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Bispidine containing a paramagnetic group was obtained for the first time by the Mannich reaction using the 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl (4-amino-TEMPO) free radical as a reagent. The structure of the target compound, tert-butyl 9-oxo-7-(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)-3,7-diazabicyclo[3.3.1]nonane-3-carboxylate, was confirmed by mass spectrometry and ESR spectroscopy, the molecular and crystal structure was established by X-ray diffraction analysis. In the synthesis of the starting 4-amino-TEMPO by the reductive amination reaction, the by-product of the further reaction of 4-amino-TEMPO with the starting ketone, the free biradical N-(2,2,6,6-tetramethyl-1-oxylpiperidin-4-yl)-2,2,6,6-tetramethyl-4-aminopiperidine-1-oxyl, was isolated and structurally characterized. [ABSTRACT FROM AUTHOR]

Conjugates of bispidines and free radicals of the (2,2,6,6-tetramethylpiperidin-1-yl)-oxyl type were synthesized for the first time. The conjugates were obtained by the alkylation reaction of NH-bispidines with electrophilic chloro derivatives containing a free radical. The structure of the latter was established by X-ray diffraction analysis. The products obtained were characterized by IR spectroscopy, ESR spectroscopy, and high-resolution mass spectrometry. [ABSTRACT FROM AUTHOR]

Samples of humic materials—humic acids and fulvic acids—derived from Tisul lignite (Kansk-Achinsk Basin) are investigated by ESR (electron spin resonance) spectroscopy. The concentration of free radicals declines in the following sequence: lignite, humic acids, fulvic acids. The proportion of aliphatic radicals increases in the same sequence. By simulation of the ESR spectra of the fulvic acids and comparison with the experimental spectra, natural complexes of fulvic acids with Fe3+ and Mn2+ ions are detected. By determining the splitting parameters in zero field (D and E), it is established that the complexes with Fe3+ have axial symmetry, with a complex multilevel structure. The internal coordination sphere of the complex consists of water molecules, whereas the external coordination sphere consists of oxygen-bearing fulvic acid groups. The calculated hyperfine structure constant of the experimental ESR spectra for the complexes with Mn2+ (79.7 G) is lower than the typical value for the octahedral Mn2+ complex [Mn(H2O)6]2+. That indicates partial replacement of the water molecules by oxygen-bearing functional groups of fulvic acids. [ABSTRACT FROM AUTHOR]

Impurity paramagnetic ions Mn2+ and high spin Fe3+ (S = 5/2) are shown to be very informative paired spin labels to investigate structural transformations in natural aluminosilicate clay minerals by ESR spectroscopy. Second derivative ESR (SD ESR) enables to detect minor narrow lines of the ions against the background of intense broad lines of other paramagnetic impurities. Complex SD ESR spectra of the ions are explained by the Jahn-Teller effect and hyperfine interactions with OH-groups. SD ESR spectra before and after heating (620 and 900°C) proved transformations of octahedral crystal cells accompanied by the loss of the OH-groups, displacement of the ions to equivalent positions. [ABSTRACT FROM AUTHOR]

Two sodalite samples (sample I is Na8Al6Si6O24Cl2⋅0.4H2O from the Kovdor alkaline ultramafic massif with carbonatites in the Murmansk region, Russia, and sample II is Na8Al6Si6O24Cl2⋅0.2H2O from the Bayan Kol nepheline syenite and miaskite massif in the Republic of Tyva) were studied by thermal and electron-microprobe analyses, powder X-ray diffraction, photoluminescence, and by IR, Raman, and ESR spectroscopy. Solution melt calorimetry was applied to determine the enthalpy of formation from elements for water-bearing sodalite samples: −13536 ± 10 (I) and −13503 ± 19 (II) kJ/mol. The enthalpy of formation of sodalite of the theoretical composition Na8Al6Si6O24Cl2 was evaluated at ΔfH0(298.15 K) = −13446 ± 11 kJ/mol. The data obtained on the enthalpy of formation of sodalite and literature data on its S0(298.15 K) were used to calculate the standard Gibbs energies of formation of anhydrous and of water-bearing sodalite. [ABSTRACT FROM AUTHOR]

A large number of studies indicated that caffeic acid represents an important natural phenolic compound with many potential uses in medications and cosmetics, but also with therapeutic implications in cardiovascular diseases, various types of cancer, and neurological diseases. In this work we studied kinetics and reaction mechanism of caffeic acid autoxidation in weakly alkaline aqueous solutions (pH 7.4 and 8.4) in the presence of Mg(II) ions by applying high performance liquid chromatography with diode-array detection (HPLC–DAD) and electron spin resonance (ESR) spectroscopy. The results of HPLC–DAD analysis revealed that the presence of Mg(II) ions enhanced the autoxidation rate to a much greater extent than the increase in pH from 7.4 to 8.4. Analysis of DAD UV–Vis and ESR spectra, as well as comparison of the calculated logP values with retention times of chromatographically separated compounds, enabled the identification of the main initial products of caffeic acid autoxidation in the presence of Mg(II) ions as caffeic acid quinone and its dimer and indicated the nature of some minor products (hydroxylated derivatives of caffeic acid and their quinones). ESR spectroscopy disclosed that prolonged autoxidation of caffeic acid leads to the formation of polymeric, humic acid like, products. These findings may be important when considering treatments and/or storage of medications, cosmetics, and foods containing caffeic acid. [ABSTRACT FROM AUTHOR]

3,3′-(1,4-Phenylene)bis[1-(4-R-phenyl)-5-phenyl-5,6-dihydro-1,2,4,5-tetrazinium] perchlorates have been transformed into stable tetrazinyl biradicals by the action of D-glucose in a slightly alkaline medium (NH4OH) in the presence of air oxygen. The tetrazinyl biradicals have been isolated in the individual state and characterized by means of cyclic voltammetry and elemental analysis as well as IR, UV, and ESR spectroscopy. [ABSTRACT FROM AUTHOR]

ESR spectra of asphaltenes from a series of crude oils from the Devonian and Carboniferous deposits of the South-Tatar Dome in Tatarstan with low vanadium content and of vanadiferous crude oils from deposits of the Melekess depression in Tatarstan are analyzed. For asphaltenes from Devonian oils, the correlation between the concentrations of stable free radicals (SFR) and vanadyl complexes (VCs) has direct trend, whereas for asphaltenes from Carboniferous oils the trend is inverse. Taking into account the previously revealed inverse trend for asphaltenes of vanadium-enriched highly viscous crude oils [1], the opposite trends in SFR–VC correlations (direct and inverse) suggest different structures of asphaltene molecules in oils with different vanadium content and, correspondingly, different sources and conditions of the formation of oil deposits. Specific features of the ESR characteristics of asphaltenes of core and extractable oils and of oils from Devonian and Carboniferous deposits are revealed. [ABSTRACT FROM AUTHOR]

The redox behaviors of macrocyclic molecules with an entirely π-conjugated system are of interest due to their unique optical, electronic, and magnetic properties. In this study, defect-free cyclic P3HT with a degree of polymerization (DPn) from 14 to 43 was synthesized based on our previously established method, and its unique redox behaviors arising from the cyclic topology were investigated. Cyclic voltammetry (CV) showed that the HOMO level of cyclic P3HT decreases from –4.86 eV (14 mer) to –4.89 eV (43 mer), in contrast to the linear counterparts increasing from –4.94 eV (14 mer) to –4.91 eV (43 mer). During the CV measurement, linear P3HT suffered from electro-oxidation at the chain ends, while cyclic P3HT was stable. ESR and UV–Vis–NIR spectroscopy suggested that cyclic P3HT has stronger dicationic properties due to the interactions between the polarons. On the other hand, linear P3HT showed characteristics of polaron pairs with multiple isolated polarons. Moreover, the dicationic properties of cyclic P3HT were more pronounced for the smaller macrocycles. [ABSTRACT FROM AUTHOR]

It has been shown for the first time that the high-temperature treatment of heavy oil with a high content of asphaltenes at 350–450 °C without a catalyst or H2 leads to the formation of new vanadium(IV) porphyrin complexes detected by ESR spectroscopy. In anisotropic spectra of treated oil samples recorded at 130 K, together with the signals of the porphyrin complex of the vanadyl ion, VO2+, another component with distinct g and A spin Hamiltonian parameters was observed. A comparative analysis of the resonance parameters of the revealed complexes allowed us to unambiguously identify them as the thiovanadyl (VS2+) porphyrins formed during the thermal treatment. Thus, the formation of thiovanadyl porphyrins from vanadyl porphyrins in asphaltene-containing heavy oils at high-temperature processing has been experimentally proven for the first time. [ABSTRACT FROM AUTHOR]

A modified procedure has been developed for the synthesis of Kuhn verdazyl radicals via conversion of 1-(4-R1-phenyl)-3-(4-R2-phenyl)-5-phenylformazan into 1-(4-R1-phenyl)-3-(4-R2-phenyl)-5-phenylver-dazylium tetrafluoroborates, followed by their reduction with D-glucose in alkaline medium to 1-(4-R1-phenyl)-3-(4-R2-phenyl)-5-phenylleucoverdazyls and oxidation of the latter with atmospheric oxygen. The formation of 1-(4-R1-phenyl)-3-(4-R2-phenyl)-5-phenylverdazyl radicals was confirmed by ESR spectroscopy. [ABSTRACT FROM AUTHOR]

Three new coordination compounds of copper(II) with glycine (HGly) and 2,2'-bipyridine (bipy) were synthesized by solution-based and mechanochemical methods: [Cu(Gly)(H2O)(bipy)][Cu(Gly)(SO4)(bipy)] ·6H2O (1a·6H2O), [Cu(Gly)(H2O)(bipy)]2SO4 (1b), [Cu(Gly)(H2O) (bipy)]2SO4 ·H2O (1b·H2O). The amount of water in the reaction mixture influenced the product of crystallization. All compounds were characterized by X-ray diffraction methods and form 1D infinite chains or 2D sheets of complex ions connected by p-interactions. Compounds 1a·6H2O and 1b were characterized by X-band electron spin resonance (ESR) spectroscopy and the values of g-tensors for Cu(II) ions were determined. Compounds 1a·6H2O and 1b showed pronounced antiproliferative activity toward a panel of six human cell lines. The most impared was HepG2 cell line at 10-5 mol dm-3 concentration (74.5 % reduction of cell growth) followed by moderate activity toward KATO III, Caco-2, MDA-MB-231, PANC-1 and MRC-5 cells at 10-4 mol dm-3 concentration of compounds 1a·6H2O and 1b. Generally, both compounds express similar antiproliferative effect on evaluated cells. [ABSTRACT FROM AUTHOR]

The structural, chemical, and physicochemical characteristics and antioxidant properties of humic acids isolated from shale in the Kenderlyk and Kiin fields are determined. Negative values of the acids' oxidation are found: –3.62 and –4.06 for Kenderlyk and Kiin shale, respectively. Thus, the shale-based humic acids are reducing agents. IR spectroscopic data show clear absorption bands of hydroxyl, functional, and carbonyl groups. ESR spectroscopy indicates a high content of paramagnetic centers in the humic acids: 9.3 × 1017 and 9.5 × 1017 spin/g for Kenderlyk and Kiin shale, respectively. The paramagnetic centers in the molecular structure of the humic acids indicate that they are promising as antioxidants. [ABSTRACT FROM AUTHOR]

The corresponding formazans were synthesized by the reaction of phenylhydrazones of nitro-substituted benzaldehydes and 4-pyridinecarbaldehyde with arenediazonium salts obtained from p-substituted anilines. Formazans were converted into the corresponding 5,6-dihydro-1,2,4,5-tetrazinium triflates by the action of formalin in the presence of CF3SO3H. When tetrazinium salts were treated with D-glucose in a weakly alkaline medium (NH4OH) in the presence of atmospheric oxygen, stable tetrazinyl radicals were formed. Formazans, tetrazinium triflates, and tetrazinyl radicals were isolated in the individual state and characterized by elemental analysis, IR, UV, NMR, or ESR (radicals) spectroscopy. [ABSTRACT FROM AUTHOR]

Anti-tubercular activity of oxindole semicarbazones increased to much larger extent on complexation with Cu(II). Binding studies and molecular modeling are in well agreement with experimental data. [Display omitted] Copper (II) acetate reacted with 2-oxindole semicarbazone (2-Hoxsc, H1L), 3-methyl 2-oxindole semicarbazone (3-MeHoxsc, H2L) and 6-Chloro-2-oxindole semicarbazone (6-ClHoxsc, H3L) in 1:2 (M:L) molar ratio to form complexes of general formula, [Cu(L 2)] (1L, 1 ; 2L 2 ; 3L 3. Stoichiometric ratio of complexes was established using UV–Vis spectroscopy. All the complexes were characterised by the CHN analysis, IR, ESR spectroscopy and Mass spectrometry. From the ESR spectrum, g values obtained (g ‖ = 2.20; g ⊥ = 2.05) for complex 2 confirms axial symmetry for this complex, whereas a broad isotropic signal in 1 and 3 (g iso = 2.060, 1 ; 2.057, 3) indicates extensive exchange coupling. All the synthesized compounds (ligands and complexes) complexes were examined for their anti-tubercular activity against M. tuberculosis H37RV strain. Compounds were also tested for their anti-bacterial (B. subtilis , K. pneumonia) and antifungal (C. auris , C. albicans) activities. Biological investigations revealed that the antimicrobial activities (anti-TB, antibacterial and antifungal) of ligands get improved on complexation with Cu (II) due to formation of chelate ring, which can make the ligand a more powerful biological agent. Complex 3 has shown excellent anti-TB (MIC = 1.6 g/ml) and antibacterial (ZOI = 26 mm at 5 mg/mL) activities. Strong binding of complex 3 was observed (K b = 24.22 × 105 M−1) with Human Serum Albumin (HSA) using fluorescence spectroscopy. Molecular modelling of complex 3 was also done with the active site of amino acid of M. tuberculosis enoyl reductase. The minimal binding energy of −10.1 kcal/mol indicated significant intermolecular interaction between M. tuberculosis enoyl reductase and complex 3 and is in well agreement with experimental data. [ABSTRACT FROM AUTHOR]

Emodin is a natural anthraquinone derivative found in nature, widely known as an herbal medicine. Here, the partition, location, and interaction of emodin with lipid membranes of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) are experimentally investigated with different techniques. Our studies have considered the neutral form of emodin (EMH) and its anionic/deprotonated form (EM−), and their interaction with a more and less packed lipid membrane, DMPC at the gel and fluid phases, respectively. Though DSC results indicate that the two species, EMH and EM−, similarly disrupt the packing of DMPC bilayers, spin labels clearly show that EMH causes a stronger bilayer disruption, both in gel and fluid DMPC. Fluorescence spectroscopy shows that both EMH and EM− have a high affinity for DMPC: the binding of EM− to both gel and fluid DMPC bilayers was found to be quite similar, and similar to that of EMH to gel DMPC, K p = (1.4 ± 0.3) x 103. However, EMH was found to bind twice more strongly to fluid DMPC bilayers, K p = (3.2 ± 0.3) x 103. Spin labels and optical absorption spectroscopy indicate that emodin is located close to the lipid bilayer surface, and suggest that EM− is closer to the lipid/water interface than EMH, as expected. The present studies present a relevant contribution to the current understanding of the effect the two species of emodin, EMH and EM−, present on different microregions of an organism, as local pH values can vary significantly, can cause in a neutral lipid membrane, either more or less packed, liked gel and fluid DMPC, respectively, and could be extended to lipid domains of biological membranes. [Display omitted] • DSC and ESR revealed that emodin strongly binds and disrupts gel and fluid membranes. • ESR clearly shows that EMH causes a stronger bilayer disruption than EM−. • Fluorescence was used to obtain EMH and EM− membrane/water partition coefficients. • The location of EMH and EM−, in both gel and fluid DMPC membranes is found. • Emodin is located close to the membrane surface, with EM− closer to the interface. [ABSTRACT FROM AUTHOR]

Although organic solar cells have started to demonstrate competitive power conversion efficiencies of >18 %, their operational lifetimes remain insufficient for wide practical use and the factors influencing the photostability of absorber materials and completed devices are still not completely understood. A systematic study of two series of structurally similar [XTBT]n and [XTTBTBTT]n polymers (16 structures in total) reveals the building blocks that enable the highest material stability towards photooxidation: fluorene, silafluorene, carbazole, diketopyrrolopyrrole, and isoindigo. Furthermore, a direct correlation is evident between the electronic properties of the conjugated polymers and their reactivity towards oxygen. The structures with the lowest highest occupied molecular orbital (HOMO) energies show the highest electrochemical oxidation potentials and appear to be the most resistant towards chemical oxidation. These relationships set important guidelines for the further rational design of new absorber materials for efficient and stable organic photovoltaics. [ABSTRACT FROM AUTHOR]

Three glass systems of Cu2+ ions doped lithium-borate with the composition of 56B2O3 + 25Li2O + 10Na2O + 5CaO + 2SrO + 2Al2O3 + 0.5TeO2 + xCuO, where x = 0.0, 0.2, and 0.3 wt% are synthesized by the conventional melt quenching method. X-ray diffraction (XRD) studies, Fourier transform infrared (FTIR) spectroscopy, electron spin resonance (ESR) spectroscopy, physical properties and ionizing radiation shielding performance of the prepared Cu2+-glasses have been investigated. All prepared Cu2+-glasses are in an amorphous structure nature. The density increases from 2.4379 to 2.4597 g.cm−3 as the Cu2+ ions content increased from 0.0 to 0.3 wt%. The FTIR spectra reveal four basic active areas in the IR spectra region (400–4000 cm−1). FTIR absorption spectra of glasses after irradiation with 10 kGy show that some of BO3 triangles are converted into BO4 groups. The ESR spectra for the investigated glasses exhibit highest intensity of the signal at the highest irradiation dose of 10 kGy. Linear attenuations coefficients (LACs) of the investigated glasses were arranged in order: (Cu0.0)LAC < (Cu0.2)LAC < (Cu0.3)LAC. Half-value layers (HVLs) values were found 0.088, 0.085, 0.083 cm, and 15.54, 15.43, 15.32 cm for Cu0.0, Cu0.2, and Cu0.3 at 0.015 and 15 MeV, respectively. MFPs arranged from 0.128 to 22.419 cm, and from 0.12 to 22.119 cm for Cu0.0–Cu0.3 at 0.015 and 15 MeV, respectively. For Cu0.3 glass, the transmission factor for gamma photon with energy 0.05 MeV decreased in order 63.53, 40.36, and 6.57% with increasing the glass thickness between 0.5, 1, and 3 cm, respectively. Finally, the results concluded that the 0.3 wt% CuO glass is considered as the best shield for gamma radiation among the other prepared glasses. [ABSTRACT FROM AUTHOR]

The cationic meso-aryl-substituted porphyrins and their metal complexes were studied as model compounds for photodynamic therapy by electron spin resonance (ESR) techniques. Symmetrical cationic porphyrins with terminal pyridinium groups on short alkyl spacers and their Zn(II) and Cu(II) complexes were synthesized. Zero-field splitting parameters of the photoexcited triplet states were determined by time-resolved ESR. For Cu(II) complexes, the hyperfine coupling between the paramagnetic ligand and the nitrogen atoms of the porphyrin ring was measured. The effect of pyridinium substituents and the ligand on the magnetic-resonance parameters of porphyrins was analyzed on the basis of the obtained results. [ABSTRACT FROM AUTHOR]

The synthesis, spectroscopic data, redox properties of B8Cl8, [B8Cl8].−, and [B8Cl8]2−, and the single‐crystal X‐ray structure analysis of [Ph4P]+2 [B8Cl8]2− ⋅ CH3CN are described. Temperature‐dependent 11B NMR measurements and theoretical studies (DFT) concerning the fluxional behavior of [B8Cl8]2− will be discussed. – B8Cl8 reacts with reductants like iodide to the intense purple colored radical anion [B8Cl8].− which is formed as well from B8Cl8 by traces of water. The colorless dianion closo‐[B8Cl8]2− is obtained by the reaction of B8Cl8 or [B8Cl8].− with iodide. The single‐crystal X‐ray structure analysis of [Ph4P]+2[B8Cl8]2− confirms the dodecahedral D2d structure of [B8Cl8]2−. The 11B NMR spectra of [B8Cl8]2− solutions show only one broad signal even at low temperatures due to the fast fluctuation of the [B8Cl8]2− polyhedron. The energy of the C2v structure isomer of [B8Cl8]2− was calculated by DFT methods to be only 0.6 kcal/mol higher in energy than the D2d form, and the activation barrier for the D2d to C2v transformation is predicted to be about 0.9 kcal/mol. [ABSTRACT FROM AUTHOR]

The synthesis, spectroscopic data, redox properties of B8Cl8, [B8Cl8].−, and [B8Cl8]2−, and the single‐crystal X‐ray structure analysis of [Ph4P]+2 [B8Cl8]2− ⋅ CH3CN are described. Temperature‐dependent 11B NMR measurements and theoretical studies (DFT) concerning the fluxional behavior of [B8Cl8]2− will be discussed. – B8Cl8 reacts with reductants like iodide to the intense purple colored radical anion [B8Cl8].− which is formed as well from B8Cl8 by traces of water. The colorless dianion closo‐[B8Cl8]2− is obtained by the reaction of B8Cl8 or [B8Cl8].− with iodide. The single‐crystal X‐ray structure analysis of [Ph4P]+2[B8Cl8]2− confirms the dodecahedral D2d structure of [B8Cl8]2−. The 11B NMR spectra of [B8Cl8]2− solutions show only one broad signal even at low temperatures due to the fast fluctuation of the [B8Cl8]2− polyhedron. The energy of the C2v structure isomer of [B8Cl8]2− was calculated by DFT methods to be only 0.6 kcal/mol higher in energy than the D2d form, and the activation barrier for the D2d to C2v transformation is predicted to be about 0.9 kcal/mol. [ABSTRACT FROM AUTHOR]

Janis Stradins (10.12.1933 – 29.11.2019) was a well-known expert in molecular electrochemistry, ESR spectroscopy and physical organic chemistry, as well as in history of sciences. His main works in electrochemistry were connected with organic molecules single electron reduction and oxidation primary and secondary products studies, these species ESR spectra hyperfine structure investigations, supplying data on various organic molecules groups' reactivity, demonstrating abilities of electrochemical studies for organic compounds reaction prediction. He was ISE member, past president of Latvian Academy of Sciences, full member of European Academy of Sciences and Arts, from 2011 its Honorary Senator. [ABSTRACT FROM AUTHOR]

[Display omitted] • Synthesis of δ Tantalum pentoxide and its nanocomposite with NRGO. • TO@NRGO exhibited enhanced hydrogen evolution (19,500 µmol g−1). • TO@NRGO exhibited improved performance in dye degradation (94%). • PL and ESR studies to prove the active species involved in dye degradation. • Simultaneous degradation of MB and RhB with good stability and reusability. Precipitation assisted facile hydrothermal method has been developed for anchoring nitrogen-doped reduced graphene oxide (NRGO) with tantalum pentoxide (TO) denoted as TO@NRGO. Synthesized materials were characterized using spectroscopic, optical and microscopic techniques and confirm transforming TO from orthorhombic to hexagonal phase (δ) upon anchoring with NRGO. TO@NRGO, TO and NRGO have been evaluated for photocatalytic hydrogen evolution, degradation of Methylene blue (MB) and Rhodamine B (RhB). The enhanced photocatalytic activity was observed in TO@NRGO nanocomposite compared to TO and NRGO due to decreased bandgap (2.5 eV) and increased surface area (312 m2 g−1). TO@NRGO evolved 19,500 µmol g−1 of hydrogen for 3 h. TO@NRGO showed better degradation efficiency of 94 and 88% at a time of 100 min for MB and RhB, respectively. The parameters involved in photocatalytic dye degradation, like the effect of pH, catalyst dosage, and initial concentration of dyes, have been carefully optimized to achieve maximum performance of the catalyst. The stability and reusability of TO@NRGO are good and managed to degrade dyes effectively even after the 5th run. Thus, TO@NRGO could serve as a choice of material in resolving the issues related to energy and the environment. [ABSTRACT FROM AUTHOR]

The results of studying electrochemical conversions of 7-R-3-X-1,2,4-triazolo[5,1-c][1,2,4]-triazin-4-ones (Triazavirin® and its derivatives) using cyclic voltammetry, chronoamperometry, and ESR spectroscopy are presented. The derivatives of 7-R-3-X-1,2,4-triazolo[5,1-c][1,2,4]-triazin-4-ones were found to be capable of electrochemical reducing in the potential range from −0.16 to −0.68 V (vs Ag/AgCl) in a Britton—Robinson buffer at pH 2–12. At the potentials of the first electroreduction step at pH 2–6, the main process of transformations is the four-electron scheme of reduction of the nitro group of Triazavirin®. The adduct of the radical substances with the spin probe N-(1-hydroxy-2,2,6,6-tetramethylpiperidin-4-yl)-2-methylpropanamide was registered after the preliminary generation of the Triazavirin® radical anion at −0.5 V vs Ag/AgCl in an acidic medium. A linear dependence of the current of the first electroreduction step of the Triazavirin® on the concentration was obtained at pH 2 (linearity range from 10−4 to 1.6 · 10−2 mol L−1, I = −1.93 · C, R2 = 0.9977). [ABSTRACT FROM AUTHOR]

Reduction of ArBIG‐bian (1, 1,2‐bis[(2,6‐dibenzhydryl‐4‐methylphenyl)imino]acenaphthene) with one molar equivalent of Li, Na or K in tetrahydrofuran (THF) affords corresponding radical‐anionic salts (ArBIG‐bian)M(THF) (M=Li, 2; Na, 3; K, 4). Compounds 2–4 were isolated in good yields and characterized by the elemental analysis, IR and ESR spectroscopy as well as the single‐crystal X‐Ray analysis. Bulky Ph2(H)C groups in ArBIG‐bian ligand prevent dimerization of complexes 2–4 and limit a number of coordinated THF molecules to one. In all three products a saturation of the alkali metal coordination sphere is achieved through an interaction with Ph rings of Ph2(H)C substituents. [ABSTRACT FROM AUTHOR]

Lingonberries contain high contents of bioactive compounds such as chlorogenic acids and anthocyanins. In addition to radical scavenging and antioxidant activities, these compounds can protect cells from DNA damage. For this reason, lingonberries might be well suited for nutraceuticals or natural biomedicines. To assess these applications, the present study characterized and identified the most effective extract, only consisting of anthocyanins, copigments or a mixture of both, obtained from a lingonberry juice concentrate. An extract was generated by using a XAD-7 column followed by fractionation into anthocyanins and copigments using adsorptive membrane chromatography. After identification of main polyphenols by HPLC–photodiode array–electrospray ionization–tandem mass spectrometry, free radical scavenging activity was analyzed by electron spin resonance spectroscopy using 2,2-diphenyl-1-picrylhydrazyl and galvinoxyl radicals. Furthermore, cyclic voltammetry analyses and the Trolox equivalent antioxidant capacity (TEAC) assay were applied. Finally, the reactive oxygen species (ROS) reducing effects of the lingonberry extract and its fractions were evaluated in HepG2 cells. While the combination of anthocyanins and copigments possessed the highest antioxidant activities, all samples (XAD-7 extract, anthocyanin and copigment fraction) protected cells from oxidative stress. Thus, synergistic effects between phenolic compounds may be responsible for the high antioxidant potential of lingonberries, enabling their use as nutraceuticals.

Two synthetic approaches were developed for the preparation of 3,6-di-tert-butyl-2-hydroxy-4-pyridinylphenolate (LH), a new zwitter-ionic redox-active diolate type ligand. Two heteroligand five-coordinate tin(IV) derivatives were prepared with this ligand: 3,6-di-tert-butyl-2-oxy-4-pyridinylphenolato(triphenyl)tin(IV) (I) and 3,6-di-tert-butyl-2-oxy-4-pyridinylphenolato(diphenyl)chlorotin(IV) (II). The molecular structures of the ligand LH ∙ 0.5Py and complex I ∙ CH3CN were determined by X-ray diffraction (CIF files CCDC nos. 1974166 (LH), 1974165 (I)). It was shown that the ligand LH and the tin(IV) compound exhibit solvatochromism, which consists in a considerable blue shift with increasing solvent polarity. [ABSTRACT FROM AUTHOR]

The complexes of superoxide radical anions formed at the zigzag edges of curved graphene sheets upon microwave excitation were studied by electron spin resonance and quantum chemical density functional theory. The binding energy of the complex decreases from 700 to 42 meV as the distance between the oxygen atom and the zigzag graphene edge increases from 1.46 to 1.64 Å. The configurations and binding energies of the complexes depend both on the topology of the underlying graphene layer (single- or double-layer, flat, or curved) and on the type of atomic groups terminating the edge carbon atoms via σ-bonds. Complexes with low dissociation energy (<70 meV) can be formed only at cryogenic temperatures as a result of electronic charge transfer from the edge towards the O2 molecule. The temperature behavior of the paramagnetic spin susceptibility of the complex indicates an antiferromagnetic interaction of the spin S = 1/2 of the radical anions with the edge spins located outside the area "demagnetized" due to its depletion by the electronic charge. At T > 50 K, the complex irreversibly dissociates and the O2 molecule is detached from the edge. The existence of complexes with a low dissociation energy expands the views on the ionic chemical bond with a large distance between the interacting species. [ABSTRACT FROM AUTHOR]

The correlation of several defects and optical and magnetic properties with Fe content in Zn1−xFexAl2O4 (0.01 ≤ x ≤ 0.40) nanocrystals has been scrutinized through X‐ray diffraction, O K‐edge X‐ray absorption near‐edge structure, FT–IR, diffuse reflectance, photoluminescence and electron spin‐resonance spectroscopies, and vibrating sample magnetometry. Increasing Fe content causes elongation in the octahedral units of the lattice, accompanied by distortion in the octahedral coordination. Fe introduces non‐radiative centres in the forbidden gap, thereby tuning the band gap from 4.37 to 3.88 eV and eliminating emission in the visible region. Zn vacancies are found to tail off, while , and FeAl× antisite defects increase in concentration with increasing Fe content. Inhomogeneous broadening of spin‐resonance signals infers strong spin‐lattice interactions of Fe3+ ions at distorted octahedral and non‐symmetric tetrahedral sites. A transition is observed from paramagnetism to superparamagnetism at higher Fe concentrations. A visual colour change from pearly white to orange–brown is observed in Zn1−xFexAl2O4 nanocrystals with increasing Fe content, revealing its potential candidature for pigments in the paint and dye industries. [ABSTRACT FROM AUTHOR]

The pathogenesis of diseases of the gastrointestinal tract in horses is accompanied by inflammation and oxidative stress and may be caused by a lack of nitric oxide, which controls various signaling pathways in the body. The level of nitrites, which are metabolites of nitric oxide in horses with various intestinal diseases, has been evaluated in blood serum at 3.60 ± 3.02 μM and 8.3 ± 6.0 μM in horses at ages of 7–26 years and 1–5 years, respectively. A sharp reduction in the nitrite concentrations was observed in all horses with intestinal diseases (3.39 ± 2.85 μM), especially in horses with tympanitic caecum (0.6 ± 0.4 μM) and obstruction of the colon (0.81 ± 0.5 μM). [ABSTRACT FROM AUTHOR]

The new complex [Cu4L2(H2AEDP)2(H2O)4] · 34H2O was prepared by the reaction of CuSO4 with bis(2-pyridyl-1,2,4-triazol-3-yl)butane (H2L) and 1-aminoethane-1,1-diphosphonic acid (H4AEDP) and studied by X-ray diffraction (CIF file CCDC no. 1913117). The complex is a spacer-armed dimer in which two dimer subunits formed with participation of diphosphonate dianions are linked to each other via two doubly deprotonated bis(pyridyl)triazoles. The bridging diphosphonate anion exists in the zwitter ion form, bis(triazolyl)butane is coordinated via the nitrogen atoms of the pyridyl moiety and the deprotonated triazole ring. Analysis of the ESR spectrum of the polycrystalline sample attests to weak exchange interactions in the dimeric moieties. [ABSTRACT FROM AUTHOR]

Abstract A series of bioactive Cu (II), Co (II), Ni (II) and Fe (III) complexes of the novel disperse azo dye ligand was obtained from the reaction between 5, 5, 7-trimethyl-4, 5, 6, 7-tetrahydro-1, 3-benzothiazol-2-amine and 2-thioxodihydropyrimidine-4, 6 (1 H , 5 H)-dione by the conventional diazo-coupling reaction at 0–5 °C. The structural characterization of the synthesized compounds were elucidated by using various physicochemical and spectroscopic techniques. The observed lower molar conductivity values for all the metal complexes suggested their non-electrolytic nature. From the spectral investigations, it is evident that the newly synthesized azo dye behaves as a tridentate ligand and its complexes with the various metal ions found to form a six-membered chelate ring with octahedral geometry except for the Cu (II) complex which has distorted octahedral geometrical environment. Thermal behaviour of the metal complexes was studied by TG-DTA technique and exhibited good thermal stabilities and also confirmed the presence of coordinated water molecules in Ni (II) complex. Electrochemical behaviour of the Cu (II) complex was studied by cyclic voltammetry in DMF solution and the results indicated well-established quasi-reversible behaviour at a scan rate of 0.05 V-1. The results of the anti-mycobacterial and anti-inflammatory activity indicated that, the metal chelates are relatively more potent than the parent ligand. The cytotoxic effect of the synthesized compounds was studied against two cancerous cell lines HeLa and A549 by MTT assay and the Cu (II) and Fe (III) complexes were proved to be potential anticancer agents. Highlights • Synthesis of novel bioactive metal chelates derived from 5, 5, 7-trimethyl-4, 5, 6, 7-tetrahydro-1, 3-benzothiazol. • ESR spectra suggested the mononuclear nature of the complexes and all of them are having octahedral geometry except the Cu (II) complex which has distorted octahedral environment around the copper ion. • The cyclic voltammogram of the Cu (II) complex exhibited a well-established quasi-reversible behaviour in DMF solution at a scan rate of 0.05 V-1. • All the metal complexes showed enhanced pharmacological properties than the free ligand. [ABSTRACT FROM AUTHOR]

Translation of environmental cues into cellular behavior is a necessary process in all forms of life. In bacteria, this process frequently involves two-component systems in which a sensor histidine kinase (HK) autophosphorylates in response to a stimulus before subsequently transferring the phosphoryl group to a response regulator that controls downstream effectors. Many details of the molecular mechanisms of HK activation are still unclear due to complications associated with the multiple signaling states of these large, multidomain proteins. To address these challenges, we combined complementary solution biophysical approaches to examine the conformational changes upon activation of a minimal, blue-light-sensing histidine kinase from Erythrobacter litoralis HTCC2594, EL346. Our data show that multiple conformations coexist in the dark state of EL346 in solution, which may explain the enzyme's residual dark-state activity. We also observe that activation involves destabilization of the helices in the dimerization and histidine phosphotransfer-like domain, where the phosphoacceptor histidine resides, and their interactions with the catalytic domain. Similar light-induced changes occur to some extent even in constitutively active or inactive mutants, showing that light sensing can be decoupled from activation of kinase activity. These structural changes mirror those inferred by comparing X-ray crystal structures of inactive and active HK fragments, suggesting that they are at the core of conformational changes leading to HK activation. More broadly, our findings uncover surprising complexity in this simple system and allow us to outline a mechanism of the multiple steps of HK activation. [ABSTRACT FROM AUTHOR]

The effect of citrulline and ammonium chloride on the nitric oxide formation by peritoneal macrophages and liver tissue cells was studied using ESR spectroscopy. In ex vivo models, the incubation of cells capable of expressing inducible NO synthase (iNOS) with interferon-γ resulted in a moderate increase in the amount of hemoglobin–nitric oxide nitrosyl complexes (Heme–NO NCs), whereas incubation with l-citrulline and ammonium chloride increased the amount of Heme–NO NCs by an order of magnitude. It was assumed that a separate cycle of L-arginine and nitric oxide synthesis exists in the peritoneal macrophages and liver cells, with the major participants of the cycle being the inducible NO synthase enzyme (iNOS) and enzymes that synthesize L-arginine from L-citrulline and a nitrogen source. Functioning of this cycle makes immunocompetent cells with iNOS able to produce NO for a long time and in large amounts. [ABSTRACT FROM AUTHOR]

The paramagnetic and photocatalytic properties of C-S co-doped TiO2 nanocatalysts were investigated. It was established, that the carbon-doped catalysts with different sulfur content show the presence of paramagnetic centers, referred to the dangling bonds in graphitized structures, intensities of this lines were drastically lowered after photocatalytic reaction. The ESR signals from Ti3+ centers were not detected. It was showed, that the light excitation of samples, regardless of doping (type and quantity), in the absorption band did not lead to the appearance of luminescence, so the recombination of charges occurs only in a non-radiation way, part of which reveals in photocatalysis, while the other part of the charges is captured/ deactivated by defects/traps. Composite samples showed enhancement of the photocatalytic activity in the destruction of safranine T under UV irradiation as compared to pure TiO2. [ABSTRACT FROM AUTHOR]

For Friedel-Crafts alkylation of aromatic hydrocarbons an ionic reaction path is considered as classical reaction mechanism. The alkylation with benzyl chloride in the presence of ion-exchanged K10 montmorillonite catalysts containing multivalent, reducible cations had an outstanding activity, therefore a radical initial step as a supplement to the ionic mechanism was proposed earlier. We made ESR investigations to clarify the existence and the nature of the suggested radical species. The ESR experiments verified that the reaction involves a radical step. [ABSTRACT FROM AUTHOR]

We synthesized two new organogold derivatives of a nitronyl nitroxide (NN) with phosphine ligands, namely NN-Au-PtBuPh2 and NN-Au-PtBu2Ph. They were characterized by X-ray diffraction analysis, cyclic voltammetry, and ESR, IR, and UV/Vis spectroscopy. The X-ray structural analysis revealed a tendency of the NN moiety to form a large number of short intermolecular contacts. This phenomenon is related to the anionic nature of the paramagnetic group NN, as evidenced by a significantly lower oxidation potential in comparison with purely organic derivatives of NN radicals. The cross-coupling reaction of NN-Au-PPh3, NN-Au-PtBuPh2, or NN-Au-PtBu2Ph with an activated bromoarene, namely, p-BrC6H4NO2, was investigated. It was shown that regardless of the presence of the bulky tert-butyl substituent, all gold derivatives have similar activities in the cross-coupling reaction and give a cross-coupling product, NN-C6H4NO2, with comparable yields.

Fish lipids are comprised of considerable quantities of polyunsaturated acids and are prone to oxidation, producing reactive oxygen species and hydroperoxides. This study aimed to evaluate the biochemical and structural alterations in Caco-2 cells following exposure to 100 μg/mL methyl linoleate or fish oil, and then radiated for 24, 48 or 72 h. Electron spin resonance spectroscopy detected free radicals in the lipid membrane, Raman microscopy observed biochemical alterations and atomic force microscopy identified changes in morphology, such as the breakdown of DNA bonds. The study showed that bioimaging and biochemical techniques can be effective at detecting and diagnosing cellular injuries incurred by lipid peroxidation.