ESR detection of wheat flour before and after irradiation

We revealed free radicals in wheat flour before and after gamma-ray irradiation and their thermal behavior during heat-treatment using electron spin resonance (ESR) spectroscopy. The ESR spectrum of wheat flour before irradiation consists of a sextet centered at g = 2.0 and a singlet signal at the same g-value position. The first one is attributable to a signal with hyperfine (hf) interactions of Mn2+ ion (hf constant: 7.4 mT). The second is originated from carbon-centered radical. Upon gamma-ray irradiation, however, a new signal with two triplet lines at the low and high field ends was detected in wheat flour on top of the Mn2+ sextet lines. We analyzed the triplet ESR lines as powder spectra (rhombic g-tensor symmetry) with nitrogen (14N) hyperfine interactions. This indicates that a new organic radical was induced in the conjugated protein portion of wheat flour by the gamma-ray irradiation. Intensity of the organic free radical at g = 2.0 detected in irradiated wheat flour increased monotonically by the thermal treatment. The analysis of the time-dependent evolution and decay process based on the theory of transient phenomena as well as the nonlinear least-squares numerical method provided a unique time constant for the radical evolution and decay in wheat flour during the heat-treatment.     

An electron spin resonance study of dry vegetables before and after irradiation

The ESR signals were successfully observed for the first time in dry vegetables (DVs) that are prominently used in oriental cuisines. We analyzed ESR signals of DV before and after irradiation. Before irradiation, the ESR signal of DV consisted of the three components: a singlet at g=2.0030, the sextet signals from Mn(2+) ion, and a singlet from Fe(3+). The first originated from a carbon centered organic free radical. The second is attributable to the sextet signal with hyperfine interactions of Mn(2+) ion centered at g=2.0020. The third is a singlet at g=4.0030 due to Fe(3+). After the gamma-ray irradiation, a new pair of signals, or twin peaks, appeared in the ESR spectrum of DV. The intensity of the organic free radical at g=2.0030 of the irradiated DV increased lineally with radiation doses. Progressive saturation behavior of the DV indicates a unique saturation and the signals obeyed various relaxation processes.     

An ESR protocol based on relaxation phenomena of irradiated Japanese pepper

We found various free radicals in a commercially available pepper in Japan before and after irradiation using electron spin resonance (ESR) spectroscopy. The typical ESR spectrum of the pepper consists of a sextet centered at g = 2.0, a singlet at the same g-value and a singlet at g = 4.0. Upon gamma ray irradiation, a new pair of signals appeared in the pepper. The progressive saturation behavior (PSB) at various microwave power levels indicated quite different relaxation behaviors of those radicals. Namely, the peak intensity of the organic free radical component decreases in a monotonic fashion, whereas the Mn2+ and Fe3+ ESR signals substantially keep constant. This reflects the evidence of three independent radicals in the pepper before irradiation. The PSB of the pair peaks as induced by irradiation possessed quite different PSB from that of the free radical located at g = 2.0. We proposed a new protocol for the ESR detection of irradiated foods by the PSB method at different microwave power levels. This would call for a major modification of the CEN protocol in European Union.     

单重态氧化学VIII.类卟啉稀土配合物光敏化产生单重态氧的ESR研究

用电子自旋共振(ESR)方法研究类卟啉稀土配合物([CO2H-APPC)Gd]Cl2)光敏产生单重态氧的II型机制。利用2,2, 6, 6-四甲基哌啶(TEMP)对单重态氧的捕捉, 测定所生成的氮氧自由基的ESR信号, 经加NaN3和CD3OD的实验, 证实了([CO2H-APPC)Gd]Cl2)光敏作用可有效地产生单重态氧, 并观察到在实验所用的浓度范围内, 随着光敏剂浓度加大, 生成的单重态氧也增加, 同时比较了几种不同稀土离子配合物产生单重态氧的差别。结合氧的消耗和氮氧自由基的ESR线宽变化对氧浓度的依赖性, 证明了类卟啉稀土配合物光敏化生成单态氧的II型反应在光动力光疗中起关键作用。     

Structure and ring-puckering motion of the σ-localized silacyclobutane radical cation: ESR evidence

The 4 K ESR spectrum of silacyclobutane radical cation in perfluorocyclohexane consists mainly of a 43 G doublet hyperfine (hf) splitting due to one equatorial hydrogen at C(3). Upon warming, the doublet spectrum is reversibly changed into a 26 G triplet due to two equivalent methylene hydrogens in the same position together with a smaller triplet of 14 G due to THE =SiH₂ hydrogens. The temperature-dependent spectra are successfully analyzed in terms of a ring-puckering motion of the σ-localized radical cation in which one of the C---Si bonds is elongated so as to give an asymmetrically distorted C₁ structure.     

NEAR UV-INDUCED FREE RADICALS IN OCULAR LENS, STUDIED BY ESR AND SPIN TRAPPING

An electron spin resonance (ESR) study on UV-photolysis of human and canine lens nuclei was carried out at room temperature. (1) At least two kinds of free radical signals, a narrow signal and a broad one, were detected at around g = 2.004. The latter is similar to that observed upon irradiation of a model solution containing both tryptophan and cysteine. (2) Two spin adducts were detected upon irradiation of canine lens in the presence of a spin trapping reagent (DMPO, 5,5-dimethyl-1-pyrroline N-oxide), i.e. a spin adduct of sulphur-centered radical (most likely glutathione thiyl radical) and the protonated adduct of solvated electron (presumably due to photo-ionization of tryptophan). (3) A tentative and simplified reaction mechanism of UV-induced damage is discussed on the basis of these observations.     

MAQO和它的环糊精包结物的电子自旋共振研究

报导2-甲基-3乙酰基喹喔啉1，4-二氧化物（MAQO）和它与α-环糊精（α-CD），β-环糊精（β-CD）包结物在室温下应用紫外光（λ＝360nm）进行原位光化学反应生成自由基的电子自旋共振研究结果，推断MAQO在紫外光作用下首先生成激发态（MAQO）*，然后进一步发生光化学反应导致N＝C双键转移而生成氮氧自由基并为ESR所检测到．从ESR检测结果猜想，在非含氢溶剂中是生成较稳定的且又相距很远的氮氧双自由基；而在含氢溶剂中，由于发生夺氢反应而生成稳定的氮氧单自由基．当MAQO－α－CD包结物在含氢溶剂中发生光化学反应时亦生成氮氧单自由基；但其ESR谱的超精细结构（hfs）和线宽均发生了变化，推断环糊精包结在MAQO分子苯环一端，受环糊精的微环境空间阻碍效应．     

Advanced protocol for the detection of irradiated food by electron spin resonance spectroscopy

Using ESR (electron spin resonance) spectroscopy, we found various free radicals in a pepper before and after irradiation. The representative ESR spectrum of the pepper composed of a sextet centered at g=2.0, a singlet at the same g-value and a singlet at g=4.0. This reflects the evidence of three independent radicals in the pepper before irradiation. Upon gamma ray irradiation, a new pair of signals appeared. The progressive saturation behavior (PSB) at various microwave power levels indicates quite different relaxation behaviors of those signals. For the evaluation of radiation-induced radicals and irradiation effects we propose a new protocol using the PSB method. This would call for an advanced protocol for the detection of irradiated foods.     

Electron spin resonance studies of polycarbonate irradiated by γ-rays and ultraviolet light

Paramagnetic species produced in polycarbonate (PC) by γ- or ultraviolet irradiation were investigated by ESR. In γ-irradiation, scissions of carbonate groups in the main chain occur. ESR spectra (g = 2.003₄) composed of a sharp singlet, some broad singlets, and a small signal with hyperfine structure are obtained, and they are assigned to trapped electrons, positive radical ions, phenoxy-type free radicals, phenyl radicals, and ? O? C₆H₄? C(CH₃)₂ radicals. The G value for total yields of paramagnetic species at 77°K is 1.8. The percentage of CO and CO₂, the dominant gases evolved, is 65.4 and 33.8%, respectively. In ultraviolet irradiation, energy is absorbed selectively at the surface region. The surface region becomes insoluble in methylene chloride because of crosslinking of phenyl groups. The ESR spectrum obtained at 77°K is a broad singlet and assigned to phenoxy-type free radicals, phenyl radicals, and polyenyl-type free radicals. Some differences in effects of γ- and ultraviolet irradiation of PC are discussed.     

Structures of the hexafluorocyclopropane, octafluorocyclobutane, and decafluorocyclopentane radical anions probed by experimental and computational studies of anisotropic electron spin resonance (ESR) spectra

Anisotropic electron spin resonance (ESR) spectra are reported for the radical anions of hexafluorocyclopropane (c-C(3)F(6)(-)), octafluorocyclobutane (c-C(4)F(8)(-)), and decafluorocyclopentane (c-C(5)F(10)(-)) generated via gamma-irradiation in plastically crystalline tetramethylsilane (TMS) and rigid 2-methyltetrahydrofuran (MTHF) matrices. By combining the analysis of these experimental ESR spectra involving anisotropic hyperfine (hf) couplings with a series of quantum chemical computations, the geometrical and electronic structure of these unusual perfluorocycloalkane radical anions have been characterized more fully than in previous studies that considered only the isotropic couplings. Unrestricted Hartree-Fock (UHF) computations with the 6-311+G(d,p) basis set predict planar ring structures for all three radical anions, the ground electronic states being (2)A(2)(") for c-C(3)F(6)(-) (D(3h) symmetry), (2)A(2u) for c-C(4)F(8)(-) (D(4h)), and (2)A(2)(") for c-C(5)F(10)(-) (D(5h)), in which the respective six, eight, and ten 19F-atoms are equivalent by symmetry. A successful test of the theoretical computation is indicated by the fact that the isotropic 19F hf couplings computed by the B3LYP method with the 6-311+G(2df,p) basis set for the optimized geometries are in almost perfect agreement with the experimental values: viz., 19.8 mT (exp) vs 19.78 mT (calc) for c-C(3)F(6)(-); 14.85 mT (exp) vs 14.84 mT (calc) for c-C(4)F(8)(-); 11.6 mT (exp) vs 11.65 mT (calc) for c-C(5)F(10)(-). Consequently, the same computation method has been applied to calculate the almost axially symmetric anisotropic 19F hf couplings for the magnetically equivalent 19F atoms: (-4.90 mT, -4.84 mT, 9.75 mT) for c-C(3)F(6), (-3.54 mT, -3.48 mT, 7.02 mT) for c-C(4)F(8)(-), and (-2.62 mT, -2.56 mT, 5.18 mT) for c-C(5)F(10)(-). ESR spectral simulations performed using the computed principal values of the hf couplings and the spatial orientations of the 19F nuclei as input parameters reveal an excellent fit to the experimental anisotropic ESR spectra of c-C(3)F(6)(-), c-C(4)F(8)(-), and c-C(5)F(10)(-), thereby providing a convincing proof of the highly symmetric D(nh) structures that are predicted for these negative ions. Furthermore, using the computed 19F principal values and their orientations, the effective 19F anisotropic hf couplings along the molecular symmetry axes were evaluated for c-C(3)F(6)(-) and c-C(4)F(8)(-) and successfully correlated with the positions of the characteristic outermost features in both the experimental and calculated anisotropic spectra. In addition, the electronic excitation energies and oscillator strengths for the c-C(3)F(6)(-) , c-C(4)F(8)(-), and c-C(5)F(10)(-) radical anions were computed for the first time using time-dependent density functional theory (TD-DFT) methods.     

Identification of irradiated sage tea (Salvia officinalis L.) by ESR spectroscopy

The use of electron spin resonance (ESR) spectroscopy to accurately distinguish irradiated from unirradiated sage tea was examined. Before irradiation, sage tea samples exhibit one asymmetric singlet ESR signal centered at g=2.0037. Besides this central signal, two weak satellite signals situated about 3 mT left and right to it in radiation-induced spectra. Irradiation with increasing doses caused a significant increase in radiation-induced ESR signal intensity at g=2.0265 (the left satellite signal) and this increase was found to be explained by a polynomial varying function. The stability of that radiation-induced ESR signal at room temperature was studied over a storage period of 9 months. Also, the kinetic of signal at g=2.0265 was studied in detail over a temperature range 313–353 K by annealing samples at different temperatures for various times.     

Structures of tetrafluorocyclopropene, hexafluorocyclobutene, octafluorocyclopentene and related perfluoroalkene radical anions revealed by electron spin resonance spectroscopic and computational studies

Isotropic and anisotropic ESR spectra were observed for the radical anions of hexafluorocyclobutene (c-C(4)F(6)(-)), octafluorocyclopentene (c-C(5)F(8)(-)) and perfluoro-2-butene (CF(3)CF=CFCF(3)(-)) in gamma-irradiated plastically crystalline neopentane, tetramethylsilane (TMS) and TMS-d(12) matrices, or the rigid 2-methyltetrahydrofuran (MTHF) matrix. The isotropic spectra of c-C(4)F(6)(-) and c-C(5)F(8)(-) are characterized by three different sets of pairs of (19)F nuclei with the isotropic hyperfine (hf) splittings of 15.2 (2F), 6.5 (2F), 1.1 (2F) mT for c-C(4)F(6)(-) and 14.7 (2F), 7.4 (2F), 1.0 (2F) mT for c-C(5)F(8)(-). By comparison with the results of ab initio quantum chemical computations, the large triplet (19)F hf splittings of ca. 15 mT are assigned to the two fluorines attached to the C=C bond. The UHF, B3LYP and MP2 computations predict that the geometrical structures of the perfluoroalkenes are strongly distorted by one-electron reduction to form their radical anions; c-C(3)F(4)(-): C(2) symmetry ((2)A state) <-- C(2)(v) ((1)A(1)), c-C(4)F(6)(-): C(1) ((2)A) <-- C(2)(v) ((1)A(1)) and c-C(5)F(8)(-): C(1) ((2)A) <-- C(s) ((1)A'). The structural distortion arises from a mixing of the pi* and higher-lying sigma* orbitals at the C=C carbons similar to that previously found for CF(2)=CF(2)(-) with a C(2)(h) distortion. The isotropic (19)F hf splittings computed with the B3LYP method with 6-311+G(2df,p) basis set for the geometry optimized by the UHF and/or MP2 methods are within 6% error of the experimental values. The experimental anisotropic spectra of c-C(4)F(6)(-), c-C(5)F(8)(-) and CF(2)=CF(2)(-) were satisfactorily reproduced by the ESR spectral simulation method using the computed hf principal values and orientation of (19)F nuclei. In addition, the electronic excitation energies and oscillator strengths for the CF(2)=CF(2)(-), c-C(3)F(4)(-), c-C(4)F(6)(-) and c-C(5)F(8)(-) radical anions were computed for the first time by TD-DFT methods.     

纳米管钛酸的ESR特性及其可见光照的影响

本文报道了纳米管钛酸在真空-0.1MPa、温度100℃的条件下,经过不同时间处理后的ESR特性及其可见光照的影响.发现纳米管钛酸经一定处理后,不经光照即出现g=2.003ESR信号,该信号是由捕获一个电子的氧空位(V_o)产生的,此信号随着处理时间的延长而增强;在532nm的可见光照射下,随着光照时间的延长信号强度随之增加,达到一定强度值后,不再随光照时间的延长而增加;光源关闭后,信号强度又逐渐减小,但不能恢复到原来信号强度的水平.     

An ESR and ENDOR study of irradiated 6Li-formate

Lithium formate ((6)LiOOCH.H(2)O), 95% (6)Li enrichment, combined with an exchange of crystallization water with D(2)O was investigated. The ESR spectrum of the radiation induced free radicals stable at room temperature consists of a singlet with a narrow line width, 0.92mT. (6)Li has smaller magnetic moment and nuclear spin, which resulted in the narrower line width accompanied with an increase in peak amplitude. In comparison with lithium formate with natural isotopic composition, (6)Li (7.5%, I=1) and (7)Li (92.5%, I=3/2), the sensitivity was increased by a factor of two. With optimised spectrometer settings (6)Li formate had seven times higher sensitivity compared to alanine. Therefore this material is proposed as a dosimeter material in a dose range down to 0.1Gy. The g and the (13)C-hyperfine (hf) tensors of the CO(2)(-) radical anion, major paramagnetic products, were evaluated to be g=(2.0037, 1.9975, 2.0017), and A((13)C)=(465.5, 447.5, 581.3) MHz for polycrystalline samples at room temperature. Furthermore, the (1)H-hf and (6)Li-hf tensors observed for the surroundings of CO(2)(-) by ENDOR technique were in fairly good agreement with DFT calculations. The CO(2)(-) radicals are found to be so stable that the formate is applicable to the ESR dosimetry, because of fully relaxing in a fully relaxed geometrical structure of the CO(2)(-) component and remaining tight binding with the surroundings after the H atom detachment from HCO(2)(-).     

Near-UV-induced radicals in Propionibacterium acnes, studied by electron spin resonance spectrometry at 77 K.

Suspensions of Propionibacterium acnes were UV irradiated and the induced radicals were measured at 77 K by electron spin resonance (ESR) spectrometry. Two types of radical were formed during irradiation and stabilized in the frozen suspensions. The relative yield of each radical was studied as a function of irradiation wavelength. The first radical, which was a singlet with a peak-to-peak width of 20 G, was insensitive to the deoxygenation of the samples and to the exchange of solvent water by heavy water. The action spectrum was similar to the absorption spectrum of NADPH. The second type of radical was not formed in deoxygenated samples and the shape of the ESR spectrum was characteristic of the superoxide radical. This radical was only formed at wavelengths below 340 nm.     

Temperature effects on egg shells investigated by XRD,IR and ESR techniques

Samples of egg shell powder were annealed in air in the temperature range 298–1173 K. Samples were analyzed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis and electron spin resonance (ESR). ESR measurements were made on annealed egg shells before and after gamma irradiation at 4 kGy. Annealing egg shells produced a range of organic radical with g-values from g=2.005 to 2.002. The thermal dependence of this signal may provide valuable information about the extent of the thermal treatment that the sample was subjected to. Samples irradiated from 3Gy to 10 kGy were analyzed by ESR in order to obtain the response curve and to show ESR signal behavior.     

The effects of temperature on ESR spectrum of gamma-irradiated ammonium tartrate

Unirradiated ammonium tartrate (AT) samples do not exhibit any ESR signal. However, irradiation produces an unresolved singlet at g=2.0034±0.0006 with two shoulders at g₁=2.0093±0.0006 and g₂=2.0048±0.0006. The dose–response curve was found to increase linearly with the applied radiation doses in the range of 0.1–2.0 kGy and the slope of this curve was increased as the modulation amplitude increased. The activation energy value E_a=69.0±1.2 kJ/mol was calculated from Arrhenius plot for the radical species responsible from ESR spectrum of irradiated AT.     

ESR Studies of A(1u) and A(2u) Oxoiron(IV) Porphyrin pi-Cation Radical Complexes. Spin Coupling between Ferryl Iron and A(1u)/A(2u) Orbitals

This study shows the ESR spectra of oxoiron(IV) porphyrin pi-cation radicals of 1-8 in dichloromethane-methanol (5:1) mixture. We reported in a previous paper that oxoiron(IV) porphyrin pi-cation radicals of 1-4 are in an a(1u) radical state while those of 5-8 are in an a(2u) radical. The ESR spectra (g( perpendicular)(eff) approximately 3.1 and g( parallel)(eff) approximately 2.0) for the a(1u) radical complexes, 1-4, appear quite different from those reported previously for the oxoiron(IV) porphyrin pi-cation radical of 5 (g(y) = 4.5, g(x) = 3.6, and g(z) = 1.99). The unique ESR spectra of the a(1u) radical complexes rather resemble those of compound I from Micrococcus lysodeikticus catalase (CAT) and ascorbate peroxidase (ASP). This is the first examples to mimic the ESR spectra of compound I in the enzymes. From spectral analysis based on a spin Hamiltonian containing an exchange interaction, the ESR spectra of 1-4 can be explained as a moderate ferromagnetic state (J/D approximately 0.3) between ferryl S = 1 and the porphyrin pi-cation radical S' = (1)/(2). The magnitudes of zero-field splitting (D) for ferryl iron and isotropic J value, estimated from the temperature-dependence of the half-saturation power of the ESR signals, are approximately 28 and approximately +8 cm(-1), respectively. A change in the electronegativity of the beta-pyrrole substituent hardly changes the ESR spectral feature while that of the meso-substituent slightly does owing to the change in the E/D value. On the basis of the present ESR results, we propose the a(1u) radical state for compound I of CAT and ASP.     

PHOTOSENSITIZED FORMATION OF ASCORBATE RADICALS BY RIBOFLAVIN: AN ESR STUDY

Abstract— The riboflavin-sensitized photooxidation of ascorbate ion (HA^-) to ascorbate radical (A^-) was followed by electron spin resonance (ESR) spectroscopy in conjunction with oxygen depletion measurements. In air-saturated aqueous media, steady-state amounts of A^- are rapidly established upon irradiation. The ESR signal disappears within a few seconds after the light is extinguished–more slowly under constant irradiation as oxygen is depleted. No photooxidation was observed in deaerated media. Similar results were obtained with other flavins and when ascorbyl palmitate was substituted for HA^-. The effect of added superoxide dismutase, catalase, desferrioxamine, and singlet oxygen scavengers (NaN₃ and tryptophan) was studied, as was replacement of water by D₂O and saturation with O₂. The results are indicative of ascorbate free radical production via direct reaction between ascorbate ion and triplet riboflavin in the presence of O₂. While the presence of superoxide ion tends to reduce the steady-state concentration of A^-, competition from the reaction of HA^- with singlet oxygen is less apparent in this system (at HA^-≥ 1 m M ) than in the previously studied aluminum phthalocyanine tetrasulfonate-photosensitized reaction.     

稀土聚乙炔的ESR研究

本文系统地研究了稀土聚乙炔的电子自旋共振(ESR)行为。发现稀土聚乙炔的ESR谱都为单线谱,符合Lorentz线型;十五种稀土环烷酸盐体系聚乙炔的ESR无明显区别,g因子为2.0028±0.0001;线宽(△H)和logN(N为未成对电子浓度)与聚乙炔的顺式含量成直线关系;未成对电子的形成服从零级动力学,其活化能为11.3kcal/mol;微量碘掺杂聚乙炔的ESR仍为单线谱、Lorentz型及g因子不变,碘掺杂浓度大于～2mol％时,没有ESR信号。