FREE RADICALS INDUCED BY PHOTOLYSIS OF FROZEN SOLUTIONS OF THYMIDINE-5'-MONOPHOSPHATE: AN ESR STUDY

Abstract— The photolysis (Δ < 220 nm) of thymidine-5'-monophosphate was studied by electron-spin resonance (ESR) in acidic and alkaline phases. In both cases, the H–addition radical at the C₆ position is detected at 77°K. At 225°K, a triplet 1:2:1 is observed, which suggests a H abstraction radical from the CH₃ group. When oxygen is present during irradiation, a peroxide–type radical is observed, which results partly from a reaction like R + O₂→ ROO and partly from an energy transfer from thymidine-5'-monophosphate to oxygen, probably in the ¹π₀ state.     

ON THE PRODUCTION OF NITROXIDE RADICALS BY SINGLET OXYGEN REACTION: AN EPR STUDY

Abstract— The production of free radicals by reaction of 2,2,6,6-tetramethyl-4-piperidinol with singlet oxygen was studied by EPR spectroscopy. The rate constant of the amine was found to be equal to 8 ×10⁵ M ^-1s^-1 in ethanol and to 4 × 10⁷M^-1s^-1 in phosphate buffer (pH 8). Competition experiments were performed with singlet oxygen quenchers such as NaN₃, DABCO and the quenching rate constants were found to be consistent with the literature values. The EPR method proved to be a valuable technique to study the reaction of singlet O₂ with the sterically hindered amine without any interfering effect.     

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.     

FORMATION OF SEMIQUINONE RADICALS BY ULTRAVIOLET IRRADIATION OF PYRIMIDINES IN METHANOL

Abstract —Ultraviolet irradiation of pyrimidine and 4- and 5-methylpyrimidine in methanol at 113 K gave the corresponding semiquinone radicals in a monophotonic process. It is likely that this process involves an n * triplet state of the photoexcited pyrimidines.     

ROLE OF COMPLEX FORMATION IN THE PHOTOSENSITIZED DEGRADATION OF DNA INDUCED BY N'-FORMYLKYNURENINE

Abstract— N'-Formylkynurenine derivatives efficiently bind to DNA or polynucleotides. Homopolynucleotides and DNA display marked differences in the binding process. Association constants are derived which indicate that the oxidized indole ring is more strongly bound to DNA than the unoxidized one. Irradiation of such complexes with wavelengths greater than 320 nm induces pyrimidine dimer formation as well as DNA chain breaks. Complex formation is shown to play an important role in these photosensitized reactions.
The photodynamic action of N'-formylkynurenine on DNA constituents is negligible at neutral pH but guanine and xanthine derivatives are sensitizable at higher pH. Thymine dimer splitting can occur in aggregated frozen aqueous solutions of N'-formylkynurenine and thymine dimer but this photosensitized splitting is negligible in liquid solutions at room temperature.     

FORMATION OF CYCLOBUTANE THYMINE DIMERS PHOTOSENSITIZED BY PYRIDOPSORALENS: A TRIPLET-TRIPLET ENERGY TRANSFER MECHANISM

The 365 nm irradiation of thymine thin films in the presence of pyridopsoralens is shown to induce the formation of cyclobutane thymine dimers, in contrast to other compounds such as 8- and 5-methoxypsoralen. In order to elucidate the mechanism of such a photosensitized reaction, we have determined the energy of the lowest triplet state (T1) of these compounds, using phosphorescence spectroscopy and CNDO/S quantum chemistry calculations. The T1 energy values were found to be significantly higher for pyridopsoralens--up to 0.3 eV--than for 8- and 5-methoxypsoralen (approximately 2.8 eV), which are not able to photoinduce cyclobutane thymine dimers. The determination of the relative efficiency of cyclobutane thymine dimer formation was performed using chromatographic analysis. A good correlation was found between the energy of the T1 state of the psoralen derivatives and the related cyclobutane thymine dimer formation. Moreover, the photosensitized cyclobutane thymine dimer formation appeared to be temperature-dependent. Our results are consistent with a mechanism involving a triplet energy transfer from the pyridopsoralen to thymine.     

内敏乳剂的ESR研究

本文制备了具有化学结构缺陷以及具有物理晶格缺陷的两种内敏核壳乳剂,并研究了它们的电子自旋共振波谱。随着化学增感时间的增加,ESR信号强度增强,达到一最大值后又下降。ESR信号强度随核壳比的下降而下降;随灰化程度的上升而下降。不同减感染料由于其减感机理的不同,对内部感光性能和ESR信号强度的影响也不同。上述结果可以用空穴在颗粒内部的行为来解释。     

利用ESR技术研究α-蒎烯,β-蒎烯光敏氧化反应机理

本文主要利用电子顺磁共振(ESR)自旋捕获技术研究9,10 二氰基蒽(DCA)敏化α-蒎烯(αP),β-蒎烯(βP)光氧化反应.提供了在乙腈中α-蒎烯和β-蒎烯的光氧化反应过程中存在超氧负离子基(O₂^-)和单重态氧(¹O₂)的直接证据;在四氯化碳溶剂中只捕获到¹O₂;在正己烷中没有捕获到O₂^-或¹O₂.ESR实验结果进一步证明在乙腈中光敏氧化反应的¹O₂可能来自O₂^-和反应底物α、β-蒎烯正离子自由基之间的电荷复合(CR).     

芳基重氮盐及其冠醚络合物光解活泼自由基的ESR研究

本文用自由基捕捉剂2,3,5,6-四甲基亚硝基苯(ND)及苯亚甲基叔丁基氮氧化物(PBN)与ESR相结合的方法研究了芳基重氮盐RC_6H_4N~+_2BF~-_4(R=F, Cl, Br, I, NO_2, COOH,OCH_3及H)及其与18-冠-6、二苯并-24-冠-8的络合物在苯中的光解过程。结果表明它们光解产生了活泼自由基RC_6H_4并可被ND及PBN捕捉....     

PROOXIDANT and ANTIOXIDANT EFFECTS OF ASCORBATE ON PHOTOSENSITIZED PEROXIDATION OF LIPIDS IN ERYTHROCYTE MEMBRANES

Abstract— Continuous blue light irradiation of resealed erythrocyte ghosts at 37°C in the presence of uroporphyrin or protoporphyrin results in ¹O₂-mediated (azide inhibitable) lipid peroxidation and membrane lysis. Lipid peroxidation was assessed by thiobarbituric acid reactivity and by quantitation of total hydroperoxides, while lysis was measured in terms of trappedglucose–6-P release. Low concentrations of ascorbate, AH^- (e.g. 0.5 m M ). present at the start of irradiation, significantly enhanced the rates of lysis and peroxidation, whereas relatively high concentrations of AH^- (e.g. 15 m M ) inhibited both processes. By way of contrast. AH^- produced only a dose-dependent inhibition of the photoinactivation of lysozyme, added as an extramembranous target. No significant AH^-induced lipid peroxidation was observed in dark or light controls, plus porphyrin or minus porphyrin, respectively. Stimulation of peroxidation and lysis by low levels of AH^- was enhanced by added Fe(III), abolished by EDTA. but unaffected by catalase or superoxide dismutase. A plausible explanation for these results is as follows. At low concentrations of AH^- prooxidant activity is favored. Redox metal-mediated breakdown of photoperoxides occurs, which tends to amplify lipid peroxidation. Neither O₂^- nor H₂O₂ appears to be involved. At significantly high concentrations, AH^- acts predominantly as an antioxidant by intercepting ¹O₂ and/or sensitizer triplet, or by scavenging free radical intermediates of lipid peroxidation.     

用电子自旋共振谱研究我国一些煤的自由基

本文用电子自旋共振谱(ESR)研究了我国十种不同变质程度的煤。电子自旋共振最重要的参数是g值、自由基的浓度、线宽和线形。用这些参数与煤中的碳、氧等元素相关联,发现ESR参数与煤的变质程度有密切关系。     

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.     

光诱导氧自由基与嘧啶碱基及其核苷反应的ESR研究

活性氧在破坏核酸结构,攻击其嘌呤碱基和嘧啶碱基,导致变异的出现和累积方面起重要作用。在生物体内,超氧自由基(O_2)是一个非常重要的活性氧,是氧分子单电子还原时首先生成的产物。由O_2衍生成过氧化氢(H_2O_2),羟基自由基(OH),单线态分子氧(~1O_2),     

COMPARATIVE STUDY OF OXIDATION OF NUCLEIC ACID COMPONENTS BY HYDROXYL RADICALS, SINGLET OXYGEN AND SUPEROXIDE ANION RADICALS

Abstract— Superoxide radicals, singlet oxygen and hydroxyl radicals are individually or in combination involved in radiation or photochemical processes and in various enzymatic reactions. The reactivity and the mechanism of reaction of these oxygen species with some biologically significant DNA components were investigated through the characterization of the final oxidation products.
Superoxide radicals appear to be unreactive with purine and pyrimidine 2'-deoxyribonucleosides. However, the autoxidation reaction of 6-hydroxydopamine leads to extensive degradation of thymine through the intermediary of hydroxyl radicals. Chemically and microwave-discharge generated singlet oxygen oxidation is specific to 2'-deoxyguanosine. The main oxidized products of these reactions were also characterized as well as an as yet unidentified nucleoside in the methylene-blue photooxydation of 2-deoxyguanosine. These results, in addition to specific deuterium effect experiments, lend support to the involvment of singlet oxygen (type II mechanism) in the methylene-blue photosentization. No singlet oxygen effect was observed in aqueous irradiated system.     

有机锡化合物光解活泼自由基的ESR研究

本文用自旋捕捉技术与ESR相结合的方法,研究了六种有机锡化合物的光解反应历程。结果表明:有机锡化合物紫外光照时,碳-锡键发生均裂,产生碳中心和锡中心自由基。其中碳中心自由基易被捕捉剂α-苯基-N-特丁基氮氧化物(PBN)或2,3,5,6-四甲基亚硝基苯(ND)所捕获;而锡中心自由基可与菲醌形成稳定的环状加合物。由于环状加合物中配体的不同,产生的空间效应也不同,从而导致加合物中的未偶电子云密度发生变化,给出相异的ESR信号。     

PHOTOSENSITIZED DEGRADATION OF DNA BY DAUNOMYCIN

Abstract Visible irradiation of DNA-daunomycin solutions resulted in a decrease of viscosity of the DNA and an increase of the rate of denaturation of DNA in formaldehyde. These changes are consistent with the induction of single-strand breaks in the DNA, some of which pair to cause fragmentation of the DNA. The DNA damage increases with drug: nucleotide ratio up to 0.2 and is diminished beyond that range. The damage also increases with ionic strength up to 0.6 M and is diminished above that value. These results suggest that the non-intercalated form of the drug is involved in the photosensitization process. Radicals that are produced accompanying the degradation have been trapped by 5,5-dimeth-yl-l-pyrroline-1-oxide and identified as hydroxyl radicals from their ESR spectrum. The DNA photosensitized damage is completely inhibited when hydroxyl radicals are removed by the spin-trap, suggesting a direct role for the hydroxyl radicals in the DNA photosensitized degradation process. The implications of the photosensitized DNA damage and the production of hydroxyl radicals in this process are discussed with respect to the medical uses and chemotherapeutic role of daunomycin.     

AN ESR STUDY OF THE VISIBLE LIGHT PHOTOCHEMISTRY OF GILVOCARCIN V

Photolysis of gilvocarcin (GV) at 405 nm in argon saturated dimethylsulfoxide (DMSO) or 50% DMSO-water solutions in the presence of the sodium salt of 3,5-dibromo-2,6-dideutero-4-nitrosobenzene sulfonic acid (DBNBS-d2) generates the CH3-DBNBS-d2.spin adduct. It is postulated that this spin adduct is produced by photoreduction of DMSO by GV and the consequent formation and trapping of the generated methyl radicals. Gilvocarcin V also photoreduces oxygen and methyl viologen with quantum yields of 0.019 and 0.0012 respectively. The quantum yield for singlet oxygen formation by GV in DMSO, determined by measuring the rate of production of the nitroxyl radical produced by the reaction of 2,2,6,6-tetramethylpiperidinol with singlet oxygen, was found to be 0.15. Thus, GV photochemistry proceeds by both Type I and Type II pathways which could contribute to the reported GV phototoxicity in biological systems.     

PHOTOSENSITIZED LYSIS OF LIPOSOMES BY HEMATOPORPHYRIN DERIVATIVE

The spectral properties and efficiency for photosensitizing the lysis of phosphatidylcholine liposomes have been measured for the components of hematoporphyrin derivative (Hpd) after alkaline hydrolysis and fractionation by polyacrylamidc gel chromatography. Two major and two minor Hpd fractions have been identified whose spectral properties correlate with the anoxic sensitizing efficiency and the oxygen enhancement ratio (OER). The fastest moving fraction, which is the putative biologically active component, comprised one-third of the starting material and had OER = 2.7. Liposome lysis by this fraction was inhibited in the presence of human serum albumin at concentration ratios comparable to those employed for photoradiation therapy. The present results show that Hpd can act as an oxic and anoxic photosensitizer of a model biomembrane and suggest that separation from serum proteins is required for in vivo photosensitization.     

INACTIVATION OF GRAM-NEGATIVE BACTERIA BY PHOTOSENSITIZED PORPHYRINS

Photosensitization of Escherichia coli and Pseudomonas aeruginosa cells by deuteroporphyrin (DP) is shown to be possible in the presence of the polycationic agent polymyxin nonapeptide (PMNP). Previous studies established complete resistance of Gram-negative bacteria to the photodynamic effects of porphyrins. The present results show that combined treatment of E. coli or P. aeruginosa cultures with DP and PMNP inhibit cell growth and viability. No antibacterial activity of PMNP alone could be demonstrated and cell viability remained unchanged. Spectroscopically, PMNP was found to bind DP, a mechanism which probably assists its penetration into the cell's membranes. Insertion of DP into the cells was monitored by the characteristic fluorescence band of bound DP at 622 nm. Binding times were 5-40 min and the extent of binding increased with decreasing the pH from 8.5 to 6.5. DP binding constants, as well as the concentrations of PMNP which were required for maximal effect on the various Gram-negative bacteria, were determined fluorometrically. By the treatment of DP, PMNP and light the growth of E. coli and P. aeruginosa cultures was stopped and the viability of the culture was dramatically reduced. Within 60 min of treatment the survival fraction of E. coli culture was 9 x 10(-6) and that of P. aeruginosa was 5.2 x 10(-4). Electron microscopy depicted ultrastructural alterations in the Gram-negative cells treated by DP and PMNP. The completion of cell division was inhibited and the chromosomal domain was altered markedly.     

形成全氟正丙基与全氟异丙基自由基的相对难易度的动力学研究

形成碳氢系列烷基自由基的相对难易度的动力学研究已有很多报道,但其中主要是测出β-断裂反应相对速度的方法,而有关全氟烷基自由基的β-断裂反应的动力学测定迄今未见报道.显然,这些数据对自由基化学和有机氟化学来说都是很基本的和重要的.专利中也都提到这类反应的相对速度,它在应用方面,如在乙烯、四氟乙烯及全氟(丙基乙烯基)醚共聚反应中对控制分子量起了重要作用.