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41.
Márta Palkó Gabriella Benedek Enikő Forró Edit Wéber Mikko Hänninen Reijo Sillanpää Ferenc Fülöp 《Tetrahedron: Asymmetry》2010,21(8):957-961
(1R,2S,6R)-2-Amino-6-hydroxycyclooctanecarboxylic acid (?)-10 was synthesized from (1R,2S)-2-aminocyclooct-5-enecarboxylic acid (+)-2 via an iodolactone intermediate, while (1R,2S,3R,4S)-2-amino-5,6-dihydroxycyclooctanecarboxylic acid (?)-12 was prepared by using the OsO4-catalyzed oxidation of Boc-protected amino ester (?)-5. The stereochemistry and relative configurations of the synthesized compounds were determined by 1D and 2D NMR spectroscopy (based on 2D NOE cross-peaks and 3J(H,H) coupling constants) and X-ray crystallography. 相似文献
42.
New isoxazoline-fused cispentacins were prepared by the 1,3-dipolar cycloaddition of nitrile oxides to β-amino esters containing a cyclopentene skeleton. This synthetic procedure gave regio- and diastereoisomers of the cispentacins. The synthetic route was extended to the synthesis of these compounds in enantiomerically pure form. 相似文献
43.
Anna R. M. Hyyryläinen Jaana M. H. Pakarinen Enikő Forró Ferenc Fülöp Pirjo Vainiotalo 《Journal of the American Society for Mass Spectrometry》2009,20(7):1235-1241
Chiral differentiation of four enantiomeric pairs of β-amino acids, cis-(1R,2S)-, cis-(1S,2R)-, trans-(1R,2R)-, and trans-(1S,2S)-2-aminocyclopentanecarboxylic acids (cyclopentane β-amino acids), and cis-(1R,2S)-, cis-(1S,2R)-, trans-(1R,2R)-, and trans-(1S,2S)-2-aminocyclohexanecarboxylic acids (cyclohexane β-amino acids) was performed successfully by using host-guest complexes and ion/molecule reactions. The experiments were conducted
by using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. The effect of a chiral host
molecule was tested by using three different host compounds; (+)-(18-Crown-6)-2,3,11,12-tetracarboxylic acid, (−)-(18-Crown-6)-2,3,11,12-tetracarboxylic
acid, and β-cyclodextrin. This is the first time that small enantiomeric pairs with two chiral centers have been differentiated using
ion/molecule reactions and host-guest complexes. 相似文献
44.
Federico A. Rojas‐Quijano Dr. Enikő Tircsóné Benyó Gyula Tircsó Dr. Ferenc K. Kálmán Dr. Zsolt Baranyai Dr. Silvio Aime Prof. A. Dean Sherry Prof. Zoltán Kovács Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(47):13188-13200
Lanthanide complexes of two tris(amide) derivatives of PCTA were synthesized and characterized. The relaxometric and luminescence properties of their lanthanide complexes were investigated as bimodal magnetic resonance (MR) and optical imaging agents. Luminescence studies show that one of the TbIII complexes dimerizes in solution at low millimolar concentrations, whereas the other may have a higher than expected coordination number in solution. The corresponding GdIII complexes display unusually high T1 relaxivities and enhanced kinetic inertness compared to GdPCTA. These features suggest that these new chelates may be suitable for in vivo applications. The fast water‐exchange rates observed for these complexes make them unsuitable as paramagnetic chemical exchange saturation transfer (PARACEST) agents. 相似文献
45.
Optimization of steam pretreatment of corn stover to enhance enzymatic digestibility 总被引:5,自引:0,他引:5
Among the available agricultural byproducts, corn stover, with its yearly production of 10 million t (dry basis), is the most
abundant promising raw material for fuel ethanol production in Hungary. In the United States, more than 216 million to fcorn
stover is produced annually, of which a portion also could possibly be collected for conversion to ethanol. However, a network
of lignin and hemicellulose protects cellulose, which is the major source of fermentable sugars in corn stover (approx 40%
of the dry matter [DM]). Steam pretreatment removes the major part of the hemicellulose from the solid material and makes
the cellulose more susceptible to enzymatic digestion. We studied 12 different combinations of reaction temperature, time,
and pH during steam pretreatment. The best conditions (200°C, 5 min, 2% H2SO4) increased the enzymatic conversion (from cellulose to glucose) of corn stover more then four times, compared to untreated
material. However, steam pretreatment at 190°C for 5 min with 2% sulfuric acid resulted in the highest overall yield of sugars,
56.1 g from 100 g of untreated material (DM), corresponding to 73% of the theoretical. The liquor following steam explosion
was fermented using Saccharomyces cerevisiae to investigate the inhibitory effect of the pretreatment. The achieved ethanol yield was slightly higher than that obtained
with a reference sugar solution. This demonstrates that baker's yeast could adapt to the pretreated liquor and ferment the
glucose to ethanol efficiently. 相似文献
46.
Mihucz VG Tatár E Virág I Cseh E Fodor F Záray G 《Analytical and bioanalytical chemistry》2005,383(3):461-466
Flow injection analysis (FIA) and high-performance liquid chromatography double-focusing sector field inductively coupled
plasma mass spectrometry (HPLC-DF-ICP-MS) were used for total arsenic determination and arsenic speciation of xylem sap of
cucumber plants (Cucumis sativus L.) grown in hydroponics containing 2 μmol dm−3 arsenate or arsenite, respectively. Arsenite [As(III)], arsenate [As(V)] and dimethylarsinic acid (DMA) were identified in
the sap of the plants. Arsenite was the predominant arsenic species in the xylem saps regardless of the type of arsenic treatment,
and the following concentration order was determined: As(III) > As(V) > DMA. The amount of total As, calculated taking into
consideration the mass of xylem sap collected, was almost equal for both treatments. Arsenite was taken up more easily by
cucumber than arsenate. Partial oxidation of arsenite to arsenate (<10% in 48 h) was observed in the case of arsenite-containing
nutrient solutions, which may explain the detection of arsenate in the saps of plants treated with arsenite. 相似文献
47.
Corn stover, the most abundant agricultural residue in Hungary, is a potential raw material for the production of fuel ethanol
as a result of its high content of carbohydrates, but a pretreatment is required for its efficient hydrolysis. In this article,
we describe the results using various chemicals such as dilute H2SO4, HCl, and NaOH separately as well as consecutively under relative mild conditions (120°C, 1h). Pretreatment with 5% H2SO4 or 5% HCl solubilized 85% of the hemicellulose fraction, but the enzymatic conversion of pretreated materials increased only
two times compared to the untreated corn stover. Applying acidic pretreatment following a 1-d soaking in base achieved enzymatic
conversion that was nearly the theoretical maximum (95.7%). Pretreatment with 10% NaOH decreased the lignin fraction >95%,
increased the enzymatic conversion more than four times, and gave a 79.4% enzymatic conversion. However, by increasing the
reaction time, the enzymatic degradability could also be increased significantly, using a less concentrated base. When the
time of pretreatment was increased three times (0.5% NaOH at 120°C), the amount of total released sugars was 47.9 g from 100
g (dry matter) of untreated corn stover. 相似文献
48.
Mónika Kéri László Palcsu Marianna Túri Enikő Heim Andrea Czébely Levente Novák István Bányai 《Cellulose (London, England)》2015,22(4):2211-2220
Alpha-cellulose is a part of the wooden material that preserves isotopic composition during tree-growth, and therefore provides important indirect data for paleoclimatological studies. For this reason, it is exceptionally important to extract the alpha-cellulose component from plants, e.g. from tree rings of wood. Since the cell wall of plant cells consists of multicomponent polysaccharides, the extraction of cellulose from wood is not an obvious task. In this paper, we describe, evaluate and compare nine methods, based on the literature and experimental observations, for obtaining cellulose from tree rings of wood. We show that the distortionless enhancement by polarization transfer (DEPT-135) variant of liquid-state 13C NMR spectroscopy is a powerful analytical method for monitoring the preparation process. Trifluoroacetic acid was applied as solvent for the NMR analysis. We proved that all the preparation methods give pure cellulose samples without hemicellulose and lignin content, and we propose methods resulting in non-fragmented cellulose. 13C and 18O isotope ratio measurements have shown that all the applied extraction methods result in similar isotope ratios, thus they are suitable for paleoclimatological studies. 相似文献
49.
Anna R. M. Hyyryläinen Jaana M. H. Pakarinen Enik Forró Ferenc Fülöp Pirjo Vainiotalo 《Journal of mass spectrometry : JMS》2010,45(2):198-204
Differentiation of β ‐amino acid enantiomers with two chiral centres was investigated by kinetic method with trimeric metal‐bound complexes. Four enantiomeric pairs of β ‐amino acids were studied: cis‐(1R,2S)‐, cis‐(1S,2R)‐, trans‐(1R,2R)‐ and trans‐(1S,2S)‐2‐aminocyclopentanecarboxylic acids (cyclopentane β ‐amino acids), and cis‐(1R,2S)‐, cis‐(1S,2R)‐, trans‐(1R,2R)‐, and trans‐(1S,2S)‐2‐aminocyclohexanecarboxylic acids (cyclohexane β ‐amino acids). The results showed that the choice of metal ion (Cu2+, Ni2+) and chiral reference compound (α‐ and β ‐amino acids) had an effect on the enantioselectivity. Especially, aromaticity of the reference compound was noted to enhance the enantioselectivity. The fixed‐ligand kinetic method, a modification of the kinetic method, was then applied to the same β ‐amino acids, with dipeptides used as fixed ligands. With this method, dipeptide containing an aromatic side chain enhanced the enantioselectivity. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
50.