Electron Spin Resonance Study of the Solvent Effect on the Conformation of Some Iminoxy Radicals

The reaction of nitrogen dioxide with carbonyl compounds having a methylene or vinyl group adjacent to the corbonyl leads to the formation of stable iminoxy radicals^1-3. Evidence^1,2,4 has been presented that the precursor of these iminoxy radicals is probably the corresponding oxime formed by rearrangements of the intermediate nitroso compounds. There have also been reports on the e.s.r. detection of some cis-trans isomers of some iminoxy radicals in methanol or in neat liquid^1,5. We wish to report here a drastic solvent effect on the conformations of some iminoxy radicals formed by the reaction of NO₂ with trifluoroacetylacetone.     

Electron Spin Resonance of Free Radicals Produced by Ultraviolet Photolysis in Some Vegetables and Their Juices

Abstract

Paramagnetic species produced by ultraviolet photolysis in various vegetables of domestic origin have been investigated by electron spin resonance technique. The ESR spectra of the small cut pieces of the vegetable fleshes and their frozen juices have been investigated before and under UV photolysis. The samples of potato and carrod exhibit too complex ESR spectra, but parsley, dill, white radish and green pepper do not exhibit any ESR signal before UV photolysis at 113 K. However both the small cut pieces of fleshes of potato, carrot, parsley, dill, white radish and green pepper and their juices exhibit ESR spectra during UV photolysis that we attributed to the H?O and CO^? ₂ radicals. The ESR parameters of these radicals have been obtained and the origins of these radicals have been shown to be the glucose molecules in the carbohydrate chains of these substances.     

Electron Spin Resonance Study of UV-Irradiated Tetraphenyldiphosphine

Although divalent organophosphinyl radicals have been frequently postulated as intermediates in many organochosphorous reactions, very few of them have been identified by e.s.r. By low temperature trapping of products from the photolysis of gaseous tetraphenyl-diphospine in a flow system, Schmidt and coworkers² have observed an e.s.r. signal of a single broad and asymmetric line centered at about g = 2.009 and have assigned this to the diphenylphosphinyl radical. We have reinvestigated the photolysis of this compound by flash photolysis and by e.s.r. at low temperatures, the preliminary e.s.r. results will be reported here.     

An Electron Spin Resonance Study of Gamma-Irradiated 5,6-Dihydropyrimidines

Electron spin resonance (ESR) spectra are observed from gamma-irradiated, poly-crystalline samples of 5,6-dihydrouracil, 5,6-dihydro-5-methyluracil, and 5,6-dihydro-6-methyluracll. The spectra indicate that the radiation-induced free radicals are formed by the loss of hydrogen atoms from the parent compounds. The crystal structure of the dihydropyrimidines is apparently such that there is a proton near the unpaired electron which can simultaneously flip with the flip of the unpaired electron resulting in the formation of satellite lines relative to the main spectral lines. Annealing the irradiated samples at 100°C produces a decrease in the radical content of all compounds except in dihydro-5-methyluracll where the radical content increases. These differences are discussed in terms of the close proximity of the radicals formed during irradiation of dihydro-5-methyluracil. The     

Electron Spin Resonance of Alkali Metal Contact Ion Pairs of 2,6-di-tert-Butylbenzoquinone in Non Polar Solvent

The question whether excited triplet states of quinones react with a number of substrates such as alcohols, phenols, and amines, via electron transfer mechanism has attracted much attention in recent years. The existence of some triplet exciplex was postulated by Kobashi et al¹ in their study of hydrogen atom abstraction by p-chloranil using laser flash spectrocopic detection. In some recent e.s.r. and CIDEP studies^2,3, however, there is no compelling evidence that the photoreduction of quinones and benzophenones undergoes an initial electron transfer mechanism. It should be noted that most of the e.s.r. studies of quinone radical anions had been carried out in polar solvents. In flash photolysis studies some evidence has indeed been obtained^1,4 in which the efficiency of hydrogen abstraction by excited triplet quinones increases with solvent polarity and therefore it is possible that the initial primary process involves electron transfer followed immediately by proton transfer. On the other hand, we     

Electron Spin Resonance Study on the Photoinduced Electron Transfer in Chlorophyll a in Reconstituted Lipid Bilayer Vesicles

Abstract  

The photoinduced electron transfer from chlorophyll a through the interface of positively charged dioctadecyltrimethylammonium chloride (DODAC), neutral dipalmitoylphosphatidylcholine (DPPC) and negatively charged dihexadecylphosphate (DHP) headgroup of the lipid bilayers was studied. The photoinduced radicals were identified by electron spin resonance (ESR) and radical yields of chlorophyll a were determined by double integration of the ESR spectra. The formation of vesicles was identified indirectly by measuring change of the λ _max value of optical absorption spectrophotometer from diethyl ether solution to vesicle solutions, and observed directly with scanning and transmission electron microscopic images. The interaction distance between chlorophyll a and interface water (D₂O) determined by deuterium modulation depth with electron spin echo modulation (ESEM) showed a decreasing order DODAC > DPPC > DHP. The interface charge of each vesicle was determined with zeta potential measurement. The interface charge of the lipid bilayers affected the radical yields of chlorophyll a more critically than the interaction distance between chlorophyll a and interface water.     

Observation of Electron Spin Resonance in the Microwave-Induced Photovoltage

JETP Letters - The microwave-induced photovoltage in two-dimensional electron systems in an AlAs quantum well and a ZnO/MgZnO heterojunction under the conditions of the quantum Hall effect is...     

电子自旋共振(ESR)技术在生物和医学中的应用

电子自旋共振(electron spin resonance,ESR)是检测自由基最直接最有效的方法,是自由基生物学和医学不可缺少的重要研究技术. 作者综述了ESR、自旋标记、自旋捕集和ESR 成像技术的最新发展及ESR技术在细胞膜、蛋白质结构和一些重大疾病如心脏病、老年痴呆症、帕金森综合症和中风等疾病研究及辐射损伤和植物疾病研究中的应用.     

微波电子自旋共振实验波形分析

详细分析了微波段用可调反射式谐振腔做电子自旋共振实验中共振信号的形成原理,分析指出下凹和上凸波形都为共振吸收信号,当波形的上下两部分等大时,为色散信号,波形的上下两部分不等大时,为色散信号和共振吸收信号的合成。从理论上解释了共振信号的变化所反映的物理过程。     

Electron Spin Resonance Spectroscopy of Gamma-Irradiated Glucose Polymers

Using electron spin resonance (ESR) spectroscopy, we revealed the irradiation-induced radicals in cellulose and starch. Before gamma-ray irradiation, no ESR signals were observed in both the glucose polymers. However, after gamma-ray irradiation, a singlet at g = 2.0 was observed, and a pair of side signals appeared simultaneously. The side signals were found at the symmetric field positions at both sides of the singlet signal. The side signals were visible in cellulose but not in starch. The side signals are found to be a precise indicator for irradiation effects in cellulose. They are originated from neither the peroxide radical of glucose polymer nor the so-called cellulosic radicals. By the simulation method, we found that the side signals are originated from a triplet due to a hyperfine interaction with two protons. By the theoretical simulation, we revealed that the signal undergo the rotational motions rather than rigid limit state (or no motion).     

Short Time Domain and Double Resonance Techniques in Electron Spin Resonance Spectroscopy

Abstract

In recent years improvements in technology have increased the amount of information obtainable from, and have broadened the areas of application of, electron spin resonance spectroscopy. Some of the techniques that have found wide use in recent years, such as pulse saturation relaxation time measurements, ENDOR and ELDOR, were originally discovered many years ago while others, such as saturation transfer spectroscopy and nanosecond time resolved techniques, are based upon more recent developments. In this review we will survey a number of these techniques, we will explain what they are and what we can learn from them, we will describe some of the spectrometer systems that are required for using them, and we will cite many representative articles which provide further details about them.     

轨道诱导Peierls相变材料MgTi_2O_4的电子自旋共振研究

用变温电子自旋共振手段(Electron Spin Resonance,ESR),对轨道诱导Peierls相变MgTi_2O_4体系进行了研究.研究发现,轨道诱导Peierls相变所伴随的自旋二聚相变对ESR谱产生了影响.在相变温度以上,MgTi_2O_4的磁性为顺磁行为.而在相变温度以下,ESR谱显示MgTi_2O_4的磁性偏离了顺磁行为.对ESR谱线的参数拟合结果显示,MgTi_2O_4在发生轨道诱导Peierls相变时,自旋耦合作用逐渐增强.这说明:自旋耦合作用的增强很有可能是导致相变的一个重要的因素.     

轨道诱导Peierls相变材料MgTi2O4的电子自旋共振研究

用变温电子自旋共振手段,对轨道诱导Peierls相变MgTi2O4体系进行了研究。研究发现,轨道诱导Peierls相变所伴随的自旋二聚相变对ESR谱产生了影响。在相变温度以上,MgTi2O4的磁性为顺磁行为。而在相变温度以下,ESR谱显示MgTi2O4的磁性偏离了顺磁行为。对ESR谱线的参数拟合结果显示,MgTi2O4在发生轨道诱导Peierls相变时,自旋耦合作用逐渐增强。这说明:自旋耦合作用的增强很有可能是导致相变的一个重要的因素。     

Absorption Lineshapes in Two-Dimensional Electron Spin Resonance and the Effects of Slow Motions in Complex Fluids

A methodology for obtaining pure absorption two-dimensional electron spin resonance spectra is presented for the case of large inhomogeneous broadening and/or slow motions. For slow motions, the spectra consist of “complex Lorentzians” superimposed with complex weighting factors, presenting a challenge to obtaining absorption spectra. It is shown how absorption-type spectra can be recovered for the two-pulse COSY and SECSY experiments in such cases. For three-pulse 2D ELDOR experiments, absorption lineshapes can be obtained for the autopeaks, whereas the cross peaks would be of mixed-mode character, in general. However, for practical cases the dispersive components in the cross peaks will be relatively small. Theoretical and experimental absorption spectra are provided to illustrate the method and to show the improved resolution obtained from absorption lineshapes. In particular, the variation in linewidths across a SECSY spectrum, which is a key component in elucidating motional dynamics, is clearly rendered in the pure absorption mode. A convenient method for introducing the necessary phase corrections for the slow-motional spectra is also provided.     

Radiostability of Allantoin by Using Electron Spin Resonance Spectroscopy

The radiosterilization potential and dosimetric feature of allantoin were investigated through the molecular degradations produced after ultraviolet and gamma irradiation using electron spin resonance, infrared, and ultraviolet spectroscopies and thermal measurement techniques (differential thermal analysis and the glass transition temperature). Although ultraviolet-irradiated allantoin presents no electron spin resonance signal, gamma irradiation exhibited an electron spin resonance signal of triplet appearance. Room temperature and high-temperature line intensity and spectrum area data and their variations with applied microwave power, storage time, annealing time, annealing temperature, and applied radiation dose were analyzed by assuming the production of two different types of radicals having different spectroscopic and decay characteristics. Based on its relatively stable nature toward gamma and ultraviolet radiations, it was concluded that allantoin itself and the products containing it can be sterilized by gamma and/or ultraviolet radiations without creating a great loss in its beneficial effects in the allowed radiosterilization dose limits.     

Electron Spin Resonance study of gamma irradiated MA-AMPS copolymer

Electron Spin Resonance (ESR) spectra of gamma irradiated methylacrylamide-2-acrylamido-2-methyl-propanesulphonic acid (MA-AMPS) are recorded to identify the radical species formed during the irradiation of the copolymer. The ESR spectrum observed for irradiated MA-AMPS copolymer at liquid nitrogen temperature (LNT) (77 r K) is an asymmetric triplet; while the spectrum observed at room temperature (RT) is a quintet. The intensity distribution of both the spectra deviated appreciably from the expected theoretical values. Computer simulations are employed to analyze the ESR spectra observed at different temperatures. The triplet spectrum observed at LNT is simulated to be a superposition of component spectra arising from macroradicals of the type～CH 2 - \dot {\rm C} H-CH 2 ～ (I), radicals of the type \dot {\rm C} H 2 SO 3 H (II), and peroxy radicals (III). In contrast, the RT spectrum is simulated to be a superposition of component spectra arising due to radicals I, II, III together with the component quartet assigned to methyl radicals ( \dot {\rm C} H 3 ). The formation of such free radicals in irradiated copolymer is discussed.     

Effect of External Factors on the Ferromagnetic Resonance Line Width in Exchange-Biased Structures

Physics of the Solid State - The external factors which influence the ferromagnetic resonance (FMR) line width in bilayer (ferromagnet/antiferromagnet) exchange-biased systems are studied. The...     

卷烟烟气中活性自由基的自旋捕获ESR研究

卷烟烟气中的瞬态自由基对人体健康是相当有害的，而检测活性自由基最常用的方法是自旋捕获方法. 本研究中使用高效新型捕捉剂DEPMPO能够直接在水相中捕捉到烷基自由基与羟基自由基，并未发现烷氧自由基加合物. 考虑到DEPMPO对活性自由基的捕捉能力和加合物ESR谱图解析特征性都优于PBN与DMPO，且在有机溶剂中溶解较多的氧分子. 因此认为以往文献中所捕获的烷氧自由基来源于烷基自由基氧化后的次级自由基产物.     

Electron Spin Resonance Study of Yttrium Aluminum Garnet Films Doped with Nd and Yb Ions

Yttrium aluminum garnet (YAG) thin films doped with optical active rare earth ions grown on YAG substrate can be used as wave-guide laser. Measured layers YAG:Yb, Nd (grown by the isothermal liquid phase epitaxy (LPE)) was additionally doped with Ga and Lu ions in order to increase film refractive index and decrease strains in layers, respectively. Electron spin resonance measurements have been performed on a number of YAG:Yb, Nd thin films with Yb concentrations ranging from 0at.% to 15at.% and Nd concentration equals to 1 at.% and 3 at.%. It was found that the measured angular dependence of the Yb^3? ion linewidth is typical for a mosaic structure. Moreover, it was shown that internal strains in the layers depend on the kind of dopant as well as on their concentration.     

Measurement of Microviscosity in Vesicular Membranes by Electron Spin Resonance

The seven vesicular formulations CER(−), CER(+), CER(I), PC(−), PC(+), DAG(B) and DAG(I) have been developed using ceramide IIIB (CER), phosphatidylcholine (PC), or diacylglycerides (DAG) as main lipid components. B and I indicate the processed hydrophilic surfactant Brij 58 and Imwitor 375, (+) and (−) symbolize the positive and negative zeta potential. The influence of the bilayer microviscosity on the features of lipid vesicles as dermal drug delivery system is widely discussed, but comparable and reproducible results could not be found. For the measurement of the microviscosity by electron spin resonance the lipophilic spin probe of 14-doxylpalmitoylic acid methyl ester (DPME) was incorporated into the bilayer. Rotational correlation times (τ_c) between 0.3 and 1.8 ns were calculated. The dynamic viscosities (η) of eight different medium-chained triglycerides–castor oil mixtures in the range between 25 and 948 mPa · s, as well as the corresponding τ_c values of DPME in these mixtures, were determined to establish a calibration curve for the estimation of the microviscosity. The microviscosities of the vesicle membranes increase from 40 to 565 mPa · s in the following order DAG(B) = DAG(I) < PC(−) ≈ CER(I) < CER(−) ≤ CER(+) < PC(+). The microviscosity of 49.8 ± 2.5 mPa · s in pure unsaturated soy PC membranes decreases on adding the sodium cholate to 28.3–29.4 mPa · s, whereas the addition of dilauroylphosphatidylcholine in repeated freeze–thaw cycles or 8.5% ethanol in the hydrophilic phase had no influence. Authors' address: Hans-Hubert Borchert, Institute of Pharmacy, Free University of Berlin, Kelchstrasse 31, Berlin 12169, Germany