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https://www.readbyqxmd.com/read/28222392/endor-with-band-selective-shaped-inversion-pulses
#1
Claudia E Tait, Stefan Stoll
Electron Nuclear DOuble Resonance (ENDOR) is based on the measurement of nuclear transition frequencies through detection of changes in the polarization of electron transitions. In Davies ENDOR, the initial polarization is generated by a selective microwave inversion pulse. The rectangular inversion pulses typically used are characterized by a relatively low selectivity, with full inversion achieved only for a limited number of spin packets with small resonance offsets. With the introduction of pulse shaping to EPR, the rectangular inversion pulses can be replaced with shaped pulses with increased selectivity...
February 12, 2017: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/28121140/-13-c-endor-spectroscopy-of-lipoxygenase-substrate-complexes-reveals-the-structural-basis-for-c-h-activation-by-tunneling
#2
Masaki Horitani, Adam R Offenbacher, Cody A Marcus Carr, Tao Yu, Veronika Hoeke, George E Cutsail, Sharon Hammes-Schiffer, Judith P Klinman, Brian M Hoffman
In enzymatic C-H activation by hydrogen tunneling, reduced barrier width is important for efficient hydrogen wave function overlap during catalysis. For native enzymes displaying nonadiabatic tunneling, the dominant reactive hydrogen donor-acceptor distance (DAD) is typically ca. 2.7 Å, considerably shorter than normal van der Waals distances. Without a ground state substrate-bound structure for the prototypical nonadiabatic tunneling system, soybean lipoxygenase (SLO), it has remained unclear whether the requisite close tunneling distance occurs through an unusual ground state active site arrangement or by thermally sampling conformational substates...
February 8, 2017: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/28120345/probing-the-electronic-structure-of-bacteriochlorophyll-radical-ions-a-theoretical-study-of-the-effect-of-substituents-on-hyperfine-parameters
#3
Sebastian Sinnecker, Wolfgang Lubitz
In reaction centers (RCs) of photosynthesis a light-induced charge separation takes place creating radical cations and anions of the participating cofactors. In photosynthetic bacteria different bacteriochlorophylls (BChl) are involved in this process. Information about the electronic structure of the BChl radical cations and anions can be obtained by measuring the electron spin density distribution via the electron-nuclear hyperfine interaction using EPR and ENDOR techniques. In this communication we report isotropic hyperfine coupling constants (hfcs) of the BChl b and g radical cations and anions, calculated by density functional theory, and compare them with the more common radical ions of BChl a and with available experimental data...
January 25, 2017: Photochemistry and Photobiology
https://www.readbyqxmd.com/read/28107011/delocalization-of-coherent-triplet-excitons-in-linear-rigid-rod-conjugated-oligomers
#4
Christian Hintze, Patrick Korf, Frank Degen, Friederike Schütze, Stefan Mecking, Ulrich E Steiner, Malte Drescher
In this work, the triplet state delocalization in a series of monodisperse oligo(p-phenyleneethynylene)s (OPEs) is studied by pulsed electron paramagnetic resonance (EPR) and pulsed electron nuclear double resonance (ENDOR) determining zero-field splitting, optical spin polarization, and proton hyperfine couplings. Neither the zero-field splitting parameters nor the optical spin polarization change significantly with OPE chain length, in contrast to the hyperfine coupling constants, which showed a systematic decrease with chain length n according to a 2/(1 + n) decay law...
January 24, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28099021/location-of-methanol-on-the-s2-state-mn-cluster-in-photosystem-ii-studied-by-proton-matrix-electron-nuclear-double-resonance
#5
Hiroki Nagashima, Hiroyuki Mino
Proton matrix electron nuclear double resonance (ENDOR) spectroscopy was performed to specify the location of the methanol molecule near the manganese cluster in photosystem II. Comparison of the ENDOR spectra in the presence of CH3OH and CD3OH revealed two pairs of hyperfine couplings, 1.2 MHz for A⊥ and 2.5 MHz for A//, arising from the methyl group in methanol. On the basis of the crystal structure, the possible location of methanol close to the manganese cluster was discussed.
January 20, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28069476/missed-adenomas-with-behind-folds-visualizing-colonoscopy-technologies-compared-with-standard-colonoscopy-a-pooled-analysis-of-3-randomized-back-to-back-tandem-colonoscopy-studies
#6
Eelco C Brand, Vincent K Dik, Martijn G H van Oijen, Peter D Siersema
BACKGROUND AND AIMS: The Third Eye Retroscope, Full Spectrum Endoscope (FUSE), and EndoRings devices have been shown to reduce overall adenoma miss rates. We evaluated the characteristics of adenomas and patient subgroups for which these behind-folds visualizing technologies mostly reduce adenoma miss rates. METHODS: Data of 3 multicenter randomized trials (NCT01044732, NCT01549535, NCT01955122) were combined. Patients underwent same-day, back-to-back tandem examinations with standard colonoscopy and Third Eye Retroscope, FUSE, or EndoRings colonoscopy, respectively...
January 6, 2017: Gastrointestinal Endoscopy
https://www.readbyqxmd.com/read/28025471/-new-colonoscopy-devices-to-improve-colon-neoplasm-detection
#7
REVIEW
Sung Jae Shin
Early detection and removal of adenomatous polyps can prevent the development of colorectal cancer. However, it is fairly common-up to 20%-for polyps to be undetected in a colonoscopy due to poor visualization of the proximal aspect of colonic folds and anatomical flexures. To overcome these limitations, many new endoscopes and accessories have been developed. A wide-angle colonoscopy did not improve the detection of adenoma compared with the standard colonoscopy. An extra-wide angle and Retroview colonoscopies showed a significantly lower miss rate of polyps in the colon model...
December 25, 2016: Korean Journal of Gastroenterology, Taehan Sohwagi Hakhoe Chi
https://www.readbyqxmd.com/read/27977149/paramagnetic-resonance-of-cobalt-ii-trispyrazolylmethanes-and-counterion-association
#8
Amy R Marts, Joshua C Kaine, Robert R Baum, Vivien L Clayton, Jami R Bennett, Laura J Cordonnier, Robert McCarrick, Abed Hasheminasab, Laura A Crandall, Christopher J Ziegler, David L Tierney
Paramagnetic resonance studies (EPR, ESEEM, ENDOR, and NMR) of a series of cobalt(II) bis-trispyrazolylmethane tetrafluoroborates are presented. The complexes studied include the parent, unsubstituted ligand (Tpm), two pyrazole-substituted derivatives (4Me and 3,5-diMe), and tris(1-pyrazolyl)ethane (Tpe), which includes a methyl group on the apical carbon atom. NMR and ENDOR establish the magnitude of (1)H hyperfine couplings, while ESEEM provides information on the coordinated (14)N. The data show that the pyrazole 3-position is more electron rich in the Tpm analogues, that the geometry about the apical atom influences the magnetic resonance, and that apical atom geometry appears more fixed in Tpm than in Tp...
January 3, 2017: Inorganic Chemistry
https://www.readbyqxmd.com/read/27731984/influence-of-ring-expanded-n-heterocyclic-carbenes-on-the-structures-of-half-sandwich-ni-i-complexes-an-x-ray-electron-paramagnetic-resonance-epr-and-electron-nuclear-double-resonance-endor-study
#9
Stefan Pelties, Emma Carter, Andrea Folli, Mary F Mahon, Damien M Murphy, Michael K Whittlesey, Robert Wolf
Potassium graphite reduction of the half-sandwich Ni(II) ring-expanded diamino/diamidocarbene complexes CpNi(RE-NHC)Br gave the Ni(I) derivatives CpNi(RE-NHC) (where RE-NHC = 6-Mes (1), 7-Mes (2), 6-MesDAC (3)) in yields of 40%-50%. The electronic structures of paramagnetic 1-3 were investigated by CW X-/Q-band electron paramagnetic resonance (EPR) and Q-band (1)H electron nuclear double resonance (ENDOR) spectroscopy. While small variations in the g-values were observed between the diaminocarbene complexes 1 and 2, pronounced changes in the g-values were detected between the almost isostructural species (1) and diamidocarbene species (3)...
November 7, 2016: Inorganic Chemistry
https://www.readbyqxmd.com/read/27711532/epr-characterization-of-mn-ii-complexes-for-distance-determination-with-pulsed-dipolar-spectroscopy
#10
Katharina Keller, Michal Zalibera, Mian Qi, Vanessa Koch, Julia Wegner, Henrik Hintz, Adelheid Godt, Gunnar Jeschke, Anton Savitsky, Maxim Yulikov
The four Mn(ii) complexes Mn-DOTA, Mn-TAHA, Mn-PyMTA, and Mn-NO3Py were characterized by electron paramagnetic resonance (EPR), electron-nuclear double resonance (ENDOR), and relaxation measurements, to predict their relative performance in the EPR pulse dipolar spectroscopy (PDS) experiments. High spin density localization on the metal ions was proven by ENDOR on (1)H, D, (14)N, and (55)Mn nuclei. The transverse relaxation of the Mn(ii) complexes appears to be slow enough for PDS-based spin-spin distance determination...
September 14, 2016: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/27659505/distance-measurements-in-peridinin-chlorophyll-a-protein-by-light-induced-peldor-spectroscopy-analysis-of-triplet-state-localization
#11
Marilena Di Valentin, Maria Giulia Dal Farra, Laura Galazzo, Marco Albertini, Tim Schulte, Eckhard Hofmann, Donatella Carbonera
Triplet-triplet energy transfer from chlorophylls to carotenoids is the mechanism underlying the photoprotective role played by carotenoids in many light harvesting complexes, during photosynthesis. The peridinin-chlorophyll-a protein (PCP) is a water-soluble light harvesting protein of the dinoflagellate Amphidinium carterae, employing peridinin as the main carotenoid to fulfil this function. The dipolar coupling of the triplet state of peridinin, populated under light excitation in isolated PCP, to the MTSSL nitroxide, introduced in the protein by site-directed mutagenesis followed by spin labeling, has been measured by Pulse ELectron-electron DOuble Resonance (PELDOR) spectroscopy...
December 2016: Biochimica et Biophysica Acta
https://www.readbyqxmd.com/read/27622672/q-band-electron-nuclear-double-resonance-reveals-out-of-plane-hydrogen-bonds-stabilize-an-anionic-ubisemiquinone-in-cytochrome-bo3-from-escherichia-coli
#12
Chang Sun, Alexander T Taguchi, Josh V Vermaas, Nathan J Beal, Patrick J O'Malley, Emad Tajkhorshid, Robert B Gennis, Sergei A Dikanov
The respiratory cytochrome bo3 ubiquinol oxidase from Escherichia coli has a high-affinity ubiquinone binding site that stabilizes the one-electron reduced ubisemiquinone (SQH), which is a transient intermediate during the electron-mediated reduction of O2 to water. It is known that SQH is stabilized by two strong hydrogen bonds from R71 and D75 to ubiquinone carbonyl oxygen O1 and weak hydrogen bonds from H98 and Q101 to O4. In this work, SQH was investigated with orientation-selective Q-band (∼34 GHz) pulsed (1)H electron-nuclear double resonance (ENDOR) spectroscopy on fully deuterated cytochrome (cyt) bo3 in a H2O solvent so that only exchangeable protons contribute to the observed ENDOR spectra...
October 11, 2016: Biochemistry
https://www.readbyqxmd.com/read/27546061/analysis-of-heme-iron-coordination-in-dgcr8-the-heme-binding-component-of-the-microprocessor-complex
#13
Hazel M Girvan, Justin M Bradley, Myles R Cheesman, James R Kincaid, Yilin Liu, Kazimierz Czarnecki, Karl Fisher, David Leys, Stephen E J Rigby, Andrew W Munro
DGCR8 is the RNA-binding partner of the nuclease Drosha. Their complex (the "Microprocessor") is essential for processing of long, primary microRNAs (pri-miRNAs) in the nucleus. Binding of heme to DGCR8 is essential for pri-miRNA processing. On the basis of the split Soret ultraviolet-visible (UV-vis) spectrum of ferric DGCR8, bis-thiolate sulfur (cysteinate, Cys(-)) heme iron coordination of DGCR8 heme iron was proposed. We have characterized DGCR8 heme ligation using the Δ276 DGCR8 variant and combined electron paramagnetic resonance (EPR), magnetic circular dichroism (MCD), electron nuclear double resonance, resonance Raman, and electronic absorption spectroscopy...
September 13, 2016: Biochemistry
https://www.readbyqxmd.com/read/27533592/photogenerated-triplet-states-in-supramolecular-porphyrin-ladder-assemblies-an-epr-study
#14
Sabine Richert, Martin D Peeks, Claudia E Tait, Harry L Anderson, Christiane R Timmel
Introducing bridging ligands such as DABCO to solutions of linear zinc porphyrin oligomers has previously been shown to lead to the formation of ladder-type assemblies in which the single porphyrin units in each strand adopt a predominantly co-planar conformation. Here, we employ transient Electron Paramagnetic Resonance (EPR) to study photogenerated triplet states of these complexes in frozen solution with a particular focus on the extent of spin delocalisation. We make use of two different techniques: (i) the zero-field splitting parameters D and E are determined using transient continuous wave (cw) EPR spectroscopy and (ii) the hyperfine coupling constants, which directly reveal the extent of spin delocalisation, are quantified by orientation-selective proton Electron Nuclear DOuble Resonance (ENDOR) spectroscopy...
September 21, 2016: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/27529724/reductive-elimination-of-h2-activates-nitrogenase-to-reduce-the-n%C3%A2-n-triple-bond-characterization-of-the-e4-4h-janus-intermediate-in-wild-type-enzyme
#15
Dmitriy Lukoyanov, Nimesh Khadka, Zhi-Yong Yang, Dennis R Dean, Lance C Seefeldt, Brian M Hoffman
We proposed a reductive elimination/oxidative addition (re/oa) mechanism for reduction of N2 to 2NH3 by nitrogenase, based on identification of a freeze-trapped intermediate of the α-70(Val→Ile) MoFe protein as the Janus intermediate that stores four reducing equivalents on FeMo-co as two [Fe-H-Fe] bridging hydrides (denoted E4(4H)). The mechanism postulates that obligatory re of the hydrides as H2 drives reduction of N2 to a state (denoted E4(2N2H)) with a moiety at the diazene (HN═NH) reduction level bound to the catalytic FeMo-co...
August 24, 2016: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/27465315/organometallic-complex-formed-by-an-unconventional-radical-s-adenosylmethionine-enzyme
#16
Min Dong, Masaki Horitani, Boris Dzikovski, Maria-Eirini Pandelia, Carsten Krebs, Jack H Freed, Brian M Hoffman, Hening Lin
Pyrococcus horikoshii Dph2 (PhDph2) is an unusual radical S-adenosylmethionine (SAM) enzyme involved in the first step of diphthamide biosynthesis. It catalyzes the reaction by cleaving SAM to generate a 3-amino-3-carboxypropyl (ACP) radical. To probe the reaction mechanism, we synthesized a SAM analogue (SAMCA), in which the ACP group of SAM is replaced with a 3-carboxyallyl group. SAMCA is cleaved by PhDph2, yielding a paramagnetic (S = 1/2) species, which is assigned to a complex formed between the reaction product, α-sulfinyl-3-butenoic acid, and the [4Fe-4S] cluster...
August 10, 2016: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/27460505/interaction-of-cr-3-with-valence-and-conduction-bands-in-the-long-persistent-phosphor-znga2o4-cr-3-studied-by-endor-spectroscopy
#17
Laurent Binet, Suchinder K Sharma, Didier Gourier
Cr(3+)-doped zinc gallate ZnGa2O4 is a red-near infrared (IR) long persistent phosphor that can be excited by orange-red light, in the transparency window of living tissues. With this property, persistent luminescence nanoparticles were recently used for in vivo optical imaging of tumors in mice. In order to understand the origin of the excitability of persistent luminescence by visible light in this material, a Q-band ENDOR investigation of (71/69)Ga and (53)Cr nuclei was performed in ZnGa2O4:Cr(3+) to get information on the interaction of Cr(3+) with valence and conduction bands...
September 28, 2016: Journal of Physics. Condensed Matter: An Institute of Physics Journal
https://www.readbyqxmd.com/read/27432259/chemical-systems-modeling-the-d-1-mo-v-states-of-molybdenum-enzymes
#18
Charles G Young
This review focuses on the synthesis, properties and electron paramagnetic resonance (EPR), electron spin echo envelope modulation (ESEEM) and electron-nuclear double resonance (ENDOR) spectroscopy of mononuclear d(1) oxo- and sulfido-Mo(V) complexes relevant to the understanding of the EPR-active Mo(V) forms of pterin-containing molybdenum enzymes.
June 4, 2016: Journal of Inorganic Biochemistry
https://www.readbyqxmd.com/read/27383423/the-unusual-hydridicity-of-a-cobalt-bound-si-h-moiety
#19
Jin Kim, Yujeong Kim, Indranil Sinha, Koeun Park, Sun Hee Kim, Yunho Lee
A paramagnetic cobalt-SiH intermediate possessing the Co-(η(1)-H-Si) moiety was studied using various spectroscopic techniques. Frozen solution ENDOR experiments show a Co-H distance of ∼1.53 Å and a Si-Co-H angle of ∼15°, whereas XRD data suggest a TBP geometry about a Co(ii) centre. Its stepwise deprotonation with base followed by dehalogenation was identified experimentally and theoretically.
August 4, 2016: Chemical Communications: Chem Comm
https://www.readbyqxmd.com/read/27312695/exploring-the-strength-of-the-h-bond-in-synthetic-models-for-heme-proteins-the-importance-of-the-n-h-acidity-of-the-distal-base
#20
Mariza N Alberti, Yevhen Polyhach, Manolis D Tzirakis, Laura Tödtli, Gunnar Jeschke, François Diederich
The distal hydrogen bond (H-bond) in dioxygen-binding proteins is crucial for the discrimination of O2 with respect to CO or NO. We report the preparation and characterization of a series of Zn(II) porphyrins, with one of three meso-phenyl rings bearing both an alkyl-tethered proximal imidazole ligand and a heterocyclic distal H-bond donor connected by a rigid acetylene spacer. Previously, we had validated the corresponding Co(II) complexes as synthetic model systems for dioxygen-binding heme proteins and demonstrated the structural requirements for proper distal H-bonding to Co(II) -bound dioxygen...
July 11, 2016: Chemistry: a European Journal
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