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Z T Zhang, C Xu, D Dmytriieva, S Molatta, J Wosnitza, Y T Wang, M Helm, Shengqiang Zhou, H Kühne
We report on the magnetic properties of monovacancy defects in neutron-irradiated graphite, probed by (13)C nuclear magnetic resonance spectroscopy. The bulk paramagnetism of the defect moments is revealed by the temperature dependence of the NMR frequency shift and spectral linewidth, both of which follow a Curie behavior, in agreement with measurements of the macroscopic magnetization. Compared to pristine graphite, the fluctuating hyperfine fields generated by the defect moments lead to an enhancement of the (13)C nuclear spin-lattice relaxation rate [Formula: see text] by about two orders of magnitude...
October 20, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
R T Harding, S Zhou, J Zhou, T Lindvall, W K Myers, A Ardavan, G A D Briggs, K Porfyrakis, E A Laird
The endohedral fullerene ^{15}N@C_{60} has narrow electron paramagnetic resonance lines which have been proposed as the basis for a condensed-matter portable atomic clock. We measure the low-frequency spectrum of this molecule, identifying and characterizing a clock transition at which the frequency becomes insensitive to magnetic field. We infer a linewidth at the clock field of 100 kHz. Using experimental data, we are able to place a bound on the clock's projected frequency stability. We discuss ways to improve the frequency stability to be competitive with existing miniature clocks...
October 6, 2017: Physical Review Letters
Matthias Mergenthaler, Junjie Liu, Jennifer J Le Roy, Natalia Ares, Amber L Thompson, Lapo Bogani, Fernando Luis, Stephen J Blundell, Tom Lancaster, Arzhang Ardavan, G Andrew D Briggs, Peter J Leek, Edward A Laird
Coupling between a crystal of di(phenyl)-(2,4,6-trinitrophenyl)iminoazanium radicals and a superconducting microwave resonator is investigated in a circuit quantum electrodynamics (circuit QED) architecture. The crystal exhibits paramagnetic behavior above 4 K, with antiferromagnetic correlations appearing below this temperature, and we demonstrate strong coupling at base temperature. The magnetic resonance acquires a field angle dependence as the crystal is cooled down, indicating anisotropy of the exchange interactions...
October 6, 2017: Physical Review Letters
Hongshin Lee, Juhee Seong, Ki-Myeong Lee, Hak-Hyeon Kim, Jaemin Choi, Jae-Hong Kim, Changha Lee
The Cu(II)-catalyzed Fenton-like reaction was found to be significantly accelerated in the presence of chloride ion (i.e., the Cu(II)/H2O2/Cl(-) system), enhancing the oxidative degradation of organic contaminants at neutral pH. The degradation of carbamazepine (a select target contaminant) by the Cu(II)/H2O2 system using 1μM Cu(II) and 10mM H2O2 was accelerated by 28-fold in the presence of 10,000mg/L Cl(-) at pH 7. The observed rate of carbamazepine degradation generally increased with increasing doses of Cu(II), H2O2, and Cl(-), and exhibited an optimal value at around pH 7...
October 12, 2017: Journal of Hazardous Materials
Joshua R Biller, Karl F Stupic, J Moreland
We present the development of a portable dynamic nuclear polarization (DNP) instrument based on the PCI eXtensions for Instrumentation (PXI) platform. The main purpose of the instrument is for study of (1) H polarization enhancements in solution through the Overhauser mechanism at low magnetic fields. A DNP probe set was constructed for use at 6.7 mT, using a modified Alderman-Grant (MAG) resonator at 241 MHz for saturation of the electron transition. The solenoid for detection of the enhanced (1) H signal at 288 kHz was constructed with Litz wire...
October 19, 2017: Magnetic Resonance in Chemistry: MRC
J P Sun, Y Y Jiao, C L Yang, W Wu, C J Yi, B S Wang, Y G Shi, J L Luo, Y Uwatoko, J-G Cheng
K2Cr3As3 is a newly discovered quasi-1D superconductor with a T c  =  6.1 K and an upper critical field µ 0 H c2(0)  ≈  40 T three times larger than the Pauli paramagnetic limit µ 0 H p that is suggestive of a spin-triplet Cooper pairing. In this paper, we have investigated the effects of hydrostatic pressure on its T c and µ 0 H c2 by measuring the ac magnetic susceptibility χ'(T) under magnetic fields at various hydrostatic pressures up to 7.5 GPa. The major findings include: (1) T c is suppressed gradually to below 2 K at 7...
October 19, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Jan Blahut, Karel Bernášek, Andrea Gálisová, Vít Herynek, Ivana Císařová, Jan Kotek, Jan Lang, Stanislava Matějková, Petr Hermann
1,8-Bis(2,2,2-trifluoroethyl)cyclam (te2f) derivatives with two coordinating pendant arms involving methylenecarboxylic acid (H2te2f2a), methylenephosphonic acid (H4te2f2p), (2-pyridyl)methyl (te2f2py), and 2-aminoethyl arms (te2f2ae) in 4,11-positions were prepared, and their nickel(II) complexes were investigated as possible (19)F MR tracers. The solid-state structures of several synthetic intermediates, ligands, and all complexes were confirmed by X-ray diffraction analysis. The average Ni···F distances were determined to be about 5...
October 19, 2017: Inorganic Chemistry
William E Vargas
Three parametric models of Drude-Lorentz (DL) are used to describe the spectral variation of the dielectric function of bulk palladium. An improved version of the acceptance-probability-controlled simulated annealing method is applied to optimize the values of the parameters involved in the models: high-frequency dielectric constant, free-electron collision frequency and corresponding relaxation time, oscillation strengths, nominal resonance frequencies, and Lorentzian widths. Normalization of the oscillation strengths allows the introduction of a new parameter in the context of the original DL model: the number density ratio, which is the ratio between the number density of conduction electrons and the number density of metal atoms...
August 10, 2017: Applied Optics
Evgeny Tretyakov, Ashok Keerthi, Martin Baumgarten, Sergey Veber, Matvey Fedin, Dmitry Gorbunov, Inna Shundrina, Nina Gritsan
The first alkyl chain-anchored heteropentacene, dithieno[2,3-d;2',3'-d']benzo-[1,2-b;3,4-b']dithiophene (DTmBDT), mono- or disubstituted with a nitronyl nitroxide group has been prepared through a cross-coupling synthetic procedure of the corresponding dibromo-derivative (Br2-DTmBDT) with a nitronyl nitroxide-2-ide gold(I) complex. The synthesized nitroxides possess high kinetic stability, which allowed us to investigate their structure and thermal, optical, electrochemical, and magnetic properties. Single-crystal X-ray diffraction of both mono- and diradicals revealed that the nitronyl nitroxide group lies almost in the same plane as the nearest side thiophene ring...
October 2017: ChemistryOpen
Karolina Hurej, Milosz Pawlicki, Lechoslaw Latos-Grazynski
The structurally prearranged carbaporphyrins: 22-methyl- and 22-ethyl-m-benziporphyrins provided the platform stabilizing aromatic rhodium(III) 22-(μ-methylene-m-benziporphyrin) and rhodium(III) 22-(μ-ethylidene-m-benziporphyrin). An intramolecular conversion facilitated by the m-phenylene reactivity and observed for both aromatic complexes efficiently leads to rhodium(III) 21-(μ-methylene)-21-carbaporphyrin and rhodium(III) 21-(μ-ethylidene)-21-carbaporphyrin. The distinctive macrocyclic environment of rhodium(III) 21-carbaporphyrin created an opportunity to trap unique organometallic transformations of inner core substituents affording the fulvene like bond pattern or the rearrangement to 21-vinyl substituent...
October 17, 2017: Chemistry: a European Journal
Minkyeong Kim, Hansol Lee, Hyung Joon Cho, Se Young Chun, Jin-Hong Shin, Eun-Joo Kim, Jae Woo Ahn, Gi Young Huh, Sun-Yong Baek, Jae-Hyeok Lee
It has been proposed that susceptibility-weighted imaging is a sensitive magnetic resonance imaging (MRI) technique for identifying white matter (WM) pathologic changes involving demyelination and iron accumulation. We identified the tree silhouette-like configuration with a paramagnetic phase shift in the frontal subcortical WM lesions of 4 patients with adult-onset leukoencephalopathy with axonal spheroids and pigmented glia who underwent 3T MRI. According to our postmortem 7T MRI and histologic correlation study to investigate the origin of the susceptibility-related phase contrast, changes in the subcortical WM architecture and central WM loss with the relative preservation of iron-rich U-fibers may contribute to the paramagnetic susceptibility...
November 1, 2017: Journal of Neuropathology and Experimental Neurology
Meng-Shan Hsieh, Huang-Jen Su, Pei-Lun Hsieh, Yun-Wei Chiang, Michael H Huang
This work has developed conditions for the synthesis of Ag3PO4 cubes, rhombic dodecahedra, {100}-truncated rhombic dodecahedra, tetrahedra, and tetrapods by tuning the amount of NH4NO3, NaOH, AgNO3, and K2HPO4 solutions added. Use of a lesser amount of AgNO3 solution can form much smaller rhombic dodecahedra and tetrahedra. Sub-micrometer-sized Ag3PO4 cubes and rhombic dodecahedra with sizes larger than 300 nm do not exhibit optical size effect, but ~290 nm rhombic dodecahedra show a smaller band gap value than that for larger cubes, and tetrahedra show the most blue-shifted absorption edge...
October 18, 2017: ACS Applied Materials & Interfaces
Benita Kopka, Kathrin Magerl, Anton Savitsky, Mehdi D Davari, Katrin Röllen, Marco Bocola, Bernhard Dick, Ulrich Schwaneberg, Karl-Erich Jaeger, Ulrich Krauss
Blue-light absorption by the flavin chromophore in light, oxygen, voltage (LOV) photoreceptors triggers photochemical reactions that lead to the formation of a flavin-cysteine adduct. While it has long been assumed that adduct formation is essential for signaling, it was recently shown that LOV photoreceptor variants devoid of the photoactive cysteine can elicit a functional response and that flavin photoreduction to the neutral semiquinone radical is sufficient for signal transduction. Currently, the mechanistic basis of the underlying electron- (eT) and proton-transfer (pT) reactions is not well understood...
October 17, 2017: Scientific Reports
Ajay Sharma, Elena K Gaidamakova, Olga Grichenko, Vera Y Matrosova, Veronika Hoeke, Polina Klimenkova, Isabel H Conze, Robert P Volpe, Rok Tkavc, Cene Gostinčar, Nina Gunde-Cimerman, Jocelyne DiRuggiero, Igor Shuryak, Andrew Ozarowski, Brian M Hoffman, Michael J Daly
Despite concerted functional genomic efforts to understand the complex phenotype of ionizing radiation (IR) resistance, a genome sequence cannot predict whether a cell is IR-resistant or not. Instead, we report that absorption-display electron paramagnetic resonance (EPR) spectroscopy of nonirradiated cells is highly diagnostic of IR survival and repair efficiency of DNA double-strand breaks (DSBs) caused by exposure to gamma radiation across archaea, bacteria, and eukaryotes, including fungi and human cells...
October 17, 2017: Proceedings of the National Academy of Sciences of the United States of America
Douha Harbaoui, Moustafa M S Sanad, Cécile Rossignol, El Kebir Hlil, Noureddine Amdouni, Saïd Obbade
Herein we report the studies of different physical properties (structural, magnetic, thermal, morphologic, electrical, and electrochemical) of two new allotropic β-Na2Ni2M(PO4)3 (NNMP) phosphates, with M = Fe and Al. Pure orthorhombic single-phase powders were prepared under air, using an autocombustion synthesis method. They crystallize in the orthorhombic Imma space group with similar unit cell parameters [a = 10.1592(2), b = 13.0321(3), c = 6.4864(2) Å] and [a = 10.3993(1), b = 13.1966(1), c = 6.4955(1) Å] for β-Na2Ni2M(PO4)3 (NNAP) and β-Na2Ni2Fe(PO4)3 (NNFP), respectively...
October 17, 2017: Inorganic Chemistry
Mariagrazia Iacomino, Juan Mancebo-Aracil, Mireia Guardingo, Raquel Martín, Gerardino D'Errico, Marco Perfetti, Paola Manini, Orlando Crescenzi, Félix Busqué, Alessandra Napolitano, Marco d'Ischia, Josep Sedó, Daniel Ruiz-Molina
The oxidative polymerization of 5,6-dihydroxybenzothiophene (DHBT), the sulfur analog of the key eumelanin building block 5,6-dihydroxyindole (DHI), was investigated to probe the role of nitrogen in eumelanin build-up and properties. Unlike DHI, which gives a typical black insoluble eumelanin polymer on oxidation, DHBT is converted to a grayish amorphous solid (referred to as thiomelanin) with visible absorption and electron paramagnetic resonance properties different from those of DHI melanin. Mass spectrometry experiments revealed gradational mixtures of oligomers up to the decamer level...
October 17, 2017: International Journal of Molecular Sciences
Alejandro Ruiz, Alex Frano, Nicholas P Breznay, Itamar Kimchi, Toni Helm, Iain Oswald, Julia Y Chan, R J Birgeneau, Zahirul Islam, James G Analytis
Magnetic honeycomb iridates are thought to show strongly spin-anisotropic exchange interactions which, when highly frustrated, lead to an exotic state of matter known as the Kitaev quantum spin liquid. However, in all known examples these materials magnetically order at finite temperatures, the scale of which may imply weak frustration. Here we show that the application of a relatively small magnetic field drives the three-dimensional magnet β-Li2IrO3 from its incommensurate ground state into a quantum correlated paramagnet...
October 16, 2017: Nature Communications
Sergey I Dikalov, Yuliya F Polienko, Igor A Kirilyuk
SIGNIFICANCE: Oxidative stress contributes to numerous pathophysiological conditions such as development of cancer, neurodegenerative and cardiovascular diseases. A variety of measurements of oxidative stress markers in biological systems have been developed, however, many of these methods are not specific, can produce artifacts and do not directly detect the free radicals and reactive oxygen species (ROS) that cause oxidative stress. Electron Paramagnetic Resonance (EPR) is a unique tool that allows direct measurements of free radical species...
October 17, 2017: Antioxidants & Redox Signaling
Zhiwei Qiao, Gage Redler, Zhiguo Gui, Yuhua Qian, Boris Epel, Howard Halpern
OBJECTIVES: This work aims to explore more accurate pixel-driven projection methods for iterative image reconstructions in order to reduce high-frequency artifacts in the generated projection image. METHODS: Three new pixel-driven projection methods namely, small-pixel-large-detector (SPLD), linear interpolation based (LIB) and distance anterpolation based (DAB), were proposed and applied to reconstruct images. The performance of these methods was evaluated in both two-dimensional (2D) computed tomography (CT) images via the modified FORBILD phantom and three-dimensional (3D) electron paramagnetic resonance (EPR) images via the 6-spheres phantom...
October 10, 2017: Journal of X-ray Science and Technology
Rosalynn Quiñones, Robbie J Iuliucci, Grayce Behnke, Ryanne Brown, Deben Shoup, Taylor M Riedel, Christine Plavchak, Brooke E Lininger, Jonathan M Spehar
Solid-state nuclear magnetic resonance (SS-NMR) spectroscopy has become a common technique to study polymorphism in pharmaceutical solids at high-resolution. However, high-throughput application of high resolution SS-NMR spectroscopy is severely limited by the long (1)H spin-lattice relaxation (T1) that is common to solid phase compounds. Here, we demonstrate the use of paramagnetic relaxation reagents such as chromium (III) acetylacetonate (Cr(acac)3) and nickel (II) acetylacetonate (Ni(acac)2) for fast data acquisition by significantly reducing the T1 value for carbamazepine Forms I, II, III, and dihydrate, cimetidine Forms A and B, nabumetone Form I, and acetaminophen Form I polymorphs...
October 3, 2017: Journal of Pharmaceutical and Biomedical Analysis
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