EPR Signal Research Articles

Влияние наночастиц на физиологические характеристики и активность ферментов растений, выращенных в соленых почвах

Lately, use of nanoparticles in ecological problems solution of agriculture rouses a great interest. One of the interesting directions in nanotechnologies is nanoparticles application in agricultural plants salt-tolerance. Normal development of the plan provision in the saline soils was tried using from nanoparticles on the basis of Al2O3, CuO, Fe2O4, ZnO, TiO2 metals. For this purpose, an influence of nanoparticles on seeds hydration, soil rhizosphere, contamination and planes shooting in the normal and saline soils was investigated. In this connection before sowing the seeds were worked out by the nanoparticle dust. An impact of nanoparticles on plants shooting energy. Growth and development, photosynthetic pigments quantity. Photosystem activity and plant ferments concern future duties. The nanoparticles diffusion in seed endosperm was studied on the basis of the EPR method in the researches. Therefore, the samples were prepared from different layers of the seeds endosperm to determine EPR signal, the plant seeds were exposed to the influence of nanoparticles in dispersible solution for one day. Influence of nanoparticles on chlorophyll quantity in shooting leaves of the grown cultures in the normal and saline soils using of the spectroscopic method was determined. It was determined as a result of the experiment that nanoparticles stimulate shoots development changing a hydration character of the seeds, diffusing to the seeds, creating an opportunity for shooting in the saline soils.

One-Electron Reduction of 2-Mono(2,6-diisopropylphenylimino)acenaphthene-1-one (dpp-mian).

The electrochemical characteristics of 2-mono(2,6-diisopropylphenylimino)acenaphthene-1-one (dpp-mian) have been investigated. One-electron reduction of dpp-mian involves the iminoketone fragment, which is revealed by the EPR spectrum obtained after the electrolysis of the dpp-mian solution in tetrahydrofuran (THF). The reduction of dpp-mian with one equivalent of metallic potassium leads to a similar EPR spectrum. The sodium complex [(dpp-mian)Na(dme)]2 (1) produces an EPR signal with hyperfine coupling on the nitrogen atom of the iminoketone fragment of the dpp-mian ligand. Dpp-mian can also be reduced in a one-electron process by SnCl2 ×(dioxane). In this case, complex (dpp-mian)2 SnCl2 (2) is formed, with the tin atom displaying an oxidation state of +4. Tin(II) chloride dihydrate, SnCl2 ×2(H2 O), also reduces dpp-mian, but the two ligands bound to tin in the product form a new carbon-carbon bond between the ketone moieties of the dpp-mian monoanions to form complex (bis-dpp-mian)HSnCl3 (3). Metallic tin reduces dpp-mian to form the (bis-dpp-mian)2 Sn (4) species. Compounds 1-4 were characterized by X-ray diffraction.

Enhancement of electrical and magnetic properties in acceptor-doped BaTiO3 ferroelectric ceramics

BaTi1−xMnxO3 (x = 0.00, 0.25, 0.50, 0.75 mol%) (BTMO) ceramics were synthesized through sol–gel combustion method. The structural studies suggested that Mn-doped BaTiO3 (BTO) ceramics exhibit a tetragonal structure with P4mm space group via Rietveld refinement analysis. Also, the phonon mode at 308 cm−1 through Raman spectral analysis confirms the local structure of tetragonal symmetries. The redshift observed in UV-absorption spectra indicates a decrease of optical band gap from 3.13 to 2.71 eV with increasing Mn2+ doping. The observed decrease in the intensity of PL emission spectra was due to an increase of Mn2+ concentration. This indicates that a decrease in oxygen vacancies and a reduction in the number of electrons attributed to the Burstein–Moss shift. The carrier hopping process between Mn2+ and Mn3+ is responsible for dielectric as well as magnetization behavior. The ferroelectric double hysteresis loops are related to a ferroelectric and anti-ferroelectric order and it increases with the increase of Mn ion concentration in BTO. Through P–E measurements, the value of remnant electric polarization and coercive field found to be increased with Mn concentration in BTO samples. For BTO sample, two EPR signals with g = 1.969 and g = 2.000 singlets can be assigned with ionized Ba and Ti-vacancy defects. In addition, the EPR signal for BTMO shows a good correlation with Ti vacancies as compensating for lattice defects. Further, the Mn doping induced a weak ferromagnetic to ferromagnetic state due to free carrier concentrations.

Radical cations of twisted acenes: chiroptical properties and spin delocalization.

We introduce the first series of enantiopure twistacene radical cations, which form reversibly upon chemical or electrochemical oxidation. Their vis-NIR chiroptical properties (Cotton effect and anisotropy factor) increase systematically with the backbone twist. The hyperfine constants observed by EPR demonstrate significant spin delocalization even for large backbone twist angles.

Electronic and spin delocalization in a switchable trinuclear triphenylene trisemiquinone bridged Ni3 complex.

A trinuclear triphenylene trisemiquinone complex containing paramagnetic NiII is obtained under ambient conditions from the reaction of deprotonated tricatecholate hexahydroxytriphenylene (H6HHTP) with NiII capped with a trispyrazolyl borate tridentate ligand. The magnetic and EPR data are consistent with delocalization of the electronic spin over the three NiII species. The two-electron reduced complex shows an EPR spectrum corresponding to a S = 1/2 species due to a large antiferromagnetic coupling between the radical and only one of the NiII ions highlighting the localization of the electronic spin. No EPR signal is observed for the one- and three-electron reduced species consistent with the closed shell of the bridging ligand.

Probing the dynamic properties of two sites simultaneously in a protein-protein interaction process: a SDSL-EPR study.

During molecular processes, protein flexibility is a fundamental property allowing protein-protein interaction. Following structural changes during these interactions is then of crucial interest. Site-Directed Spin Labeling (SDSL) combined to EPR spectroscopy is a powerful technique to follow structural modifications within proteins and during protein-protein interactions. Usual nitroxide labels target cysteine residues and afford a 3-line spectrum, whose shape is informative of the structural environment of the label. However, it is not possible to probe two regions of a protein or two partner proteins at the same time because of the overlapping of EPR signatures. Previously, we reported the design and the characterization of a spin label based on a β-phosphorylated (PP) nitroxide yielding a 6-line spectrum. Here, we report the use of two labels with different EPR signatures, namely maleimido-proxyl (P) and PP, to follow structural changes during a protein-protein interaction process in one single experiment. As a model system, we chose a disordered protein that undergoes an induced α-helical folding upon binding to its partner. We show that the EPR spectrum of a mixture of labeled interacting proteins can be analyzed in terms of structural changes during the interaction. This study represents an important step forward in the extension of the panoply of SDSL-EPR approaches.

Calculation of single crystal and polycrystalline pulsed EPR signals including relaxation by phonon modulation of hyperfine and $\tilde{g}$ matrices by solving Liouville von Neumann equation

Calculation of single crystal and polycrystalline pulsed EPR signals including relaxation by phonon modulation of hyperfine and $\tilde{g}$ matrices by solving Liouville von Neumann equation

Nickel complexes of ligands derived from (o-hydroxyphenyl) dichalcogenide: delocalised redox states of nickel and o-chalcogenophenolate ligands.

Two monoanionic nickel complexes Bu4N[Ni(LSeO)2] (1) and Bu4N[Ni(LSO)2] (2) (H2LSeO = 3,5-di-tert-butyl-2-hydroxyselenophenol and H2LSO = 3,5-di-tert-butyl-2-hydroxythiophenol) were synthesised by reductive cleavage of the respective 2,2'-dichalcogenobis(4,6-di-tert-butylphenol) (H2LX-X; X = Se, S) with nickel(ii) salts. The crystal structures of 1 and 2 confirm the reductive X-X bond cleavage with the concomitant formation of the corresponding monoanionic square planar complex, where quinoidal distortions of the aromatic rings are observed. The monoanionic complexes (1 and 2) are paramagnetic (S = 1/2), exhibiting rhombic EPR signals, and the g anisotropies are well correlated with the spin-orbit coupling of chalcogenides. The spectral data indicate that the ligands H2LXO in 1 and 2 are redox non-innocent and stabilise the square planar S = 1/2 nickel complexes with a highly delocalised unpaired electron. DFT calculations further support the delocalised electronic structures of the nickel complexes.

Nanocoatings on 2D Macroporous Silicon Structures

Macroporous silicon formed by photoanodic etching with high aspect ratio and large effective surface is one of the promising materials for the development of 2D photonic structures. We fabricated nanocoatings of CdTe, ZnO, CdS surface nanocrystals and SiO2 layers on macroporous silicon surface. The near-IR optical absorption was investigated and well-separated oscillations with giant amplitude were observed in the spectral ranges of surface level absorption. This process is because of resonance electron scattering on the surface impurity states with the difference between two resonance energies equal to the Wannier-Stark ladder. Macroporous silicon structures with SiO2 nanolayers and CdS nanocrystals are proposed to enhance the photoluminescence of CdS nanoparticles with quantum yield 28%. Addition functionalization of 2D macroporous silicon is a result of the high-pressure oxidation. The structural SiO2 reorganization to orthorhombic phase increases the concentration of paramagnetic Pb centers, EPR signal amplitude and GHz radiation absorption.

Локализованные экситоны в спектре оптического поглощения оксида цинка, легированного марганцем

AbstractThe results of the study of optical absorption and EPR signals of single crystals of zinc oxide doped with manganese are presented. A broad impurity absorption band with the threshold energy about 2.1 eV, which was treated as a result of charge transfer transitions, has been observed for a long time in ZnO : Mn absorption spectra. In absorption spectra of a polarized light at 4.2 and 77.3 K, we first detected several lines of different intensity in a 1.877–1.936 eV range of energies of the light quanta. The observed lines are attributed to a donor exciton [( d ^5 + h ) e ] that emerges as a result of the Coulomb binding a free s electron and a hole, which is localized on p – d hybridized states. The EPR spectra of Mn^2+ ion signals, when corresponding to the impurity absorption band exposed to light, are found to be not photosensitive. The obtained results indicate that the ZnO : Mn impurity absorption is due to transitions from antibonding p – d hybridized DBH states to the conduction band.

Reduction of molecular oxygen by redox active thiols: comparison of glutathione, N-acetylcysteine, cysteine, and homocysteine.

The reaction properties of the thiol compounds, cysteine (Cys), N-acetyl-l-cysteine (NAC), the reduced form glutathione (GSH), and homocysteine (HCS) were compared. The main purpose of this study was to find a thiol-based anti-oxidant suitable for biological experiments and to provide clear reasoning for its selection. The availability of thiol compounds to generate superoxide by reducing molecular oxygen (O2) at a hyperthermal temperature was discussed. An oxidative atmosphere, i.e., superoxide generation by the hypoxanthine-xanthine oxidase reaction, hydroxyl radical generation by X-ray irradiation, or direct one-electron oxidation by ferricyanide, was prepared in a reaction mixture containing 0.1 mM TEMPOL and 1 mM test compound, and the EPR signal decay of TEMPOL was observed. A reaction mixture containing 0.1 mM TEMPOL and 1 mM thiol compound was incubated at 44°C, and the EPR signal decay of TEMPOL was observed. Thiols could function as H-donors to the oxoammonium cation and produce the hydroxylamine form of TEMPOL in an oxidative atmosphere. Thiols could also irreversibly react with the oxoammonium cation. GSH and Cys could reduce O2 to form superoxide/hydroperoxyl radical at hyperthermal temperatures, but HCS and NAC could not reduce O2. GSH and Cys may cause reductive stress, whereas NAC is a simple tractable antioxidant.

Ricinoleic Acid as a Green Alternative to Oleic Acid in the Synthesis of Doped Nanocrystals

AbstractRicinoleic acid, extracted from the castor bean, is a cheap, abundant and naturally sourced capping agent for nanocrystals that offers the ability to functionalise the as‐synthesized nanocrystals through the use of the hydroxyl group, an advantage over oleic acid obtained from olives. In this work, we demonstrate the use of zinc and manganese ricinoleate complexes as green precursors for the synthesis of manganese‐doped zinc sulphide, MnxZn1‐xS. The metal ricinoleate complexes perform well as precursors for MnxZn1‐xS making the parent binary materials and alloys up to approx.x=0.07. The MnxZn1‐xS nanocrystals behave in the same manner as demonstrated previously in the literature with the photoluminescent performance decreasing and the EPR signals undergoing spectral line broadening with increased Mn doping beyond the dilute limit,i. e. x> 0.02.

Orthopalladated 1,4-iminonaphthoquinone derivative: Syntheses, redox series, molecular and electronic structures

Reaction of 2-((2-(phenylthio)phenyl)amino)-4-((2-(phenylthio)phenyl)imino)naphthalene-1(4H)-one (LH2) that is a N,S-chelating 1,4-iminonaphthoquinone derivative, with [Pd(DMSO)2Cl2] in boiling MeOH promotes an aromatic CH activation reaction affording an orthopalladated iminonaphthoquinone derivative, [PdII(LH−)Cl] (1). The molecular geometries and the bond parameters of LH2 and 1 were confirmed by single crystal X-ray crystallography. The redox activity of 1 is notably different from LH2. The 1/1− and 1−/12− redox couples are reversible due to successive reduction of LH− to 1,4-iminonapthasemiquinone anion radical (LH2−) and 1,4-imidonaphtholate (LH3−), while the LH2/ LH2− redox couple is irreversible. 1− exhibits an EPR signal at g = 2.002 and the spin density obtained from the unrestricted B3LYP/DFT calculation is localized on the 1,4-iminoquinone fragment. The UV–vis-NIR absorption spectrum of 1− recorded by a spectroelectrochemical measurement displays a characteristic NIR band at 800 nm that is absent in 1 and 12−.

Tetranuclear [MnIIIMn3IVO4] Complexes as Spectroscopic Models of the S2 State of the Oxygen Evolving Complex in Photosystem II.

Despite extensive biochemical, spectroscopic, and computational studies, the mechanism of biological water oxidation by the oxygen evolving complex (OEC) of Photosystem II remains a subject of significant debate. Mechanistic proposals are guided by the characterization of reaction intermediates such as the S2 state, which features two characteristic EPR signals at g = 2 and g = 4.1. Two nearly isoenergetic structural isomers have been proposed as the source of these distinct signals, but relevant structure-electronic structure studies remain rare. Herein, we report the synthesis, crystal structure, electrochemistry, XAS, magnetic susceptibility, variable temperature CW-EPR, and pulse EPR data for a series of [MnIIIMn3IVO4] cuboidal complexes as spectroscopic models of the S2 state of the OEC. Resembling the oxidation state and EPR spectra of the S2 state of the OEC, these model complexes show two EPR signals, a broad low field signal and a multiline signal, that are remarkably similar to the biological system. The effect of systematic changes in the nature of the bridging ligands on spectroscopy were studied. Results show that the electronic structure of tetranuclear Mn complexes is highly sensitive to even small geometric changes and the nature of the bridging ligands. Our model studies suggest that the spectroscopic properties of the OEC may also react very sensitively to small changes in structure; the effect of protonation state and other reorganization processes need to be carefully assessed.

Probing the role of Valine 185 of the D1 protein in the Photosystem II oxygen evolution

In Photosystem II (PSII), the Mn4CaO5-cluster of the active site advances through five sequential oxidation states (S0 to S4) before water is oxidized and O2 is generated. The V185 of the D1 protein has been shown to be an important amino acid in PSII function (Dilbeck et al. Biochemistry 52 (2013) 6824–6833). Here, we have studied its role by making a V185T site-directed mutant in the thermophilic cyanobacterium Thermosynechococcus elongatus. The properties of the V185T-PSII have been compared to those of the WT*3-PSII by using EPR spectroscopy, polarography, thermoluminescence and time-resolved UV–visible absorption spectroscopy. It is shown that the V185 and the chloride binding site very likely interact via the H-bond network linking TyrZ and the halide. The V185 contributes to the stabilization of S2 into the low spin (LS), S = 1/2, configuration. Indeed, in the V185T mutant a high proportion of S2 exhibits a high spin (HS), S = 5/2, configuration. By using bromocresol purple as a dye, a proton release was detected in the S1TyrZ → S2HSTyrZ transition in the V185T mutant in contrast to the WT*3-PSII in which there is no proton release in this transition. Instead, in WT*3-PSII, a proton release kinetically much faster than the S2LSTyrZ → S3TyrZ transition was observed and we propose that it occurs in the S2LSTyrZ → S2HSTyrZ intermediate step before the S2HSTyrZ → S3TyrZ transition occurs. The dramatic slowdown of the S3TyrZ → S0TyrZ transition in the V185T mutant does not originate from a structural modification of the Mn4CaO5 cluster since the spin S = 3 S3 EPR signal is not modified in the mutant. More probably, it is indicative of the strong implication of V185 in the tuning of an efficient relaxation processes of the H-bond network and/or of the protein.

COMPARATIVE EPR SPECTROSCOPY OF MEAT AND FISH RAW MATERIALS

The spread of radiation technologies requires the control of irradiated food raw materials.The possibility of identification of irradiated meat and fish raw materials by bone and pulp tissues, for fish raw materials also by skin with scales has been Experimentally established. The area of the EPR signal of samples of bone tissue in meat raw materials and samples of scales from the fish skin the raw materials most sensitive to amplitude variations with a high degree of correlation (up to 0.99).

Effect of the Irradiation Conditions on the Yield of Hydrogen Peroxide in Frozen Aqueous Solutions of Adenine Derivatives

Comparative results are presented from detecting hydrogen peroxide (H2O2) in aqueous solutions of adenine derivatives irradiated at 77 K in the near-UV range of wavelengths (λ = 260–400 and 290–460 nm). It is shown that the efficiency of H2O2 formation, estimated from the ratio of [H2O2] to the integral intensity of EPR signals observed in the irradiated samples, grew in the latter case. Based on the literature data, this increase is assumed to be due to specific features of the photoexcitation of aggregates of adenine derivatives that form in frozen aqueous solutions.

Proton-Coupled Oxidation of a Diarylamine: Amido and Aminyl Radical Complexes of Ruthenium(II).

Diarylamido, Q-N--Py (L-), complexes of ruthenium(II), trans-[(L-H+)RuII(PPh3)2Cl2] (1-H+) and trans-[(L-)RuII(PPh3)2(CO)Cl] (2), using N-(5-nitropyridin-2-yl)quinolin-8-amine (HL) as a ligand are disclosed (Q and Py refer to quinoline and 5-nitropyridine fragments). 1-H+ contains a zwitterionic amido ligand (Q-N--PyH+) that undergoes a concerted proton electron transfer (CPET) reaction in air, generating trans-[(L)Ru(PPh3)2Cl2] (1·CH2Cl2). The ground electronic state of 1 is delocalized as [(L-)RuIII ↔ (L•)RuII] (L• is an aminyl radical of type Q-N•-Py). The 1-H+/1 redox potential depends on the electrolytes, and the potentials are -1.57 and -1.40 V, respectively, in the presence of [N( n-Bu)4]PF6 and [N( n-Bu)4]Cl. The rate of 1-H+ → 1 conversion depends also on the medium and follows the order kD2O-CH2Cl2 > kH2O-CH2Cl2 > kCH2Cl2. In contrast, 2 containing the corresponding amido (L-) is stable and endures oxidation at 0.14 V, affording trans-[(L•)RuII(PPh3)2(CO)Cl] (2+). The electronic structures of the complexes were authenticated by single-crystal X-ray diffraction studies of HL, 1·CH2Cl2, and 2·(toluene), EPR spectroscopy, and density functional theory (DFT) calculations. Notably, the CQ-N (1.401(2) Å) and CPy-N (1.394(2) Å) lengths in 1·CH2Cl2 are relatively longer than the CQ-Namido (1.396(4) Å)and CPy-Namido (1.372(4) Å) lengths in 2·(toluene). Spin density obtained from DFT calculations scatters on both N and ruthenium atoms, revealing a delocalized state of 1. The notion was further confirmed by variable-temperature EPR spectra of a powder sample and CH2Cl2 solution, where the contributions of both [(L-)RuIII] and [(L•)RuII] components were detected. In contrast, 2+ is an aminyl radical complex of ruthenium(II), where the spin is dominantly localized on the ligand backbone (64%), particularly on N (27%). 2+ exhibits a strong EPR signal at g = 2.003. 1 and 2+ exhibit absorption bands at 560-630 and 830-840 nm, and the origins of these excitations were elucidated by TDDFT calculations on 1 and 2 in CH2Cl2.

CaO2 based Fenton-like reaction at neutral pH: Accelerated reduction of ferric species and production of superoxide radicals

One challenge in H2O2 based Fenton-like reaction is to break through the limitation of slow reduction of ferric species (FeIII). Present work describes a dramatic acceleration of Fenton-like reaction at neutral pH by using calcium peroxide (CaO2) as a source of hydrogen peroxide (H2O2) and EDTA as a chelating agent of ferric ions. In an optimized condition, phenol degradation in the H2O2 system displayed an initial latent time of 60 min, while phenol can be degraded immediately and removed completely in 30 min in the CaO2 system. Visual MINTEQ analyses indicated Fe-EDTA− was the active species in the reaction. The contribution of 1O2 in CaO2 system was excluded by the poor selectivity in phenol conversion and the comparable 1O2-TEMP EPR signals in both CaO2 and H2O2 systems. Kinetic analyses using chloroform as the probe of O2·− suggested the high production rate of O2·−, which is four orders of magnitude higher than that in H2O2 system. The mechanism of the accelerated CaO2 based Fenton-like reactions was featured by that two electrons coming from CaO2 can be utilized to promote reduction of FeIII: an inner sphere electron transfer takes place to reduce FeIII-EDTA and produce O2·−, and subsequently O2·− provides an electron to reduce another FeIII-EDTA. The revealed intrinsic reducibility in CaO2 based Fenton-like reaction represents a new strategy to break through the well-known rate limiting step of FeIII reduction in Fenton-like reaction and facilitate the removal of organic pollutants at neutral pHs, and also indicates a promising source of O2·− for diverse applications.

Mechanism of Optical Charge Exchange of Magnetic Centers in BSO : Fe

High-resistance photosensitive crystals of Bi12SiO20 (BSO) doped with iron ions were studied. X-ray diffraction analysis reveals the compression of a unit cell in a BSO : Fe crystal with increasing impurity concentration. Electron paramagnetic resonance demonstrates a decrease in the intensity of the EPR signal when the BSO: Fe crystal is exposed to light that generates photocarriers. It is found that the characteristic time of the EPR signal decrease is close to the value of the Maxwellian relaxation time measured with the help of the longitudinal electrooptical effect. A physical model of the mechanism of optical charge exchange of magnetic iron centers is discussed, based on the statement that the nature of the crystal bonds of the iron ion with ligands without structural modification of the crystal lattice changes during the photogeneration of carriers. A physical model is proposed, according to which a trivalent Fe3+ ion transforms into a divalent state of Fe2+ with a change in the total spin from 5/2 to 2. The compression of the unit cell with increasing iron ion concentration in the framework of the model under discussion is due to the transformation of atomic orbitals upon replacement of silicon ions by iron ions. The transformation process affects the cells unoccupied by iron, which is proved by the absence of a bifurcation of X-ray reflections and indicates the long-range nature of the intracrystalline interactions in sillenites.