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1.
The analysis of the interaction of micelles formed by a blockcopolymer is given by means of small-angle X-ray (SAXS) and
small-angle neutron scattering (SANS). The blockcopolymer consists of poly(styrene) and poly(ethylene oxide) (molecular weight
of each block: 1000 g/mol) and forms well-defined micelles (weight-association number: 400, weight-average diameter: 15.4 nm)
in water. The internal structure has been studied previously (Macromolecules 29:4006 (1996)) by SAXS. There it has been shown
that the micelles are spherical objects. The structure factor S(q) as a function of the scattering vector q (q=(4π/λ) sin (θ/2); λ: wavelength of the radiation in the medium; θ: scattering angle) can be extracted from both sets of small-angle
scattering data (SANS: q≤0.4 nm-1; SAXS: q≤0.6 nm-1). It is shown that particle interaction in the present system can be described by assuming soft interaction which is modeled
by a square-step potential.
Received: 12 May 1997 Accepted: 9 July 1997 相似文献
2.
Sol and Gel state properties of aqueous gelatin solutions of concentrations 4%, 6%, 8% and 10% (w/v) have been investigated
through dielectric relaxation studies done at various temperatures in the range T=20–60 °C carried out over a frequency range f=20 Hz–10 MHz and no relaxation of any nature was observed. The sharp transition observed at the gelation temperature T
gel provided an excellent matching with the same measured through differential scanning calorimetry (DSC). The capacitance (C
p) values above f=100 kHz became increasingly negative as the gel was melted to the sol state. However, in the gel state C
p was found to be almost independent of temperature for frequencies above 100 kHz. At frequencies lower than 10 kHz, C
p measured was ∼105 F, implying pronounced interfacial polarization either due to electro-chemical reaction or because of ions getting trapped
at some interface within the bulk.
Received: 10 February 1997 Accepted: 2 September 1997 相似文献
3.
A. N. Araújo José A. M. Catita José L. F. C. Lima Elias A. G. Zagatto 《Fresenius' Journal of Analytical Chemistry》1998,360(1):100-103
A monosegmented flow system (MCFA) is proposed to achieve slow enzymatic spectrophotometric determinations, here applied
to the determination of triglycerides in blood serum. The sample (4.5 μL), enzymatic reagent (150 μL) and an air plug (100 μL)
are simultaneously inserted into a carrier stream buffered to pH 7.9 (Tris ⋅ HCl). In order to avoid the cumbersome step of
air removal, a relocating detector was used. This system handles about 60 samples/h, yielding precise results (r.s.d. usually<2.5%).
Sensitivity is 56 mAU ⋅ L/mmol up to 6 mmol/L triglycerides. Accuracy was assessed by running 50 samples already analysed
by a conventional procedure yielding the equation CMCFA(mmol/L)=1.00(±0.04) CRef(mmol/L)−0.03(±0.08); r=0.990.
Received: 22 January 1997/Revised: 12 March 1997/Accepted: 28 March 1997 相似文献
4.
Crystal hardness and average distance between stable entanglements in melt crystallized polyethylene
Microhardness of a series of linear PE samples with a wide range of molecular weights has been determined. The influence
of the mode of crystallization from the melt on the mechanical properties has been examined. It is shown that crystal hardness
is correlated to the thickness of the amorphous layer for each series of samples. A new expression which describes the microhardness
(H) of polyethylene as a function of the average distance between stable entanglements (knots) s is proposed. A value of s=360 Å, for the mean length between knots in the network is obtained. Analysis of data reveals that the H value can be expressed in terms of the following morphological parameters: 1) average number of chain folds in a lamellar
crystal, 2) the nature of the interface between the crystalline and the amorphous layer and 3) the linear crystallinity.
Received: 6 May 1996 Accepted: 2 December 1996 相似文献
5.
The hydrolysis of SbCl3 in hydrochloric acid solution (2.0 mol dm-3 HCl) at 0 °C yields an amor-phous product consisting of uniform spherical particles (d∼0.5 μm), which on continuous aging at the same temperature transform to larger crystals, indicated by XRD to be Sb4O5Cl2. In contrast, in the same solution kept at 25 °C crystalline particles of the same composition form directly after an induction
period and then grow with time. The final products, obtained at 0 °C and 25 °C consist of aggregated subunits. These powders
on calcination in nitrogen are converted to Sb2O3 and in air to Sb2O4.
Received: 23 June 1997 Accepted: 1 July 1997 相似文献
6.
Al-Dirbashi OY Al-Hassnan ZN Rashed MS 《Analytical and bioanalytical chemistry》2006,386(7-8):2013-2017
A liquid chromatography tandem mass spectrometric method is described for the analysis of homocitrulline in human urine, a
key metabolite in the differential diagnosis of hyperammonemia, hyperornithinemia, homocitrullinuria (HHH) syndrome. Urine
samples were prepared by mere five-fold dilution with a mixture of internal standards (2H2-citrulline and 2H3-creatinine) used for the simultaneous quantification of creatinine. Analytes were separated on a cyano column and eluted
isocratically within seven min. Detection was achieved by monitoring transitions of 190 > 84 and 190 > 127 for homocitrulline,
178 > 115 for 2H2-citrulline, 114 > 44 for creatinine and 117 > 47 for 2H3-creatinine. Calibration curves were linear up to 100 micromol/L. Intraday (n = 7) and interday (n = 6) variations were less than 10%. In urine samples from three siblings confirmed to have HHH syndrome, homocitrulline levels
were at 13.3 (74), 21.1 (50) and 108.2 (103) mmol/mol creatinine (micromol/L). Control values were 0–9 mmol/mol creatinine
(n = 120). The current method solves specificity issues in homocitrulline determination often encountered with some ninhydrin-based
systems (coelution with methionine) and some o-phthalaldehyde-based ones (coelution with taurine), and presents an attractive alternative with a relatively high throughput. 相似文献
7.
8.
A novel surfactant peptide consisting of an arginine cation with laurate anion has been synthesized, purified and characterized.
The critical micellar concentration (cmc) of peptide in aqueous solutions has been determined using spectroscopic techniques
and is found to increase from 0.06 to 0.11 mM with increasing temperature (15–45 °C). Cmc is also determined in the presence
of salts like NaCl, KCl and sodium acetate and it is found that these electrolytes hinder aggregation with a significant increase
in the case of sodium acetate. The aggregation number of the surfactant peptide has been determined using fluorescence quenching
measurements and is observed to decrease from 14 to 6 with increasing temperature (15–45 °C). The standard free energy change
(ΔG
0
m) and standard enthalpy change (ΔH
0
m) of the peptide aggregate are found to be negative with a small positive value for standard entropy change (ΔS
0
m). The peptide aggregate seems to undergo phase transition above 50 °C as observed from UV–vis and fluorescence spectroscopy.
From pyrene binding studies, it is shown that the interior dielectric constant increases from 5.08 at 34 °C to 8.77 at 50 °C
and further decreases with increase in temperature indicating a phase change at 50 °C. Also, the ratio of excimer intensity
to monomer intensity, which is a measure of microviscosity of the aggregate, decreases with increase in temperature with a
change at 50 °C indicating a phase change.
Received: 14 February 1997 Accepted: 13 August 1997 相似文献
9.
P. C. Schulz M. A. Morini M. E. Gschaider de Ferreira 《Colloid and polymer science》1998,276(3):232-238
The system dodecyltrimethylammonium hydroxide (DTAOH)–water was studied by surface tension, ion-selective electrodes and
evaporation in an electrobalance. Results confirmed earlier conclusions about a stepwise aggregation mechanism in DTAOH solutions.
The aggregation process started at a total concentration C
T=(2.51±0.10)×10-4 mol dm-3) which probably corresponds to the formation of dimers. At C
T= (1.300±0.041)×10-3 mol dm-3 there was a change in the surface and evaporation behavior, corresponding to the formation of small, fully ionized aggregates
which grew with increasing concentration. At C
T= (1.108±0.010)×10-2 mol dm-3 the formation of true micelles with hydroxide counterions in the Stern layer did not change significantly the evaporation
and adsorption behavior. This means that between this concentration and C
T=(3.02±0.28)× M28.8n10-2 mol dm-3, the changes in structure were gradual. At the latter concentration there was a sudden change in the monolayer state at the
air/water interface, with a strong surfactant desorption, and a major change in evaporation behavior. The changes are compatible
with the formation of few, large aggregates reducing the total concentration of kinetically independent solute units, which
in turn increased the activity of the solvent. This phenomenon is in agreement with literature information. The reduction
in the evaporation rate of water was mainly due to the reduction of the water activity, caused by colligative effects. The
reduction of the effective area available for evaporation had only a slight effect in water evaporation.
Received: 9 January 1997 Accepted: 19 October 1997 相似文献
10.
A flow analysis system with an amperometric H2S detector and a gas extraction unit as well as an integrated coulometric calibration unit is described, which allows an on-line
determination of hydrogen sulphide in aquatic samples. By variation of different parameters (e.g. flow rate, gas injection
volume, pH of solution) a wide dynamic working range of concentrations from 1 μmol/l H2S to 750 μmol/l is accessible. The sampling rate is about 36 samples h−1 using an average flow rate of 1.78 ml/min and a gas injection volume of 28 μl. The measuring system is designed as a portable
device. In combination with the polyethylene-tube of a PTFE-underwater pump field-measurements on board are possible.
Received: 16 February 1995/Revised: 5 April 1995/Accepted: 11 April 1995
Acknowledgements. This work was supported by the Bundesminister für Forschung und Technologie under the project “DYSMON II” (03F0123D) and
by the Fonds der Chemischen Industrie zur F?rderung von Chemie und Biologischer Chemie.
Correspondence to: P. Jeroschewski 相似文献
11.
A column preconcentration method has been established for the spectrophotometric determination of traces of nitrite using
diazotization and coupling on an naphthalene-tetradecyldimethylbenzylammonium (TDBA)-iodide (I) adsorbent. Nitrite ion reacts
with sulfanilic acid (SA) in the pH range 1.8–3.0 for the SA-1-naphthol system and in the pH range 2.3–3.2 for the SA-1-naphthylamine-4-sulfonate
system (SA-NAS system) in hydrochloric acid medium to form water-soluble colourless diazonium cations. These cations were
coupled with 1-naphthol in the pH range 1.6–4.6 and with NAS in the pH range 2.6–5.0 to be retained on naphthalene-TDBA-I
packed in a column. The solid mass was dissolved from the column with 5 mL of dimethylformamide (DMF) and the absorbance measured
at 418 nm for the SA-1-naphthol system and at 485 nm for the SA-NAS system. The calibration curve was linear over the concentration
range 0.02–0.87 mg/L for SA-1-naphthol and 0.02–0.80 mg/L in the sample for SA-NAS. The molar absorptivity was calculated
to be 1.70×104 L mol-1 cm-1 for SA-1-naphthol and 1.66×104 L mol-1 cm-1 for SA-NAS. The detection limits were found to be 0.014 and 0.016 mg/L for SA-1-naphthol and SA-NAS, respectively. The preconcentration
factors were 8 and 6 for SA-1-naphthol and SA-NAS, respectively. Replicate determinations of seven sample solutions containing
6.6 μg of nitrite for SA-1-naphthol and 5.3 μg of nitrite for SA-NAS gave mean absorbances of 0.486 and 0.382 with relative
standard deviations of 0.49 and 0.58%, respectively. Interferences due to various foreign ions have been studied and the method
has been applied to the determination of 27–65 μg/L levels of nitrite in natural waters. The recovery and relative standard
deviation for water samples were 98–102% and 0.49–0.58% for both systems.
Received: 1 December 1995/Revised: 22 April 1996/Accepted: 22 April 1996 相似文献
12.
Sorption of copper on filter-paper with chemically attached hexamethylenediamino-groups (HMDA-filter) allows to obtain the
sorbent (Cu/HMDA-filter) stable in respect to desorption of copper. A nitrogen-containing herbicide imazapyr (imaz) is retained on Cu/HMDA-filters at pH 5.5–7.0 forming a relatively stable complex. Imazapyr is determined directly on the
sorbent by its activating effect in the oxidation of hydroquinone with H2O2 catalyzed by Cu(II) with the formation of a product absorbing at 490 nm. The copper ions serve both to preconcentrate imazapyr
and to catalyze the indicator reaction. The use of 1-μL sample aliquots pipetted onto the Cu/HMDA-filters allows to determine
1 × 10−3–0.03 μmol of imazapyr, whereas preconcentration of the analyte by pumping of its solution through the same sorbent expands
the linear range to 1 × 10−4–1 × 10−1 μmol of imazapyr. When the indicator reaction is carried out in solution, the range of activating action of imazapyr is narrower
(0.06–0.1 μmol a for a solution volume of 10 mL). The determination is selective: 5–100-fold amounts of amines, aminoacids,
carboxylic acid derivatives and other model compounds do not interfere. Soil extracts and carrot juice samples spiked with
imazapyr have been analyzed.
Received January 10, 2000. Revision July 28, 2000. 相似文献
13.
Robert Koeber R. Niessner Josep Maria Bayona 《Analytical and bioanalytical chemistry》1997,359(3):267-273
The performance of two liquid chromatography-mass spectrometry (LC/MS) interfacing techniques, thermospray (TSP) and atmospheric
pressure chemical ionization (APCI), for the analysis of benzo[a]pyrene (BaP) metabolites (hydroxy, epoxy and quinone derivatives) was compared. Interface and detection parameters such as
source temperature, eluent composition or flow rate were optimized using negative ion mode. In TSP, the main ions are mostly
[M]-, [M−H2O]- or [M+CH3COO]-, whereas APCI gives mainly the [M]- and [M−H]- ions. Quantification was carried out by flow injection. Calibration graphs were linear in the range of 10 ng to 1000 ng in
TSP and 0.1 ng to 10 ng in APCI. Detection limits were in the range of 1 ng to 20 ng in TSP and 0.002 ng to 0.2 ng in APCI.
The presence of BaP-1,6-dione, BaP-3,6-dione, and BaP-6,12-dione was confirmed in environmental samples of air particulate
matter.
Received: 6 January 1997/Accepted: 18 April 1997 相似文献
14.
Many semicrystalline polymers undergo a process of aging when they are stored at temperatures higher than their glass-transition
temperature (T
g). Syndiotactic polypropylene was quenched from the melt to −40 °C, crystallized from the glassy state at 20 or 40 °C and
stored at the respective temperature for different aging times up to 7200 h. A significant increase in the tensile modulus
and stress at yield and a decrease in strain at yield were observed for both aging temperatures. Differential scanning calorimetry
(DSC) scans of aged material showed an endothermic annealing peak 15–30 °C above the previous aging temperature, the maximum
temperature and enthalpic content of which increased with aging time. The position and the shape of the melting peak were
not affected by aging. Scans of the storage modulus obtained from dynamic mechanical analyser measurements indicated a softening
process starting at about 20 °C above the aging temperature and correlating with the annealing peak detected by DSC. Density
measurements and wide-angle X-ray scattering investigations revealed that neither the crystallinity increased significantly
nor did the crystal structure change. So the observed property changes induced by aging are attributed to microstructural
changes within the amorphous phase. Furthermore, it could be shown by annealing experiments carried out at 60 °C, that aging
above T
g is, analogous to aging below T
g (physical aging), a thermoreversible process.
Received: 18 September 2000 Accepted: 2 January 2001 相似文献
15.
Christopher J. G. Plummer Rudolf Gensler Hans-Henning Kausch 《Colloid and polymer science》1997,275(11):1068-1077
Melt crystallized isotactic polypropylene thin films of thickness between 30 and 100 nm have been investigated by high-resolution
transmission electron microscopy at room temperature. The c-axis projection of the 2*31 helices and their packing in the lattice were clearly visible in flat-on lamellae of the α-phase following reconstruction
from the components of the image Fourier transform corresponding to the (1 1 0) and (0 4 0) lattice planes, and the image
power spectra also indicated contributions from (1 3 0) and (0 6 0) relfections, corresponding to a line resolution of about
0.35 nm. These results are discussed in terms of Bloch wave calculations based on the generally accepted structure for the
α-phase. Attempts to obtain lattice images of the β-phase in isotactic polypropylene and melt crystallized syndiotactic polypropylene
under similar operating conditions are also briefly discussed, although these provided relatively little structural information.
Received: 27 June 1997 Accepted: 15 August 1997 相似文献
16.
Robert Koeber R. Niessner Josep Maria Bayona 《Fresenius' Journal of Analytical Chemistry》1997,359(3):267-273
The performance of two liquid chromatography-mass spectrometry (LC/MS) interfacing techniques, thermospray (TSP) and atmospheric
pressure chemical ionization (APCI), for the analysis of benzo[a]pyrene (BaP) metabolites (hydroxy, epoxy and quinone derivatives) was compared. Interface and detection parameters such as
source temperature, eluent composition or flow rate were optimized using negative ion mode. In TSP, the main ions are mostly
[M]-, [M−H2O]- or [M+CH3COO]-, whereas APCI gives mainly the [M]- and [M−H]- ions. Quantification was carried out by flow injection. Calibration graphs were linear in the range of 10 ng to 1000 ng in
TSP and 0.1 ng to 10 ng in APCI. Detection limits were in the range of 1 ng to 20 ng in TSP and 0.002 ng to 0.2 ng in APCI.
The presence of BaP-1,6-dione, BaP-3,6-dione, and BaP-6,12-dione was confirmed in environmental samples of air particulate
matter.
Received: 6 January 1997/Accepted: 18 April 1997 相似文献
17.
In the presence of carbonate and uranine, the chemiluminescent intensity from the reaction of luminol with hydrogen peroxide
was dramatically enhanced in a basic medium. Based on this fact and coupled with the technique of flow-injection analysis,
a highly sensitive method was developed for the determination of carbonate with a wide linear range. The method provided the
determination of carbonate with a wide linear range of 1.0 × 10−10–5.0 × 10−6 mol L−1 and a low detection limit (S/N = 3) of carbonate of 1.2 × 10−11 mol L−1. The average relative standard deviation for 1.0 × 10−9–9.0 × 10−7 mol L−1 of carbonate was 3.7% (n = 11). Combined with the wet oxidation of potassium persulfate, the method was applied to the simultaneous determination
of total inorganic carbon (TIC) and total organic carbon (TOC) in water. The linear ranges for TIC and TOC were 1.2 × 10−6–6.0 × 10−2 mg L−1 and 0.08–30 mg L−1 carbon, respectively. Recoveries of 97.4–106.4% for TIC and 96.0–98.5% for TOC were obtained by adding 5 or 50 mg L−1 of carbon to the water samples. The relative standard deviations (RSDs) were 2.6–4.8% for TIC and 4.6–6.6% for TOC (n = 5). The mechanism of the chemiluminescent reaction was also explored and a reasonable explanation about chemical energy
transfer from luminol to uranine was proposed.
Figure Chemiluminescence profiles in batch system. 1, Injection of 100 μL of K2CO3 into 1.0 mL luminol-1.0 mL H2O2 solution; 2-3 and 4-5, Injection in sequence of 100 μL of K2CO3 and 100 μL of uranine into 1.0 ml luminol-1.0 mL H2O2 solution; Cluminol = 1.0 × 10−7 mol/L, CH2O2 = 1.0 × 10−5 mol/L, Curanine = 1.0 × 10−5 mol/L, CK2CO3 = 1.0 × 10−7 mol/L except for 4-5 where CK2CO3 = 1.0 × 10−4 mol/L 相似文献
18.
Enzyme-linked immunosorbent assay (ELISA), horseradish peroxidase (HRP)-catalyzed fluorescent reaction, and oxalate chemiluminescence
imaging analysis have been combined to develop a sensitive, simple, and rapid method for analysis of interferon alpha (α-IFN)
in human serum samples. A typical “sandwich type” immunoassay was used. Reaction of o-phenylenediamine (OPD) with hydrogen peroxide (H2O2), catalyzed by HRP, produced 2,3-diaminophenazine (PDA), which was detected by chemiluminescence imaging analysis with the
bis(2,4,6-trichlorophenyl)oxalate (TCPO)–H2O2–glyoxaline–PDA chemiluminescent system. The TCPO chemiluminescent imaging system is more sensitive and the chemiluminescence
quantum yield is at least five times higher than for the luminol–H2O2–HRP–PIP (p-iodophenol) chemiluminescent imaging system. The results showed there was a very good linear correlation between response
and amount of α-IFN in the range 1.3–156.0 pg mL−1 (R = 0.9991) and the detection limit was 0.8 pg mL−1 (S/N=3). The relative standard deviation (n = 9) was 4.7%. The proposed method has been used for successful analysis of the amount of α-IFN in human serum. The results
obtained compared well with those obtained by conventional colorimetric ELISA and luminol chemiluminescent ELISA.
Figure Procedures of the proposed method 相似文献
19.
Stefan E. Boiadjiev David A. Lightner 《Monatshefte für Chemie / Chemical Monthly》2002,1(1):1469-1480
Malonic ester derivatives of ethyl and methyl 3,5-dimethyl-4-(1′-iodoneopentyl)-1H-pyrrole-2-carboxylate exhibit restricted rotation about the pyrrole C(4)–C(1′) bond due to the bulky 1′-tert-butyl and malonic ester groups and the ortho effect at C(4) of the sterically crowded 3,5-dimethylpyrrole. The malonates belong to a rare class of atropisomers with restricted rotation about an sp3–sp2 C–C bond, and they undergo diastereomeric separation by TLC and crystallization: the diastereomers are stable in solution at room temperature. A crystal of one of the diastereomers, suitable for X-ray crystallography, gave the relative configuration of the chiral axis and stereogenic center at C(1′). Dynamic NMR studies of the purified diastereomers provide kinetic and thermodynamic parameters associated with the atropisomerism: ΔG ‡ = 132–134 kJ/mol (∼32 kcal/mol) at 383 K in C2D2Cl4 solvent. 相似文献
20.
《Theoretical chemistry accounts》1997,95(5-6):201-213
Summary. Thermal one- and two-bond dissociation processes of cis- and trans-azomethane were studied by ab initio computation with DZP and TZ2P basis sets, using the d(N–C) bond lengths as the reaction coordinates. The geometries were optimized at the MP2 level, and the dissociation energies
obtained exploiting a single-point, fourth-order M?ller–Plesset calculations [MP4SDTQ/TZ2P]. At this level of theory including
zero-point energies, the trans-isomer is by 9.3 kcal/mol more stable than the cis-isomer. The results show that the energetically more favourable one-bond cleavage proceeds without transition state with
the predicted bond dissociation energy D
0 of 47.8 kcal/mol for trans-azomethane and 38.5 kcal/mol for cis-azomethane. With calculated barrier heights the unimolecular dissociation rate constants have been determined by means of
the RRKM theory. The second-order saddle points localized for synchronous decomposition pathways lie 13 (trans)-23(cis) kcal/mol above the one-bond dissociation energies [MP2/DZP].
Received May 28, 1996/Final version received November 1, 1996 / Accepted November 1, 1996 相似文献