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https://www.readbyqxmd.com/read/28537732/rapid-flame-synthesis-of-atomically-thin-moo3-down-to-monolayer-thickness-for-effective-hole-doping-of-wse2
#1
Lili Cai, Connor J McClellan, Ai Leen Koh, Hong Li, Eilam Yalon, Eric Pop, Xiaolin Zheng
Two-dimensional (2D) molybdenum trioxide (MoO3) with mono- or few-layer thickness can potentially advance many applications, ranging from optoelectronics, catalysis, sensors, and batteries to electrochromic devices. Such ultrathin MoO3 sheets can also be integrated with other 2D materials (e.g., as dopants) to realize new or improved electronic devices. However, there is lack of a rapid and scalable method to controllably grow mono- or few-layer MoO3. Here, we report the first demonstration of using a rapid (<2 minutes) flame synthesis method to deposit mono- and few-layer MoO3 sheets (several microns in lateral dimension) on a wide variety of layered materials, including mica, MoS2, graphene and WSe2, based on van der Waals epitaxy...
May 24, 2017: Nano Letters
https://www.readbyqxmd.com/read/28537721/multivariate-chiral-covalent-organic-frameworks-with-controlled-crystallinity-and-stability-for-asymmetric-catalysis
#2
Jie Zhang, Xing Han, Xiaowei Wu, Yan Liu, Yong Cui
The modular construction of covalent organic frameworks (COFs) provides a convenient platform for designing high-performance functional materials, but the synthetic control over their chirality has been relatively little attended. Here we report a multiple-component strategy to construct chiral COFs (CCOFs) with controlled crystallinity and stability for heterogeneous asymmetric catalysis. By crystallizing mixtures of triamines with and without chiral organocatalysts and a dialdehyde, a family of two- and three-component 2D porous CCOFs that adopt three different stacking modes is prepared...
May 24, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28537708/nonsynonymous-polymorphisms-in-the-human-as3mt-arsenic-methylation-gene-implications-for-arsenic-toxicity
#3
Jiaojiao Li, Charles Packianathan, Toby G Rossman, Barry P Rosen
Arsenic methylation, the primary biotransformation in the human body, is catalyzed by the enzyme As(III) S-adenosylmethionine (SAM) methyltransferases (hAS3MT). This process is thought to be protective from acute high-level arsenic exposure. However, with long term low-level exposure, hAS3MT produces intracellular methylarsenite (MAs(III)) and dimethylarsenite (DMAs(III)), which are considerably more toxic than inorganic As(III) and may contribute to arsenic-related diseases. Several single nucleotide polymorphisms (SNPs) in putative regulatory elements of the hAS3MT gene have been shown to be protective...
May 24, 2017: Chemical Research in Toxicology
https://www.readbyqxmd.com/read/28535479/adsorption-of-vocs-onto-engineered-carbon-materials-a-review
#4
REVIEW
Xueyang Zhang, Bin Gao, Anne Elise Creamer, Chengcheng Cao, Yuncong Li
Volatile organic compounds (VOCs) severely threaten human health and the ecological environment because most of them are toxic, mutagenic, and carcinogenic. The persistent increase of VOCs together with the stringent regulations make the reduction of VOC emissions more imperative. Up to now, numerous VOC treatment technologies have emerged, such as incineration, condensation, biological degradation, absorption, adsorption, and catalysis oxidation et al. Among them, the adsorption technology has been recognized as an efficient and economical control strategy because it has the potential to recover and reuse both adsorbent and adsorbate...
May 12, 2017: Journal of Hazardous Materials
https://www.readbyqxmd.com/read/28535055/ionic-liquid-anion-controlled-nanoscale-gold-morphology-grown-at-a-liquid-interface
#5
Nakara Bhawawet, Jeremy B Essner, Durgesh Vinod Wagle, Gary A Baker
Two different ionic liquids comprising the tetrabutylphosphonium cation ([P4444]) paired with the strongly-coordinating anions 6-aminocaproate ([6-AC]) or taurinate ([tau]) were prepared and employed in an aqueous/organic liquid bilayer system to generate nanoscale gold by Au(OH)4- photoreduction. Generally, as the concentration of ionic liquid in the organic phase was increased, the resulting quasi-spherical gold nanoparticles reduced in size and presented less aggregation, leading to marked increases in the catalytic efficiency for 4-nitrophenol reduction using borohydride...
May 23, 2017: Langmuir: the ACS Journal of Surfaces and Colloids
https://www.readbyqxmd.com/read/28534897/seed-mediated-co-reduction-in-a-large-lattice-mismatch-system-synthesis-of-pd-cu-nanostructures
#6
Meredith R Kunz, Sophia M McClain, Dennis P Chen, Kallum M Koczkur, Rebecca G Weiner, Sara E Skrabalak
Metal nanoparticles (NPs) are of interest for applications in catalysis, electronics, chemical sensing, and more. Their utility is dictated by their composition and physical parameters such as particle size, particle shape, and overall architecture (e.g., hollow vs. solid). Interestingly, the addition of a second metal to create bimetallic NPs adds multifunctionality, with new emergent properties common. However, synthesizing structurally defined bimetallic NPs remains a great challenge. One synthetic pathway to architecturally controlled bimetallic NPs is seed-mediated co-reduction (SMCR) in which two metal precursors are simultaneously co-reduced to deposit metal onto shape-controlled metal seeds, which direct the overgrowth...
May 23, 2017: Nanoscale
https://www.readbyqxmd.com/read/28534837/electrophilic-selenium-catalysis-with-electrophilic-n-f-reagents-as-the-oxidants
#7
REVIEW
Ruizhi Guo, Lihao Liao, Xiaodan Zhao
A suitable oxidative system is crucial to electrophilic selenium catalysis (ESC). This short review offers the overview of recent development in ESC with electrophilic N-F reagents as the oxidants. Several highly selective transformations of alkenes such as allylic or vinylic imidation, pyridination, syn-dichlorination, oxidative cyclization and asymmetric cyclization have been described.
May 19, 2017: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
https://www.readbyqxmd.com/read/28534562/k-junction-structure-mediated-exponential-signal-amplification-strategy-for-microrna-detection-in-electrochemiluminescence-biosensor
#8
Xue Li, Anyi Chen, Yaqin Chai, Ruo Yuan
Based on the novel designed K-junction structure, an economic and efficient exponential signal amplification strategy with simple protocol combining hemin/G-quadruplex, a mimetic peroxidase, as a catalyzer was proposed and utilized in an electrochemiluminescence biosensor for sensitive microRNA detection. It was noteworthy that the K-junction structure was formed with guanine-rich reporter DNA and substrate DNA modified by phosphate at the 5'-terminus. Thus, the activity of the reporter DNA could be inhibited and the recognition domain for the target microRNA constructed through the K-junction structure formed...
May 23, 2017: Analyst
https://www.readbyqxmd.com/read/28534477/decoding-and-reprogramming-fungal-iterative-nonribosomal-peptide-synthetases
#9
Dayu Yu, Fuchao Xu, Shuwei Zhang, Jixun Zhan
Nonribosomal peptide synthetases (NRPSs) assemble a large group of structurally and functionally diverse natural products. While the iterative catalytic mechanism of bacterial NRPSs is known, it remains unclear how fungal NRPSs create products of desired length. Here we show that fungal iterative NRPSs adopt an alternate incorporation strategy. Beauvericin and bassianolide synthetases have the same C1-A1-T1-C2-A2-MT-T2a-T2b-C3 domain organization. During catalysis, C3 and C2 take turns to incorporate the two biosynthetic precursors into the growing depsipeptide chain that swings between T1 and T2a/T2b with C3 cyclizing the chain when it reaches the full length...
May 23, 2017: Nature Communications
https://www.readbyqxmd.com/read/28534396/tailoring-active-sites-via-synergy-between-graphitic-and-pyridinic-n-for-the-enhanced-catalytic-efficiency-of-carbocatalyst
#10
Jieyuan Li, Shi Yin, Fan Dong, Wanglai Cen, Yinghao Chu
Due to the limited characterization methods of structures and morphology of N doped carbocatalysts that are available at the atomic level, the detailed promotion mechanism of the catalytic efficiency is unspecific and the particular active sites introduced by the N atoms require further evaluation. Herein, this challenging issue is tackled by extensive theoretical simulation. It is firstly proposed that the active sites, where O2 molecules become adsorbed and activated, are tailored by synergistic graphitic and pyridinic N atoms, which remarkably accelerate the generation of highly chemical reactive O-containing species...
May 23, 2017: ACS Applied Materials & Interfaces
https://www.readbyqxmd.com/read/28533982/lid-opening-and-conformational-stability-of-t1-lipase-is-mediated-by-increasing-chain-length-polar-solvents
#11
Jonathan Maiangwa, Mohd Shukuri Mohamad Ali, Abu Bakar Salleh, Raja Noor Zaliha Raja Abd Rahman, Yahaya M Normi, Fairolniza Mohd Shariff, Thean Chor Leow
The dynamics and conformational landscape of proteins in organic solvents are events of potential interest in nonaqueous process catalysis. Conformational changes, folding transitions, and stability often correspond to structural rearrangements that alter contacts between solvent molecules and amino acid residues. However, in nonaqueous enzymology, organic solvents limit stability and further application of proteins. In the present study, molecular dynamics (MD) of a thermostable Geobacillus zalihae T1 lipase was performed in different chain length polar organic solvents (methanol, ethanol, propanol, butanol, and pentanol) and water mixture systems to a concentration of 50%...
2017: PeerJ
https://www.readbyqxmd.com/read/28533413/confined-catalysis-under-two-dimensional-materials
#12
Haobo Li, Jianping Xiao, Qiang Fu, Xinhe Bao
Confined microenvironments formed in heterogeneous catalysts have recently been recognized as equally important as catalytically active sites. Understanding the fundamentals of confined catalysis has become an important topic in heterogeneous catalysis. Well-defined 2D space between a catalyst surface and a 2D material overlayer provides an ideal microenvironment to explore the confined catalysis experimentally and theoretically. Using density functional theory calculations, we reveal that adsorption of atoms and molecules on a Pt(111) surface always has been weakened under monolayer graphene, which is attributed to the geometric constraint and confinement field in the 2D space between the graphene overlayer and the Pt(111) surface...
May 22, 2017: Proceedings of the National Academy of Sciences of the United States of America
https://www.readbyqxmd.com/read/28533382/interplay-of-catalysis-fidelity-threading-and-processivity-in-the-exo-and-endonucleolytic-reactions-of-human-exonuclease-i
#13
Yuqian Shi, Homme W Hellinga, Lorena S Beese
Human exonuclease 1 (hExo1) is a member of the RAD2/XPG structure-specific 5'-nuclease superfamily. Its dominant, processive 5'-3' exonuclease and secondary 5'-flap endonuclease activities participate in various DNA repair, recombination, and replication processes. A single active site processes both recessed ends and 5'-flap substrates. By initiating enzyme reactions in crystals, we have trapped hExo1 reaction intermediates that reveal structures of these substrates before and after their exo- and endonucleolytic cleavage, as well as structures of uncleaved, unthreaded, and partially threaded 5' flaps...
May 22, 2017: Proceedings of the National Academy of Sciences of the United States of America
https://www.readbyqxmd.com/read/28531234/directed-evolution-to-improve-the-catalytic-efficiency-of-urate-oxidase-from-bacillus-subtilis
#14
Wenjie Li, Shouteng Xu, Biao Zhang, Yelin Zhu, Yan Hua, Xin Kong, Lianhong Sun, Jiong Hong
Urate oxidase is a key enzyme in purine metabolism and catalyzes the oxidation of uric acid to allantoin. It is used to treat hyperuricemia and gout, and also in a diagnostic kit. In this study, error-prone polymerase chain reaction and staggered extension process was used to generate a mutant urate oxidase with improved enzyme activity from Bacillus subtilis. After several rounds of mutagenesis and screening, two mutants 6E9 and 8E279 were obtained which exhibited 2.99 and 3.43 times higher catalytic efficiency, respectively...
2017: PloS One
https://www.readbyqxmd.com/read/28531160/synthesis-and-characterization-of-constrained-geometry-oxygen-and-sulphur-functionalized-cyclopentadienylchromium-complexes-and-their-use-in-catalysis-for-olefin-polymerization
#15
Ruiguo Zhao, Jun Ma, Hao Zhang, Jiling Huang
A series of constrained geometry O-functionalized cyclopentadienylchromium complexes (1-6) and a S-functionalized cyclopentadienylchromium complex (7) were first synthesized, characterized, and tested as catalyst precursors for the olefin polymerization. In the presence of MAO, the complexes exhibited high catalytic activity for the polymerization of ethylene. It is shown that ligand variations can have a substantial effect on catalyst activity and stability. The effect of Al/Cr ratio on catalytic activity was also studied...
May 22, 2017: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
https://www.readbyqxmd.com/read/28530821/exploring-the-reducing-ability-of-organic-dye-acr-mes-for-fluorination-and-oxidation-of-benzylic-c-sp-3-h-bonds-under-visible-light-irradiation
#16
Ming Xiang, Zhi-Kun Xin, Bin Chen, Chen-Ho Tung, Li-Zhu Wu
The excellent oxidizing capability of acridinium-based organic dye (Acr(+)-Mes) is fully studied in photoredox catalysis. However, its reducing ability is always considered weak for organic transformation. The reducing ability of Acr(+)-Mes is developed by Selectfluor to achieve effective fluorination and oxidation of benzylic C(sp(3))-H bonds under visible light irradiation, which is not available for the direct use of oxidizing ability of excited Acr(+)-Mes. Mechanistic insights provided strong evidence for the oxidative quenching of Acr(+)-Mes...
May 22, 2017: Organic Letters
https://www.readbyqxmd.com/read/28530798/heterogeneous-molecular-catalysis-of-electrochemical-reactions-volcano-plots-and-catalytic-tafel-plots
#17
Cyrille Costentin, Jean-Michel Savéant
We analyze here, in the framework of heterogeneous mo-lecular catalysis the reasons of occurrence or non-occurrence of volcanoes upon plotting the kinetics of the catalytic reaction versus the stabilization free energy of the primary intermediate of the catalytic process. As in the case of homogeneous molecular catalysis or catalysis by surface active metallic sites, a strong motivation of such studies relates to modern energy challenges, particularly those involving small molecules such as water, hydrogen, oxygen, proton and carbon dioxide...
May 22, 2017: ACS Applied Materials & Interfaces
https://www.readbyqxmd.com/read/28530742/a-survey-of-the-different-roles-of-polyoxometalates-in-their-interaction-with-amino-acids-peptides-and-proteins
#18
Mina Arefian, Masoud Mirzaei, Hossein Eshtiagh-Hosseini, Antonio Frontera
One of the most attractive areas in inorganic chemistry is the synthesis of polyoxometalates (POMs) exhibiting new properties and applications. Since the impact of POMs in biochemistry and related fields of research has increased in the last few years, there has been a special interest in this topic. Significant progress in biological applications has been made where the interaction of POMs with amino acids, peptides and proteins is relevant. Versatile POMs play a series of different roles in the interaction with these biomolecules as described in this review...
May 22, 2017: Dalton Transactions: An International Journal of Inorganic Chemistry
https://www.readbyqxmd.com/read/28530384/divalent-metal-ion-activation-of-a-guanine-general-base-in-the-hammerhead-ribozyme-insights-from-molecular-simulations
#19
Haoyuan Chen, Timothy J Giese, Barbara L Golden, Darrin M York
The hammerhead ribozyme is a well-studied nucleolytic ribozyme that catalyzes the self-cleavage of the RNA phosphodiester backbone. Despite experimental and theoretical efforts, there remain key questions about details of the mechanism with regard to the activation of the nucleophile by the putative general base guanine (G12). Straight-forward interpretation of the measured activity-pH data implies the pKa value of the N1 position in the G12 nucleobase is significantly shifted by the ribozyme environment. Recent crystallographic and biochemical work has identified pH-dependent divalent metal ion binding at the N7/O6 position of G12, leading to the hypothesis that this binding mode could induce a pKa shift of G12 towards neutrality...
May 22, 2017: Biochemistry
https://www.readbyqxmd.com/read/28529817/coordinated-and-iterative-enzyme-catalysis-in-fungal-polyketide-biosynthesis
#20
Leibniz Hang, Nicholas Liu, Yi Tang
Fungal polyketides are natural products with great chemical diversity that exhibit a wide range of biological activity. This chemical diversity stems from specialized enzymes encoded in the biosynthetic gene cluster responsible for the natural product biosynthesis. Fungal polyketide synthases (PKS) are the megasynthases that produce the carbon scaffolds for the molecules. Subsequent downstream tailoring enzymes such as oxygenases will then further modify the organic framework. In fungi, many of these enzymes have been found to work iteratively-catalyzing multiple reactions on different sites of the substrate...
September 2, 2016: ACS Catalysis
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