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https://www.readbyqxmd.com/read/28937164/a-capped-trigonal-pyramidal-molybdenum-hydrido-complex-and-an-unusually-mild-sulfur-carbon-bond-cleavage-reaction
#1
Robert H Morris
DFT calculations reveal that a reported molybdenum hydride complex has an unprecedented geometry with the molybdenum in the base of trigonal pyramid defined by three thiolate ligands with a phosphine ligand on the apex and a hydride capping a PS2 face. This complex reacts with methanol to produce a sulfido complex by a new reaction: the protonation of an ipso carbon of a thiolate ligand by coordinated methanol.
September 22, 2017: Chemical Communications: Chem Comm
https://www.readbyqxmd.com/read/28934505/combining-asymmetric-13c-labeling-and-isotopic-filter-edit-noesy-a-novel-strategy-for-rapid-and-logical-rna-resonance-assignment
#2
Regan M LeBlanc, Andrew P Longhini, Stuart F J Le Grice, Bruce A Johnson, Theodore K Dayie
Although ∼98% of the human genomic output is transcribed as non-protein coding RNA, <2% of the protein data bank structures comprise RNA. This huge structural disparity stems from combined difficulties of crystallizing RNA for X-ray crystallography along with extensive chemical shift overlap and broadened linewidths associated with NMR of RNA. While half of the deposited RNA structures in the PDB were solved by NMR methods, the usefulness of NMR is still limited by the high cost of sample preparation and challenges of resonance assignment...
September 19, 2017: Nucleic Acids Research
https://www.readbyqxmd.com/read/28926956/carbonic-anhydrase-inhibition-and-the-management-of-hypoxic-tumors
#3
REVIEW
Claudiu T Supuran
Hypoxia and acidosis are salient features of many tumors, leading to a completely different metabolism compared to normal cells. Two of the simplest metabolic products, protons and bicarbonate, are generated by the catalytic activity of the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1), with at least two of its isoforms, CA IX and XII, mainly present in hypoxic tumors. Inhibition of tumor-associated CAs leads to an impaired growth of the primary tumors, metastases and reduces the population of cancer stem cells, leading thus to a complex and beneficial anticancer action for this class of enzyme inhibitors...
September 16, 2017: Metabolites
https://www.readbyqxmd.com/read/28919881/genomic-and-transcriptomic-analysis-of-growth-supporting-dehalogenation-of-chlorinated-methanes-in-methylobacterium
#4
Pauline Chaignaud, Bruno Maucourt, Marion Weiman, Adriana Alberti, Steffen Kolb, Stéphane Cruveiller, Stéphane Vuilleumier, Françoise Bringel
Bacterial adaptation to growth with toxic halogenated chemicals was explored in the context of methylotrophic metabolism of Methylobacterium extorquens, by comparing strains CM4 and DM4, which show robust growth with chloromethane and dichloromethane, respectively. Dehalogenation of chlorinated methanes initiates growth-supporting degradation, with intracellular release of protons and chloride ions in both cases. The core, variable and strain-specific genomes of strains CM4 and DM4 were defined by comparison with genomes of non-dechlorinating strains...
2017: Frontiers in Microbiology
https://www.readbyqxmd.com/read/28919500/hydrogen-and-oxygen-trapping-at-the-h-cluster-of-fefe-%C3%A2-hydrogenase-revealed-by-site-selective-spectroscopy-and-qm-mm-calculations
#5
Stefan Mebs, Ramona Kositzki, Jifu Duan, Moritz Senger, Florian Wittkamp, Ulf-Peter Apfel, Thomas Happe, Sven T Stripp, Martin Winkler, Michael Haumann
[FeFe]‑hydrogenases are superior hydrogen conversion catalysts. They bind a cofactor (H-cluster) comprising a four‑iron and a diiron unit with three carbon monoxide (CO) and two cyanide (CN(-)) ligands. Hydrogen (H2) and oxygen (O2) binding at the H-cluster was studied in the C169A variant of [FeFe]‑hydrogenase HYDA1, in comparison to the active oxidized (Hox) and CO-inhibited (Hox-CO) species in wildtype enzyme. (57)Fe labeling of the diiron site was achieved by in vitro maturation with a synthetic cofactor analogue...
September 14, 2017: Biochimica et Biophysica Acta
https://www.readbyqxmd.com/read/28918686/sensitivity-of-post-treatment-positron-emission-tomography-computed-tomography-to-detect-inter-fractional-range-variations-in-scanned-ion-beam-therapy
#6
Josefine Handrack, Thomas Tessonnier, Wenjing Chen, Jakob Liebl, Jürgen Debus, Julia Bauer, Katia Parodi
BACKGROUND: Ion therapy, especially with modern scanning beam delivery, offers very sharp dose gradients for highly conformal cancer treatment. However, it is very sensitive to uncertainties of tissue stopping properties as well as to anatomical changes and setup errors, making range verification highly desirable. To this end, positron emission tomography (PET) can be used to measure decay products of β(+)-emitters created in interactions inside the patient. This work investigates the sensitivity of post treatment PET/CT (computed tomography) to detect inter-fractional range variations...
September 18, 2017: Acta Oncologica
https://www.readbyqxmd.com/read/28917800/%C3%AE-cyclodextrins-incorporated-multi-walled-carbon-nanotubes-modified-electrode-for-the-voltammetric-determination-of-the-pesticide-dichlorophen
#7
Karolina Sipa, Mariola Brycht, Andrzej Leniart, Paweł Urbaniak, Agnieszka Nosal-Wiercińska, Bartłomiej Pałecz, Sławomira Skrzypek
In this work, a glassy carbon electrode modified with β-cyclodextrins and multi-walled carbon nanotubes (β-CDs/MWCNTs/GCE) was constructed and applied for the square-wave adsorptive stripping voltammetric (SWAdSV) determination of the pesticide dichlorophen (Dcp). For the first time, this compound was electrochemically investigated. The voltammetric measurements were conducted in phosphate buffer (PBS) at pH 6.5 as a supporting electrolyte, and SWAdSV technique parameters were optimized. A linear calibration curve in the wide concentration range from 5...
January 1, 2018: Talanta
https://www.readbyqxmd.com/read/28916461/metabolic-engineering-of-escherichia-coli-for-the-synthesis-of-the-quadripolymer-poly-glycolate-co-lactate-co-3-hydroxybutyrate-co-4-hydroxybutyrate-from-glucose
#8
Zheng-Jun Li, Kangjian Qiao, Xue-Mei Che, Gregory Stephanopoulos
Escherichia coli was metabolically engineered to effectively produce a series of biopolymers consisted of four types of monomers including glycolate, lactate, 3-hydroxybutyrate and 4-hydroxybutyrate from glucose as the carbon source. The biosynthetic route of novel quadripolymers was achieved by the overexpression of a range of homologous and heterologous enzymes including isocitrate lyase, isocitrate dehydrogenase kinase/phosphatase, glyoxylate/hydroxypyruvate reductase, propionyl-CoA transferase, β-ketothiolase, acetoacetyl-CoA reductase, succinate semialdehyde dehydrogenase, 4-hydroxybutyrate dehydrogenase, CoA transferase and PHA synthase...
September 13, 2017: Metabolic Engineering
https://www.readbyqxmd.com/read/28911223/direct-sampling-and-analysis-of-atmospheric-particulate-organic-matter-by-proton-transfer-reaction-mass-spectrometry
#9
Markus Muller, Philipp Eichler, Barbara D'Anna, Wen Tan, Armin Wisthaler
We report on a new method for analyzing atmospheric submicrometer particulate organic matter which combines direct particle sampling and volatilization with on-line chemical ionization mass spectrometric analysis. Technically, the method relies on the combined use of a CHARON ("Chemical Analysis of Aerosol On-line") particle inlet and a proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS). Laboratory studies on target analytes showed that the ionization conditions in the PTR-ToF-MS lead to extensive fragmentation of levoglucosan and cis-pinonic acid, while protonated oleic acid and 5-cholestane molecules remain intact...
September 15, 2017: Analytical Chemistry
https://www.readbyqxmd.com/read/28911056/carbon-concentrating-mechanisms-in-seagrasses
#10
Anthony William D Larkum, Peter A Davey, John Kuo, Peter J Ralph, John A Raven
Seagrasses are unique angiosperms that carry out growth and reproduction submerged in seawater. They occur in at least three families of the Alismatales. All have chloroplasts mainly in the cells of the epidermis. Living in seawater, the supply of inorganic carbon (Ci) to the chloroplasts is diffusion limited, especially under unstirred conditions. Therefore, the supply of CO2 and bicarbonate across the diffusive boundary layer on the outer side of the epidermis is often a limiting factor. Here we discuss the evidence for mechanisms that enhance the uptake of Ci into the epidermal cells...
June 1, 2017: Journal of Experimental Botany
https://www.readbyqxmd.com/read/28911053/co-ordination-of-ndh-and-cup-proteins-in-co2-uptake-in-cyanobacterium-synechocystis-sp-pcc-6803
#11
Xunling Han, Nan Sun, Min Xu, Hualing Mi
High and low affinity CO2-uptake systems containing CupA (NDH-1MS) and CupB (NDH-1MS'), respectively, have been identified in Synechocystis sp. PCC 6803, but it is yet unknown how the complexes function in CO2 uptake. In this work, we found that deletion of cupB significantly lowered the growth of cells, and deletion of both cupA and cupB seriously suppressed the growth below pH 7.0 even under 3% CO2. The rate of photosynthetic oxygen evolution was decreased slightly by deletion of cupA but significantly by deletion of cupB and more severely by deletion of both cupA and cupB, especially in response to changed pH conditions under 3% CO2...
June 1, 2017: Journal of Experimental Botany
https://www.readbyqxmd.com/read/28901758/single-atomic-iron-catalysts-for-oxygen-reduction-in-acidic-media-particle-size-control-and-thermal-activation
#12
Hanguang Zhang, Sooyeon Hwang, Maoyu Wang, Zhenxing Feng, Stavros Karakalos, Langli Luo, Zhi Qiao, Xiaohong Xie, Chongmin Wang, Dong Su, Yuyan Shao, Gang Wu
It remains a grand challenge to replace platinum group metal (PGM) catalysts with earth abundant materials for the oxygen reduction reaction (ORR) in acidic media, which is crucial for large-scale deployment of proton exchange membrane fuel cells (PEMFCs). Here, we report a high-performance atomic Fe catalyst derived from chemically Fe-doped zeolitic imidazo-late frameworks (ZIFs) by directly bonding Fe ions to imidazolate ligands within 3D frameworks. Although the ZIF was iden-tified as a promising precursor, the new synthetic chemistry enables well-dispersed atomic Fe sites embedded into porous carbon without the formation of aggregates...
September 13, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28895649/enhanced-trace-co2-capture-on-heteroatom-substituted-rho-zeolites-under-humid-conditions
#13
Quan-Li Ke, Tian-Jun Sun, Xiao-Li Wei, Ya Guo, Shu-Dong Wang
In this paper, boron and copper heteroatoms were successfully incorporated into the frameworks of high-silica RHO zeolite by adopting a bulky alkali metal-crown ether (AMCE) complex as the template. As a consequence, these heteroatom-doped zeolites show both larger micropore surface areas and volumes than those of their aluminosilicate analogue. Proton-type RHO zeolites were then applied for separation of CO2 / CH4 / N2 mixtures so as to weaken the electric field of these zeolites and then decrease the adsorption heat...
September 12, 2017: ChemSusChem
https://www.readbyqxmd.com/read/28892610/catalysis-and-inhibition-in-the-electrochemical-reduction-of-co2-on-platinum-in-the-presence-protonated-pyridine-new-insights-into-mechanisms-and-products
#14
Hachem Dridi, Clement Comminges, Cláudia Morais, Jean-Claude Meledje, Kouakou Boniface Kokoh, Cyrille Costentin, Jean-Michel Savéant
In the framework of modern energy challenges, the reduction of CO2 into fuels widely call to electrogenerated low-valent transition metal complexes catalystsdesigned with considerable ingenuity and sophistication. For this reason, the report that a molecule as simple as protonated pyridine (PyH+) could catalyze the formation of methanol from the reduction of CO2 on a platinum electrode triggered great interest and excitement. Further synthetic and mechanistic investigations reveal that no methanol is produced...
September 11, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28892349/a-proton-conducting-la-doped-ceria-based-internal-reforming-layer-for-direct-methane-solid-oxide-fuel-cells
#15
Jie Zhao, Xiaoyong Xu, Wei Zhou, Idriss Blakey, Shaomin Liu, Zhonghua Zhu
Performance degradation caused by carbon deposition substantially restricts the development of direct methane solid oxide fuel cells (SOFCs). Here, an internal reforming layer composed of Ni supported on proton conducting La-doped ceria such as La2Ce2O7 (LDC) and La1.95Sm0.05Ce2O7 (LSDC) is applied over conventional Ni-Ce0.8Sm0.2O2-x (SDC) anodes for direct methane SOFCs. The proton conducting layer can adsorb water for internal reforming thus significantly improving the performance of the direct methane SOFCs...
September 11, 2017: ACS Applied Materials & Interfaces
https://www.readbyqxmd.com/read/28891968/biogenetic-relationships-of-bioactive-sponge-merotriterpenoids
#16
REVIEW
Thomas E Smith
Hydroquinone meroterpenoids, especially those derived from marine sponges, display a wide range of biological activities. However, use of these compounds is limited by their inaccessibility; there is no sustainable supply of these compounds. Furthermore, our knowledge of their metabolic origin remains completely unstudied. In this review, an in depth structural analysis of sponge merotriterpenoids, including the adociasulfate family of kinesin motor protein inhibitors, provides insight into their biosynthesis...
September 10, 2017: Marine Drugs
https://www.readbyqxmd.com/read/28889056/voltammetric-behavior-of-mammeisin-ma-at-a-glassy-carbon-electrode-and-its-interaction-with-bovine-serum-albumin-bsa
#17
Jules-Blaise Mabou Leuna, Sergeot Kungo Sop, Suzanne Makota, Evangeline Njanja, Thiery Christophe Ebelle, Anatole Guy Azebaze, Emmanuel Ngameni, Achille Nassi
The electrochemical oxidation of Mammeisin (MA) was studied in a solution containing acetone and 0.1M phosphate buffer +0.1M KCl (pH=5.3) at a glassy carbon electrode (GCE), using cyclic (CV) and square wave voltammetry (SWV). MA showed a quasi-reversible process, which is pH dependent and that involves the exchange of two electrons and two protons. The oxidation product was adsorbed by the electrode surface to form a film that blocks active sites over repetitive cyclic. Moreover, the interaction of MA and bovine serum albumin (BSA) was studied by CV and SWV at different pHs (5...
September 7, 2017: Bioelectrochemistry
https://www.readbyqxmd.com/read/28886211/homogeneity-study-of-proton-and-carbon-ion-scanning-beams-using-combinations-of-different-spot-sizes-and-grid-sizes
#18
Ying Xing, Xianwei Wu, Yongqiang Li, Jun Zhao
PURPOSE: Different scanning ion beam delivery systems have different delivery accuracies, and the resulting delivery errors will affect field homogeneity. This study was performed to determine an appropriate combination of spot size (FWHM) and spot grid size (GS), which can provide homogenous dose distributions for both proton and carbon ion scanning beam radiotherapy. The combination of the two parameters is represented by a combination factor named n, which is the quotient of FWHM divided by GS...
September 8, 2017: Medical Physics
https://www.readbyqxmd.com/read/28884175/protonation-reduction-dynamics-at-the-4fe-4s-cluster-of-the-hydrogen-forming-cofactor-in-fefe-hydrogenases
#19
Moritz Senger, Stefan Mebs, Jifu Duan, Olga Shulenina, Konstantin Laun, Leonie Kertess, Florian Wittkamp, Ulf-Peter Apfel, Thomas Happe, Martin Winkler, Michael Haumann, Sven T Stripp
The [FeFe]-hydrogenases of bacteria and algae are the most efficient hydrogen conversion catalysts in nature. Their active-site cofactor (H-cluster) comprises a [4Fe-4S] cluster linked to a unique diiron site that binds three carbon monoxide (CO) and two cyanide (CN(-)) ligands. Understanding microbial hydrogen conversion requires elucidation of the interplay of proton and electron transfer events at the H-cluster. We performed real-time spectroscopy on [FeFe]-hydrogenase protein films under controlled variation of atmospheric gas composition, sample pH, and reductant concentration...
September 8, 2017: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/28883414/a-general-mechanistic-model-enables-predictions-of-the-biological-effectiveness-of-different-qualities-of-radiation
#20
Stephen J McMahon, Aimee L McNamara, Jan Schuemann, Harald Paganetti, Kevin M Prise
Predicting the responses of biological systems to ionising radiation is extremely challenging, particularly when comparing X-rays and heavy charged particles, due to the uncertainty in their Relative Biological Effectiveness (RBE). Here we assess the power of a novel mechanistic model of DNA damage repair to predict the sensitivity of cells to X-ray, proton or carbon ion exposures in vitro against over 800 published experiments. By specifying the phenotypic characteristics of cells, the model was able to effectively stratify X-ray radiosensitivity (R (2) = 0...
September 7, 2017: Scientific Reports
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