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Samuel Nkrumah-Agyeefi, Carmen Scholz
A novel approach to the post-biosynthetic chemical modification of bromo and alkyne functionalized poly(3-hydroxyalkanoates), (PHAs), via copper-catalyzed azide-alkyne cycloaddition (CuAAC) and strain promoted azide alkyne cycloaddition (SPAAC) is reported. Optimum conditions for the biosynthesis of the PHA copolymers, poly(3-hydroxynonanoate-co-3-hydroxy-11-bromoundecanoate) (PHNUBr) and poly(3-hydroxynonanoate-co-3-hydroxy-10-undecynoate) (PHNUD), using Pseudomonas oleovorans as cell factories were 20h of fermentation time and a total carbon substrate concentration of 40mM...
December 2, 2016: International Journal of Biological Macromolecules
Vera Herbel, Julia Sieber-Frank, Michael Wink
Antimicrobial peptides (AMPs) are produced by all living organisms and play an important role in innate immunity because they are readily available and non-specific against invading pathogenic microorganisms. Snakin-2 (SN2) from tomato is a short, cationic peptide that forms lethal pores in biomembranes of microbes. In plant cells, SN2 is produced as a prepeptide with a signal sequence for ER targeting and an acidic region to decrease toxicity in the producing organism. Gene expression analysis by qRT-PCR in tomato plants demonstrated that SN2 is constitutively expressed, mostly in leaves and flowers...
November 9, 2016: Journal of Plant Physiology
L Fernandez-Gonzalez, K Jewgenow
Assisted reproductive techniques are a valuable tool for conservation breeding of endangered species. Cryopreservation methods are the basis of gamete banks, supporting genetic diversity preservation. Unfortunately, cryopreservation of feline oocytes is still considered an experimental technique. The aim of this study was to compare two commercial kits, with our protocol for vitrification of cat oocytes (IZW), which comprises a three-step method with ethylene glycol, DMSO, fetal calf serum, trehalose and Ficoll PM-70...
November 24, 2016: Reproduction in Domestic Animals, Zuchthygiene
Sergi Ruiz-Barragan, Jordi Ribas Ariño, Motoyuki Shiga
The use of high-temperature liquid water (HTW) as a reaction medium is a very promising technology in the field of green chemistry. In order to fully exploit this technology, it is crucial to unravel the reaction mechanisms of the processes carried out in HTW. In this work, the reaction mechanism of 2,5-hexanediol dehydration in HTW has been studied by means of three different ab initio simulations: the string method, metadynamics and molecular dynamics in real time. It is found that the whole reaction involving protonation, bond exchange and deprotonation occurs in a single step without a stable intermediate...
November 30, 2016: Physical Chemistry Chemical Physics: PCCP
Alexander Hinz, Jose M Goicoechea
We report fundamental studies on the reactivity of the 2-arsaethynolate anion (AsCO(-) ), a species that has only recently become synthetically accessible. The reaction of AsCO(-) with the bulky stannylene Ter2 Sn (Ter=2,6-bis[2,4,6-trimethylphenyl]phenyl) is described, which leads to the unexpected formation of a [Ter3 Sn2 As2 ](-) cluster compound. On the reaction pathway to this cluster, several intermediates were identified and characterized. After the initial association of AsCO(-) to Ter2 Sn, decarbonylation occurs to give an anion featuring monocoordinate arsenic, [Ter2 SnAs](-) ...
November 15, 2016: Angewandte Chemie
Peng Liu, Dunyou Wang, Yulong Xu
Atomic-level, bimolecular nucleophilic substitution reaction mechanisms have been studied mostly in the gas phase, but the gas-phase results cannot be expected to reliably describe condensed-phase chemistry. As a novel, double-inversion mechanism has just been found for the F(-) + CH3Cl SN2 reaction in the gas phase [Nat. Commun., 2015, 6, 5972], here, using multi-level quantum mechanics methods combined with the molecular mechanics method, we discovered a new, double-inversion mechanism for this reaction in aqueous solution...
November 15, 2016: Physical Chemistry Chemical Physics: PCCP
Djemel Hamdane, Henri Grosjean, Marc Fontecave
RNA methylation is the most abundant and evolutionarily conserved chemical modification of bases or ribose in noncoding and coding RNAs. This rather simple modification has nevertheless major consequences on the function of maturated RNA molecules and ultimately on their cellular fates. The methyl group employed in the methylation is almost universally derived from S-adenosyl-L-methionine via a simple SN2 displacement reaction. However, in some rare cases, the carbon originates from N5,N10-methylenetetrahydrofolate (CH2=THF)...
November 5, 2016: Journal of Molecular Biology
Yazhong Wang, Fei-Ting Huang, Xuan Luo, Bin Gao, Sang-Wook Cheong
Sr3 Sn2 O7 is the first room-temperature ferroelectric Sn insulator with switchable electric polarization. The ferroelastic twin domains are observed using polarized optical microscope. Polarization hysteresis loop clearly demonstrates the ferroelectric property. The intriguing polarization switching kinetics are observed through an in situ poling process using a dark-field transmission electron microscopy technique.
October 31, 2016: Advanced Materials
Chulho Choi, Philippe Nuhant, James J Mousseau, Xiaojing Yang, Brian S Gerstenberger, Jessica M Williams, Stephen W Wright
The stereocontrolled synthesis of a range of substituted bicyclic morpholine and piperazine derivatives is reported from substituted pyroglutaminols via an intramolecular SN2 cyclization as the key step. This enantiospecific approach toward chiral bicyclic morpholines and piperazines offers new opportunities to access these challenging ring systems, which are becoming increasingly common motifs in drug discovery.
October 27, 2016: Organic Letters
István Szabó, Gábor Czakó
We report a detailed quasiclassical trajectory study for the dynamics of the ground-state and CH/CD stretching-excited F(-) + CHD2Cl(vCH/CD = 0, 1) → Cl(-) + CHD2F, HF + CD2Cl(-), and DF + CHDCl(-) SN2, proton-, and deuteron-abstraction reactions using a full-dimensional global ab initio analytical potential energy surface. The simulations show that (a) CHD2Cl(vCH/CD = 1), especially for vCH = 1, maintains its mode-specific excited character prior to interaction, (b) the SN2 reaction is vibrationally mode-specific,...
October 7, 2016: Journal of Chemical Physics
Yusuke Hashimoto, Saki Tanikawa, Ryota Saito, Kaname Sasaki
β-Stereoselective mannosylation using donors bearing the 2,6-lactone moiety is described. In general, glycosylation is a nucleophilic substitution reaction between an alcoholic nucleophile and a sugar moiety containing a leaving group at the anomeric position. Owing to stereoelectronic effects, the reaction tends to proceed via an SN1 mechanism to afford α-glycosides. We found that the introduction of a 2,6-lactone bridge can circumvent the competing SN1 reaction, affording β-glycosides with stereoinversion via SN2(-like) mechanisms...
October 26, 2016: Journal of the American Chemical Society
Abhijit Mal, Masthanvali Sayyad, Imtiyaz Ahmad Wani, Manas K Ghorai
A highly enantioselective synthetic route to hexahydropyrrolo[2,3-b]indoles via Lewis acid-catalyzed SN2-type ring opening of activated aziridines with indoles having substitutions at 3- and other positions followed by cyclization in a domino fashion has been developed. Hexahydropyrrolo[2,3-b]indoles have been detosylated in the same pot to afford the corresponding products with free NH group in excellent yields (up to 95%) and enantioselectivity (up to >99%).
October 19, 2016: Journal of Organic Chemistry
Jone Corrales, Lauren A Kristofco, W Baylor Steele, Gavin N Saari, Jakub Kostal, Edward Spencer Williams, Margaret Mills, Evan P Gallagher, Terrance J Kavanagh, Nancy Simcox, Longzhu Q Shen, Fjodor Melnikov, Julie B Zimmerman, Adelina M Voutchkova-Kostal, Paul T Anastas, Bryan W Brooks
Sustainable molecular design of less hazardous chemicals presents a potentially transformative approach to protect public health and the environment. Relationships between molecular descriptors and toxicity thresholds previously identified the octanol-water distribution coefficient, log D, and the HOMO-LUMO energy gap, ∆E, as two useful properties in the identification of reduced aquatic toxicity. To determine whether these two property-based guidelines are applicable to sublethal oxidative stress (OS) responses, two common aquatic in vivo models, the fathead minnow (Pimephales promelas) and zebrafish (Danio rerio), were employed to examine traditional biochemical biomarkers (lipid peroxidation, DNA damage, total glutathione) and antioxidant gene activation following exposure to eight structurally diverse industrial chemicals (bisphenol A, cumene hydroperoxide, dinoseb, hydroquinone, indene, perfluorooctanoic acid, R-(-)-carvone, tert-butyl hydroperoxide)...
October 17, 2016: Chemical Research in Toxicology
Manuel A Ortuño, Nasarella A Jasim, Adrian C Whitwood, Agustí Lledós, Robin N Perutz
A computational study of the C(methyl)-O bond activation of fluorinated aryl methyl ethers by a platinum(0) complex Pt(PCyp3)2 (Cyp = cyclopentyl) (N. A. Jasim, R. N. Perutz, B. Procacci and A. C. Whitwood, Chem. Commun., 2014, 50, 3914) demonstrates that the reaction proceeds via an SN2 mechanism. Nucleophilic attack of Pt(0) generates an ion pair consisting of a T-shaped platinum cation with an agostic interaction with a cyclopentyl group and a fluoroaryloxy anion. This ion-pair is converted to a 4-coordinate Pt(ii) product trans-[PtMe(OAr(F))(PCyp3)2]...
October 17, 2016: Dalton Transactions: An International Journal of Inorganic Chemistry
Starr Dostie, Michel Prévost, Philippe Mochirian, Kashif Tanveer, Nicholas Andrella, Ariana Rostami, Guillaume Tambutet, Yvan Guindon
Nucleoside analogues bearing a fluorine in the C2'-position have been synthesized by SN2-like cyclizations of acyclic thioaminal precursors. This strategy provides access to two scaffolds, D-1',2'-cis thiofuranosides and D-1',2'-trans furanosides, that are difficult to generate using the standard approach for nucleoside synthesis. The addition of silylated nucleobases onto model C2-fluorinated dithioacetal substrates resulted in 1,2-syn diastereoselectivity which is consistent with the C2-F and S-alkyl moiety being in close proximity...
October 13, 2016: Journal of Organic Chemistry
Arantxa Fernandes, David McKay, Scott Sneddon, Daniel M Dawson, Sebastian Lawson, Richard Veazey, Karl R Whittle, Sharon E Ashbrook
An NMR crystallographic approach, involving the combination of (119)Sn NMR spectroscopy, XRD, and DFT calculations, is demonstrated for the characterization of La2Sn2-x Ti x O7 ceramics. A phase change from pyrochlore (La2Sn2O7) to a layered perovskite phase (La2Ti2O7) is predicted (by radius ratio rules) to occur when x ≈ 0.95. However, the sensitivity of NMR spectroscopy to the local environment is able to reveal a significant two-phase region is present, extending from x = 1.8 to ∼0.2, with limited solid solution at the two extremes, in broad agreement with powder XRD measurements...
September 15, 2016: Journal of Physical Chemistry. C, Nanomaterials and Interfaces
Laura Milena Pedraza-González, Johan Fabian Galindo, Ronald Gonzalez, Andrés Reyes
The solvent effect on the nucleophile and leaving group atoms of the prototypical F(-) + CH3Cl → CH3F + Cl(-) backside bimolecular nucleophilic substitution reaction (SN2) is analyzed employing the reaction force and the atomic contributions methods on the intrinsic reaction coordinate (IRC). Solvent effects were accounted for using the polarizable continuum solvent model. Calculations were performed employing eleven dielectric constants, ε, ranging from 1.0 to 78.5, to cover a wide spectrum of solvents...
October 9, 2016: Journal of Physical Chemistry. A
L Szatkowski, M B Hall
The nickel(i) octaethylisobacteriochlorin anion ([OEiBCh-Ni((I))](-)) is commonly used as a synthetic model of cofactor F430 from Methyl-Coenzyme M Reductase. In this regard, experimental studies show that [OEiBCh-Ni((I))](-) can catalyze dehalogenation of aliphatic halides in DMF solution by a highly efficient SN2 reaction. To better understand this process, we constructed theoretical models of the dehalogenation of chloromethane by a simple nickel(i) isobacteriochlorin anion and compared its reactivity with that of similar Ni((I)) complexes with other porphyrin-derived ligands: porphyrin, chlorin, bactreriochlorin, hexahydroporphyrin and octahydroporphyrin...
September 28, 2016: Dalton Transactions: An International Journal of Inorganic Chemistry
Emiliano Sorrentino, Stephen J Connon
The first strategy for bringing about highly enantioselective alkylative enolate kinetic resolutions using a simple phase-transfer protocol via SN2 chemistry has been developed. In the presence of a new squaramide-based quaternized cinchona alkaloid-derived catalyst and aqueous base, benzyl, allyl, and propargyl halides react with racemic substituted oxindoles to generate densely functionalized products with the two contiguous stereocenters, one of which is an all-carbon quaternary.
October 4, 2016: Organic Letters
Jeffrey S Cannon, Larry E Overman
Allylic amides, amines, and esters are key synthetic building blocks. Their enantioselective syntheses under mild conditions is a continuing pursuit of organic synthesis methods development. One opportunity for the synthesis of these building blocks is by functionalization of prochiral double bonds using palladium(II) catalysis. In these reactions, nucleopalladation mediated by a chiral palladium(II) catalyst generates a new heteroatom-substituted chiral center. However, reactions where nucleopalladation occurs with antarafacial stereoselectivity are difficult to render enantioselective because of the challenge of transferring chiral ligand information across the square-planar palladium complex to the incoming nucleophile...
October 18, 2016: Accounts of Chemical Research
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