共查询到20条相似文献,搜索用时 15 毫秒
1.
Diana Uría Fernández Valérie Geoffroy Mathias Sch?fer Jean-Marie Meyer Herbert Budzikiewicz 《Monatshefte für Chemie / Chemical Monthly》2003,12(4):1421-1431
The structural revision on the basis of spectroscopic and degradation results of several pyoverdins from Pseudomonas spp. is reported. Siderotyping studies by the isoelectrofocusing technique and by ferri-pyoverdin uptake experiments had prompted a re-investigation of some structures proposed in the literature. 相似文献
2.
Summary. 1H and 13C NMR signal assignments derived from 2D NMR experiment based correlations are presented for 22-deoxocucurbitacin D and cucurbitacin D. Both derivatives have been isolated from Ecballium elaterium L. (Cucurbitaceae). 相似文献
3.
U. S. Makhmudov Sh. B. Rakhimov B. Tashkhodzhaev M. G. Levkovich V. I. Vinogradova 《Chemistry of Natural Compounds》2008,44(2):208-212
The molecular structures of N-(o-and p-hydroxybenzyl)cytisine were investigated by NMR spectroscopy, x-ray structure analysis, and molecular modeling. It was found
that NMR resonances of the OH and aromatic protons in N-(o-hydroxybenzyl)cytisine were doubled because of the presence of two conformers in solution.
__________
Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 165–168, March–April, 2008. 相似文献
4.
Abdel-Mawgoud AM Aboulwafa MM Hassouna NA 《Applied biochemistry and biotechnology》2009,157(2):329-345
Rhamnolipid produced by Pseudomonas aeruginosa isolate Bs20 is viscous sticky oily yellowish brown liquid with a fruity odor. It showed solubility at aqueous pH > 4 with
optimum solubility at pH 7–7.5 and freely soluble in ethyl acetate. This biosurfactant has a very high surface activity as
it could lower the surface tension of water to 30 mN/m at about 13.4 mg/L, and it exhibited excellent stabilities at high
temperatures (heating at 100°C for 1 h and autoclaving at 121°C for 10 min), salinities (up to 6% NaCl), and pH values (up
to pH 13). The produced biosurfactant can be used in the crude form either as cell-free or cell-containing culture broth of
the grown bacteria, since both preparations showed high emulsification indices ranged between 59% and 66% against kerosene,
diesel, and motor oil. These characters make the test rhamnolipid a potential candidate for use in bioremediation of hydrocarbon-contaminated
sites or in the petroleum industry. High-performance thin-layer chromatography densitometry revealed that the extracted rhamnolipid
contained the two most active rhamnolipid homologues dirhamno dilipidic rhamnolipid and monorhamno dilipidic rhamnolipid at
44% and 56%, respectively, as compared to 51% and 29.5%, respectively, in a standard rhamnolipid preparation. The nature and
ratio of these two rhamnolipid homologues showed to be strain dependent rather than medium-component dependent. 相似文献
5.
Summary. Condensation of (2-iodophenyl)ethylamines with cyclohexanoylacetaldehyde provided the corresponding aldimines which were reduced yielding secondary phenethylcyclohexanoylethylamines. These in turn were appropriate intermediates to prepare several erythrinanes by a sequential intramolecular Strecker and intramolecular Bruylants reaction. In contrast, the C-ring homologue schelhammeranes were not available on this route.Part of PhD thesis, LMU München, D 相似文献
6.
Xu Feng Dong Jiang Yu Shan Tingbo Dai Yunfa Dong Weixing Cao 《Chemistry of Natural Compounds》2008,44(2):171-173
Two new flavonoid-C-glycosides named triticuside A (1a) and triticuside B (1b) were isolated from bran of Triticum aestivum L. The structures of the two new compounds were elucidated by spectral techniques including 1H NMR, 13C NMR as well as HSQC, HMBC, and COSY.
Published in Khimiya Prirodnykh Soedinenii, No. 2, pp. 135–137, March–April, 2008. 相似文献
7.
Jiří Dybal Emanuel Makrlík Jan Budka Petr Vaňura 《Monatshefte für Chemie / Chemical Monthly》2008,139(11):1353-1355
Using DFT calculations, two of the most probable structures (A, B) of the tetraphenyl p-tert-butylcalix[4]arene tetraketone·H3O+ cationic complex species were derived. The hydroxonium ion H3O+, placed in the coordination cavity formed by the calix[4]arene lower-rim groups, is bound by strong hydrogen bonds to the
phenoxy oxygen atoms of the calix[4]arene ligand (structures A, B) and also to one carbonyl oxygen (structure B).
Correspondence: Emanuel Makrlík, Faculty of Applied Sciences, University of West Bohemia, Pilsen, Czech Republic. 相似文献
8.
Lang SM Claes P Neukermans S Janssens E 《Journal of the American Society for Mass Spectrometry》2011,22(9):1508-1514
Structural information on free transition metal doped aluminum clusters, Al
n
TM
+ (TM = Ti, V, Cr), was obtained by studying their ability for argon physisorption. Systematic size (n = 5 – 35) and temperature (T = 145 – 300 K) dependent investigations reveal that bare Al
n
+ clusters are inert toward argon, while Al
n
TM
+ clusters attach one argon atom up to a critical cluster size. This size is interpreted as the geometrical transition from
surface-located dopant atoms to endohedrally doped aluminum clusters with the transition metal atom residing in an aluminum
cage. The critical size, n
crit
, is found to be surprisingly large, namely n
crit = 16 and n
crit = 19 – 21 for TM = V, Cr, and TM = Ti, respectively. Experimental cluster–argon bond dissociation energies have been derived as function of cluster size from
equilibrium mass spectra and are in the 0.1–0.3 eV range. 相似文献
9.
Paizs B Bythell BJ Maître P 《Journal of the American Society for Mass Spectrometry》2012,23(4):664-675
The structure of the a
4
ion from protonated YGGFL was studied in a quadrupole ion trap mass spectrometer by ‘action’ infrared spectroscopy in the
1000–2000 cm–1 (‘fingerprint’) range using the CLIO Free Electron Laser. The potential energy surface (PES) of this ion was characterized
by detailed molecular dynamics scans and density functional theory calculations exploring a large number of isomers and protonation
sites. IR and theory indicate the a
4
ion population is primarily populated by the rearranged, linear structure proposed recently (Bythell et al., J. Am. Chem.
Soc. 2010, 132, 14766). This structure contains an imine group at the N- terminus and an amide group –CO–NH2 at the C-terminus. Our data also indicate that the originally proposed N-terminally protonated linear structure and macrocyclic
structures (Polfer et al., J. Am. Chem. Soc. 2007, 129, 5887) are also present as minor populations. The clear differences between the present and previous IR spectra are
discussed in detail. This mixture of gas-phase structures is also in agreement with the ion mobility spectrum published by
Clemmer and co-workers recently (J. Phys. Chem. A
2008, 112, 1286). Additionally, the calculated cross-sections for the rearranged structures indicate these correspond to the most abundant
(and previously unassigned) feature in Clemmer’s work. 相似文献
10.
11.
Summary. A new synthetic route was developed for the preparation of trans-3-hydroxy-16,17-seco-pregna-5,17(20)-dien-16-al, using Grob fragmentation as the key step. This seco-steroid contains a formyl group and an unsaturated side-chain in a sterically favourable position, and is therefore a promising starting material for the synthesis of novel condensed steroid heterocycles.Received March 22, 2003; accepted April 22, 2003
Published online September 25, 2003 相似文献
12.
Chai Y Wang L Sun H Guo C Pan Y 《Journal of the American Society for Mass Spectrometry》2012,23(5):823-833
In this study, the fragmentation reactions of various N-benzylammonium and N-benzyliminium ions were investigated by electrospray ionization mass spectrometry. In general, the dissociation of N-benzylated cations generates benzyl cations easily. Formation of ion/neutral complex intermediates consisting of the benzyl cations and the neutral fragments was observed. The intra-complex reactions included electrophilic aromatic substitution, hydride transfer, electron transfer, proton transfer, and nucleophilic aromatic substitution. These five types of reactions almost covered all the potential reactivities of benzyl cations in chemical reactions. Benzyl cations are well-known as Lewis acid and electrophile in reactions, but the present study showed that the gas-phase reactivities of some suitably ring-substituted benzyl cations were far richer. The 4-methylbenzyl cation was found to react as a Brønsted acid, benzyl cations bearing a strong electron-withdrawing group were found to react as electron acceptors, and para-halogen-substituted benzyl cations could react as substrates for nucleophilic attack at the phenyl ring. The reactions of benzyl cations were also related to the neutral counterparts. For example, in electron transfer reaction, the neutral counterpart should have low ionization energy and in nucleophilic aromatic substitution reaction, the neutral counterpart should be piperazine or analogues. This study provided a panoramic view of the reactions of benzyl cations with neutral N-containing species in the gas phase. 相似文献
13.
Viktoria S. Moskvina Olexander V. Turov Volodymyr P. Khilya Myroslav M. Garazd Ulrich M. Groth 《Monatshefte für Chemie / Chemical Monthly》2008,139(11):1391-1396
New functionalized derivatives of 8,8,10-trimethyl-4-phenyl-7,8-dihydro-2H,6H-pyrano[3,2-g]-chromene-2,6-dione – analogues of the natural compound graveolone – possessing hydrazine, hydroxylamine, and thiosemicarbazide
residues were synthesized and their reactions with acetic anhydride were studied. The structure of the obtained compounds
was confirmed by NMR spectroscopy.
Correspondence: Viktoria Moskvina, Chemistry Department, Kyiv National Taras Shevchenko University, 60, ul. Vladimirskaya,
01033 Kyiv, Ukraine. 相似文献
14.
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
15.
Summary. A convenient synthesis of several 6-heterocyclically appended tri-O-methyl 6-desmethyl emodin derivatives including the tetrazolyl, oxazolyl, oxazolinyl, benzimidazolyl, benzoxazolyl, and benzothiazolyl derivatives of potential biological and medicinal interest was achieved starting from the tri-O-methyl protected emodin aldehyde or nitrile. In addition, these derivatives could serve as synthons for heterocyclic hypericin derivatives. 相似文献
16.
Eberhard Reimann Rainer Hertel Jürgen Krauss 《Monatshefte für Chemie / Chemical Monthly》2008,139(6):673-684
Alkylation of Reissert compounds derived from 3-methylisoquinolines with several 2-cyanobenzylbromides followed by hydrolytic cleavage provided the corresponding 1-benzyl-3-methylisoquinolines. Treatment of the latter with methylmagnesiumiodide caused cyclization to the title compounds rather than formation of 2-acetylbenzylisoquinolines. 相似文献
17.
Summary. Transfer of sterical hindrance from the periphery to the center of biliverdins by placing a methyl group at N23 and hydrogens at the -carbons in position 12 and 13 changes the conformation of the chromophore from (10syn,14syn) to (10anti,14anti). Additional reduction of sterical hindrance by placing a further hydrogen at the -carbon in position 8 induces a change in configuration from (9Z) to (9E). 相似文献
18.
Summary. Treatment of meso-tetra(tert-butyl)porphyrin with sulfuric acid/n-butanol affords a mixture of porphyrin and mono-tert-butylporphyrin in relatively high yield. 相似文献
19.
A. V. Lezov G. E. Polushina A. A. Lezov P. S. Vlasov N. S. Domnina 《Polymer Science Series A》2011,53(2):93-101
The hydrodynamic and conformational properties of molecules of poly(N,N-diallyl-N,N-dimethylammonium chloride) and N,N-diallyl-N,N-dimethylammonium chloride-maleic acid copolymers of different compositions in solutions with various ionic-strength and pH
values, as well as of the polyelectrolyte complex based on the copolymer with dodecyl sulfate anions in chloroform, are studied.
For poly(N,N-diallyl-N,N-dimethylammonium chloride) molecules in a 1 M NaCl solution, the Kuhn segment length and the hydrodynamic diameter of the
chain are estimated as A = 3.9 nm and d = 0.48 nm, respectively. In acidic solutions with pH 3.5, the copolymers demonstrate behavior typical for polyelectrolytes.
In an alkaline solution with pH 13, when 1 M NaCl is added to the solution of the copolymer containing 29 mol % maleic acid
units, there is an antipolyelectrolyte effect that manifests itself as an increase in the intrinsic viscosity of the copolymer
and in the hydrodynamic radius of its molecules. It is found that an increase in the fraction of maleic acid units in the
copolymer from 12 to 42 mol % brings about a reduction in the equilibrium rigidity of its macromolecules from 4.1 to 2.2 nm.
The equilibrium rigidity of polyelectrolyte-complex molecules is higher than that of initial copolymer molecules owing to
steric interactions arising between the aliphatic chains of dodecyl sulfate anions. In an electric field, the molecules of
the complex are oriented owing to the induced dipole moment resulting from the displacement of dodecyl sulfate anions along
the chain contour. 相似文献
20.
Eleftheria Katechaki Theodoros Solomonidis Argyro Bekatorou Athanasios A. Koutinas 《Applied biochemistry and biotechnology》2010,162(5):1270-1285
Lactobacillus bulgaricus grown on whey was dried by a simple thermal drying method at the range 35–55°C and its efficiency for lactic acid fermentation
of whey was evaluated. Drying of cells in whey suspension in the examined temperature range did not affect significantly their
viability (82–87% survival), indicating a protective effect of whey as both growth and drying medium. The kinetics of fermentation
of whey and mixtures of whey/molasses using the dried culture were comparable to those of non-dried cells, and only low pH
had a detrimental effect on the fermentation ability of the dried cells. Furthermore, dried L. bulgaricus, free or immobilized on casein coagulates, was used as starter for the production of unsalted hard-type cheese. The effects
of the amount of starter culture and the immobilization technique, the evolution of microbial counts, and the sensory properties
of the produced cheeses were evaluated during ripening at various temperatures. 相似文献