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Journal of the American Chemical Society

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https://read.qxmd.com/read/30768905/towards-an-atomic-scale-understanding-of-electrochemical-interface-structure-and-dynamics
#1
Olaf M Magnussen, Axel Gross
For the knowledged-based development of electrochemical processes, a better fundamental understanding of the interfaces between electrodes and electrolytes is necessary. This requires insight into the interface structure and dynamics on the atomic-scale, including that of the liquid electrolyte in the near-surface region, i.e., in the inner and outer part of the electrochemical double layer. This prespective describes current studies of simple and well-defined electrochemical interfaces by first-principles electronic structure calculations and in situ structure-sensitive methods...
February 15, 2019: Journal of the American Chemical Society
https://read.qxmd.com/read/30768895/1-2-diazacyclopentane-3-5-diyl-diradicals-electronic-structure-and-reactivity
#2
Shohei Yoshidomi, Manabu Abe
Localized singlet diradicals are key intermediates in bond-homolyses. A thorough study of the reactive species is needed to clarify the mechanisms of the homolytic bond-cleavage and formation processes. In general the singlet diradicals are quite short-lived due to the fast radical-radical coupling reactions. The short-lived characteristic has retarded the thorough study on bond-homolyses. In this study, a new series of long-lived singlet diradicals, viz. 1,2-diazacyclopentane-3,5-diyl, were identified, and their electronic structures and novel reactivities were thoroughly studied using laser-flash photolysis (LFP), product analysis, and computational studies...
February 15, 2019: Journal of the American Chemical Society
https://read.qxmd.com/read/30768257/mitigation-of-hydrophobicity-induced-immunotoxicity-by-sugar-poly-orthoesters
#3
Sampa Maiti, Saikat Manna, Jingjing Shen, Aaron P Esser-Kahn, Wenjun Du
Polymeric nanoparticles (NPs) derived from self-assemblies of amphiphilic polymers have demonstrated great potentials in clinical applications. However, there are challenges ahead. Notably, immunotoxicity remains as a major roadblock that deters the NPs further applications. Studies suggested that the hydrophobic component is a primary cause, yet biocompatible hydrophobic carbohydrate-based polymers may help mitigate this issue. Herein we design and synthesize novel NP systems having glucose poly(orthoesters) hydrophobic scaffold and polyethylene glycol (PEG) hydrophilic shell...
February 15, 2019: Journal of the American Chemical Society
https://read.qxmd.com/read/30768254/strong-and-confined-acids-enable-a-catalytic-asymmetric-nazarov-cyclization-of-simple-divinyl-ketones
#4
Jie Ouyang, Jennifer L Kennemur, Chandra Kanta De, Christophe Farès, Benjamin List
We report a catalytic asymmetric Nazarov cyclization of simple, acylic, alkyl-substituted divinyl ketones using our recently disclosed strong and confined imidodiphosphorimidate Brønsted acids. The corresponding monocyclic cyclopentenones are formed in good yields and excellent regio-, diastereo-, and enantioselectivities. Further, the chemical utility of the obtained enantiopure cyclopentenones is demonstrated.
February 15, 2019: Journal of the American Chemical Society
https://read.qxmd.com/read/30768253/macrocyclic-peptides-as-drug-candidates-recent-progress-and-remaining-challenges
#5
Alexander A Vinogradov, Yizhen Yi, Hiroaki Suga
Peptides as a therapeutic modality attract much attention due to their synthetic accessibility, high degree of specific binding, and the ability to target protein surfaces traditionally considered "undruggable". Unfortunately, at the same time, other pharmacological properties of a generic peptide, such as metabolic stability and cell permeability, are quite poor, which limits the success of de novo discovered biologically active peptides as drug candidates. Here, we review how macrocyclization as well as the incorporation of non-proteogenic amino acids and various conjugation strategies may be utilized to improve on these characteristics to create better drug candidates...
February 15, 2019: Journal of the American Chemical Society
https://read.qxmd.com/read/30768250/highly-efficient-photo-and-electroluminescence-from-two-coordinate-cu-i-complexes-featuring-nonconventional-n-heterocyclic-carbenes
#6
Shuyang Shi, Moon Chul Jung, Caleb Coburn, Abegail Tadle, Daniel Sylvinson M R, Peter I Djurovich, Stephen R Forrest, Mark E Thompson
A series of six luminescent two-coordinate Cu(I) complexes were investigated bearing nonconventional N-heterocyclic carbene ligands, monoamido-aminocarbene (MAC*) and diamidocarbene (DAC*), along with carbazolyl (Cz) as well as mono- and dicyano-substituted Cz derivatives. The emission color can be systematically varied over 270 nm, from violet to red, through proper choice of the acceptor (carbene) and donor (carbazolyl) groups. The compounds exhibit photoluminescent quantum efficiencies up to 100% in fluid solution and polystyrene films with short decay lifetimes (τ ≈ 1 μs)...
February 15, 2019: Journal of the American Chemical Society
https://read.qxmd.com/read/30767524/rational-reprogramming-o-methylation-regioselectivity-for-combinatorial-biosynthetic-tailoring-of-benzenediol-lactone-scaffolds
#7
Xiaojing Wang, Chen Wang, Lixin Duan, Liwen Zhang, Hang Liu, Ya-Ming Xu, Qingpei Liu, Tonglin Mao, Wei Zhang, Ming Chen, Min Lin, A A Leslie Gunatilaka, Yuquan Xu, Istvan Molnar
O-Methylation modulates the pharmacokinetic and pharmacodynamic (PK/PD) properties of small molecule natural products affecting their bioavailability, stability, and binding to targets. Diversity-oriented combinatorial biosynthesis of new chemical entities for drug discovery, and optimization of known bioactive scaffolds during drug development both demand efficient O-methyltransferase (OMT) biocatalysts with considerable substrate promiscuity and tunable regioselectivity that can be deployed in a scalable and sustainable manner...
February 15, 2019: Journal of the American Chemical Society
https://read.qxmd.com/read/30767520/scalable-total-synthesis-of-vinigrol
#8
Xuerong Yu, Lianghong Xiao, Zechun Wang, Tuoping Luo
Vinigrol is a structurally and stereochemically complex natural product that displays various potent pharmacological activities, including the capability to modulate TNF-α. A new and efficient synthetic route towards this natural product has been developed to complete the asymmetric synthesis of (-)-vinigrol and provide over 600 mg material, manifesting the power of macrocyclic stereocontrol and transannular Diels-Alder reaction.
February 15, 2019: Journal of the American Chemical Society
https://read.qxmd.com/read/30767518/length-selective-synthesis-of-acylglycerol-phosphates-through-energy-dissipative-cycling
#9
Claudia Bonfio, Cécile Caumes, Colm D Duffy, Bhavesh H Patel, Claudia Percivalle, Maria Tsanakopoulou, John D Sutherland
The main aim of origins of life research is to find a plausible sequence of transitions from prebiotic chemistry to nascent biolo-gy. In this context, understanding how and when phospholipid membranes appeared on early Earth is critical to elucidating the prebiotic pathways that led to the emergence of primitive cells. Here we show that exposing glycerol-2-phosphate to acylating agents leads to the formation of a library of acylglycerol-phosphates. Medium-chain acylglycerol-phosphates were found to self-assemble into vesicles stable across a wide range of conditions and capable of retaining mono- and oligonucleotides...
February 15, 2019: Journal of the American Chemical Society
https://read.qxmd.com/read/30764608/1-1-digoldallylium-complexes-diaurated-allylic-carbocations-indicate-new-prospects-of-the-coordination-chemistry-of-carbon
#10
Florian F Mulks, Patrick W Antoni, Jürgen H Gross, Jürgen Graf, Frank Rominger, A Stephen K Hashmi
Reacting (NHC)(cyclopropenyl)gold(I) complexes with cationic gold complexes [(IPr)AuX] afforded extremely reactive allylium-1,1-diido-bridged digold intermediates. We prove the existence and constitution of this structure with FT-ICR-MS/MS, NMR, and UV-Vis-NIR experiments and isolated the nucleophilic addi-tion product [(Me)(Ph)(CCHC){Au(IPr)}2(SOMe2)]NTf2 with DMSO. Our computational investigation unveiled that the bond-ing situation of this -allylium-1,1-diido digold domain was best described as a three-center four electron bond with -backbond...
February 14, 2019: Journal of the American Chemical Society
https://read.qxmd.com/read/30764605/cobalt-in-nitrogen-doped-graphene-as-single-atom-catalyst-for-high-sulphur-content-lithium-sulphur-batteries
#11
Zhenzhen Du, Xingjia Chen, Wei Hu, ChengHao Chuang, Shuai Xie, Ajuan Hu, Wensheng Yan, Xianghua Kong, Xiaojun Wu, Hengxing Ji, Li-Jun Wan
Due to their high theoretical energy density and low cost, lithium-sulphur (Li-S) batteries are promising next-generation energy storage devices. The electrochemical performance of Li-S batteries largely depends on the efficient reversible conversion of Li polysulphides to Li2 S in discharge, and to elemental S during charging. Here, we report on our discovery that monodisperse cobalt atoms embedded in nitrogen-doped graphene (Co-N/G) can trigger the surface-mediated reaction of Li polysulphides. Using a combination of operando X-ray absorption spectroscopy and first-principles calculation, we reveal that the Co-N-C coordination centre serves as a bifunctional electrocatalyst to facilitate both the formation and the decomposition of Li2 S in discharge and charge processes, respectively...
February 14, 2019: Journal of the American Chemical Society
https://read.qxmd.com/read/30763089/a-kas-iii-heterodimer-in-lipstatin-biosynthesis-nondecarboxylatively-condenses-c-8-and-c-14-fatty-acyl-coa-substrates-by-a-variable-mechanism-during-the-establishment-of-a-c-22-aliphatic-skeleton
#12
Daozhong Zhang, Fang Zhang, Wen Liu
β-Ketoacyl-acyl carrier protein (ACP) synthase-III (KAS-III) and its homologs are thiolase-fold proteins that typically behave as homodimers functioning in diverse thioester-based reactions for C-C, C-O or C-N bond formation. Here, we report an exception observed in the biosynthesis of lipstatin. During the establishment of the C22 aliphatic skeleton of this β-lactone lipase inhibitor, LstA and LstB, which both are KAS-III homologs but phylogenetically distinct from each other, function together by forming an unusual heterodimer to catalyze a nondecarboxylating Claisen condensation of C8 and C14 fatty acyl-CoA substrates...
February 14, 2019: Journal of the American Chemical Society
https://read.qxmd.com/read/30763082/a-two-enzyme-pathway-links-l-arginine-to-nitric-oxide-in-n-nitroso-biosynthesis
#13
Haiyan He, Alyssa C Henderson, Yi-Ling Du, Katherine S Ryan
Nitric oxide (NO) has wide-ranging roles in biology, but less is known about its role in building chemical diversity. Here we report a new route to NO from the biosynthetic pathway to the N-nitroso compound streptozocin. We show that the N-nitroso of streptozocin comes from biosynthetic reassembly of L-arginine, with the guanidino nitrogens forming a nitrogen-nitrogen bond. To understand this biosynthetic process, we identify the biosynthetic gene cluster of streptozocin and demonstrate that free L-arginine is N-methylated by StzE to give Nω -monomethyl-L-arginine...
February 14, 2019: Journal of the American Chemical Society
https://read.qxmd.com/read/30763079/zeolitic-intermetallics-lnnisi-ln-la-nd
#14
Hiroshi Mizoguchi, Sang-Won Park, Kazuhisa Kishida, Masaaki Kitano, Junghwan Kim, Masato Sasase, Takashi Honda, Kazutaka Ikeda, Toshiya Otomo, Hideo Hosono
LnNiSi (Ln = La-Nd) comprising a three-dimensional NiSi framework has electrons in the crystallographic cavity space. In the temperature region 473-773 K, it accepts the insertion/de-insertion of hydrogen topotactically without a change in unitcell volume. The insertion of hydrogens into the cavity space is accompanied by a redox reaction with the orbitals of atoms constituting the cavity wall. Having small work functions, such intermetallic electrides exhibit metallic electrical and magnetic properties. Owing to a high electron-donating power and reversible exchange between hydrogen and the electrons, Ru5wt%-loaded LaNiSi powder worked as an efficient catalyst for ammonia synthesis under ambient pressure...
February 14, 2019: Journal of the American Chemical Society
https://read.qxmd.com/read/30763078/solution-nmr-analysis-of-ligand-environment-in-quaternary-ammonium-terminated-self-assembled-monolayers-on-gold-nanoparticles-the-effect-of-surface-curvature-and-ligand-structure
#15
Meng Wu, Ariane M Vartanian, Gene Chong, Arun Kumar Pandiakumar, Robert J Hamers, Rigoberto Hernandez, Catherine J Murphy
We report a solution NMR-based analysis of (16-mercaptohexadecyl)trimethylammonium bromide (MTAB) self-assembled monolayers (SAMs) on colloidal gold nanospheres (AuNSs) with diameters from 1.2 nm to 25 nm, and gold nanorods (AuNRs) with aspect ratios from 1.4 to 3.9. The chemical shift analysis of the proton signals from the solvent-exposed headgroups of bound ligands suggests that the headgroups are saturated on the ligand shell as the sizes of the nanoparticles increase beyond ~10 nm. Quantitative NMR shows that the ligand density of MTAB-AuNSs is size-dependent...
February 14, 2019: Journal of the American Chemical Society
https://read.qxmd.com/read/30762369/c3n5-a-low-bandgap-semiconductor-containing-an-azo-linked-carbon-nitride-framework-for-photocatalytic-photovoltaic-and-adsorbent-applications
#16
Pawan Kumar, Ehsan Vahidzadeh, Ujwal Kumar Thakur, Piyush Kar, Kazi Mohammad Alam, Ankur Goswami, Najia Mahdi, Kai Cui, Guy M Bernard, Vladimir K Michaelis, Karthik Shankar
Modification of carbon nitride based polymeric 2D materials for tailoring their optical, electronic and chemical properties for various applications has gained significant interest. The present report demonstrates the synthesis of a novel modified carbon nitride framework with a remarkable 3:5 C:N stoichiometry (C3N5) and an electronic bandgap of 1.76 eV, by thermal deammoniation of melem hydrazine precursor. Characterization revealed that in C3N5 polymer, two s-heptazine units are bridged together with azo linkage, which constitutes an entirely new and different bonding fashion from g-C3N4 where three heptazine units are linked together with tertiary nitrogen...
February 14, 2019: Journal of the American Chemical Society
https://read.qxmd.com/read/30762365/oxidatively-induced-reductive-elimination-exploring-the-scope-and-catalyst-systems-with-ir-rh-and-ru-complexes
#17
Jinwoo Kim, Kwangmin Shin, Seongho Jin, Dongwook Kim, Sukbok Chang
Direct conversion of C-H bonds into C-C bonds is a promising alternative to the conventional cross-coupling reactions, thus giving rise to a wide range of efficient catalytic C-H functionalization reactions. Among the elementary stages in the catalytic C-C bond formation, reductive elimination constitutes a key step of the catalytic cycle, and, therefore, extensive studies have been made to facilitate this process. In this regard, oxidation on the metal center of a post-transmetalation intermediate would be an appealing approach...
February 14, 2019: Journal of the American Chemical Society
https://read.qxmd.com/read/30762360/bioinspired-syntheses-of-herqulines-b-and-c-from-cyclodipeptide-mycocyclosin
#18
Xu Zhu, Christopher C McAtee, Corinna S Schindler
A bioinspired approach for the syntheses of herqulines B and C is reported that takes advantage of an L-tyrosine-derived diketopiperazine, a mycocyclosin analog, as a synthetic precursor. The strategy relies on a series of consecutive reductions to adjust the mycocyclosin oxidation state to that observed in the herquline class of natural products. The strained and distorted L-tyrosine-based biaryl system characteristic for mycocyclosin is selectively converted to the 1,4-diketone structural motif common to the herqulines via initial hypervalent iodine-mediated dearomatization and a subsequent directed Birch reduction, enabled by an intramolecular H-source...
February 14, 2019: Journal of the American Chemical Society
https://read.qxmd.com/read/30761898/measurement-of-electric-fields-experienced-by-urea-guest-molecules-in-the-18-crown-6-urea-1-5-host-guest-complex-an-experimental-reference-point-for-electric-field-assisted-catalysis
#19
Ming W Shi, Sajesh P Thomas, Venkatesha R Hathwar, Alison J Edwards, Ross O Piltz, Dylan Jayatilaka, George A Koutsantonis, Jacob Overgaard, Eiji Nishibori, Bo B Iversen, Mark A Spackman
High resolution synchrotron and neutron single crystal diffraction data of 18-crown-6:(pentakis)urea measured at 30 K are combined, with the aim to better appreciate the electrostatics associated with intermolecular interactions in condensed matter. With two 18-crown-6 molecules and five different urea molecules in the crystal, this represents the most ambitious combined X-ray/synchrotron and neu-tron experimental charge density analysis to date on a co-crystal or host-guest system incorporating such a large number of unique mole-cules...
February 14, 2019: Journal of the American Chemical Society
https://read.qxmd.com/read/30761897/machine-learning-identifies-chemical-characteristics-that-promote-enzyme-catalysis
#20
Brian M Bonk, James W Weis, Bruce Tidor
Despite tremendous progress in understanding and engineering enzymes, knowledge of how enzyme structures and their dynamics induce observed catalytic properties is incomplete, and capabilities to engineer enzymes fall far short of industrial needs. Here we investigate the structural and dynamic drivers of enzyme catalysis for the rate-limiting step of the industrially important enzyme ketol-acid reductoisomerase (KARI) and identify a region of the conformational space of the bound enzyme-substrate complex that, when populated, leads to large increases in reactivity...
February 14, 2019: Journal of the American Chemical Society
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