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1.
Abstract— The use of cyclic 1,3-dienes and polycyclic aromatic hydrocarbons as xenobiotic substrates for the interception of electronically excited (singlet) molecular oxygen (1O2) in biological systems is reviewed and criticized, and the possibility of utilization of reactive endogenous substrates for 1O2 interception is considered. The common sterols, cholesterol, 5α-cholest-7-en-3β-ol, and 5α-lanost-8-en-3β-ol each give oxidation products with 1O2 different from those with ground-state molecular oxygen that can be distinguished from one another by simple chromatographic means.  相似文献   

2.
The energy barrier to inorganic ion conduction through bilayer lipid membranes (BLM) is investigated as a function of molecular packing and dipolar potential characteristics. Arrhenius energy barrier information is derived from temperature-dependent electrochemical experiments with phosphatidyl choline/steroid BLM. The steroids studied at 0.65 mole fraction in phospholipid were 5-cholesten-3β-ol, 5,7-cholestadien-3β-ol, 5-cholesten-3β,7α-diol, 5α-cholestan-3β,5α,6β-triol, 5α-cholestan-5α,6α-epoxy-3β-ol, 5-cholesten-3β-ol-7-one and 5α-cholestan-3-one. Correlation of the barrier magnitude with molecular packing characteristics, obtained by collecting monolayer data from a Langmuir-Blodgett trough, indicates that the BLM ion current is almost completely controlled by molecular density. The sensitivity of the energy barrier as a function of molecular packing is as great as 0.1 eV for a 0.01-nm2 adjustment.  相似文献   

3.
Summary. This study was aimed at analyzing the daughter ion spectra of 7 toxicologically relevant cholesterol oxidation products (COPs) i.e. cholestanetriol (cholestane-3β,5α,6β-triol), 7-ketocholesterol (cholest-5-en-3β-ol-7-one), 7α-hydroxycholesterol (cholest-5-en-3β,7α-diol), 7β-hydroxycholesterol (cholest-5-en-3β,7β-diol), 25-hydroxycholesterol (cholest-5-en-3β,25-diol), α-epoxycholesterol (cholestane-5α,6α-epoxy-3β-ol) and β-epoxycholesterol (cholestane-5β,6β-epoxy-3β-ol). In addition, 19-hydroxycholesterol (cholest-5-en-3β,19-diol) was analyzed as this serves as internal standard in COPs determination by HPLC-MS. Mass spectrometry was performed using a triple quadrupol mass spectrometer that was equipped with an APCI ion source. Our results indicate a common fragmentation pattern for COPs. The main breaking sites identified were in the sterol ring system between the carbon atoms with the position numbers 11–12, 12–13, and 8–14. Typical daughter ions of m/z = 81, 95, and 195 were used for multiple reaction monitoring analysis.  相似文献   

4.
The core linker polypeptide Lc8.9 was isolated from Mastigocladus laminosus and purified on a preparative scale. A method for the reconstitution of allophycocyanin (AP)—linker complexes from isolated polypeptides was developed. The complex (αAPAP)3 Lc8.9 was reconstituted and compared to (αAPβAP) and (αAPβAP)3 by sucrose density gradient ultracentrifugation, absorption, fluorescence emission and circular dichroism spectroscopy. Differences in the spectra of reconstituted and of directly isolated AP complexes are discussed.  相似文献   

5.
A chloroform-methanol extract of the musculocutaneous sac of the Far-Eastern holothurianC. japonica has yielded a fraction of sterol sulfates (13% of the weight of the extract, 0.8% of the weight of the dry biomass), the main components of which were derivatives of cholest-5-en-3-ol, 24-methylene-, 24-ethyl-, and 24-ethylidenecholest-5-en-3-ols, 5-cholestan-3-ol, and 24-methyl- and 24-methylene-5-cholesten-3-ol; among the minor components were found the sulfates of 24-ethyl-5-cholestan-3-ol of cholesta-5,22-dien-3-ol, of a 5-C30 sterol, and also of dienic and trienic C26 sterols.Institute of Immunology, Ministry of Health of the USSR, Moscow. M. M. Shemyakin Institute of Bioorganic Chemistry, Academy of Sciences of the USSR, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 470–477, July–August, 1984.  相似文献   

6.
The steady-state UVA (350 nm) photolysis of ( E )-β-ionone ( 1 ) in aerated toluene solutions was studied by 1H NMR spectroscopy. The formation of the 1,2,4-trioxane ( 2 ) and 5,8-endoperoxide ( 5 ) derivatives in the ratio of 4:1 was observed. Time-resolved laser induced experiments at 355 nm, such as laser-flash photolysis, photoacoustic and singlet oxygen 1O2 phosphorescence detection, confirmed the formation of the excited triplet state of 1 with a quantum yield Φ T = 0.50 as the precursor for the generation of singlet oxygen 1O2 ( Φ Δ = 0.16) and the isomeric α-pyran derivative ( 3 ), which was a reaction intermediate detected by NMR. In turn, the reaction of 1O2 with 1 and 3 occurred with rate constants of 1.0 × 106 and 2.5 × 108  m −1s−1 to yield the oxygenated products 5 and 2 , respectively, indicating the relevance of the fixed s-cis configuration in the α-pyran ring in the concerted [2+4] cycloaddition of 1O2.  相似文献   

7.
The total sterols have been isolated fromHalocynthia aurantium by column chromatography on silica gel. The following steroid alcohols have been identified in it with the aid of GLC, GLC-MS, and1H NMR: 5-cholestan-3-ol, 24-methylcholestan-3-ol, 24-ethylcholestan-3-ol, 4-methyl-24-ethyl-5-cholestan-3-ol, cholest-5-en-3-ol, 24-methylcholest-5-en-3-ol, 24-ethylcholes-5-en-3-ol, 5-cholest-22-en-3-ol, 24-nor-5-cholest-22-en-3-ol, cholesta-5,22-dien-3-ol, 24-methylcholesta-5,22-dien-3-ol, 24-norcholesta-5,22-dien-3-ol, 24-ethylcholesta-5,24(28)-dien-3-ol, and 24-methylcholesta-5,24(28)-dien-3-ol.Pacific Ocean Institute of Bioorganic Chemistry of the Far Eastern Scientific Center of the Academy of Sciences of the USSR, Vladivostok, and Far-Eastern State University, Vladivostok. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 581–585, September–October, 1981.  相似文献   

8.
The conformational changes of the bovine lens protein "α-crystallin" have been investigated in the presence of the photosensitizer Rose Bengal (RB), in the dark as well as after visible light irradiation. Absorption and fluorescence emission spectra of RB [5 × 10−6  m ] and Fourier transform-IR spectra of α-crystallin [5 mg mL−1] were significantly altered upon RB α-crystallin complex formation. RB was found to bind to α-crystallin in a molecular pocket characterized by a low polarity, with Trp most likely involved in this interaction. The binding constant ( K b) has been estimated to be of the order of 2.5 (mg/mL)−1. The intrinsic fluorescence of α-crystallin was quenched through both dynamic and static mechanisms. Light-induced photosensitized effects showed structural modifications in α-crystallin, including tertiary and secondary structure (an increase in unordered structure) alterations. Notwithstanding those photoinduced structural variations detected in α-crystallin when complexed with RB, the protein still retains its ability to play the role of chaperone for β-crystallin.  相似文献   

9.
Abstract— We measured 6β-cholesterol hydroperoxide (6β-CHP), a specific singlet-oxygen (O2(δg)) product, during irradiation of unilamellar dimyristoyl 1-α-phosphatidylcholine liposomes containing cholesterol and zinc phthalocyanine (ZnPC). The effects of liposome size, the hydrophobic (O2(1δg)) quencher, β-carotene, and hydrophilic O2(1δg) quenchers upon the amount of 6β-CHP formed were determined and interpreted in terms of a one dimensional model of 2(1δg) quenching and diffusion. The model correctly predicted (1) that the amount of 6β-CHP was increased with increasing liposome size, (2) that P-carotene was more effective at reducing 6β-CHP formation in 400 nm diameter liposomes than 100 nm diameter liposomes and (3) that the hydrophilic quencher, water, was also more effective in large liposomes than in small liposomes.
The hydrophobic quencher, β-carotene, was more effective at reducing the formation of 6β-CHP than at reducing the 1270 nm O2(1δg) emission. This difference was found to be due to the size distribution present in the liposome preparations because the difference between the 6β-CHP data and the 1270 nm emission data was much smaller in liposome preparations with a narrow size distribution. When a significant size distribution was present, the 6β-CHP data were weighted more heavily with large-diameter liposomes, while the 1270 nm emission data were weighted more heavily with small-diameter liposomes.  相似文献   

10.
Abstract— The relative reactivity of singlet molecular oxygen, 02(1Δg), α-,β-,Γ-and δ with -tocopherol (vitamin E) was investigated using microwave discharge generation as a uniquely clean source of singlet oxygen and using a hydrocarbon solvent to approximate the membrane environment. The relative efficiencies of the tocopherols for O2(1Δg) were found to decrease in the order: D-α-tocopherol > D-β-tocopheroI > D–Γ-tocopherol > D-δ-tocopherol. The reaction products in all cases were found to be mixtures of quinone and quinone epoxides apparently resulting from decomposition of the primary product, the hydroperoxydienone.  相似文献   

11.
Abstract— Milled wood lignin produced from alkaline hydrogen peroxide-bleached softwood thermomechanical pulp (TMP) fibers was adsorbed on pure cellulose and irradiated for variable periods of time under oxygen and/or nitrogen. The absolute amounts of β-O-4 ethers, phenolic hydroxyl groups, carboxylic acids and various condensed phenolic units were quantified, nondestructively, using 31P NMR spectroscopy. Photoirradiation was found to severely cleave the β-O-4 ethers present in lignin with the concomitant formation of new phenolic units. The rate of this cleavage was found to be faster under oxygen than under nitrogen. The catalytic role of oxygen can be rationalized by invoking the formation of peroxy free radicals that may initiate new sites of radical generation ( e.g. ketyl radicals) within the lignin causing the subsequent breakdown of the β-O-4 linkage. The photoirradiation was found to cause a net increase of the C5-related condensed phenolic units in lignin. Among these, Cα-C5 and/ or Cβ-C5 phenolic moieties were found to predominate. Similar irradiation of a binary mixture of model compounds resembling structures present in softwood lignin resulted in 18 products that were identified and quantified using gas chromatography coupled to mass spectrometry. The photochemical products obtained supported the phenacyl and ketyl mechanistic pathways to pho-toyellowing, whereas the detection of β-5 coupling products (common in both the model compound and milled wood lignin studies) may point a new avenue toward the formation of light-induced products that has not been previously considered in the solid state.  相似文献   

12.
4,5-Seco-19,28-epoxy-18-olean-3,5-dione wasprepared by ozonation of 19,28-epoxy-18-olean-3(5)-ene. The structures of the synthesized compounds were confirmed using spectral data.  相似文献   

13.
Excitation energy transfer in C-phycocyanin is modeled using the Forster inductive resonance mechanism. Detailed calculations are carried out using coordinates and orientations of the chromophores derived from X-ray crystallographic studies of C-phycocyanin from two different species (Schirmer et al, J. Mol. Biol. 184 , 257–277 (1985) and ibid. , 188 , 651-677 (1986)). Spectral overlap integrals are estimated from absorption and fluorescence spectra of C-phycocyanin of Mastigocladus laminosus and its separated subunits. Calculations are carried out for the β-subunit, αβ-monomer, (αβ)3-trimer and (αβ)0-hexamer species with the following chromophore assignments: β155 = 's'(sensitizer), β84 ='f (fluorescer) and α84 ='m'(intermediate):]:. The calculations show that excitation transfer relaxation occurs to 3=98% within 200 ps in nearly every case; however, the rates increase as much as 10-fold for the higher aggregates. Comparison with experimental data on fluorescence decay and depolarization kinetics from the literature shows qualitative agreement with these calculations. We conclude that Forster transfer is sufficient to account for all of the observed fluorescence properties of C-phycocyanin in aggregation states up to the hexamer and in the absence of linker polypeptides.  相似文献   

14.
A new method of capillary zone electrophoresis (CZE) was established by simultaneous assay of four eremophilenolides, 3β-acetoxy-9β-angeloyloxy-1β,10β-epoxy-8α-hydroxyeremophil-7(11)-en-8β (12)-olide (1), 3β-senecioyloxy -1β,10β-epoxy-8α-hydroxyeremophil-7(11)-en-8β (12)-olide (2), 6α-hydroxy-1β,10β-epoxy-8α-hydroxyeremophil-7(11)-en-8β (12)-olide (3) and 3β-acetoxy- 6β-angeloyloxy-1β,10β-epoxy-8α-hydroxyeremophil-7(11)-en-8β (12)-olide (4) in the Chinese herbal extract from Ligulariopsis shichuana. The optimum buffer system was 20 mM borate buffer (pH 10.00). Voltage was 25 kV and detection at 214 nm. Regression equations revealed linear relationships (correlation coefficients 0.9986, 0.9990, 0.9992 and 0.9995) between the peak area of each compound and its concentration. The relative standard deviations of migration times and peak areas were <1.35 and 3.94% within 1 day, respectively. The effects of several CE parameters on the resolution were studied systematically. The contents of four eremophilenolides in Ligulariopsis shichuana were successfully determined with satisfactory repeatability and recovery.  相似文献   

15.
Abstract— A photobiological assay based upon inhibition of growth in the DNA repair-deficient bacterium E. coli B s-1, is described for the analysis of a number of photosensitizing agents. The lower limits of detection were as follows: psoralen 5 × 10-11g; 5-methoxypsoralen 1 × 10-9 g; 8-methoxypsoralen 1 × 10-9 g; 4,5',8-trimethylpsoralen 1 × 10-11 g; angelicin 5 × 10-9 g; 5,7-di-methoxycoumarin 1 × 10-7 g; isoimperatorin 5 × 10-9 g; dictamnine 1 × 10-8 g; oxypeucedanin 5 × 10-7 g; 5-nitroxanthotoxin 5 × 10-7 g; and α-terthienyl 1 × 10-6 g. All active compounds with the exception of α-terthienyl were more easily detected by several orders of magnitude by E. coli B s-1 than with the normal wild type E. coli. 5—Geranoxypsoralen and isopimpinellin were not active. The application of this technique, after TLC, to the analysis of complex mixtures from lemon oil, oil of bergamot, Heracleum lanatum, Angelica dawsonii , and celery and parsnip is illustrated. The bioassay described is more rapid and sensitive than previously published methods, permits replica plates to be made, and allows tentative identification of the photosensitized molecular target.  相似文献   

16.
Abstract Sparteine, the tetracyclic saturated amine alkaloid, is highly fluorescent in n-hexane solution (Φf= 0.64; ζ= 63 ns) and has a large Stokes shift [λmax (abs) = 203 nm; λmax (fluor) = 325 nm]. Its isomer, α-isosparteine, has similar properties: Φf= 0.55; ζf= 50 ns; λmax (fluor) = 338 nm. Oxidized derivatives, such as lupanine, thermopsine, and α-diplospartyrine, are weakly fluorescent. Based on a comparison with spectroscopic and photophysical properties of the monoamine, quinolizidine, it is concluded that the excitation energy is delocalized over the two N-atoms in starteine and a-isosparteine. The self quenching rate constant for sparteine, ca. 1 times 107M-1 s-1, is about 100 times smaller than that for quinolizidine, consistent with excited state derealization. The significant fluorescence quenching in lupanine is rationalized by the fact that N-methyl-2-piperidone mfe/molecularly quenches the fluorescence of quinolizidine at nearly the diffusion controlled rate in -hexane. Comparisons are made with the fluorescence properties of other diamines such as N, N'-dimethylbispidine and N, N'-disubstituted piperazines.  相似文献   

17.
Abstract—Reaction rate constants for the reaction of singlet oxygen with a series of 24 sulfides in chloroform have been measured by inhibition of the self-sensitized photooxidation of rubrene. The reaction rate constant is sensitive to steric effects, decreasing as the carbons α- to sulfur become more highly substituted. Addition of a methyl group to each of the carbons α- to sulfur decreases the rate constant by about a factor of 10. From a series of p - and m -substituted thioanisoles, a ρ of -1.67 ± 0.09 was found. A much better correlation was found with σ than with σ+ indicating there is no resonance interaction with the reaction center. Typical rate constants are: di- n -butyl sulfide, 2.3 × 107 M -1 s-1; CBZ-L-methionine methyl ester, 1.4 × 107; di-s-butyl sulfide, 1.8 × 106; di- t -butyl sulfide, 1.3 × 105; and thioanisole, 2.3 × 106.  相似文献   

18.
Triplet formation quantum yields (Φτ) of psoralen in a set of 17 pure solvents ranging from n -hexane to water and in dioxane: water mixtures were obtained by nanosecond laser flash photolysis. The triplet yield increases with solvent polarity. The extremum values are 0.009 and 0.545 in n -hexane and water, respectively. Good correlations of the experimental Φτ values with empirical "polarity" scales (Dimroth/Reichardt's ET [30], Kamlet/Taft's solva-tochromic parameters β, and α, and Swains acity/basity AS/BS) were obtained: Ln(φT-1 - 1) = 8.86 - 0.143ET(30) Ln(φT-1 - 1) = 4.40 - 2.34τ - 1.70α Ln(φT-1 - 1) = 4.65 - 3.72As - 1.12Bs The results are discussed in terms of the sensitivity of psoralen triplet quantum yield to solvent polarity and hydrogen-bonding abilities.  相似文献   

19.
Abstract— While superoxide anion radical does not normally react with olefins, it does react with activated double bonds. Thus O-2 oxidatively cleaves certain α,β-unsaturated ketones such as chalcones and tetracyclone and electron poor olefins such as 1,1-dicyano and 1,1-dinitro olefins. Similarly O-2 can react with substituted nitrobenzenes to yield the corresponding nitrophenols. EPR and oxygen labeling (KO362) experiments confirm an electron transfer mechanism.  相似文献   

20.
By chromatography on Polikhrom-1, silica gel, and Florisil, an ethanolic extract of the digestive organs of the starfishPatiria pectinifera has yielded the steroid polyols 5-cholestan-3,6,8,15,16,26-hexaol and 5-cholestan-3,4,6,7,8,15,16,26-octaol 6-(sodium sulfate). The structures of the compounds have been shown by spectral characteristics and chemical transformations.Pacific Ocean Institute of Bioorganic Chemistry, Far Eastern Scientific Center, Academy of Sciences of the USSR, Vladivostok. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 738–741, November–December, 1984.  相似文献   

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