EPR spectra of γ-irradiated hydrated barium dithionate single crystals

EPR spectra of barium dithionate hydrate single crystals γ-irradiated at low (80 Gy) and high (10 kGy) doses are studied. Four lines, the strongest of which is due to the SO₃⁻ radical, are observed in the EPR spectrum of the low-irradiated samples. Another line seems to belong to SO₂⁻. The strong line and weak lines with hyperfine structure and lines for pairs of closely spaced SO₃⁻ centers with a strong angular dependence are observed at high irradiation doses. The main values of the SO₃⁻ hyperfine coupling tensor and the dipole-dipole coupling constants of the SO₃⁻ pairs are determined. A quantum-chemical calculation of the electronic structure of isolated SO₃⁻ and SO₂⁻ radicals is performed. Values of the g tensors and hyperfine couplings are calculated. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 1, pp. 18–22, January–February, 2008.     

爆炸法合成纳米碳集聚体和纳米金刚石的EPR研究

爆炸法合成的纳米碳集聚体和纳米金刚石具有大量的结构缺陷和表面官能团. 电子顺磁共振（EPR）研究表明,它们均含有大量的自由基,而且纳米碳集聚体和纳米金刚石的EPR谱的形状、峰面积、g因子以及线宽ΔH_pp等都存在着较大的差异. 此外,还探讨了制备方法、化学处理条件、粒径大小、表面改性及掺杂对纳米碳集聚体和纳米金刚石的自由基密度的影响.     

小鼠甲醇氧化应激的电子顺磁共振的研究

建立了小鼠甲醇中毒的氧化应激模型,研究了甲醇诱导小鼠产生氧化应激状态,探讨了大黄中草药和维生素C对小鼠甲醇氧化应激的保护作用. 模型小鼠共分为5个组：空白组、对照组、甲醇应激组、大黄组、维生素C（Vc）组. 利用电子自旋捕捉技术研究了小鼠甲醇氧化应激不同模型组小鼠体内的肝、肾、脾、心、肺和脑中产生的自由基强度的变化. 结果表明： 甲醇诱发了小鼠体内自由基的产生,甲醇组和生理盐水组相比,自由基的强度明显增强（显著性差异统计指标P<0.01);而大黄和Vc对小鼠甲醇氧化应激有保护作用,大黄组、Vc 组和甲醇组相比自由基的强度则明显降低（P<0.01).     

Hyperfine Interaction Constants of the HCCS and DCCS Radicals Studied by Fourier Transform Millimeter-Wave Spectroscopy

The rotational spectral lines of HCCS and DCCS have been observed with a Fourier transform millimeter-wave spectrometer in combination with a pulsed discharge nozzle. The HCCS radical is produced by discharging a mixture of C₂H₂ and CS₂ diluted in Ar. The DCCS radical is produced by using C₂D₂ instead of C₂H₂. The spectral lines of HCCS and DCCS in both the ²Π_3/2 and ²Π_1/2 states are measured in the frequency range from 16 to 48 GHz, and the molecular constants are determined accurately from a joint least-squares analysis with the reported millimeter- and submillimeter-wave data. The hyperfine interaction constants of the hydrogen and deuterium nuclei are determined for the first time, and are discussed in relation to the Renner-Teller effect on this molecule.     

Tetravalent vanadium in CaF2 and SrF2 crystals: An EPR study

An EPR study of tetravalent vanadium centers created by room temperature X-irradiation in CaF₂ and SrF₂ is presented. The production efficiency of these centers is enhanced by previous annealing of the samples at 1000 K in air. The symmetry of V⁴⁺ ions is tetragonal and its EPR spectrum can be described by an axial spin Hamiltonian including a Zeeman and hyperfine term with $\text{S =}\text{1}\text{2}$ and $\text{I =}\text{7}\text{2}$ (corresponding to ⁵¹V nuclei). The following values for the spin Hamiltonian parameters are obtained g_∥ = 1.947 ± 0.002, g_⊥ = 1.935 ± 0.005, A_∥ = 500 ± 5 MHz, A_⊥ = 150 ± 10 MHz in the case of SrF₂ and g_∥ = 1.945 ± 0.002, A_∥ = 505 ± 5 MHz and A_⊥ < 200 MHz, in the case of CaF₂. A model for the center including an interstitial O^2? ion is tentatively proposed.     

The solution conformation of triarylmethyl radicals

Hyperfine coupling tensors to 1H, 2H, and natural abundance 13C were measured using X-band pulsed electron nuclear double resonance (ENDOR) spectroscopy for two triarylmethyl (trityl) radicals used in electron paramagnetic resonance imaging and oximetry: methyl tris(8-carboxy-2,2,6,6-tetramethyl-benzo[1,2d:4,5-d']bis(1,3)dithiol-4-yl) and methyl tris(8-carboxy-2,2,6,6-tetramethyl(-d3)-benzo[1,2d:4,5-d']bis(1,3)dithiol-4-yl). Quantum chemical calculations using density functional theory predict a structure that reproduces the experimentally determined hyperfine tensors. The radicals are propeller-shaped with the three aryl rings nearly mutually orthogonal. The central carbon atom carrying most of the unpaired electron spin density is surrounded by the sulfur atoms in the radical and is completely shielded from solvent. This structure explains features of the electron spin relaxation of these radicals and suggests ways in which the radicals can be chemically modified to improve their characteristics for imaging and oximetry.     

Reversible Photoisomerization of β-Methyl-β-Nitrostyrene: The Role of Triethylamine

The photolysis of trans-β-nitro-βmethylstyrene in acetonitrile solution gives the cisisomer with a quantum yield of 0.8. Addition of triethylamine to the system leads to a small decrease in the photoisomerization quantum yield and the appearance of a strong EPR signal. This signal remains for several hours at the end of the irradiation. It is demonstrated that the EPR signal is associated to an intermediary produced during the triethylamine catalyzed thermal back formation of the trans isomer. This intermediary bears an unpaired electron mostly associated to the nitro group and suggest that the thermal back reaction takes place by an initial electron transfer from the amine to the nitro group, leading to a long lived zwitterionic biradical.     

Radiation effect studies in single crystal of Trifluoroacetyl-α-Aminoisobutyric acid

In this study, electron paramagnetic resonance of γ-irradiated single crystals of N-Trifluoroacetyl-α-amino isobutyric acid (F₃Ac-Aib-OH) was investigated at room temperature and analyzed for different orientations of the crystal in the magnetic field. The paramagnetic species in N-Trifluoroacetyl-α-aminoisobutyric acid was attributed to the ?F₂-R radical (R= CONHC(CH₃)COOH). Hyperfine coupling constants and g value were also determined. In addition, the single crystal of F₃Ac-Aib-OH was UV-irradiated and paramagnetic species formed was studied at room temperature. The effects of gamma irradiation on fluoroamino acid and stability were discussed.     

A tunable reentrant resonator with transverse orientation of electric field for in vivo EPR spectroscopy

There has been a need for development of microwave resonator designs optimized to provide high sensitivity and high stability for EPR spectroscopy and imaging measurements of in vivo systems. The design and construction of a novel reentrant resonator with transversely oriented electric field (TERR) and rectangular sample opening cross section for EPR spectroscopy and imaging of in vivo biological samples, such as the whole body of mice and rats, is described. This design with its transversely oriented capacitive element enables wide and simple setting of the center frequency by trimming the dimensions of the capacitive plate over the range 100-900 MHz with unloaded Q values of approximately 1100 at 750 MHz, while the mechanical adjustment mechanism allows smooth continuous frequency tuning in the range +/-50 MHz. This orientation of the capacitive element limits the electric field based loss of resonator Q observed with large lossy samples, and it facilitates the use of capacitive coupling. Both microwave performance data and EPR measurements of aqueous samples demonstrate high sensitivity and stability of the design, which make it well suited for in vivo applications.     

在体电子自旋共振(EPR)波谱和成像技术在生物医学中的应用

活性氧和氮自由基(ROS/RNS)在一系列的人类疾病中扮演着双重角色. 它们可以是氧化剂, 诱导氧化状态, 导致组织损伤. 它们又可以是信号传导因子, 诱发保护性反应, 使得被调节的组织器官经受得起更强的损伤. 鉴于它们在生物医学中的重要作用, 检测它们产生和分布的技术的研究因而变得必要和紧迫. 在体电子自旋共振(EPR)波谱和成像技术渐已被应用于活体生物体系中用以表针和显像ROS/RNS. EPR 波谱特性(包括线宽、强度和寿命)以及空间分布信息已为动物甚至人体病理模型中氧化还原状态和氧分布的检测提供不可缺少的依据. 该文将简单描述和讨论一系列在体EPR 波谱和成像技术在器官和组织中的应用, 其中包括活体组织氧化还原状态, 活体组织氧分布和时间演化, 自由基空间以及谱-空间成像等.     

中国自由基捕获技术发展30年

本文简要回顾了30年来国内在自由基捕获技术（spin trapping）领域的研究进展,其中包括新型自由基捕获探针的分子设计与合成,探针结合EPR波谱方法在光、电化学反应以及生物领域的应用实例. 最后,结合国内外自由基捕获技术现状讨论了它的未来发展前景.     

Sensitivity of whole human teeth to fast neutrons and gamma-rays estimated by L-band EPR spectroscopy

This paper reports the first attempt to use L-band spectroscopy for estimating the sensitivity of whole teeth to fast neutrons and gamma-rays. Three teeth were successively irradiated first with fast neutrons with a wide energy spectrum (mean energy around 30 MeV) up to 160 Gy and then with gamma-rays up to 14 Gy. After each irradiation, L-band (1 GHz) EPR spectra of each whole tooth surrounded by the surface–coil resonator were recorded, yielding a single composite line principally due to CO₂⁻ and native radicals. The sensitivities are estimated by the slopes of the linear dose response curves of the dosimetric CO₂⁻ radicals. The ratios of the gamma/neutron sensitivities were found to be in the range 8–9 (±2) for the three teeth.     

γ辐射引发淀粉目由基衰减的动力学研究

用ESR方法研究了红薯淀粉在y射线预辐照下,产生的淀粉自由基特性及其室温下的自由基衰减动力学反应。结果表明在室温条件下,淀粉自由基的相对浓度随辐射剂量的增大而增加。自由基相对浓度的室温衰减用二级反应动力学处理,求得了衰减速率常数和淀粉自由基反应的半衰期。     

Application of magnetic field over-modulation for improved EPR linewidth measurements using probes with Lorentzian lineshape

Magnetic field modulation in CW electron paramagnetic resonance (EPR) is used for signal detection. However, it can also distort signal lineshape. In experiments where the linewidth information is of particular importance, small modulation amplitude is usually used to limit the lineshape distortion. The use of small modulation amplitude, however, results in low signal-to-noise ratio and therefore affects the precision of linewidth measurements. Recently, a new spectral simulation model has been developed enabling accurate fitting of modulation-broadened EPR spectra in liquids. Since the use of large modulation amplitude (over-modulation) can significantly enhance the EPR signal, the precision of linewidth measurements is therefore greatly improved. We investigated the over-modulation technique in EPR oximetry experiments using the oxygen-sensing probe lithium octa-n-butoxy-substitued naphthalocyanine (LiNc-BuO). Modulation amplitudes 2-18 times the intrinsic linewidth of the probe were applied to increase the spectral signal-to-noise ratio. The intrinsic linewidth of the probe at different oxygen concentrations was accurately extracted through curve fitting from the enhanced spectra. Thus, we demonstrated that the over-modulation model is also applicable to particulate oxygen-sensing probes such as LiNc-BuO and that the lineshape broadening induced by oxygen is separable from that induced by over-modulation. Therefore, the over-modulation technique can be used to enhance sensitivity and improve linewidth measurements for EPR oximetry with particulate oxygen-sensing probes with Lorentzian lineshape. It should be particularly useful for in vivo oxygen measurements, in which direct linewidth measurements may not be feasible due to inadequate signal-to-noise ratio.     

Formation of Radical Anions by Electrochemical Reduction of Nitroimidazoles in Aprotic Solvents and Mixed Solvent

The EPR spectra of radicals obtained by electrolytical reduction of 2-nitroimidazole and 4-nitroimidazole were measured in mixed solvents. The behavior of the nitrogen coupling constants with the solvent composition is discussed in terms of equilibria between radicals in different solvents. The equilibrium constants of the DMSO/water system were determinated. Molecular orbital calculations in the frame of LCAO-HMO method account correctly for the spin distribution of both compounds investigated.