摘要:

Abstract—The oxazine dye, oxonine (3,7‐diaminophenoxazin‐5‐ium chloride), 1, is photoreduced by Fe (II) sulfate in dilute sulfuric acid. The reaction mechanism is analogous to that for the photoreduction of thiazine dyes by Fe (II), the most important difference being that reduction of oxonine occurs predominantly from its excited singlet state, S1, rather than from the triplet state, T1. The latter is formed with an intersystem crossing (isc) quantum yield ofca1.7×10‐3. The quenching of S1by Fe (II) has a rate constantksQ= 2.2 ± 0.1 × 109M‐1s‐1and affords the one electron reduced product, semioxonine (R), with a limiting quantum yield, φSR, of 0.26 ± 0.02. In contrast, quenching of T1, generated by bromide ion quenching of S1or by diacetyl sensitization, occurs withkQt1.2×106M‐1s‐1, extrapolated to zero ionic strength, and affords R with a limiting probability, φTR= 1.1×0.2. Three possible reasons for the lower quantum yield of the more exothermic S1reduction are discussed. These are energy transfer from S1to Fe (II), different rates of escape of R from the encounter complex as a consequence of the different states of protonation of R as initially formed from S1and T1, and spin allowed back electron transfer in an exciplex formed between S1and Fe (II). Evidence is also presented for a very low probability (ca1%) induced isc from the encounter of S1with paramagnetic Fe (II). Rate parameters for other processes important to the overall reduction mechanism such as disproportionation of R to leucooxonine L and oxonine,kRDIS= 1.7 ±0.2 × 109M‐1s‐1, oxidation of R by Fe (III),kROX= 1.5 ± 0.1 × 105M‐1s‐1, and oxidation of L by Fe (III),kLOX= 1.1 ± 0.1 × 103M‐1s‐1, have also been measured. These results are contrasted with those for the closely related thionine/Fe(II) photoredox reaction, the most well understood

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb08484.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—We present an infrared study of 3‐hydroxyflavone in 12 K Ar and O2matrices. Although it is extremely photostable in an Ar matrix, a remarkable oxygenation reaction for 3‐hydroxyflavone takes place upon photoexcitation in an O2matrix. The primary photoproduct is concluded to be a keto‐hydroperoxide. On further photolysis the keto‐hydroperoxide affords the photostable secondary product 2‐(benzoyloxyl)benzoic acid, as well as CO and CO2through two independe

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb08485.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—Several studies in the literature indicate that histones (lysine rich proteins found associated with DNA in eukaryotic chromatin), as well as poly‐L‐lysine, can be photocross‐linked by ultraviolet (UV) light to DNA in which 5‐bromo‐2′‐deoxyuridine has been substituted for thymidne. To gain some insight into the possible nature of this cross‐linking, we have studied the photoreactions occurring in deoxygenated aqueous solutions containing 5‐bromouracil (I) (BrUra) or 5‐bromo‐2′‐deoxyuridine (III) (BrdUrd) and ethylamine, a lysine side chain analog. In the case of I this reaction produced the ring opened compoundN‐(N′‐ethylcarbamoyl)‐3‐amino‐2‐bromoacrylamide (Ia). A small amount ofN‐(N′‐ethylcarbamoyl)‐3‐ethylamino‐2‐bromoacrylamide (Ic) was also isolated. It was found that purified Ia, standing in the presence of ethylamine, was gradually converted to Ic in a dark reaction. The βandαanomers ofN‐(N′‐ethylcarbamoyl)‐3‐(2′ deoxyribofuranos‐1′‐yl)amino‐2‐bromoacrylamide (IIIa and IIIb respectively) were isolated as products in the photoreaction of III with ethylamine; the α anomer was produced in a dark reaction from the β anomer. The identity of these anomers was established by comparison of their proton NMR spectra with those of the four corresponding α and β furanosyl and pyranosyl isomeric nucleosides of thymine, which are presented in the Appendix. A study was also made of the reaction of I with methylamine; a ring opened product analogous to In,viz. N‐(N′‐methylcarbamoyl)‐3‐amino‐2‐bromoacrylamide(IIa) was formed. A similar study with 5‐bromo‐1‐methyluracil producedN‐(N′‐methylcarbamoyl)‐3‐methylamino‐2‐bromoacrylamide (IIc) as a product. Likewise, the reaction of 5‐chlorouracil with ethylamine was studied andN‐(N′‐ ethylcarbamoyl)‐3‐amino‐2‐chloroacrylamide (Ie), which is analogous in structure toIa, was found to be produced. Structural identifications were made through use of UV spectroscopy, high resolution1H‐NMR spectroscopy, mass spectrometry and, in the case ofIaandIIa,13C‐NMR spectroscopy. In the BrUra and BrdUrd reaction systems, described above, dehalogenation reactions accounted for a major portion of the products. The yields of ring opened products, determined at pH 10, ranged from a high of 10.3% in the BrUra‐ethylamine system to a low of 1.7% in the MeBrUra‐methylamine system.The pH profile of the relative quantum yields for production of total opened ring product (IIIa+IIIb) in the photoreaction ofIIIwith ethylamine indicates that this quantity increases rapidly over the pH range between 7.5 and 9.5 and then decreases above 10.5.An additional reaction

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb08486.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—Cyclic AMP receptor protein (CRP) is a regulatory protein implicated in the transcription of several operons inEscherichia coli.Its activity is modulated by effectors, such as cAMP or cGMP, which could induce (or not) structural changes in the protein, and activate (or not) the transcription. CRP can bind non‐specifically to DNA, and we investigated the photocross‐linking of the protein toE. coli5‐bromouracil‐substituted DNA, in the absence and in the presence of effectors. The photochemistry of the protein alone, under the conditions used for the cross‐linking reaction, was studied. We show that tryptophyl residues are more photoreactive than tyrosyl ones. Photocross‐linking of the protein implicates only one of the two subunits, and the rate of the reaction is not modified upon cAMP binding. Binding of cGMP reduces the rate of photocross‐linking by a factor of two. These new results show that the protein in the CRP‐cGMP complex behaves differently from

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb08487.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—Tyrosine‐linked pyropheophorbidea(2) and tryptophan‐linked pyropheophorbidea(3) were synthesized. Neither the phenol group of the tyrosine end nor the indole group of the tryptophan end showed upfield shifts as observed for the tyrosine‐linked mesoporphyrin II (17) and the tryptophanlinked mesoporphyrin II (18). When the keto group at the C‐9 of2and3was reduced to methylene group [tyrosine‐linked 9‐deoxopyropheophorbidea(5) and tryptophan‐linked 9‐deoxopyropheophorbidea(6)], the phenol group of the tyrosine and the indole group of the tryptophan showed upfield shifts, indicating the intramolecular hydrogen bonds between amino acid moieties and the keto group at the C‐9 in2and3. Irradiation of2and 1,4‐benzoquinone (BQ) in benzene led to a clean formation of a quinone‐linked pyropheophorbidea(8) in 56% yield. Triplet radical pair composed of tyrosine radical and semiquinone radical was assigned as the reaction intermediate for the formation of 8 by means of CIDNP technique. Irradiation of5under the identical conditions led to the formation of benzoquinone‐linked 9‐deoxo‐mesopyropheophorbidea(10) and benzoquinone‐linked 9‐deoxophylloerythrina(11) in 45 and 22%, respectively. Magnesium and zinc complexes of2underwent the similar photoaddition reaction much less efficiently. However, irradiation of the tryptophan‐linked model compounds3and6in the presence of B

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb08488.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—A monolayer of rhodamine 6G on quartz in air exhibited photochemistry upon laser irradiation in the first absorption band. The course of the reaction was followed in real time by the surface second harmonic generation method. It was observed that the photoproduct had an enhanced non‐linear coefficient, relative to rhodamine 6G. Absorption spectra showed that this was not a result of a stronger resonance enhancement of the signal by the photoproduct. Consideration of the factors to which the surface second harmonic signal is sensitive suggested that the enhancement arose from an increased charge transfer character of the photoproduct's electronic transitions, and a reorientation of its transition dip

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb08489.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—Psoralen‐sensitized photodamage (PUVA) of rat peritoneal exudate cells was investigated. Quartz‐activated luminol‐dependent chemiluminescence (ChL) was registered and the amount of trypan‐positive cells was determined.Irradiation of peritoneal exudate cells in the presence of psoralen resulted in a dose‐dependent monotonous inhibition of ChL. The reciprocity law of irradiation intensity and duration of irradiation was not valid for the observed inhibition of ChL; the inhibition increased with higher intensity.When psoralen previously photooxidized in ethanol (POP) was added to peritoneal exudate cell suspension, a double‐phase response depending on psoralen irradiation dose was obtained: ChL activation was observed at low doses of UVA, ChL inhibition at high doses. Chemiluminescence inhibition correlated well with the increase in the number of trypan‐positive cells.It may be supposed that the observed effects of PUVA or POP treatment are caused by cell cytoplasmic

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb08490.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—This experiment investigated the effect on ultraviolet (UV) radiation‐induced tumorigenesis of feeding the histamine type 2 receptor antagonist, cimetidine, to Skh:HR mice. Cimetidine was fed to one group during a 70 day period of chronic UVR (5 day/week for 10 weeks), to a second group from the end of this period to the end of the experiment at 286 days and a third group was fed a control diet only throughout the experiment. Feeding mice cimetidine during the 70 day period of irradiation protected them against the later development of skin tumo

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb08491.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—Photoreactivation in the extreme halophilic archaebacteriumHalobacterium cutirubrumwas studied bothin vivoandin vitro.Cells irradiated with ultraviolet (UV)‐fluences up to 350 J/m2could be completely photoreactivated, indicating very efficient repair of pyrimidine dimers in UV‐irradiated DNA. Dark repair is apparently absent inHalobacteriumsince liquid holding under non‐growth conditions did not influence the survival of UV‐irradiated cells, while cells remained completely photoreactivable with no change in the kinetics of photoreactivation. Experiments withHalobacteriumisolates of different carotenoid content indicated that carotenoids do not influence either UV‐inactivation or photoreactivation. Small differences in the rates of UV‐inactivation and photoreactivation could be assigned to the occurrence of gas vesicles. Flash experiments and the temperature dependence of photoreactivation indicated an enzymatical reaction. This was confirmed byin vitroexperiments with partially purified photoreactivating enzyme. Thein vivoaction spectrum of photoreactivation showed a main band in the 400‐470 nm region with a maximum at 440 nm. Comparison with action spectra of other microorganisms classified theHalobacteriumenzyme as a 8‐hydroxy‐5‐deazaflavin type pho

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb08492.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract—The binding of neutral red to purple membrane has been studied. The intrinsic pKaand the apparent pKa, of bound neutral red were determined by titration and by measuring the binding ratio of neutral red to purple membrane as a function of pH. The surface potential of purple membrane was inferred from the difference between these two pKas. The H+/M412 ratio at different ionic strengths was also measured and compared with the surface potential. The results show that the H+/M412 decreased as the surface potential increased due to decreased salt concentrations. However, this correlation holds only for KCl concentrations higher than 30 mM. At lower salt concentrations, the change in surface potential is always less than the variation in the H+/M412 rati

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1991.tb08493.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY