摘要:

Abstract—The poor water solubility of typical photochemotherapeutic psoralens restricts their utility in aqueous solutions and commonly requires the use of organic co‐solvents in photobiological studies. This paper describes the preparation of readily water‐soluble “pre‐psoralens”, (Z)‐3‐[5‐(4,6‐dimethoxy)benzofuranyl]propenoic acid (3) and (Z)‐3‐[5‐(6,7‐dimethoxy)benzofuranyl]propenoic acid (4), and their novel photocyclization in aqueous media to give 5‐methoxypsoralen (5‐MOP) and 8‐methoxypsoralen (8‐MOP), respectively. Quantum efficiencies, measured at 308 nm for the cyclization, are 12. 1 × 10‐3for 3 → 5‐MOP and 2.7 × 10‐3for 4 → 8‐MOP. 5‐Methoxyisopsoralen (5‐MOiP, 5) is a side product from the photolysis of 3. Photocross‐linking of calf thymus DNA is effected when the “pre‐

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb08504.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—In order to investigate the photoreactions between the thymidine and the psoralen chromophores and to devise a synthetic route to prepare thymidine‐5‐methoxypsoralen adducts, we have prepared and studied a compound in which thymidine is linked to a 5‐methoxypsoralen derivative by a diester chain. Irradiation at 365 nm carried out at usual concentrations (10–3M) leads exclusively to one diastereoisomer of an intramolecular 3,4cis‐anti[2+2] adduct. No photodimerization is observed in these conditions. These results are compared to those obtained for models studied previously in which the thymine and the psoralen rings are linked by polymethylenic chains of var

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb08505.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—We have studied the photoreactions occurring whenp‐aminobenzoic acid (PABA), a component of some sunscreens, is irradiated in aqueous solution. These studies were carried out in the presence and absence of oxygen, using light of Λ= 254 nm as well as light of wavelengths greater than 290 nm. In deoxygenated solution between pH 7.5 and 11.0, we found two photoproducts that were identified as 4‐(4′‐aminophenyl)aminobenzoic acid (I) and 4‐(2′‐amino‐5′‐carboxy‐phenyl)aminobenzoic acid (V); we used H and13C NMR, electron impact mass spectrometry and synthesis by an independent route to identify each of these compounds. Rapid discoloration of the photolyzed sample was observed when PABA was irradiated in aerated solution. Although a number of products were detected under these conditions, the three most abundant stable compounds have been isolated and identified as 4‐amino‐3‐hydroxybenzoic acid, 4‐aminophenol and 4‐(4′‐hydroxyphenyl)aminobenzoic acid (IV). The latter compound was shown to result from rapid photo‐induced oxidation of I in the presence of oxygen. Even in the presence of trace amounts of oxygen, the yield of I was significantly reduced in favor ofIV.Studies of the thermal oxidation of I, coupled with evidence gathered from studies of the photochemistry of incompletely deoxygenated PABA solutions, indicate that 4‐(2,5‐cyclohexadien‐4‐one)iminobenzoic acid (III) is an intermediate on the pathway between I and IV.Qualitatively, we found that the photochemical reactions resulting from irradiation of PABA solutions with Λ= 254 nm light and light with Λ>290 nm were the same. The quantum yields for formation of I and V are highly pH dependent, both being less than 10–4at pH 7 and rising steadily to values greater than 10–3at pH 11. The detailed pH dependence suggests that the deprotonated PABA radical cation may be an important int

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb08506.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—Several studies in the literature have shown that DNA is damaged after UV irradiation in the presence of the sunscreen agentp‐aminobenzoic acid (PABA), bothin vivoandin vitro.One type of damage has been shown to be the result of increased yields of pyrimidine cyclobutane dimer formation. However, it has been suggested that other types of lesions are produced as well. We have studied the photochemistry of the thymine‐PABA and thymidine‐PABA systems and report here the isolation and characterization of thymine‐PABA and thymidine‐PABA photoadducts. These products have been identified, respectively, as 5‐(2‐amino‐5‐carboxyphenyl)‐5,6‐dihydrothymine and isomeric forms of 5‐(2‐amino‐5‐carboxyphenyl)‐5,6‐dihydrothymidine. The quantum yields for the formation of these adducts in deaerated aqueous solutions at pH 7.0 have been determined to be 9.5 × 10–4and 4.3 × 10–3for the thymine and thymidine based adducts respectively. A pH profile for the thymine‐PABA system indicated a maximum quantum yield for adduct formation at pH 6.5, although it could be detected ov

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb08507.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—Numerous 3‐position derivatives of 2‐hydroxy pyridine, also known as 2‐pyridone, were synthesized and their optical absorption and fluorescence spectra examined. The quantum yield of emission varied from near zero to near unity depending on the kind of substitution made and the solvent. Data are presented that argue for the π‐π* nature of the first excited state in all cases. It was concluded that intramolecular hydrogen bonding controls the extent of internal conversion and hence the amount of fluorescence. It is proposed that this hydrogen bonding suppresses the low energy out of plane vibrations necessary for internal conversion as required by the proximity effect. From studies of the temperature dependence of the emissions, it appeared that the energy separation of the first two excited states, in all cases ˜12.6 ± 2 kJ/mol (3000 ± 500 cal/mol), is not correlated to the exten

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb08508.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—The tryptophan phosphorescence from a series of derivatives ofPseudomonas aeruginosaazurin has been monitored at 30°C in pH 8.5 buffer solution. The phosphorescence lifetimes fall in the range of 230–270 ms for deoxygenated solutions of derivatives containing Cd(II), Cu(I), Co(II), Ni(II), Hg(II) or apoazurin. A weak signal with a lifetime ofca130 ms is observed from solutions of oxidized native azurin, but this component is ascribed to a modified form of azurin in solution,i.e.protein heterogeneity, on the basis of the unique sensitivity to quenching by dioxygen. Aside from this minor component, the tryptophan phosphorescence in the Cu(II) protein appears to be fully quenched. The quenching is assigned an electron‐transfer mechanism involving transient reduction of the metal center. The same mechanism is deemed to be responsible for fluorescence quenching in oxidized native azurin as well. These observations are of interest because aromatic groups like tryptophan may be conduits for physiological electron‐transfer processes involving the coppe

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb08509.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—The synthesis and the properties of l,4‐dibutoxy‐2,3‐dicyanotriptycene, of a metal‐free tetradibenzobarrelenooctabutoxyphthalocyanine, and of the corresponding zinc phthalocyanine are described. The two phthalocyanines do not aggregate when dissolved in benzene at concentrations up to 450 μM. For the metal‐free and the zinc compounds, the red band maxima are at 736 and 757 nm, the triplet maxima are at 590 and 605 nm, the triplet state lifetimes are 58 and 177μs, and the protoporphyrin‐IX dimethyl ester‐to‐compound bimolecular rate constants for triplet energy transfer are 2.61 × 108and 1.47 × 108M‐1s‐1. Triplet energy transfer from the metal‐free compound to O2is endoergonic by 1.0 kcal mol‐1. The potential of the zinc compound for photody

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb08510.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—The luminescence quenching of ruthenium‐tris‐l,4,5,8‐tetraazaphenanthrene [Ru(tap)32+] by nucleotides approaches the diffusion rate only with guanosine‐5′‐monophosphate (GMP), the most reducing nucleotide, and leads to an electron transfer with the production of the monoreduced complex and the oxidized base. The resulting deprotonated GMP(‐H)radical recombines with the monoreduced complex according to a bimolecular equimolar process.The pH dependence of the decay of the transient reduced complex, in the presence of an oxidant (oxygen or benzoquinone) indicates the formation of Ru(tap)2(tapH)2+i.e.the reduced protonated species, subsequent to the electron transfer, with a pKaof 7.6 as confirmed from pulse radiolysis experiments. As the non‐protonated reduced complex, Ru(tap)2(tap2)+ has a higher reducing power than the protonated one, oxygen is able to reoxidize only the non‐protonated species, whereas benzoquinone reoxidizes both species but with different rate constants.The flash photolysis of Ru(tap),2+in the presence of DNA and the effect of Mg2+ions and GMP as supplementary additives also show the existence of a photo‐induced electron transfer with the nucleic acid, which can be correlated to the photosensitized cleavage o

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb08511.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—Using the direct measurement of the photosensitized luminescence of singlet molecular oxygen (1O2) the rate constants (kq) have been determined for1O2quenching by the monomeric molecules of the following phthalocyanines and naphthalocyanines in chloroform: tetra‐(4‐tert‐butyl) phthalocyanine (I); octa‐(3,6‐butoxy) phthalocyanine (II), tetra‐(6‐tert‐butyl)‐2,3 naphthalocyanine (III), aluminium tetra‐(l‐tert‐phenyl)‐2,3 naphthalocyanine (IV), tri‐(n‐hexyl‐siloxy) derivatives of silicon‐(V), tin‐(VI), aluminium‐(VII) and gallium‐(VIII) 2,3 naphthalocyanine. The followingkqvalues were obtained (kq× 10–8M‐1s‐1): 2.9 (I), 59 (II), 100 (III), 20 (IV), 3.9 (V), 53 (VI), 33 (VII), 110 (VIII). As most of the quenchers have the low‐lying triplet levels, a contribution of the quenching mechanism based on the energy transfer from1O2to these levels has been analysed. A formula is proposed describing the relation betweenkqvalues caused by this mechanism, and photophysical constants of the quencher triplet state. This formula was applied to phthalocyanines, naphthalocyanines,p‐carotene and bacterochlorophylla.The data suggest that the energy transfer can fully explain the activity ofVand strongly contributes into the activities ofII,IIIandVI‐VIII. A charge transfer interaction might be an additional mechanism involved in1O2quenching by compounds studied. As some phthalocyanines and naphthalocyanines are strong physical quenchers of singlet oxygen they can be used as efficient inhibitors f

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb08512.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—The cytotoxicity (in the dark), phototoxicity (red light) and subcellular localization (using confocal laser scanning microscopy) were determined for 15 porphyrins (1–15) in C6glioma cells. The partition coefficient in 2‐octanol was also determined for each porphyrin at pH 7.4. The cytotoxicity increased with π (log of partition coefficient) up to π values of +2. The 7 porphyrins with cationic side chains exhibited a classical parabolic correlation between phototoxicity and π, with maximal activity at a π value of approximately 1.0. There was also a significant correlation between subcellular localization and degree of phototoxicity, with the three most photosensitive porphyrins all possessing cationic side chains, and all three localizing in mit

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb08513.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY