共查询到20条相似文献,搜索用时 0 毫秒
1.
D. W. Young 《Journal of Chemical Sciences》1994,106(5):1157-1164
Syntheses of stereospecifically labelled samples ofL- andD-amino acids and of enzyme inhibitors are reviewed, together with a discussion of the use of these compounds in elucidating
the mechanism of action of enzymes involved in amino acid metabolism. 相似文献
2.
Th. Breyhan 《Fresenius' Journal of Analytical Chemistry》1955,148(4):288-289
Ohne Zusammenfassung 相似文献
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4.
The wavefunction generated by the scaled one-electron Hamiltonian (soeh) model has been modified further by including all single excitations from the space of thesoeh function. A perturbation-variation ansatz has been invoked for obtaining the corresponding energy correction (ΔE
2). [E(soeh)+ΔE
2] is shown to reproduceE(Roothaan) very closely. It has been demonstrated that by making ΔE
2 stationary with respect to change in μ results. The correctedsoeh [E(soeh)+ΔE
2] is shown to be quite useful for the calculation of geometrical parameters of open-shell systems even though it lacks the
‘upper-boundedness’ exhibited byE(soeh). 相似文献
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7.
G. Sankar P. R. Sarode A. Srinivasan C. N. R. Rao S. Vasudevan J. M. Thomas 《Journal of Chemical Sciences》1984,93(3):321-334
A detailed investigation of sulphided Co/Mo/Al2O3 catalysts, their oxide precursors and several model oxides and sulphides of cobalt and molybdenum has been carried out using
x-ray photoelectron spectroscopy and x-ray absorption spectroscopy (xanes andexafs). Octahedrally coordinated Co(II) and Mo(IV) are shown to be present in a sulphidic environment on the surfaces of these
catalysts. The surface species contain an excess of sulphur, probably involving disulphide linkages. The surface compositions
of the catalysts examined conform to the general formula Co11 Mo
2n
IV
(2n + 3)S
2
2−
(2n -2)S2−. 相似文献
8.
Raluca Ripan und E. Popper 《Fresenius' Journal of Analytical Chemistry》1943,125(7-8):269-276
Ohne Zusammenfassung 相似文献
9.
We propose a decagram synthesis of commercially unavailable fluorocitric acid. The synthesis begins with benzyl fluoroacetate, which is converted to dibenzyl 2-fluoro-3-oxosuccinate, followed by condensation with malonic acid or its monobenzyl ester and subsequent hydrogenolysis. 相似文献
10.
Electronic structures of 3 halopropenes have been investigated through semiempiricalscf-mo calculations using valence basis sets of atomic orbitals (ao) constructed from Slater type orbitals (sto). The electronic structures of stable conformers have been predicted and the corresponding calculated dipole moments show
good agreement with experimental data. The considerable differences between the dipole moments of various conformers confirm
the hindrance to internal rotation about the C−C bond, i.e., the existence of a definite potential barrier to rotation. The
barrier heights hindering the internal rotation in each system are also estimated. 相似文献
11.
The ambiguity in the assignment of stereochemistry and co-ordination to Cu(II) complexes can be resolved by using x-ray absorption
spectroscopic technique. The difficulty in the structural assignment of the Cu-glutamate complex is studied in detail. The
Cu-acetylacetonate complex has also been studied as an example of square planar geometry. The Cu-glutamate complex is a distorted
octahedral molecule. 相似文献
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13.
Vladislav Tomii Nives Gali Branimir Bertoa Leo Frkanec Vladimir Simeon Mladen
ini 《Journal of inclusion phenomena and macrocyclic chemistry》2005,53(3):263-268
Complexation of alkali metal cations with 5,11,17,23-tetra-tert-butyl-26,28,25,27-tetrakis(O-methyl-D-α-phenylglycylcarbonylmethoxy)calix[4]arene (L) was studied by means of spectrophotometric, conductometric and potentiometric titrations at 25 °C. The solvent effect on the binding ability of L was examined by using two solvents with different affinities for hydrogen bonding, viz. methanol and acetonitrile. Despite the presence of intramolecular NH···O=C hydrogen bonds in L, which need to be disrupted to allow metal ion binding, this calix[4]arene amino acid derivative was shown to be an efficient binder for smaller Li+ and Na+ cations in acetonitrile (lg KLiL > 5, lg KNaL = 7.66), moderately efficient for K+ (lg KKL = 4.62), whereas larger Rb+ and Cs+ did not fit in its hydrophilic cavity. The complex stabilities in methanol were significantly lower (lg KNaL = 4.45, lg KKL = 2.48). That could be explained by different solvation of the cations and by competition between the cations and methanol molecules (via hydrogen bonds) for amide carbonyl oxygens. The influence of cation solvation on complex stability was most pronounced in the case of Li+ for which, contrary to the quite stable LiL+ complex in acetonitrile, no complexation was observed in methanol under the conditions used. 相似文献
14.
Baker''s yeast: production of d- and l-3-hydroxy esters 总被引:7,自引:0,他引:7
Baker's yeast grown under oxygen limited conditions and used in the reduction of 3-oxo esters results in a shift of the stereoselectivity of the yeast towards
-hydroxy esters as compared with ordinary baker's yeast. The highest degree of stereoselectivity was obtained with growing yeast or yeast harvested while growing. In contrast, the stereoselectivity was shifted towards
-hydroxy esters when the oxo esters were added slowly to ordinary baker's yeast supplied with gluconolactone as co-substrate. The reduction rate with gluconolactone was increased by active aeration. Ethyl
-(S)-3-hydroxybutanoate was afforded in>99% ee. Both enantiomers of ethyl 3-hydroxypentanoate,
-(R) in 96% ee and
-(S) in 93% ee, and of ethyl 4-chloro-3-hydroxybutanoate,
-(S) in 98% ee and
-(R) in 94% ee, were obtained. The results demonstrate that the stereoselectivity of baker's yeast can be controlled to a large extent without the use of inhibitors, heat treatment, etc. 相似文献
15.
Afshin Rajabi Khorrami Parvin Kiani Ayoob Bazgir 《Monatshefte für Chemie / Chemical Monthly》2011,9(6):287-295
Abstract
l-Proline was found to be a versatile organocatalyst for the synthesis of new spirooxindole derivatives in good yields under mild reaction conditions using 1-propanol as a solvent. 相似文献16.
A poly-
-histidine(PLH)-copper(II) complex can be used as an alternative biocatalyst in an O2 detection-type amperometric enzyme-less
-ascorbate (AsA) sensor. The PLH–Cu(II) membrane was simply prepared by entrapping the PLH in polyacrylamide gel and subsequent treatment of the gel with CuCl2 solution. This enzyme-less biosensor can be used over a relatively wide pH region from 4 to 11 and enables precise determination of AsA (RSD less than 3%, n=10) at pH 7.0. The fundamental performance characteristics (sensitivity, response time, and linear range) of this PLH–Cu(II)-based sensor is comparable to those of a native ascorbate oxidase-based sensor. Unfortunately, the selectivity is inherently rather low and, as a result, the response was degraded in the presence of higher concentrations (more than mM order) of quinones. However, reducing sugars caused no interference and the sensor could be used to detect AsA in some fruits and drinks. This enzyme-less sensor has excellent stability for at least 3 months of repeated analysis (more than 300 samples) without loss of ordinal activity. 相似文献
17.
Yan Liu Wei Liao Chuanbin Liu Shulin Chen 《Applied biochemistry and biotechnology》1996,131(1-3):844-853
Lactic acid is used as a food additive for flavor and preservation and a precursor in the development of poly-lactic acid,
a product used to make biodegradable plastics and textiles. Rhizopus oryzae NRRL 395 is known to be a strain that produces optically pure l-(+)-lactic acid. The morphology of Rhizopus cultures is complex, forming filamentous, clumps, and pellet mycelia. Different morphology growth has significant effects
on lactic acid production. In bioreactors, the filamentous or clump mycelia increase the viscosity of the medium, wrap around
impellers, and block the nutrient transportation, leading to a decrease in production efficiency and bioreactor performance.
Growing fungi in pellet form can significantly improve these problems. In this study, factors that affect lactic acid production
in pelletized flask cultures using R. oryzae NRRL 395 were investigated in detail. Completely randomized designs were used to determine the influence of culture temperature,
time, concentration of glucose, and inoculum size. Lactic acid fermentation using clump and pellet morphologies were performed
in a 5 L fermentor at the optimal values obtained from flask culture. Finally, fed-batch culture was used to enhance the lactate
concentration in broth. The final lactate concentration of fed-batch culture reached 92 g/L. The data presented in the article
can provide useful information on optimizing lactic acid production using alternative source materials. 相似文献
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19.
Attila Makó áron Sz?ll?sy Gy?rgy Keglevich Dóra K. Menyhárd Péter Bakó László T?ke 《Monatshefte für Chemie / Chemical Monthly》2008,40(3):525-535
New chiral monoaza-15-crown-5 compounds anellated to methyl-4,6-O-(1-naphthyl)methylene-α-d-glucopyranoside (2a–2b), to methyl-4,6-O-isopropylidene-α-d-glucopyranoside (3a–3b) and to methyl-α-d-glucopyranoside (4a–4b) have been synthesized. Several representatives of these crown ethers showed significant asymmetric induction as chiral phase
transfer catalysts, among them 2a proved to be the most efficient one inducing 90% ee in the Michael addition of 2-nitropropane to chalcone, 48% ee in the Darzens condensation of phenacyl-chloride with benzaldehyde and 89% ee in the epoxidation of chalcone with tert-butyl hydroperoxide. The catalytic results were compared with those obtained earlier with macrocycles 1a–1b incorporating a 4,6-O- benzylidene protecting moiety. It occurred that the enantioselectivity is influenced to a great extent by the substituents
on the C(4) and C(6) atoms of the monosaccharide. Lower enantioselectivities were obtained in the reactions of the chalcone
analogues in the presence of catalyst 2a than in the case of the proper chalcone. 相似文献
20.
Guo-Quan Zhu 《Chemical Papers》2009,63(6):683-688
Poly(γ-benzyl l-glutamate)-graft-poly(ethylene glycol) (PBLG-graft-PEG) copolymer was synthesized by the ester exchange reaction of the PBLG homopolymer with PEG. NMR spectroscopy was used
to confirm the composition of the PBLG-graft-PEG copolymer. FTIR spectroscopy was used to characterize the chain conformation of polypeptide segments in the PBLG-graft-PEG copolymer in solid state. The self-assembly behavior of PBLG-graft-PEG and its mixtures with PBLG in ethanol were investigated by transmission electron microscopy (TEM) and viscometry. Experimental
results showed that the PBLG-graft-PEG copolymer can self-assemble to form polymeric micelles with a core-shell structure of a thin shuttle-like shape. The
introduction of the PBLG homopolymer into the mixed system not only decreases the critical micelle concentration (CMC) but
also changes the morphology of the micelles from their shuttle-like shape to cylindrical shape. The effects of test temperature
on the critical micelle concentration of PBLG-graft-PEG were also studied. 相似文献