PHOTOCHEMICAL DEGRADATION OF KERATINS

Abstract— Twenty-nine samples of fur, hair. wool and feathers have been irradiated with a Sunlamp (Λ max. 310 nm) and with a 2 kW mercury vapour lamp emitting mixed U.V. and visible radiation resembling sunlight. Photodegradation is accompanied by progressive yellowing when irradiated with the Sunlamp. It is accompanied by bleaching followed by yellowing, or by bleaching throughout irradiation if the initial yellowness is high, when exposed to the 2 kW lamp. A group of nine fur and hair samples, representing four different orders of mammals, are the most sensitive to yellowing, followed by a group of ten wool and hair samples from the Artiodactyla and finally by the feather keratins which are less susceptible than the α-keratins. Amino acid analysis of the keratins before and after Sunlamp irradiation shows strong correlation of yellowing both with the initial concentration of tryptophan and with its destruction during irradiation. Similar correlations of yellowing with destruction of other amino acids are less significant. Preliminary washing with non-ionic detergent increases susceptibility to u.v. yellowing.     

PHOTOCHEMICAL REACTIONS OF AZIDOCOUMARINS

Abstract— Photochemical reactions of 6-azidocoumarin and 7-azido-4-methylcoumarin in the presence of secondary amines have been investigated for their potential applications in photoaffinity labeling. It was found that the singlet nitrene generated from 6-azidocoumarin isomerized to a dehydroazepine intermediate that reacted with an amine to yield two isomeric adducts. Photolysis of 7-azido-4-meth-ylcoumarin, in contrast, gave a triplet nitrene that abstracted hydrogen atoms from secondary amine molecules to form 7-amino-4-methylcoumarin as the major product. The difference in the intersystem crossing rate between the two compounds originates from the azido position relative to the carbonyl group. Because of its ability to form a covalent linkage with a nucleophile, 6-azidocoumarin is deemed to have a greater potential as a photoaffinity label than 7-azido-4-methylcoumarin.     

PHOTOCHEMICAL REACTIONS OF DIBROMOTHYMOQUINONE

Abstract The photosynthetic electron transport inhibitor dibromothymoquinone was found to mediate the photoreduction of horse heart cytochrome c in aqueous solution. This process appears to involve the reduction of dibromothymoquinone to the corresponding hydroquinone followed by direct electron transfer to cytochrome c. A subsequent'autoxidation'of the reduced cytochrome c takes place which requires the presence of both oxygen and quinone. Irradiation of ethanolic stock solutions of dibromothymoquinone generates a hydroquinone species which is (1) capable of reducing cytochrome c directly in aqueous solution in the dark and (2) chemically distinct from the parent compound. This photore-duced species is stabilized in ethanolic solution but undergoes autoxidation ( t _1/2= 24 s) when placed in an aqueous medium. Because dibromothymoquinone is used in photosynthetic studies, some care must be taken to avoid complications which might arise from the above reactions; suitable precautions are discussed.     

PHOTOCHEMICAL STUDIES OF ARTIFICIAL BACTERIORHODOPSINS

Abstract— Three artificial bacteriorhodopsins are prepared [from synthetic aromatic and bicyclic analogues of retinal and exposed to spectroscopic and pulsed lader photolysis studies. The spectra of the pigments, all perturbed in the ring region of the molecule, are markedly blue shifted in respect to natural bacteriorhodopsin. The shift is attributed to a decreased effect of a protein charge in the vicinity of the ring, in agreement with the point-charge model of Nakanishi et al. , 1980. The photocycles of the synthetic pigments exhibit a primary red-shifted (K) intermediate and a blue shifted (M) transient, analogous to those observed for the natural pigment. Such observations impose considerable limitations, both on the possible chromophore conformational changes and on the effects of neighbouring protein charges associated with the photocycle.
It is concluded that only the Schiff base counter-ion, but not the ring charge, may be associated with the generation of the primary red shifted K species. Moreover, the rigidity imposed on the polyene by the additional ring in the bicyclic analogue shows that the photocycle can not be initiated by conformational changes in the retinyl moiety up to the C₉ carbon in the polyene chain. It is also observed that the K→L process in the photocycle is considerably slower in the case of the synthetic pigments. The observation is rationalized by attributing the process to a conformational change in the polyene moiety catalyzed by the ring protein charge.     

PHOTOCHEMICAL ESTIMATION OF OXYGEN SOLUBILITY

Abstract— A photochemical technique for estimating the solubility of oxygen in a solvent has been developed and used to estimate the solubility of oxygen in chloroform. From a measurement of the change in rubrene concentration and rubrene fluorescence lifetime as a sealed rubrene solution is irradiated and from the fluorescence lifetime of rubrene in nitrogen, air and oxygen-saturated solvent the oxygen solubility constant and rate constant for oxygen quenching of rubrene fluorescence can be measured. For chloroform these values are 9.8 m M /atm and 7.9 10₉ M _-1 s_-1 respectively.     

PHOTOCHEMICAL PROPERTIES OF FLAVIN DERIVATIVES

Abstract— The triplet yields of 15 derivatives of riboflavin modified either in position 8 or in the ribityl side chain have been determined. The triplet yields measured range from 0.002 to 0.9. In addition, estimates for the rate constants of the photoreaction with EDTA and for the complex formation constants with EDTA at pH 7.0 are given. Evidence for an interaction in solution of at least the 2' and 5' hydroxyl groups of RF with the isoalloxazine ring is presented.     

PHOTOCHEMICAL ONE-POT SYNTHESIS OF VINBLASTINE and VINCRISTINE

The naturally occurring cytostatic dimer alkaloids vinblastine 1 and vincristine 2 were photochemically synthesized in slightly acidic aqueous solution from the monomer alkaloids catharanthine 3 and vindoline 4. Multi-centre reactions should obviously be involved and some of the principal photochemistry-associated phenomena here discussed are quite likely to be characteristic even to the biosynthetic reactions yielding vinblastine 1 and vincristine 2 in the cells of Catharanthus roseus.     

THE PHOTOCHEMICAL SYNTHESIS OF THE PYRIDINE ADDUCT OF TETRAPHENYLPORPHYRINATORHODIUM(Ⅱ)AND THE MECHANISM OF PHOTOCHEMICAL REACTION

A new rhodium(Ⅱ)porphyrin complex was isolated by chromatography from the photochemical reac-tion of(μ—tetraphenylporphyrinato)bis[dicarbonylrhodium(Ⅰ)]with pyridine in benzene and has been charac-terized.From the results,the reaction mechanism is proposed.     

SPECTRAL AND PHOTOCHEMICAL PROPERTIES OF CURCUMIN

Curcumin, bis(4-hydroxy-3-methoxyphenyl)-l,6-heptadiene-3,5-dione, is a natural yellow-orange dye derived from the rhizome of Curcuma longa, an East Indian plant. In order to understand the photobiology of curcumin better we have studied the spectral and photochemical properties of both curcumin and 4-(4-hydroxy-3-methoxy-phenyl)-3-buten-2-one (hC, half curcumin) in different solvents. In toluene, the absorption spectrum of curcumin contains some structure, which disappears in more polar solvents, e.g. ethanol, acetonitrile. Curcumin fluorescence is a broad band in acetonitrile (λ_max= 524 nm), ethanol (λ_max= 549 nm) or micellar solution (λ_max= 557 nm) but has some structure in toluene (λ_max= 460, 488 nm). The fluorescence quantum yield of curcumin is low in sodium dodecyl sulfate (SDS) solution (φ= 0.011) but higher in acetonitrile (φ= 0.104). Curcumin produced singlet oxygen upon irradiation (φ > 400 nm) in toluene or acetonitrile (Φ= 0.11 for 50 μM curcumin); in acetonitrile curcumin also quenched ¹O₂ (k_q, = 7 × 10⁶ M^?1 s^?1). Singlet oxygen production was about 10 times lower in alcohols and was hardly detectable when curcumin was solubilized in a D₂O micellar solution of Triton X-100. In SDS micelles containing curcumin no singlet oxygen phosphorescence could be observed. Curcumin photogenerates superoxide in toluene and ethanol, which was detected using the electron paramagnetic resonance/spin-trapping technique with 5,5-dimethyl-pyrroline-.N-oxide as a trapping agent. Unidentified carbon-centered radicals were also detected. These findings indicate that the spectral and photochemical properties of curcumin are strongly influenced by solvent. In biological systems, singlet oxygen, superoxide and products of photodegradation may all participate in curcumin phototoxicity depending on the environment of the dye.     

一些全氟磺酰氟的光化学反应

本文报道全氟(4-甲基-3,6-二氧杂-7-辛烯)磺酰氟(1)、全氟(3-氧杂-4-氟羰基戊)磺酰氟(2)和全氟(4,6-二甲基-3-氧杂庚-5-酮)磺酰氟(3)的光化学反应.     

THE PHOTOCHEMICAL PROPERTIES OF FLUOROALUMINUM PHTHALOCYANINE

Abstract Fluoride is known to inhibit the photodynamic activity of aluminum phthalocyanine in a variety of biological systems. In order to gain insight into this phenomenon, the effect of fluoride on the photophysical properties of free and albumin-bound chloroaluminum phthalocyanine sulfonate (AlPcS_n.) were studied. The association constant of NaF with AlPcS_n, in aqueous solution was measured as 500 ± 20 M^?1. This binding affects the photophysical properties of the dye: the absorption bands in the visible range are blue-shifted by 6–8 nm, and this effect is mirrored in the fluorescence emission spectrum. Human serum albumin significantly quenched the dye fluorescence independent of the presence of fluoride ion. The transient absorption spectrum of the excited dye triplet is unchanged by NaF, but the quantum yield for its generation is increased by 50%, with no decrease in its lifetime. Formation of fluoroaluminum phthalocyanine complexes was also observed in tetrabutylammonium fluoride-assisted solutions in wet acetonitrile. The fluoro-AlPcS_n, complex is a better photosensitizer for generation of singlet oxygen than the original dye-hydroxyl ion complex, as confirmed using the imidazole-N,N-dimethyl-4-nitrosoaniline method. On the other band, the fluoro-AlPcS_n. complex exhibits an intense inhibitory effect on photohemolysis of red blood cells (RBC) even after the cells are washed to remove free dye and fluoride prior to irradiation, indicating that once the dye is attached to the cellular site, the fluoride ligand is no longer prone to displacement (by hydroxyl ion, for example). Nonetheless, it is clear from the spectroscopic data that the new fluoro complex is an efficient sensitizer for photo-oxidation. Therefore, the reduced photodynamic action of the fluoro-AlPcS_n. complex on RBC (Ben-Hur et al., Photochem. Photobiol. 58 , 351–355, 1993) may result from a lowering of the efficiency of interaction of the fluorodye complex with sensitive cell target moieties.     

光化学荧光分析法研究进展

对近年来光化学荧光分析法的研究进展及其在医药、农药及维生素等方面的应用作了评述,引用文献46篇。     

PHOTOCHEMICAL PROPERTIES OF ERYTHROCYTE GHOSTS CONTAINING PORPHYRIN

Abstract— Rabbit erythrocyte cell ghosts were prepared containing tetrasodium meso-tetra (4-sulfona-to-phenyl) porphine (12-hydrate), a water soluble porphyrin. Laser flash kinetic spectroscopy of the suspension revealed a difference spectrum consistent with the porphyrin T, state. The time profiles of the signal decay were bi-exponential, and oxygen quenched each of the two components differently. Triplet-triplet extinction coefficients and quantum yields were lower for the ghost suspension than for porphyrin in solution. Fluorescence lifetime studies of the suspension also showed the presence of two components. Singlet oxygen luminescence, as measured by germanium diode detection, was observed, with a lifetime of 46 (jls and a 4>A of 0.09.     

异戊二烯和四氟乙烯-丙烯共聚物的光化学接枝反应

在紫外光作用下,二苯甲酮、蒽醌和安息香能通过夺氢反应使异戊二烯在四氟乙烯-丙烯共聚物中接枝,接枝反应按三重态自由基引发机理进行,接枝率随光照时间的增长而增加,但不会超过40%。和异戊二烯的自由基聚合反应不一样,接枝物中聚异戊二烯接枝链的微结构以3,4-和1,2-聚合为主,而前者以1,4-聚合为主。Ce⁺⁴及Fe⁺²-H₂O₂等氧化还原体系对该接枝反应不产生作用.极性溶剂四氢呋喃的加入,对接枝链微结构的影响很小。     

SYNTHESIS AND PHOTOCHEMICAL PROPERTIES OF NITROTHIENYL DERIVATIVES

Abstract Some 2-nitrothienyl derivatives characterized by the presence of an aryl or heteroaryl substituent in the C-5 position were synthesized by using a photochemical coupling procedure. All synthesized compounds were demonstrated to be singlet oxygen sensitizers in the trans-α,α'-dimethylstilbene photooxidation.     

AM/AMPS共聚物光化学改性

水溶性高分子AM/AMPS系由丙烯酰胺(AM)和2-丙烯酰胺基-2-甲基丙磺酸(AMPS)组成.本文应用光化学方法对AM/AMPS共聚物进行改性,得到活性可聚合产物.应用这种方法,在高分子链上生成的过氧化物含量随UV光照时间有明显变化,照射5-10 min过氧化物含量最高.值得指出,较高的过氧化物生成量仅在采用二苯酮作为光敏剂和保持低温的条件下才能得到.这种活性改性AM/AMPS共聚物,可用光聚合或热聚合方法引发不同烯类单体共聚合,得到不同用途的接枝/交联共聚物产品.