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Abstract— The kinetics and the direct, the 9,10-dibromo- (DBA) and the 9,10-diphenylanthracene- (DPA) enhanced chemiluminescence of tert-butyl α-peroxylactone 1, with and without α-deuteration, was investigated in order to probe the mechanism of direct chemiexcitation by these hyperenergetic molecules. The small secondary isotope effect on the rates and activation parameters suggests that a diradical mechanism is obtained. The partitioning of the diradical intermediate into excited vs ground state product and the yield of triplet excited product are moderately (ca. 5-fold) increased by α-deuteration, but the singlet yield is unaffected. A convenient and useful chemiluminescence method for the determination of fluorescence quantum yields has been developed. 相似文献
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Abstract The a-oxidase activity of higher plants acting on long chain fatty acids generates the lower aldehyde in the ground state; however if chlorophyll or chioroplasts are present the chlorophylls are excited most likely by a chemically initiated electron exchange (CIEEL) luminescence process with the putative a-peroxylactone intermediate. When the aldehyde is substituted for the acid, the lower aldehyde appears in the triplet state. The chiral discrimination observed in the quenching by D- and L-tryptophan of the chlorophyll sensitized emission indicates that the triplet aldehyde is generated within the enzymatic preparation and transfers energy while still bound to the enzyme.
Chlorophylls in chioroplasts are excited by addition of a long chain fatty acid or aldehyde. The mechanism, however, is unknown. 相似文献
Chlorophylls in chioroplasts are excited by addition of a long chain fatty acid or aldehyde. The mechanism, however, is unknown. 相似文献
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Abstract— Acid-base equilibria of five azaphenanthrenes (1-and 4-aza; 1,10-, 1,7-, and 4,7-diaza) in the two lowest excited (τ,τ) states have been determined by Förster's cycle. Pure electronic levels of the free bases and their conjugate acids have been located from the absorption, fluorescence and phosphorescence spectra. In diazaphenanthrenes the increase of the first pKa and the decrease of the second pKa under excitation has been observed, and an explanation is offered. In many cases the reactivity of the molecule excited to the lowest triplet state differs considerably from that in the ground state. The Pariser-Pam-Pople (PPP) calculations of the free bases have been performed. From the theoretical results, the changes of the net charge on nitrogen atoms under excitation and the magnitude of the S-T splitting in the La and Lb states have been discussed and compared with experiment. 相似文献
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Abstract— –Pulse radiolysis has been used to excite the triplet states of β-carotene (τ# 9μ sec) and lycopene (τ= 8μsec) in hexane solution, both in the presence and absence of naphthalene as a triplet sensitiser. The absorption spectra of both triplets have been measured in the range 430–550 nm and have thus been extended into the region of the corresponding singlet absorptions. The overlap of the triplet and singlet spectra is discussed in relation to in vivo studies. Extinction coefficients of 1.3±0.1 × 105 l/mole cm for β-carotene triplet 515 nm and 3.9±0.2 × 105 l/mole cm for lycopene triplet at 525 nm were obtained. Isomerisation of the all- trans polyenes used was detected and preliminary measurements indicate that the yield of isomerisation was greater than the triplet yield. The rate of triplet energy transfer from naphthalene to β-carotene was estimated to be 1.5 × 1010 l/mole sec. The corresponding value for lycopene was 1.4× 1010 l/mole sec. The measured efficient quenching of triplet β-carotene by oxygen may occur by an energy transfer mechanism, leading to the formation of singlet oxygen (1 Δg . This would suggest that the triplet energy level of β-carotene lies between 121 and 94 kJ mole-1 . 相似文献
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Alexei V. Trofimov‡ Rostislav F. Vasil'ev Karsten Mielke Waldemar Adam 《Photochemistry and photobiology》1995,62(1):35-43
Abstract— The thermal generation of singlet and triplet excited states from silyloxyaryl-substituted spiroadamantyl dioxetanes lab and the adamantylidineadamantane dioxetane (1c) was investigated by direct and enhanced chemiluminescence (CL). 9,10-Diphenylanthracene (DPA) and 9-fluorenone were used as energy acceptors in the singlet-singlet (S-S), naphthalene and europium chelate Eu(TTA)3Phen (TTA = thenoyltrifluoroacetone, Phen = 1,10-phenanthroline) in the triplet-triplet (T-T) and 9,10-di-bromoanthracene (DBA) in triplet-singlet (T-S) energy transfer experiments. The direct chemiluminescence observed in the thermolysis of dioxetanes lab consisted of fluorescence derived from the singlet-excited adamantanones 2a,b. In the presence of naphthalene, selective T-S energy transfer with DBA (napthalene as quencher) displayed the adamantanone triplets 2a,b and with Eu(TTA)3Phen (naphthalene as mediator) also the silyloxyaryl ester 3 triplets. From the Stern-Volmer constants (kTNTT0) the triplet lifetimes t0t of these triplet state products were assessed. By using the Hastings-Weber standard, the total triplet excitation yield (φt) was estimated to be ca 20%. The energies of the first excited singlet and triplet states of the adamantanones 2a,b and the silyloxyaryl ester 3, the products of the thermally induced decomposition of dioxetanes la-c , were determined by semiempirical calculations (AMI-based configuration interaction), which included explicitly solvent effects on the excitation energies in terms of a self-consistent reaction field approach. The calculations revealed that the first excited singlet and triplet states of the adamantanones 2a,b are expectedly n,π*-type excitations while the silyloxyaryl ester 3 possesses π,π* character. The semiempirical computations suggest that excitation of the adamantanones 2a,b as well as the silyloxyaryl ester 3 is feasible in the thermolysis of the spiroadamantyl dioxetanes lab , which has been confirmed by the experimental energy transfer studies. 相似文献
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Witold Korytowski Gary J. Bachowski Albert W. Girotti 《Photochemistry and photobiology》1992,56(1):1-8
Singlet oxygen (1O2) can react with cholesterol (Ch) to give three possible ene-addition hydroperoxides: 3 beta-hydroxy-5 alpha-cholest-6-ene-5-hydroperoxide (5 alpha-OOH), 3 beta-hydroxycholest-4-ene-6 alpha-hydroperoxide (6 alpha-OOH), and 3 beta-hydroxycholest-4-ene-6 beta-hydroperoxide (6 beta-OOH). The rates of dye-sensitized photogeneration and also the fates of 5 alpha-OOH and 6 beta-OOH in membrane bilayers have been studied and compared. Irradiation of unilamellar [14C]Ch/phospholipid vesicles in the presence of aluminum phthalocyanine tetrasulfonate or merocyanine 540 resulted in formation of 5 alpha-OOH and 6 beta-OOH, as determined by high performance liquid chromatography with radiochemical or electrochemical detection. The initial rate of 6 beta-OOH formation was 30-35% that of 5 alpha-OOH in a variety of liposomal systems. However, after a lag, 5 alpha-OOH invariably decayed via allylic rearrangement to 7 alpha-OOH (also known to be a free radical product), whereas 6 beta-OOH accumulated in unabated fashion until Ch depletion became limiting. Photooxidation of Ch in an isolated natural membrane (erythrocyte ghost) or in L1210 leukemia cells gave similar results. When the reaction was carried out in pyridine or methanol, the rate of 6 beta-OOH formation relative to 5 alpha-OOH was reduced by approximately half, with essentially no isomerization of the latter to 7 alpha-OOH.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
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Abstract— The triplet-triplet absorption spectra of six polyenes have been characterised using flash photolysis, in the presence of anthracene as sensitizer, and pulse radiolysis, in the absence of a sensitizer. The polyenes include several which contain carbonyl groups whose triplet states, unlike retinal , could not be detected unsensitized by flash photolysis. The triplet lifetimes appear to be a function of the number of conjugated double bonds, and vary between 7 and 14 μ sec. In general, the longer the polyene, the shorter the lifetime. An empirical linear relation was found between the frequencies of the polyene triplet-triplet absorption maxima, and the frequencies of the corresponding ground singlet-singlet maxima. The rate constants for quenching by oxygen of nine polyene triplet states were determined to lie in the range 2–7 × 109 M -1 sec-1 . The possible mechanisms for oxygen quenching of triplet states are discussed and analogies between the results for oxygen quenching of polyenes and of polyacenes are drawn. The rate constant for oxygen quenching of all- trans -β-carotene triplet was the same in benzene and hexane. 相似文献
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Abstract— The solid-matrix luminescence properties of (±)- trans -7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene-DNA ([±]-anti-BPDE-DNA) adducts were compared on α-cyclo-dextrin (CD)/NaCl and trehalose/NaCl solid matrices. Both the optimum composition for the solid matrices and the best solvent system were obtained experimentally for acquiring the maximum room-temperature fluorescence (RTF) and room-temperature phosphorescence (RTP) signals for the (±)- anti -BPDE-DNA. Most of the solid-matrix RTF and RTP data were obtained at 296 K and 93 K for (±)-anti-BPDE-DNA adducts adsorbed on 1%α-CD/NaCl and 80% trehalose/NaCl. The RTF signals were strong for (±)-BPDE-DNA adducts on both solid matrices, but RTP was only obtained on the trehalose/NaCl solid matrices with the 80% trehalose yielding the strongest RTP signal for (±)-anti-BPDE-DNA. The fluorescence lifetime data for (±)-anti-BPDE-DNA gave two components on 1 %α-CD/NaCl. For 80% trehalose/NaCl, three components were revealed, but two components were obtained with 80% trehalose/NaCl after ether extraction of the solid matrix. The third component was ascribed to the formation of the tetrols from (±)- anti -BPDE-DNA adducts during the drying step in the sample preparation of 80% trehalose/NaCl. The results give the first reported data on the solid-matrix luminescence of the (±)- anti -BPDE-DNA adducts. These results should be of considerable interest not only from an analytical viewpoint but as a new means of studying the luminescence characteristics of the adducts. 相似文献
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Abstract— The corrected normalized emission spectrum, quantum yield, and emission anisotropy are reported for partially-stacked CpA excited at 266 nm. Utilizing parameters determined separately for cytidine and AMP, the emission spectrum of CpA is quantitatively resolved into components characteristic of the two monomers plus a red shifted emission characteristic of complex formation. The results fit accurately to a simple stacking model in which monomer-like fluorescence originates only from the unstacked fraction and "complex" fluorescence from the stacked fraction. It is shown that the stacked fraction absorbs in a manner qualitatively distinct from the unstacked fraction and the "complex" emission is really the excited state of a ground state complex. This emission, which peaks at 440 nm and contains at least two species can be resolved into three Gaussian components. It is suggested that the emitting species may originate in distinct stacked conformations. 相似文献
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Journal of Structural Chemistry - Inclusion compounds of nitrogen-containing aromatic chromophores 4,4′-bispyridylethylene (bpe) and 4,4′-azopyridine (apy) in the cavities of mesoporous... 相似文献
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K. Rittenhouse-Diakun H. VAN Leengoed J. Morgan E. Hryhorenko G. Paszkiewicz J. E. Whitaker A. R. Oseroff 《Photochemistry and photobiology》1995,61(5):523-528
Endogenously generated protoporphyrin IX (PpIX) from exogenous ALA can be an effective photosensitizer. PpIX accumulation is inversely dependent on available intracellular iron, which is required for the conversion of PpIX to heme. Iron also is necessary for cell replication. Since iron can be toxic, intracellular iron levels are tightly controlled. Activated and proliferating cells respond to the demand for intracellular iron by upregulating membrane expression of the transferrin receptor (CD71) which is needed for iron uptake. We predicted that activated lymphocytes (CD71 +) would preferentially accumulate PpIX because of their lower intracellular iron levels and because of competition for iron between ALA-induced heme production and cellular growth processes. Thus, the CD71+ cells could serve as PDT targets. Stimulation of human peripheral blood lymphocytes (PBL) with the mitogens, phytohemagglutinin A, concanavalin A and pokeweed prior to incubation with ALA results in PpIX accumulation correlating with level of activation. Activated lymphocytes expressing high levels of surface CD71 transferrin receptors generated more PpIX than those with low CD71 expression. Incubating activated cells in transferrin depleted medium (thereby decreasing the iron availability) further increased PpIX levels. Malignant, CD71 + T lymphocytes from a patient with cutaneous T-cell lymphoma (CTCL)/Sezary syndrome also accumulated increased PpIX levels in comparison to norma] lymphocytes. PDT of activated lymphocytes and Sezary cells after ALA incubation demonstrated preferential killing compared to normal, unstimulated PBL. These findings suggest a possible mechanism for the selectivity of ALA PDT for activated CD71+ cells. They also indicate a clinical use for ALA-PDT in therapy directed towards the malignant lymphocytes in leukemias and lymphomas, and as animmunomodulatory agent. 相似文献
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铬(Ⅲ)四苯基卟啉-亚碘酰苯体系在温和条件下能催化氧化碳氢化合物,是细胞色素P-450很好的模拟体系。分离和表征细胞色素P-450模拟体系的活性中间体,不仅能解释细胞色素P-450模拟体系催化氧化碳氢化合物的反应机理,而且也有助于深入了解细胞色素P-450催化氧化碳氢化合物的反应机理及其活性中间体的结构。我们首先分离和表征的细胞色素P-450模拟体系的一种活性中间体-氧配位铬(V)四苯基卟啉配合物[1],具有氧化碳氢化合物的活性。这篇论文报道细胞色素P-450模拟体系的另一种活性中间体-亚碘酰苯铬(Ⅳ)四苯基卟啉配合物的分离,表征和对环已烯的氧化性质。 相似文献
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铬(Ⅲ)四苯基卟啉-亚碘酰苯体系在温和条件下能催化氧化碳氢化合物,是细胞色素P-450很好的模拟体系。分离和表征细胞色素P-450模拟体系的活性中间体,不仅能解释细胞色素P-450模拟体系催化氧化碳氢化合物的反应机理,而且也有助于深入了解细胞色素P-450催化氧化碳氢化合物的反应机理及其活性中间体的结构。我们首先分离和表征的细胞色素P-450模拟体系的一种活性中间体-氧配位铬(V)四苯基卟啉配合物,具有氧化碳氢化合物的活性。这篇论文报道细胞色素P-450模拟体系的另一种活性中间体-亚碘酰苯铬(Ⅳ)四苯基卟啉配合物的分离,表征和对环已烯的氧化性质。 相似文献
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Abstract— Visible radiation can substantially influence the degree to which plant photosynthesis is inhibited by UV-B radiation. This study was designed to separate the immediate effects of visible radiation on UV-B photosynthetic inhibition from the indirect influence of visible irradiation on morphological and physiological properties of leaves during leaf development. Soybean plants were pretreated in growth chambers with either high or low visible irradiance (750 and 70 μmol m-2 s-1 quantum flux in the 400–700 nm waveband, respectively) during the development of leaves used subsequently for UV irradiation. Test leaves still attached to the plant were exposed to 5 h of polychromatic UV-B irradiation and the photosynthetic capacity (net CO2 exchange) was determined before and after the UV irradiation. During the UV irradiation, plants from both pretreatment groups received either high or low visible flux. Development of leaves in the high visible flux pretreatment conditions resulted in thicker leaves, higher chlorophyll a/b ratios, more UV-absorbing pigments, and reduced sensitivity to the UV-B irradiation. However, higher visible flux during the UV-B irradiation resulted in greater depression of photosynthesis by the UV-B irradiation. The relative magnitude of photosynthetic depression under these treatment combinations was the same when photosynthesis was measured under either light-limited or light-saturated conditions. 相似文献
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Abstract— –The u.v. photolysis (Λ= 185 nm) of 2 M aqueous solutions of ethylene glycol was studied at 22°C. Products (quantum yields) are hydrogen (0.204) formaldehyde (0.194), glycolaldehyde (0.08), methanol (0.074), glycerol (0.06), erythritol (0.03), acetaldehyde (0.02), 3,4-dihydroxybutanal (0.01) and succinaldehyde (0.001). With increasing temperature the yields of all products remain essentially unchanged except that of acetaldehyde (φ= 0.32 at 90°C) which is formed in a chain reaction. The photolysis of (CD2OH)2 yields 91% HD, indicating that the most important primary process is the homolytic splitting of the O-H bond. The resulting oxy radicals fragmentate largely into formaldehyde and CH2OH radicals. Molecular fragmentation processes yielding hydrogen and glycolaldehyde, as well as formaldehyde and methanol, are discussed in the proposed decomposition scheme. 相似文献