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Journal of the American Chemical Society

Harshkumar H Patel, Matthew S Sigman
In this report, we describe the generation of remote allylic quater-nary stereocenters β, γ, and δ relative to a carbonyl in high enanti-oselectivity. We utilize the redox-relay Heck reaction between alkenyl triflates and acyclic trisubstituted alkenols of varying chain lengths. A wide array of terminal (E)-alkenyl triflates are suitable for this process. The utility of this functionalization is validated further by conversion of the products, via simple organic processes to access remotely functionalized chiral tertiary acid, amine and alcohol products...
October 21, 2016: Journal of the American Chemical Society
Allegra T Aron, Morten O Loehr, Jana Bogena, Christopher J Chang
Iron is essential for sustaining life, as its ability to cycle between multiple oxidation states is critical for catalyzing chemical transformations in biological systems. However, without proper regulation, this same redox capacity can trigger oxidative stress events that contribute to aging along with diseases ranging from cancer to cardiovascular and neurodegenerative disorders. Despite its importance, methods for monitoring biological iron bound weakly to cellular ligands-the labile iron pool-to generate a response that preserves spatial and temporal information remain limited, owing to the potent fluorescence quenching ability of iron...
October 21, 2016: Journal of the American Chemical Society
Shuai Gao, Man Pan, Yong Zheng, Yichao Huang, Qingyun Zheng, Demeng Sun, Lining Lu, Xiaodan Tan, Xianglong Tan, Huan Lan, Jiaxing Wang, Tian Wang, Jiawei Wang, Lei Liu
Racemic or quasi-racemic crystallography recently emerges as a useful technology for solution of the crystal structures of biomacromolecules. It remains unclear to what extent the biomacromolecules of opposite handedness can differ from each other in racemic or quasi-racemic crystallography. Here we report a finding that monomeric d-ubiquitin (Ub) has propensity to cocrystallize with different dimers, trimers, and even a tetramer of l-Ub. In these cocrystals the unconnected monomeric d-Ubs can self-assemble to form pseudomirror images of different oligomers of l-Ub...
October 21, 2016: Journal of the American Chemical Society
Caitlin D Allen, A James Link
Lasso peptides exist naturally in a threaded state as [1]rotaxanes, and we reasoned that lasso peptides cleaved in their loop region could serve as building blocks for catenanes. Mutagenesis of the lasso peptide microcin J25 (MccJ25) with two cysteine residues followed by cleavage of the peptide with trypsin led to a [2]rotaxane structure that self-assembled into a [3]catenane and [4]catenanes at room temperature in aqueous solution. The [3]catenane represents the smallest ring size of a catenane composed solely of polypeptide segments...
October 21, 2016: Journal of the American Chemical Society
Tao Peng, Howard C Hang
Over the past years, fluorescent proteins (e.g., green fluorescent proteins) have been widely utilized to visualize recombinant protein expression and localization in live cells. Although powerful, fluorescent protein tags are limited by their relatively large sizes and potential perturbation to protein function. Alternatively, site-specific labeling of proteins with small-molecule organic fluorophores using bioorthogonal chemistry may provide a more precise and less perturbing method. This approach involves site-specific incorporation of unnatural amino acids (UAAs) into proteins via genetic code expansion, followed by bioorthogonal chemical labeling with small organic fluorophores in living cells...
October 21, 2016: Journal of the American Chemical Society
Pravas Deria, Diego A Gómez-Gualdrón, Idan Hod, Randall Q Snurr, Joseph T Hupp, Omar K Farha
Catalytic activity for acyl transfer from N-acetylimidazole (NAI) to different pyridylcarbinol (PC) regioisomers (2-PC, 3-PC, and 4-PC) is demonstrated for a set of topologically diverse, zirconium-based (porphinato)zinc metal-organic frameworks (MOFs). The MOFs studied are PCN-222, MOF-525, and NU-902, which are based on the csq, ftw, and scu topologies, respectively. The experimentally obtained reaction kinetics are discussed in light of molecular modeling results. The catalytic activity is shown to vary across the series of MOFs due to the different extent to which each topology facilitates reactant preconcentration and alignment of PC and NAI via coordination to framework porphyrin sites (orientation effects)...
October 21, 2016: Journal of the American Chemical Society
Lei Sun, Sarah S Park, Dennis Sheberla, Mircea Dinca
Electrically conductive metal-organic frameworks (MOFs) are emerging as a subclass of porous materials that can have a transformative effect on electronic and renewable energy devices. Systematic advances in these materials depend critically on the accurate and reproducible characterization of their electrical properties. This is made difficult by the numerous techniques available for electrical measurements and the dependence of metrics on device architecture and numerous external variables. These challenges, common to all types of electronic materials and devices, are especially acute for porous materials, whose high surface area make them even more susceptible to interactions with contaminants in the environment...
October 21, 2016: Journal of the American Chemical Society
Christophe Kahlfuss, Sandrine Denis-Quanquin, Nathalie Calin, Elise Dumont, Marco Garavelli, Guy Royal, Saioa Cobo, Eric Saint-Aman, Christophe Bucher
Viologen-centered electron transfer is used to trigger a complete dissociation of a porphyrin-based coordination polymer. In the oxidized state, self-assembly is induced by iterative association of individual porphyrin-based tectons. Dissociation of the self-assembled species is actuated upon changing the redox state of the bipyridium units involved in the tectons from their dicationic state to their radical cation state, the driving force of the disassembling process being the formation of an intramolecularly locked conformation partly stabilized by π-dimerization of both viologen cation radicals...
October 21, 2016: Journal of the American Chemical Society
Zhi-Long Yu, Sen Xin, Ya You, Le Yu, Yue Lin, Da-Wei Xu, Chan Qiao, Zhi-Hong Huang, Ning Yang, Shu-Hong Yu, John B Goodenough
Hard carbons attract myriad interests as anode materials for high-energy rechargeable batteries due to their low costs and high theoretical capacities; practically they deliver unsatisfied performance due to their intrinsically disordered microarchitecture. Here we report a facile ion-catalyzed synthesis of phenol-formaldehyde resin-based hard carbon aerogel by taking advantages of the chelation effect of phenol and Fe3+, which consists of a three-dimensionally interconnected carbon network embedded with hydrogen-rich, ordered microstructures of expanded nanographites and carbon micropores...
October 21, 2016: Journal of the American Chemical Society
Zhen Wang, Eric P Chang, Vern L Schramm
Transition path sampling simulations have proposed that human heart lactate dehydrogenase (LDH) employs protein promoting vibrations (PPVs) on the femtosecond (fs) to picosecond (ps) timescale to promote crossing of the chemical barrier. This chemical barrier involves both hydride and proton transfers to pyruvate to form L-lactate, using reduced nicotinamide adenine dinucleotide (NADH) as the cofactor. Here we report experimental evidence from three types of isotope effect experiments that support coupling of the promoting vibrations to barrier crossing and the coincidence of hydride and proton transfer...
October 21, 2016: Journal of the American Chemical Society
Miles A White, Gordon J Miller, Javier Vela
The first example of polytypism in the I-II-V semiconductors has been demonstrated with the synthesis of cubic LiZnSb by low temperature solution phase methods. This phase exhibits a unique coloring pattern that is novel for this class of compounds. The choice of site configuration has considerable impact on the band structure of these materials which, in turn, effects the transport properties. While the hexagonal polytype has been suggested as a promising n-type and extremely poor p-type thermoelectric material, the cubic analogue is calculated to have high efficiencies at 600K for both n- and p-type derivatives of 1...
October 21, 2016: Journal of the American Chemical Society
Deven P Estes, Georges Siddiqi, Florian Allouche, Kirill V Kovtunov, Olga E Safonova, Alexander L Trigub, Igor V Koptyug, Christophe Copéret
The activation and conversion of hydrocarbons is one of the most important challenges in chemistry. Transition-metal ions (V, Cr, Fe, Co…) isolated on silica surfaces are known to catalyze these processes. The mechanisms of these processes are currently unknown but are thought to involve C-H activation as the rate determining step. Here, we synthesize well-defined Co(II) ions on a silica surface using a metal siloxide precursor followed by thermal treatment under vacuum at 500°C. We show that these isolated Co(II) sites are catalysts for a number of hydrocarbon conversion reactions, such as the dehydrogenation of propane, the hydrogenation of propene, and the trimerization of terminal alkynes...
October 21, 2016: Journal of the American Chemical Society
Gosuke Hayashi, Kenta Koyama, Hidefumi Shiota, Asuka Kamio, Takayoshi Umeda, Genta Nagae, Hiroyuki Aburatani, Akimitsu Okamoto
5-hydroxymethylcytosine (hmC) is an essential intermediate in the active DNA demethylation pathway. Here we report a new base-resolution method for measuring hmC by combining peroxotungstate-mediated oxidation and sequencing analysis. We reveal that an oxidized product of hmC, trihydroxylated thymine (thT), tolerated the incorporation of dATP as a substrate in the process of DNA polymerase elongation. By comparing the results of Sanger sequencing before and after the oxidation, we observed that hmC sites on single-stranded DNAs could be discriminated from unmethylated cytosines...
October 21, 2016: Journal of the American Chemical Society
Hiroaki Kurouchi, Ivonne L Andújar-de Sanctis, Daniel A Singleton
The comparison of experimental and predicted kinetic isotope effects in the α-cleavage of alkoxy radicals is used here to judge the applicability of statistical rate theories. It is found that the governing rate theory and the statistical versus nonstatistical nature of the cleavage depend on the cleavage barrier and how much energy is imparted to the radical. The latter can then be controlled by changing the size of substituents in the system. With a large alkyl group substituent, the vibrational energy of the alkoxy radical is increased but this energy is not statistically distributed, lead-ing to a lower isotope effect than predicted by statistical the-ories...
October 21, 2016: Journal of the American Chemical Society
Wenmei Ming, Mina Yoon, Mao-Hua Du, Kimoon Lee, Sung Wng Kim
Two-dimensional (2D) electrides, emerging as a new type of layered material whose electrons are confined in interlayer spaces instead of at atomic proximities, are receiving interest for their high performance in various (opto)electronics and catalytic applications. Experimentally, however, 2D electrides have been only found in a couple of layered nitrides and carbides. Here, we report new thermodynamically stable alkaline-earth based 2D electrides by using a first-principles global structure optimization method, phonon spectrum analysis, and molecular dynamics simulation...
October 21, 2016: Journal of the American Chemical Society
Shengfa Ye, Claudia Kupper, Steffen Meyer, Erik Andris, Rafael Navrátil, Oliver Krahe, Bhaskar Mondal, Mihail Atanasov, Eckhard Bill, Jana Roithová, Franc Meyer, Frank Neese
In biology, high valent oxo-iron(IV) species have been shown to be pivotal intermediates for functionalization of C-H bonds in the catalytic cycles of a range of O2-activating iron enzymes. This work details an electronic-structure investigation of [Fe(IV)(O)(L(NHC))(NCMe)](2+) (L(NHC) = 3,9,14,20-tetraaza-1,6,12,17-tetraazoniapenta-cyclohexacosane-1(23),4,6(26),10,12(25),15,17(24),21-octaene, complex 1) using helium tagging infrared photodissociation (IRPD), absorption, and magnetic circular dichroism (MCD) spectroscopy, coupled with DFT and highly correlated wave function based multireference calculations...
October 21, 2016: Journal of the American Chemical Society
Kunsu Park, Kyunghan Ahn, Joonil Cha, Sanghwa Lee, Sue In Chae, Sung-Pyo Cho, Siheon Ryee, Jino Im, Jaeki Lee, Su-Dong Park, Myung Joon Han, In Chung, Taeghwan Hyeon
Thermoelectrics directly converts waste heat into electricity and is considered a promising means of sustainable energy generation. While most of the recent advances in the enhancement of the thermoelectric figure of merit (ZT) resulted from a decrease in lattice thermal conductivity by nanostructuring, there have been very few attempts to enhance electrical transport properties, i.e., the power factor. Here we use nanochemistry to stabilize bulk bismuth telluride (Bi2Te3) that violates phase equilibrium, namely, phase-pure n-type K0...
October 20, 2016: Journal of the American Chemical Society
Jie Guang, Qiyong Peter Liu, Russell Hopson, Gerald Kagan, Weibin Li, Thomas B Monroe, Paul G Williard
A metastable, polymorphic hexameric crystal structure of lithium pinacolone enolate (LiOPin) is reported along with three preparation methods. NMR-based structural characterization implies that the lithium pinacolate hexamer deaggregates to a tetramer in toluene but retains mainly the hexameric structure in non-aromatic hydrocarbon solvents such as cyclohexane. Moreover, the presence of a small amount of lithium aldolate (LiOA) dramatically influences the aggregation state of LiOPin by forming a mixed aggregate with a 3:1 ratio (LiOPin3•LiOA)...
October 20, 2016: Journal of the American Chemical Society
Khoa D Nguyen, Daniel Herkommer, Michael J Krische
The first catalytic enantioselective C-C couplings of methanol (>30 × 10(6) tons/year) are reported. Insertion of 2-substituted dienes into the methanol C-H bond occurs in a regioselective manner to form all-carbon quaternary centers with excellent levels of enantioselectivity using an iridium-PhanePhos catalyst. Mechanistic studies corroborate a Curtin-Hammett scenario in which methanol dehydrogenation triggers rapid, reversible diene hydrometalation en route to regioisomeric allyliridium-formaldehyde pairs, yet single constitutional isomers are formed...
October 20, 2016: Journal of the American Chemical Society
Angad P Mehta, Han Li, Sean A Reed, Lubica Supekova, Tsotne Javahishvili, Peter G Schultz
Several modified bases have been observed in the genomic DNA of bacteriophages, prokaryotes, and eukaryotes that play a role in restriction systems and/or epigenetic regulation. In our efforts to understand the consequences of replacing a large fraction of a canonical nucleoside with a modified nucleoside, we previously replaced around 75% of thymidine (T) with 5'-hydroxymethyl-2'-deoxyuridine (5hmU) in the Escherichia coli genome. In this study, we engineered the pyrimidine nucleotide biosynthetic pathway using T4 bacteriophage genes to achieve approximately 63% replacement of 2'-deoxycytidine (dC) with 5-hydroxymethyl-2'-deoxycytidine (5hmC) in the E...
October 20, 2016: Journal of the American Chemical Society
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