- Oxidative decarboxylation of pyruvate by 1-deoxy-D-xyulose 5-phosphate synthase, a central metabolic enzyme in bacteria
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The underexploited antibacterial target 1-deoxy-D-xyluose 5-phosphate (DXP) synthase catalyzes the thiamin diphosphate (ThDP)-dependent formation of DXP from pyruvate and D-glyc-eraldehyde 3-phosphate (D-GAP). DXP is an essential intermediate in the biosynthesis of ThDP, pyridoxal phosphate, and isoprenoids in many pathogenic bacteria. DXP synthase catalyzes a distinct mechanism in ThDP decarboxylative enzymology in which the first enzyme-bound pre-decarboxylation intermediate, C2α-lactyl-ThDP (LThDP), is stabilized by DXP synthase in the absence of D-GAP, and D-GAP then induces efficient LThDP decarboxylation. Despite the observed LThDP accumulation and lack of evidence for C2α-carbanion formation in the absence of D-GAP, CO2 is released at appreciable levels under these conditions. Here, seeking to resolve these conflicting observations, we show that DXP synthase catalyzes the oxidative decarboxylation of pyruvate under conditions in which LThDP accumulates. O2-dependent LThDP decarboxylation led to one-electron transfer from the C2α-carbanion/enamine to O2, with intermediate ThDP-enamine radical formation, followed by peracetic acid formation en route to acetate. Thus, LThDP formation and decarboxylation and DXP formation were studied under anaerobic conditions. Our results support a model in which O2-dependent LThDP decarboxylation and peracetic acid formation occur in the absence of D-GAP, decreasing the levels of pyruvate and O2 in solution. The relative pyruvate and O2 concentrations then dictate the extent of LThDP accumulation, and its buildup can be observed when [pyruvate] > [O2]. The finding that O2 acts as a structurally distinct trigger of LThDP decarboxylation supports the hypothesis that a mechanism involving small molecule– dependent LThDP decarboxylation equips DXP synthase for diverse, yet uncharacterized cellular functions.
- DeColli, Alicia A.,Nemeria, Natalia S.,Majumdar, Ananya,Gerfen, Gary J.,Jordan, Frank,Freel Meyers, Caren L.
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- Hydrogen and chemicals from alcohols through electrochemical reforming by Pd-CeO2/C electrocatalyst
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The development of low-cost and sustainable hydrogen production is of primary importance for a future transition to sustainable energy. In this work, the selective and simultaneous production of pure hydrogen and chemicals from renewable alcohols is achieved using an anion exchange membrane electrolysis cell (electrochemical reforming) employing a nanostructured Pd-CeO2/C anode. The catalyst exhibits high activity for alcohol electrooxidation (e.g. 474 mA cm?2 with EtOH at 60 °C) and the electrolysis cell produces high volumes of hydrogen (1.73 l min?1 m?2) at low electrical energy input (Ecost = 6 kWh kgH2?1 with formate as substrate). A complete analysis of the alcohol oxidation products from several alcohols (methanol, ethanol, 1,2-propandiol, ethylene glycol, glycerol and 1,4-butanediol) shows high selectivity in the formation of valuable chemicals such as acetate from ethanol (100%) and lactate from 1,2-propandiol (84%). Importantly for industrial application, in batch experiments the Pd-CeO2/C catalyst achieves conversion efficiencies above 80% for both formate and methanol, and 95% for ethanol.
- Bellini, Marco,Pagliaro, Maria V.,Marchionni, Andrea,Filippi, Jonathan,Miller, Hamish A.,Bevilacqua, Manuela,Lavacchi, Alessandro,Oberhauser, Werner,Mahmoudian, Jafar,Innocenti, Massimo,Fornasiero, Paolo,Vizza, Francesco
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- Broadband laser-based mid-IR spectroscopy for analysis of proteins and monitoring of enzyme activity
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Laser-based infrared (IR) spectroscopy is an emerging key technology for the analysis of solutes and for real-time reaction monitoring in liquids. Larger applicable pathlengths compared to the traditional gold standard Fourier transform IR (FTIR) spectroscopy enable robust measurements of analytes in a strongly absorbing matrix such as water. Recent advancements in laser development also provide large accessible spectral coverage thus overcoming an inherent drawback of laser-based IR spectroscopy. In this work, we benchmark a commercial room temperature operated broadband external cavity-quantum cascade laser (EC-QCL)-IR spectrometer with a spectral coverage of 400 cm?1 against FTIR spectroscopy and showcase its application for measuring the secondary structure of proteins in water, and for monitoring the lipase-catalyzed saponification of triacetin. Regarding the obtained limit of detection (LOD), the laser-based spectrometer compared well to a research-grade FTIR spectrometer employing a liquid nitrogen cooled detector. With respect to a routine FTIR spectrometer equipped with a room temperature operated pyroelectric detector, a 15-fold increase in LOD was obtained in the spectral range of 1600–1700 cm?1. Characteristic spectral features in the amide I and amide II region of three representative proteins with different secondary structures could be measured at concentrations as low as 0.25 mg mL?1. Enzymatic hydrolysis of triacetin by lipase was monitored, demonstrating the advantage of a broad spectral coverage for following complex chemical reactions. The obtained results in combination with the portability and small footprint of the employed spectrometer opens a wide range of future applications in protein analysis and industrial process control, which cannot be readily met by FTIR spectroscopy without recurring to liquid nitrogen cooled detectors.
- Schwaighofer, Andreas,Akhgar, Christopher K.,Lendl, Bernhard
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- Size-Dependent Activity and Selectivity of Atomic-Level Copper Nanoclusters during CO/CO2 Electroreduction
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As a favorite descriptor, the size effect of Cu-based catalysts has been regularly utilized for activity and selectivity regulation toward CO2/CO electroreduction reactions (CO2/CORR). However, little progress has been made in regulating the size of Cu nanoclusters at the atomic level. Herein, the size-gradient Cu catalysts from single atoms (SAs) to subnanometric clusters (SCs, 0.5–1 nm) to nanoclusters (NCs, 1–1.5 nm) on graphdiyne matrix are readily prepared via an acetylenic-bond-directed site-trapping approach. Electrocatalytic measurements show a significant size effect in both the activity and selectivity toward CO2/CORR. Increasing the size of Cu nanoclusters will improve catalytic activity and selectivity toward C2+ productions in CORR. A high C2+ conversion rate of 312 mA cm?2 with the Faradaic efficiency of 91.2 % are achieved at ?1.0 V versus reversible hydrogen electrode (RHE) over Cu NCs. The activity/selectivity-size relations provide a clear understanding of mechanisms in the CO2/CORR at the atomic level.
- Duan, Lele,Hu, Junhui,Ji, Yongfei,Long, Baihua,Rong, Weifeng,Wei, Shuting,Xi, Shibo,Zang, Wenjie,Zou, Haiyuan
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supporting information
p. 466 - 472
(2020/10/29)
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- Modulation of aggregation behavior, antimicrobial properties and catalytic activity of piperidinium surfactants by modifying their head group with a polar fragment
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To establish the effect of surfactants structure on their functional activity a number of alkyl-N-hydroxyethylpiperidinium bromides with different length of the hydrophobic tail were synthesized and characterized. Aggregation parameters of these surfactan
- Gumerova, Sumbela K.,Kushnazarova, Rushana A.,Kuznetsov, Denis M.,Lenina, Oxana A.,Mirgorodskaya, Alla B.,Nikitin, Eugeny N.,Tyryshkina, Anna A.,Voloshina, Alexandra D.,Zakharova, Lucia Ya.
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- Operando Investigation of Ag-Decorated Cu2O Nanocube Catalysts with Enhanced CO2 Electroreduction toward Liquid Products
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Direct conversion of carbon dioxide into multicarbon liquid fuels by the CO2 electrochemical reduction reaction (CO2RR) can contribute to the decarbonization of the global economy. Here, well-defined Cu2O nanocubes (NCs, 35 nm) uniformly covered with Ag nanoparticles (5 nm) were synthesized. When compared to bare Cu2O NCs, the catalyst with 5 at % Ag on Cu2O NCs displayed a two-fold increase in the Faradaic efficiency for C2+ liquid products (30 % at ?1.0 VRHE), including ethanol, 1-propanol, and acetaldehyde, while formate and hydrogen were suppressed. Operando X-ray absorption spectroscopy revealed the partial reduction of Cu2O during CO2RR, accompanied by a reaction-driven redispersion of Ag on the CuOx NCs. Data from operando surface-enhanced Raman spectroscopy further uncovered significant variations in the CO binding to Cu, which were assigned to Ag?Cu sites formed during CO2RR that appear crucial for the C?C coupling and the enhanced yield of liquid products.
- Herzog, Antonia,Bergmann, Arno,Jeon, Hyo Sang,Timoshenko, Janis,Kühl, Stefanie,Rettenmaier, Clara,Lopez Luna, Mauricio,Haase, Felix T.,Roldan Cuenya, Beatriz
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supporting information
p. 7426 - 7435
(2021/02/26)
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- Electroreduction of CO2to Formate on a Copper-Based Electrocatalyst at High Pressures with High Energy Conversion Efficiency
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Electrocatalytic CO2 reduction (CO2RR) to valuable fuels is a promising approach to mitigate energy and environmental problems, but controlling the reaction pathways and products remains challenging. Here a novel Cu2O nanoparticle film was synthesized by square-wave (SW) electrochemical redox cycling of high-purity Cu foils. The cathode afforded up to 98percent Faradaic efficiency for electroreduction of CO2 to nearly pure formate under ≥45 atm CO2 in bicarbonate catholytes. When this cathode was paired with a newly developed NiFe hydroxide carbonate anode in KOH/borate anolyte, the resulting two-electrode high-pressure electrolysis cell achieved high energy conversion efficiencies of up to 55.8percent stably for long-term formate production. While the high-pressure conditions drastically increased the solubility of CO2 to enhance CO2 reduction and suppress hydrogen evolution, the (111)-oriented Cu2O film was found to be important to afford nearly 100percent CO2 reduction to formate. The results have implications for CO2 reduction to a single liquid product with high energy conversion efficiency.
- Chiang, Ching-Yu,Dai, Hongjie,Guo, Jinyu,Hung, Wei-Hsuan,Ku, Ching-Shun,Kuang, Yun,Li, Aowen,Li, Jiachen,Meng, Yongtao,Sun, Xiaoming,Tian, Xin,Xu, Mingquan,Zhang, Xiao,Zhou, Wu,Zhu, Guanzhou
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supporting information
p. 7276 - 7282
(2020/08/06)
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- Highly Selective Production of Ethylene by the Electroreduction of Carbon Monoxide
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Conversion of carbon monoxide to high value-added ethylene with high selectivity by traditional syngas conversion process is challenging because of the limitation of Anderson-Schulz–Flory distribution. Herein we report a direct electrocatalytic process for highly selective ethylene production from CO reduction with water over Cu catalysts at room temperature and ambient pressure. An unprecedented 52.7 % Faradaic efficiency of ethylene formation is achieved through optimization of cathode structure to facilitate CO diffusion at the surface of the electrode and Cu catalysts to enhance the C?C bond coupling. The highly selective ethylene production is almost without other carbon-based byproducts (e.g. C1–C4 hydrocarbons and CO2) and avoids the drawbacks of the traditional Fischer–Tropsch process that always delivers undesired products. This study provides a new and promising strategy for highly selective production of ethylene from the abundant industrial CO.
- Chen, Ruixue,Su, Hai-Yan,Liu, Deyu,Huang, Rui,Meng, Xianguang,Cui, Xiaoju,Tian, Zhong-Qun,Zhang, Dong H.,Deng, Dehui
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supporting information
p. 154 - 160
(2019/12/15)
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- Energy- And cost-effective non-sterilized fermentation of 2,3-butanediol by an engineered: Klebsiella pneumoniae OU7 with an anti-microbial contamination system
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Microbial contamination is a serious challenge that needs to be overcome for the successful biosynthesis of 2,3-butanediol (2,3-BD). However, traditional strategies such as antibiotic administration or sterilization are costly, have high energy demands, and may increase the risk of antibiotic resistance. Here, we intend to develop a robust strategy to achieve non-sterilized fermentation of 2,3-BD. Briefly, the robust strain can metabolize unconventional chemicals as essential growth nutrients, and therefore, outcompete contaminant microbes that cannot use unconventional chemicals. To this end, Klebsiella pneumoniae OU7, a robust strain, was confirmed to rapidly exploit urea and phosphite (unconventional chemicals) as the primary sources of nitrogen (N) and phosphorus (P), and withstand deliberate contamination in the possibly contaminated systems. Secondly, metabolic engineering, pathogenicity elimination and adaptive laboratory evolution were successively performed, endowing the best strain with an excellent fermentation performance for safe 2,3-BD production. Finally, 84.53 g L-1 of 2,3-BD was synthesized with a productivity of 1.17 g L-1 h-1 and a yield of 0.38 g g-1 under the non-sterilized system. In summary, our technique reduces labor and energy costs and simplifies the fermentation process because sterilization does not need to be performed. Thus, our work will be beneficial for the sustainable synthesis of 2,3-BD. This journal is
- Guo, Ze-Wang,Ou, Xiao-Yang,Xu, Pei,Gao, Hui-Fang,Zhang, Liao-Yuan,Zong, Min-Hua,Lou, Wen-Yong
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p. 8584 - 8593
(2020/12/31)
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- Discovery and mechanistic investigation of Pt-catalyzed oxidative homocoupling of benzene with PhI(OAc)2
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We present a Pt-catalyzed direct coupling of benzene to biphenyl. This catalytic reaction employs a cyclometalated platinum(ii) complex [PtMe(bhq)(SMe2)] (bhq = benzo[h]quinolate) with PhI(OAc)2 as an oxidant and does not require an acid, a co-catalyst or a solvent. The reaction kinetics and characterization of potential catalytic species are reported. The reaction is first-order in Pt and second-order in benzene, which implicates the second C-H activation step as rate-determining. A Pt(ii)/Pt(iv) catalytic cycle is suggested. The reaction commences by oxidation of the Pt(ii) complex to give the platinum(iv) species [Pt(bhq)(SMe2)(OAc)2](OAc) followed by C-H activation of benzene to afford the intermediate [PtPh(bhq)(SMe2)(OAc)](OAc) concurrently with the release of HOAc. A second benzene molecule reacts similarly to give the diphenyl intermediate [PtPh2(bhq)(SMe2)](OAc). C-C bond forming reductive elimination ensues to regenerate Pt(ii) and complete the catalytic cycle. The proposed mechanism has been examined by DFT computations, which provide support to experimental findings.
- Abu-Omar, Mahdi M.,Nabavizadeh, S. Masoud,Niroomand Hosseini, Fatemeh,Park, Chan,Wu, Guang
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supporting information
p. 2477 - 2486
(2020/03/05)
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- Investigating the Origin of Enhanced C2+Selectivity in Oxide-/Hydroxide-Derived Copper Electrodes during CO2Electroreduction
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Oxide-/hydroxide-derived copper electrodes exhibit excellent selectivity toward C2+ products during the electrocatalytic CO2 reduction reaction (CO2RR). However, the origin of such enhanced selectivity remains controversial. Here, we prepared two Cu-based electrodes with mixed oxidation states, namely, HQ-Cu (containing Cu, Cu2O, CuO) and AN-Cu (containing Cu, Cu(OH)2). We extracted an ultrathin specimen from the electrodes using a focused ion beam to investigate the distribution and evolution of various Cu species by electron microscopy and electron energy loss spectroscopy. We found that at the steady stage of the CO2RR, the electrodes have all been reduced to Cu0, regardless of the initial states, suggesting that the high C2+ selectivities are not associated with specific oxidation states of Cu. We verified this conclusion by control experiments in which HQ-Cu and AN-Cu were pretreated to fully reduce oxides/hydroxides to Cu0, and the pretreated electrodes showed even higher C2+ selectivity compared with their unpretreated counterparts. We observed that the oxide/hydroxide crystals in HQ-Cu and AN-Cu were fragmented into nanosized irregular Cu grains under the applied negative potentials. Such a fragmentation process, which is the consequence of an oxidation-reduction cycle and does not occur in electropolished Cu, not only built an intricate network of grain boundaries but also exposed a variety of high-index facets. These two features greatly facilitated the C-C coupling, thus accounting for the enhanced C2+ selectivity. Our work demonstrates that the use of advanced characterization techniques enables investigating the structural and chemical states of electrodes in unprecedented detail to gain new insights into a widely studied system.
- Lei, Qiong,Zhu, Hui,Song, Kepeng,Wei, Nini,Liu, Lingmei,Zhang, Daliang,Yin, Jun,Dong, Xinglong,Yao, Kexin,Wang, Ning,Li, Xinghua,Davaasuren, Bambar,Wang, Jianjian,Han, Yu
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p. 4213 - 4222
(2020/03/04)
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- Characterizing Cation Chemistry for Anion Exchange Membranes - A Product Study of Benzylimidazolium Salt Decompositions in the Base
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Imidazolium functionality has played a prominent role in research on anion exchange membranes for use in alkaline electrochemical devices. Base stability and degradation of these materials has been much studied, but in many instances, product pathways have not been thoroughly delineated. We report an NMR study of base-induced decomposition products from three benzylimidazolium salts bearing varying extents of methyl substitution on the imidazolium ring. The major products are consistent with a hydrolytic ring fragmentation pathway as the principal mode of decomposition. We observe several new products not previously reported in the literature on imidazolium salt degradation, including benzilic acid rearrangement products formally derived from intermediate 1,2-dicarbonyl compounds or their equivalents. However, the overall reactions are complex, the yields of observed products do not account for all consumed starting materials, and mechanistic ambiguities remain.
- Pellerite, Mark J.,Kaplun, Marina M.,Webb, Robert J.
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p. 15486 - 15497
(2019/11/19)
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- Formation of carbon–nitrogen bonds in carbon monoxide electrolysis
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The electroreduction of CO2 is a promising technology for carbon utilization. Although electrolysis of CO2 or CO2-derived CO can generate important industrial multicarbon feedstocks such as ethylene, ethanol, n-propanol and acetate, most efforts have been devoted to promoting C–C bond formation. Here, we demonstrate that C–N bonds can be formed through co-electrolysis of CO and NH3 with acetamide selectivity of nearly 40% at industrially relevant reaction rates. Full-solvent quantum mechanical calculations show that acetamide forms through nucleophilic addition of NH3 to a surface-bound ketene intermediate, a step that is in competition with OH– addition, which leads to acetate. The C–N formation mechanism was successfully extended to a series of amide products through amine nucleophilic attack on the ketene intermediate. This strategy enables us to form carbon–heteroatom bonds through the electroreduction of CO, expanding the scope of products available from CO2 reduction.
- Jouny, Matthew,Lv, Jing-Jing,Cheng, Tao,Ko, Byung Hee,Zhu, Jun-Jie,Goddard, William A.,Jiao, Feng
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p. 846 - 851
(2019/09/03)
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- Bipyridine-Assisted Assembly of Au Nanoparticles on Cu Nanowires To Enhance the Electrochemical Reduction of CO2
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We report a new strategy to prepare a composite catalyst for highly efficient electrochemical CO2 reduction reaction (CO2RR). The composite catalyst is made by anchoring Au nanoparticles on Cu nanowires via 4,4′-bipyridine (bipy). The Au-bipy-Cu composite catalyzes the CO2RR in 0.1 m KHCO3 with a total Faradaic efficiency (FE) reaching 90.6 % at ?0.9 V to provide C-products, among which CH3CHO (25 % FE) dominates the liquid product (HCOO?, CH3CHO, and CH3COO?) distribution (75 %). The enhanced CO2RR catalysis demonstrated by Au-bipy-Cu originates from its synergistic Au (CO2 to CO) and Cu (CO to C-products) catalysis which is further promoted by bipy. The Au-bipy-Cu composite represents a new catalyst system for effective CO2RR conversion to C-products.
- Fu, Jiaju,Zhu, Wenlei,Chen, Ying,Yin, Zhouyang,Li, Yuyang,Liu, Juan,Zhang, Hongyi,Zhu, Jun-Jie,Sun, Shouheng
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supporting information
p. 14100 - 14103
(2019/09/03)
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- A Highly Porous Copper Electrocatalyst for Carbon Dioxide Reduction
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Electrochemical reduction of carbon dioxide (CO2) is an appealing approach toward tackling climate change associated with atmospheric CO2 emissions. This approach uses CO2 as the carbon feedstock to produce value-added chemicals, resulting in a carbon-neutral (or even carbon-negative) process for chemical production. Many efforts have been devoted to the development of CO2 electrolysis devices that can be operated at industrially relevant rates; however, limited progress has been made, especially for valuable C2+ products. Herein, a nanoporous copper CO2 reduction catalyst is synthesized and integrated into a microfluidic CO2 flow cell electrolyzer. The CO2 electrolyzer exhibits a current density of 653 mA cm?2 with a C2+ product selectivity of ≈62% at an applied potential of ?0.67 V (vs reversible hydrogen electrode). The highly porous electrode structure facilitates rapid gas transport across the electrode–electrolyte interface at high current densities. Further investigations on electrolyte effects reveal that the surface pH value is substantially different from the pH of bulk electrolyte, especially for nonbuffering near-neutral electrolytes when operating at high currents.
- Lv, Jing-Jing,Jouny, Matthew,Luc, Wesley,Zhu, Wenlei,Zhu, Jun-Jie,Jiao, Feng
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- Metal-Organic Frameworks Mediate Cu Coordination for Selective CO2 Electroreduction
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The electrochemical carbon dioxide reduction reaction (CO2RR) produces diverse chemical species. Cu clusters with a judiciously controlled surface coordination number (CN) provide active sites that simultaneously optimize selectivity, activity, and efficiency for CO2RR. Here we report a strategy involving metal-organic framework (MOF)-regulated Cu cluster formation that shifts CO2 electroreduction toward multiple-carbon product generation. Specifically, we promoted undercoordinated sites during the formation of Cu clusters by controlling the structure of the Cu dimer, the precursor for Cu clusters. We distorted the symmetric paddle-wheel Cu dimer secondary building block of HKUST-1 to an asymmetric motif by separating adjacent benzene tricarboxylate moieties using thermal treatment. By varying materials processing conditions, we modulated the asymmetric local atomic structure, oxidation state and bonding strain of Cu dimers. Using electron paramagnetic resonance (EPR) and in situ X-ray absorption spectroscopy (XAS) experiments, we observed the formation of Cu clusters with low CN from distorted Cu dimers in HKUST-1 during CO2 electroreduction. These exhibited 45% C2H4 faradaic efficiency (FE), a record for MOF-derived Cu cluster catalysts. A structure-activity relationship was established wherein the tuning of the Cu-Cu CN in Cu clusters determines the CO2RR selectivity.
- Nam, Dae-Hyun,Bushuyev, Oleksandr S.,Li, Jun,De Luna, Phil,Seifitokaldani, Ali,Dinh, Cao-Thang,García De Arquer, F. Pelayo,Wang, Yuhang,Liang, Zhiqin,Proppe, Andrew H.,Tan, Chih Shan,Todorovi?, Petar,Shekhah, Osama,Gabardo, Christine M.,Jo, Jea Woong,Choi, Jongmin,Choi, Min-Jae,Baek, Se-Woong,Kim, Junghwan,Sinton, David,Kelley, Shana O.,Eddaoudi, Mohamed,Sargent, Edward H.
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p. 11378 - 11386
(2018/09/06)
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- S-allyl-L-cysteine sulfoxide, a garlic odor precursor, suppresses elevation in blood ethanol concentration by accelerating ethanol metabolism and preventing ethanol absorption from gut
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Alcoholic beverages are enjoyed together with meals worldwide, but their excessive intake is associated with an increased risk of various diseases. We investigated whether S-allyl-L-cysteine sulfoxide (ACSO), a sulfuric odor precursor of garlic, suppresses elevation in plasma ethanol concentration by accelerating ethanol metabolism and preventing ethanol absorption from the gut in rats. ACSO and garlic extract with a high ACSO content (Garlic-H) suppressed elevation in concentrations of ethanol and acetaldehyde in plasma and promoted the activities of alcohol dehydrogenase and aldehyde dehydrogenase. However, ACSO and Garlic-H did not affect plasma acetate so much. Furthermore, we examined the change in plasma ethanol concentration by injecting ACSO or Garlic-H into the ligated stomach or jejunum together with ethanol solution. ACSO and Garlic-H suppressed the absorption of ethanol from the stomach and jejunum, but suppression in the jejunum was less than in the stomach. In conclusion, ACSO inhibits ethanol absorption and accelerates ethanol metabolism.
- Uto-Kondo, Harumi,Hase, Ayumu,Yamaguchi, Yusuke,Sakurai, Ayaka,Akao, Makoto,Saito, Takeshi,Kumagai, Hitomi
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p. 724 - 731
(2018/04/12)
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- A high-throughput pH-based colorimetric assay: application focus on alpha/beta hydrolases
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Research involving α/β hydrolases, including α-amino acid ester hydrolase and cocaine esterase, has been limited by the lack of an online high throughput screening assay. The development of a high throughput screening assay capable of detecting α/β hydrolase activity toward specific substrates and/or chemical reactions (e.g., hydrolysis in lieu of amidase activity and/or synthesis instead of thioesterase activity) is of interest in a broad set of scientific questions and applications. Here we present a general framework for pH-based colorimetric assays, as well as the mathematical considerations necessary to estimate de novo the experimental response required to assign a ‘hit’ or a ‘miss,’ in the absence of experimental standard curves. This combination is valuable for screening the hydrolysis and synthesis activity of α/β hydrolases on a variety of substrates, and produces data comparable to the current standard technique involving High Performance Liquid Chromatography (HPLC). In contrast to HPLC, this assay enables screening experiments to be performed with greater efficiency.
- Paye, Mariétou F.,Rose, Harrison B.,Robbins, John M.,Yunda, Diana A.,Cho, Seonggeon,Bommarius, Andreas S.
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- Role of the Adsorbed Oxygen Species in the Selective Electrochemical Reduction of CO2 to Alcohols and Carbonyls on Copper Electrodes
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The electrochemical reduction of CO2 into fuels has gained significant attention recently as source of renewable carbon-based fuels. The unique high selectivity of copper in the electrochemical reduction of CO2 to hydrocarbons has called much interest in discovering its mechanism. In order to provide significant information about the role of oxygen in the electrochemical reduction of CO2 on Cu electrodes, the conditions of the surface structure and the composition of the Cu single crystal electrodes were controlled over time. This was achieved using pulsed voltammetry, since the pulse sequence can be programmed to guarantee reproducible initial conditions for the reaction at every fraction of time and at a given frequency. In contrast to the selectivity of CO2 reduction using cyclic voltammetry and chronoamperometric methods, a large selection of oxygenated hydrocarbons was found under alternating voltage conditions. Product selectivity towards the formation of oxygenated hydrocarbon was associated to the coverage of oxygen species, which is surface-structure- and potential-dependent.
- Le Duff, Cécile S.,Lawrence, Matthew J.,Rodriguez, Paramaconi
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p. 12919 - 12924
(2017/10/07)
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- Acetaldehyde as an Intermediate in the Electroreduction of Carbon Monoxide to Ethanol on Oxide-Derived Copper
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Oxide-derived copper (OD-Cu) electrodes exhibit unprecedented CO reduction performance towards liquid fuels, producing ethanol and acetate with >50% Faradaic efficiency at -0.3 V (vs. RHE). By using static headspace-gas chromatography for liquid phase analysis, we identify acetaldehyde as a minor product and key intermediate in the electroreduction of CO to ethanol on OD-Cu electrodes. Acetaldehyde is produced with a Faradaic efficiency of ≈5% at -0.33 V (vs. RHE). We show that acetaldehyde forms at low steady-state concentrations, and that free acetaldehyde is difficult to detect in alkaline solutions using NMR spectroscopy, requiring alternative methods for detection and quantification. Our results represent an important step towards understanding the CO reduction mechanism on OD-Cu electrodes.
- Bertheussen, Erlend,Verdaguer-Casadevall, Arnau,Ravasio, Davide,Montoya, Joseph H.,Trimarco, Daniel B.,Roy, Claudie,Meier, Sebastian,Wendland, Jürgen,N?rskov, Jens K.,Stephens, Ifan E. L.,Chorkendorff
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supporting information
p. 1450 - 1454
(2016/02/14)
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- Mechanistic Studies on the Palladium-Catalyzed Direct C-5 Arylation of Imidazoles: The Fundamental Role of the Azole as a Ligand for Palladium
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An in-depth mechanistic study on the palladium-catalyzed direct arylation of imidazoles at the C-5 position is presented. The interactions of triphenylphosphine (PPh3)-ligated aryl-Pd species with 1,2-dimethyl-1H-imidazole (dmim) have been studied in detail. In contrast with previous suggestions, phosphine-ligated organo-Pd species are not active and the reaction proceeds through imidazole-ligated organo-Pd intermediates. The kinetics of the oxidative addition of aryl halides with dmim-ligated Pd(0) species have been characterized in a Pd(dba)2/dmim model system. A thorough study of the equilibria involving novel [ArPd(dmim)2X] complexes (X=I, OAc) and the unexpected cationic [ArPd(dmim)3]+ is also reported. The ability of these species to effect the C-H arylation of dmim at room temperature in the presence of acetate is also demonstrated.
- Perego, Luca Alessandro,Grimaud, Laurence,Bellina, Fabio
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p. 597 - 609
(2016/02/27)
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- Probing the Active Surface Sites for CO Reduction on Oxide-Derived Copper Electrocatalysts
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CO electroreduction activity on oxide-derived Cu (OD-Cu) was found to correlate with metastable surface features that bind CO strongly. OD-Cu electrodes prepared by H2 reduction of Cu2O precursors reduce CO to acetate and ethanol with nearly 50% Faradaic efficiency at moderate overpotential. Temperature-programmed desorption of CO on OD-Cu revealed the presence of surface sites with strong CO binding that are distinct from the terraces and stepped sites found on polycrystalline Cu foil. After annealing at 350 °C, the surface-area corrected current density for CO reduction is 44-fold lower and the Faradaic efficiency is less than 5%. These changes are accompanied by a reduction in the proportion of strong CO binding sites. We propose that the active sites for CO reduction on OD-Cu surfaces are strong CO binding sites that are supported by grain boundaries. Uncovering these sites is a first step toward understanding the surface chemistry necessary for efficient CO electroreduction.
- Verdaguer-Casadevall, Arnau,Li, Christina W.,Johansson, Tobias P.,Scott, Soren B.,McKeown, Joseph T.,Kumar, Mukul,Stephens, Ifan E. L.,Kanan, Matthew W.,Chorkendorff, Ib
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p. 9808 - 9811
(2015/08/24)
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- Microbial electrosynthesis of butyrate from carbon dioxide
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This work proves for the first time the bioelectrochemical production of butyrate from CO2 as a sole carbon source. The highest concentration of butyrate achieved was 20.2 mMC, with a maximum butyrate production rate of 1.82 mMC d-1. The electrochemical characterisation demonstrated that the CO2 reduction to butyrate was hydrogen driven. Production of ethanol and butanol was also observed opening up the potential for biofuel production.
- Ganigué,Puig,Batlle-Vilanova,Balaguer,Colprim
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p. 3235 - 3238
(2015/06/08)
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- Micellar effects upon the rate of alkaline hydrolysis of triflusal
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The rate of hydrolysis for triflusal was measured at varying concentrations of NaOH at four different temperatures (i.e. 25, 35, 45 and 55 °C). The micelles of cetyltrimethylammonium bromide (CTABr), cetyltrimethylammonium chloride (CTACl), cetyltrimethylammonium hydroxide (CTAOH) and dodecyltrimethyl-ammonium bromide (DTABr) had catalytic effect on the rate of hydrolysis. CTABr, CTACl and DTABr gave maxima like curve for the rate-[surfactant] plot while CTAOH gave plateau like curve. The anionic sodium dodecyl sulfate (SDS) did not influence the rate of alkaline hydrolysis of triflusal. The non-ionic Brij-35 inhibited the rate of the hydrolytic reaction. The catalytic effect by cationic micelles was treated by applying the pseudophase ion exchange model while the inhibitive effect by non-ionic micelles has been described by using the Poisson-Boltzmann pseudophase model. The variation in kψ with the change in [surfactant] was used to determined various kinetic parameters e.g., binding constant (Ks), and micellar rate constant (km). The addition of electrolytes decreased the reaction rate in CTABr and CTAOH micelles.
- Al-Lohedan, Hamad A.,Al-Blewi, Fawziah F.,Rafiquee,Issa, Zuheir A.
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p. 321 - 327
(2015/03/18)
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- Polyfunctional supramolecular systems based on surfactants containing the hydroxyalkyl moiety in the head group
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The critical micelle concentration, surface potential, and degree of binding of counterions in aqueous micellar solutions of N-cetyl-N-methylmorpholinium bromide and its analog containing the hydroxyethyl moiety in the head group were determined using a c
- Yackevich,Mirgorodskaya,Lukashenko,Zakharova
-
p. 1801 - 1806
(2015/05/20)
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- The nonenzymatic decomposition of guanidines and amidines
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To establish the rates and mechanisms of decomposition of guanidine and amidine derivatives in aqueous solution and the rate enhancements produced by the corresponding enzymes, we examined their rates of reaction at elevated temperatures and used the Arrhenius equation to extrapolate the results to room temperature. The similar reactivities of methylguanidine and 1,1,3,3-tetramethylguanidine and their negative entropies of activation imply that their decomposition proceeds by hydrolysis rather than elimination. The influence of changing pH on the rate of decomposition is consistent with attack by hydroxide ion on the methylguanidinium ion (k2 = 5 × 10 -6 M-1 s-1 at 25 C) or with the kinetically equivalent attack by water on uncharged methylguanidine. At 25 C and pH 7, N-methylguanidine is several orders of magnitude more stable than acetamidine, urea, or acetamide. Under the same conditions, the enzymes arginase and agmatinase accelerate substrate hydrolysis 4 × 1014-fold and 6 × 1012-fold, respectively, by mechanisms that appear to involve metal-mediated water attack. Arginine deiminase accelerates substrate hydrolysis 6 × 1012-fold by a mechanism that (in contrast to the mechanisms employed by arginase and agmatinase) is believed to involve attack by an active-site cysteine residue.
- Lewis, Charles A.,Wolfenden, Richard
-
supporting information
p. 130 - 136
(2014/01/23)
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- Synthesis and chemical and biological comparison of nitroxyl- and nitric oxide-releasing diazeniumdiolate-based aspirin derivatives
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Structural modifications of nonsteroidal anti-inflammatory drugs (NSAIDs) have successfully reduced the side effect of gastrointestinal ulceration without affecting anti-inflammatory activity, but they may increase the risk of myocardial infarction with chronic use. The fact that nitroxyl (HNO) reduces platelet aggregation, preconditions against myocardial infarction, and enhances contractility led us to synthesize a diazeniumdiolate-based HNO-releasing aspirin and to compare it to an NO-releasing analogue. Here, the decomposition mechanisms are described for these compounds. In addition to protection against stomach ulceration, these prodrugs exhibited significantly enhanced cytotoxcity compared to either aspirin or the parent diazeniumdiolate toward nonsmall cell lung carcinoma cells (A549), but they were not appreciably toxic toward endothelial cells (HUVECs). The HNO-NSAID prodrug inhibited cylcooxgenase-2 and glyceraldehyde 3-phosphate dehydrogenase activity and triggered significant sarcomere shortening on murine ventricular myocytes compared to control. Together, these anti-inflammatory, antineoplasic, and contractile properties suggest the potential of HNO-NSAIDs in the treatment of inflammation, cancer, or heart failure.
- Basudhar, Debashree,Bharadwaj, Gaurav,Cheng, Robert Y.,Jain, Sarthak,Shi, Sa,Heinecke, Julie L.,Holland, Ryan J.,Ridnour, Lisa A.,Caceres, Viviane M.,Spadari-Bratfisch, Regina C.,Paolocci, Nazareno,Velázquez-Martínez, Carlos A.,Wink, David A.,Miranda, Katrina M.
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supporting information
p. 7804 - 7820
(2013/11/06)
-
- Hydrolytic catalysis and structural stabilization in a designed metalloprotein
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Metal ions are an important part of many natural proteins, providing structural, catalytic and electron transfer functions. Reproducing these functions in a designed protein is the ultimate challenge to our understanding of them. Here, we present an artif
- Zastrow, Melissa L.,Peacock, Anna F. A.,Stuckey, Jeanne A.,Pecoraro, Vincent L.
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body text
p. 118 - 123
(2012/04/10)
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- Micellization and catalytic properties of cationic surfactants with head groups functionalized with a hydroxyalkyl fragment
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The catalytic activity of two homological series of cationic surfactants bearing a hydroxyalkyl fragment in the head groups R(CH3)2N+(CH2CH2OH)Br-and R(CH3)2N+/s
- Mirgorodskaya, Alla B.,Yackevich, Ekaterina I.,Syakaev, Victor V.,Zakharova, Lucia Ya.,Latypov, Shamil K.,Konovalov, Alexander I.
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p. 3153 - 3163
(2013/01/15)
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- The crystal structure of the cephalosporin deacetylating enzyme acetyl xylan esterase bound to paraoxon explains the low sensitivity of this serine hydrolase to organophosphate inactivation
-
Organophosphorus insecticides and nerve agents irreversibly inhibit serine hydrolase superfamily enzymes. One enzyme of this superfamily, the industrially important (for β-lactam antibiotic synthesis) AXE/CAH (acetyl xylan esterase/cephalosporin acetyl hy
- Montoro-Garcia, Silvia,Gil-Ortiz, Fernando,Garcia-Carmona, Francisco,Polo, Luis Mariano,Rubio, Vicente,Sanchez-Ferrer, Alvaro
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experimental part
p. 321 - 330
(2012/03/10)
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- Catalytic activity of enzyme in water/organic cosolvent mixtures for the hydrolysis of p-nitrophenyl acetate and p-nitrophenyl benzoate
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The dependence of the catalytic activities of α-chymotrypsin on the concentration of organic cosolvents (acetonitrile, dimethyl sulfoxide, dimethyl formamide, ethylene glycol, methanol, ethanol, propan-2-ol and tert-butanol) in mixed aqueous media has bee
- Verma, Santosh Kumar,Ghosh, Kallol K.
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experimental part
p. 1041 - 1046
(2011/01/10)
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- Osmium(VIII) catalysed and uncatalysed oxidation of aspirin drug by diperiodatocuprate(III) complex in aqueous alkaline medium: A mechanistic approach
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The kinetics of oxidation of a non-steroidal analgesic drug, aspirin (ASP) by diperiodatocuprate(III)(DPC) in the presence and absence of osmium(VIII) have been investigated at 298 K in alkaline medium at a constant ionic strength of 0.10 mol dm-3 spectrophotometrically. The reaction showed a first-order in [DPC] and less than unit order in [ASP] and [alkali] for both the osmium(VIII) catalysed and uncatalysed reactions. The order with respect to Os(VIII) concentration was unity. The effects of added products, ionic strength, periodate and dielectric constant have been studied. The stoichiometry of the reaction was found to be 1:4 (ASP:DPC) for both the cases. The main oxidation product of aspirin was identified by spot test, IR, NMR and GC-MS. The reaction constants involved in the different steps of the mechanisms were calculated for both reactions. Activation parameters with respect to slow step of the mechanisms were computed and discussed for both the cases. The thermodynamic quantities were also determined for both reactions. The catalytic constant (KC) was also calculated for catalysed reaction at different temperatures and the corresponding activation parameters were determined.
- Hosamani, Ragunatharaddi R.,Mahesh,Nandibewoor, Sharanappa T.
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scheme or table
p. 1443 - 1452
(2010/05/01)
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- Polyphenolic Bioprecursors
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Cosmetic and therapeutic, in particular dermatological bioprecursors have the formula [A]n—PP—[B]m wherein PP is a polyphenol radical in which each hydroxyl function is protected by a group A or a group B, A is a saturated or unsaturated, substituted or unsubstituted alkyl radical having 1 to 20 carbon atoms which is bonded to the polyphenol, n is an integer not less than 1, and B is a precursor of a biologically active molecule, which is also bonded to the polyphenol, and m is an integer also not less than 1.
- -
-
Page/Page column 9-10
(2009/09/07)
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- A study on a primitive artificial esterase model: Reactivity of a calix[4]resorcinarene bearing carboxyl groups
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The host molecule octacarboxymethyl calix[4]resorcinarene 1 catalyses the hydrolysis of substituted phenyl N-methylpyridinium-4-carboxylate esters 3a-f by complexation followed by intracomplex reaction via an anhydride intermediate. The reactivity in the
- Cevasco, Giorgio,Galatini, Andrea,Pirinccioglu, Necmettin,Thea, Sergio,Williams, Andrew
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scheme or table
p. 498 - 504
(2009/04/11)
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- Acid-base properties and nucleophilicity of o-aminomethylphenols in aqueous micellar solutions and microemulsions
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The pK a values and constants of tautomeric equilibrium of several o-aminomethylphenols with different hydrophilic-lipophilic ability were measured in aqueous micellar solutions and in direct microemulsions based on cetyltrimethylammonium bromi
- Mirgorodskaya,Erzikova,Kudryavtseva,Konovalov
-
p. 1788 - 1793
(2008/02/08)
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- The α-effect in micelles: Nucleophilic substitution reaction of p-nitrophenyl acetate with N-phenylbenzohydroxamate ion
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Pseudo-first-order rate constants have been determined for the nucleophilic substitution reactions of p-nitrophenyl acetate with p-chlorophenoxide (4-ClC6H4O-) and N-phenylbenzohydroxamate (C6H5CON(C
- Ghosh, Kallol K.,Vaidya, Jyoti,Satnami, Manmohan Lal
-
-
- Synthesis, structure and hydrolytic properties of a family of new Zn complexes containing hexaazamacrocyclic ligands
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The synthesis, structure and spectroscopic properties of a family of Zn complexes containing a dinucleating hexaazamacrocyclic ligand (L) and anionic ligands (X) of general formula [Zn2(X)4-n(L)]n+ (1-8; L = H2p, H3p, Me2p
- Costas, Miquel,Anda, Carmen,Llobet, Antoni,Parella, Teodor,Evans, Helen Stoeckli,Pinilla, Elena
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p. 857 - 865
(2007/10/03)
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- Influence of the structure of cetyltrimethylammonium bromide based microemulsions on base hydrolysis of carboxylic acid esters
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The structure of water/cetyltrimethylammonium bromide/n-butanol/hexane microemulsions was studied by conductometry, viscometry, and Fourier transform 1H NMR spectroscopy with pulse magnetic field gradient. The regions of phase inversion from in
- Zuev,Mirgorodskaya,Kudryavtseva,Idiyatullin,Khamidullin
-
p. 1051 - 1056
(2007/10/03)
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- Acyl vs Sulfonyl Transfer in N-Acyl β-Sultams and 3-Oxo-β-sultams
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(Matrix presented) N-Acylsulfonamides usually react with nucleophiles by acyl transfer and C-N bond fission. However, the hydrolysis of N-acyl β-sultams is a sulfonyl transfer reaction that occurs with S-N fission and opening of the four-membered ring. Similar to other β-sultams, the N-acyl derivatives are at least 106-fold more reactive than N-acyl sulfonamides. 3-Oxo-β-sultams are both β-lactams and β-sultams but also hydrolyze with preferential S-N bond fission.
- Ahmed, Naveed,Tsang, Wing Y.,Page, Michael I.
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p. 201 - 203
(2007/10/03)
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- The hydrolysis of an activated ester by a tris(4,5-di-n-propyl-2-imidazolyl)phosphine-Zn2+ complex in neutral micellar medium as a model for carbonic anhydrase
-
The properties of tris(4,5-di-n-propyl-2-imidazolyl)phosphine-M2+ complexes (3-M2+, M = Zn, Co) in neutral micellar media of Brij-35 and Triton X-100 have been studied in water with respect to their quantitative potentimetric titrati
- Koerner, Terry B.,Brown
-
p. 183 - 191
(2007/10/03)
-
- Nucleophilic substitution in carboxylic esters in oil-in-water microemulsions
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In hydrolysis and aminolysis of p-nitrophenyl esters of carboxylic acids in oil-in-water microemulsions on the basis of surfactants of various nature, a complex mechanism of the effect of the medium is operative, including shift of acid-base equilibria in the nucleophile. The rate constants of the processes studied are quantitatively related to the surface potential of the microdroplet. Varied hydrophobicity of the nucleophile and substrate changes the site of the reaction act and the relative contributions of aminolysis and hydrolysis.
- Mirgorodskaya,Kudryavtseva
-
p. 1261 - 1265
(2007/10/03)
-
- Nucleic acid triggered catalytic drug and probe release: A new concept for the design of chemotherapeutic and diagnostic agents
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Recently, we described a new concept for the design of highly selective antiviral and anticancer chemotherapeutic agents that makes use of a disease-specific nucleic acid sequence to template the association of a prodrug with a catalyst which catalyzes th
- Ma, Zhaochun,Taylor, John-Stephen
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p. 2501 - 2510
(2007/10/03)
-
- Origin of rate-acceleration in ester hydrolysis with metalloprotease mimics
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Mimics of carboxypeptidase A, a prototypical metalloprotease, were synthesized by linking macrocyclicpolyamines to the primary side of β-cyclodextrin followed by complexing with Zn(II). These enzyme mimics exhibit saturation kinetics in hydrolysis of p-ni
- Kim, Dong H.,Lee, Soo Suk
-
p. 647 - 652
(2007/10/03)
-
- Modelling of the periodic anaerobic baffled reactor (PABR) based on the retaining factor concept
-
The fact that the active biomass is continuously removed from the continuously stirred anaerobic digesters, leading to long retention times, has been overcome in a number of high rate systems based on immobilization of the active biomass, such as the Upflow Anaerobic Sludge Blanket Reactor (UASBR) and the Anaerobic Baffled Reactor (ABR). A kinetic model of glucose consumption, which was developed based on a batch kinetic experiment, was used for the development of a dynamic model for the prediction of the behaviour of the recently developed flexible reactor called the Periodic Anaerobic Baffled Reactor (PABR). The PABR may be operated as a UASBR, an ABR or at an intermediate mode. The key assumption of the model is that the hydraulic behaviour of a PABR is equivalent with the behaviour of CSTRs in series as concerning the dissolved matter, whereas the biomass is allowed to be retained in the PABR through a retention factor accounting for precipitation. The model adequately predicted the experimental behaviour of a glucose fed PABR. The model was subsequently used to examine the behaviour of the PABR as a function of operating conditions, both for constant and varying loading rates. It was shown that for different cases, the reactor should best be operated as a UASBR or as an ABR. The fact that the active biomass is continuously removed from the continuously stirred anaerobic digesters, leading to long retention times, has been overcome in a number of high rate systems based on immobilisation of the active biomass, such as the Upflow Anaerobic Sludge Blanket Reactor (UASBR) and the Anaerobic Baffled Reactor (ABR). A kinetic model of glucose consumption, which was developed based on a batch kinetic experiment, was used for the development of a dynamic model for the prediction of the behaviour of the recently developed flexible reactor called the Periodic Anaerobic Baffled Reactor (PABR) [(1998) Wat. Sci. Technol. 38(8-9), 401- 408]. The PABR may be operated as a UASBR, an ABR or at an intermediate mode. The key assumption of the model is that the hydraulic behaviour of a PABR is equivalent with the behaviour of CSTRs in series as concerning the dissolved matter, whereas the biomass is allowed to be retained in the PABR through a retention factor accounting for precipitation. The model adequately predicted the experimental behaviour of a glucose fed PABR. The model was subsequently used to examine the behaviour of the PABR as a function of operating conditions, both for constant and varying loading rates. It was shown that for different cases, the reactor should best be operated as a UASBR or as an ABR. (C) 2000 Elsevier Science Ltd.
- Skiadas,Gavala,Lyberatos
-
p. 3725 - 3736
(2007/10/03)
-
- Formation of interim by-products in methanogenic degradation of butyrate
-
The formation of interim by-products during the methanogenic degradation of butyrate was monitored and analyzed in this study. Two series of experiments were conducted at various butyrate concentrations and under the influence of increased partial pressur
- Fang, Herbert H. P.,Jia, Xiao-Shan
-
p. 1791 - 1798
(2007/10/03)
-
- Hydrogen bonding in anion recognition: A family of versatile, nonpreorganized neutral and acyclic receptors
-
The diamides and disulfonamides m-C6H4(CONHAr)2 (Ar = Ph, 1; p-n-BuC6H4, 2, 2,4,6-Me3C6H2, 3), m-C6H4(SO2NHPh)2, 4, and 2,6
- Kavallieratos, Konstantinos,Bertao, Christina M.,Crabtree, Robert H.
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p. 1675 - 1683
(2007/10/03)
-
- Stability of 1:1 and 2:1 α-cyclodextrin-p-nitrophenyl acetate complexes and the effect of α-cyclodextrin on acyl transfer to peroxide anion nucleophiles
-
The presence of a rate maximum rather than simple saturation-type kinetics in a study of the effect of α-cyclodextrin on the hydrolysis of p-nitrophenyl acetate (PNPA) indicates that α-cyclodextrin forms not only 1:1 but also 2:1 complexes with PNPA. This is confirmed using a spectrophotometric method to determine binding constants directly for PNPA, giving values of 46 ± 9 and 66 ± 19 dm3 mol-1 for the first and second binding steps respectively. These results contradict the majority of literature studies of this reaction in which it is assumed that only a 1:1 complex is formed. Formation of a 1 :1 complex with cyclodextrin increases the reactivity of PNPA towards hydrolysis, as has been widely reported, whereas the addition of a second cyclodextrin molecule to the complex results in the PNPA taking up a less reactive configuration. The effect of α-cyclodextrin on the reaction between PNPA and the anions of hydrogen peroxide, peroxomonosulfate, peracetic acid, perbenzoic acid, 4-methylperbenzoic acid, 4-nitroperbenzoic acid, 4-sulfonatoperbenzoic acid, 3-chloroperbenzoic acid and 4-tert-butylperbenzoic acid is described. Linear free energy studies for transition state stabilisation of the reaction by one molecule of cyclodextrin reveal that the main pathway involves the bound PNPA reacting with free peroxide anions, although for m-chloroperbenzoic acid an alternative pathway may be significant. This is in contrast to the behaviour observed for the α-cyclodextrin-mediated reaction of the molecular acid form of these peroxides with a series of aryl alkyl sulfides in which the main pathway involves nucleophilic attack of the free sulfide on the cyclodextrin-peracid complex. With the exception of the m-chloroperbenzoic acid anion there is no evidence of transition state stabilisation of the title reaction by two molecules of cyclodextrin.
- Davies, D. Martin,Deary, Michael E.
-
p. 1027 - 1034
(2007/10/03)
-
- Molecular recognition by natural macrocycles. Part II. Esterolytic activity and chiral discrimination of amino acid derivatives by the zwitterionic form of (+)-tubocurarine
-
The esterase and complexation properties of the zwitterionic form of a macrocyclic alkaloid (+)-tubocurarine possessing two phenolic nucleophilic groups are described. Cleavage of 4-nitrophenyl esters of N-protected phenylalanine enantiomers involves reac
- Godoy-Alcantar, Carolina,Nelen, Marina I.,Eliseev, Alexey V.,Yatsimirsky, Anatoly K.
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p. 353 - 361
(2007/10/03)
-
- Zn2+ inclusion complexes of endodentate tripodands as carbonic anhydrase-inspired artificial esterases. Part 2. Micellar systems
-
Facile syntheses of two lipophilic, endo-tridentate tris-imidazole podands (3 and 4) are reported. These were designed for micellar media, where pre-organization for metal binding was anticipated to better reproduce the active site of carbonic anhydrase (
- Jairam, Rick,Potvin, Pierre G.,Balsky, Steven
-
p. 363 - 367
(2007/10/03)
-
- Dissection of Nucleophilic and General Base Roles for the Reaction of Phosphate with p-Nitrophenyl Thiolacetate, p-Nitrophenyl Thiolformate, and Phenyl Thiolacetate
-
Phosphate buffers are well-known to catalyze the decomposition of various active acyl compounds. This study was undertaken to determine the extent to which it acts as a nucleophile and general base toward some activated esters and thiolesters. Thus, the hydrolyses of p-nitrophenyl acetate (3a), p-nitrophenyl thiolacetate (3b), phenyl acetate (4a), phenyl thiolacetate (4b), and p-nitrophenyl thiolformate (5) have been studied in aqueous phosphate, μ = 1.0 (K2SO4). Both phosphate monoanion and dianion are reactive toward the thiolesters 3b, 4b, and 5. For 3b, reaction of the dianion exhibits a solvent kinetic isotope effect (SKIE) of 1.00 ± 0.11 while that for the monoanion is 2.13 plusmn; 1.1. For the reaction of phosphate dianion with 5, the SKIE is 0.8 ± 0.2 and that for the monoanion at pH 3.05 is roughly 1.5. Phosphate dianion reacts with each thiolacetate and its oxygen analogue at comparable rates: the reactivity ratio of the formyl to acetyl thiolesters, 5:3b, toward phosphate dianion is 685. 1H NMR analysis of the 3b hydrolysis mixtures in H2O and D2O containing phosphate shows the transient formation, and subsequent hydrolysis, of acetyl phosphate. Analysis of the kinetics of these processes indicates that in H2O at pH = 8.5, phosphate dianion functions as both a nucleophile and general base toward 3b, the nucleophilic role comprising 80-93% of the reaction. In D2O, the process is entirely nucleophilic. For the reaction of phosphate dianion with 4b, the 1H NMR analysis indicates that the nucleophilic role comprises 40-50% of the reaction, the general base role being 50-60%. The reaction of phosphate dianion with 5 is entirely nucleophilic, while the monoanion reacts as a general base. The data are interpreted in terms of standard carbonyl addition/elimination mechanisms in which the ability of the attacking phosphate di- or monoanion to displace a given leaving group is tied to the pKa of the conjugate acids of the nucleophile and leaving groups.
- Gill, Manjinder S.,Neverov, Alexei A.,Brown
-
p. 7351 - 7357
(2007/10/03)
-