FREE RADICALS FROM PHOTOREDUCTION OF HEMATOPORPHYRIN IN AQUEOUS SOLUTION

—The anaerobic photoreduction of hematoporphyrin by organic reducing agents in fluid aqueous solutions has been studied by electron spin resonance spectroscopy. Efficient photoreduction occurs with many hydrogen-atom or electron donors, including catechols, pyrogallol. hydroquinone. ascorbate, p -phenylenediamine, cysteine and glutathione. A combination of direct and spin-trapping measurements (using 2-methyl-2-nitrosopropane) has been used to confirm production of radicals from both the porphyrin and the reducing agent in each system.     

COMPARISON OF FREE RADICALS PRODUCED BY LASER AND ULTRASOUND ABLATION OF CARDIOVASCULAR TISSUE

Abstract— We have used the method of spin trapping and EPR to study the nature of the free radicals produced by laser photoreaction of cardiovascular tissue. The results obtained with argon-ion (cw) and excimer (pulsed) lasers have been compared with radicals produced by ultrasonic disruption of the tissue samples. These comparative studies provide an understanding of the mechanism by which laser light energy effects photoablation of cardiovascular tissue in the pulsed vs cw mode of operation.     

SPIN TRAPPING OF FREE RADICALS PRODUCED FROM NITROSOAMINE CARCINOGENS

Abstract— Using the spin trap 5,5-dimethylpyrroline-1-oxide we have demonstrated that the nitrosoamine carcinogen, 1-nitrosopiperidine, upon incubation with rat liver microsomes and nuclei produces two trapped free radical species. One trapped species is the hydroxyl free radical whereas the other is a free radical of unknown structure of the carcinogen itself. Three other nitrosoamine carcinogens tested, including diethylnitrosoamine, dimethylnitrosoamine and 1-nitrosopyrroline yielded similar results with the exception that the trapped carcinogen radical differs dependent upon the compound used. Oxygen was required to produce the hydroxyl free radical but its presence decreased the yield of the carcinogen radical. Both cyanide and α-tocopherol acetate caused a decrease in the yield of the carcinogen free radical. Some heat-labile inhibitor(s) of radical production was/were present in the cytosol. The amount of radical produced was not proportional to the P₄₅₀ content.     

PHOTOCHEMICAL INTERACTIONS BETWEEN NITROXIDE FREE RADICALS AND PHENOTHIAZINES IN SOLUTION

Abstract— Ultraviolet irradiation of photosensitive molecules like phenothiazine derivatives leads to the formation of short lived free radicals which are able to reduce stable nitroxide free radicals generally used as spin labels. The measurement of the electron spin resonance signal decay of nitroxides offers a tool for studying the photochemical reaction of phenothiazine derivatives in solution at room temperature, in a 10^-5 to 10^-2 M concentration range. Analysis of the reaction mechanism shows that the paramagnetic nitroxide is an efficient quencher of the phenothiazine triplet state; this reaction was used to demonstrate the influence of the solvent, quenching by oxygen and the role of the chemical structure of six phenothiazine derivatives on their photoreactivity in solution.     

CONCERNING THE PRODUCTION OF FREE RADICALS IN PROTEINS BY ULTRAVIOLET LIGHT

Abstract— Using electron paramagnetic resonance techniques, the response to u.v. light of several solid proteins and model compounds has been studied in vacuum and at low temperature. Emphasis has been placed on determining the response as a function of the wavelength (Λ 250 nm) and intensity of the incident radiation. Correlation of the parameters of radical production with sample luminescence, molecular amino-acid sequence and tertiary structure, light intensity and total irradiation time has allowed some insight into the mechanisms of free radical formation.
It is shown that the details of amino acid composition, sequence and the tertiary structure of a protein are important in determining both the rate of, and the mechanism for, radical production (two basic mechanisms are described), and in determining the conditions under which sulfur-type radicals can be produced. The results are related to enzyme inactivation and to the u.v. stability of proteins generally.     

烟草中自由基的研究进展

自由基是卷烟烟气中主要的一类有害物质，能导致人体组织和细胞的氧化，损害细胞膜上的脂类和蛋白质。引发癌症等疾病。对烟草中自由基的研究情况、自由基的检测方法、降低卷烟中自由基含量的研究等方面进行了综述。     

苯甲醛及对溴苯甲醛光解初级过程自由基的ESR研究

苯甲醛的光解与其在放置过程中的自氧化引发机理密切相关,因此确定光解过程的主要中间产物有重要意义。自氧化的全过程比较复杂,但单纯的光解本身显然相对简单一些。本文用自旋捕捉-ESR技术研究了苯甲醛及与其相类似的对溴苯甲醛在紫外和可见光作用下生成的活泼中间体,并讨论了在本文实验条件下的光解初级过程。     

香烟烟雾中自由基的检测

对香烟焦油中的Q/H2Q自由基及气相中的自由基进行了测定，同时对香烟燃烧产生自由基的机理进行了探讨。     

THE ACTION SPECTRA OF FREE RADICALS PRODUCED BY THE IRRADIATION OF KERATIN CONTAINING BOUND IRON(III) IONS

Abstract—The action spectra have been determined for two free radical species produced by irradiating wool protein containing bound iron(III) ions with light between 330 and 540 nm. The faster growing free radical displays an action spectrum with a peak at 405–415 nm. It is suggested that an iron (III) ion-sulphur complex is the chromophore responsible for the formation of this carbon type radical.     

DECAY KINETICS OF FREE RADICALS IN IRRADIATED PROTEINS

Abstract— A detailed analysis is presented of the decay kinetics of free radicals in irradiated biopolymers. Available data in the literature are critically evaluated and new data for irradiated keratin are presented. It is shown that a rigorous analysis of the data available in the literature leads to more detailed information on the decay mechanisms than the conclusions which have been previously given; in some cases the analysis leads to mechanisms contradicting those claimed in the literature.
Our results suggest that the free radicals in illuminated keratin consist of three distinct species: one of the species decays with a half life of approximately 20 hr, the second has a half life of about 4600 hr, while the half life of the third is so long that the free radical concentration is practically constant. A similar behaviour is obtained on assumption of second order decay.
The consistency of the kinetic constants obtained has been verified in kinetic experiments using samples prepared under very different experimental conditions.     

ESR STUDY OF FREE RADICALS IN IRRADIATED POLYAMIDE-1010

Polyamide-1010 samples were irradiated in vacuum at room temperature by Cobalt-60 γ-rays. The free radicals formed in irradiation were studied by means of electron spin resonance (ESR)techniques.The ESRspectra consisted of a quartet and a superimposed singlet which were attributed to radical -CO-NH-CH-CH_2 and -CH_2-C=O, respectively. The effects of temperature and crystaUinity on the radicals were discussed and the mechanism for the production and decay of the radicals was also proposed.     

FREE RADICALS DETECTED BY ESR FROM PHENYLHEPTATRIYNE IN LIPOSOMES IRRADIATED WITH UV-A

Abstract— When irradiated with UV-A liposome bilayers composed of distearoyl phosphatidylcholine and containing phenylheptatriyne produced a free radical signal detected by electron spin resonance spectroscopy. The spectrum contained one broad peak characterized by a linewidth of 19 G and a g value of 2.0017. The rate of formation of the signal amplitude was dependent upon light intensity, concentration of PHT within the bilayer and concentration of the PHT-liposome suspension. Enhancement of the signal under an anaerobic atmosphere indicated a non-photodynamic mechanism for free radical formation. Once formed however, the free radical was stable to the presence of oxygen and decayed very slowly with a half-life of 8 h. Formation of the free radical species was demonstrated to be dependent upon a highly ordered lipid environment since incorporation of lysophosphatidylcholine, stearoyl which perturbs lipid packing, decreased the levels of the free radical species. On the other hand, when PHT was present in a liposome with a more fluid bilayer such as egg yolk phosphatidylcholine, the levels of free radical species were even lower. Conversely, the levels increased when cholesterol which increases lipid order, was incorporated into the egg yolk phosphatidylcholine liposomes. Cells of E. coli, B , containing PHT, produced a similar free radical signal upon irradiation demonstrating in vivo generation of free radicals from PHT.     

SIMULTANEOUS GROWTH AND DECAY OF FREE RADICALS IN IRRADIATED PROTEINS

Abstract— The electron paramagnetic resonance signals due to free radicals created in illuminated keratin have been studied during illumination and also during the decay of the signal in the dark. A number of mechanisms suggested to account for the simultaneous growth and decay of radicals during illumination is considered but only one of these is capable of accounting for the experimental results.     

OXIDATIVE COUPLING OF THIOLS BY PYRIDINIUM CHLOROCHROMATE IN SOLUTION AND SOLVENT FREE CONDITIONS

Oxidative coupling of aromatic and aliphatic thiols is achieved efficiently by pyridinium chlorochromate in solution and solvent free conditions. Omitting the solvent does not change the reaction time and product yield significantly, while the need of using the solvent is suppressed and workup procedure becomes easier.     

FREE RADICALS FROM PHOTODECOMPOSITION OF BISPHENOL-A

Abstract— Irradiation of 2,2-bis-(4-hydroxyphenyl)-propane (bisphenol-A) with UV light causes photo-decomposition of the compound. Spin-trapping with α-phenyl-N-tert-butyl-nitrone showed that free radicals were cleaved from the molecule. No direct ESR-spectroscopic information concerning the structure of the remaining radical skeleton could be obtained. Gas chromatographic mass spectrometric analysis of the decomposition products indicated the existence of a semiquinone structure following cleavage of a methyl radical from 2,2-bis-4–(hydroxyphenyl)-propane. The capacity of 2,2-bis-(4- hydroxyphenyl)-propane to give rise to radicals might explain its photoallergenic properties.     

AN EPR STUDY OF π-CATION RADICALS IN DINUCLEOSIDE PHOSPHATES AND DNA PRODUCED BY PHOTOIONIZATION

In this work we have produced the π-cation radicals of a number of nucleotides, dinucleoside phosphates, and DNA in aqueous glasses (8M NaCIO₄) by photoionization and investigated these species by EPR spectroscopy. Results found for nucleotides and dinucleoside phosphates containing one type of DNA base, e.g. TpT, GpG, or dApdA, were used in the analysis of spectra found for mixed dinucleoside phosphates, e.g. TpdG. For TpdG and TpdA in neutral glasses photoionization takes place from the purine base and no transfer of charge to the pyrimidine base is found. In basic conditions both the adenine and thymine π-cations are observed in TpdA. In both neutral and basic conditions the results found for mixed dinucleoside phosphates containing guanine show that the guanine cation is formed preferentially by photolysis. This result was found to extend to DNA. Photolysis of DNA in 8M NaC1O₄ produced principally the guanine cation. Computer simulations using parameters determined by other workers from a study of γ-irradiated oriented DNA closely match the spectrum found in this work attributed to the guanine cation in dinucleoside phosphates and DNA. This work thus confirms the presence of the guanine cation in γ-irradiated DNA.     

INDUCTION OF FREE RADICALS IN DNA BY PROFLAVINE AND VISIBLE LIGHT: INFLUENCE OF OXYGEN AND IONIC STRENGTH

Abstract —The photosensitization of native DNA is observed as an induction of free radicals in the DNA moiety of proflavine-DNA complexes. The intensity of the electron paramagnetic resonance spectra (at 77 K) is a measure of the number of free radicals present in frozen solutions of DNA-proflavine complexes after irradiation with visible light (Λ > 320 nm). In the absence of O₂, the photosensitization is significant but very low; it increases slightly with increasing NaCl ionic strength; it appears to be due to intercalated dye molecules and the qualitative analysis of the spectra obtained shows that mainly thymidine is involved. The reaction measured after saturation with O₂ is the same as the reaction in air but is quantitatively higher; the free radicals observed are peroxides. This induction of free radicals appears to be due to the intercalated dye molecules, each molecule acting independently. The important observation is a very sharp and large (around a hundred-fold) increase in the photosensitizing efficiency of the bound dye molecules occurring in NaCl between μ, # 0–25 and μ= 0–5 and in MgCl₂ between μ# 0–01 and μ=0–1.     

运用等键反应能估算自由基和正碳离子的相对稳定性

自由基和正碳离子是化学反应中的活性中间体 ,它们的相对稳定性与其结构有密切关系。例如 ,烷基自由基、烷基正碳离子的稳定性顺序为3°>2°>1°。对于前者 ,一般是从 R- H键的离解能( D值 )进行推断的结果 ,D值越高 ,自由基越不稳定。而正碳离子的稳定性则与其生成热有关。生成热越大 ,正碳离子越不稳定。这就是人们判断上述活性中间体相对稳定性的一般方法 [1] 。那么 ,我们能否用一种统一的方法来评价自由基和正碳离子的相对稳定性呢 ?近年来 ,在物质的结构和性能关系研究方面 ,出现了一个很有应用价值的新概念——“等键反应能”( Iso…     

LIGHT-INDUCED FREE RADICALS IN ORIENTED DNA-PROFLAVINE COMPLEXES

Abstract— Oriented wet DNA-proflavine complexes were illuminated with visible light, Λ > 395 nm, at 77 K, in the presence or absence of oxygen. The electron paramagnetic resonance spectra at 77 K and low microwave power (3 μ W) indicated formation of anionic free radicals in thymine and cationic free radicals, probably in guanine, identical to those induced by y rays at 77 K in similar samples of pure DNA.
The free-radical formation rate showed a quadratic dependence on light intensity, indicating a biphotonic mechanism. The proflavine triplet spectrum was observed during illumination. If the exciting light includes wavelengths below 390 nm, significant amounts of hydrogen addition radicals in thymine are found.     

EPR PERSISTENCE MEASUREMENTS OF UV-INDUCED MELANIN FREE RADICALS IN WHOLE SKIN

Electron paramagnetic resonance is used to detect the formation of free radicals caused by exposure to ultraviolet radiation in chemically untreated rabbit skin. A fast jump in EPR signal level, occurring over a few seconds, is observed immediately after a skin sample is exposed to UV. This is followed by a slower increase toward an elevated steady-state signal over a period of hours as the skin is continuously exposed to a UV light source. Upon cessation of UV light exposure, EPR signal levels undergo an abrupt drop followed by a slower decay toward natural levels. Elevated free radical concentrations following UV exposure are found to persist for several hours in whole skin. These results are consistent with time-resolved EPR measurements of photoinduced radicals in various natural melanins.