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Xin Yu, Wei Li, Jian Huang, Zhonghua Li, Jiawen Liu, PingAn Hu
Superstructured mesocrystalline Ta2O5 nanosheets were successfully prepared from mesocrystalline (NH4)2Ta2O3F6 nanorods by the annealing method for the first time. The as-prepared mesocrystalline Ta2O5 nanosheets in this work showed remarkable visible light absorption, mainly due to the formation of oxygen vacancy defects in the mesocrystalline Ta2O5 nanosheets, which was also confirmed by XPS spectra, Raman spectra and EPR spectra. Besides, the mesocrystalline Ta2O5 nanosheets showed a highly enhanced photocatalytic activity of 11 268...
January 18, 2018: Dalton Transactions: An International Journal of Inorganic Chemistry
Max M Hansmann, Mohand Melaimi, Guy Bertrand
Readily available room temperature stable organic mixed valence compounds are prepared by one-electron reduction of cyclic bis(iminium) salts [derived from cyclic (alkyl)(amino)carbenes] bridged by various spacers. These compounds show characteristic intervalence charge transfer (IV-CT) bands in the near-infrared (NIR). Cyclic voltammetry, EPR, IR, UV-VIS and X-ray studies, as well as DFT calculations, show that depending on the nature of the spacer, these mixed valence compounds range from class III to borderline class I/II...
January 17, 2018: Journal of the American Chemical Society
Victoria N Syryamina, Marta De Zotti, Claudio Toniolo, Fernando Formaggio, Sergei A Dzuba
The antimicrobial action of the peptide antibiotic alamethicin (Alm) is commonly related to peptide self-assembling resulting in the formation of voltage-dependent channels in bacterial membranes, which induces ion permeation. To obtain a deeper insight into the mechanism of channel formation, it is useful to know the dependence of self-assembling on peptide concentration. With this aim, we studied Alm F50/5 spin-labeled analogs in a model 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) membrane, for peptide-to-lipid (P/L) ratios varying between 1/1500 and 1/100...
January 17, 2018: Physical Chemistry Chemical Physics: PCCP
Jessica Sarver, Michael Zhang, Lishan Liu, David Nyenhuis, David S Cafiso
Bacterial outer membrane TonB-dependent transporters function by executing cycles of binding and unbinding to the inner membrane protein TonB. In the vitamin B12 transporter BtuB and the ferric citrate transporter FecA, substrate binding increases the periplasmic exposure of the Ton box, an energy-coupling segment. This increased exposure appears to enhance the affinity of the transporter for TonB. Here, continuous wave and pulse EPR spectroscopy were used to examine the state of the Ton box in the Escherichia coli ferrichrome transporter, FhuA...
January 17, 2018: Biochemistry
Salen Kuresepi, Bertrand Vileno, Philippe Turek, Jean-Pierre Lepoittevin, Elena Giménez-Arnau
The first step in the development of skin sensitisation to a chemical, and in the elicitation of further allergic contact dermatitis (ACD), is the binding of the allergen to skin proteins after penetrating into the epidermis. The so-formed antigenic adduct is then recognised by the immune system as foreign to the body. Sensitising organic hydroperoxides derived from autoxidation of natural terpenes are believed to form antigens through radical-mediated mechanisms, although this has not yet been established...
January 15, 2018: Free Radical Research
Paul Kaufmann, Benjamin R Duffus, Biljana Mitrova, Chantal Iobbi-Nivol, Christian Teutloff, Manfred Nimtz, Lothar Jänsch, Ulla Wollenberger, Silke Leimkühler
The well-studied enterobacterium Escherichia coli present in the human gut is able to reduce TMAO to trimethylamine (TMA) during anaerobic respiration. The TMAO reductase TorA is a monomeric, bis-molybdopterin guanine dinucleotide (bis-MGD) cofactor-containing enzyme belonging to the dimethylsulfoxide (DMSO) reductase family of molybdoenzymes. We report on a system for the in vitro reconstitution of TorA with molybdenum cofactors (Moco) from different sources. Higher TMAO reductase activities for TorA were obtained when using Moco-sources containing a sulfido ligand at the molybdenum atom...
January 15, 2018: Biochemistry
Livia S Meszaros, Brigitta Nemeth, Charlene Esmieu, Pierre Ceccaldi, Gustav Berggren
EPR spectroscopy reveals the formation of two different semi-synthetic hydrogenases in vivo. [FeFe] hydrogenases are metalloenzymes that catalyse the interconversion of molecular hydrogen and protons. The reaction is catalyzed by the H-cluster, consisting of a canonical iron-sulfur cluster and an organometallic [2Fe] subsite. It was recently shown how the enzyme can be reconstituted with synthetic cofactors mimicking the composition of the [2Fe] subsite, resulting in semi-synthetic hydrogenases. Here we employ EPR spectroscopy to monitor the formation of two such semi-synthetic enzymes in whole cells...
January 15, 2018: Angewandte Chemie
Xun Liu, Jingxing Si, Qianzhi Zhang, Qian Huang, Danxia Gu, Hao Yang, Xu Chen, Youqing Shen, Meihua Sui
The enhanced permeability and retention (EPR) effect of tumors is much more complex than initially defined, and it alone is not sufficient for targeted delivery of nanosized agents. Meanwhile, poor tumor penetration is another major challenge for the treatment of solid tumors using nanoparticles. Development of delivery systems for SN38, the active metabolite of CPT-11 in human and a very potent anticancer molecule, has become an attractive research area. PEGx -p(HEMASN38)y (x and y are viable), a prodrug synthesized by using polyethylene glycol (PEG) as initiator and SN38 as monomer through atom transfer radical polymeration (ATRP) method, is previously reported...
January 15, 2018: Advanced Healthcare Materials
Kathryn M Schultz, Candice S Klug
The use of pressure is an advantageous approach to the study of protein structure and dynamics because it can shift the equilibrium populations of protein conformations toward higher energy states that are not of sufficient population to be observable at atmospheric pressure. Recently, the Hubbell group at the University of California, Los Angeles, reintroduced the application of high pressure to the study of proteins by electron paramagnetic resonance (EPR) spectroscopy. This methodology is possible using X-band EPR spectroscopy due to advances in pressure intensifiers, sample cells, and resonators...
December 2017: Applied Magnetic Resonance
James S Hyde, Richard R Mett
The dielectric tube resonator (DTR) for EPR spectroscopy is introduced. It is defined as a metallic cylindrical TE011 microwave cavity that contains a dielectric tube centered on the axis of the cylinder. Contour plots of dimensions of the metallic cylinder to achieve resonance at 9.5 GHz are shown for quartz, sapphire, and rutile tubes as a function of wall thickness and average radius. These contour plots were developed using analytical equations and confirmed by finite element modeling. They can be used in two ways: design of the metallic cylinder for use at 9...
December 2017: Applied Magnetic Resonance
Jevgenij Kusakovskij, Kwinten Maes, Freddy Callens, Henk Vrielinck
The electron paramagnetic resonance (EPR) spectra of radiation-induced radicals in organic solids are generally composed of multiple components that largely overlap due to their similar weak g anisotropy and a large number of hyperfine (HF) interactions. Such properties make these systems difficult to study using standard cw EPR spectroscopy even in single crystals. Electron-nuclear double resonance (ENDOR) spectroscopy is a powerful and widely used complementary technique. In particular, ENDOR-induced EPR (EIE) experiments are useful for separating the overlapping contributions...
January 14, 2018: Journal of Physical Chemistry. A
Hiroki Makita, Gary Hastings
Time-resolved FTIR difference spectroscopy has been used to study photosystem I (PSI) particles with three different benzoquinones [plastoquinone-9 (PQ), 2,6-dimethyl-1,4-benzoquinone (DMBQ), 2,3,5,6-tetrachloro-1,4-benzoquinone (Cl4BQ)] incorporated into the A1 binding site. If PSI samples are cooled in the dark to 77 K, the incorporated benzoquinones are shown to be functional, allowing the production of time-resolved (P700+A1--P700A1) FTIR difference spectra. If samples are subjected to repetitive flash illumination at room temperature prior to cooling, however, the time-resolved FTIR difference spectra at 77 K display contributions typical of the P700 triplet state (3P700), indicating a loss of functionality of the incorporated benzoquinones, that occurs because of double protonation of the incorporated benzoquinones...
January 13, 2018: Photosynthesis Research
Justyna Polak, Mariola Bartoszek
A new equation for converting EC50 into TEAC values and TEAC into EC50 is presented in this paper. The model was fitted to 180 data points of electron paramagnetic resonance (EPR) spectroscopy measurements of various food products. The model was tested basing on 75 EPR spectroscopy measurements. Moreover, the equation was tested on literature data. The determination coefficient between EC50cal and EC50exp was found to be R2 = 0.9762, while the determination coefficient between TEACcal and TEACexp was found to be R2 = 0...
May 15, 2018: Food Chemistry
Olga A Zakurdaeva, Sergey V Nesterov, Natalya A Sokolova, Pavel V Dorovatovskii, Yan V Zubavichus, Victor N Khrustalev, Andrey F Asachenko, Gleb A Chesnokov, Mikhail Sergeevich Nechaev, Vladimir I Feldman
Ionic Liquid/Crown Ether compositions are an attractive alternative to traditional extractants in the processes for spent nuclear fuel and liquid radioactive wastes reprocessing. These compositions are exposed to ionizing radiation, and their radiation stability, especially in the presence of metal salts, is a crucial issue. In the present study, the macrocyclic 18C6·Sr(BF4)2 and 18C6·Sr(PF6)2 complexes simulating the components of metal loaded Ionic Liquid/Crown Ether extractants were synthesized and their structures were characterized by FTIR spectroscopy and single-crystal X-ray diffraction analysis...
January 12, 2018: Journal of Physical Chemistry. B
Peter C E Moody, Emma L Raven
Aerobic organisms have evolved to activate oxygen from the atmosphere, which allows them to catalyze the oxidation of different kinds of substrates. This activation of oxygen is achieved by a metal center (usually iron or copper) buried within a metalloprotein. In the case of iron-containing heme enzymes, the activation of oxygen is achieved by formation of transient iron-oxo (ferryl) intermediates; these intermediates are called Compound I and Compound II. The Compound I and II intermediates were first discovered in the 1930s in horseradish peroxidase, and it is now known that these same species are used across the family of heme enzymes, which include all of the peroxidases, the heme catalases, the P450s, cytochrome c oxidase, and NO synthase...
January 12, 2018: Accounts of Chemical Research
A Kharchenko, V Zholobenko, A Vicente, C Fernandez, H Vezin, V De Waele, S Mintova
The state of copper species stabilized in nanosized LTL zeolite subjected to various post-synthesis treatments was unveiled by a range of spectroscopic techniques. FTIR and UV-Vis studies demonstrated that the reduction process of copper in the LTL nanosized zeolite leads to the formation of different species including Cu2+, Cu+ and Cu nanoparticles (Cu NPs). The adsorption of probe molecules (NO and CO) was used to selectively monitor the copper species in the LTL nanosized zeolite upon oxidation and reduction post-synthesis treatments...
January 12, 2018: Physical Chemistry Chemical Physics: PCCP
Dnyaneshwar B Gophane, Burkhard Endeward, Thomas F Prisner, Snorri Th Sigurdsson
A new isoindoline-derived benzimidazole nitroxide spin label, ImUm, was synthesized and incorporated into RNA oligoribonucleotides. ImUm is the first example of a conformationally unambiguous spin label for RNA, in which the nitroxide N-O bond lies on the same axis as the single bond used to attach the rigid isoindoline-based spin label to a uridine base. This results in minimal displacement of the nitroxide upon rotation of this single bond, which is a useful property for a label to be used for distance measurements...
January 12, 2018: Organic & Biomolecular Chemistry
Manfred Scheer, Luis Dütsch, Martin Fleischmann, Stefan Welsch, Gabor Balaszs, Werner Kremer
A comparison of the oxidation chemistry of the complexes [{CpMo(CO)2}2(µ,η2:η2-E2)] (E = P (A), As (B), Sb (C), Bi (D)) is presented. The oxidation of A-D with [Thia]+ (= [C12H8S2]+) results in the selective formation of the dicationic E4 complexes [{CpMo(CO)2}4(µ4,η2:η2:η2:η2-E4)]2+ (E = P (1), As (2), Sb (3), Bi (4)) stabilized by four [CpMo(CO)2] fragments. The formation of the corresponding monocations [A]+, [C]+ and [D]+ could not be detected by cyclovoltammetry, EPR or NMR spectroscopy. This suggests a fast dimerization and no dissociation in solution, which is also predicted by DFT calculations...
January 11, 2018: Angewandte Chemie
Y Gorbanev, C C W Verlackt, S Tinck, E Tuenter, K Foubert, P Cos, A Bogaerts
The vast biomedical potential of cold atmospheric pressure plasmas (CAPs) is governed by the formation of reactive species. These biologically active species are formed upon the interaction of CAPs with the surroundings. In biological milieu, water plays an essential role. The development of biomedical CAPs thus requires understanding of the sources of the reactive species in aqueous media exposed to the plasma. This is especially important in case of the COST RF plasma jet, which is developed as a reference microplasma system...
January 11, 2018: Physical Chemistry Chemical Physics: PCCP
Julie Kengen, Jean-Philippe Deglasse, Marie-Aline Neveu, Lionel Mignion, Céline Desmet, Florian Gourgue, Jean-Christophe Jonas, Bernard Gallez, Bénédicte F Jordan
The ability of certain cancer cells to maintain a highly reduced intracellular environment is correlated with aggressiveness and drug resistance. Since the gluthathione (GSH) and thioredoxin (TRX) systems cooperate to a tight regulation of ROS in cell physiology, and to a stimulation of tumor initiation and progression, modulation of the GSH and TRX pathways are emerging as new potential targets in cancer. In vivo methods to assess changes in tumor redox status are critically needed to assess the relevance of redox-targeted agents...
January 10, 2018: Free Radical Research
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