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1.
Abstract— The photodecomposition of sulfanilamide, 4-aminobenzoic acid and related analogs in aqueous solution has been studied with the aid of spin traps 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) and CH3NO2 as well as by direct electron spin resonance techniques. The NH2 radical was trapped by DMPO during the photolysis of aqueous solutions of sulfanilamide with a Xe arc lamp. Studies with [15N1]-sulfanilamide indicated that the NH2 radical was generated by homolytic fission of the sulfur-nitrogen bond. Under the same conditions DMPO trapped the H and SO3 radicals during photolysis of sulfanic acid. Direct photolysis of sulfanilamide, sulfanilic acid and Na2SO3 in the absence of any spin trap yielded the SO3 radical. Photolysis of 4-aminobenzoic acid at pH 7 gave the H radical which was trapped by DMPO. At low pH values OH and C6H4COOH radicals were generated during the photolysis of 4-aminobenzoic acid. No eaq were trapped by CH3NO2 when acid (pH 4) and neutral aqueous solutions of sulfanilamide or 4-aminobenzoic acid were photoirradiated. The mechanism of formation of known photoproducts from the free radicals generated by sulfanilamide and 4-aminobenzoic acid during irradiation are discussed. The free radicals generated by these agents may play an important role in their phototoxic and photoallergic effects.  相似文献   

2.
Abstract— Experiments on the photooxidation of N -allylthiourea, thiourea, and N-allylurea sensitized by the dye phenosafranine show that in N -allylthiourea the thiourea group is the site of singlet oxygen attack, while the allyl moiety neither reacts with nor quenches this metastable form of O2 (in neutral aqueous solutions). Low concentrations of N-3 (a known quencher of singlet oxygen) strongly reduce the photooxidation of allylthiourea by a mechanism which apparently obeys simple competition kinetics. From these results the rate constant of the reaction between allylthiourea and singlet oxygen is obtained ( k = 4 × 106 M -1 s-1; pH = 7.1).  相似文献   

3.
The photochemistry of 5,5-dimethyl-l-pyrroline N -oxide (DMPO) has been studied in benzene, cyclohexane and aqueous buffer solutions (pH 7.4) by means of electron paramagnetic resonance (EPR) and the spin trapping technique. Ultraviolet irradiation of DMPO in aqueous buffer with unfiltered UV radiation from a Xe arc lamp results in photoionization of the spin trap and the generation of the DMPO cation radical, DMPO+. The aqueous electron, eaq, was trapped by DMPO and detected as the DMPO/H adduct. The DMPO+- reacted with the water to yield the DMPO/OH adduct. Ultraviolet irradiation of DMPO in nitrogen-saturated benzene gave an unidentified carbon-centered DMPO adduct that was replaced by hydroperoxyl and alkoxyl adducts of DMPO when oxygen was present. Experiments employing 17O2 gas indicated that the oxygen in the DMPO alkoxyl adduct was derived from molecular oxygen. However, UV irradiation of DMPO in cyclohexane yielded the cyclohexyl and cyclohexyloxyl adducts of DMPO in nitrogen-saturated and air-saturated solutions, respectively. These observations suggest that in aprotic solvents UV irradiation of DMPO generates a carbon-centered radical (R), derived from the trap itself, which in benzene reacts with oxygen to yield an alkoxyl radical (RO), possibly via a peroxyl radical (ROO) intermediate. In cyclohexane R abstracts a hydrogen atom from the solvent to yield the cyclohexyl radical in the absence of oxygen and the cyclohexyloxyl radical in the presence of oxygen. These findings indicate that when DMPO is used as a spin trap in studies employing short-wavelength UV radiation (λ < 300 nm) the photochemistry of DMPO cannot be ignored.  相似文献   

4.
Abstract— Using high-intensity actinic light, the chlorophyll a fluorescence transient from HCO-3-depleted chloroplasts shows a rapid initial rise (O → I) followed by a slow phase (I → P). In the presence of HCO-3, the O → I rise is delayed but the I → P phase is much more rapid. Using low-intensity actinic light, the chlorophyll a fluorescence transient from 3-(3,4-dichlorophenyl)-1,1 dimethylurea (DCMU)-treated chloroplasts is delayed in the presence of HCO-3. Bicarbonate increases the amount of delayed light emission from chloroplasts given 10 s illumination with weak blue light (0·4 W/m2). DCMU greatly increases the amount of delayed light seen in the presence of HCO-3 under these conditions but decreases the amount seen in the absence of HCO-3. It is suggested that HCO-3 may somehow form or stabilize, in the dark, a number of reaction centers corresponding to the S1 state in the model of B. Forbush, B. Kok and M. McGloin ( Photochem. Photobiol. 14, 307–321, 1971).  相似文献   

5.
Abstract Phcophorbide a (PPa), a causal substance of food intoxication, when excited by exposure to light wavelengths of over 600 nm, caused the photohemolysis of goat erythrocytes in proportion to the incubation time of the cells. The addition of N-3, an effective scavenger of 1O2, to the medium markedly inhibited the hemolysis of erythrocytes in a concentration-dependent manner, whereas the addition of superoxide dismutase (SOD) and catalase, inhibitors of O-2 and H2O2 generation, respectively, to the medium had little effect on it.
Methods for converting 1O2 to a nitroxide radical by 2,2,6,6-tetramethyl-4-piperidone (TMPD) and for trapping O-2 and OH by 5,5-dimethyl-l-pyrroline-A'-oxide (DMPO) were employed to observe directly these activated oxygens by electron spin resonance (ESR). The methods provided evidence that only 1O2, was produced by PPa, which was excited by light wavelengths of over 600 nm. Both the addition of N3 to the solution and the removal of oxygen from the solution inhibited the generation of 1O2.
These results led us to conclude that 1O2 was mainly responsible for the hemolysis of erythrocytes by photoexcited PPa.  相似文献   

6.
MECHANISM OF PHOTOINACTIVATION OF PLANT PLASMA MEMBRANE ATPASE   总被引:1,自引:0,他引:1  
Abstract UV radiation at 290 and 365 nm inactivates two forms of the K+-stimulated ATPase associated with the plasma membrane of suspension-cultured cells of Rosa damascena . One form is 15 and 36 times more sensitive than the other to 290 and 365 nm, respectively. For both forms, the inactivation requires oxygen, is inhibited by azide and diazobicyclo(2.2.2.2)octane, but not glycerol, and is enhanced up to 7.5 times in deuterium oxide solvent. Inactivation occurs concomitantly with loss of absorbance at 290 nm. Cs+ and NO3, quenchers of tryptophan fluorescence, inhibit inactivation. The results suggest that inactivation involves singlet-oxygen mediated destruction of tryptophans in the ATPases.  相似文献   

7.
Abstract— While superoxide anion radical does not normally react with olefins, it does react with activated double bonds. Thus O-2 oxidatively cleaves certain α,β-unsaturated ketones such as chalcones and tetracyclone and electron poor olefins such as 1,1-dicyano and 1,1-dinitro olefins. Similarly O-2 can react with substituted nitrobenzenes to yield the corresponding nitrophenols. EPR and oxygen labeling (KO362) experiments confirm an electron transfer mechanism.  相似文献   

8.
Abstract. Photosynthetic reduction of nitrite to ammonia with type C chloroplasts from the heterocont alga Bumilleriopsis filiformis was investigated using 3,6-diaminodurene/ascorbate and 3,6-diaminodurene/dithioerythritol (DAD/DTE) as electron donor couple. Rates approach 6–10 μmol NO-2 reduced/mg chlorophyll/h and are steady for up to 30 min. The presence of oxygen or NADP+ only slightly diminished the rates of nitrite reduction obtained with DAD/DTE. Illuminated chloroplasts reduce oxygen in the presence of DAD/DTE at 135 μmol/mg chlorophyll/h without acceptor supplied. Photosynthetic oxygen uptake by this system in the presence of ferredoxin and NO-2, however, is inhibited to 42% by nitrite reductase with concurrent nitrite reduction. NO-3 and NO-2 have no effect on photosystem I-mediated NADP+ reduction, NO-2 (10 m M ) inhibits ferricyanide-mediated oxygen evolution to 72%. Also photosystem II reactions assayed e.g. with silicomolybdate are inhibited significantly by NO-2 (1 m M ), but only slightly by NO-3. Nitrite reductase is inhibited by p -chloromercuribenzoate ( p CMB), and this inhibition is prevented by DTE. Results suggest that photosynthetic nitrite reduction can cope with low concentrations of either compound, provided relevant thiol groups are protected.  相似文献   

9.
PHOTOREDUCTION OF NAD TO NADH IN SEMICONDUCTOR DISPERSIONS   总被引:1,自引:0,他引:1  
Abstract— Band gap illumination of TiO2 (anatase) dispersions in weakly alkaline solutions of nicotinamide-adenine-dinucleotide (NAD+) leads in the presence of rhodium trisbipyridyl complex [Rh(bipy)3+3], to continuous generation of biologically active cofactor NADH. Effects of pH, NAD+ and Rh(bipy)3+3 concentration on the efficiency of this photoconversion process are investigated. The reaction proceeds already in aqueous solution in the absence of external electron donors but it is enhanced significantly in the presence of 10% methanol.  相似文献   

10.
Abstract— The concentration dependence of the lifetimes of the charge transfer excited states of Cu(dmp)+2 and Cu(dpp) +2 has been investigated in CH2C12 solution at 20°C. (dmp denotes 2,9-dimethyf-1,10-phenanthroline, and dpp denotes 2,9-diphenyl-l,10-phenanthroline.) In dilute solution (< 30 μM) the lifetime of Cu(dmp)+2, is 95 ± 5 ns, independent of the anion. At higher concentrations the lifetime decreases, in most cases, to a limiting value that depends upon the counterion. The measured limiting lifetimes range from 38 ± 3 ns for CIO-4 to 78 ± 5 ns for PF-6. The anion-induced quenching is attributed to exciplex quenching which is mediated by an ion pair which exists in the ground state. The results imply that the quenching ability of the anions follows the order BPh-4 < PF -6, < BF-4 < CIO -4 < NO-3 which is consistent with previous estimates of donor strength. The lifetime of Cu(dpp)+2 is also concentration dependent, but the effect is much smaller because the phenyl substituents impede attack by the anion.  相似文献   

11.
Abstract. Thiols and disulfides protect both φX174 phage and its isolated DNA from the lethal action of proflavine plus light. The protective ability of these compounds appears to be attributed to the -SH or the -S-S- group and the property to interact with the proflavine-phage DNA complex. The phage inactivation efficiency per proflavine bound to DNA is reduced by 50 to 30% upon addition of cysteine or cystamine. Substances that affect the lifetime of singlet oxygen modify the rate of phage photoinactivation in the presence of proflavine; the inactivation rate is decreased by N-3 and increased by D2O. Irradiation under N2 atmosphere markedly decreases the phage photosensitization by proflavine. Irradiation with monochromatic light of 440 nm is less efficient than irradiation with light of 440 nm plus 360 nm, and the difference is more pronounced in N2 than in air. These results are discussed in relation to various possible photochemical pathways.  相似文献   

12.
Abstract— The fluorescence quenching of the indole chromophore by NO2 and the fluorescence depolarization of several luminescence probes in aqueous solutions containing hexadecyltrimethylammonium bromide (HDTBr) were measured as a function of added C2–C4 aliphatic alcohol concentration. The fluorescence decay profiles of pyrene in the micellar solutions were also measured to estimate the aggregation number of the micelles. The addition of n -butyl alcohol significantly reduces the fluorescence quenching rate and the aggregation number and increases the extent of fluorescence depolarization in HDTBr micellar systems. The addition of ethyl alcohol shows a similar but smaller effect.  相似文献   

13.
PHOTOCLEAVAGE OF DNA IN THE PRESENCE OF SYNTHETIC WATER-SOLUBLE PORPHYRINS   总被引:6,自引:0,他引:6  
In the presence of oxygen and visible light, various synthetic water-soluble porphyrins cleave pBR 322 plasmid supercoiled DNA (form I) producing relaxed (form II) and linear (form III) DNA corresponding to single-strand and double-strand breaks respectively. Large variations are observed in the efficiency of the porphyrins containing a diamagnetic metal or no metal at all. Singlet oxygen (1O2) seems to be involved in the mechanism of cleavage consistent with the inhibitory effect of the azide anion, N3. The higher efficiency of cationic porphyrins (as compared to anionic ones) is due to their greater affinity for DNA as shown by experiments carried out at either high ionic strength or in the presence of the surfactant, sodium dodecyl sulfate.  相似文献   

14.
ON THE PHOTOIONIZATION ENERGY THRESHOLD OF TRYPTOPHAN IN AQUEOUS SOLUTIONS   总被引:1,自引:0,他引:1  
Abstract— To investigate the existence and energy position of a photoionization threshold. tryptophan (Trp) has been photoionized in desecrated neutral aqueous or alcoholic solution under monochromatic light of variable frequency, in presence of N2O to scavenge the photoelectron.
Present findings and some literature data converge to show the existence of a threshold for the one photon ionization process. This threshold is located at 4.5 ± 0.1 eV and 4.85 ± 0.1 cV for Trp in aqueous and ethanol solutions. respectively, which corresponds to a lowering with respect to the gas phase ionization potential of 3.4 and 3.0 eV.
The photoionization quantum yields for Trp is found about 4 times greater at 250 nm than at Λcx= 265 nm, where φe-4M=0.080±0.025. In such spectral range. at most one photoelectron out of 4–5 escaping geminate recombination would lead to Trp photodegradation in acrated solutions.
These results also point out that the neutral radical Trp. which has been previously observed for Λcx > 275 nm, i.e. below the ionization threshold energy—would not necessarily derive from Trp + deprotonation or cation-electron dissociative recombination. Similarly, the opening of the indole ring with formylkynurenine (FK) formation which is observed under aerobic conditions and Λcx >, 280 nm would not imply an electron attachment on O2 but reactions such as Trp +3O2 or Trp*+3O2 or else
  相似文献   

15.
The main DNA-3-CPs furan side adduct has been isolated following acidic hydrolysis of photomodified DNA and subsequent reversed-phase high performance liquid chromatography purification. This photoadduct has been identified as a thymine-3-CPs C4-cycloadduct Thy<5 4'6 5', >3-CPs based on its optical spectroscopic features and of its plasma desorption mass spectrometric characteristics. Moreover, its reversed-phase high performance liquid chromatography retention time is in agreement with a cis-syn stereochemistry as compared to the chromatographic properties of the cis-syn model adduct Thy< 5 4'6 5' >3-CPs previously identified. Further support for the cis-syn stereoconfiguration assignment was provided by fluorescence quenching experiments using iodide and silver ions as external and internal quenchers respectively. These data strongly indicate that the Thy< 5 4'6 5' >3-CPs photoadduct is located inside the DNA helix in agreement with its cis-syn stereochemistry.  相似文献   

16.
Abstract— The radiolytic studies of oxyhemoglobin or methemoglobin in neutral aerated aqueous solutions with formate ions, lead to three conclusions:
The oxidation of oxyhemoglobin by O-2 is not important. The observed low oxidation yield is probably due to the slow reaction with hydrogen peroxide produced by O-2 disproportionation.
The reduction of methemoglobin in γ radiolysis reaches a plateau which could be explained by structural considerations.
The reduction of methemoglobin by O-2 ions, if it occurs, is relatively slow: k = 1.4 × 103 M -1 s-1. But a problem remains concerning the spectral characteristics of the product.  相似文献   

17.
Free radicals were trapped and observed by ESR when photoallergens bithionol and fentichlor were irradiated in the presence of spin traps N- t -butyl-α-phenylnitrone (PBN) and 5,5-dimethyl-pyrroline-N-oxide (DMPO). In the absence of air, both PBN and DMPO trapped a carbon-centered radical. The carbon-centered radical, which was capable of abstracting a hydrogen atom from cysteine, glutathione, ethanol and formate, was identified as an aryl radical derived from the homolytic cleavage of the carbon-chlorine bond. In the presence of air, both carbon-centered radicals and hydroxyl radicals were trapped by DMPO. Under similar conditions, the yield of the hydroxyl radicals was greater from bithionol than from fentichlor. The presence of the hydroxyl radical was confirmed by kinetic experiments employing hydroxyl radical scavengers (ethanol, formate). Superoxide and H2O2 were not involved. Experiments with oxygen-17O indicated that the hydroxyl radicals came exclusively from dissolved oxygen. The precursor of the hydroxyl radical is postulated to be a peroxy intermediate (ArOO*) derived from the reaction of an aryl radical (Ar*) with molecular oxygen. Both bithionol and fentichlor photoionized only when excited in the UVC (<270 nm) region. Free radicals have long been postulated in the photodechlorination of bithionol and fentichlor and the present study provides supporting evidence for such a mechanism. Aryl and hydroxyl radicals are reactive chemical species which may trigger a series of events that culminate in photoallergy.  相似文献   

18.
Abstract— Toluidine blue, a thiazine dye, was shown to have in vivo photodynamic activity through singlet oxygen (O21Δ g ) production. This was based mainly on the effective protection by N-3 and the marked enhancement in D2O for the sensitized inactivation of yeast cells. The mode of the in vivo activity was, however, quite different from that of acridine orange, for which the singlet oxygen mechanism has also been proposed. The most characteristic feature in the toluidine blue-sensitization was the total lack of the induction of gene conversion (at trp 5), while the survival went down below 10%. The non-induction of genetic changes was confirmed at several pH's in the neutral region, whereas the inactivation was seen in parallel to the reported pH dependence of singlet oxygen production in vitro . Direct measurements by microspectrophotometry showed none of the toluidine blue was accumulated in the cell. It was also ascertained from acridine-sensitized induction of gene conversion that toluidine blue never interfered with the binding of acridine orange to cellular DNA. These findings suggested that the unique mode of photodynamic activity of toluidine blue is attributable to its action from outside of the cell. Furthermore, comparisons between the photodynamically treated cells (with toluidine blue) and non-treated cells with respect to the response to UV irradiation excluded certain cell functions relating to the expression of gene conversion from the possible damage sites. The photo-reactivation process of UV induced gene conversion was not disturbed by the pre-toluidine blue sensitition. In view of the foregoing results, the plasma membrane was tentatively suggested as the most likely site of damage.  相似文献   

19.
Abstract— The one-electron reduction and oxidation of 5,10-methenyltetrahydrofolate has been studied in aqueous solution in the acidity range H0= -1 to pH = 7 using the reducing species CO-2 and (CH3)2-COH and oxidising species Br-2, and H2SeO+3. The spectral and other properties of the radicals so formed were found to be indcpendent of the reductant/oxidant used. Two protolytic forms of both the oxidised and reduced radicals were observed with approximate p K , values of 0.5 ± 0.3 being determined. Both the bridged form (5.10-methenyltetrahydrofolate) and the unbridged form (5- formyltetrahydrofolate) were found to be easily oxidised, whereas only the former could be reduced.  相似文献   

20.
Abstract— We have described the covalent binding of 124-kDa oat phytochrome to large unilamellar liposomes composed of either dioleoyl phosphatidylcholine or dipalmkoyl phosphatidylcholine or soybean lecithin, without affecting the photochromic properties of the protein. These phytochrome-liposome systems have now been studied by laser flash photolysis. The liposomes, independent of their membrane rigidity (liquid-crystal vs gel-like phase), do not influence the ratio and reactivity of the two primary photoproducts, Ii700- of the red absorbing form of phytochrome, Pl Thus, the lifetimes of the Ii700 intermediates and the activation parameters associated with Ii700Iibl are the same as those measured for nonbound phytochrome in buffer solution. The temperature increase from about 273 K. to 297 K lowers the population of the shorter-lived Ii700 intermediate to the same extent both in the liposome-Pl and in nonbound Pl, whereas it does not affect the relative population of the Ii700 intermediates from non-bound Pl in the presence of 25% ethylene glycol added to the buffer solution (ionic strength 0.17).  相似文献   

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