Short‐lived Phenoxyl Radicals Formed from Green‐Tea Polyphenols and Highly Reactive Oxygen Species: An Investigation by Time‐Resolved EPR Spectroscopy

Polyphenols are effective antioxidants and their behavior has been studied in depth. However, a structural characterization of the species formed immediately upon hydrogen‐atom transfer (HAT), a key reaction of oxidative stress, has not been achieved. The reaction of catechin and green‐tea polyphenols with highly reactive O‐centered H‐abstracting species was studied at the molecular level and in real time by using time‐resolved electron paramagnetic resonance (EPR) spectroscopy. This mirrors the reaction of highly reactive oxygen species with polyphenols. The results show that all phenolic OH groups display essentially identical reactivity. Accordingly, there is no site specificity for HAT and initial antioxidative events are demonstrated to be largely ruled by statistical (entropic) factors.     

The synthesis of some ferrocenyl tin hydrides

Tin hydrides containing a ferrocenyl (Fc) group have been synthesized. They reduce haloalkanes in good yields and their decomposition products are easily separated from the products by oxidizing the ferrocene compounds to ferrocenium ions.     

白桦液及白桦液复方清除自由基防止沙土鼠脑缺血再灌注氧化损伤的研究

本文用化学发光体系检测白桦液及其复方的清除活性氧自由基的功能。用羟胺法测实验动物化及脑组织的SOD活性,硫代巴比妥酸法测定MDA含量,细胞化学发光法测PMN细胞的免疫功能,化学发光法测脑组织的自发发光,直接法检测GSH-PX活性,氰高铁Hb法测Hb浓度,放免法测血浆TXB2的含量。结果表明,白桦液及其复方在离体体系中有清除O2-、OH-、H2O2的作用,在沙土鼠胞缺点再灌注模型中,可提高血和脑组织的SOD、GSH-PX活性,增强PMN细胞的免疫功能,降低血浆和脑组织LPO,TXB2及Hb浓度。本研究首次发现白桦液及其复方有抗氧化功能。     

Distribution of the methyl radical adduct of N‐benzylidene‐1‐diethoxyphosphoryl‐1‐methylethylamine N‐oxide‐type nitrones in water–sodium dodecyl sulfate micelles: an electron paramagnetic resonance spin trapping study

The behavior of the methyl radical adduct of six β‐phosphorylated nitrones in the N‐benzylidene‐1‐diethoxyphosphoryl‐1‐methylethylamine N‐oxide series in the presence of sodium dodecyl sulfate (SDS) micelles was followed by electron paramagnetic resonance spectroscopy. Except when the highly hydrophilic trap 4‐PyOPN (2) was used, all the adducts were found to partition significantly between micelles and the bulk aqueous phase. The average correlation time τ of the exchange of spin adducts between SDS micelles and water was found to be in the range 5 × 10^?8—4 × 10^?7 s, which is in the region of the life time of an SDS monomer in the micelle structure. In each case, the adduct affinity for the micelles has been quantified by evaluating its micelle–water distribution coefficient K_d. Copyright © 2002 John Wiley & Sons, Ltd.     

金属-氮氧自由基层状配合物磁性体系

介绍了金属与氮氧自由基所形成的层状体系的结构特点、磁耦合特征及其发展前景。     

Photoinduced degradation by iron(III): removal of triphenyltin chloride from water

The photoredox process taking place in iron(III) aquacomplexes was used to cause the complete degradation of triphenyltin (TPT). TPT elimination was proved to come only from attack by hydroxyl radicals generated upon irradiation at 365 nm of Fe(H₂O)₅OH²⁺, the iron(III) species present under the experimental conditions ([Fe(III)] in the range (3–6) × 10^?4 mol l^?1). The first step is the formation of an adduct between hydroxyl radicals and the benzene ring. The main process is a stepwise dephenylation of the starting TPT. Hydroxylated phenyltin derivatives were also formed, but only as minor photoproducts. The process was shown to be efficient with artificial light as well as with solar light. Copyright © 2001 John Wiley & Sons, Ltd.     

Recent applications of density functional theory calculations to biomolecules

The purpose of this overview is to highlight the broad scope and utility of current applications of density functional theory (DFT) methods for the study of the properties and reactions of biomolecules. This is illustrated using examples selected from research carried out within our research group and in collaboration with others. The examples include the hyperfine coupling constants of amino acid radicals, the use of an amino acid as a chiral catalyst for the formation of carbon–carbon bonds in the aldol reaction, hydrogen-bond mediated catalysis of an aminolysis reaction, radiation-induced protein–DNA cross-links, and the mechanism by which an antitumor drug cleaves DNA. We demonstrate that DFT-based methods can be applied successfully to a broad range of problems that remain beyond the scope of conventional electron-correlation methods. Furthermore, we show that contemporary computational quantum chemistry complements experiment in the study of biological systems. Received: 19 December 2001 / Accepted: 8 April 2002 / Published online: 4 July 2002     

A linear and non-linear electron spin resonance study of orientational relaxation in semi-crystalline polymeric liquid crystals

Summary Linear and non-linear Electron Spin Resonance spectroscopies have been designed to study the decay of the orientation correlations on different time scales. The reorientation of radicals (?spin probes?) dissolved in host phases (in the present case a polymeric liquid crystal (PLC)) may be investigated in the time window 10⁻¹¹–10⁻⁵ s. Evidence of the non-exponential regression of fluctuations is given. The temperature dependence of the correlation time of the spin probe orientation is discussed in the case of semi-crystalline PLCs and contrasted with the case of amorphous PLCs. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Synthesis and spectroscopic studies of 4-Formyl-4′-N,N-dimethylamino-1,1′-biphenyl: The unusual red edge effect and efficient laser generation

The synthesis and photophysics of 4-formyl-4-N,N-dimethylamino-1,1-biphenyl are reported. The emission spectrum in various solvent polarities demonstrates solvatochromism, indicating that the fluorescence originates from an electronically excited species with a strong charge transfer character. The change in [ _max(absorption) – _max(emission)] varies from 1500 cm^–1 inn-heptane to as much as 7500 cm^–1 in acetonitrile. In protic solvents, the unusual excitation energy-dependent steady-state emission (red edge effect), resulting from solvent dielectric relaxation, was observed in media with a low viscosity. The large Stokes-shifted and high-yield fluorescence led to the observation of the efficient lasing action. The frequency tunability of the laser output is strongly solvent dependent, generating a new charge transfer laser dye in the blue-green region.