共查询到20条相似文献,搜索用时 31 毫秒
1.
E. N. Brazhnikova Yu. Yu. Gavronskaya V. N. Pak 《Russian Journal of General Chemistry》2009,79(7):1421-1424
The two-stage synthesis of nanosize silver in the pore space of a perfluorosulfonic membrane by ion-exchange fixation of Ag+ cations with the subsequent photoreduction in formaldehyde vapor was fulfilled. The study of the obtained composites shows
that they contain silver “near-wall” form and nanoparticles weakly connected with the membrane surface. 相似文献
2.
Multivariate analysis of HT/GC-(IT)MS chromatographic profiles of triacylglycerol for classification of olive oil varieties 总被引:1,自引:0,他引:1
Cristina Ruiz-Samblás Luis Cuadros-Rodríguez Antonio González-Casado Francisco de Paula Rodríguez García Paulina de la Mata-Espinosa Juan Manuel Bosque-Sendra 《Analytical and bioanalytical chemistry》2011,399(6):2093-2103
The ability of multivariate analysis methods such as hierarchical cluster analysis, principal component analysis and partial
least squares-discriminant analysis (PLS-DA) to achieve olive oil classification based on the olive fruit varieties from their
triacylglycerols profile, have been investigated. The variations in the raw chromatographic data sets of 56 olive oil samples
were studied by high-temperature gas chromatography with (ion trap) mass spectrometry detection. The olive oil samples were
of four different categories (“extra-virgin olive oil”, “virgin olive oil”, “olive oil” and “olive-pomace” oil), and for the
“extra-virgin” category, six different well-identified olive oil varieties (“hojiblanca”, “manzanilla”, “picual”, “cornicabra”,
“arbequina” and “frantoio”) and some blends of unidentified varieties. Moreover, by pre-processing methods of chemometric
(to linearise the response of the variables) such as peak-shifting, baseline (weighted least squares) and mean centering,
it was possible to improve the model and grouping between different varieties of olive oils. By using the first three principal
components, it was possible to account for 79.50% of the information on the original data. The fitted PLS-DA model succeeded
in classifying the samples. Correct classification rates were assessed by cross-validation. 相似文献
3.
Petr Kluson Hana Luskova Libor Cerveny Tomas Cajthaml 《Reaction Kinetics and Catalysis Letters》2005,86(2):281-289
Summary Unexpected photocatalytic properties of templated precursors of nanostructured TiO2(titania) were observed in the development of a generally applicable method for the synthesis of a truly nanocrystalline titania
at temperatures compatible with plastic catalytic supports. It specifically comprised the “self-activation”feature of the
TiO2nanostructured precursor (produced within the non-ionic surfactant template) likely induced by the preparation method “imprinted”photoactivity.
Such behavior complied with the principal aim to develop the photocatalytic material without recourse to any significant thermal
step. 相似文献
4.
Victor V. Dotsenko Sergey G. Krivokolysko Victor P. Litvinov 《Monatshefte für Chemie / Chemical Monthly》2008,139(6):657-661
Morpholinium 3-cyano-4-methyl-6-oxo-1,6-dihydropyridine-2-thiolate upon treatment with primary amines and a formaldehyde excess
under mild conditions produces bis(pyrido[2,1-b][1,3,5]thiadiazin-7-yl)methane derivatives in good yields (67–87%).
Correspondence: Victor V. Dotsenko, State Enterprise “Luganskstandartmetrology”, 91021 Lugansk, Ukraine. 相似文献
5.
Summary The enantiomers of chiral carboxylic acids were separated as their diastereomeric amides with (1R,2R)-(−)-1-(4-nitrophenyl)-2-amino-1,3-propanediol
(“levobase”) and with “dextrobase” (the enantiomer of levobase) by high-performance liquid chromatography using a conventional
C-18 column and various solvent systems containing acetonitrile, methanol, water, and phosphoric acid. 相似文献
6.
Alevtina T. Mevkh Alla K. Yuskovich Vladlen S. Duzhenko Elena D. Lee Arcadiy L. Vertkin Irina A. Pishkina 《Applied biochemistry and biotechnology》1996,61(1-2):199-204
To check the proposed hypothesis that the relative content of individual polyunsaturated fatty acids (PUFAs)—substrates and
inhibi tors of prostanoid synthesis—in plasma can be regarded as a quantita tive risk factor of blood clotting, a test was
conducted on free fatty acids content in blood plasma of healthy people (group 0) and patients with heart ischemia before
(group 1) and after (group 2) they were treated for a month with a food additive called “Eiconol,” enriched with PUFA ω3.
Different proportions of PUF As have been calculated in all cases, accounting for the contribution of each acid to the process
of primary clotting. Comparison of PUFA rations among the three groups showed significant differences of means between groups
0 and 1 and also group 1 and 2 for 6 out of 7 proposed coefficients, which disappeared after “Eiconol” treatment (comparison
of groups 0 and 2). The results led to the conclusion that out of the proposed PUFA proportions, the coefficients describing
the relative content of arachidonic acid in blood plasma may be the most informative for diagnosis and treatment efficiency
in evaluation of heart and vascular diseases. 相似文献
7.
Characterization of groundwater humic and fulvic acids of different origin by GPC with UV/Vis and fluorescence detection 总被引:1,自引:0,他引:1
R. Artinger G. Buckau J. I. Kim S. Geyer 《Fresenius' Journal of Analytical Chemistry》1999,364(8):737-745
Gel permeation chromatography (GPC) was applied for recognizing the origin of groundwater humic and fulvic acids. GPC was
performed with Fraktogel TSK HW-50 in 0.1 M NaCl, pH 8.5 (0.05 M phosphate buffer), 1 mM EDTA, with 10% by volume methanol
added. Humic substances from groundwaters and sediments of four different aquifer systems in Germany were isolated, purified
and characterized. Both UV/Vis and fluorescence detection were applied. UV/Vis detection was found to be more powerful in
identifying differences between the various humic and fulvic acids. The four aquifer systems investigated (“Gorleben”, “Fuhrberg”,
“Franconian Albvorland” and “Munich”) differed from one another with respect to hydrological and geochemical conditions. The
results showed that the GPC-elution behavior reflects the geochemical environment and origin (source material and generation
process) of aquatic humic and fulvic acids.
Received: 17 November 1998 / Revised: 18 March 1999 / Accepted 23 March 1999 相似文献
8.
Jianhua Zu Zhiqiang Hu Weitao Wang Jianqiu Zhang E. S. Pino Jianzhong Gu Long Tong 《Journal of Radioanalytical and Nuclear Chemistry》2007,273(2):479-484
A kind of ion-exchange membrane with strong acid and weak acid groups was prepared by radiation-induced grafting of acrylic
acid (AA) and sodium styrene sulfonate (SSS) onto high-density polyethylene membrane (HDPE). The effect of additives such
as sodium acetate, sodium chloride on grafting yield was studied. It was found that for either pre-irradiation method or simultaneous
radiation method, the weak acid salt of strong alkali sodium acetate had a complex effect on the grafting yield by “pH effect”
and “ion pair effect”, and the neutral salt sodium chloride was helpful to the increase of grafting yield by “ion pair effect”. 相似文献
9.
Thermal analysis of the two systems, (NaF/AlF3)-FeF3 and (NaF/AlF3)-FeO, was carried out with three different cryolite ratios. In these systems, “impurity compounds” decreased the temperature
of primary crystallisation with decreasing cryolite ratios. From the slope of the dependencies, it can be assumed that the
excess of AlF3 plays a more significant role in changes in the “Fe(III)” systems than in “Fe(II)” systems. 相似文献
10.
Yinqiu Zhen Sheng-e Wang Wenxiang Xiao Hongyan Yuan Dan Xiao 《Mikrochimica acta》2007,159(3-4):305-310
Based on the Nash reagent embedded in silica gel beads as a recognition element, a fluorescent dosimeter for formaldehyde
determination is established. The system can act as a fluorescent off–on switch for the qualitative detection of formaldehyde.
The fluorescence emission of the Nash reagent-loaded silica gel beads is “switches off” (or very low) before exposure to formaldehyde,
while fluorescence can be switched on when the beads are contacted with formaldehyde. The slope of fluorescence time scan
spectra changes with formaldehyde concentration, which constitutes the basis of quantitative determination of formaldehyde
concentration. The formaldehyde can also be semi-quantitatively measured in a naked-eye-detectable fashion. No response of
this dosimeter to primary alcohols, ketones and other common substances was observed. The dosimeter is sensitive, inexpensive,
a disposable, and simple in operation. 相似文献
11.
A hypothesis on the correlation between the origin of “cold” (∼53 K) water molecules released by a growing crack and a low
(∼123 K) temperature of stretched and then thermoelastically cooled polymer chains that ruptured at the crack top is advanced.
A mechanism behind the formation of “cold” water molecules is suggested. It includes their “soft” desorption due to mechanical
action onto thermoelastically cooled side groups with adsorbed cooled water molecules from an unloading wave that is induced
by the rupture of the main chain and that travels along it. 相似文献
12.
Chromatography: The separation technique of the 20th century 总被引:3,自引:0,他引:3
L. S. Ettre 《Chromatographia》2000,51(1-2):7-17
Summary M. S. Tswett contemplated the possibility of “chromatography” in 1899–1901 while carrying out his first research work on the
physico-chemical structure of plant chlorophylls, and he reported “on a new category of adsorption analysis” in 1903. The
evolution of chromatography followed the advances of this century: each decade brought new innovations based logically from
the previous one. By the end of the 20th Century chromatography has became the most widely used separation technique in chemistry
and biochemistry: thus, it is no exaggeration to call it the separation technique of the 20th Century. This paper investigates
the evolution of the various branches of chromatography.
An essential condition for all fruitful research is to have at one’s disposal a satisfactory technique. “Tout progrès scientific
est un progrès de méthode” as somebody once remarked. Unfortunately the methodology is frequently the weakest aspect of scientific
investigations. 相似文献
13.
P. G. Khalatur V. A. Ivanov N. P. Shusharina A. R. Khokhlov 《Russian Chemical Bulletin》1998,47(5):855-860
The model ofAB copolymers with a “protein-like” primary sequence was developed. This type of copolymers was obtained in a computer experiment.
First, the conformation of a collapsed dense homopolymer globule was generated and then, based on this conformation, the primaryAB sequence was determied by denoting the monomeric units located near the surface of the globule as unitsA and those constituting the core of the globule as unitsB. After that, the primary structure of the chain was fixed, and different interaction potentials for theA andB units were introduced. Drawing an analogy of this model to aqueous solutions of globular proteins,A units were interpreted as hydrophilic, andB units were regarded as hydrophobic. By means of Monte Carlo simulation using the bond fluctuation model, the coli—globule
transition in “protein-like”AB copolymer, induced by an increase in the attraction between the hydrophobicB units, was studied. The coil—globule transition in a copolymer with the “protein-like” primary sequence occurs at a higher
temperature and has higher rate and is sharper than that in a random copolymer with the sameA/B composition and in a random block copolymer with the sameA/B composition and the same “degree of blockiness”.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 884–889, May, 1998. 相似文献
14.
The current development and future prospects of nanotechnology are discussed with special emphasis on the pros and cons of the “bottom-up” and “top-down” approaches to nanotechnology, and the eventual merging of the two, at the scale of about 30 nm in feature size, to form a new “hybrid” technology. At the scale of about 3 nm in feature size, this “hybrid” technology will be challenged by the emerging “supramolecular” and “molecular” technologies epitomized by large-scale integration of single-molecule devices. Ultimately the “supramolecular” and “molecular” technologies will yield to “atomic” or “nuclear” technologies at the dimension of below 0.3 nm whereby single-atom, single-electron, single-spin, single-photon devices become realities. 相似文献
15.
Roman G. Efremov Gérard Vergoten Alexander S. Arseniev 《Theoretical chemistry accounts》1999,101(1-3):73-76
We present a “hydrophobic template” method enabling recognition of α-helix bundles in membrane channels from sequence analysis.
Inspection of hydrophobic properties of pore-forming helices in proteins with known structure (A-B5 toxins) permits delineation of a common polarity motif: two hydrophobic surface stretches separated by polar areas. The bundles
are stabilized by nonpolar interhelical contacts. A number of transmembrane segments were checked for presence of this motif,
and it was detected for pore-forming helices of several ion transporters (segments M2 of acetylcholine and GABAA receptors, α5 peptide of δ-endotoxin), which reveal five α-helix bundle architecture. Applications of the method to modeling
of membrane channels are discussed.
Received: 24 April 1998 / Accepted: 3 September 1998 / Published online: 7 December 1998 相似文献
16.
Oana Moldovan Pedro Lameiras Eric Henon Flavia Popa Agathe Martinez Dominique Harakat Carmen Sacalis Yvan Ramondenc Mircea Darabantu 《Central European Journal of Chemistry》2012,10(4):1119-1136
The highly chemoselective preparation of new elaborated N-unsymmetrically substituted chlorodiamino-s-triazines and melamines, seen as building-blocks for iterative synthesis, is reported. It consisted of amination of cyanuric
chloride with commercial C-2-substituted 2-aminopropane-1,3-diols (“serinols”), playing the role as “open-chain” unit and enantiopure (1S,2S)-2-amino-1-(4-nitrophenyl)propane-1,3-diols (“p-nitrophenylserinols”) based amino-1,3-dioxanes (“closed-chain” unit). Issued from the restricted rotation about C(s-triazine)-N(exocyclic) partial double bonds, seen as axes of (pro)diastereomerism,
a global four-component rotational equilibrium involving the title compounds is discussed based on DFT computation and (VT)
NMR data. Depending on π-deficiency of the s-triazine core, an (un)synchronised deblocking of the generated rotational diastereomers was observed. They are discussed
as influence of intra-vs. intermolecular NH...OH (dynamic) interactions occurring in the “open-chain” unit and the anancomeric, axial vs. equatorial, amino-anchorage of the “closed-chain” unit.
相似文献
17.
When pine wood decayed by white- and brown-rot fungi was observed in TEM after fixation and staining with glutaraldehyde/osmium
tetroxide/ uranylacetate and embedding in Spurr’s ultralow viscosity resin electron dense particles, called “osmiophilic particles,”
a typical distribution for the two decay types could be observed: in white-rotted wood the particles could be found in and
around the hyphae and on the lumen surface of the wood cell wall, mostly aggregated to thick clusters. During the whole course
of decay the wood cell walls were free of the particles, but they were present on the corroded surfaces. In brown-rotted wood
the “osmiophilic particles” also could be found in and around the hyphae, but in contrast the particles were distributed over
all the wood cell wall layers from the early to late stages of decay.
The distribution of the “osmiophilic particles” coincides with the place where the major cell wall degradation takes place:
in white-rot the cell walls are degraded from the lumen to the middle lamella; in brown-rot a depolymerization and degradation
of the carbohydrates takes place all over the wood cell wall. Since the “osmiophilic particles” can be found where the degradation
takes place, it can be concluded that they are causally connected with wood decay.
The fact that they also were found in, and some of them also around, hyphae grown on malt-agar or Sabouraud-dextrose-agar
proves that they are produced by the fungi and cannot be degradation products.
The possibility that they could be preparative artifacts can be excluded because uncolonized wood was free of “osmiophilic
particles.”
Since the “osmiophilic particles” are produced by the fungi and can be found in places where wood is decaying, it can be further
concluded that they are a fungal agent that is involved in wood degradation, probably fungal enzymes. The observation that
the large “osmiophilic particles,” which may have a size of up to 20 nm, are composed of globular subunits of a diameter of
2—3 nm also speaks for their enzymatic nature.
To find out which type of enzyme they might be, the white-rot fungusTrametes hirsuta was grown on wood pulp with 7% lignin, on delignified wood pulp containing cellulose and hemicellulose, and on filterpaper
(pure cellulose). The hyphae on wood pulp containing 7% lignin were surrounded by thick sheaths of “osmiophilic particles,”
whereas with the hyphae grown on delignified wood pulp and pure cellulose only a few particles could be found. This makes
it clear that the production of the “osmiophilic particles” is induced by lignin. 相似文献
18.
A flow-injection method is proposed for the simultaneous catalytic determination of formaldehyde and methanol on the basis
of the catalytic action of formaldehyde upon the redox reaction between crystal violet and potassium bromate in a phosphoric
acid medium and on-line oxidization of methanol into formaldehyde using a lead dioxide solid-phase reactor. The indicator
reaction is monitored spectrophotometrically by measuring the decrease in the absorbance of crystal violet at the maximum
absorption wavelength of 610 nm. A technique based on three sampling loops with a single injection valve is developed. The
flow-injection system produces a signal of main peak with two shoulders of the same height. The height of the shoulders corresponds
to the formaldehyde concentration, and the height difference between the shoulders and the main peak corresponds to the methanol
concentration. The detection limit is 0.1 μg/mL for formaldehyde and 1.0 μg/mL for methanol with the sampling rate of 10 samples
per hour. The relative standard deviations for 11 replicate determinations of formaldehyde (1.0 μg/mL) and methanol (10 μg/mL)
are 1.1 and 2.1%, respectively. The method has been successfully applied to the simultaneous determination of formaldehyde
and methanol in some gas samples.
The text was submitted by the authors in English. 相似文献
19.
A. A. Khassin T. M. Yurieva V. I. Zaikovskii V. N. Parmon 《Reaction Kinetics and Catalysis Letters》1998,64(1):63-71
The behavior of Co−MgO catalysts in the reaction of CO disproportionation was studied in the temperature range up to 800°C.
Two temperature regions that differ by the morphology of graphite produced (“egg-shells” or nanotubes) were detected. The
experimental data obtained were analyzed in terms of the phase equilibria “amorphous carbon”—“carbon solution in metallic
Co” and “graphite”— “carbon solution in metallic Co”. Under certain assumptions, the Co° particles are considered to dissolve
amorphous carbon under the reaction conditions and transform to oversaturated fluidized carbon-cobalt solution, these fluidized
particles being responsible for the formation of carbon nanotubes. 相似文献
20.
N. E. Bores M. K. Schultz J. M. Rankin A. J. Denton G. F. Payne 《Journal of Radioanalytical and Nuclear Chemistry》2009,282(3):985-990
The Intercomparison Studies Program (ISP) at the Oak Ridge National Laboratory (ORNL, Oak Ridge, TN USA) provides natural-matrix
human urine quality-assurance/quality-control (QA/QC) samples to radiobioassay analysis laboratories. Samples are provided
to these laboratories as “single-blind” or “double-blind” unknowns, spiked with radioactive-solution standards at “low” levels
(e.g., 0.7–7 Bq g−1 for 3H and 0.7–7 Bq kg−1 for 90Sr). Participants use the results as a tool for self-evaluation and a measure of performance. In this paper, sample preparation
and the results of testing during the years 2001–2005 for 3H and 90Sr are presented and discussed. 相似文献