摘要:

Abstract—A labile intermediate in the photolytic rearrangement of the antibacterial drug, metronidazole, was identified by isolating the product of photolysis of metronidazole benzoate in methanol. The intermediate, 1‐hydroxyethyl‐2‐methyl‐4‐hydroxyimino‐5‐oxo‐imidazole, was shown to act as a bidentate chelating agent for copper(II) ions, whereas metronidazole forms a weak monodentate complex. The intermediate may be relevant to the bioactivation mechanism

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1988.tb08834.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract—From time‐resolved measurements of the decay of singlet molecular oxygen phosphorescence at 1270 nm in D2O, direct estimates have been gained for the rate constants of the singlet oxygen reactions with a group of sulphur compounds in the pD range 5 to 13. In the case of most of the thiols, the results are consistent with singlet oxygen reacting exclusively with the thiolate anions. At the normal physiological pH 7, the apparent rate constants (in units ofM‐1s‐1) were 8.9 times 106(cysteine), 2.5 times 106(N‐acetyl cysteine), 2.9 times 106(glutathione), 3.0 times 105(2‐mercaptoethanol), 2.3 times 107(ergothioneine) and 2.7 times 106(2‐mercaptopropionyl glycine). For methionine the rate constant, 1.4 times 107, was independent of pD in the range studied. These sulphur compounds, in particular N‐acetyl cysteine and ergothioneine, or related compounds, might be considered as possible candidates for protection against skin photosensitivity side effects associated with the photodynamic therapy of solid tumours and as observed in the disease erythropoietic

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1988.tb08835.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract—Abstract‐The products of photochemical reaction of a family of phototoxic tricyclic antidepressants have been determined, both in the presence and absence of oxygen. Under all conditions photofrag‐mentation of the phototoxic compounds is an important reaction‐in some cases it is virtually the only photoreaction observed. The mechanism of photoreaction appears to involve excited state electron transfer from the side chain to give a reactive exciplex, which fragmentsviaboth radical and ionic pathways. These reactive intermediates are likely to contribute to thein vivophototoxicity of these co

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1988.tb08836.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract—The photochemistry of 3‐ and 4‐nitrobenzoyl azides was studied to examine their suitability for use in photolabeling procedures. These aroyl azides absorb light in the near UV‐spectral region. Their irradiation leads both to photo‐Curtius rearrangement with formation of the analogous isocyan‐ates and to generation of nitrenes by loss of nitrogen. The chemical and spectroscopic properties of the aroyl nitrenes indicate that they are singlets in their ground states. These singlet nitrenes insert rapidly into unactivated, aliphatic carbon‐hydrogen bonds, trap nucleophiles, and add to olefins to form aziridines with retention of stereochemistry. Photolabeling agents based on these azides may offer some advantages over conventional agents for the labeling of lip

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1988.tb08837.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract—As models for novel fluorescent probes, we have synthesized three isomeric hydroxystilbazole systems (4′‐hydroxy‐substituted 2‐, 3‐, and 4‐stiIbazoles), examined their photocyclization‐oxi‐dation to four hydroxyazaphenanthrene systems, and made a preliminary study of their absorption and fluorescence spectra. All three stilbazoles can be prepared easily by addition of the isomeric picoline anions to 4‐methoxybenzaldehyde, followed by dehydration and deprotection. Photocyclization proceeds efficiently, furnishing a single product isomer from each of the 2‐ and 4‐stilbazole systems, and two isomeric azaphenanthrenes from the 3‐stilbazole. The stilbazoles all have intense UV absorbance bands whose maxima depend upon solvent and pH; all three isomers have relatively similar spectra under neutral conditions and all three show a large red shift in base; in acid, however, the 2‐and 4‐stilbazole isomers show a greater red shift than the 3‐stilbazole. The fluorescence of the stilbazoles is also solvent dependent, shifting to the red in more polar medium; red shifts are also observed in acid and base, but in acid, the 3‐stilbazole shows a larger shift. The azaphenanthrene photocyclization products show absorbance spectra typical for quinolines and isoquinolines; their absorptivities are less than the stilbazoles, but their fluorescence is more intense. In general, the benzoquinolines have longer wavelength but weaker fluorescence than the benzoisoquinolines. Also, those isomers in which the resonance effects of the hydroxy and nitrogen groups can reinforce one another show longer wavelength emissions of greater intensity. All seven systems show dual fluorescence in water under neutral conditions, suggesting the emission from both non‐ionized and ionized species in the excited state. In one case, the benzoisoquinoline system derived from 4′‐hydroxy‐4‐stilbazole, an emission at 640 nm, observed in water over a wide pH range, is ascribed to a zwitterionic phototautomer. These stilbazoles, benzoquinolines and benzoisoquinolines

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1988.tb08838.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract—A Xenon‐chloride excimer laser emitting energy at 308 nm was used to induce single‐strand breaks (SSBs, frank breaks plus alkali‐labile lesions as assayed by alkaline sucrose sedimentation techniques) in purified DNA fromBacillus subtilis. A fluence response study and a peak pulse intensity study were performed. At a pulse energy of 0.1 mJ/pulse, the radiation induced SSBs in a linear fashion (91 SSB/108Da per MJ/m2) to a maximum exprimental fluence of 1.28 MJ/m2. The pulse intensity study showed that there were no significant changes in DNA breakage (105 SSB/108Da) between 2.93 times 109and 5.86 times 1011W/m2(0.11 and 22.0 mJ/pulse) at a constant total fluence of 1.1 MJ/m2(27000 mJ dose). This study has verified and extended previous work by quantifying the yield of SSBs induced in DNA by this laser ra

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1988.tb08839.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract—The cleavage of phosphodiester bonds in DNA exposed to high intensity UV laser pulses in aerated aqueous solution has been investigated using a krypton fluoride excimer laser (248 nm) and bacterial plasmid DNA. The dependence of strand breakage on fluence and intensity has been studied in detail and shows that the process is non‐linear with respect to intensity. The relationship between the quantum yield for strand breakage and intensity shows that the strand breakage reaction involves two‐photon excitation of DNA bases. The quantum yield rises with intensity from a lower value of 7 times 10‐5until a maximum value of 4.5 times 10‐4is attained at intensities of 1011W m‐2and above. This value is approximately fifty‐fold higher than the quantum yield for strand breakage induced by exposure to low density UV irradiation (254 nm, 12 W m‐2). DNA sequencing experiments have shown that strand breakage occurs by the specific cleavage of the phosphodiester bond which lies immediately 3′ to guanine residues in the DNA, leaving some alkali‐labile remnant attached to the terminal phosphate. A mechanism for DNA strand breakage which involves the generation of guanine radical

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1988.tb08840.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract—Furocoumarins, potent skin therapy and tanning agents, form covalent adducts in a photochemical reaction with unsaturated fatty acids. These adducts and the chemical kinetics of their formation have been characterized by chromatography, isotopic tracers, electronic absorbance and fluorescence spectroscopy and mass spectrometry. Adduct formation does not require oxygen. The quantum yield of adduct formation in ethanol or methanol‐water solutions is comparable to the quantum yield for formation of furocoumarin‐thymine adducts i

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1988.tb08841.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract—New Rose Bengal oniurn salts containing one or two iodonium, sulfonium, phosphonium, and pyrylium ions have been prepared as part of a program to develop sensitizers which can function as Type I radical photoinitiators and Type II energy transfer donors depending on experimental conditions. The absorption spectra of the onium salts in different solvents indicate an equilibrium between tight and loose ion pairs which depends on the solvent polarity, the cation and concentration. Typical Rose Bengal photochemistry requires the structure be that of the loose ion pair in the solvent of choice. Similar factors also influence bleaching behavior, and bleaching is the result of electron transfer processes. The quantum yields of singlet oxygen production from the onium salts in polar solvents are similar to that of the parent, Rose Bengal disodium sal

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1988.tb08842.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Abstract—Rose Bengal derivatives (I‐VI) have been synthesized as part of a program to study the spectroscopy of model systems for Hpd dimer. The absorption and emission spectra as a function of solvent are diagnostic for the formation of aggregated conformers. Based on our spectroscopic results we conclude that these compounds exist in open conformation in ethanol and other organic solvents, and that they form intramolecular dimers in aqueous solut

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1988.tb08843.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY