共查询到20条相似文献,搜索用时 359 毫秒
1.
Yu. E. Morozova Ya. V. Shalaeva N. A. Makarova V. V. Syakaev E. Kh. Kazakova A. I. Konovalov 《Russian Chemical Bulletin》2009,58(1):95-100
The conditions for the formation and existence of capsular dimeric associates in a solution were studied. The associates are
formed by the oppositely charged resorcinarene derivatives (tetrakis(dimethylaminomethyl)calix[4]resorcinarene hydrochloride
and tetrakis(sulfonato- methyl)calix[4]resorcinarene). Possibilities of formation of a capsule in the presence of the molecules
giving inclusion complexes with one of the macrocycles were considered. Switching between two states “capsular associate—mixture
of original macrocycless” is achieved by controlling the ionic strength of the solution. The interaction of the host—guest
complexes with complementary resorcinarene leads to capsular associate closure with the synchronous displacement of the guest
molecules into the aqueous solution bulk. 相似文献
2.
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
3.
Bahram Hemmateenejad Saeed Yousefinejad 《Analytical and bioanalytical chemistry》2009,394(7):1965-1975
This article describes the use of the net analyte signal (NAS) concept and rank annihilation factor analysis (RAFA) for building
two different multivariate standard addition models called “SANAS” and “SARAF.” In the former, by the definition of a new
subspace, the NAS vector of the analyte of interest in an unknown sample as well as the NAS vectors of samples spiked with
various amounts of the standard solutions are calculated and then their Euclidean norms are plotted against the concentration
of added standard. In this way, a simple linear standard addition graph similar to that in univariate calibration is obtained,
from which the concentration of the analyte in the unknown sample and the analytical figures of merit are readily calculated.
In the SARAF method, the concentration of the analyte in the unknown sample is varied iteratively until the contribution of
the analyte in the response data matrix is completely annihilated. The proposed methods were evaluated by analyzing simulated
absorbance data as well as by the analysis of two indicators in synthetic matrices as experimental data. The resultant predicted
concentrations of unknown samples showed that the SANAS and SARAF methods both produced accurate results with relative errors
of prediction lower than 5% in most cases. 相似文献
4.
Ricardo J. N. Bettencourt da Silva Maria Filomena G. F. C. Camões 《Accreditation and quality assurance》2010,15(12):691-704
The dispersion of results from proficiency tests for the analysis of pesticide residues in foodstuffs suggests that improvements
in the compatibility of measurement results are needed. Currently observed divergences can make the evaluation conclusion
on foodstuffs compliance with certain legislation dependent on the consulted laboratory. This work discusses the origin and
impact of this lack of compatibility, following the metrological concepts presented at the latest version of the “International
Vocabulary of Metrology” (VIM3), thus allowing for a clear diagnostic of the problem. The reporting of results from different
measurement methods uncorrected for the observed analyte recovery makes them traceable to different “operationally defined
measurement procedures” (VIM3) and, therefore, not comparable. When results from different measurement methods are reported
corrected for analyte recovery, R, and R is different for spiked and incurred residues, measurement results may be not compatible if this effect is not considered
on the uncertainty budget. This discussion is illustrated with metrological models for any possible combination of “measurement
performance” and “maximum residue level”. These models are complemented with experimental data of the analysis of pesticide
residues in a sample of ginseng powder from a proficiency test. The adopted experimental design allowed the identification
of additional threats to metrological compatibility in this field. Solutions to the faced problem are discussed for practicability
and impact on regulatory issues. The use of a universal “reference measurement procedure” proves to be the most feasible way
of ensuring comparability of measurements in this field. 相似文献
5.
P. Tighe 《Accreditation and quality assurance》2000,5(12):488-490
The need for “quality” in near patient testing (NPT) has been acknowledged since the mid 1980s. The commonest biochemical
NPT device is the dry reagent strip or “dipstick” for urinalysis. Dipsticks may be read in three ways, against the color chart
printed along the side of the bottle, using a benchreader (the color chart printed on a flat card) or using an electronic
reader. This report uses the results of a urinalysis quality assurance (QA) program, over 1998, to evaluate the “error” rates
which occur using the three different reading methods. The QA samples are buffered aqueous solutions which are “spiked” to
give concentrations midway between two color blocks for each analyte. Results are scored as ±1 if a color block adjacent to
the target value, ±2 for results two color blocks (defined as “error”) and ±3 for results three color blocks (defined as “gross
error”) from the target value. Analysis of the results show that the error rates are similar reading visually by either method,
but greatly reduced when read electronically. Some persisting errors when using the electronic reader are explained by observation
studies. The study highlights the value of a urinalysis QA program for NPT urinalysis in understanding the error rates of
this simple but ubiquitous test.
Received: 10 July 2000 / Accepted: 10 July 2000 相似文献
6.
Liu TC Zhang HL Wang JH Wang HQ Zhang ZH Hua XF Cao YC Luo QM Zhao YD 《Analytical and bioanalytical chemistry》2008,391(8):2819-2824
Mouse anti-human CD71 monoclonal antibody (anti-CD71) was conjugated with red quantum dots (QDs; 5.3 nm, emission wavelength
λ
em = 614 nm) and used to label HeLa cells successfully. Then green QD-labeled goat anti-mouse immunoglobulin G (IgG; the size
of the green QDs was 2.2 nm; λ
em = 544 nm) was added to bind the red-QD-conjugated anti-CD71 on the cell surface by immunoreactions. Such interaction between
anti-CD71 and IgG lasted 4 min and was observed from the fluorescence spectra: the fluorescence intensity of the “red” peak
at 614 nm increased by 32%; meanwhile that of the “green” one at 544 nm decreased by 55%. The ratio of the fluorescence intensities
(I
544 nm/I
614 nm) decreased from 0.5 to 0.2. The fluorescence spectra as well as cell imaging showed that fluorescence resonance energy transfer
took place between these two kinds of QDs on the HeLa cells through interactions between the primary antibody and the secondary
antibody. 相似文献
7.
Shcherbyna SV Bohme DK Baranov VI Loboda A Swartz CR Anthony JE 《Journal of the American Society for Mass Spectrometry》2006,17(2):222-229
A high-performance orthogonal time-of flight (TOF) mass spectrometer, in combination with the matrix assisted laser desorption/ionization
(MALDI) source operating at elevated pressure (∼1 torr in N2), was used to perform MALDI-TOF analyses of pentacene and some of its derivatives with and without an added matrix. These
molecules are among the most interesting semiconductor materials for organic thin film transistor applications (OTFT). The
observation of ion-molecule reactions between “cold” analyte ions and neutral analyte molecules in the gas phase has provided
some insight into the mechanism of pentacene cluster formation and its functionalized derivatives. Furthermore, some of the
matrices employed to assist the desorption/ionization process of these compounds were observed to influence the outcome via
ion-molecule reactions of analyte ions and matrix molecules in the gas phase. The stability and reactivity of the compounds
and their clusters in the MALDI plume during gas-phase expansion were evaluated; possible structures of the resulting clusters
are discussed. The MALDI-TOF technique was also helpful in distinguishing between two isomeric forms of bis-[(triisopropylsilyl)-ethynyl]-pentacene. 相似文献
8.
9.
An approach is proposed for the quantum-chemical investigation of “hydride ion” transfer based on analysis of the similarity
of the order of variation in the ionization potentials, enthalpies, and free energies of affinity to the hydride ion, the
hydrogen atom, and the proton in the substrate molecules and also the derivatives of their cations, radicals, and ions to
the experimentally established “hydride” series. It was established that the experimental “hydride” mobility series of six
chalcogenopyrans based on “semicyclic” 1,5-diketones agrees with the quantum-chemically calculated ionization potentials of
the molecules and with the affinity of the respective radicals to the hydrogen atom participating in the transfer. It was
found that direct removal of a hydride ion and initial deprotonation of the substrates followed by the removal of two electrons
are unlikely. “Hydride” shift mechanisms, in which the first stage is transfer of an electron or hydrogen atom from the chalcogenopyran
molecules, are feasible.
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1305–1311, September, 2005. 相似文献
10.
Alvaro de Jesús Martínez-Gómez Sorin O. Manolache Víctor Gónzalez-Álvarez Raymond A. Young Ferencz Sandor Denes 《Cellulose (London, England)》2009,16(3):501-517
The surface functionalization process was accomplished in a consecutive 3 step process including: (1) Argon- and oxygen-plasma
enhanced generation of free radical sites on cellophane surfaces; (2) “In situ” gas phase derivatization in the absence of
plasma using hydrazine, ethylene diamine, or propylene diamine; (3) Second “in situ”, gas phase derivatization in the absence
of plasma using oxallyl chloride or “ex situ” derivatization in the presence of glutaraldehyde. The presence of free radical
sites on the plasma exposed cellophane surfaces was demonstrated using “in situ” sulfur dioxide and nitric oxide labeling
techniques. It was shown that the free radical sites readily react under “in situ” conditions with the stable chain-precursor
components and generate the desired spacer-chain molecules. ESCA, ATR-FTIR analysis and dying techniques were used to monitor
the cellophane surface changes. A factorial design was used for selecting the optimal plasma parameters. Functionalized cellophane
substrates were used for immobilization of α-chymotrypsin in the presence of spacer-chain molecules. The activity of the immobilized
α-chymotrypsin was found to be lower in comparison to the activity of the free enzyme and the presence of virgin cellophane
in the free enzyme solution also reduced significantly the activity of the enzyme. It is suggested that the swollen state
of the cellophane plays a significant role in the decrease of the immobilized enzyme activity. 相似文献
11.
We demonstrate the synthesis of copper selenide quantum dots (QDs) by element directed, inexpensive, straight forward wet
chemical method which is free from any surfactant or template. Copper selenide QDs have been synthesized by elemental copper
and selenium in the presence of ethylene glycol, hydrazine hydrate, and a defined amount of water at 70 °C within 8 h. The
product is in strong quantum confinement regime, phase analysis, purity and morphology of the product has been well studied
by X-ray diffraction (XRD), UV–Visible spectroscopy (UV–Vis), Photo-luminescent spectroscopy (PL), Fourier transform infrared
spectroscopy (FTIR), Transmission electron microscopy (TEM), High resolution transmission electron microscopy (HRTEM), and
by Atomic force microscopy (AFM) techniques. The absorption and photoluminescence studies display large “blue shift”. TEM
and HRTEM analyses revealed that the QDs diameters are in the range 2–5 nm. Due to the quantum confinement effect copper selenide
QDs could be potential building blocks to construct functional devices and solar cell. The possible mechanism is also discussed. 相似文献
12.
Yan Zhao Juan Gu Wen Hui Xi Rong Huang Bi Jing Hao Shi Hong You Zhu Bang Jing Wang 《Monatshefte für Chemie / Chemical Monthly》2009,35(5):1395-1400
Abstract
Binding behavior of 4,4′-ethylenedianiline-bridged bis(6-amino-6-deoxy-β-cyclodextrin) with seven nonaromatic oligopeptides, i.e., Leu-Gly, Gly-Leu, Glu-Glu, Met-Met, Gly-Gly, Gly-Gly-Gly, and Gly-Pro, was investigated at 25 °C in phosphate buffer (pH 7.20) by fluorescence and 2D NMR spectroscopy. The result obtained from the ROESY spectrum shows that the phenyl moieties in the linker of the bis(β-cyclodextrin) are partly self-included in the cyclodextrin cavity and are entirely expelled out of the cyclodextrin cavity upon complexation with guest oligopeptides. Owing to the cooperative “cyclodextrin–guest–cyclodextrin” sandwich binding mode, the bis(β-cyclodextrin) exhibits relatively high sequence selectivity up to 5.3 for the Gly-Leu/Leu-Gly pair and length-selectivity up to 4.6 for the Gly-Gly-Gly/Gly-Gly pair. The molecular binding ability and selectivity are discussed from the viewpoints of induced fit and multiple recognition between host and guest. 相似文献13.
A method to obtain laser desorption/ionization mass spectra of organic compounds by depositing sample solutions onto a carbon substrate surface is demonstrated. The substrate consists of a thin layer of activated carbon particles immobilized on an aluminum support. In common with the porous carbon suspension samples used in previous “surface-assisted laser desorption/ionization” (SALDI) work, the mass spectra contain only a few “matrix” background ion peaks, minimizing interference with analyte ion peaks. The presence of glycerol ensured that the ion signals were stable over hundreds of laser shots. In addition, the carbon substrate surface has several advantages over the suspension samples. The use of a very thin layer of carbon significantly improves the sensitivity. Detection limits range from attomoles for crystal violet to femtomoles for bradykinin. Very little sample preparation is required as the analyte solution is simply pipetted onto the substrate surface and glycerol added. When using an alternate sample deposition method, a mass resolution for bradykinin of 1800 is achieved in linear time-of-flight mode. This is close to the resolution limit set by the detector system and above instrument specification for matrix-assisted laser desorption/ionization mass spectra. 相似文献
14.
Yan Zhao Juan Gu Yong Cun Yang Hao Shi Hong You Zhu Rong Huang Bi Jing 《Research on Chemical Intermediates》2009,35(5):597-605
Binding behavior of 4,4′-diaminodiphenyl ether-bridged-bis (6-amino-6-deoxy-β-cyclodextrin) 1 with the aliphatic oligopeptides, i.e., Leu-Gly, Gly-Leu, Glu-Glu, Met-Met, Gly-Gly, Gly-Gly-Gly, and Gly-Pro was investigated
at 25°C in phosphate buffer (pH 7.20) by fluorescence and 2-D NMR spectroscopy. Owing to the cooperative “cyclodextrin-guest-cyclodextrin”
sandwich binding mode, bis(β-cyclodextrin) 1 not only afford high binding constants of up to 103–104 M−1 for guest oligopeptides, but can also recognize the size and hydrophobicity of oligopeptides. As a result of multiple recognition
mechanisms, bis(β-cyclodextrin) 1 gives high length-selectivity up to 5.8 for the Gly-Gly-Gly/Gly-Gly pair and sequence-selectivity up to 2.8 for the Gly-Leu/Leu-Gly
pair, respectively. The molecular binding ability and selectivity are discussed from the viewpoints of induced-fit and multiple
recognition between host and guest. 相似文献
15.
Nadira Ibri?imovi? Mirza Ibri?imovi? Margit Barth Ulrich Bohrn 《Monatshefte für Chemie / Chemical Monthly》2010,205(2):125-130
Abstract
Spoilage of products can mainly be attributed to microorganisms which “live on the product”, i.e. which are able to utilize and/or metabolize components and/or molecules of the product. The objective of this work was to develop and optimize sensor prototypes indicating the quality of a product “in real time”, i.e. at the time the consumer is looking at the product. The design of the presented sensors relates to optical phenomena, for example anomalous absorption and remission of light. The crucial point of the sensor prototypes is a layer sensitive to the analyte, a polymer degradable by enzymes produced by the respective microorganisms. After incubation of the sensor setup with contaminated products, the lytic enzymes released from decaying cell material change the thickness of the polymer layer and generate a colour change visible by the naked eye. Production of the sensor prototypes is very simple and inexpensive and they might be successfully integrated into product packaging. 相似文献16.
A large succinic acid (HOOC(CH2)2COOH) matrix containing 7 × 7 × 7 unit cells with guest oligonucleotide AGCAGCT was modeled with molecular dynamics simulation
for infrared matrix-assisted laser desorption ionization. We simulated the laser heating of the succinic acid (this data is
still missing from the literature) with λ=2.94 μm infrared laser pulses and compared it to ultraviolet excitation. We did
this in order to elucidate the cluster formation of succinic acid in the gas phase in itself and around the analyte. At this
wavelength, the laser energy is coupled into the matrix through the OH vibrations of the carboxyl groups. The most pronounced
difference we observed at 1,500 K simulation is that infrared heating generates about 10–15 more succinic acid molecules bound
to the analyte in noncovalent complex form than the ultraviolet mode, which generates about 2 molecules thus bound. We report
energy redistribution within the matrix between the host and guest species as well as other dynamical properties. The parameter
and topology data for succinic acid that we used are reported and ready for use in CHARMM computer code environment for simulation.
Revised: 12 October 2001 / Accepted: 27 February 2002 / Published online: 13 June 2002 相似文献
17.
Total arsenic concentrations in groundwater samples determined by hydride generation quartz furnace atomic absorption spectrometry
may underestimated due to a loss of quartz cell surface “conditioning.” This loss of quartz cell surface “conditioning” is
due to the analysis of many samples that do not contain measurable quantities of the analyte. This process is further accelerated
by the use of high concentrations of sodium tetrahydroborate and hydrochloric acid. Analysis of the highest calibration standard
in between the samples and the use of low concentrations of sodium tetrahydroborate and hydrochloric acid could minimize the
error arising from this source. 相似文献
18.
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
19.
V. E. Kuzmin V. A. Chelombitko I. V. Yudanova I. B. Stelmakh I. S. Rublev 《Journal of Structural Chemistry》1998,39(3):452-456
Stereoanalysis of molecules by partitioning a spatial structure into a system of simplices is described in detail. Potentialities
of simplex representation of molecules in defining stereochemistry are demonstrated for chiral structures of various complexity
and planar unsaturated molecules (“two-dimensional stereochemistry”). A concept of “stereochemical charge” is introduced.
A. V. Bogatskii Physicochemical Institute, Ukrainian Academy of Sciences. Odessa State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 3, pp. 553–558, May–June, 1998. 相似文献
20.
V. V. Zhuikov 《Russian Journal of Electrochemistry》2000,36(2):117-127
Electrochemical reduction of organochlorosilanes and oxidation of hexaorganodisilanes may occur via dissociative and stepwise
mechanisms, the choice between which is determined by the balance between fundamental structural parameters of elementoorganic
molecules. The formation of radical anions of silyl-substituted chloromethane in the conditions of an electrochemical experiment
is shown. The formation is due to α-silicon stabilization of the intermediate during the electron transfer. The role of conjugation
and hyperconjugation in the organosilicon compounds’ reactivity is analyzed.
When employing terms “ stepwise ” and “ dissociative ” mechanisms of the electron transfer, we follow tradition introduced
and developed by J.-M. Saveant’s group [1] and recommended by the IUPAC Commission on Electrochemical Nomenclature [2]. The
terms refer to an electrochemically reversible transfer of electron whose kinetics does not limit the process rate as a whole
and to an electrochemically irreversible transfer which involves a bond cleavage in an elementary act of electron transfer.
The term “ activation ” mechanism, which is sometimes applied to electrochemically irreversible processes, is more universal;
however, it is somewhat not unique as compared with the term “ dissociative.” Coupled with “ associative,” the latter may
be used for indicating processes that involve the formation of a bond in an elementary act of electron transfer. 相似文献