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1.
James Elver Johnson Mohammad Arfan Richard Hodzi Lyman R. Caswell Susan Rasmussen 《Photochemistry and photobiology》1990,51(2):139-144
Abstract— Photolysis at 254 nm of alkyl benzohydroxamates [C, H, CONHOR: R = CH3 H2 CH3 CH(CH3 )2 , CH2 C6 H5 CH(CH3 )C2 H5 CH(CH3 )- n -C6 H13 ] in acetonitrile or hydrocarbon solvents gives benzamide. These reactions can be sensitized by benzophenone (at ca. 350 nm) and are quenched by cis-piperylene. Racemization occurred when 2-octyl (+)-benzohydroxamate was irradiated in cyclohexane. These results are consistent with a mechanism involving a triplet biradical. Photolysis of phenyl benzohydroxamate [C6 H5 CONHOC6 H5 ] and benzyl N -methylbenzohydroxamate [C6 H5 CON-(CH3 )OCH2 Q6 H5 ] cannot be quenched with ris-piperylene and appear to be singlet reactions. 相似文献
2.
Gerald J. Smith Kenneth R. Markham W. Hugh Melhuish 《Photochemistry and photobiology》1994,60(3):196-198
Abstract Solvent-cleaned Merino wool, which was enzymatically digested with protease K, displayed a fluorescence maximum at 500 nm when excited at 430 nm. The yield of this emission was approximately 15 times greater for a fiber tips digest than for a digest of the mid-length region of the same fibers.
Separation of the components in the wool tip digest by silica gel thin-layer chromatography revealed the presence of several fluorescent species. The chromatographic mobility of these species was similar to the behavior observed in a preparation of authentic 1-methyltetrahydro-P-carboline, 1,3-dicarboxylic acid.
Mass spectroscopy of the fluorescent compounds in the wool tip digest displayed molecular ions, [M + H]+ with m/z = 273.0890 and 257.0560, and molecular weights that define the formulae C14 H12 N2 O4 and C11 H8 O4 N2 , respectively, which correspond to β-carboline 1,3-dicarboxylic acids. Mass spectral evidence also indicates the presence of two other β-carbolines. 相似文献
Separation of the components in the wool tip digest by silica gel thin-layer chromatography revealed the presence of several fluorescent species. The chromatographic mobility of these species was similar to the behavior observed in a preparation of authentic 1-methyltetrahydro-P-carboline, 1,3-dicarboxylic acid.
Mass spectroscopy of the fluorescent compounds in the wool tip digest displayed molecular ions, [M + H]
3.
Abstract— An investigation has been made of the reaction between methylene, formed by the photolysis of ketene, and hydrogen. Ethane, ethylene and methane are the major hydrocarbon products, and it has been shown that the formation of these products may be adequately described by the sequence of processes
CH2 CO + hv → CH2 + CO (1)
CH2 + H2 → CH3 +H (2)
2CH3 → C2 H6 (3)
CH3 + H2 + CH4 + H (4)
CH2 + CH2 CO → C2 H4 + CO (7)
In particular, the relative rates of ethane and methane formation are consistent with the known rate constants for reactions (3) and (4), and it is not therefore necessary to postulate the participation of an 'insertion' process
CH2 + H2 → CH4 (6) to account for the formation of methane.
Decrease of the energy possessed by the methylene, either by increase of the wavelength of ketene photolysis, or by increase of gas pressure, is shown to result in an increase in the reactivity of the methylene towards ketene relative to its reactivity towards hydrogen (i.e. the ratio k2 /k2 increases). 相似文献
CH
CH
2CH
CH
CH
In particular, the relative rates of ethane and methane formation are consistent with the known rate constants for reactions (3) and (4), and it is not therefore necessary to postulate the participation of an 'insertion' process
CH
Decrease of the energy possessed by the methylene, either by increase of the wavelength of ketene photolysis, or by increase of gas pressure, is shown to result in an increase in the reactivity of the methylene towards ketene relative to its reactivity towards hydrogen (i.e. the ratio k
4.
K. Wyrzykowska M. Grodowski K. Weiss T. Latowski † 《Photochemistry and photobiology》1978,28(3):311-318
Abstract. The quantum yields of HCI (φHC1 ) formation have been measured for the photolysis of N -methyldiphenylamine (MeDPA), triphenylamine (TPA) and diphenylamine (DPA) in the presence of CCl4 in polar solvents. The quantum yields of N-methylcarbazole formation (φmφca ) have also been determined for the system MeDPA-CCl4 . With increasing CCl4 concentration, φHCl increases as φMeCA decreases, and φHCl reaches maximum values 2.7 at 1 M CCl4 . Using laser photolysis, transient spectra have been recorded for MeDPA in the absence and presence of CCl4 in polar and non-polar solvents, and for TPA. Transient absorption due to the triplet states and photocyclization products (without CCU), exciplexes, the (C6 H5 )2 NCHi radical, the MeDPA+ cation radical, the (TPA+ ., CCl4 ) ion pair, and the TPA+ cation radical have been identified. The mechanistic implications of these results are discussed. 相似文献
5.
Abstract— Bacteriorhodopsin is a light activated proton pump which generates proton and electric gradients across the cytoplasmic membrane of Halobacterium halobium. In this study, a dye whose fluorescence intensity responds rapidly to membrane potential was used to follow the evolution of the potential on liposomes reconstituted with bacteriorhodopsin, in the microseconds time domain. By comparing the formation kinetics of the potential to those of the long-lived intermediate species in the bacteriorhodopsin photocycle, M412 , both in H2 O and 2 H2 O suspensions, we can draw the following conclusion: the electric potential onset time is 20 μs after initiation of the illumination. The triggering of the potential is not the formation of the M412 intermediate, which was hitherto considered to be the first species in the bacteriorhodopsin cycle which has an unprotonated Schiff base linkage at the retinal chromophore. Rather, the potential forms at the transition of the L550 intermediate to the species X which precedes M412 or even at the preceding conversion of K590 to L550 . 相似文献
6.
The photodecomposition of sulfanilamide (4-aminobenzenesulfonamide), sulfacetamide. sulfathiazole. sulfadiazine, carbutamide and tolbutamide has been studied using the spin traps 2-methyl-2-nitrosopropanc and 5,5-dimethyl-l-pyrroline-l-oxide. The following radicals were trapped during the photolysis of sulfanilamide in aqueous solution: H' and HNC6 H4 SO2 NH, (α-fission). SO2 NH2 and C6 H4 NH2 (δ fission). H2 NC6 H4 SO2 and NH2 (δ-fission). Although the C.,H4 SO2 NH2 and the SO; radicals were also detected these were not formed directly by homolytic bond fission. Homolytic bond fission was also observed during the irradiation of sulfacetamide (α.δ), sulfadiazine (α). carbutamide (α,δ) and tolbutamide (δ). All of the analogs, with the exception of tolbutamide, generated the SO; radical. Sulfacetamide, sulfadiazine and carbutamide generated the C6 H4 SO2; NHR radical by some process that did not involve homolytic bond fission. The free radicals generated by these agents may play an important role in their phototoxic and photoallergic effects. 相似文献
7.
Paul A. Liddell John P. Sumida Alisdair N. Macpherson Lori Noss Gilbert R. Seely Kristine N. Clark Ana L. Moore Thomas A. Moore Devens Gust 《Photochemistry and photobiology》1994,60(6):537-541
Abstract Porphyrin-C60 dyads in which the two chromophores are linked by a bicyclic bridge have been synthesized using the Diels-Alder reaction. The porphyin singlet lifetimes of both the zinc (Pzn -C60 ) and free base (P-C60 ) dyads, determined by time-resolved fluorescence measurements, are ≦17 ps in toluene. This substantial quenching is due to singlet-singlet energy transfer to C60 The lifetime of Pzn-1 C60 is -5 ps in toluene, whereas the singlet lifetime of an appropriate C60 model compound is 1.2 ns. This quenching is attributed to electron transfer to yield Pzn bull; +-C60 bull; -. In toluene, P-1 C60 is unquenched; the lack of electron transfer is due to unfavorable thermodynamics. In this solvent, a transient state with an absorption maximum at 700 ran and a lifetime of-10 μs was detected using transient absorption methods. This state was quenched by oxygen, and is assigned to the C60 triplet. In the more polar benzonitrile, P-1 C60 underoes photoinduced electron transfer to give P• + -C60 bull; -. The electron transfer rate constant is −2 × 1011 s−1 . 相似文献
8.
Abstract— C18 formate ester (5) [2-(6-methyl-8-(2,6,6-trimethyl-1-cyclohexen-1-yl)-3E,5E,7E-octatrienyl formate], a highly reactive analog of retinal, was synthesized and its interaction with bacterioopsin studied. The formate ester, in the absence of purple or bleached membrane, undergoes very rapid reaction (tl/2 = 0.9 min) in neutral buffer but with membrane present it diffuses more rapidly into the membrane where it reacts slowly. Incorporation of 5 in the membrane results in a 38 nm (3900 cm-1 ) red shift which remains after reconstitution with retinal. Similar experiments with the corresponding C18 alcohol (4) results in a red shift, but this absorption blue shifts upon reconstitution with retinal. Washing the formate ester-treated membrane with bovine serum albumin or the corresponding lyophilized preparation with hexane, treatments that remove retinal oxime, fails to remove the UV-visible absorption, suggesting that a covalent bond between the C18 moiety and a nucleophilic group of the protein has probably formed. 相似文献
9.
Abstract— The photoreduction of methyl viologene by ZnTPP triplet excited states was studied in mixed micelles containing the functional surfactant JV-dodecyl, N -methyl viologene (C12 MV2+ ) as one and Cetyltrimethylammoniumchloride (CTAC) as the other component. Using the laser photolysis technique the kinetics of the redox reaction were studied at various CTAC/C12 MV2+ ratios. The average time for the electron transfer decreases linearly with the C12 MV2+ occupancy. The back transfer from C12 MV2+ to ZnTPP2+ can be intercepted if a donor such as NADH is cosolubilized in the micelle. In such a system irreversible methyl viologene reduction is achieved which in the presence of a suitable redox catalyst can be used to produce hydrogen from water. 相似文献
10.
Colin F. Chignell B. Kalyanaraman Robert H. Sik Ronald P. Mason 《Photochemistry and photobiology》1981,34(2):147-156
Abstract— The photodecomposition of sulfanilamide, 4-aminobenzoic acid and related analogs in aqueous solution has been studied with the aid of spin traps 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) and CH3 NO2 as well as by direct electron spin resonance techniques. The NH2 radical was trapped by DMPO during the photolysis of aqueous solutions of sulfanilamide with a Xe arc lamp. Studies with [15 N1 ]-sulfanilamide indicated that the NH2 radical was generated by homolytic fission of the sulfur-nitrogen bond. Under the same conditions DMPO trapped the H and SO− 3 radicals during photolysis of sulfanic acid. Direct photolysis of sulfanilamide, sulfanilic acid and Na2 SO3 in the absence of any spin trap yielded the SO− 3 radical. Photolysis of 4-aminobenzoic acid at pH 7 gave the H radical which was trapped by DMPO. At low pH values OH and C6 H4 COOH radicals were generated during the photolysis of 4-aminobenzoic acid. No e− aq were trapped by CH3 NO2 when acid (pH 4) and neutral aqueous solutions of sulfanilamide or 4-aminobenzoic acid were photoirradiated. The mechanism of formation of known photoproducts from the free radicals generated by sulfanilamide and 4-aminobenzoic acid during irradiation are discussed. The free radicals generated by these agents may play an important role in their phototoxic and photoallergic effects. 相似文献
11.
L. Huang H. Deng Y. Koutalos T. Ebrey M. Groesbeek J. Lugtenburg M. Tsuda R. H. Callender 《Photochemistry and photobiology》1997,66(6):747-754
Abstract— Previous resonance Raman spectroscopic studies of bovine and octopus rhodopsin and bathorhodopsin in the C–C stretch fingerprint region have shown drastically different spectral patterns, which suggest different chromophore-protein interactions. We have extended our resonance Raman studies of bovine and octopus pigments to the C=C stretch region in order to reveal a more detailed picture about the difference in retinal-protein interactions between these two pigments. The C=C stretch motions of the protonated retinal Schiff base are strongly coupled to form highly delocalized ethylenic modes located in the 1500 to 1650 cm−1 spectral region. In order to decouple these vibrations, a series of 11,12-D2 -labeled retinals, with additional 13C labeling at C8 , C10 , C11 and C14 , respectively, are used to determine the difference of specific C=C stretch modes between bovine and octopus pigments. Our results show that the C9 =C10 and C13 =C14 stretch mode are about 20 cm−1 lower in the Raman spectrum of octopus bathorhodopsin than in bovine bathorhodopsin, while the other C=C stretch modes in these two bathorhodopsins are similar. In contrast, only the C9 =C10 stretch mode in octopus rhodopsin is about 10 cm−1 lower than in bovine rhodopsin, while other C=C stretches are similar. 相似文献
12.
Abstract The crystal and molecular structure of the title compound 4 have been determined by single crystal X-ray crystallography. The structure shows the typical S,-ruffled conformation observed for Ni(II) tetrapyrroles. Compared to the structure of the methyl ester of (132 -demethoxycarbonyl-pheophorbidato a)nickel(II), 4 shows a smaller Ca -Cm -Cm angle and a higher degree of conformational distortion at the methyl-substituted C20 position. This local distortion of the macrocycle might account for the bathochromic shifted absorption spectra of the bacteriochlorophylls c compared to the d-series. Crystal data: C35 H38 N4 NiO3 ; tetragonal, P43 21 2, a = 15.335(7) Å, c = 25.11(2) Å, V = 5904, Z = 8, λ(Mo Kα) = 0.71069 Å, μ= 0.701 mm−1 , P(000) = 2624, 130 K, R = 0.058 for 5700 reflections with F > 4.0σ(F). 相似文献
13.
Abstract
C18 formate ester (5) [2-(6-methyl-8-(2,6,6-trimethyl-1-cyclohexen-1-yl)-3E,5E,7E-octatrienyl formate], a highly reactive analog of retinal, was synthesized and its interaction with bacterioopsin studied. The formate ester, in the absence of purple or bleached membrane, undergoes very rapid reaction (tl/2 = 0.9 min) in neutral buffer but with membrane present it diffuses more rapidly into the membrane where it reacts slowly. Incorporation of 5 in the membrane results in a 38 nm (3900 cm-1 ) red shift which remains after reconstitution with retinal. Similar experiments with the corresponding C18 alcohol (4) results in a red shift, but this absorption blue shifts upon reconstitution with retinal. Washing the formate ester-treated membrane with bovine serum albumin or the corresponding lyophilized preparation with hexane, treatments that remove retinal oxime, fails to remove the UV-visible absorption, suggesting that a covalent bond between the C18 moiety and a nucleophilic group of the protein has probably formed. 相似文献
C
14.
Cells of the photosynthetic purple bacterium Chromatium vinosum generate a transmembrane electrochemical proton gradient (δμH+ H+ ) on illumination. The steady state values of the two components of δμH+ m+ , δpH and the membrane potential (δψ) have been measured as a function of both the pH and ion composition of the external medium. While δψ and δpH vary considerably as the external pH is varied from 5.5 to 7.5, the magnitude of δμH+ h+ remains relatively constant over this pH range. δψ is relatively unaffected by the ion composition of the medium but δpH and δμH+ H+ both vary considerably depending upon the cation present in the medium. The use of specific ionophores to eliminate either δpH or δψ results in changes in the magnitude of the other component. The δpH values determined here were used to predict the direction of Tl+ flux via the potassium-proton antiport and to demonstrate the reversibility of this antiport. 相似文献
15.
MIGUEL G. NEUMANN J. IOAN MATTHEWS† SILVIA E. BRASLAVSKYdR† 《Photochemistry and photobiology》1984,39(1):31-36
Abstract— The photoreduction of methylene blue in the presence of arylaminomethanesulfonates (RAMS = RC6 H4 NHCH2 SO3 Na) was studied by laser and conventional flash photolysis. These compounds quenched the methylene blue triplet deviating from a normal Stern-Volmer behaviour. For low quencher concentrations, a Rehm-Weller relationship was found between the k q 's and the DL G 's obtained for the electron transfer reactions. The lack of further quenching at higher [RAMS] is ascribed to the formation of a ground state ion pair between the dye and the anionic quencher which, on excitation, forms a triplet state unable to under go electron transfer for steric reasons. A second order decay rate constant was found for the semireduced species (MB') ( ca. 5 × 109 M -1 s-1 , independent of the RAMS used) and is attributed to a proton transfer from the radical zwitterion (RC6 H4 NH CH2 SO3 − ) to MB. The overall dependence on the substituent of the bleaching observed by continuous irradiation follows the triplet behaviour. 相似文献
16.
Direct photolyses of pyrazinopsoralen (PzPs) with excess olefins such as dimethyl fumarate (DMFu), dimethyl maleate (DMMa) and dimethyl ethylidenemalonate (DMEM) gave C4 -photocycloadducts. The photoproducts were determined to be 1:1 C4 -cycloadducts formed through the addition of 4',5'-furan double bond of the excited Pz Ps to the olefins. The fluorescence of Pz Ps was quenched by olefins with rate constants on the order of 109 –1010 M -1 /s. The appearance of the long-lived fluorescence component implies a singlet exciplex mechanism for the photocycloaddition reaction of PzPs with excess olefins. 相似文献
17.
OscarH Will III David E. Sawtelle Pamela Iverson Kara Jorve 《Photochemistry and photobiology》1988,48(3):305-309
Abstract— The accumulation of (J-carotene in the ph/ph + y diploid strain of the smut fungus Ustilago violacea was associated with reduced killing and lower levels of induced mitotic recombination compared to the β-carotene lacking ph/ph+ w strain in response to both incandescent photosensitization and treatment with H2 02 . The ph/ph+ y strain was only slightly more resistant to killing by exogenous toluidine blue (TB) photosensitization. The ph/ph+ y strain exhibited significantly greater levels of survival when exposed to incandescent radiation and 1.5 μ.M TB for 15 min, as well as 3.0. 0.3, 0.03, 0.003% H2 02 in the dark. The ph/ph+ y strain also exhibited lower levels of mitotic recombination after endogenous TB photosensitization and the latter two H2 02 treatments. Similar survival results were obtained for the carotene accumulating haploid strain l.C2y and the carotene lacking haploid strain l.C2iv in response to H2 02 exposure. 相似文献
18.
Giuliana Valduga Santiago Nonell Elena Reddi Giulio Jori Silvia E. Braslavsky 《Photochemistry and photobiology》1988,48(1):1-5
Abstract— Zn(II)phthalocyanine (ZnPc) generates O2 (1 Δg ) with a quantum yield of ca. 0.4 upon photocxcitation at 354 or 600 nm in ethanolic solution as determined by time-resolved phosphorescence studies at 1270 nm and photooxidation experiments using 1,3-diphenylisobenzofuran (DPBF) as substrate. The quantum yield of photooxidation slightly increases upon incorporation of ZnPc into unilamellar liposomes of dipalmitoylphosphatidylcholine. Under our irradiation conditions (600 nm, 18° C, and short light exposure times), DPBF(5–50 μM) undergoes photooxidation by a pure Type II mechanism; the rate constant for the O2 (1 Δg ) + DPBF reaction is (1.1 ±0.1) x 109 M-1 s_1 in ethanol solution and determined to be about two orders of magnitude smaller when both ZnPc and DPBF are embedded into liposomes. 相似文献
19.
Abstract— Results on the photolysis of ethyl chloroacetate, CICH2 COOC2 H5 , at A°≅ 254 nm in liquid phase are presented. GLC and i.r. methods revealed as products: hydrogen chloride and ethyl acetate; in smaller quantities–ethyl succinate and ethyl oxalate; in traces–ethyl malonate, CO2 , CO and CH3 CI; yet other, unidentified products with higher boiling points. Quantum yields are determined for some products. Similar studies were performed in the presence of I2 as a radical scavenger. In the present case, ethyl iodoacetate I – CH2 COOC2 H5 was found to arise in the system. The following primary process may be written on the basis of the experimental data:
CICH2 COOC2 H5 ← CI + CH2 COOC2 H5
Attempts to explain the production of these compounds are based mainly on the properties of the CH2 COOC2 H5 radical. 相似文献
CICH
Attempts to explain the production of these compounds are based mainly on the properties of the CH
20.
INVOLVEMENT OF SINGLET OXYGEN IN THE PHOTOTOXICITY MECHANISM FOR A METABOLITE OF PIROXICAM 总被引:1,自引:0,他引:1
A. Western J. R. Van Camp R. Bensasson E. J. Land I. E. Kochevar 《Photochemistry and photobiology》1987,46(4):469-475
It has been previously shown that a metabolite of piroxicam but not piroxicam itself causes phototoxicity to cells in vitro after exposure to UVA (320–400 nm) radiation. The phototoxicity mechanism for this metabolite, 2-methyl-4-oxo-2H-l,2-benzothiazine-l,l-dioxide (Compound I), was investigated. In vitro phototoxicity to human mononuclear cells was assayed using 0.5 m M Compound I and UVA radiation. The UVA fluence required for phototoxicity of Compound I was lower by a factor of 2-3 in D2 O buffer compared to H2 O buffer. Superoxide dismutase and mannitol, which remove O2 - and OH", respectively, do not decrease the phototoxicity. The photodecomposition of Compound I was inhibited by sodium azide, enhanced by human serum albumin and unaffected by mannitol. Stable photoproducts of Compound I were not toxic to the cells. The quantum yield of singlet oxygen based on its emission at 1270 nm was 0.19 and 0.35 for Compound I and s2 ± 10-3 and 10-2 for piroxicam in D2 O and C6 H6 , respectively. While the extremely low quantum yield for singlet oxygen from piroxicam appears to account for its lack of phototoxicity, the phototoxicity mechanism for its metabolite, Compound I, most likely does involve singlet oxygen. 相似文献