PHOTOCHEMICAL FORMATION OF NITROXIDE RADICALS FROM CARCINOGENIC N-METHYL-N'-NITRO-N-NITROSOGUANIDINE AND RELATED COMPOUNDS

Abstract— Potent carcinogenic N -methyl- N '-nitro- N -nitrosoguanidine (MNNG) was found to be converted into a free radical by photoirradiation in organic solvents. The structure of the free radical produced was investigated by means of the electron paramagnetic resonance (EPR) method using isotope-replaced compounds and also considering the results of the molecular orbital calculations. Upon illumination, release of the nitroso group and oxygen attack at the N -methyl nitrogen occurred, and the radical was identified as a nitroxide radical. Similar types of nitroxide radical were obtained from other N -alkyl- N -nitroso compounds, such as N -ethyl-, N -propyl-, and N -butyl- N '-nitro- N -nitroso-guanidine.     

酯-二苯酮光化夺氢反应活泼自由基的ESR研究

自旋捕捉技术与ESR相结合,为检测反应过程中产生的自由基活泼中间体提供一个方便且有效的方法。近年来,国内外研究工作者利用这一方法,对固相,液相和气相中产生的活泼自由基已进行了广泛的研究^[1-12]。     

脂二胺在颜料分散体中光化学反应活泼自由基的ESR研究

用自旋捕捉技术与ESR相结合的方法研究了脂二胺在ZnO、TiO₂的庚烷或苯的分散体系中光诱导的电子转移过程。观察到DMPO与氮中心自由基加合物的ESR信号,表明捕捉到的自由基是脂二胺与光生空穴作用而产生的胺的阳离子自由基。     

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.     

FREE RADICALS PRODUCED IN A RIGID SOLUTION OF TRYPTOPHAN BY A BIPHOTONIC PROCESS

Abstract— Free radicals were trapped by irradiation of tryptophan in an ethylene glycol/water glass with 250 nm U.V. light at 77°K. The ESR-spectrum was attributed to approximately equal amounts of trapped electrons and ethyl radicals. The electrons could be transformed into the ethyl type radicals by heating or bleaching with near u.v. or visible light. The quantum yield of trapped radicals increased with increasing intensity of the irradiation by more than one order of magnitude over the range of intensities studied. A kinetic model was formulated on the assumption that the radicals were produced by the successive absorption of two light quanta, the absorption of the first giving rise to a transient intermediate which subsequently absorbs a second quantum to produce the radicals. The experiments confirmed the applicability of this model to the present case. The decay time obtained for the intermediate was 6.8 sec which equals the phosphorescence decay time of tryptophan under similar conditions, indicating that the intermediate involved was the lowest triplet level of this molecule. The absorption cross section of this intermediate at 250 nm with regard to the formation of trapped radicals was found to be 8000 l./mol cm.     

醇-二苯甲酮光化夺氢反应活泼自由基的ESR研究

本文用自由基捕捉剂2,3,4,6-四甲基亚硝基苯(ND)及苯亚甲基叔丁基氮氧化合物(PBN)与ESR相结合的方法研究了CnH_2n+1OH(n=1,2,…8)、(CH₃)₂CH(CH₂)_nOH(n=0,1,2)、CH₂=CHCH₂OH及C₆H₅CH₂OH等十三种醇与二苯甲酮的光化夺氢反应中的活泼自由基,结果表明: 1.用ND时,二苯酮分别夺取CnH_2n+1OH、(CH₃)₂CH(CH₂)_nOH及RCH₂OH(R=CH₂=CH、C₆H₅)中α-C、叔-C及α-C上的氢,而捕捉到C_n-1H_2n-1CHOH、(CH₃)₂CH(CH₂)_nOH及RCHOH自由基。 2.用PBN时,捕捉的自由基与ND捕获的相同。     

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.     

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。     

PHOTOCHEMICAL INTERACTIONS OF CHLORPROMAZINE WITH PHOSPHOLIPIDS AND CHOLESTEROL IN ARTIFICIAL AND NATURAL MEMBRANES

Abstract— Dipalmitoylphosphatidyl-choline (DPPC) liposomes do not modify the nature of the photoproducts formed by UV irradiation of chlorpromazine. However, when cholesterol is added to DPPC liposomes, new photoproducts are formed which demonstrate the photoaddition of chlorpromazine to cholesterol. Similar results are obtained with phosphatidyl-serine and phosphatidyl-inositol. The reactivity of irradiated chlorpromazine towards lipidic components of myelin, taken as an example of biological membrane, is also demonstrated.     

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。     

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.     

辛基甲基亚砜与离子型表面活性剂在水溶液中的相互作用

本文用测定表面张力的方法研究了非离子表面活性剂辛基甲基亚砜(OMS)分别与离子型表面活性剂C_(10)H_(21)SO_4N_a(SDeS)、C_7F_(15)COONa(SPFO), C_(10)H_(21)N(CH_3)_3B_r(DeTAB)等在水溶液中的相互作用。发现上述混合体系的胶团形成及表面吸附都有不同程度的增效作用; 表面活性分子在吸附层中的相互作用参数β~s以及在胶团中的相互作用参数β~m均为负值并有一定变化规律; OMS与DeTAB的相互作用较OMS与SDeS或SPFO的相互作用弱得多; 此现象自OMS分子在水溶液中的质子化作用得到解释。     

四氯乙烯光解活泼自由基及其与烃或醇的夺氢反应的ESR研究

本文用自由基捕捉剂2,3,5,6-四甲基亚硝基苯(ND)与ESR相结合的方法研究了四氯乙烯光解活泼自由基及其与烃或醇的夺氢反应, 结果表明:1. Cl_2C=CCl_2光解首先产生Cl_2C=CCl及Cl, 而又可进一步加成为Cl_2C-CCl_3.2. 对于CH_3(CH_2)_nOH(n=3,7)及(CH_3)_2CH(CH_2)_nOH(n=1,2)而言, Cl_2C=CCl(或Cl)分别夺取其α-碳及叔碳上的氢, 以形成CH_3(CH_2)_(n-1)CHOH及(CH_3)_2C(CH_2)_nOH, 并为ND所捕获。3. Cl_2C=CCl(或Cl)分别夺取CH_3(CH_2)_nCH3(n=3,4,5,6), C_6H_5-CH_2CH_3及(CH_3)_2CH(CH_2)_nCH_3(n=1,4), (C_2H_5)_2CHCH_3, C_6H_5CH(CH_3)_2中亚甲基及叔碳上的氢, 以形成CH_3(CH_2)_mCH(CH_2)_(n-m-1)CH_3, C_6H_5CHCH_3及(CH_3)_2C(CH_2)_nCH_3, (C_2H_5)_2CCH_3, C_6H_5C(CH_3)_2.     

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.     

PHOTOCHEMICAL INTERACTION BETWEEN XANTHYLETINE AND DNA

Abstract— Xanthyletine, a dimethyl-pyranocoumarin having a structural relationship to psoralen, has been studied in connection with its interaction with DNA. In the dark, it forms a weak molecular complex with DNA, which is not of the intercalated type. Under irradiation at 365nm, it is able to bind covalently to DNA, with, however, a much lower rate relative to psoralen. In this photobinding, it behaves as a pure monofunctional reagent, involving only its 3 ,4-double bond of the α-pyronic ring.
3-(α,α-dimethyl-allyl)-xanthyletine, studied for a comparison, showed only a very low photoreactivity with DNA for covalent addition; this is attributed to the presence of a bulky group at position 3 , which prevents almost completely the photoreaction of the 3 ,4-double bond.
Because of the low capacity of photobinding with DNA and the inability to form cross-links, the photobiological effects of xanthyletine are accordingly reduced: Inhibition of DNA and RNA synthesis in Ehrlich ascites tumor cells, killing of E. coli bacterial cells, inactivation of T₂ bacteriophage have been observed. By contrast, it was inactive in producing erythema on guinea pig skin.     

咔唑与氯代烷烃的光化反应

本文研究了咔唑与氯代烷烃在光照下的相互作用,并用荧光发射光谱、激发光谱、咔唑的氯代烷烃溶液光照后与二甲基黄溶液混合发生的颜色变化,证明了光照下咔唑与氯代烷烃产生了化学反应,同时通过荧光猝灭和燐光实验证实了该反应是通过激基复合物进行的,简短地讨论了反应初期的反应机理。     

水介质中氢键吸附与疏水吸附协同作用的研究

研究了丙烯酸型树脂(D152)在水、乙醇和正己烷中对苯胺、N-甲基苯胺和N,N-二甲基苯胺的吸附行为.在水中D152树脂对3种吸附质的吸附亲合性随N上甲基数的增加而增大,说明疏水作用是主要的吸附机理,但其吸附焓己超出范德华力的范围而在氢键的键能范围内,故氢键吸附也同时在起作用.在正己烷中,D152树脂对3种吸附质的吸附亲合性随N上甲基数的增加而减小,与水中呈相反的趋势,说明氢键作用是主要的吸附机理.在乙醇中,D152树脂对3种吸附质均无吸附,因为疏水作用和氢键作用均受到的乙醇抑制.在水中,吸附质与树脂间的氢键作用同样受到水的抑制,但氢键吸附却依然存在,说明水介质中氢键吸附和疏水吸附可能存在一种协同作用.在热力学上对水介质中氢键吸附和疏水吸附的协同作用给于合理的解释.     

THE FORMATION OF FREE RADICALS AND THE CONSEQUENCES OF THEIR REACTIONS IN VIVO

Abstract— Mechanisms for the initiation of free radical reactions in vivo are reviewed, including ozone and ¹O₂ reactions, radiation, one-electron transfer processes, and enzymatic reactions. The roles that radical reactions might play in aging processes and in carcinogenesis are discussed.     

A FLUORESCENCE STUDY OF TRYPTOPHAN-HISTIDINE INTERACTIONS IN THE PEPTIDE ANANTIN AND IN SOLUTION

Abstract—Anantin is a heptadecapeptide in which the C-terminal peptide chain pierces the covalently cyclized peptide ring formed by an amide link between the α-NH₂ end group and the β-carboxyl group of Asp(8). It contains a tryptophan and a histidine at positions 5 and 12 , respectively. Des-Phe(17)-anantin lacks the C-terminal phenylalanine. Fluorescence emission intensity as a function of pH follows the ionization of a single residue. The pK_a amounts to 7.23 ± 0.03 for anantin and is attributed to His(12). At pH 9 the quantum yield is 0.12 ± 0.01 for anantin, whereas at pH 4.5 the quantum yield decreases more than two-fold (0.05 2 0.01). Practically identical parameters are observed for des-Phe(17)-anantin. This pH dependency reveals intramolecular quenching of the excited indole ring of Trp(5) by the imidazole of His(12), which results in a marked decrease of the tryptophan fluorescence at low pH. In a multifrequency phase fluorometric study the fluorescence lifetimes for both peptides at pH 4.5 and pH 9 are determined. At both, pH fluorescence decay is well described by a sum of two exponentials. For anantin at pH 4.5 the lifetimes are 0.72 ± 0.07 ns and 1.67 ± 0.07 ns. At pH 9 the lifetimes are 1.11 ±0.12 ns and 2.55 ± 0.03 ns. In methanol we find two lifetimes for anantin: 0.68 ± 0.01 ns and 2.57 ± 0.01 ns. The lifetimes are found to be slightly dependent upon emission wavelength. For des-Phe(17)-anantin practically the same values are observed. The quenching of tryptophan fluorescence by histidine is further studied in solution using N-acetyl-tryptophanamide in the presence of increasing concentrations of imidazole in the protonated (pH 4.5) and unprotonated (pH 9) state and in methanol. At both pH values and in methanol, a linear increase in both the inverse of the steady-state fluorescence F_o/F and the inverse of the lifetime 1/τ with increasing imidazole concentration indicates that a collisional mechanism is at the root of the observed quenching. The quenching efficiency values, γ, are calculated and amount to about 0.32 at pH 4. 5 , 0.02 at pH 9 and 0.002 in methanol, showing that protonated imidazole is a better quencher than the unprotonated form, and that the nature of the solvent is involved even in the quenching by unprotonated imidazole. Tryptophan-histidine interactions in solution and in the peptide are compared.     

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。