共查询到20条相似文献,搜索用时 15 毫秒
1.
Abstract 125 I- N 6 -(N-[6-N-{5-iodo-4-azidosalicyl}-aminohexyl]-aminocarbamoylmethyl)-nicotinamide adenine dinucleotide (125 I- N 6 -I-ASA-AH-NAD+ ) was synthesized by coupling N 6 -([6-aminohexyl]-carbamoylmethyl)-NAD+ with 4-azidosalicylic acid N-hydroxysuccinimide ester followed by radioiodination. The utility of 125 I-N 6 -I-ASA-AH-NAD+ as an effective site-directed photoprobe was demonstrated by the photolabeling of both glutamate dehydro-genase and 15-hydroxyprostaglandin dehydrogenase. Both enzymes can be saturated with labeled probe with apparent dissociation constants comparable to those reported for NAD+ . Photoincorporation of the probe into both enzymes was found to be protected specifically by NAD+ . These results indicate that 125 I- N 6 -I-ASA-AH-NAD+ can be a specific photoprobe for NAD+ -linked enzymes. 相似文献
2.
Abstract— We have characterized the spectra, acidity constants and decay kinetics of the triplet and semireduced radical species of Safranin-O. Between pH 3.0 and 10.6, there are three triplet species denoted 3 DH2 + 2 , 3 DH+ and 3 D, the p K a s being 7.5 and 9.2. All three triplet species exhibit first order decay, the rate constant for 3 DH+ being ca. 5-fold lower than the rate constants of 3 DH+ and 3 D. Ascorbic acid and ethylenediaminetetraacetic acid (EDTA) quench the triplet state under appropriate pH conditions and the pH dependencies of the yield of semireduced dye indicate that 3 DH+ is more reactive than 3 DH+ or 3 D. With EDTA as the reducing agent, there is the additional requirement that at least one of the amino nitrogens be deprotonated to obtain a significant yield of semireduced dye. In these reactions, ascorbic acid is oxidized reversibly, but EDTA is oxidized irreversibly, so that with the latter reducing agent photolysis causes buildup of the leucodye, which on subsequent photolysis can reduce triplet state dye. With ascorbic acid as the reducing agent, the regeneration of the ground state dye is reversible, the decay of the semireduced radical being second order. In general, the transient photochemistry of Safranin-O resembles that of Thionine, the major difference being that the lifetimes of 3 DH2 + 2 and 3 DH+ are much longer for Safranin-O than for Thionine. 相似文献
3.
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 CH2 C12 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
4.
Abstract— Laser flash photolysis of trans -[Rh(dppe)2 X2 ][PF6 ] (X=Br and I; dppe=bis(diphenylphosphino)ethane) in CH2 Cl2 or CH3 CN produces the d7 Rh(II) radicals, [Rh(dppe)2 X]+ , and halogen atoms. The kinetics of the disappearance of [Rh(dppe)2 X]+ radicals in CH2 Cl2 or CH3 CN were mixed order: H-atom abstraction from solvent to produce the rhodium hydrides, [RhH(dppe)2 X][PF6 ], and Rh/X recombination. In the poor H-atom donor solvent, benzonitrile, Rh/Br recombination was observed to be uncomplicated by competing H-atom abstraction. The hydride complexes [RhH(dppe)2 X][PF6 ], formed by H-atom abstraction were completely characterized by 31 P{1 H}-NMR, 1 H-NMR, and mass specrometry. Cyclohexene was used as an effective trap for photogenerated Br atoms and yielded bromocyclohexane and 3-bromocyclohexene in a relative yield, 1:9. The photochemical mechanism is discussed in light of the transient absorbance and trapping studies. 相似文献
5.
Abstract— A novel method for the determination of singlet oxygen reaction rate constants is described and applied to studies of cyclohexadiene in methanol and gelatins in H2 O and D2 O. The technique uses tris (2,2'-bipyridine) ruthenium(II) dication (Ru(bipy)32+ ) as both singlet oxygen sensitizer and in situ oxygen concentration monitor during irradiation of sealed samples. Because of the high efficiency with which the luminescence of Ru(bipy)3 2+* can be detected, and the fact that emission lifetimes are used, the method offers some advantages over those previously described. The advantages and disadvantages of the method are discussed. A rate constant of 2.1 (±0.3) x 106 mol-1 dm3 s-1 has been determined for the reaction of 1 O2 with cyclohexadiene in methanol. For two different photographic gelatins the sums of reaction and quenching rate constants are 2.0 (±0.4) x 106 and 3.1 (±2.0) x 105 mol-1 dm3 s-1 ; for swine skin gelatin this value is 3.9 (±2.4) × 105 mol-1 dm3 s-1 . Chemical reaction, rather than physical quenching, is the dominant reaction route for gelatins and 1 O2 . 相似文献
6.
Ekehardt Vogelmann Wolfgang Rauscher Horst E. A. Krameer 《Photochemistry and photobiology》1979,29(4):771-776
Abstract—Rate constants, k q , for the reaction of cationic and neutral acridine orange and 10-methylacridine orange triplet states (3 AOH + , 3 AO, 3 MAO+ ) with a series of electron donors have been measured. Two different protolytic forms of the semireduced dye radical are produced by acridine orange triplet quenching at various pHM values in methanolic solution.
It is found that k4 decreases with increasing oxidation potential of the reducing agent for all triplet states in a manner which is expected for electron transfer reactions. The different reactivities of the cationic and neutral triplet forms can, therefore, be attributed to the difference in reduction potentials of these species. The difference in reduction potentials is related to the p K M values of triplet state, p K T M , and semireduced dye radical, p K M S , by thermodynamic consideration. p K T M (3 AOH+ /3 AO) is determined to be 11.2. From thisp K S M (AOH./AO;) is estimated to be 17–18. This is in striking contrast to the protolytic equilibrium of the semireduced dye radicals found to be pKF = 4.1. We conclude that the last value represents the second protonation equilibrium (AOH+ 2 ./AOH). This conclusion is confirmed by spectroscopic data. 相似文献
It is found that k
7.
PULSE RADIOLYSIS STUDIES IN MODEL LIPID SYSTEMS: FORMATION AND BEHAVIOR OF PEROXY RADICALS IN FATTY ACIDS 总被引:1,自引:0,他引:1
Abstract— Radiolytic formation and peroxidation of fatty acid radicals have been investigated by pulse radiolysis techniques in oleate, linoleate, linolenate and arachidonate systems. A strong absorption band at 280 nm associated with conjugated radicals, Rconj , formed in polyunsaturated fatty acid moieties has been used as a probe for kinetic processes occurring at doubly allylic sites in the hydrocarbon chain. Formation of Rconj by O- has been found to be more efficient than the less selective OH radical. Peroxidation of Rconj is shown to be somewhat slower, ( k R + O2 ˜ 3 × 108 M -1 s-1 ), than O2 reactions with radicals in oleate ( k R + O2 = 1 × 109 M -1 s-1 ). Peroxy radicals generated in these reactions disappear slowly by essentially second order processes (2 k RO1 ˜ 107 M -1 s-1 ). The superoxide radical, O- 2 , shows little if any reactivity towards 0.01 M linolenate or arachidonate over periods of 20 s. 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.
Christiane Ferradini Jacques Foos Lucien Gilles Didier Haristoy Jacques Pucheault 《Photochemistry and photobiology》1978,28(4-5):851-855
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
The oxidation of oxyhemoglobin by O
The reduction of methemoglobin in γ radiolysis reaches a plateau which could be explained by structural considerations.
The reduction of methemoglobin by O
10.
S. A. Naman 《Photochemistry and photobiology》1990,52(4):649-654
Abstract— –Flash photolysis at 450 nm over the temperature range 0.8–60°C was used to determine Arrhenius parameters for the first and second order disappearance of triplet lumiflavin (1.66 µ .M ) at a flash energy of 2 kj in deaerated phosphate buffer at varying pH:
3 Lf → Lf0
3 Lf +3 Lf → Lf0 + Lf0
Arrhenius parameters were also determined for the pseudo first-order quenching of triplet lumiflavin by 10 µ M ferri- and ferrocyanide ions,
3 Lf + Fe3+ → Fe3+ → Lf0 + Fe3+ (energy transfer)
3 Lf + Fe2+ → Lf- + Fe3+ (electron transfer)
and for disappearance of the semireduced lumiflavin in the presence of ferrocyanide at pH 6.8, by the second-order reaction
Lf- +Lf - → Lf0 + Lf= . 相似文献
Arrhenius parameters were also determined for the pseudo first-order quenching of triplet lumiflavin by 10 µ M ferri- and ferrocyanide ions,
and for disappearance of the semireduced lumiflavin in the presence of ferrocyanide at pH 6.8, by the second-order reaction
Lf
11.
Abstract— The rapid bimolecular reaction SO + O3 = SO2 +O2 + 106 kcal/mole
yields electronically excited SO2 in the 3 B 1 and 1 B2 states with some vibrational excitation, as well as SO2 in its electronic ground state. It is shown that k1 = 1.5 x 1012 exp (-2100/ RT ) cm2 mole-1 s-1 and that the formation of electronically excited SO2 involves higher activation energies. 相似文献
yields electronically excited SO
12.
A. J. W. G. Visser G. J. van Ommen G. van Ark F. Müller J. D. W. van Voorst 《Photochemistry and photobiology》1974,20(3):227-232
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
13.
Abstract— The influence of chloride ion on the rate of decay of triplet methylene blue in 0.01 M acid in the absence and presence of ferrous ions was investigated by means of laser flash-photolysis monitored by kinetic spectrophotometry. Chloride weakly accelerates decay of 3 MBH2± in aqueous solution in the absence of Fe(II). Quenching of 3 MBH2+ by Fe(II) is more strongly catalyzed by Cl- in both water and 50 v/v% aq. CH3 CN. The uncatalyzed quenching constant, k 5 , is of the order of 1 × 106 M -1 s-1 while in 4.8 M aqueous chloride ( μ – 7.2 M ) k 5 = (37.2 ± 1.8) × 106 M -1 s-1 . A possible role of chloride is as a bridging species in quenching via electron transfer between 3 MBH2+ and Fe(II). 相似文献
14.
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 N2 O 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 +3 O2 or Trp*+3 O2 or else
相似文献
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 Λ
These results also point out that the neutral radical Trp. which has been previously observed for Λ
相似文献
15.
Abstract— A very efficient quenching of singlet oxygen (1 O2 ) by N3 - ions has been applied to the determination of rate constants of reactions of 1 O2 with various substrates (A). This determination has been made possible by choosing experimental conditions which give simple competition between N3 - and A for 1 O2 formed in the steady state irradiation of convenient sensitizing dye (S). The consumption of oxygen by the substrate, as followed with an oxygen analyzer, decreases in the presence of low concentrations of N3 - . Using neutral air saturated aqueous solutions containing the dye phenosafranine + A and varying concentrations of N3 - , the 1 O2 rate constants for reactions with biological substrates and some radiation protective agents have been determined. 相似文献
16.
Abstract— From spectroscopic data and rate constants in the literature, equilibrium constants and rates of thermal formation of singlet oxygen (1 Δg and 1 Σg + ) were calculated for a number of conditions. For the gas phase we estimate K eq (1 Δg 3 Σg - ) = 1.67 exp(-94.31 KJ/RT) and K eq (1 Σg + /3 Σg - ) = 0.33 exp(-157.0 KJ/RT). The calculated rate constants for the 3 Σg + →1 Δg transition of O2 at 25°C varied from 2.5 × 10-11 s-1 in water to 4.8 × 10-16 s-1 in air, assuming equal solvent interactions with the ground and excited states. Physical quenchers for singlet oxygen are expected to be catalysts for its thermal formation. Equations are presented which allow one to estimate whether such catalysis by quenchers will result in a pro-oxidant effect. 相似文献
17.
Abstract— 3-Azidopyridine adenine dinucleotide, an azide analog of NAD+ , has been synthesized as a potentially general photochemical labeling reagent for the active sites of NAD-dependent dehydrogenases. The analog is a competitive inhibitor of NAD reduction by yeast alcohol dehydrogenase (YADH). Upon photolysis of the 3 H-analog in the presence of YADH, 7% of the label becomes covalently bound. The results are discussed in terms of desired properties of a photochemical labeling reagent. 相似文献
18.
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
19.
Wenqiu Liu Michelle Gaines Rong Bao Jacquelynn Clifford Yuzhou Li 《Photochemistry and photobiology》1996,63(6):793-799
Two pyridine-modified NAD'analogs, 3–(3-azido benzo-yl) pyridine adenine dinucleotide 1 and N -(3-azido-5-car-boxyl) phenyl nicotinamide adenine dinucleotide 2 have been prepared and evaluated for photoaffinity labeling experiments. The syntheses were accomplished via a mammalian NADase-catalyzed base exchange reaction. The new NAD+ analogs retained the carbonyl or carhox-amido functional group at the 3 position of the pyridine ring. The analog 1 is the first pyridine-modified azido derivative of NAD+ that has shown coenzyme activity in a stereospecific hydride transfer reaction catalyzed by a dehydrogenase. Both NAD+ analogs have shown potential for the study of active sites of NAD+ -utilizing enzymes. 相似文献
20.
MECHANISM OF PHOTOSENSITIZATION BY PHEOPHORBIDE a STUDIED BY PHOTOHEMOLYSIS OF ERYTHROCYTES AND ELECTRON spIN RESONANCE SPECTROSCOPY 总被引:1,自引:0,他引:1
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 1 O2 , 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 H2 O2 generation, respectively, to the medium had little effect on it.
Methods for converting1 O2 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 1 O2 , 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 1 O2 .
These results led us to conclude that1 O2 was mainly responsible for the hemolysis of erythrocytes by photoexcited PPa. 相似文献
Methods for converting
These results led us to conclude that