摘要:

Abstract—The photovoltaic properties ofmeso‐tetraphenylporphyrin and its derivatives with variouspara‐substituents, meso‐tetrakis(2,4‐dimethoxyphenyl)porphyrin andmeso‐tetrakis (2‐fluorenyl)porphyrin have been investigated. The forward dark current‐voltage characteristics of Al/porphyrin/Ag cells are attributed to the MIS Schottky barriers consisting of Al/Al2O3/porphyrin. The barrier parameters such as the apparent diffusion potentialV0the barrier width w0and the density of ionized impurityNare estimated by using the capacitor discharge method. The action spectra of photocurrents closely follow the optical absorption spectra of the porphyrin films. The photocurrents vary asipαIγ, whereIis the incident light intensity, and the Sight exponentsyrange between 0.83 and 1.0. The sublinear difference from unity could be related to the exponential distribution of hole traps in films of the porphyrins. No obvious correlation between the photocurrent and the fluorescence quantum yields of the sublimed porphyrin films is found. The electron donating substituents such as OCH3and CH3strikingly increase the photocurrents. The photocurrent quantum yields correlate exponentially with the first ring oxidation potentials of the porphyrins and also with the substituent constants for the Hammett linear free‐energy relationship. The current quantum yields estimated for the porphyrins studied, range in the order of 10‐4–10‐2with power conversi

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb03803.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—We have determined the dimerization and monomerization cross sections of the ThyThy (cyclobutyl dimer of thymine and thymine) and the CytThy (cyclobutyl dimer of cytosine and thymine) dimers inEscherichia coti[3H]‐DNA ([3H]‐thymine labeled DNA) at five wavelengths in the range 240–300 nm. It may be concluded from the dimerization action spectra for the two dimers that the excitation of Thy (thymine) is mainly responsible for the photochemical dimerization reaction in both cases. The calculated quantum yields of dimerization and monomerization are also presented in this paper and several questions, raised by the results obtained at 300 nm, are di

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb03804.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—Pyrene fluorescence spectra have been run in 62 solvents of widely differing solvent polarity. As has been noted previously, the intensity ratio of the first (the 0–0 band) and third bands in vibronic fine structure of these spectra are very sensitive to solvent polarity. TheseI1/I3values, however, are not sensitive to hydrogen bonding aspects of solvent‐solute interactions. Correlations are reported with Winstein'sYvalues and with Dimrotb'sETvalues. On this basis theI1/I3values for pyrene fluorescence are suggested as the basis for a new empirical scale of solvent polarity, called thePyscale, which offers certain conveniences over other scales of solvent pol

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb03805.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—The photochromic behavior of 2,6‐dinitrodiphenyl ethers is described. In the course of a study for the photoaffinity labeling of the binding site for thyroxine on human prealbumin, it was found that the thyroxine analog 3‐[4‐(4‐hydroxy‐3,5‐diiodophenoxy)‐3,5‐dinitrophenyl]propionic acid (1), on irradiation with>350nm light in the presence of prealbumin, gave a pink species (λmax508 nm). In the absence of prealbumin, no color formation was observed. Irradiation of 3‐[4‐(4‐hydroxyphenoxy‐3,5‐dinitrophenyl]propionic acid (2) and 3‐(4‐phenoxy‐3,5‐dinitrophenyl)propionic acid (3), analogs of 1, in acetonitrile, aqueous bicarbonate, or ethanol gave a colored species (λmax500–520 nm depending on the solvent) in the absence of a host molecule. In the presence of β‐cyclodextrin, which may be considered a model for a binding site on a protein, photocoloration occurred at a faster rate than in the absence of ß‐cyclodextrin. For both2and3, the colored species underwent thermal back reaction to the starting compound. The activation energy for the thermal back

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb03806.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—Naphthalene was oxidized by carbonyi oxides produced by singlet oxygen oxidation ofp, p‐disubstituted diphenyldiazomethanes. Yields of naphthol products correlate with Hammett σ constants giving ρ=+0.93. The results are interpreted as indicating the electrophilic character of these oxida

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb03807.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—As a model for studies involving biologic systems, rates of hematoporphyrin and protopor‐phyrin‐sensitized photooxidation of tryptophan were measured in water‐methanol mixtures. Absorption and fluorescence‐emission spectra associated with solutions of porphyrins in different water‐methano! mixtures were also examined. The optimal rate of photooxidation by hematoporphyrin occurred in 30% methanol; by protoporphyrin, in 60% methanol. Absorption spectra were examined to characterize dispersion of hematoporphyrin into monomeric form in 90% methanol, and the dimer formation which predominates in 30% methanol. With the more hydrophobic protoporphyrin, an absorption spectrum characteristic of drug monomer was seen in 100% methanol, a dimer spectrum was observed in 60% methanol. At methanol concentrations<60%, we observed impaired photooxidation and another alteration in the absorption pattern apparently reflecting drug aggregation beyond the dimer stage. Fluorescence emission maxima of both porphyrins were blue‐shifted with increasing solvent dielectric constant, but an additional blue shift was detected in an aqueous environment which was apparently related to porphyrin aggregation. Absorption and fluorescence‐emission spectra appear helpful for characterizing environmental determinants of porphyrin‐sensitiz

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb03808.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—The UV‐photolysis of peptides containing tyrosine (Tyr) was investigated in aqueous solutions at room temperature at 220 and 265 nm. The short‐lived free radicals formed during photolysis were spin‐trapped by t‐nitrosobutane and identified by electron spin resonance. For N‐acetyl‐ and N‐formyl‐L‐Tyr and for peptides containing L‐Tyr as the middle residue, photolysis at 265 nm under neutral conditions produced mainly spin‐adducts due to the scission between the alpha carbon and the methylene group attached to the aromatic ring, while at 220 nm decarboxylation radicals were spin‐trapped. Photolysis of di‐ and tripeptides at 275 nm in alkaline solutions predominantly generated deamination radicals. The radicals produced in the photolysis of the oxidized A chain of insulin were tentatively characterized by comparison with the resu

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb03809.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—The UV photolysis of tryptophan (Trp) and Trp‐containing peptides in aerated aqueous solutions has been studied by ESR and spin‐trapping techniques using f‐nitrosobutane as the spin‐trap. The photolysis of Trp alone at 290 nm gave rise to the addition of the spin‐trap to carbon 3 of the indole ring. A large ESR signal from the hydronitroxide spin‐adduct was also observed revealing the formation of hydrated electrons. Generally, the photolysis of Trp‐containing dipeptides generated the deamination radical of the N‐terminal amino acid followed by addition to the spin‐trap. In the case of lysyl‐Trp, a deamination radical from the side chain of lysine was proposed. A sensitization experiment with Trp as sensitizer and glycine (Gly) as substrate led to the generation of the deamination radical of Gly. Most of the observed free radicals resulting from the photolysis of Trp‐containing peptides can be explained in terms of hydrated electrons reacting with the carbonyl group followed by deamin

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb03810.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—The naturally occurring furoquinoline alkaloid, dictamnine, is phototoxic to Gram‐positive bacteria, yeasts and filamentous fungi in the presence of long‐wave UV light. Prior to photobinding to DNA dictamnine forms a complex with the macromolecule in the dark. Photobinding to DNA is shown with [3H]‐dictamnine. In contradiction to an earlier finding, dictamnine proved to be incapable of forming interstrand crossiinkages with native DNA. This fact was ascertained by the use of methods additional to hydroxyapatite column chromatography, e.g. alkaline sucrose gradient centrifugation and hyperchromicity tests. The alkaloid therefore represents a new monofunctional photoreagent towards DNAin vitro.It is assumed that it binds through its furyl‐C=C to DNA. The inability to form crosslinks may be attributed to the stability of the lateral aromatic nucleus. As no photoreactivity against human erythrocytes could be observed, it is possible that nucleic acids represent the major target of dama

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb03811.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abstract—The phosphorescence of 1‐bromonaphthalene and 1‐chloronaphthalene is readily observable in nitrogen purged aqueous solutions containing ß‐cyclodextrin. Addition of acetonitrile increases both the phosphorescence intensity and lifetime. The quenching of halonaphthalene phosphorescence in aqueous solution by nitrite is substantially inhibited upon addition of ß‐cyclodextrin, as a result of a guest‐host complex. The rate constants for formation and dissociation of the l‐bromonaphthalene/ß‐cyclodextrin complex are evaluated from an analysis of the dependence of phosphorescence lifetimes on nit

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb03812.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY