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61.
Novel vibrational circular dichroism (VCD) studies in the CH region of a series of methyl glycosidic carbohydrates were examined. The specific CH stretching VCD band predicts absolute stereochemistries of their anomeric positions. The C-1 chiral information was extracted to the methoxy substituent as a probe. The concept of the vibrational chirality probe from a single chiral center in the presence of numerous such centers might be useful in determining the absolute configuration, when a multiplicity of chiral centers is present in a molecule such as a carbohydrate. 相似文献
62.
Three flavonoid glycosides including orientin, vitexin, quercetin-3-O-neohesperidoside and one unknown compound were isolated and purified by high-speed counter-current chromatography (HSCCC) and semi-preparative HPLC from Trollius ledebouri Reichb., a traditional Chinese medicine. Preparative HSCCC with a two-phase solvent system composed of ethyl acetate-n-butanol-water (2:1:3, v/v/v) was successfully performed by increasing the flow-rate of the mobile phase from 1.5 to 2.5 ml/min after 190 min. Consequently, 95.8 mg orientin, 11.6 mg vitexin, 9.3 mg unknown compound with purities of over 97% and one partially purified peak fraction (contained quercetin-3-O-neohesperidoside at 85.1% purity) were obtained from 500 mg of the crude extract. Then the partially purified fraction was further purified by reversed-phase semi-preparative high-performance liquid chromatography. The structure identification of all pure fractions was carried out by UV, MS, 1H NMR and 13C NMR. 相似文献
63.
Two polyether bridged dihydroxamic acids and their mono-and binuclear manganese(Ⅱ), zinc(Ⅱ) complexes have been synthesized and employed as models to mimic hydrolase in catalytic hydrolysis of p-nitrophenyl picolinate (PNPP). The reaction kinetics and the mechanism of hydrolysis of PNPP have been investigated. The kinetic mathematical model for PNPP cleaved by the complexes has been proposed. The effects of the different central metal ion, mono-and binuclear metal, the pseudo-macrocyclic polyether constructed by polyethoxy group of the complexes, and reactive temperature on the rate for catalytic hydrolysis of PNPP have been examined. The results showed that the transition metal dthydroxamates exhibited high catalytic activity to the hydrolysis of PNPP, the catalytic activity of binuclear complexes was higher than that of mononuclear ones, and the pseudo-macrocyclic polyether might synergetically activate H20 coordinated to metal ion with central metal ion together and promote the catalytic hydrolysis of PNPP. 相似文献
64.
A thermophilic microorganism growing within the temperature range of 40–65 °C (optimum at 55 °C) was isolated from hot water
springs near Konkan, Maharashtra, India. Based on 16S rDNA sequence analysis, it was concluded that the isolate belongs to
the genus Brevibacillus. The present paper reports the isolation, identification, and standardization of fermentation conditions for the production
of enzyme, bile salt hydrolase (EC 3.5.1.24) which is produced intracellularly at high temperatures. This is the first report
regarding the production of bile salt hydrolase from a thermophilic source. Optimization of fermentation conditions resulted
in a 2.9-fold enhancement in enzyme production. 相似文献
65.
Xiao Ling WANG Wei JIAO Xun LIAO Shu Ling PENG Li Sheng DING 《中国化学快报》2006,17(7):916-918
The roots of Paeonia lactiflora Pall. is one of the most important traditional Chinese medicines, which has been used for the treatment of dizziness, spasm, menstrual disorder, spontaneous and night sweating, and as a general analgesic1. Chemical constitu… 相似文献
66.
Grell E. Lewitzki E. Schacht A. Stolz M. 《Journal of Thermal Analysis and Calorimetry》2004,77(2):471-481
Microcalorimetric titrations allow to recognize and investigate high-affinity ligand binding to Na,K-ATPase. Titrations with
the cardiac glycoside Ouabain, which acts as a specific inhibitor of the enzyme, have provided not only the thermodynamic
parameters of high-affinity binding with a stoichiometric coefficient of about 0.6 but also evidence for low-affinity binding
to the lipid. The marked enthalpic contribution of -95 kJ mol-1 at 298.2 K is partially compensated by a large negative entropy change, attributed to an increased interaction between water
and the protein. The calorimetric ADP and ATP titrations at 298.2 K are indicative of high-affinity nucleotide binding either
in 3 mM NaCl, 3 mM MgCl2 or at high ionic strength such as 120 mM choline chloride. However, no binding is detected in the buffer solution alone at
low ionic strength. The affinities for ADP and ATP are similar, around 106 M-1 and the stoichiometric coefficients are close to that of Ouabain binding. The exothermic binding of ADP is characterized
by a ΔH and ΔS value of -65 kJ mol-1 and -100 J mol-1 K-1, respectively. TheΔH value for ATP binding is larger than for ADP and is compensated by a larger, unfavorable ΔS value. This
leads to an enthalpy/entropy compensation, which could express that H-bond formation represents the major type of interaction.
As for Ouabain, the negative ΔS values that are also characteristic of nucleotide binding can indicate an increase of solvate
interaction with the protein due to a conformational transition occurring subsequent to the binding process. The resulting
binding constants are discussed with regard to the results of other studies employing different techniques. A molecular interaction
model for nucleotide binding is suggested.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
67.
From the ethanol extract of Selaginella moellendorffii Hieron., a new flavone O-glycoside and three known flavone C-glycosides have been isolated and identified as 5-carboxymethyl-4′-hydroxyflavone-7-O-β-D-glucopyranoside 1, 6,8-di-C-β-D-glueopyranosylapigenin 2, 6-C-[3-D-glucopyranosyl-8-C-β-D-xylopyranosyl apigenin 3, 6-C-B-D-xylopyranosyl-8-C-β-glucopyranosylapigenin 4, respectively. Their structures were elucidated by spectroscopic methods. 相似文献
68.
Three new cyanogenic glycosides named hydracyanosides A (1), B (2), and C (3) were isolated from the leaves and/or stems of Hydrangea macrophylla in China. The absolute stereostructures of hydracyanosides were characterized on the basis of chemical and physiochemical evidence including single crystal X-ray crystallographic analysis. To the best of our knowledge, this is the first scientific report of cyanogenic glycosides from Hydrangea plants. 相似文献
69.
Tzy-Ming Lu 《Tetrahedron letters》2007,48(31):5415-5419
Two novel carbonic acid esters conjugated with oligomeric phenyl glycosides have been isolated and characterized from the wood of Rhamnus nakaharai. The structures are characterized as 5,7-dihydroxyphthalide 5-O-β-[6-O-{3″-methoxy-4″-O-β-[6?-O-(4?-O-carboxy-3?,5?-dimethoxy)phenyl]glucopyranosyl}phenyl]glucopyranoside (1) and 6-O-{3′-methoxy-4′-O-β-[6″-O-(3?-mercapto-5?-methoxy-4?-O-methylcarboxy)phenyl]glucopyranosyl}phenyl β-glucopyranose (2), namely, rhamnakoside A (1) and B (2), all by NMR and other spectral methods, respectively. They could be a novel case of phase II detoxification products and biogenetic diversity in plant kingdom. 相似文献
70.