaps by a bimolecular SN2 type reaction, and as a reducing agent...
May 24, 2018: Journal of Agricultural and Food Chemistry
https://www.readbyqxmd.com/read/29771532/electrical-and-optical-tunability-in-all-inorganic-halide-perovskite-alloy-nanowires
#12
Teng Lei, Minliang Lai, Qiao Kong, Dylan Lu, Woochul Lee, Letian Dou, Vincent Wu, Yi Yu, Peidong Yang
Alloying different semiconductors is a powerful approach to tuning the optical and electronic properties of semiconductor materials. In halide perovskites (ABX3), alloys with different anions have been widely studied and great band gap tunability in the visible range has been achieved. However, perovskite alloys with different cations at the "B" site are less understood due to the synthetic challenges. Herein, we firstly have developed the synthesis of single crystalline CsPbxSn1-xI3 nanowires (NWs)...
May 17, 2018: Nano Letters
https://www.readbyqxmd.com/read/29770508/asymmetric-sulfur-ylide-mediated-formal-4-1-annulation-reaction-scope-and-mechanism
#13
Sébastien Clergue, Rousseau Olivier, Delaunay Thierry, Dequirez Geoffroy, Tran Trieu-Van, El Aakchioui Soumia, Barozzino-Consiglio Gabriella, Raphael Robiette
A formal (4+1) annulation strategy between sulfur ylides and 1,3-dienes has been developed to afford functionalized cyclopentanoids. The process consists of a stereoselective cyclopropanation reaction followed, in situ, by a stereospecific MgI2-catalyzed vinylcyclopropane-cyclopentene rearrangement. The use of chiral sulfur ylides provides cyclopentanoids with an excellent enantiocontrol. A combined experimental and computational mechanistic study shows that the stereospecificity of the rearrangement can be accounted for by a double SN2 reaction mechanism involving iodide...
May 16, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29765623/theoretical-investigation-of-banert-cascade-reaction
#14
S Bhattacharyya, K Hatua
Computational inside of Banert cascade reaction for triazole formation is studied with B3LYP/6-31G(d,p) level of theory. The reaction proceeds mainly by SN2 initial chloride displacement rather than SN2'-type attack. Furthermore, according to the rate of reaction calculation, SN2 displacement is much faster than SN2' displacement in the order of 8. The [3,3]-sigmatropic rearrangement for the conversion of propargyl azide into triazafulvene has been proved as the rate-determining step having highest activation energy parameter...
April 2018: Royal Society Open Science
https://www.readbyqxmd.com/read/29762892/understanding-the-chemical-reactivity-of-phosphonium-based-ionic-liquids-with-tellurium
#15
Tao Zhang, Kai Schwedtmann, Jan J Weigand, Thomas Doert, Michael Ruck
The chemical reactivity of phosphonium based ionic liquids (ILs) towards tellurium at temperatures above 220 °C was systematically investigated by a series of dissolution experiments, tracking the solute tellurium species by nuclear magnetic resonance, and characterizing the reaction products by X-ray diffraction and scanning electron microscopy. The initial step is the thermal elimination of an alkyl group of the phosphonium cation of the ILs, most probably via an SN2 mechanism. The addition of tellurium follows to form trialkylphosphane tellurides as evidenced by ³¹P and ¹²⁵Te NMR spectroscopic experiments...
May 15, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29750510/pathways-of-metabolite-related-damage-to-a-synthetic-p53-gene-exon-7-oligonucleotide-using-magnetic-enzyme-bioreactor-beads-and-lc-ms-ms-sequencing
#16
Spundana Malla, Karteek Kadimisetty, Di Jiang, Dharamainder Choudhary, James F Rusling
Reactive metabolites of environmental chemicals and drugs can cause site-specific damage to p53 tumor suppressor gene in a major pathway for genotoxicity. We report here a high throughput, cell-free, 96-well plate magnetic bead-enzyme system interfaced with LC-MS/MS sequencing to bioactivate test chemicals and identify resulting adduction sites on genes. Bioactivated aflatoxin B1 was reacted with a 32 bp exon 7 fragment of the p53 gene using 8 microsomal cyt P450 enzymes from different organs coated on magnetic beads...
May 11, 2018: Biochemistry
https://www.readbyqxmd.com/read/29740672/visual-colorimetric-detection-of-tin-ii-and-nitrite-using-a-molybdenum-oxide-nanomaterial-based-three-input-logic-gate
#17
Jiayan Du, Mengxin Zhao, Wei Huang, Yuequan Deng, Yi He
We report a molybdenum oxide (MoO3 ) nanomaterial-based three-input logic gate that uses Sn2+ , NO2 - , and H+ ions as inputs. Under acidic conditions, Sn2+ is able to reduce MoO3 nanosheets, generating oxygen-vacancy-rich MoO3-x nanomaterials along with strong localized surface plasmon resonance (LSPR) and an intense blue solution as the output signal. When NO2 - is introduced, the redox reaction between the MoO3 nanosheets and Sn2+ is strongly inhibited because the NO2 - consumes both H+ and Sn2+ . The three-input logic gate was employed for the visual colorimetric detection of Sn2+ and NO2 - under different input states...
May 9, 2018: Analytical and Bioanalytical Chemistry
https://www.readbyqxmd.com/read/29737804/effects-of-palm-olein-and-olive-oil-on-serum-lipids-in-a-chinese-population-a-randomized-double-blind-cross-over-trial
#18
Guiju Sun, Hui Xia, Yuexin Yang, Shushu Ma, Haiteng Zhou, Guofang Shu, Shaokang Wang, Xian Yang, Huali Tang, Fengling Wang, Yaqiong He, Rong Ding, Hong Yin, Yanyan Wang, Yang Yang, Hangju Zhu, Ligang Yang
BACKGROUND AND OBJECTIVES: As the most widely produced edible vegetable oil, palm oil is known as to contain a high level of saturated fatty acid, which was thought to adversely affect serum lipid profiles. However, recent studies have shown no influence or benefits of palm oil on serum lipids. The potential nutritional value of palm oil is attributed to the high mono-unsaturation at the crucial sn2-position of the oil's triacylglycerols, as with the so-called 'healthy' olive oil (OO)...
2018: Asia Pacific Journal of Clinical Nutrition
https://www.readbyqxmd.com/read/29736138/a-rebco-persistent-current-switch-immersed-in-solid-nitrogen-operating-at-temperatures-near-10-k
#19
Philip C Michael, Jiho Lee, John Voccio, Juan Bascuñán, Seungyong Hahn, Yukikazu Iwasa
We present design and test results for a thermally-activated persistent-current switch (PCS) applied to a double pancake (DP) coil (151 mm ID, 172 mm OD), wound, using the no-insulation (NI) technique, from a 120-m long, 76-μm thick, 6-mm wide REBCO tape. For the experiments reported in this paper, the NI DP assembly was immersed in a volume of solid nitrogen (SN2), cooled to a base temperature of 10 K by conduction to a two-stage cryocooler, and energized at up to 630 A. The DP assembly operated in quasi-persistent mode, with the conductor tails soldered together to form a close-out joint with resistance below 6 nΩ...
April 2018: IEEE Transactions on Applied Superconductivity: a Publication of the IEEE Superconductivity Committee
https://www.readbyqxmd.com/read/29701065/total-synthesis-of-natural-hyacinthacine-c-5-and-six-related-hyacinthacine-c-5-epimers
#20
Anthony W Carroll, Kongdech Savaspun, Anthony C Willis, Masako Hoshino, Atsushi Kato, Stephen G Pyne
The total synthesis of natural (+)-hyacinthacine C5 was achieved, which allowed correction of its initially proposed structure, as well as six additional hyacinthacine C-type compounds. These compounds were readily accessible from two epimeric anti-1,2-amino alcohols. Keeping a common A-ring configuration, chemical manipulation occurred selectively on the B-ring of the hyacinthacine C-type products through methods of syn-dihydroxylation, SN 2 ring-opening of a cyclic sulfate, and also employing either ( R)- or ( R, S)-α-methylallyl amine for the Petasis borono Mannich reaction...
May 18, 2018: Journal of Organic Chemistry
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