keyword
MENU ▼
Read by QxMD icon Read
search

Endorings

keyword
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
#1
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)...
October 12, 2016: Inorganic Chemistry
https://www.readbyqxmd.com/read/27711532/epr-characterization-of-mn-ii-complexes-for-distance-determination-with-pulsed-dipolar-spectroscopy
#2
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
#3
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
#4
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
#5
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
#6
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
#7
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
#8
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
#9
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
#10
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
#11
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
#12
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
https://www.readbyqxmd.com/read/27157978/what-computational-chemistry-and-magnetic-resonance-reveal-concerning-the-oxygen-evolving-centre-in-photosystem-ii
#13
Richard Terrett, Simon Petrie, Rob Stranger, Ron J Pace
Density Functional Theory (DFT) computational studies of the Mn4/Ca Oxygen Evolving Complex (OEC) region of Photosystem II in the paramagnetic S2 and S3 states of the water oxdizing catalytic cycle are described. These build upon recent advances in computationally understanding the detailed S1 state OEC geometries, revealed by the recent high resolution Photosystem II crystal structures of Shen et al., at 1.90Å and 1.95Å (Petrie et al., 2015, Angew. Chem. Int. Ed., 54, 7120). The models feature a 'Low Oxidation Paradigm' assumption for the mean Mn oxidation states in the functional enzyme, with the mean oxidation levels being 3...
April 8, 2016: Journal of Inorganic Biochemistry
https://www.readbyqxmd.com/read/27119347/new-developments-in-mechanical-enhancement-of-colonoscopy-cuffs-caps-and-rings
#14
Deepanshu Jain, Naemat Sandhu, Shashideep Singhal
BACKGROUND: Colorectal cancer (CRC) is a common cause of cancer-related deaths. Early detection of precursor lesions in the adenoma-carcinoma sequence via colonoscopy can decrease mortality from CRC. SUMMARY: In this review article, we have summarized retrospective studies, prospective single center, multicenter studies and randomized controlled trials describing the efficacy of endocuff colonoscopy (EC), cap-assisted colonoscopy (CAC) and endorings colonoscopy (ERC)...
2016: Digestion
https://www.readbyqxmd.com/read/27044055/fourth-stable-radical-species-in-x-irradiated-solid-state-sucrose
#15
Jevgenij Kusakovskij, Ignacio Caretti, Sabine Van Doorslaer, Freddy Callens, Henk Vrielinck
High-energy radiation produces radicals in crystalline sucrose. As such, sucrose is considered as a relevant model system for studying radiation damage to the sugar units of DNA. Many of these radicals are stable, detectable at room temperature with electron paramagnetic resonance (EPR) and their concentration is proportional to the absorbed dose in a considerable range. This makes sucrose also an interesting system for dosimetry. Dose assessment protocols rely on measurements of the total intensity of the EPR powder spectrum, so it is likely that they could be further improved if the composite nature of the spectrum was understood completely...
April 28, 2016: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/26986225/endoscopic-improvement-of-the-adenoma-detection-rate-during-colonoscopy-where-do-we-stand-in-2015
#16
Martin Floer, Tobias Meister
BACKGROUND: The presence of colorectal adenomas is considered a major risk factor for colorectal cancer development. The implementation of screening colonoscopy programs in the Western world has led to a substantial reduction of colorectal cancer death. Many efforts have been made to reduce the adenoma miss rates by the application of new endoscopic devices and techniques for better adenoma visualization. SUMMARY: This special review gives the readership an overview of current endoscopic innovations that can aid in the increase of the adenoma detection rate (ADR) during colonoscopy...
2016: Digestion
https://www.readbyqxmd.com/read/26907976/electronic-structure-of-a-cu-ii-alkoxide-complex-modeling-intermediates-in-copper-catalyzed-alcohol-oxidations
#17
Ellen C Hayes, Thomas R Porter, Charles J Barrows, Werner Kaminsky, James M Mayer, Stefan Stoll
In the copper-catalyzed oxidation of alcohols to aldehydes, a Cu(II)-alkoxide (Cu(II)-OR) intermediate is believed to modulate the αC-H bond strength of the deprotonated substrate to facilitate the oxidation. As a structural model for these intermediates, we characterized the electronic structure of the stable compound Tp(tBu)Cu(II)(OCH2CF3) (Tp(tBu) = hydro-tris(3-tert-butyl-pyrazolyl)borate) and investigated the influence of the trifluoroethoxide ligand on the electronic structure of the complex. The compound exhibits an electron paramagnetic resonance (EPR) spectrum with an unusually large gzz value of 2...
March 30, 2016: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/26814427/excitation-wavelength-dependent-epr-study-on-the-influence-of-the-conformation-of-multiporphyrin-arrays-on-triplet-state-delocalization
#18
Claudia E Tait, Patrik Neuhaus, Martin D Peeks, Harry L Anderson, Christiane R Timmel
The optoelectronic properties of conjugated porphyrin arrays render them excellent candidates for use in a variety of molecular electronic devices. Understanding the factors controlling the electron delocalization in these systems is important for further developments in this field. Here, we use transient EPR and ENDOR (Electron Nuclear Double Resonance) to study the extent of electronic delocalization in the photoexcited triplet states of a series of butadiyne-linked porphyrin oligomers. We are able to distinguish between planar and twisted arrangements of adjacent porphyrin units, as the different conformations are preferentially excited at different wavelengths in the visible range...
February 21, 2016: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/26802219/gd-iii-complexes-as-paramagnetic-tags-evaluation-of-the-spin-delocalization-over-the-nuclei-of-the-ligand
#19
A Collauto, A Feintuch, M Qi, A Godt, T Meade, D Goldfarb
Complexes of the Gd(III) ion are currently being established as spin labels for distance determination in biomolecules by pulse dipolar spectroscopy. Because Gd(III) is an f ion, one expects electron spin density to be localized on the Gd(III) ion - an important feature for the mentioned application. Most of the complex ligands have nitrogens as Gd(III) coordinating atoms. Therefore, measurement of the (14)N hyperfine coupling gives access to information on the localization of the electron spin on the Gd(III) ion...
February 2016: Journal of Magnetic Resonance
https://www.readbyqxmd.com/read/26788586/reversible-photoinduced-reductive-elimination-of-h2-from-the-nitrogenase-dihydride-state-the-e-4-4h-janus-intermediate
#20
Dmitriy Lukoyanov, Nimesh Khadka, Zhi-Yong Yang, Dennis R Dean, Lance C Seefeldt, Brian M Hoffman
We recently demonstrated that N2 reduction by nitrogenase involves the obligatory release of one H2 per N2 reduced. These studies focus on the E4(4H) "Janus intermediate", which has accumulated four reducing equivalents as two [Fe-H-Fe] bridging hydrides. E4(4H) is poised to bind and reduce N2 through reductive elimination (re) of the two hydrides as H2, coupled to the binding/reduction of N2. To obtain atomic-level details of the re activation process, we carried out in situ 450 nm photolysis of E4(4H) in an EPR cavity at temperatures below 20 K...
February 3, 2016: Journal of the American Chemical Society
keyword
keyword
61445
1
2
Fetch more papers »
Fetching more papers... Fetching...
Read by QxMD. Sign in or create an account to discover new knowledge that matter to you.
Remove bar
Read by QxMD icon Read
×

Search Tips

Use Boolean operators: AND/OR

diabetic AND foot
diabetes OR diabetic

Exclude a word using the 'minus' sign

Virchow -triad

Use Parentheses

water AND (cup OR glass)

Add an asterisk (*) at end of a word to include word stems

Neuro* will search for Neurology, Neuroscientist, Neurological, and so on

Use quotes to search for an exact phrase

"primary prevention of cancer"
(heart or cardiac or cardio*) AND arrest -"American Heart Association"