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Alessandro Agostini, Jens Niklas, Tim Schulte, Marilena Di Valentin, Marco Bortolus, Eckhard Hofmann, Wolfgang Lubitz, Donatella Carbonera
The peridinin-chlorophyll-a protein (PCP) is a water-soluble light harvesting protein of the dinoflagellate Amphidinium carterae, employing peridinin (Per) as the main carotenoid to fulfil light harvesting and photo-protective functions. Per molecules bound to the protein experience specific molecular surroundings which lead to different electronic and spectral properties. In the refolded N89 L variant PCP (N89 L-RFPCP) a significant part of the intensity on the long wavelength side of the absorption spectrum is shifted to shorter wavelengths due to a significant change in the Per-614 site energy...
May 18, 2018: Biochimica et Biophysica Acta
Mantas Šimėnas, Aneta Ciupa, Gediminas Usevičius, Kęstutis Aidas, Daniel Klose, Gunnar Jeschke, Mirosław Mączka, Georg Völkel, Andreas Pöppl, Jūras Banys
We report a continuous-wave (CW) and pulse electron paramagnetic resonance (EPR) as well as pulse electron nuclear double resonance (ENDOR) study of Cu2+ doped [(CH3)2NH2][Zn(HCOO)3] hybrid perovskite which exhibits a structural phase transition. The multifrequency (X, Q and W-band) CW EPR measurements allow the temperature evolution of the Cu2+ ion local environment to be studied. The spectrum of the ordered (low-temperature) phase reveals an axially distorted octahedral Cu2+ site confirming the successful replacement of the Zn2+ ions and formation of the CuO6 octahedra...
April 20, 2018: Physical Chemistry Chemical Physics: PCCP
Georgia Prokopiou, Michael D Lee, Alberto Collauto, Elwy H Abdelkader, Thorsten Bahrenberg, Akiva Feintuch, Marie Ramirez-Cohen, Jessica Clayton, James D Swarbrick, Bim Graham, Gottfried Otting, Daniella Goldfarb
The C7-Gd and C8-Gd tags are compact hydrophilic cyclen-based lanthanide tags for conjugation to cysteine residues in proteins. The tags are enantiomers, which differ in the configuration of the 2-hydroxylpropyl pendant arms coordinating the lanthanide ion. Here, we report the electron paramagnetic resonance (EPR) performance of the C7-Gd ( S configuration) and C8-Gd ( R configuration) tags loaded with Gd(III) on two mutants of the homodimeric ERp29 protein. The W-band EPR spectra were found to differ between the tags in the free state and after conjugation to the protein...
April 9, 2018: Inorganic Chemistry
Hiroki Nagashima, Mizue Asada, Hiroyuki Mino
The electronic structure of manganese (Mn) cluster in photosystem II was investigated by electron paramagnetic resonance (EPR) spectroscopy. In order to determine the spin density distribution in magnetically coupled Mn in the S2 state Mn cluster, pulsed electron-electron double resonance (PELDOR) measurement was performed. The local environment of the Mn cluster was investigated by electron-nuclear double resonance (ENDOR). Using spin projections determined by PELDOR, ENDOR signals were assigned to the water molecules ligated to the Mn cluster...
2018: Biophysics and Physicobiology
Douglas K Rex, Alessandro Repici, Seth A Gross, Cesare Hassan, Prasanna L Ponugoti, Jonathan R Garcia, Heather M Broadley, Jack C Thygesen, Andrew W Sullivan, William W Tippins, Samuel A Main, George J Eckert, Krishna C Vemulapalli
BACKGROUND AND AIMS: Devices used to improve polyp detection during colonoscopy have seldom been compared with each other. METHODS: We performed a 3-center prospective randomized trial comparing high-definition (HD) forward-viewing colonoscopy alone to HD with Endocuff to HD with EndoRings to the full spectrum endoscopy (FUSE) system. Patients were age ≥50 years and had routine indications and intact colons. The study colonoscopists were all proven high-level detectors...
March 9, 2018: Gastrointestinal Endoscopy
Yishay Manassen, Michael Averbukh, Moamen Jbara, Bernhard Siebenhofer, Alexander Shnirman, Baruch Horovitz
We performed STM-ENDOR experiments where the intensity of one of the hyperfine components detected in ESR-STM is recorded while an rf power is irradiated into the tunneling junction and its frequency is swept. When the latter frequency is near a nuclear transition a dip in ESR-STM signal is observed. This experiment was performed in three different systems: near surface SiC vacancies where the electron spin is coupled to a next nearest neighbor 29 Si nucleus; Cu deposited on Si(111)7x7 surface, where the unpaired electron of the Cu atom is coupled to the Cu nucleus (63 Cu, 65 Cu) and on Tempo molecules adsorbed on Au(111), where the unpaired electron is coupled to a Nitrogen nucleus (14 N)...
April 2018: Journal of 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...
February 15, 2018: Journal of Physical Chemistry. A
David A Marchiori, Paul H Oyala, Richard J Debus, Troy A Stich, R David Britt
The Mn4 CaO5 oxygen-evolving complex (OEC) of photosystem II catalyzes the light-driven oxidation of two substrate waters to molecular oxygen. ELDOR-detected NMR along with computational studies indicated that ammonia, a substrate analogue, binds as a terminal ligand to the Mn4A ion trans to the O5 μ4 oxido bridge. Results from electron spin echo envelope modulation (ESEEM) spectroscopy confirmed this and showed that ammonia hydrogen bonds to the carboxylate side chain of D1-Asp61. Here we further probe the environment of OEC with an emphasis on the proximity of exchangeable protons, comparing ammonia-bound and unbound forms...
February 8, 2018: Journal of Physical Chemistry. B
Yilei Wu, Ji-Min Han, Michael Hong, Matthew D Krzyaniak, Anthea K Blackburn, Isurika R Fernando, Dennis D Cao, Michael R Wasielewski, J Fraser Stoddart
The synthesis of stable organic polyradicals is important for the development of magnetic materials. Herein we report the synthesis, isolation, and characterization of a series of X-shaped pyromellitimide (PI) oligomers (Xn -R, n = 2-4, R = Hex or Ph) linked together by single C-C bonds between their benzenoid cores. We hypothesize that these oligomers might form high-spin states in their reduced forms because of the nearly orthogonal conformations adopted by their PI units.1 H and13 C nuclear magnetic resonance (NMR) spectroscopies confirmed the isolation of the dimeric, trimeric, and tetrameric homologues...
January 10, 2018: Journal of the American Chemical Society
Raffaella Comitato, Roberto Ambra, Fabio Virgili
Vitamin E is a generic term frequently used to group together eight different molecules, namely: α-, β-, γ- and δ-tocopherol and the corresponding tocotrienols. The term tocopherol and eventually Vitamin E and its related activity was originally based on the capacity of countering foetal re-absorption in deficient rodents or the development of encephalomalacia in chickens. In humans, Vitamin E activity is generally considered to be solely related to the antioxidant properties of the tocolic chemical structure...
November 18, 2017: Antioxidants (Basel, Switzerland)
Klaus Möbius, Wolfgang Lubitz, Anton Savitsky
In this minireview, we report on our year-long EPR work, such as electron-nuclear double resonance (ENDOR), pulse electron double resonance (PELDOR) and ELDOR-detected NMR (EDNMR) at X-band and W-band microwave frequencies and magnetic fields. This report is dedicated to James S. Hyde and honors his pioneering contributions to the measurement of spin interactions in large (bio)molecules. From these interactions, detailed information is revealed on structure and dynamics of macromolecules embedded in liquid-solution or solid-state environments...
2017: Applied Magnetic Resonance
Antonio Facciorusso, Valentina Del Prete, Rosario Vincenzo Buccino, Nicola Della Valle, Maurizio Cosimo Nacchiero, Fabio Monica, Renato Cannizzaro, Nicola Muscatiello
BACKGROUND & AIMS: Several add-on devices have been developed to increase rates of colon adenoma detection (ADR). We assessed their overall and comparative efficacy, and estimated absolute magnitude of benefit through a network meta-analysis. METHODS: We searched the PubMed/Medline and Embase database through March 2017 and identified 25 randomized controlled trials (comprising 16,103 patients) that compared the efficacy of add-on devices (cap, Endocuff and Endorings) with each other or with standard colonoscopy...
November 11, 2017: Clinical Gastroenterology and Hepatology
Michal Zalibera, Denis S Krylov, Dimitrios Karagiannis, Paul-Anton Will, Frank Ziegs, Sandra Schiemenz, Wolfgang Lubitz, Sebastian Reineke, Anton Savitsky, Alexey A Popov
The endohedral fullerene Y3 N@C80 exhibits luminescence with reasonable quantum yield and extraordinary long lifetime. By variable-temperature steady-state and time-resolved luminescence spectroscopy, it is demonstrated that above 60 K the Y3 N@C80 exhibits thermally activated delayed fluorescence with maximum emission at 120 K and a negligible prompt fluorescence. Below 60 K, a phosphorescence with a lifetime of 192±1 ms is observed. Spin distribution and dynamics in the triplet excited state is investigated with X- and W-band EPR and ENDOR spectroscopies and DFT computations...
January 2, 2018: Angewandte Chemie
Andrew J Fielding, Kednerlin Dornevil, Li Ma, Ian Davis, Aimin Liu
CYP121 is a cytochrome P450 enzyme from Mycobacterium tuberculosis that catalyzes the formation of a C-C bond between the aromatic groups of its cyclodityrosine substrate (cYY). The crystal structure of CYP121 in complex with cYY reveals that the solvent-derived ligand remains bound to the ferric ion in the enzyme-substrate complex. Whereas in the generally accepted P450 mechanism, binding of the primary substrate in the active-site triggers the release of the solvent-derived ligand, priming the metal center for reduction and subsequent O2 binding...
December 6, 2017: Journal of the American Chemical Society
Alexander T Taguchi, Patrick J O'Malley, Colin A Wraight, Sergei A Dikanov
Determining the complete electron spin density distribution for protein-bound radicals, even with advanced pulsed electron paramagnetic resonance (EPR) methods, is a formidable task. Here we present a strategy to overcome this problem combining multifrequency HYSCORE and ENDOR measurements on site-specifically (13)C-labeled samples with DFT calculations on model systems. As a demonstration of this approach, pulsed EPR experiments are performed on the primary QA and secondary QB ubisemiquinones of the photosynthetic reaction center from Rhodobacter sphaeroides (13)C-labeled at the ring and tail positions...
October 31, 2017: Journal of Physical Chemistry. B
Anna Nalepa, Marco Malferrari, Wolfgang Lubitz, Giovanni Venturoli, Klaus Möbius, Anton Savitsky
Using isotope labeled water (D2 O and H2 17 O) and pulsed W-band (94 GHz) high-field multiresonance EPR spectroscopies, such as ELDOR-detected NMR and ENDOR, the biologically important question of detection and quantification of local water in proteins is addressed. A bacterial reaction center (bRC) from Rhodobacter sphaeroides R26 embedded into a trehalose glass matrix is used as a model system. The bRC hosts the two native radical cofactor ions (primary electron donor) and (primary electron acceptor) as well as an artificial nitroxide spin label site-specifically attached to the surface of the H-protein domain...
October 25, 2017: Physical Chemistry Chemical Physics: PCCP
Ellen Ross, Patricia McKenna, John H Anderson
This review addresses the management of sigmoid colon diverticular disease associated with foreign bodies. In addition, two novel cases are presented. One case describes the management of diverticular bleeding secondary to a chicken bone and the other case reports retrieval of a retained EndoRings™ Device. The review identified 40 relevant publications including 50 subjects. Foreign bodies within sigmoid diverticular disease may be associated with inflammation, perforation, abscess and fistula. In current practice, diagnosis is often achieved with CT scan...
December 2017: Clinical Journal of Gastroenterology
Masaki Horitani, Katarzyna Grubel, Sean F McWilliams, Bryan D Stubbert, Brandon Q Mercado, Ying Yu, Prabhuodeyara M Gurubasavaraj, Nicholas S Lees, Patrick L Holland, Brian M Hoffman
A bio-organometallic intermediate, denoted PA, was previously trapped during the reduction of propargyl alcohol to allyl alcohol (AA) by nitrogenase, and a similar one was trapped during acetylene reduction, representing foundational examples of alkene binding to a metal center in biology. ENDOR spectroscopy led to the conclusion that these intermediates have η(2) binding of the alkene, with the hydrogens on the terminal carbon structurally/magnetically equivalent and related by local mirror symmetry. However, our understanding of both the PA intermediate, and of the dependability of the ENDOR analysis on which this understanding was based, was constrained by the absence of reference iron-alkene complexes for EPR/ENDOR comparison...
September 1, 2017: Chemical Science
Nadine Ritterskamp, Katherine Sharples, Emma Richards, Andrea Folli, Mario Chiesa, James A Platts, Damien M Murphy
The interaction of imidazole with a [Cu(acac)2 ] complex was studied using electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR), hyperfine sublevel correlation spectroscopy (HYSCORE), and density functional theory (DFT). At low Im ratios (Cu:Im 1:10), a 5-coordinate [Cu(acac)2 Imn=1 ] monoadduct is formed in frozen solution with the spin Hamiltonian parameters g1 = 2.063, g2 = 2.063, g3 = 2.307, A1 = 26, A2 = 15, and A3 = 472 MHz with Im coordinating along the axial direction. At higher Im concentrations (Cu:Im 1:50), a 6-coordinate [Cu(acac)2 Imn=2 ] bis-adduct is formed with the spin Hamiltonian parameters g1 = 2...
October 2, 2017: Inorganic Chemistry
Pauline Burner, Atul D Sontakke, Mathieu Salaün, Michel Bardet, Jean-Marie Mouesca, Serge Gambarelli, Anne-Laure Barra, Alban Ferrier, Bruno Viana, Alain Ibanez, Vincent Maurel, Isabelle Gautier-Luneau
Yttrium aluminum borate (YAB) powders prepared by sol-gel process have been investigated to understand their photoluminescence (PL) mechanism. The amorphous YAB powders exhibit bright visible PL from blue emission for powders calcined at 450 °C to broad white PL for higher calcination temperature. Thanks to (13) C labelling, NMR and EPR studies show that propionic acid initially used to solubilize the yttrium nitrate is decomposed into aromatic molecules confined within the inorganic matrix. DTA-TG-MS analyses show around 2 wt % of carbogenic species...
September 11, 2017: Angewandte Chemie
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