首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
—The absorption spectrum of chlorophyll a, adsorbed with the amphiphilic amide, N-methylmyristamide. to particles of polyethylene swollen with tetradecane, is unusual in that the red band apparently consists of three main components, which by Gaussian deconvolution are located at 664.5, 678 and 687 nm. The last is very narrow, with a band width of only 5-6 nm at half maximum. At low amide concentration, the 744 nm band of chlorophyll hydrate is also observed. Room temperature fluorescence is weak, and indistinctly resolved into bands. However, on gradual cooling to 80 K, the fluorescence intensifies greatly and becomes resolvable into at least eight bands. The circular dichroism spectrum of the red band region shows optical rotatory strength in two narrow bands at 677 and 686 nm which is enormous, compared to that of monomeric chlorophyll or even the 744 nm hydrate. It is suggested that cyclic oligomer structures, in which adjacent chlorophylls are linked through the amide group of N-methylmyristamide, might be responsible for the spectral phenomena. Unsubstituted myristamide and N.N-dimethylmyristamide do not produce these narrow-banded phenomena with chlorophyll at all.  相似文献   

2.
Fourier transform infrared spectra in the low frequency region (500–150cm?1) of Langmuir-Blodgett films of chlorophyll a (Chi a), chlorophyll b (Chi b) and pheophytin a have been studied. Correlations between spectral changes in monolayer and multilayers of Chi a and Chi b and their adducts with water and dioxane have been established. Spectroscopic evidence has indicated that, although there are no individual absorption bands that can be assigned to pure Mg-nitrogen and/or Mg-oxygen stretching or bending modes, there are several bands in the400–200 cm?1 region of the spectra containing considerable contributions from metal-nitrogen and metal-oxygen vibrational modes. These specific vibrations exhibit marked intensity changes and shifts upon water and dioxane interaction. The different states of chlorophyll aggregation in Langmuir-Blodgett mono- and multilayers films resulted in noticeable changes in their far-IR spectra.  相似文献   

3.
Abstract— A model is developed for the optimization of signal-to-noise ratio for the detection of bioluminescence by fireflies during twilight. The relative degree of optimization is derived in terms of a dimensionless ratio, a biologically effective adaptation. The numerical values of this adaptation can be used to predict the sequence of adaptations of both visual spectral sensitivities and bioluminescence spectral emissions that result in the range of colors of bioluminescence of fireflics from green through yellow. It is shown that a narrowing of visual spectral sensitivity via a screening pigment pathway in order to discriminate against green ambient light is more efficient than a shift in visual spectral sensitivity via change in the opsin photoprotein. The model predicts that the range of wavelengths for the peak intensities of bioluminescence for North American fireflies should be between 550 and 580 nm and provides the physical basis for the observations that in general dark-active firefly species cmit green bioluminescence and twilight-active firefly species emit yellow bioluminescence.  相似文献   

4.
Abstract— By combining independent, dominant, niodifier genes of the albino cl1 mutant it is possible to produce a spectrum of phenotypes ranging from normal green to albino. Analysis of plastid pigments reveals that the albino possesses the ability to produce as much or more chlorophyll than normal siblings and that this ability is not impaired by the presence of the modifier genes. The modifiers do influence, however, the amount of carotene and xanthophyll the plants produced. The level of the three plastid pigments (chlorophyll, carotene and xanthophyll) vary simultaneously and, in most modified phenotypes, occur in approximately the same concentrations relative to their normal siblings. Since chlorophyll production appears to be normal in these mutants, it is suggested that the modifier genes do not directly influence the concentration of this pigment. Rather, the ultimate amount of chlorophyll will not rise above that which can be protected from photodestruction by the carotenoid levels determined by the various modifier genotypes.  相似文献   

5.
Abstract— Biologically active f2-RNA, Obtained from bacteriophage f2, was inactivated by ultraviolet (u.v) light (2537 Å) with a quantum yield of 3.3 ± 0.3 times 10-3 when assayed in the dark with protoplasts of an F- strain of E. coli k12. Assay under “black light” gave a quantum yield of 2.7 ± 0.5 times 10-3 which was just enough lower to suggest that 17 per cent photorecovery of the u.v. lesions has taken place. Intact phage f2 was inactivated by u.v. radiation with a quantum yield of 0.7 ± 0.12 times 10-3, Thus the whole phage is much less sensitive than the free RNA. No evidence of photorecovery was found in u.v.-irradiated RNA phage 7S assayed in its host Pseudomonas aeruginosa.  相似文献   

6.
Chlorophyll-a was incorporated into cellulose acetate films and the triplet state decay kinetics and electron transfer from triplet to p-benzoquinone in aqueous solution was studied using laser flash photolysis and EPR. The triplet was found to decay by first order kinetics with a rate constant which was independent of Chl concentration. The triplet yield, however, was concentration dependent. These properties are due to quenching which occurs only at the singlet state level. In the presence of quinone, the triplet is quenched and, when the quinone is in an aqueous solution in contact with the film, Chl cation radical (C±) as well as the semiquinone anion radical (Q±) can be observed. The C decays by second order kinetics with a rate constant of 1.5 × 106M-1 s-1. Although triplet conversion to radicals is slightly lower in the films as compared to fluid solutions (? 3 times), the lifetimes of the radicals are greatly increased (? 103 times).  相似文献   

7.
本文利用凝胶模量测定法、气相色谱法和紫外光谱法对丙烯酰胺与N,N’-亚甲基双丙烯酰胺水溶液共聚反应进行了研究,证实了N,N’-亚甲基双丙烯酰胺的反应活性明显大于丙烯酰胺的反应活性。用气相色谱法测得单体的竞聚率分别为r_(AM)=0.117,,r_(Bis)=5.756;用紫外光谱法研究了聚合反应中氧化还原引发剂浓度和反应温度对聚合反应速率的影响,得出共聚反应速率方程中,氧化剂的方次为0.66,还原剂浓度的方次为0.55,并求出共聚反应表现活化能为37.1KJ/mol。  相似文献   

8.
Abstract— Studies of purine absorption and emission in seven solvents differing greatly in dielectric constant and hydrogen bonding potential, reveal a variety of solvent effects. For example, the resolution of structure in the absorption spectrum, the position and/or intensity of the X2 absorption band, the intensity of fluorescence, the magnitude of the long wave-lenth tail, and the position of the X1 absorption band are differentially affected—in the order listed—by the solvents tested. Even though it is possible to correlate the extent of decrease in the n-π* tail with increasing solvent dielectric constant, probably alterations in all of these spectroscopic parameters depend most critically upon the ability of the various solvents to form hydrogen bonds with the hydrogen on N9 and/for with the non-bonding electrons on the purine nitrogens: it is tentatively concluded that the probability of hydrogen bonding is directly correlated with the electronegativity of the aza nitrogens (N7 > N3 > N1). In solvents like isopropanol not all of the non-bonding electrons must be solvated maximally in most purine molecules since there is appreciable fluorescence under conditions where a long wavelength tail is readily observed in the absorption spectrum (alternatively some noa-bonding electrons may not te relevant to fluorescence quenching.) Decreases in fluorescence yield are associated with red shifts in the fluorescence maximum, and in the solvents of highest polarity the fluorescence yield is again small indicating that glycerol and water can enhance radiationless tunneling—presumably by altering Franck-Condon configurations and/or improving electronic-vibrational coupling between solute and solvent. The quantum yield is uniform throughout the atsorption band for a given solvent, but studies in aqueous buffers varying from pH 1 to 11 show that the fluorescence yield is greater for charged than for neutral molecules. Further, the fluorescence excitation peak is red shifted in powders. Since phosphorescence is the predominant emission at 777deg;K and increases in fluorescence can be correlated with the presumed solvation of non-bonding electrons, the singlet excited state of lowest energy in ‘unperturbed’ purine must be n-π* in nature. The shape of the phosphorescence band and the decay lifetime of ? 1 sec at 77°K lead to the conclusion that the emitting triplet is a π-π* state. The eight vibrational structures in phosphorescence emission can be readily grouped into two progressions: there is an average separation of about 1300 cm-1 between peaks within a given progression, and the two sets are mutually displaced by about 500 cm-l. Individual vibrational peaks are favoured in different solvents and the whole band may be shifted up to 500 cm-l. Even larger shifts are observed in charged purine molecules and in powders (up to 3000 cm-l) and the presumed 0–0 band is not observed.  相似文献   

9.
Abstract— Electron spin resonance studies have shown that chlorophyll and bacteriochlorophyll can be photo-oxidized in a variety of solvents via their lowest excited singlet states to produce cation radicals. Pheophytin does not undergo this reaction. The mechanism of this photoprocess and its implications for photosynthesis are discussed.  相似文献   

10.
Abstract— Methionine (Met) photooxidation sensitized by rose bengal has been studied as a function of pH and other variables. At pH ≤ 6, the reaction is a simple one, 2 Met + O2→ 2 Methionine sulfoxide (MetO). At pH 6–10, another mechanism becomes important, leading to dehydromethionine; the structure of this compound was correctly assigned by Lavine (1945) as the heterocyclic N-S compound 2. One mole of H2O2 is also produced in this process. Dehydromethionine hydrolyzes slowly to MetO. Above pH9, a process leading directly to MetO + H2O2 becomes important. The stoichiometry of the latter two processes are Met + O2+ H2O → MetO + H2O2; competition among these three processes accounts for the puzzling variations in O2 uptake. N-Formylated derivatives of methionine undergo only the first and third processes. Substantial catalytic effects of buffers complicate the picture. All the reactions appear to involve singlet oxygen, since there is the predicted effect of D2O vs H2O on the rate of reaction, although the situation is complicated by apparent aggregation of Met above 5 mM.  相似文献   

11.
Abstract— Chlorophyll, pheophytin and bacteriochlorophyll sensitize a one-electron transfer in the presence of quinones in ethanol, to produce a ternary complex of ground state porphyrin analog, alcohol cation radical and semiquinone anion radical as the primary photo-product at low temperature. A similar photo-oxidation of alcohol to produce a binary complex is caused by direct excitation of quin-one in the absence of chlorophyll. The mechanisms of these reactions and their implications for photosynthesis are discussed.  相似文献   

12.
The fate of excitation energy and electron transfer to quinones within Chl-a-containing phosphatidyl choline liposomes has been investigated. The bilayer membrane of the liposome stabilizes the Chl triplet state, as evidenced by a three-fold increase in the lifetime over that observed in ethanol solution. The relative triplet yield follows the relative fluorescence yield, indicative of quenching at the singlet level. Triplet state lifetimes are markedly shortened as the Chl concentration is increased, demonstrating that quenching occurs at the triplet level as well. This process is shown to be due to a collisional de-excitation. In the presence of quinones, the Chl triplet reduces the quinone resulting in production of long-lived electron transfer products. The percent conversion of Chl triplet to cation radical when benzoquinone is employed as acceptor is approximately 60 ± 10%, which is slightly less than in ethanol solution (70 ± 10%). The lifetime of the radical, however, can be as much as 1900 times longer. With respect to potentially useful photochemical energy conversion, the magnitude of this increased lifetime is far more significant than is the decreased radical yield.  相似文献   

13.
Abstract— Both DNA bacteriophage and RNA bacteriophage were inactivated when they were irradiated with near-UV light (black light) in the presence of chlorpromazine. The far-UV sensitive mutants of T4D, i.e. T4D v , T4D px and T4D y , were no more sensitive to near-UV light plus chlorpromazine than the wild type. Electron microscopic observations showed that adsorption of T4D was greatly influenced by the treatment. The present results may indicate that the inactivation of T4D is due to the loss of adsorption caused by impairment in the tail or the tail fiber protein rather than the inactivation of DNA.  相似文献   

14.
Abstract— The anaerobic photobleaching of 6, 7-dimethyl-9-(2′-hydroxyethyl)-isoalloxazine, 9-(2′-hydroxyethyl)-isoalloxazine and 6,7-dimethyl-9-(formylmethyl)-isoalloxazine have been compared. Polarographic and spectrophotometric techniques were used for rate studies. The methyl groups on the aromatic ring at the 6 and 7 positions affects the product distributtion in these simple flavins. Formylmethylflavin is postulated to undergo a bimolecular photoredox reaction which is novel to flavin photochemistry. It was demonstrated that there is a common type of leucoflavin formed during anaerobic photobleaching of riboflavin, formylmethylflavin and hydroxyethylflavin. This leucocompound also formed during the photoreduction of formylmethylflavin but not during the photoreduction of the other flavins.  相似文献   

15.
Abstract— DNA and RNA syntheses were inhibited immediately after proflavine treated HeLa cells were irradiated with visible light (400–500 nm). The molecular mechanism for this photooxidation may be either a free radical-mediated (Type I) or singlet oxygen-mediated (Type II) reaction. Non-toxic free radical and singlet oxygen quenchers were added to cells and sensitizer before irradiation to quench the appropriate excited state intermediate. Photooxidative damage (the inhibition of incorporation of [14C]-thymidine) in this system was greatly reduced in the presence of free radical quenchers (glutathione, penicillamine) and not significantly affected by the presence of singlet oxygen quenchers (α-tocopherol, β-carotene, DABCO). This suggests that at least part of the photodynamic damage in HeLa cells is via a Type I mechanism.  相似文献   

16.
Abstract —Anthocyanin synthesis in cabbage and mustard seedlings depends upon duration and irradiance of the light treatment. The relative effectiveness of radiation in various spectral regions depends upon the length of the irradiation and decreases with increasing dose. In intermittent light treatments, far-red light can reverse the promoting action of red light if the dark interval between successive irradiations is longer than one hour. If the length of the dark interval is less than one hour, far-red applied immediately after each red irradiation, enhances anthocyanin accumulation. Anthocyanin accumulation under various light treatments seems to correlate, to some extent, with the rate of phytochrome decay, but not with chlorophyll production. Anthocyanin accumulation is inhibited by 2,4-dinitrophenol and by the ammonium ion, but not by DCMU. The ammonium ion inhibits anthocyanin accumulation induced by a single, short red irradiation. This suggest that the ammonium ion may have a wider spectrum of action in vivo than in chloroplast preparations where it acts as a specific uncoupler of photophosphorylation. Streptomycin inhibits chlorophyll synthesis and enhances anthocyanin accumulation. These results suggest that there is very little, if any, interaction between photosynthesis and ‘high-irradiance-reaction’ anthocyanin synthesis in cabbage and mustard seedlings.  相似文献   

17.
Abstract— The determination of the α-ketoacids, glyoxylic and pyruvic in partial hydrolysates of fibrous proteins (keratin and fibroin) after exposition to u.v. light has allowed us to suggest a photooxydation mechanism for the α-aminoacid residues of glycine and alanine in proteins. The primary reaction is believed to be the formation of the peptide radical -NH-CR-CO-, and the breakdown of polypeptide chains is explained by the formation of α-ketoacyl peptide linkages.  相似文献   

18.
Abstract— Hydrophilic products of chlorophyll a photodegradation are structurally identified using UV/visible and fourier transform infrared spectrophotometry and gas chromatography-mass spectrometry. The major peak detected during reverse-phase high performance liquid chromatography of the colourless photodegradation products is identified as glycerol. Lactic, citric, succinic and malonic acids, as well as alanine, are also identified.  相似文献   

19.
Abstract— The anaerobic photolysis of the flavins containing hydroxyethyl and formythmethyl side-chains in place of the ribityl group of riboflavin has been studied employing spectro-photmetry, thin-layer chromatography and other mehtods. Both flavins are shown to decompose, in part, directly to lumichrome. Acetaldehyde arises from the hudoxyethyl by the flavin nucleus as has been observed previously for riboflavin. The side-chain of the hydroxyethylflavin, is shown to be oxidized to the formylmethyl group. Formylmethylflavin is converted in part to lumichrome and unknown products from the side-chain and in part to a reduced flavin. Formaldehyde could not be detected among the products. Possible mechanisms are discussed briefly.  相似文献   

20.
十六烷基三甲基溴化铵相转移催化合成N,N-二乙基苯胺的研究田庆伟(大连铁道学院应用化学系大连116028)关键词十六烷基三甲基溴化铵相转移催化N,N-二乙基苯胺中图分类号0625.631N,N-二乙基苯胺是制备染料、药物和彩色显影剂的重要中间体,用途...  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号