共查询到20条相似文献,搜索用时 15 毫秒
1.
Shi Nian-Qing Prahl Kristine Hendrick Jim Cruz Jose Lu Ping Cho Jae-Yong Jones Sharon Jeffries Thomas 《Applied biochemistry and biotechnology》2000,84(1-9):201-216
Pichia stipitis CBS 6054 will grow on d-xylose, d-arabinose, and l-arabinose. d-Xylose and l-arabinose are abundant in seed hulls of maize, and their utilization is important in processing grain residues. To elucidate
the degradation pathway for l-arabinose, we obtained a mutant, FPL-MY30, that was unable to grow on d-xylose and l-arabinose but that could grow on d-arabinitol. Activity assays of oxidoreductase and pentulokinase enzymes involved in d-xylose, d-arabinose, and l-arabinose pathways indicated that FPL-MY30 is deficient in d-xylitol dehydrogenase (D-XDH), d- and l-arabinitol dehydrogenases, and d-ribitol dehydrogenase. Transforming FPL-MY30 with a gene for xylitol dehydrogenase (PsXYL2), which was cloned from CBS 6054 (Gen Bank AF127801), restored the D-XDH activity and the capacity for FPL-MY30 to grow on
l-arabinose. This suggested that FPL-MY30 is critically deficient in XYL2 and that the d-xylose and l-arabinose metabolic pathways have xylitolas a common intermediate. The capacity for FPL-MY30 to grow on d-arabinitol could proceed through d-ribulose. 相似文献
2.
Application of l-cysteine-capped nano-ZnS as a fluorescence probe for the determination of proteins 总被引:1,自引:0,他引:1
Zhu CQ Zhao DH Chen JL Li YX Wang le Y Wang L Zhou YY Zhuo SJ Wu YQ 《Analytical and bioanalytical chemistry》2004,378(3):811-815
Nanometer-sized l-cysteine-capped ZnS particles have been synthesized and used as a fluorescence probe to investigate the effect of proteins on fluorescent intensity. With =190 nm, maximum and constant synchronous fluorescence enhancement was produced at 267 nm and pH 5.12 in the presence of proteins. A highly sensitive synchronous fluorescence method for the rapid determination of proteins has been developed. Under optimum conditions, calibration graphs are linear over the range 0.03–8.0 g mL–1 for bovine serum albumin (BSA), 0.01–6.0 g mL–1 for human serum albumin (HSA), 0.05–8.0 g mL–1 for -globulin (-G), and 0.04–4.0 g mL–1 for ovalbumin, respectively. The relative standard deviations of seven replicate measurements were 1.75% for 1.0 g mL–1 BSA, 1.90% for 1.0 g mL–1 HSA, 1.65% for 1.0 g mL–1 -G, and 2.32% for 1.0 g mL–1 ovalbumin. 相似文献
3.
Infrared absorption spectroscopy has been applied for the identification of the minerals associated with natural goethite
(α-FeO·OH) from Saudi Arabia. The thermal transformation of natural goethite as well as the effects of the presence of the
associated minerals on the reaction products were investigated. The results revealed that at 300°C protohematite is formed
which at 600°C is slightly crystallized. Further recrystallization and hematite formation takes place at 1000°C. It was also
found that the presence of other minerals found in goethite samples has no effect on the reaction products. 相似文献
4.
V. V. Potekhin 《Russian Chemical Bulletin》2007,56(5):875-882
The oxidation of lower aliphatic alcohols C1–C4 with dioxygen to form the corresponding carbonyl compounds in the presence of the PdII tetraaqua complexes and FeII-FeIII aqua ions in an aqueous medium was studied at 40–80 °C. The introduction of an aromatic compound (acetophenone, benzonitrile,
phenylacetonitrile, o-cyanotoluene, nitrobenzene) and FeII aqua ion instead of the FeIII aqua ion into the reaction system increases substantially the catalytic activity and the yield of the carbonyl compound.
The key role of the Pd species in the intermediate oxidation state stabilized by the aromatic additive in the catalytic cycle
of alcohol oxidation with dioxygen to the carbonyl compound was shown. An increase in the kinetic isotope effect with an increase
in the temperature of methanol oxidation indicates a change in the rate-determining step of alcohol oxidation with dioxygen
in the presence of PdII-FeII-FeIII and the aromatic compound. At temperatures below 60 °C, the catalytically active palladium species are mainly formed upon
the reduction of the PdII tetraaqua complex with the FeII aqua ion, whereas at higher temperatures the reaction between the alcohol and PdII predominates. The mechanism and kinetic equation of the process were proposed.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 842–848, May, 2007. 相似文献
5.
M. A. Proskurnin V. V. Chernysh M. Yu. Kononets S. V. Pakhomova 《Russian Chemical Bulletin》2005,54(1):124-134
The potential of thermal lens spectrometry in the determination of stability constants of complex compounds was explored using copper(I) and iron(II) complexes with 1,10-phenanthroline and 2,9-dimethyl-1,10-phenanthroline as examples. Thermal lens spectrometry offers advantages over conventional spectrophotometry in the determination of stability constants both in aqueous and nonaqueous media. The overall and stepwise stability constants of iron(II) tris(1,10-phenanthrolinate), copper(I) bis(2,9-dimethyl-1,10-phenanthrolinate), and copper(I) bis(1,10-phenanthrolinate) were determined at levels as low as 10−8–10−6 mol L−1.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 123–133, January, 2005. 相似文献
6.
Substrate selectivity of Gluconobacter oxydans (ATCC 9937) for 2,5-diketo-d-gluconic acid (2,5-DKG) production was investigated with glucose, gluconic acid, and gluconolactone in different concentrations
using a resting-cell system. The results show that gluconic acid was utilized favorably by G. oxydans as substrate to produce 2,5-DKG. The strain was coupled with glucose dehydrogenase (GDH) and 2,5-DKG reductase for synthesis
of 2-keto-l-gulonic acid (2-KLG), a direct precursor of l-ascorbic acid, from glucose. NADP and NADPH were regenerated between GDH and 2,5-DKG reductase. The mole yield of 2-KLG of
this multienzyme system was 16.8%. There are three advantages for using the resting cells of G. oxydans to connect GDH with 2,5-DKG reductase for production of 2-KLG: gluconate produced by GDH may immediately be transformed into
2,5-DKG so that a series of problems generally caused by the accumulation of gluconate would be avoided; 2,5-DKG is supplied
directly and continuously for 2,5-DKG reductase, so it is unnecessary to take special measures to deal with this unstable
substrate as it was in Sonoyama’s tandem fermentation process; and NADP(H) was regenerated within the system without any other
components or systems. 相似文献
7.
A chiral liquid chromatographic method for determination of the enantiomeric purity of both l-carnitine and acetyl-l-carnitine is described. Separation of the enantiomers of dl-carnitine and acetyl-dl-carnitine was achieved on a commercial chiral column (Chiralcel OD-R) after derivatization with (alpha-bromo)methyl phenyl ketone. Introduction of this lipophilic UV chromophoric group to the carnitine and acetylcarnitine molecules improved their retention, resolution, and UV detection. The mobile phase was 74:26 (v/v) 0.5 mol L-1 sodium perchlorate–acetonitrile, pH 3.8, and the flow rate was 0.4 mL min-1. Detection was performed at 235 nm. The method is selective and reliable for determination of the enantiomeric purity of bulk drug substances l-carnitine and acetyl-l-carnitine. 相似文献
8.
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
9.
V. N. Leibzon L. V. Michalchenko M. Yu. Leonova V. P. Gultyai 《Russian Chemical Bulletin》2005,54(5):1203-1207
Small additives of iron(II) or copper(II) salts change the regioselectivity of 2,4,6-trinitrotoluene monoreduction with titanium(III) chloride affording predominantly less accessible 2-amino-4,6-dinitrotoluene over 4-amino-2,6-dinitrotoluene (from 25% when
the reduction occurs in the absence of the iron and copper salts to 70% in the presence of these salts). A possible mechanism
of the process is discussed.
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. 1172–1176, May, 2005. 相似文献
10.
An enzymatic method for determining L-malic acid in wine based on an L-malate sensing layer with nicotinamide adenine dinucleotide (NAD+), L-malate dehydrogenase (L-MDH) and diaphorase (DI), immobilized by sol-gel technology, was constructed and evaluated. The sol-gel glass was prepared
with tetramethoxysilane (TMOS), water and HCl. L-MDH catalyzes the reaction between L-malate and NAD+, producing NADH, whose fluorescence (λ
exc = 340 nm, λ
em = 430 nm) could be directly related to the amount of L-malate. NADH is converted to NAD+ by applying hexacyanoferrate(III) as oxidant in the presence of DI. Some parameters affecting sol-gel encapsulation and the
pH of the enzymatic reaction were studied. The sensing layer has a dynamic range of 0.1–1.0 g/L of L-malate and a long-term storage stability of 25 days. It exhibits acceptable reproducibility [s
r(%)≈10] and allows six regenerations. The content of L-malic acid was determined for different types of wine, and polyvinylpolypyrrolidone (PVPP) was used as a bleaching agent
with red wine. The results obtained for the wine samples using the sensing layer are comparable to those obtained from a reference
method based on UV-vis molecular absorption spectrometry, if the matrix effect is corrected for. 相似文献
11.
T. N. Kropacheva V. I. Kornev D. A. Loginov V. I. Meshcheryakov E. V. Mutseneck D. V. Muratov D. S. Perekalin L. S. Shul’pina A. R. Kudinov 《Russian Chemical Bulletin》2005,54(10):2354-2358
New dinuclear ruthenium manganese complexes of general composition (bpy)2Ru(L)MnClx(H2O)2 (L is 1,10-phenanthroline-5,6-dione, 3,3′-dicarboxy-2,2′-bipyridyl, or bis(pyrazolyl); x = 2 or 4) were synthesized by the reaction of (bpy)2Ru(L) with MnCl2 · 4H2O. These compounds and the starting mononuclear ruthenium complexes were studied by spectrophotometric and electrochemical
methods in MeCN. The position of the charge-transfer band RuII → L in the spectra depends on the donor-acceptor characteristics of the ligand L. For the dinuclear complex under study,
the formal potentials of reversible one-electron oxidation of RuII are in the range of 0.9–1.2 V (vs. the standard hydrogen electrode), whereas oxidation of MnII occurs at more positive (by 0.1–0.2 V) potentials.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2281–2285, October, 2005. 相似文献
12.
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
13.
J. Csapó J. Schmidt Zs. Csapó-Kiss É. Varga-Visi G. Pohn É. Csokona 《Chromatographia》2002,56(1):S169-S171
Summary In recent decades several methods have been developed for determination of the proportion of nitrogen-containing substances
passed from the rumen into the abomasum, or small intestine, which are of microbial origin. Recently, when examining thed-amino acid content of foodstuffs, particularly milk and milk products, it was observed that, in addition tod-alanine (d-Ala,d-glutamic acid (d-Glu) andd-aspartic acid (d-Asp) can also be detected in similar quantities, primarily in products which have links with bacterial activity. This gave
rise to the idea of examining the diaminopimelic acid (DAPA),d-Glu, andd-Asp content of bacteria extracted from the rumen of cattle, and that of chyme from the same cattle, to establish whetherd-Asp andd-Glu can be used to estimate protein of bacterial origin.
The investigations performed have provided evidence that bothd-Asp andd-Glu might be appropriate for determination of protein of bacterial origin. The results obtained using these two bacterial
markers (d-Asp andd-Glu) proved to the approximately 10% lower than those obtained using DAPA; this was not because of to error attributable
to the new markers but rather to the unreliability of determination using DAPA Analyses performed on samples of known bacterial
protein content indicate thatd-Asp andd-Glu gave almost identical results for bacterial protein content which were very close to the theoretical (calculated) values.
Presented at Balaton Symposium '01 on High-Performance Separation Methods, Siófok, Hungary, September 2–4, 2001. 相似文献
14.
Marek Pietraszkiewicz Malgorzata Kozbial 《Journal of inclusion phenomena and macrocyclic chemistry》1992,14(3-4):339-348
Chiral 18-crown-6 incorporating ad-mannopyranoside unit displays noticeable enantioselectivity in the recognition of amino acids and their sodium and potassium salts in transport experiments across a liquid membrane containing the carrier.d-phenylalanine andd-phenylglycine were transported faster than their correspondingl-enantiomers, whereas the enantioselectivity was reversed with tryptophan. 相似文献
15.
Pauliukaite R Zhylyak G Citterio D Spichiger-Keller UE 《Analytical and bioanalytical chemistry》2006,386(2):220-227
An amperometric biosensor has been developed for measurement of Umami, or the taste based on the amount of L-glutamate, in tomato foods. The biosensor is based on an enzyme-mediator system in which L-glutamate oxidase is used for biochemical oxidation of L-glutamate and a tetrafulvalene-tetracyanoquinodimethane (TTF-TCNQ) paste, prepared from the mixture of TTF-TCNQ salt, graphite powder, and silicone oil, serves as the mediator. The limit of detection, calculated by use of a four-parameter logistic model, was 0.05 mmol L(-1), and the limit of quantification was 0.15 mmol L(-1). The correlation coefficient (R2) was 0.990 and the relative standard deviation was no more than 1% (n=5). The response time (tau (95)) was 20-50 s, depending on concentration. The repeatability of the sensor was better than 5% (n=10). The sensor developed was stable for more than ten days. 相似文献
16.
N. V. Zyk E. K. Beloglazkina S. E. Sosonyuk M. N. Bulanov R. L. Antipin 《Russian Chemical Bulletin》2005,54(6):1488-1491
Electrophilic sulfenylation, selenenation, and halogenation of bicyclo[2.2.1]heptenes containing CF3 or NO2 group in position endo-5 were studied. The sulfenylation and selenenation were accomplished by arylsulfene- and arylselenenamides activated by POHal3 (Hal = Br, Cl), and iodination was performed by KICl2. The reactions are regiospecific and involve an exo-attack of the electrophilic fragment (arylthio or arylseleno group or iodine) on the C=C bond atom located closer to the
CF3 or NO2 group.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1445–1448, June, 2005. 相似文献
17.
Francisco Claudece Pereira Maria Valnice Boldrin Zanoni 《Journal of Solid State Electrochemistry》2008,12(1):63-70
The present work describes the preparation and characterization of polyelectrolyte coatings of poly-l-lysine (PLL) to modify a glassy carbon electrode and its application to the pre-accumulation of nitroprusside (NP). The effects
of the coating on the electrochemical reduction of NP were investigated. The performance of the modified electrode indicates
that the drug can be immobilized by electrostatic interaction and the voltammetric signal monitored at all pH values in the
range of 2–12. The strong interaction between NP and PLL stabilizes the complex on the electrode surface and minimizes the
chemical reaction of lost CN− ions as a subsequent reaction of electron transfer, which could improve the action mechanism of NP. 相似文献
18.
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
19.
S Yashonath P K Basu A Srinivasan M S Hedge C N R Rao 《Journal of Chemical Sciences》1982,91(2):101-128
Ultraviolet and x-ray photoelectron spectroscopy have been employed to investigate the adsorption of methanol, ethanol, diethylether,
acetaldehyde, acetone, methyl acetate and methylamine on surfaces of Fe, Ni and Cu. All these molecules adsorb molecularly
at low temperatures (≤100 K). Lone pair orbitals of these molecules are stabilized on these metal surfaces (by 0·4–1·0eV)
due to molecular chemisorption. The molecules generally undergo transformations as the temperature is raised to 120 K or above.
The new species produced seems to depend on the metal surface. Some of the product species identified are methoxy species,
formaldehyde and carbon monoxide in the case of methanol and methyl acetate, ethoxy species in the case of ethanol and 2-propanol
in the case of acetone.
Contribution No. 166 from the Solid State and Structural Chemistry Unit. 相似文献
20.
A new synthesis of l-norvaline is described. Using valeric acid as the raw material, α-brominevaleryl chloride was achieved by acyl chlorination and α-position bromination in one-pot with the yield of 84.7%. The yields of the following ammoniation of α-brominevaleryl chloride and resolution of dl-norvaline were 88.7% and 26.7%, respectively. d-Norvaline was also obtained in a similar method from the waste resolution solution. Other optical active amino acids, valine,
α-aminobutyric acid and alanine were also synthesized in similar ways. 相似文献