Nadolinny V.A.,RAS Institute of Chemistry |
Pal'yanov Y.N.,Novosibirsk State University |
Kalinin A.A.,RAS Institute of Geology and Mineralogy |
Kupriyanov I.N.,RAS Institute of Geology and Mineralogy |
And 2 more authors.
Applied Magnetic Resonance | Year: 2011
This communication presents new data on phosphorus-containing centers in synthetic diamonds grown in the P-C system by high-pressure high-temperature (HTHP) method and annealed in the temperature range of 2,073-2,573 K. The electron paramagnetic resonance (EPR) study has shown that as-grown at 1,873 K diamonds contain single substitutional nitrogen (P1) and single substitutional phosphorus (MA1) centers. The main part of the spin density in the MA1 center locates on the carbon atom C1 separated from phosphorus by one carbon atom. HPHT annealing (7 GPa, 2,073-2,273 K) results in aggregating substitutional nitrogen and phosphorus atoms. On the first step of annealing (2,073 K) of as-grown diamonds nitrogen-phosphorus NIRIM8 (NP1) centers are created. It is supposed that nitrogen and phosphorus atoms in this center are separated by two carbons. Further temperature increasing shifts the nitrogen atom toward phosphorus and creates two new nitrogen-phosphorus centers NP2 and NP3 with the supposed structures C1-N-C-P and N-P-C1, respectively. The main part of the spin density in MA1, NIRIM8 (NP1), NP2 and NP3 is located on the carbon atom C1. Annealing these samples in the temperature range of 2,073-2,273 K has shown vanishing of NIRIM8 and increasing of NP2 and NP3 centers. HPHT annealing of diamonds at 2,573 K significantly changes the electron paramagnetic resonance (EPR) spectra: all previous nitrogen-phosphorus centers disappear and two new phosphorus centers NP4 and NP5 are created. Features of these centers are g ≈ 2. 001 and high spin density located on the phosphorus atoms. The NP5 center is sensitive to X-ray irradiation and low-temperature annealing. The EPR spectra of both these centers are due to the hyperfine structure of one phosphorus atom. The structures of all phosphorus-containing centers are discussed. © 2011 Springer-Verlag.
PubMed | Technical University of Delft, University of Bath and International Tomography Center
Type: | Journal: Scientific reports | Year: 2016
Metal-organic frameworks (MOFs) containing d(0) metals such as NH2-MIL-125(Ti), NH2-UiO-66(Zr) and NH2-UiO-66(Hf) are among the most studied MOFs for photocatalytic applications. Despite structural similarities, we demonstrate that the electronic properties of these MOFs are markedly different. As revealed by quantum chemistry, EPR measurements and transient absorption spectroscopy, the highest occupied and lowest unoccupied orbitals of NH2-MIL-125(Ti) promote a long lived ligand-to-metal charge transfer upon photoexcitation, making this material suitable for photocatalytic applications. In contrast, in case of UiO materials, the d-orbitals of Zr and Hf, are too low in binding energy and thus cannot overlap with the * orbital of the ligand, making both frontier orbitals localized at the organic linker. This electronic reconfiguration results in short exciton lifetimes and diminishes photocatalytic performance. These results highlight the importance of orbital contributions at the band edges and delineate future directions in the development of photo-active hybrid solids.
Shakirova O.G.,RAS Nikolaev Institute of Inorganic Chemistry |
Kuratieva N.V.,RAS Nikolaev Institute of Inorganic Chemistry |
Lavrenova L.G.,RAS Nikolaev Institute of Inorganic Chemistry |
Bogomyakov A.S.,International Tomography Center |
And 2 more authors.
Journal of Structural Chemistry | Year: 2010
A method is developed to prepare a complex of copper(II) chloride with 3-(hydroxyiminomethyl)-5-(2,5-dimethylphenyl)isoxazole (L) of the composition [Cu2L2(μ-Cl)2Cl2]. Its molecular and crystal structure is determined by single crystal X-ray diffraction. Examination of the curve μef(T) within the 2-300 K temperature range reveals the presence of antiferromagnetic interactions between unpaired electrons of copper(II). © 2010 Pleiades Publishing, Ltd.
Nasalevich M.A.,Technical University of Delft |
Becker R.,University of Amsterdam |
Ramos-Fernandez E.V.,University of Alicante |
Castellanos S.,Technical University of Delft |
And 6 more authors.
Energy and Environmental Science | Year: 2015
We present a synthetic strategy for the efficient encapsulation of a derivative of a well-defined cobaloxime proton reduction catalyst within a photoresponsive metal-organic framework (NH2-MIL-125(Ti)). The resulting hybrid system Co@MOF is demonstrated to be a robust heterogeneous composite material. Furthermore, Co@MOF is an efficient and fully recyclable noble metal-free catalyst system for light-driven hydrogen evolution from water under visible light illumination. © 2015 The Royal Society of Chemistry.
Voronov V.K.,Irkutsk State University |
Ushakov I.A.,Irkutsk State University |
Shmelev V.V.,Irkutsk State University |
Sagdeev D.R.,International Tomography Center
Magnetic Resonance in Chemistry | Year: 2012
The 1H NMR spectra of semiquinalate cobalt complex have been analyzed in a wide range of temperatures. It has been established that the intramolecular exchange requires the obligatory presence of a paramagnetic structure containing non-compensated electron spin localized on the carbon atom of the ligand aromatic ring, the cobalt atom being trivalent. The presence of such a structure leads to the appearance of satellite signals in the NMR spectra because of the superfine interactions. Copyright © 2012 John Wiley & Sons, Ltd.
Pedersen J.B.,University of Southern Denmark |
Mojaza M.,University of Southern Denmark |
Lukzen N.N.,International Tomography Center
Chemical Physics Letters | Year: 2010
A multi-channel kinetic description is used to study the magnetic isotope effect (MIE) in zero magnetic field. The maximal isotope effect is equal to the number of channels, two for the hyperfine interaction but four for the electron spin dipole-dipole interaction of the intermediate radical pair. Quantum mechanical calculations agree with these conclusion and show that large MIE may be obtained even in the presence of a strong exchange interaction. The observed magnesium isotope effect on the rate of enzymatic synthesis of adenosine triphosphate (ATP) is approximately 3 implying that the dipolar interaction is responsible for the effect. Our calculations provide support for the proposed mechanism. © 2010 Elsevier B.V. All rights reserved.
Veber S.L.,Novosibirsk State University |
Suturina E.A.,RAS Institute of Chemical Kinetics and Combustion |
Fedin M.V.,RAS Institute of Organic Chemistry |
Boldyrev K.N.,Kazan Federal University |
And 5 more authors.
Inorganic Chemistry | Year: 2015
"Breathing crystals" based on copper(II) hexafluoroacetylacetonates and pyrazolyl-substituted nitronyl nitroxides comprise the exchange-coupled clusters within the polymeric chains. Owing to an interplay of exchange interaction between copper(II) and nitroxide spins and Jahn-Teller nature of copper(II) complex, the breathing crystals demonstrate thermally and light-induced magnetostructural transitions in many aspects similar to the classical spin crossover. Herewith, we report the first application of variable temperature (VT) far/mid Fourier transform infrared (FTIR) spectroscopy and mid FTIR microscopy to breathing crystals. This VT-FTIR study was aimed toward clarification of the transitions mechanism previously debated on the basis of superconducting quantum interference device, X-ray diffraction, and electron paramagnetic resonance data. VT-FTIR showed the onset of new vibrational bands during phase transitions occurring at the expense of several existing ones, whose intensity was significantly reduced. The most pronounced spectral changes were assigned to corresponding vibrational modes using quantum chemical calculations. A clear-cut correlation was found between temperature-dependent effective magnetic moment of studied compounds and the observed VT-FTIR spectra. Importantly, VT-FTIR confirmed coexistence of two types of copper(II)-nitroxide clusters during gradual magnetostructural transition. Such clusters correspond to weakly coupled and strongly coupled spin states, whose relative contribution depends on temperature. The pronounced difference in the VT-FTIR spectra of two states in breathing crystals is a fingerprint of magnetostructural transition, and understanding of these characteristics achieved by us will be useful for future studies of breathing crystals as well as their diamagnetic analogues. © 2015 American Chemical Society.
Ivanov K.L.,International Tomography Center |
Lukzen N.N.,International Tomography Center |
Morozova O.B.,International Tomography Center |
Mok K.H.,Trinity College Dublin |
Yurkovskaya A.V.,International Tomography Center
Applied Magnetic Resonance | Year: 2011
A quantitative theoretical approach to protein chemically induced dynamic nuclear polarization (CIDNP) is formulated in the present work, which is based on the theory of sterically specific chemical reactions in liquids. Kinetic equations for polarization of all CIDNP-active accessible amino acid residues are presented. Relations between the kinetic parameters and the total side-chain accessibility (TSA) values are established. Numerical calculations of the CIDNP kinetics are also shown to demonstrate how the time behavior of polarization depends on TSA. The present theoretical approach was applied to model time-resolved protein CIDNP data obtained for Tyr59 and His68 of ubiquitin in the native state. Comparison of theoretical predictions with the experimental data confirms the accuracy of the approach. © 2011 Springer-Verlag.
Tretyakov E.V.,International Tomography Center |
Romanenko G.V.,International Tomography Center |
Tolstikov S.E.,International Tomography Center |
Ovcharenko V.I.,International Tomography Center
Journal of Structural Chemistry | Year: 2013
Molecular and crystal structures are determined for amino-substituted nitronyl nitroxide 1, the products of its subsequent oxidation, acylation, and reduction: zwitter-ions 3a, 3b and salts K(4b) and K2(4b)(CF 3CO2). © 2013 Pleiades Publishing, Ltd.
PubMed | Research Institute of Molecular Biology and Biophysics and International Tomography Center
Type: Journal Article | Journal: Bulletin of experimental biology and medicine | Year: 2016
fMRI-EEG dynamics of brain activity in volunteers was studied during the course of EEG alpha-stimulation training (20 sessions). Twenty-three healthy men (20-35 years) were subjected to 3-fold mapping in a feedback loop (EEG alpha-rhythm biofeedback with acoustic reinforcement). This procedure was performed at the beginning, middle, and end of the course. During the first neurofeedback training session, deactivation (p<0.001) was found in the right angular gyrus, supramarginal, and superior temporal gyri, Brodmann area 39, and cerebellum. Activation (p<0.001) was observed in the medial frontal and cingulate gyri, motor areas of both hemispheres, and Brodmann area 32. During final (third) neurofeedback training session, we observed strong deactivation (p<0.05 with FDR) of zones responsible for spatial thinking and motor functions: left medial frontal and left medial temporal gyri; right postcentral, lingual, and superior frontal gyri; insula and right side of the cerebellum; and precuneus and cuneus (Brodmann areas 6, 9, 7, 31, 8, 13, and 22). Changes in the alpha wave power were most pronounced in the primary and secondary somatosensory cortex of the left hemisphere (Brodmann areas 2L and 5L).