Hexachlororhenate(IV) salts of organic radical cations

The ionic salts (p-rad)₂[ReCl₆] (1) and (m-rad)₂[ReCl₆] (2) (p/m-rad = 2-(4/3-N-methylpyridinium)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl-3-N-oxide) have been prepared and their crystal structures determined by single-crystal X-ray diffraction. The nitronyl nitroxide cations in compound 1 show a layered disposition, whereas the [ReCl₆]²⁻ units are placed between these layers. The nitronyl nitroxide cations in compound 2 adopt an hexagonal array but they do not result in layers. Bulk magnetic properties of 1 and 2 have been investigated in the temperature range 2-300 K. Both compounds show weak but significant intermolecular antiferromagnetic interactions.     

Cation distribution in faujasite-type zeolites: A test of semi-empirical force fields for Na cations

(N,V,T) Monte Carlo (MC) simulations have been performed in order to test three available force fields for sodium cations in faujasite-type zeolites. A rigid framework faujasite model, using an average T atom scheme and the cation force field proposed by [Jaramillo, E. and Auerbach, S.M. J. Phys. Chem. 103 (1999) 9589] was found to reproduce quite well the experimentally observed cation location in NaY and could thus be used in future works for predicting cation distributions and possible cation migration upon adsorption in faujasites.     

ESR and UV-Vis studies of semiquinone radical anion and hydroquinone generated by irradiation of 15-Deacetyl-13-glycine substituted hypocrellin B

15-Deacetyl-13-glycine substituted hypocrellin B (GDHB) is a new type of hypocrellin derivative with enhanced red absorption longer than 600 nm and water solubility. When an anaerobic DMSO or DMSO-buffer (pH 7.4) solution of GDHB was illuminated with > 470 nm light, a strong electron spin resonance (ESR) signal was formed. The ESR signal was assigned to the semiquinone anion radical of GDHB (GDHB^·-) based on a series of experiments. GDHB^·- was predominantly photoproducted via the self-electron transfer between the excited- and ground-state species. Decay of this species, both in the presence and absence of electron donor, was consistent with second-order kinetics. In aqueous solution, the TEMPO counterspin experiment indicated the formation of GDHB^·- that could not be detected by ESR method directly. The formation of GDHB^·- and hydroquinone of GDHB (GDHBH^·-) was also confirmed by spectrometric method. These findings suggested that GDHB was at least a favorable type I phototherapeutic agent.     

ESR signals of NADH and NADPH under illumination

ESR method was applied to investigate the formation of NADH and NADPH free radicals. It was shown that under the action of light (340 nm) in water and other solutions of these compounds a reaction occurred resulting in the formation of free radicals having the typical ESR spectrum. The analysis of the temperature dependence showed the light-induced ESR signals to be registered at −30°C to −120°C, the most intensive ones being observed at −50°C. It was concluded that the observed ESR signals belonged to the products of one-electron oxidation of the coenzymes-free radicals NAD^. and NADP^..     

用ESR技术研究含硒蛋白抗羟基自由基作用的活性

用ＥＳＲ技术研究含硒蛋白抗羟基自由基作用的活性。与ＳＯＤ、茶多酚相比较,含硒蛋白对羟基自由基的清除也有显著作用。找到了一种有实用价值,天然无毒,抗羟基自由基的新资源。     

Carotenoid radical cations and dications: EPR, optical, and electrochemical studies

Investigations of the structure and properties of paramagnetic carotenoid radical cations and diamagnetic carotenoid dications using electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) spectroscopy in conjunction with electrochemical, optical, and HPLC measurements, and molecular orbital calculations are described. These methods were applied to determine how the carotenoid radical cations and dications can be formed, their electron-transfer properties and stability in various media, and the mechanism by which carotenoid radical cations can isomerize.     

Long-term ozone exposure of potato: free radical content and leaf injury analysed by Q-band ESR spectroscopy and image analysis

This paper presents Q-band electron spin resonance (ESR) studies on free radicals (FR) generated in potato leaves exposed to different O₃ levels in open-top chambers (OTC), together with a quantitative study of the relationship between FR signal intensity and area of potato leaf damage. The advantages of Q-band when compared to X-band ESR spectroscopy are analysed, the main advantage being an absence of overlapping between Mn(II) and FR signals, allowing a quantitative study of FR signal intensity. This study also reports on a graphical method developed to quantitatively measure the damaged area on leaves caused by ozone exposure. Results indicate a direct relationship between FR signal intensity (measured as area under the signal) and percentage of O₃ damage and clearly demonstrate a close relationship between visible ozone-induced symptoms and permanent FR concentration in potato leaves.     

Spin label saturation transfer ESR studies of protein-lipid interactions in Photosystem II-enriched membranes

Saturation transfer ESR has been used to study the dynamic behaviour of lipids in the appressed regions of thylakoid membranes from pea seedlings. Four different phospho- and galacto-lipid spin labels (phosphatidylcholine labelled at the 12 or 14 C-atom positions of the sn-2 chain, phosphatidylglycerol labelled at the 14-position of the sn-2 chain, and monogalactosyldiacylglycerol labelled at the 12-position of the sn-2 chain) were used to probe the lipid environment in photosystem II-enriched membranes prepared by detergent extraction. The ESR spectra show that the majority of the lipid in these preparations is strongly motionally restricted. Values for the effective rotational correlation times of the labelled chains were deduced from the lineheight ratios and integrals of thhe saturation transfer ESR spectra. The effective rotational correlation times were found to be in the 10⁵ range, indicating a very low lipid chain mobility which correlates with the low lipid content of these preparations. Comparison of the effective rotational correlation times deduced from the different diagnostic regions of the spectrum revealed little anisotropy in the chain mobility, indicating that the dominant motional mode was trans-gauche isomerization. The effective rotational correlation times deduced from the spectral integrals were similar to those deduced from the lineheight ratios, consistent with the absence of any appreciable fluid lipid component in these preparations. The results also indicate some selectivity of interaction between the lipid species, with phosphatidylcholine exhibiting appreciably slower motion than either phosphatidylglycerol or monogalactosyldiacylglycerol.     

用顺磁共振研究家蝇衰老过程蝇头自由基特性的改变

用顺磁共振（ＥＳＲ）方法直接测量家蝇头中自由基浓度和性质及ＳＯＤ活性随龄变化情况。结果蝇头内自由基浓度随龄显著增加,且自由基升高的同时,对应ＳＯＤ活性下降。两种主要自由基成份的浓度比也随龄发生改变,其中一宽谱信号组份与衰老的关系可能更为密切。提示除自由基浓度外,自由基组份的比例改变,在衰老中也有重要作用。     

Improvement of the method to estimate the relative reaction rate constants of hydroxyl radical with polyphenols using ESR spin trap: X-ray irradiation of water with a flowing system

UV-photolysis of hydrogen peroxide is a useful technique to produce hydroxyl radical. However, it is not an appropriate method to estimate the reactivity of polyphenols with hydroxyl radicals because many of the polyphenol derivatives also absorb the UV-light to generate hydroxyl radicals. In this study, X-ray irradiation of water with a flowing system was applied to estimate the reactivity of hydroxyl radicals with polyphenols using electron spin resonance (ESR) spin trap. The obtained relative reaction rates reasonably agreed with previous data by pulse radiolysis. This method will be a useful technique to estimate the reactivity of antioxidants including polyphenols with hydroxyl radicals.     

Lipophilic triphenylphosphonium cations as tools in mitochondrial bioenergetics and free radical biology

Lipophilic phosphonium cations were first used to investigate mitochondrial biology by Vladimir Skulachev and colleagues in the late 1960s. Since then, these molecules have become important tools for exploring mitochondrial bioenergetics and free radical biology. Here we review why these molecules are useful in mitochondrial research and outline some of the ways in which they are now being utilized.Translated from Biokhimiya, Vol. 70, No. 2, 2005, pp. 273–283.Original Russian Text Copyright ¢ 2005 by Ross, Kelso, Blaikie, James, Cochemé, Filipovska, Da Ros, Hurd, Smith, Murphy.This revised version was published online in April 2005 with corrections to the post codes.     

Effect of chlorogenic acid on hydroxyl radical

Chlorogenic acid (CGA) is considered to act as an antioxidant. However, the inhibitory effects of CGA on specific radical species are not well understood. Electron spin resonance (ESR) in combination with spin trapping techniques was utilized to detect free radicals. 5,5-Dimethyl-1-pyrroline-N-oxide (DMPO) was used as a spin trapping reagent while the Fenton reaction was used as a source of hydroxyl radical (·OH). We found that CGA scavenges ·OH in a dose-dependent manner. The kinetic parameters, IC₅₀ and V_max, for CGA scavenging of ·OH were 110 and 1.27 M/sec, respectively. The rate constant for the scavenging of ·OH by CGA was 7.73 × 10⁹ M^–1 sec^–1. Our studies suggest that the antioxidant properties of CGA may involve a direct scavenging effect of CGA on ·OH.     

Formation of radical cations in a model for the metabolism of aromatic hydrocarbons

To test the hypothesis that electrophilic radical cations are the major ultimate electrophilic and carcinogenic forms of benz[a]anthracene (BA), dibenz[a,h]anthracene (DBA), and benzo[a]pyrene (BP), we have focused on a chemical model of metabolism which parallels and duplicates known or potential metabolites of some polycyclic hydrocarbons formed in cells. Studies of this model system show that radical cations are hardly formed, if at all, in the case of BA or DBA but are definitely formed in the cases of the carcinogen BP as well as the non-carcinogenic hydrocarbons, pyrene and perylene. We conclude that the carcinogenicities of BA, DBA, BP, pyrene, and perylene are independent of one-electron oxidation to radical cation intermediates.     

黄芪有效成分对氧自由基清除作用的ESR研究

用电子自旋共振技术研究了黄芪总黄酮(TFA)、黄芪总皂甙(TSA)和黄芪总多糖(TPA)对次黄嘌呤／黄嘌呤氧化酶体系产生的超氧阴离子自由基和H₂O₂－Fe²⁺体系产生的羟自由基的清除作用．结果表明,这3种成分均有清除氧自由基的作用;对超氧阴离子自由基的清除效能大于对羟自由基的清除作用;其作用强度依次为TFA＞TSA＞TPA．结果提示清除氧自由基可能是黄芪抗衰老的主要机理之一,TFA和TSA是黄芪抗氧化作用的主要药理活性成分．     

含硒银杏叶清除羟基自由基的ESR研究

利用电子自旋共振技术(ESR)研究了含硒银杏叶提取物对H_2O_2-Fe~(2 )体系产生的羟基自由基的清除作用.与SOD、茶多酚相比,含硒银杏叶提取物对羟基自基也有很强的清除效果.增添了有实用价值的天然、无公害的清除羟基自由基的新资源.     

Non-invasive analysis of reactive oxygen species generated in NH4OH-induced gastric lesions of rats using a 300 MHz in vivo ESR technique

Free radicals are reportedly involved in mucosal injury, including NH_{>^{••- derived from neutrophils caused gastric lesion formation, while Opact">•-} or H2O2 derived from the xanthine oxidase system in endothelial cells was involved in neutrophil infiltration.}     

Generation of Oxygen Radicals from Iron Complex of Orellanine, A Mushroom Nephrotoxin; Preliminary ESR and Spin-Trapping Stukes

Orellanine, [2,2'-bipyridine]-3,3',4,4'-tetrol-l,I'-dioxide, is the toxin responsible for the lethal nephrotoxicity of some Cortinarius mushrooms. Our present ESR and spin-trapping studies of the redox properties of the system of non-illuminated orellanine, ferrous iron and dioxygen contribute to understanding the molecular mechanism of its toxicity. UV-visible spectrophoto-metry, cyclic voltammetry and ESR in frozen medium showed the formation of a wine-red tris complex, Fe(III)Or₃. This ferric complex is easily reducible (E_P =-565 mV vs Ag/AgCl/3M KCl at pH7), involving a one-electron reversible process. Spin-trapping using DMPO is employed to detect the generation of super-oxide anion and hydroxyl radicals. The instantaneous one-electron oxidation of ferrous ions in the presence of the toxin under air is concomitant with dioxygen consumption as supported by dioxygen consumption. GSH involves the toxin and ferrous ions under air in a redox cycling process resulting in the production of glutathionyl and oxygen free radicals, observed for the first time with an iron complex of a mushroom toxin. In most cases, EDTA is not able to prevent the Fe(III)Or₃ and radical formation. The ortho-dihydroxylated groups borne by the di-N-oxidized bipyridine structure and not the bipyridine structure itself, are responsible for the formation of a stable ferric complex at pH 7, as they are for the generation of an apparently stable ortho-semiquinone anion radical. These one-electron mechanisms may play a major role in some of the known toxic effects of orellanine.     

Modelling of hydrated Ca-rich zeolites

The successful modelling of the structure of two hydrated calcium-rich natural zeolites is described, showing how modelling can reproduce their complex structure, in excellent agreement with experiment. Furthermore, we demonstrate how such methods are able to determine the preferred Al ordering in the mineral Goosecreekite. The dehydration behaviour of Goosecreekite is also predicted. The interatomic potentials for water, evaluated here, are found to be robust and transferable to zeolitic materials.     

Kinetic studies of reactions of iron(IV)-oxo porphyrin radical cations with organic reductants

Iron(IV)-oxo porphyrin radical cations are observed intermediates in peroxidase and catalase enzymes, where they are known as Compound I species, and the putative oxidizing species in cytochrome P450 enzymes. In this work, we report kinetic studies of reactions of iron(IV)-oxo porphyrin radical cations that can be compared to reactions of other metal-oxo species. The iron(IV)-oxo radical cations studied were those produced from 5,10,15,20-tetramesitylporphryinato-iron(III) perchlorate (1), 5,10,15,20-tetramesitylporphryinato-iron(III) chloride (2), both in CH(3)CN solvent, and that from 5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato-iron(III) perchlorate (3) in CH(2)Cl(2) solvent. The substrates studied were alkenes and activated hydrocarbons diphenylmethane and ethylbenzene. For a given organic reductant, various iron(IV)-oxo porphyrin radical cations react in a relatively narrow kinetic range; typically the second-order rate constants vary by less than 1 order of magnitude for the oxidants studied here and the related oxidant 5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato-iron(IV)-oxo porphyrin radical cation in CH(3)CN solvent. Charge transfer in the transition states for epoxidation reactions of substituted styrenes by oxidants 1 and 2, rho(+) values of -1.9 and -0.9, respectively, mirrors results found previously for related species. Competition kinetic reactions with a catalytic amount of porphyrin iron(III) species and a terminal oxidant give relative rate constants for oxidations of competing substrates that are somewhat smaller than the ratios of absolute rate constants. Water in CH(3)CN solutions has an apparent modest stabilizing effect on oxidant 1 as indicated in slightly reduced rate constants for oxidation reactions. The iron(IV)-oxo porphyrin radical cations are orders of magnitude less reactive than porphyrin-manganese(V)-oxo cations and a corrole-iron(V)-oxo species. The small environment effects found here suggest that high energy demanding hydrocarbon oxidation reactions catalyzed by cytochrome P450 enzymes might require highly reactive iron(V)-oxo transients as oxidants instead of the more stable, isomeric iron(IV)-oxo porphyrin radical cations.