The effect of inclusion inβ-cyclodextrin on the chemistry of peroxides: Reactions of radicals withβ-cyclodextrin

Studies by electron paramagnetic resonance (EPR), differential scanning calorimetry, thermogravimetric analysis, HPLC and NMR showed that radicals produced by thermolysis and photolysis of benzoyl peroxide,t-butyl peroxide and cumene hydroperoxide included in-cyclodextrin (-CD), undergo significant reaction with the-CD. The formation of-CD radicals was observed by EPR. Products formed by addition of radicals to-CD were also observed. Such host:guest radical reactions explain the reported stabilization of peroxides, found with-CD inclusion, as being primarily due to the interruption of chain reactions by trapping of the chain carriers. A small increase in activation barrier for cleavage of the included peroxide in-CD was also observed.     

An optional explanation for nickel sites of nickel-zinc phosphate glasses by their optical spectra and EPR g factor

In this paper, the nickel site, optical spectra and electron paramagnetic resonance (EPR) g factor of nickel-zinc phosphate glasses have been studied by ligand-field theory. The orbital mixing effect between p and d orbits has been included in the calculation by two-spin-orbit parameter model. The present study shows that nickel occupies the tetrahedral zinc site with cubic symmetry in nickel-zinc phosphate glasses. Unlike the result of previous study that assigns nickel to an octahedral interstitial site, it is an optional explanation for nickel sites in nickel-zinc phosphate glasses by analysing the optical absorption spectra and EPR g factor.     

Synthesis of a new stable and water-soluble tris(4-hydroxysulfonyltetrachlorophenyl)methyl radical with selective oxidative capacity

A new stable organic free radical of the PTM (perchlorotriphenylmethyl) series very soluble in water is reported. This free radical is sensitive to electron transfer processes, and the selectivity of these reactions in the presence of ascorbic acid, pyrogallol, and catechol as reducing species is described. The electron paramagnetic resonance spectrum and the electrochemical behavior are also presented.     

Exogenous bridging and nonbridging in Cu(II) complexes of Mannich base ligands: Synthesis and physical properties

Preparation of pentadentate ligands L¹, L², L³ and L⁴, where L¹ = 4-chloro-3-methyl-2[(prolin-1-yl)methyl]-6-[N-phenyl piperazin-1-yl)methyl]phenol, L² = 4-ethyl-2-[(prolin-1-yl)methyl]-6-[(N-phenyl piperazin-1-yl)methyl]phenol, L³ = 4-chloro-3-methyl-2-[(prolin-1-yl)methyl]-6-[N-methyl piperazin-1-yl]methyl phenol, L⁴ = 4-methoxy-2-[(prolin-1-yl)methyl]-6-[(N-phenyl piperazin-1-yl)methyl]phenol is described together with that of the corresponding Cu(II) complexes with various bridging motifs like OH, OAc and NO₂. The complexes are characterized by elemental analysis, electrochemical and electron paramagnetic spectral studies. Redox properties of the complexes in acetonitrile are highly quasireversible due to the chemical or/and stereochemical changes subsequent to electron transfer. The complexes show resolved copper hyperfine EPR at room temperature, indicating the presence of weak antiferromagnetic coupling between the copper atoms. Strengths of the antiferromagnetic interactions are in the order NO₂>OAc>OH.     

Review of Spin–Orbit Coupled Semimetal SrIrO3 in Thin Film Form

Spin–orbit coupling, locking the momentum of an electron to its spin, has been shown essential for giving rise to many novel physical behaviors. SrIrO₃ is a typical metallic member of the strong spin–orbit coupling iridate family. Its orthorhombic phase has been confirmed as a paramagnetic semimetal resulted from the interplay among spin–orbit coupling, electron correlation, and crystal field, and was theoretically predicted to host versatile topological phases. This article reviews the current knowledge on the preparation and the tunable properties of orthorhombic SrIrO₃ films. Experiments have demonstrated that orthorhombic SrIrO₃ can be successfully synthesized as films under substrate lattice constraint without high pressure, and the films frequently display metal-insulator transition due to disorder and weak-antilocalization owing to spin-orbit coupling. The properties of orthorhombic SrIrO₃ film are sensitive to the rotation and tilting of the IrO₆ octahedral, and consequently can be significantly tuned through strain engineering. Simultaneously, thickness-dependent size effect is also remarkable in SrIrO₃ films. The accumulated research on SrIrO₃ films suggests an urgent demand for research on superlattices constructed with orthorhombic SrIrO₃, to better understand the mechanism of the electron structure evolution, and thus the relevant magnetic states and topological phases in orthorhombic SrIrO₃ and its family.     

利用EPR研究三氧化钼中氧还活性位点形成的温度依赖性

本文利用热处理还原法,利用三氧化钼诱导形成具有氧化还原活性的中间产物及其温度相关特性. 电子顺磁共振波谱(EPR)实验结果表明,热处理后在Mo^VI离子被还原成Mo^V离子并形成了超氧阴离子自由基O₂^-. 这两种活性中心的最佳热还原温度约300∽350 ^°C. 自350 ^°逐渐升温,两种EPR信号强度迅速下降,下降∽50%所对应的温度是400∽450 ^°C;当温度升至600 ^°C或更高时,EPR信号降至0. 结果表明,较高温处理或持续长时间处理都使热还原更容易发生,积累了越来越多的电子,在基底中形成类似于反铁磁耦合的电子离域. 随着离域程度增大,EPR信号强度开始下降并直至消失.     

Theoretical Studies of g Factors and Defect Structures for Cubic, Tetragonal, and Orthorhombic Fe^＋ Centers in Alkali Halides MX （M=Li, Na; X = F, C1）

The EPR 9 factors for cubic, tetragonal and orthorhombic Fe^＋ centers in alkali halides MX （M= Li, Na; X = F, CI） are calculated from second-order perturbation formulas of g factors based on cluster approach for 3d^7 ions in three symmetries. From calculations, the g factors of these Fe^＋ centers in MX crystals are reasonably explained and the defect structural data for the tetragonal and orthorhombic Fe^＋ centers are estimated. The results are discussed.     

In situ catalyst systems for ring-opening metathesis polymerization

Several new in situ tungsten catalyst systems for ring-opening metathesis polymerizations (ROMP) by reaction injection molding (RIM) have been developed by adding BF₃ promoter to binary catalyst systems, by using metal hydride cocatalysts, and by altering the ligands on the procatalyst metal center. BF₃ etherates improved catalyst efficiency and reduced induction times for formation of active catalysts from reaction of aryloxytungsten complexes [e.g., (ArO)_y(WX_x)] with organotin hydrides. Coordinatively unsaturated cationic intermediates, such as [(ArO)_yWX_x-1]⁺ BF₃X⁻, are proposed to facilitate formation of the active catalysts. Tougher poly(dicyclopentadiene) (polyDCPD) composites were produced using < 5 wt % of styrene-butadiene block copolymers due to formation of small “shell-core” rubber morphologies when BF₃ promoter was added to the catalyst system. Nonalkylating metal hydrides besides R₃SnH, including (PPh₃)₂CuBH₄, (PPh₃CuH)₆, and Cp₂ZrClH, were shown to be cocatalysts. The optimum 2 : 1 stoichiometric ratio of organotin hydride cocatalyst to tungsten, revealed by BF₃-promoted catalyst systems, and W^V EPR resonances (g ∼ 1.7) observed in the reaction of aryloxytungsten with organotin hydride are consistent with an overall reduction and reoxidation mechanism for formation of the active metathesis catalysts. Some tungsten complexes derived from 9-hydroxyfluorene, 2,2′-(and 4,4′)-biphenols, and 1,4-hydroquinones were found to be very reactive procatalysts, even in the absence of cocatalyst in some cases. These procatalysts also were paramagnetic, characterized by unusual EPR spectra consistent with W^V (g = 1.6–1.9) and “ligand-centered” (g = 2.003) resonances. Valence tautomeric species, analogous to catecholate-semiquinonate complexes, are proposed. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 3027–3047, 1997     

Structure,atomic Hirshfeld surface,spectroscopic studies and magnetic and dielectric properties of new mixed solid solution (NH4)2Mn0.17Cu0.83Cl4⋅2H2O

The tetrachlorocupratmanganate dehydrate (NH₄)₂Mn_0.17Cu_0.83Cl₄?2H₂O has been prepared and characterized using various physicochemical techniques including Fourier transform infrared and Raman spectroscopies, differential scanning calorimetry and dielectric and magnetic measurements. A preliminary single‐crystal X‐ray diffraction structural analysis reveals that the title compound belongs to the tetragonal system with P4₍₂₎/mnm space group. The unit cell dimensions are: a = b = 7.5817(2), c = 7.9312(2) Å, with Z = 2. Its crystal structure was determined and refined down to R = 2%. The structure of this compound consists of discrete [Cu/MnCl₄?2H₂O]^2? octahedra interleaved with alkali cations. The cohesion and stabilization of the structure are provided by hydrogen bond interactions (N─H…Cl and O─H…Cl) between [NH₄]⁺ cation and [Cu/MnCl₄?2H₂O]^2? anion. Hirshfeld surface analysis has been performed to explore the behaviour of these weak interactions. Dielectric measurements confirm the transition temperatures determined using differential scanning calorimetry. The temperature dependence of the magnetic susceptibility was measured in the temperature range 10–300 K at various magnetic field intensities. Magnetic measurements reveal the occurrence of weak ferromagnetic behaviour at low temperature (T_c = 12 K). The ferromagnetic ordering is further confirmed by the presence of hysteresis loops.     

Application of commercially available fluorophores as triplet spin probes in EPR spectroscopy

ABSTRACT

In recent years, photoexcited molecular triplet states became increasingly popular in magnetic resonance, e.g. as spin probes to measure distances relative to other electron-paramagnetic species or as moieties that transfer light-generated electron–spin polarisation of the triplet state to surrounding magnetic nuclei. In this study, the triplet states of three commercially available dyes, Erythrosin B, Rose Bengal and Atto Thio 12, all typically utilised as fluorophores in optical spectroscopies and microscopies, are investigated in aqueous solutions by using transient absorption spectroscopy and transient electron paramagnetic resonance (EPR). From these methods, the triplet-state lifetimes as well as their zero-field splitting parameters, D and E, which reflect the electronic structures of the triplet state wavefunctions, were obtained. Atto Thio 12 exhibits much smaller D and E values as compared to Rose Bengal and Erythrosin B. On the basis of density functional theory calculations of the triplets’ energy splittings at zero magnetic field, these findings were rationalised. As a proof of concept for applications, the triplet-state properties of Atto Thio 12 bound to an aptamer were also determined and the results are discussed.