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11.
Antonio Gomez Sanchez Manuel Mancera Francisco Rosado Manuel Rico 《Carbohydrate research》1984,134(1):75-82
3,4,5,6,7-Penta-O-acetyl-1,2-dideoxy-1-nitro-d-gluco-hept-1-enitol reacts with methyl acetoacetate in an unusual Michael reaction, giving the normal adduct (6), and a bicyclic derivative (9) that arises from quasi-dimerization of the former when a high concentration of the base is used. Acetylation of compound 9 gives the hydroxylamine O-acetate (10).From the reactions of 3,4,5,6,7-penta-O-acetyl-1,2-dideoxy-1-nitro-d-galacto-hept-1-enitol with ethyl and tert-butyl acetoacetate, the normal adducts (7 and 8) were isolated. The structures of compounds 6 to 10 were established on the basis of their spectral properties (u.v., i.r., mass, and 1H- and 13C-n.m.r.) 相似文献
12.
Solid-phase synthesis was used for the preparation of pyroglutamyl-histidyl-p-nitrophenylalanyl-phenylalanyl-alanyl-leucine amide (I) and glycyl-glycyl-histidyl-p-nitrophenylalanyl-phenylalanyl-alanyl-leucine amide (II), two water-soluble and sensitive chromophoric substrates of chicken pepsin, hog pepsin A, and bovine spleen cathepsin D. The kinetic constants of hydrolysis of the p-nitrophenylalanyl-phenylalanyl bond of the substrates were measured by difference spectrophotometry at 308 nm (Δ? = 860 m?1 cm?1) and by ninhydrin colorimetry (substrate I, ?570 = 2.31 × 104m?1 cm?1). The pH optimum of cleavage is 5 for the pepsins and 3.7 for cathepsin D. Since all three proteinases still have a significant activity at pH 5.5–6 a new, simple assay was designed for submicrogram quantities of pepsins in the presence of pepsinogens without interference of the latter. The method is particularly suitable for the analyses of the zymogen activation mixtures. 相似文献
13.
Summary Infrared and proton resonance spectra have been used to characterize fraction extracted sequentially from humic and fulvic
acids by diethylether, acetone, dioxane, tetrahydrofuran, pyridine and dimethylformamide. The results showed that the same
solvents extracted structurally similar components from both humic and fulvic acids. On the other hand, the spectra showed
solvent-dependent differences, some being characteristic for a preponderance of aliphatic structures, others for aromatic
structures. 相似文献
14.
Natalia G. Stoicheva Christopher L. Davey Gerard H. Markx Douglas B. Kell 《Biocatalysis and Biotransformation》1989,2(4):245-255
Dielectric spectroscopy provides a convenient means of determining the degree of intactness of biological cells. 4-terminal dielectric measurements of suspensions of Saccharomyces cerevisiae at 0.4 MHz show that, as with all other biological cells, these organisms possess a substantial β-dispersion. The additional of octanol to such suspensions causes a rapid decrease in the electrical capacitance of the suspension, which parallels the cellular viability as determined by methylene blue staining. The kinetics of cell death are determined in part by the rate of dissolution of the organic solvent in the aqueous phase. The toxicity of several organic solvents to S. cerevisiae is studied using this technique, and is found to be dependent upon the polarity of the solvent. The present method provides a simple and rapid means for assessing the biocompatibility of solvents used in biotransformations. 相似文献
15.
红松越冬针叶的电子自旋共振(ESR)波谱 总被引:3,自引:2,他引:1
用ESR波谱仪在越冬红松针叶及叶绿体冻干粉中检出了g值分别为2.0044和2.0037的明确的单峰信号。针叶伤害愈重,信号愈强。此信号可被Vc或富含SOD等多种自由基清除剂的沙棘果汁所抑制。针叶受害愈重,沙棘果汁对信号的抑制作用愈强,Vc的抑制作用愈弱。据此认为红松苗越冬伤害和有机自由基的形成有关。在伤害发展的不同阶段,有机自由基的种类组成也不同。 相似文献
16.
Plant community structure in an oligohaline tidal marsh 总被引:2,自引:0,他引:2
An oligohaline tidal marsh on the northern shore of Lake Pontchartrain, LA was characterized with respect to the distributions and abundances of plant species over spatial and temporal gradients using Detrended Correspondence Analysis (DCA). In addition, the species distributions were correlated to several physical environmental factors using Detrended Canonical Correspondence Analysis (DCCA). The distributions of species were best correlated with distance from Lake Pontchartrain, and to a lesser extent with elevation and substrate organic matter. They were least correlated with mean soil salinity (referred to here as background salinity). Of the three mid-seasonal dominant species, the perennial grass, Spartina patens, is the most salt tolerant and was found closest to the lake. Further inland the dominant perennial was Sagittaria lancifolia, which has a salt tolerance less than that of Spartina patens. The perennial sedge, Cladium jamaicense, which is the least salt tolerant of the three, was dominant furthest inland. Background salinity levels were generally low (<5 ppt.) and did not explain species distributions. We hypothesize that the distribution of species is regulated by occasional storm-generated salt pulses that generate strong, short-lived salinity gradients as a function of distance from the lake. Biotic interactions likely also play a role in structuring the plant community. The distributions of several annuals depended on the size and life history of the mid-seasonal dominant perennials. Most of the annuals frequently co-occurred with Sagittaria lancifolia, which was the shortest in stature and had the least persistent canopy of the three mid-seasonal dominant perennials.Abbreviations DCA
Detrended Correspondence Analysis
- DCCA
Detrended Canonical Correspondence Analysis 相似文献
17.
Abstract: Microbial samples were collected from sulfurous, near neutral pH, thermal waters of Yellowstone Park. Thermophilic mixed cultures were identified that removed 90% of pyritic and sulfate sulfur and 33% of the organic sulfur from North Dakota lignite. The 30–40% organic desulfurization barrier was studied for possible inhibitors to organic sulfur removal from coal. 相似文献
18.
Dipl. Geol. Jens Hefter Dipl. Geol. Volker Thiel Dr. Angela Jenisch Dr. Ursula Galling Dr. Stephan Kempe Dr. habil. Walter Michaelis 《Facies》1993,29(1):93-105
Summary Biomarker investigations were applied to the hydrocarbon fractions of three Recent (cyanobacterial mat, Lake Van microbialite
and Lake Satonda microbialite) and two Late Jurassic carbonate samples obtained from sponge bioherms. The relative concentrations
ofn-alkanes, monomethyl alkanes, acyclic isoprenoids, steroids and hopanoids in these samples are studied and their probable
biological precursors are discussed. Normal alkanes with carbon chain lengths ranging from C15 to C34 and monomethyl alkanes ranging from C17 to C21 with a varying methyl branching pattern are found. The major hydrocarbons are low molecular weight (LMW)n-alkanes (C15–C21) with a slight to strong predominance ofn-heptadecane (C17). High molecular weight (HMW)n-alkanes occur in low to moderate relative concentrations showing a preference of odd-carbon numbered compounds with a maximum
at C29. Within the acyclic isoprenoids, pristane, phytane/phytene, pentamethyl-eicosane, squalane and lycopane could be identified.
Polycyclic terpenoids of the sterane and/or hopane type are present in all carbonate samples. The carbon numbers of these
components range from 27 to 29 and 27 to 32, respectively. These organic compounds identified can be attributed to various
source organisms such as cyanobacteria, archaebacteria, algae and vascular plants. All hydrocarbon fractions of the samples
are characterized by moderate to high relative concentrations of compounds derived from cyanobacteria, signifying the role
of these organisms as contributors to the Recent as well as to the Late Jurassic carbonate deposits. 相似文献
19.
Effect of organic loading on nitrification and denitrification in a marine sediment microcosm 总被引:3,自引:0,他引:3
Abstract The effects of organic additions on nitrification and dentrification were examined in sediment microcosms. The organic material, heat killed yeast, had a C/N ratio of 7.5 and was added to sieved, homogenized sediments. Four treatments were compared: no addition (control), 30 g dry weight (dw) m−2 mixed throughout the 10 cm sediment column (30M), 100 g dw m−2 mixed throughout sediments (100M), and 100 g dw m−2 mixed into top 1 cm (100S). After the microcosms had been established for 7–11 days, depth of O2 penetration, sediment-water fluxes and nitrification rates were measured. Nitrification rates were measured using three different techniques: N-serve and acetylene inhibition in intact cores, and nitrification potentials in slurris. Increased organic additions decreased O2 penetration from 2.7 to 0.2 mm while increasing both O2 consumption, from 30 to 70 mmol O2 m−2 d−1 , and NO3 − flux into sediments. Nitrification rates in intact cores were similar for the two methods. Highest rates occurred in the 30M treatment, while the lowest rate was measured in the 100S treatment. Total denitrification rates (estimated from nitrification and nitrate fluxes) increased with increased organic addition, because of the high concentrations of NO3 − (40 μM) in the overlaying water. The ratio of nitrification: denitrification was used as an indication of the importance of nitrification as the NO3 − supply for denitrificaion. This ratio decreased from 1.55 to 0.05 iwth increase organic addition. 相似文献
20.
荔枝果实以10ppm的6-BA、NAA、GA_3 NAA或PVP(1%) NAA处理2min,1℃贮藏8天后再于室温放2天。EPR分析表明果皮的有机自由基(g因子2.0030)比对照低9%—22%,花色素苷含量高5%—46%。离体果皮小圆片经同法浸泡1h或16h,有机自由基反而比对照高。O_2~-的捕获剂Tiron和抗氧化剂PG CA处理果皮小圆片1h,有机自由基降低8%—11%,处理16h则自由基高于对照。邻苯二酚(pH 8.4)和H_2O_2加速果色变褐,有机自由基增高10%—370%。果皮离体后自由基的EPR波谱特征也发生变化,除了一个g因子2.0026—2.0027的主峰外,尚出现另一个小峰。结果表明荔枝果皮褐变的部分原因是有机自由基增高之故。 相似文献