Electrochemical C-H Amination from a Primary Amine via a Cobalt Nitrene Intermediate

Origin of electron paramagnetic resonance signal in anthracite

Photocatalysis opens up a new window for carbonyl chemistry. Despite a multitude of photochemical reactions of carbonyl compounds, visible light-induced catalytic asymmetric transformations remain elusive and pose a formidable challenge. Accordingly, the development of simple, efficient, and economic catalytic systems is the ideal pursuit for chemists. Herein, we report an enantioselective radical photoaddition to ketones through a Lewis acid-enabled photoredox catalysis wherein the in situ formed chiral N,N'-dioxide/Sc(III)-ketone complex serves as a temporary photocatalyst to trigger single-electron transfer oxidation of silanes for the generation of nucleophilic radical species, including primary, secondary, and tertiary alkyl radicals, giving various enantioenriched aza-heterocycle-based tertiary alcohols in good to excellent yields and enantioselectivities. The results of electron paramagnetic resonance (EPR) and high-resolution mass spectrum (HRMS) measurements provided favorable evidence for the stereocontrolled radical addition process involved in this reaction.

Magnetic properties and vanadium oxidation state in α-Li3V2(PO4)3/C composite: Magnetization and ESR measurements

High-frequency electron spin resonance (ESR) measurements of S = 1/2 one-dimensional Heisenberg antiferromagnetic zig-zag chain substance (VO)(SO4)(2,2-bpy) were performed in the temperature region from 1.8 to 265 K. ESR measurements at 265 K show typical powder pattern spectra of the V4+ ion and g || = 1.925 ± 0.001 and g ⊥ = 1.976 ± 0.001 were obtained. Although the magnetic susceptibility shows a maximum at 3.1 K suggesting the existence of a short-range order, no g-shift and line width broadening were observed down to 1.8 K. We suggest that these temperature-independent features of ESR can be attributed to the result of frustration in (VO)(SO4)(2,2-bpy).

Electrical, magnetic, and EPR studies of the quaternary chalcogenides Cu 2AIIBIVX4 prepared by iodine transport

Vanadium‐doped La3Ga5.5Ta0.5O14 single crystal (0.05 mol% in the melt with respect to Ga) grown by the Czochralski method has been investigated using electron paramagnetic resonance (EPR) and optical absorption measurements. The optical energy gap of pure La3Ga5.5Ta0.5O14 single crystal is equal to 4.94 eV, while the value for vanadium‐doped La3Ga5.5Ta0.5O14 single crystal is 3.44 eV. Optical absorption measurements have revealed 444 nm, 700 nm and 1100 nm bands arising mainly from V3+ ions at octahedral sites. Moreover, V4+ ions were found at octahedral sites (525 nm band) for the “as‐grown” crystals and at tetrahedral positions (380 nm CT band and 600‐ and 800 nm dd transitions) for crystals irradiated with γ‐quanta with a dose of 1.2 × 105 Gy. The X‐band EPR measurements have been done at room temperature while rotating the single‐crystal sample around a, b * and c crystal axes. For each rotation direction the observed spectra consist of an intense multiline signal centred at ∼340 mT and a second, weak one at ∼150 mT. The dominant signal can be ascribed to the V4+ ions (S = 1/2, I = 7/2) occupying the Ga1, Ta octahedral positions, with an axial D 3 point symmetry. The principal tensor values are determined as g ∥ = 1.925(5), g ⊥ = 1.958(5), A ∥ = 17.0(5) mT and A ⊥ = 5.8(5) mT. Each principal axis of the vanadium paramagnetic centres indeed reveals three different orientations in La3Ga5.5Ta0.5O14 crystal with respect to the space orientation of the Ga3 tetrahedra connected with the Ga1 octahedron. The low‐field resonance signal could neither be ascribed to iron impurities nor to the V4+ ions (S = 1/2, I = 7/2) occupying other (tetrahedral) positions simultaneously creating the vacancy state. This signal was too weak to perform detailed analysis. There are also presented low‐temperature EPR spectra that did not reveal any new lines. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

This paper describes the design considerations for a dual mode X-band continuous wave (CW) Electron Paramagnetic Resonance (EPR) cavity, for simultaneous EPR measurement and microwave heating of the same sample. An elliptical cavity geometry is chosen to split the degeneracy of the TM110 mode, allowing for a well resolved EPR signal with the TM110,a and TM110,b modes resonating at around 10 GHz and 9.5 GHz, respectively, the latter of which is used for EPR measurements. This geometry has the benefit that the TM010 mode used for microwave heating resonates at 6.1 GHz, below the cut off frequency of the X-band waveguide used for the EPR channel, providing effective isolation between the heating and EPR channels. The use of a pair of 9 µm thick copper clad laminates as the flat cavity walls allows for sufficient penetration of the modulation field (Bmod) into the cavity, as well as maintaining a high cavity Q factor (> 5700) for sensitive EPR measurements. Locating the heating port at an angle of 135° to the EPR port provides additional space for easier coupling adjustment and for larger sample access to be accommodated. The associated decrease of EPR signal strength is fully compensated for by using a 7.2 GHz low pass filter on the heating port. EPR spectra using 1.6 mm and 4.0 mm sample tubes are shown at room temperature (298 K) and 318 K for a standard Cu(acac)2 solution, demonstrating the effectiveness of this dual-mode EPR cavity for microwave heating during EPR detection.

π-Pimer, π-Dimer, π-Trimer, and 1D π-Stacks in a Series of Benzene Triimide Radical Anions: Substituent-Modulated π Interactions and Physical Properties in Crystalline State

Theory of excitation modes in diamond chain compound [formula omitted

Dynamic electron spin resonance (ESR) measurements compare the paramagnetic and antiferromagnetic (AF) properties of superconducting oxides in the range 4 K to room temperature, at 8 MHz and 9.36 GHz. Two are derivatives of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$: I: Nd(${\mathrm{Nd}}_{0.05}$${\mathrm{Ba}}_{0.95}$${)}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$, ${\mathit{T}}_{\mathit{c}0}$=72 K and II: ${\mathrm{Y}}_{0.2}$${\mathrm{Ca}}_{0.8}$${\mathrm{Sr}}_{2}$[${\mathrm{Cu}}_{2}$(${\mathrm{Tl}}_{0.5}$${\mathrm{Pb}}_{0.5}$)]${\mathrm{O}}_{7}$, ${\mathit{T}}_{\mathit{c}0}$=108 K and two are cases where AF ordering dominates the weak superconductivity: III: ${\mathrm{NbO}}_{1.1}$, 1.25\ensuremath{\le}${\mathit{T}}_{\mathit{c}0}$\ensuremath{\le}10 K and IV: ${\mathrm{La}}_{2}$${\mathrm{NiO}}_{4.00}$, 70 K \ensuremath{\ge}${\mathit{T}}_{\mathit{c}0}$\ensuremath{\ge}40 K. At temperatures 298\ensuremath{\ge}T\ensuremath{\ge}64 K, the ESR absorption by I indicates orthorhombic symmetry. The peaks at ${\mathit{g}}_{\mathit{c}}$=2.06, ${\mathit{g}}_{\mathit{b}}$=2.13, and ${\mathit{g}}_{\mathit{a}}$=2.24 are identified with the presence of 5% ${\mathrm{Nd}}^{3+}$${(}^{4}$${\mathit{I}}_{9/2}$) in the Ba layer because the characteristic ${\mathrm{Cu}}^{2+}$ impurity hyperfine structure is absent and the ESR signal disappears several degrees below ${\mathit{T}}_{\mathit{c}}$. Near ${\mathit{T}}_{\mathit{c}}$ the ESR absorption is reduced by two orders of magnitude.Proximity effects give rise to interference fringes with period ${\mathrm{\ensuremath{\tau}}}_{\mathit{f}}$(T) independent of the field B and the rate of sweep ${\mathit{dB}}_{\mathit{z}}$/dt. ESR is observed below ${\mathit{T}}_{\mathit{c}}$ because flux penetrates the superconductor. The temperature dependence of ${\mathrm{\ensuremath{\tau}}}_{\mathit{f}}$ leads to an activation energy for the flux motion ${\mathit{E}}_{\mathit{a}}$(I)/R\ensuremath{\le}16 K and ${\mathit{E}}_{\mathit{a}}$ (III)/R\ensuremath{\simeq}3 K \ensuremath{\simeq}${\mathit{T}}_{\mathit{c}}$/4. In the superconducting state a coherent flux expulsion response to a change in ${\mathit{B}}_{\mathit{z}}$ from 500 mT to zero is observed in times ${\mathrm{\ensuremath{\tau}}}_{\mathit{r}}$=8 to 10 s. The inverse rate of noise spikes due to flux expulsion, when the samples are cooled through ${\mathit{T}}_{\mathit{c}}$ in a magnetic field, varies from ${\mathrm{\ensuremath{\tau}}}_{\mathrm{noise}}$=3.5 s for III to 21 s for IV. The microwave absorption spectra identify three temperature regimes: (i) For 3.5 K T${\mathit{T}}_{\mathit{m}}$\ensuremath{\simeq}${\mathit{T}}^{\mathrm{*}}$${\mathit{T}}_{\mathit{c}}$, superconducting behavior was confirmed by the energy loss near zero magnetic field and the kinetics of high-field noise due to flux expulsion. Near g=2.00 ESR absorption is observed for all materials. A broad absorption near 50 to 100 mT at 9.36 GHz has been attributed to AF resonance. (ii) ${\mathit{T}}_{\mathit{m}}$\ensuremath{\simeq}${\mathit{T}}^{\mathrm{*}}$\ensuremath{\le}T\ensuremath{\le}${\mathit{T}}_{\mathit{c}}$ identifies the range where flux motion gives rise to interference fringes in the ESR absorption. (iii) ESR and AF resonance are observed immediately after warming above ${\mathit{T}}_{\mathit{c}}$.

To design and synthesize long-chain substituted 2-[(4'-hydroxyethoxy) phenyl]-4,4,5,5-tetramethyl-2-imidazoline-1-oxyl 3-oxide (HPN) derivatives with enhanced anti-hypoxic activity. HPN derivatives 1, 3, 5 containing lipophilic long chains were synthesized via the alkylation of HPN with 6-bromohexan-1-ol, ethyl 6-bromohexanoate or 6-bromohexane, respectively using acetonitrile as the solvent and K 2CO 3 as the acid-binding agent at 60 ℃. Derivative 2 was synthesized via hydrolysis reactions of derivative 1 in the NaOH/CH 3OH/H 2O system. Using dichloromethane as the solvent and N, N'-diisopropylcarbodiimide as the dehydrating agent, HPN underwent esterification with hexanoic acid to obtain derivative 4. The structures of derivatives 1-5 were characterized by infrared spectroscopy, electron paramagnetic resonance and high resolution mass spectrometry. The purities of derivatives were detected by high performance liquid chromatography, and the lipid solubilities of derivatives were evaluated by calculating the oil-water partition coefficients (log P). Anti-hypoxia activities of HPN and its long-chain lipophilic derivatives 1-5 were evaluated using normobaric hypoxia test and acute decompression hypoxia test. The structures of the derivatives were confirmed by infrared spectroscopy, electron paramagnetic resonance and high resolution mass spectroscopy. The yields of target derivatives were all above 92%, and the purities were all above 96%. The log P values of derivatives 1-5 were 2.78, 2.00, 2.04, 2.88 and 3.10, which were higher than that of HPN (0.97). Derivatives 1-5 significantly prolonged the survival time of mice at the dose of 0.3 mmol/kg in normobaric hypoxic test and reduced the mortality rate of acute decompression hypoxic mice to 60%, 70%, 60%, 70% and 40%, respectively. The synthesis of derivatives 1-5 is convenient, and the yield is high. The synthesized derivatives especially derivative 5 show anti-hypoxic activity similar to or better than HPN at lower doses.

Reconstruction of doses absorbed by radiotherapy patients by means of EPR dosimetry in tooth enamel

ROS: a step closer to elucidating their role in the etiology of light-induced skin disorders.

The electrochemical study of Sm(III) ions was conducted on Sn film electrode in eutectic LiCl-KCl in the temperature range from 773 K to 923 K by a series of electrochemical techniques. The results of current reversal chronopotentiometry of Sm(III) on W electrode showed that the redox reaction related to Sm(III) is a kind of soluble/soluble system, which meant that Sm(III) was reduced to Sm(II) on W electrode. On Sn film electrode, the reduction of Sm(III) was found to be two-step process: Linear polarization (LP) and Tafel techniques were conducted to measure the exchange current density (j0) of Sm(II)/SmSn3 couple. The variation of j0 with temperature accords with the Arrhenius law, and the activation energy was evaluated to be 14.32 kJ mol−1 and 14.08 kJ mol−1, respectively. Moreover, the feasibility of extracting Sm on Sn film electrode was examined by constant potential electrolysis at −1.45 V in the LiCl-KCl-SmCl3-SnCl2 molten salt for 3 h. XRD result indicated the formation of SmSn3. Constant current and potential electrolysis were performed to extract metallic Sm on liquid Sn pool electrode. The alloy samples were characterized by SEM-EDS and XRD, which displayed the existence of SmSn3 and Sm4Sn3 phases in Sm-Sn alloys.

Room-temperature ferromagnetism and hydrogen shallow donors in rare-earth Eu-doped ZnO nanorods