共查询到20条相似文献,搜索用时 125 毫秒
1.
I. M. Aladzheva O. V. Bykhovskaya P. V. Petrovskii T. A. Mastryukova 《Russian Chemical Bulletin》2007,56(12):2456-2459
Two methods for the synthesis of N-(2-chloroethyl)glycine and-DL-alanine esters are proposed: 1) reductive amination of the C=O group of glyoxilic or pyruvic acids upon treatment with 2-chloroethylamine
and sodium cyanoborohydride in methanol and 2) alkylation of 2-chloroethylamine with α-haloalkanoic acid esters in K2CO3-MeCN two-phase system.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2372–2374, December, 2007. 相似文献
2.
A new flavonoid, kaempferol-3,4′-di-O-α-L-rhamnopyranoside (1), and three known flavonoids (2–4) were isolated from the aerial parts of T. communis L. The structure of the new compound was elucidated on the basis of spectroscopic data. Compounds 1 and 2 showed significant antioxidant activity (IC50 187.151 ± 0.821 μM, and 92.079±0.513 μM, respectively), whereas compounds 3 and 4 showed moderate activity in DPPH free radical scavenging assays.
Published in Khimiya Prirodnykh Soedinenii, No. 3, pp. 295–297, May–June, 2009. 相似文献
3.
N. K. Utkina 《Chemistry of Natural Compounds》2009,45(6):849-853
Aaptamine (1) and isoaaptamine (2) were isolated from the marine sponge Aaptos aaptos; 6-bromo-2′-de-N-methylaplysinopsin (3) from the marine sponge Hyrtios sp. Alkaloids 1–3 were tested for the ability to trap 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical, to reduce Folin–Ciocalteau reagent (FCR),
and to inhibit oxidation of linoleic acid (LA) induced by peroxide radicals. Compounds 1 (IC50 18 μM), 2 (IC50 16 μM), and 3 (IC50 18 μM) reacted strongly with DPPH, comparable with trolox (IC50 16 μM) and showed high reducing ability for FCR. The inhibition of LA oxidation by 1–3 was comparable with that of ionol (BHT). It was shown that the antioxidant activity of 1–3 was related to their ability to release both electrons and H atoms. 相似文献
4.
Nakamura N Negishi K Hirano A Sugawara M 《Analytical and bioanalytical chemistry》2005,383(4):660-667
Real-time monitoring of L-glutamate release from various neuronal regions of mouse hippocampal slices under ischemia (a glucose-free hypoxia condition)
is described. A glass capillary microelectrode with a tip size of ∼10 μm containing a very small volume (∼2 μL) of a solution
of glutamate oxidase (GluOx) and ascorbate oxidase was used. First, the amperometric response behavior of the electrode at
0 V versus Ag/AgCl was characterized with a standard glutamate solution in terms of continuous measurements, effect of oxygen,
viscosity of solution and concentration dependence. The electrode was applied to the real-time monitoring of L-glutamate released from different neuronal regions of acute hippocampal slices submerged in a hypoxia solution. The time-resolved
amounts of L-glutamate released at various neuronal regions (CA1, CA3 and DG) of mouse hippocampal slices were quantified and compared
with the reported L-glutamate fluxes using difference-image analysis during ischemia. 相似文献
5.
The polymerization of o-phenylenediamine (OPD) on l-tyrosine (Tyr) functionalized glassy carbon electrode (GCE) and its electro-catalytic oxidation towards ascorbic acid (AA)
had been studied in this report. l-Tyrosine was first covalently grafted on GCE surface via electrochemical oxidation, which was followed by the electrochemical
polymerization of OPD on the l-tyrosine functionalized GCE. Then, the poly(o-phenylenediamine)/l-tyrosine composite film modified GCE (POPD-Tyr/GCE) was obtained. X-ray photo-electron spectroscopy (XPS), field emission
scanning electron microscope (SEM), and electrochemical techniques have been used to characterize the grafting of l-tyrosine and the polymerization and morphology of OPD film on GCE surface. Due to the doping of the carboxylic functionalities
in l-tyrosine molecules, the POPD film showed good redox activity in neutral medium, and thus, the POPD-Tyr/GCE exhibited excellent
electrocatalytic response to AA in 0.1 mol l−1 phosphate buffer solution (PBS, pH 6.8). The anode peak potential of AA shifted from 0.58 V at GCE to 0.35 V at POPD-Tyr/GCE
with a greatly enhanced current response. A linear calibration graph was obtained over the AA concentration range of 2.5 × 10−4–1.5 × 10–3 mol l−1 with a correlation coefficient of 0.9998. The detection limit (3δ) for AA was 9.2 × 10−5 mol l−1. The modified electrode showed good stability and reproducibility and had been used for the determination of AA content in
vitamin C tablet with satisfactory results. 相似文献
6.
Glucose 2-oxidase (pyranose oxidase, pyranose:oxygen-2-oxidoreductase, EC 1.1.3.10) from Coriolus versicolor catalyses the oxidation of d-glucose at carbon 2 in the presence of molecular O2 producing d-glucosone (2-keto-glucose and d-arabino-2-hexosulose) and H2O2. It was used to convert d-glucose into d-glucosone at moderate pressures (i.e. up to 150 bar) with compressed air in a modified commercial batch reactor. Several
parameters affecting biocatalysis at moderate pressures were investigated as follows: pressure, [enzyme], [glucose], pH, temperature,
nature of fluid and the presence of catalase. Glucose 2-oxidase was purified by immobilized metal affinity chromatography
on epoxy-activated Sepharose 6B-IDA-Cu(II) column at pH 6.0. The rate of bioconversion of d-glucose increased with the pressure since an increase in the pressure with compressed air resulted in higher rates of conversion.
On the other hand, the presence of catalase increased the rate of reaction which strongly suggests that H2O2 acted as inhibitor for this reaction. The rate of bioconversion of d-glucose by glucose 2-oxidase in the presence of either nitrogen or supercritical CO2 at 110 bar was very low compared with the use of compressed air at the same pressure. The optimum temperature (55°C) and
pH (5.0) of d-glucose bioconversion as well as kinetic parameters for this enzyme were determined under moderate pressure. The activation
energy (E
a) was 32.08 kJ mol−1 and kinetic parameters (V
max, K
m, K
cat and K
cat/K
m) for this bioconversion were 8.8 U mg−1 protein, 2.95 mM, 30.81 s−1 and 10,444.06 s−1 M−1, respectively. The biomass of C. versicolor as well as the cell-free extract containing glucose 2-oxidase activity were also useful for bioconversion of d-glucose at moderate pressures. The enzyme was apparently stable at moderate pressures since such pressures did not affect
significantly the enzyme activity. 相似文献
7.
Kuehnelt D Juresa D Kienzl N Francesconi KA 《Analytical and bioanalytical chemistry》2006,386(7-8):2207-2212
Selenium species were determined using HPLC/ICPMS and HPLC/vapor generation/ICPMS in the urine from seven human volunteers
investigated at background selenium concentrations and at slightly elevated concentrations after ingestion of 200 μg Se as
a selenite supplement. Trimethylselenonium ion (TMSe) was present, together with selenosugars, in the urine samples, a result
that dispels recent doubts about its possible previous misidentification with a cationic selenosugar. Although TMSe was present
as only a trace metabolite in urine from five of the seven volunteers (0.02–0.28 μg Se/L, equivalent to 1–5% of the sum of
selenosugars and TMSe), it was a significant metabolite (up to 4.6 μg Se/L, 22%) in one volunteer, and it was the major identified
metabolite (up to 15 μg Se/L, 53%) in another volunteer. This marked individual variability in the formation of TMSe was maintained
in a duplicate investigation of urine from the same seven volunteers. 相似文献
8.
Yodthong Baimark Mangkorn Srisa-ard Jirasak Threeprom Nual-Anong Narkkong 《Colloid and polymer science》2007,285(13):1521-1525
Nanoparticle colloids of methoxy poly(ethylene glycol)-b-poly(D,L-lactide) (MPEG-b-PDLL) diblock copolymer were prepared by a modified spontaneous emulsification solvent diffusion method using acetone/ethanol
as the mixture organic solvents. The MPEG-b-PDLL was synthesized by ring-opening polymerization of D,L-lactide using stannous octoate and MPEG with molecular weight of 5,000 g/mol as the initiating system. The MPEG-b-PDLL obtained was an amorphous polymer with molecular weight of 73,600 g/mol. Influences of acetone/ethanol (v/v) ratios
and Tween 80 surfactant concentrations on characteristics of the colloidal nanoparticles were investigated and discussed.
Light-scattering analysis showed that average diameters of the surfactant-free colloidal nanoparticles were in the range of
86–124 nm. The nanoparticle sizes decreased as the ethanol ratio increased. The Tween 80 did not show the significant effect
on the nanoparticle sizes. Scanning electron micrographs of dried nanoparticles that demonstrated the aggregation of most
particles suggested they were the soft nanoparticles. However, the dried nanoparticle morphology can be observed from scanning
electron microscopy as having a spherical shape and smooth surfaces. 相似文献
9.
The results of IR and single crystal X-ray diffraction studies on the dynamics of molecular groups and structural changes
in L-alanine and DL-alanine (NH3+-CH(CH3)-COO−) with temperature variation are given. An analysis of changes in the 4000–600 cm−1 frequency range of the IR spectra with temperature variation reveals the occurrence of the anomaly for the ∼974 cm−1 band in DL-alanine, which is similar to the anomaly for the 955 cm-1 band, previously described for L-alanine. The X-ray diffraction data for L and DL-alanine show that no dramatic changes in the unit cell parameters, conformations of amino acid molecules themselves, and
hydrogen bond lengths occur with temperature variation, which would indicate the structural phase transition. Changes in the
IR spectra of L-alanine and DL-alanine with temperature variation are compared to the changes in the vibrational spectra of other amino acids on cooling. 相似文献
10.
I. E. Paukov Yulia A. Kovalevskaya Elena V. Boldyreva 《Journal of Thermal Analysis and Calorimetry》2010,100(1):295-301
Heat capacity C
p(T) of the crystalline dl-cysteine was measured on heating the system from 6 to 309 K by adiabatic calorimetry; thermodynamic functions were calculated
based on these data smoothed in the temperature range 6–273.15 K. The values of heat capacity, entropy, and enthalpy at 273.15 K
were equal to 142.4, 153.3, and 213.80 J K−1 mol−1, respectively. At about 300 K, a heat capacity peak was observed, which was interpreted as an evidence of a first-order phase
transition. The enthalpy and the entropy of the transition are equal, respectively, to 2300 ± 50 and 7.6 ± 0.1 J K−1 mol−1. 相似文献
11.
P. I. Abronina L. V. Backinowsky A. A. Grachev S. L. Sedinkin N. N. Malysheva 《Russian Chemical Bulletin》2005,54(5):1287-1293
Methyl 2,4-di-O-benzoyl-α-D-mannopyranoside was used as a key intermediate in the synthesis of 3,6-branched mannopentaoside bearing one terminal D-[1-13C]mannopyranose residue, viz., methyl 6-O-[3,6-di-O-(α-D-mannopyranosyl)-α-D-mannopyranosyl)-3-O-{α -D-[1-13C]mannopyranosyl}-α-D-mannopyranoside.
Dedicated to Academician N. K. Kochetkov on the occasion of his 90th birthday.
__________
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1250–1255, May, 2005. 相似文献
12.
Li-Min Dai Jian Tang Hui-Liang Li Yun-Heng Shen Cai-Yun Peng Wei-Dong Zhang 《Chemistry of Natural Compounds》2009,45(3):325-329
A new stilbene glycoside, 5-methylresveratrol-3,4′-O-β-D-diglucopyranoside (1), was isolated from the n-butanol fraction of the rhizomes of Veratrum dahuricum, together with five known stilbenoids: resveratrol-3-O-β-D-glycoside (2), 4′-methylresveratrol-3-O-β-D-glycoside (3), oxyresveratrol-4′-O-β-D-glycoside (4), oxyresveratrol-3-O-β-D-glycoside (5), and oxyresveratrol-3,4′-O-β-D-diglycoside (6), and found for the first time in the investigated plant. The structures of six isolates were identified on the basis of
1D and 2D NMR data. Compounds 1–6 showed platelet aggregation inhibition, and compound 1 had an IC50 value of 383.6 μM against platelet aggregation induced by AA.
Published in Khimiya Prirodnykh Soedinenii, No. 3, pp. 279–282, May–June, 2009. 相似文献
13.
The amount of volatile dimethylselenide (DMSe) in breath has been monitored after ingestion of sub-toxic amounts of selenium
(300 μg 77Se, as selenite) by a healthy male volunteer. The breath samples were collected in Tedlar bags every hour in the first 12 h
and then at longer intervals for the next 10 days. The samples were subjected to speciation analysis for volatile selenium
compounds by use of cryotrapping–cryofocussing–GC–ICP–MS. Simultaneously, all urine was collected and subjected to total selenium
determination by use of ICP–MS. By monitoring m/z 82 and 77, background or dietary selenium and selenium from the administered selenite were simultaneously determined in the
urine and in the breath—dietary selenium only was measured by monitoring m/z 82 whereas the amount of spiked 77Se (99.1% [enriched spike]) and naturally occurring selenium (7.6% [natural abundance]) were measured by monitoring m/z 77. Quantification of DMSe was performed by using DMSe gas samples prepared in Tedlar bags (linear range 10–300 pg, R
2=0.996, detection limit of Se as DMSe was 10 pg Se, or 0.02 ng L−1, when 0.5 L gas was collected). Dimethylselenide was the only selenium species detected in breath samples before and after
the ingestion of 77Se-enriched selenite. Additional DM77Se was identified as early as 15 min after ingestion of the isotopically-labelled selenite. Although the maximum concentration
of 77Se in DMSe was recorded 90 min after ingestion, the natural isotope ratio for selenium in DMSe (77/82) was not reached after
20 days. The concentration of DMSe correlated with the total Se concentration in the urine during the experiment (R
2=0.80). Furthermore, the sub-toxic dose of 300 μg selenium led to a significant increase of DMSe and renal excretion of background
selenium, confirming that selenium ingested as selenite is homeostatically controlled by excretion. The maximum concentration
of DMSe resulting from the spiked selenite was 1.4 ng Se L−1 whereas the dietary background level was less than 0.4 ng Se L−1. Overall excretion as DMSe was calculated to be 11.2% from the ingested selenite within the first 10 days whereas urinary
excretion accounts for nearly 18.5%. 相似文献
14.
N. V. Ivanchina T. V. Malyarenko A. A. Kicha A. I. Kalinovskii P. S. Dmitrenok 《Russian Chemical Bulletin》2008,57(1):204-208
Nine steroidal compounds including three new steroidal glycosides, viz., sodium (24S)-3,24-di-O-(β-D-xylopyranosyl)-5α-cholestane-3β,6β,8,15α,24-pentol 15-sulfate (fuscaside A), (24S)-3,24-di-O-(β-D-xylopyranosyl)-5α-cholestane-3β,6β,8,15α,24-pentol (fuscaside B), and (22E,24R)-24-O-(β-D-xylopyranosyl)-5α-cholest-22-ene-3β,6α,8,15β,24-pentol (desulfated minutoside A); three previously known glycosides, viz., distolasterosides D1 and D2 and pycno-podioside A; two previously known polyhydroxysteroids, viz., 5α-cholestane-3β,6α,8,15β,16β,26-hexaol and 5α-cholestan-3β,4β,6α,7⇇8,15β,16β,26-octol; and the known sodium 24,25-dihydro-marthasterone
3-sulfate were isolated from the Far-Eastern starfish Lethasterias fusca. The structures of these compounds were elucidated by NMR spectroscopy and mass spectrometry.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 196–200, January, 2008. 相似文献
15.
Endo H Hayashi Y Kitani Y Ren H Hayashi T Nagashima Y 《Analytical and bioanalytical chemistry》2008,391(4):1255-1261
l-Lysine (l-Lys) in living bodies is critical for metabolism; therefore, determination of its levels in food is important. Most enzymatic
methods for l-Lys analysis are performed using l-lysine oxidase (LyOx), but commercially manufactured LyOx is generally not highly selective for l-Lys among amino acids. We previously isolated LyOx as an antibacterial protein secreted from the skin of the rockfish Sebastes schlegeli. In the present study, we developed an optical enzyme sensor system for rapid and continuous determination of l-Lys using this LyOx. The system comprised an immobilized LyOx membrane, an optical oxygen probe, a flow system, and a personal
computer. The amount of l-Lys was detected as a decrease in the oxygen concentration due to the LyOx reaction. The specificity of the sensor was examined
against various amino acids. The sensor response was specific for l-Lys. Good reproducibility was obtained in 58 assays. The response of the sensor using commercially prepared LyOx was unstable
compared with the response using LyOx isolated in our laboratory. Our sensor system could be used for 5 weeks without our
having to change the enzyme membrane. The calibration curve for a standard l-Lys solution was linear from 0.1 to 3.0 mmol L−1. One assay could be completed within 2 min. The sensor was applied to determine the l-Lys content in food samples such as bonito cooking water and scallop hepatopancreas. The values obtained using the sensor
and conventional high-performance liquid chromatography methods were well correlated. 相似文献
16.
Xu Z Li S Fu F Li G Feng X Xu H Ouyang P 《Applied biochemistry and biotechnology》2012,166(4):961-973
d-tagatose is a ketohexose that can be used as a novel functional sweetener in foods, beverages, and dietary supplements. This
study was aimed at developing a high-yielding d-tagatose production process using alginate immobilized Lactobacillus fermentum CGMCC2921 cells. For the isomerization from d-galactose into d-tagatose, the immobilized cells showed optimum temperature and pH at 65 °C and 6.5, respectively. The alginate beads exhibited
a good stability after glutaraldehyde treatment and retained 90% of the enzyme activity after eight cycles (192 h at 65 °C)
of batch conversion. The addition of borate with a molar ratio of 1.0 to d-galactose led to a significant enhancement in the d-tagatose yield. Using commercial β-galactosidase and immobilized L. fermentum cells, d-tagatose was successfully obtained from lactose after a two-step biotransformation. The relatively high conversion rate and
productivity from d-galactose to d-tagatose of 60% and 11.1 g l−1 h−1 were achieved in a packed-bed bioreactor. Moreover, lactobacilli have been approved as generally recognized as safe organisms,
which makes this L. fermentum strain an attracting substitute for recombinant Escherichia coli cells among d-tagatose production progresses. 相似文献
17.
Zahradnícková H Husek P Simek P Hartvich P Marsálek B Holoubek I 《Analytical and bioanalytical chemistry》2007,388(8):1815-1822
A rapid and simple method was developed for the determination of free amino acids (AAs) released from cyanobacteria. The procedure
involves trapping of AAs from the centrifuged cyanobacterial culture fluid on a cation-exchange resin, their release together
with the resin by direct treatment with the reaction medium, followed by immediate derivatization with a corresponding chloroformate.
The extractive alkylation transfers the analytes into an organic phase, an aliquot of which is subjected to GC analysis. Identification
and quantification of AAs was performed by GC/MS and GC/FID, respectively, using propyl chloroformate (PCF) as the derivatization
reagent. For chiral analysis, the cyanobacteria extracts were treated with 2,2,3,3,3-pentafluoropropyl chloroformate (PFPCF)
to create more volatile analytes. Separation of the AA enantiomers was accomplished on a Chirasil-Val capillary column and
the D/L enantiomeric ratios were determined. AAs of cyanobacteria are considered to be important for the assessment of energy flow
in an aquatic food web, nutrition value of cyanobacteria in a food web and for cell–cell communication within cyanobacteria.
The highest levels of AAs were found in the summer period at the beginning of the season (July). In the September and October
samples, the amount of AAs was lower, the number of D-AAs decreased and the D/L ratio was higher than in the July sample. Based on the obtained results it can be assumed that young populations excrete
AAs in higher concentrations and a different composition compared to actively growing populations.
Figure PFPCF derivatization scheme 相似文献
18.
V. Ya. Kavun A. E. Panasenko L. A. Zemnukhova A. B. Slobodyuk 《Russian Chemical Bulletin》2008,57(7):1379-1383
Ionic mobility in the NaSbClF3 · H2O, KSbClF3, and NH4SbClF3 fluorochloride complexes was studied by 1H and 19F NMR spectroscopy in the temperature interval from 150 to 480 K. The types of ionic motions in the compounds were determined.
Their physicochemical characteristics were compared with those of the earlier studied sodium, potassium, and ammonium tetrafluoroantimonates(iii). The replacement of one F atom by the Cl atom in MSbF4 (M = Na, K, NH4) changes both the structure of the Sb polyhedra forming the structure of the antimony(iii) fluorochloride complex and the character of ionic motions in the compounds. The ionic conductivity in the 324–436 K range
was determined for NH4SbClF3: σ = 1.07 · 10−4 S cm−1 at T = 423 K.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1353–1357, July, 2008. 相似文献
19.
Meijuan Xu Zhiming Rao Hong Xu Chunyan Lan Wenfang Dou Xiaomei Zhang Hongyu Xu Jian Jin Zhenghong Xu 《Applied biochemistry and biotechnology》2011,163(6):707-719
Corynebacterium crenatum SYPA 5-5 is an aerobic and industrial l-arginine producer. It was proved that the Corynebacterium glutamicum/Escherichia coli shuttle vector pJC1 could be extended in C. crenatum efficiently when using the chloramphenicol acetyltransferase gene (cat) as a reporter under the control of promoter tac. The expression system was applied to over-express the gene vgb coding Vitreoscilla hemoglobin (VHb) to further increase the dissolved oxygen in C. crenatum. As a result, the recombinant C. crenatum containing the pJC-tac-vgb plasmid expressed VHb at a level of 3.4 nmol g−1, and the oxygen uptake rates reached 0.25 mg A562−1 h−1 which enhanced 38.8% compared to the wild-type strain. Thus, the final l-arginine concentration of the batch fermentation reached a high level of 35.9 g L−1, and the biomass was largely increased to 6.45 g L−1, which were 17.3% and 10.5% higher than those obtained by the wild-type strain, respectively. To our knowledge, this is the
first report that the efficient expression system was constructed to introduce vgb gene increasing the oxygen and energy supply for l-arginine production in C. crenatum, which supplies a good strategy for the improvement of amino acid products. 相似文献
20.
Several optically active aromatic polyamides have been synthesized via direct polycondensation of chiral diacid monomer 1 containing l-methionine moiety with diverse aromatic diamines 2a–2h in a green medium, namely 1,3-dipropylimidazolium bromide as a room temperature ionic liquid. In order to evaluate the advantages
of microwave promotion of these polymerization reactions, we compared microwave irradiation (method I) with conventional oil
bath heating (method II) by means of reaction rates, conversions, and inherent viscosities. The inherent viscosities of resulting
polymers were ranging between 0.47–0.65 and 0.35–0.57 dL/g in methods I and II, respectively. These polymers were characterized by means of 1H-NMR, FT-IR, elemental, organosolubility, differential scanning calorimetry, and thermal gravimetric analysis techniques.
The obtained polymers show thermal stability up to 273 °C under nitrogen atmosphere and good solubility in polar organic solvents.
Polymerization reactions proceeded in higher yields and moderate inherent viscosities under microwave irradiation conditions
besides the dramatically shorter reaction times and achieving the more pure products. 相似文献