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1.
The specificity of the exchange between divalent (Di2+ = Ca2+ or Ba2+) and monovalent (M+ = Li+, Na+ or K+) ions onto a polyacrylic chain is examined using conductometric and microcalorimetric techniques. Assuming the formation
of a bidentate complex between the Di2+ and the carboxylate groups, the conductometric data give the exchange ratio (Di2+/M+) and the speciation of the acrylic groups. No significant difference is observed between the three alkali-metal ions for
a given Di2+ ion. Comparisons between Ca2+ and Ba2+ show a stronger hydrophobicity of the former as it precipitates at a complexation ratio r = 0.33 versus r = 0.45 for the Ba2+ salt. Microcalorimetric data show that all Di2+/M+ exchange energies are positive and depend significantly on the type of cations. The largest displacement energy (the more
positive) is found for the binding of Ca2+ with sodium polyacrylate (8.13 kJ · mol−1) and the smallest for Ba2+ with lithium polyacrylate (1.88 kJ · mol−1). The interpretation of the data leads to the conclusion that specificity of the Di2+ binding originates in the dehydration phenomenon and specificity between the three alkali-metal ions is due to the decrease
in the electrostatic bond strength with an increase in the ionic radii. The Di2+/M+ exchange is entropically driven.
Received: 28 January 1999 Accepted in revised form: 7 April 1999 相似文献
2.
The alkalization of carboxylated acrylic polymer latexes by sodium hydroxide gives rise to swelling of the particles. For
a poly(n-butyl acrylate) latex copolymerized with 15 wt % methacrylic acid (MAA) and 7 wt % acrylonitrile the particle volume increases
by a factor of 30. The alkali-swelling does not depend on the type of monovalent cation used in the base (LiOH, NaOH, KOH,
NH4OH). In contrast, when bivalent cation bases such as Ca(OH)2 are employed no latex swelling is observed during neutralization because of ionic crosslinking of the copolymer chains. Crosslinking
also takes place when the bivalent cations (Ca2+, Zn2+, Mg2+) are added as chlorides to dispersions with latexes previously swollen by sodium hydroxide. In these experiments the original
size of the latexes is reached again at a molar ratio MAA: bivalent metal ion of 2:1, i.e. at charge compensation of the carboxyl
groups. The shrinking behavior is almost independent of the type of bivalent metal ion used. On the other hand, it is more
pronounced when trivalent cations such as Fe3+ are added. In general, the experiments demonstrate that the alkali swelling of acrylic latexes is dominated by electrostatic
forces.
Received: 18 August 1998 Accepted in revised form: 26 October 1998 相似文献
3.
Binding of a cationic surfactant ion, dodecylpyridinium ion, to poly(acrylic acids) of low charge densities was examined
by potentiometry using surfactant-selective electrodes in the solutions, where the pH was kept constant by employing a pH
buffering system. The binding of the surfactant counterions was thus able to be studied at a constant pH during the binding
process. The binding took place in two steps, the first cooperative binding step and the second gradual binding step. The
critical association concentration decreased as the pH increased, indicating the predominant role of the electric interaction
in the binding. The binding isotherms obtained at different but constant pH values were analyzed by the matrix method, taking
into account the nearest-neighbor interactions among three different kinds of sites on the polymer: ionized, protonated, and
surfactant-bound. The theoretical analysis could describe only the first step but could not explain the second step. A relatively
large cooperativity parameter, u, was found for the first step and it can be between 3 × 103 and 1 × 104. When the ionic strength was decreased tenfold, the cooperativity of the binding decreased (u∼1 × 103). The binding constants of the isolated site were 5.5–6.0 × 104 kg mol−1 and slightly increased to 6.5 × 104 kg mol−1 as the ionic strength decreased. The deviation of the second step from the theoretical analysis was supposed to arise from
a change of proton dissociation constant in the nonpolar space formed by the bound surfactants.
Received: 29 November 2000/Accepted: 24 January 2001 相似文献
4.
The osmotic pressures of –polyelectrolyte solutions without added salt was measured in the concentration ranges 0.001–0.02
and 0.2–1.9 mol kg-1. Our results show that the osmotic coefficients φp were strongly dependent on the chemical structures of polyelectrolyte through the polyion radius and the interaction between
the ionic moiety and counterions. The osmotic pressures in polyelectrolyte solutions without added salt, calculated on the
basis of the counterion contribution, are in agreement with the experimental results. We conclude that the counterion contribution
is dominant in the osmotic pressures and thus, the polymer contribution is negligible in the examined concentration range
0.2–1.9 mol kg-1. The P–B approach gave a fair prediction of the absolute values of the osmotic pressures with λ=4.5, where λ is the charge
density parameter, except for NaPA. In other words, the concentration dependence of the φp values can be explained in terms of the counterion contribution.
Received: 11 June 1997 Accepted: 19 August 1997 相似文献
5.
Caglar P Tuncel SA Malcik N Landers JP Ferrance JP 《Analytical and bioanalytical chemistry》2006,386(5):1303-1312
A newly designed glass-PDMS microchip-based sensor for use in the determination of Ca2+ ions has been developed, utilizing reflectance measurements from arsenazo III (1,8-dihydroxynaphthalene-3,6-disulfonic acid-2,7-bis[(azo-2)-phenyl
arsenic acid]) immobilized on the surface of polymer beads. The beads, produced from cross-linked poly(p-chloromethylstyrene) (PCMS), were covalently modified with polyethylenimine (PEI) to which the Arsenazo III could be adsorbed.
The maximum amount of Arsenazo III which could be immobilized onto the PEI-attached PCMS beads was found to be 373.71 mg g−1 polymer at pH 1. Once fabricated, the beads were utilized at the detection point of the microfluidic sensor device with a
fiber optic assembly for reflectance measurements. Samples were mobilized past the detection point in the sensor where they
interact with the immobilized dye. The sensor could be regenerated and re-used by rinsing with HCl solution. The pH, voltage,
linear range, and the effect of interfering ions were evaluated for Ca2+ determination using this microchip sensor. At the optimum potential, 0.8 kV, and pH 9.0, the linear range of the microchip
sensor was 3.57 × 10−5 – 5.71 × 10−4 M Ca2+, with a limit of detection (LOD) of 2.68 × 10−5 M. The microchip biosensor was then applied for clinical analysis of calcium ions in serum with good results.
Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users. 相似文献
6.
Jiawei Zhang Xiaobin Huang Hao Wei Jianwei Fu Yawen Huang Xiaozhen Tang 《Journal of Solid State Electrochemistry》2012,16(1):101-107
Solid composite polymer electrolytes consisting of polyethylene oxide (PEO), LiClO4, and porous inorganic–organic hybrid poly (cyclotriphosphazene-co-4, 4′-sulfonyldiphenol) (PZS) nanotubes were prepared using the solvent casting method. Differential scanning calorimetry
and scanning electron microscopy were used to determine the characteristics of the composite polymer electrolytes. The ionic
conductivity, lithium ion transference number, and electrochemical stability window can be enhanced after the addition of
PZS nanotubes. The electrochemical impedance showed that the conductivity was improved significantly. Maximum ionic conductivity
values of 1.5 × 10−5 S cm−1 at ambient temperature and 7.8 × 10−4 S cm−1 at 80 °C were obtained with 10 wt.% content of PZS nanotubes, and the lithium ion transference number was 0.35. The good
electrochemical properties of the solid-state composite polymer electrolytes suggested that the porous inorganic–organic hybrid
polyphosphazene nanotubes had a promising use as fillers in SPEs and the PEO10–LiClO4–PZS nanotube solid composite polymer electrolyte might be used as a candidate material for lithium polymer batteries. 相似文献
7.
pH- and ionic-strength-dependent aggregation of permanently and conditionally charged clay mineral (montmorillonite) and
iron oxide (magnetite) particles was investigated by means of dynamic light scattering and rheology. An indifferent electrolyte
(NaCl) was used. The surface charging of solids was determined by acid–base titration. The point of zero charge (PZC) of magnetite
seemed to be at pH 8.0 ± 0.1. The permanent negative charges on the basal plane of montmorillonite influence the interfacial
distribution of H+ and Na+ ions. The pH dependence of the electrophoretic mobility showed directly the dominance of negative charges on montmorillonite
lamellae independently of pH, while for magnetite the sign of the mobility reversed at pH ˜ 8.0. Montmorillonite particles
formed stable suspensions; coagulation did not take place below 35 mM 1:1 electrolyte independently of pH. The aggregation
of magnetite sol becomes significant near the pH of the PZC even at low ionic strength. Colloidal stability in composite systems
was investigated at pH ˜ 4, where oxide and clay mineral particles are oppositely charged. At the lowest NaCl concentrations
(1, 5 mM) the mixed systems remained stable and aggregation of oppositely charged particles could not be observed at all.
Heterocoagulation of dissimilar particles needed a definite amount of dissolved electrolytes (about 8 mM). Mixed clay mineral
and oxide systems are more sensitive to electrolyte under acidic conditions than those separately. Rheological investigation
of the mixed clay mineral–oxide suspensions at pH ˜ 4 provided proof for the absence of attractive particle interaction at
low ionic strength (2 mM). A physical network of oppositely charged particles could form only at higher salt concentration,
for example, in the presence of 10 mM NaCl. The yield value of plastic systems showed a significant maximum at 1:15 magnetite/montmorillonite
mass ratio.
Received: 21 November 2000 Accepted: 20 December 2000 相似文献
8.
Adsorption of iodide ions at the Bi(111) and Cd(0001) electrodes from the aqueous solutions with constant ionic strength 0.1x M KI + 0.1(1−x) M KF and 0.1x M KI + 0.033(1−x) M K2SO4 has been studied by impedance spectroscopy. It was found that, to a first approximation, the classical Frumkin–Melik–Gaikazyan
equivalent circuit with the slow diffusion-like and adsorption steps can be applied for fitting the experimental impedance
data for iodide ions adsorption on Bi(111) and Cd(0001) from aqueous solutions with constant ionic strength. The modified
Grafov–Damaskin circuit can be used in the region of electrode potentials, where parallel faradic processes (electroreduction
of protons, oxygen traces) are probable. The more complicated Ershler equivalent circuit, taking into account the slow diffusion-like,
adsorption and charge transfer steps, is not applicable for characterization of the adsorption process of I− at Bi(111) and Cd(0001) electrodes. 相似文献
9.
Pronobesh Chattopadhyay Pallab Chaudhury Arun Kumar Wahi 《Applied biochemistry and biotechnology》2010,160(7):1968-1977
The mechanism of action of the anti-apoptotic oncogene Bcl-2 and Ca+2 regulation in ischemia–reperfusion injury is still obscure. In this present study, we investigated mitochondrial Ca+2 overloads and mechanism of action of Bcl-2. Eighteen Wistar rats were divided into sham-operated control group (I) (n = 6), ischemia and reperfusion group (II) (n = 6), and amlodipine-treated group (1 mg kg−1 body weight/daily by oral route for 7 days before inducing ischemia–reperfusion maneuver) (III) (n = 6). Rats were subjected to 1 h of hepatic ischemia followed by 3-h reperfusion. Mitochondrial Ca2+ content was determined and damage was confirmed by transmission electron microscopy. Decrease of mitochondrial Ca+2 level is related to reduction of apoptosis and cellular changes, viz. increased Bcl-2 expression followed by reduction in
secondary endoplasmic reticulum, whereas ischemia/reperfusion group shows overloading Ca+2 ions and decrease in Bcl-2 expression as compared to sham-operated rats. Thus, Bcl-2-dependent reduction of Ca+2 is an important component of the anti-apoptotic program in ischemia–reperfusion injury. 相似文献
10.
The effect of the melting of the collagen-like acid and alkaline gelatin aggregates on the stability against aggregation
of bovine casein micelles was investigated by turbidimetry, DSC and circular dichroism in the wide range of biopolymers concentrations,
gelatin/casein ratio (R) in initial mixture (R=0.03–20), pH (4.9–6.7), ionic strength (I=10−3 to 1.0/NaCl/), and temperature (10°–70 °C), using glucono-δ-lactone (GL) as acidifier. At low ionic strength (10−3/milk salts/) and neutral pH interaction between gelatin molecules and casein micelles is suppressed significantly above 36 °C.
The melting of the collagen-like acidic gelatin above this temperature shifts the pH at which the complex formation is maximal
to the acidic range. The cause may be that some of the functional ionized groups of gelatin molecules are inaccessible due
to the conformational changes. The presence of gelatin B molecules had no effect on the aggregation stability of micellar
casein in the range 0.03<R<20. At very high total protein concentration (above 10%) depletion flocculation of casein micelles
was observed. The reason for the very high stability of casein micelles in this case cannot be explained by volume exclusion.
Received: 28 March 2000 Accepted: 5 October 2000 相似文献
11.
Pandey G. P. Agrawal R. C. Hashmi S. A. 《Journal of Solid State Electrochemistry》2011,15(10):2253-2264
Effect of fumed silica dispersion on poly(vinylidene fluoride-co-hexafluoropropylene)-based magnesium ion-conducting gel polymer
electrolyte has been studied using various physical and electrochemical techniques. The composite gel electrolytes are free-standing
and flexible films with enough mechanical strength. The optimized composition with 3 wt.% filler offers a maximum ionic conductivity
of ∼1.1 × 10−2 S cm−1 at ∼25 °C with good thermal and electrochemical stabilities. The Mg2+ ion conduction in the gel nanocomposite film is confirmed from the cyclic voltammetry, impedance spectroscopy, and transport
number measurements. The space-charge layers formed between filler particles and gel electrolyte are responsible for the enhancement
in ionic conductivity. The applicability of the gel nanocomposite to a rechargeable battery is examined by fabricating a prototype
cell consisting of Mg [or Mg-multiwalled carbon nanotube (MWCNT) composite] and MoO3 as negative and positive electrodes, respectively. The discharge capacity and the rechargeability of the cell have been improved
when Mg metal is substituted by Mg-MWCNT composite. The discharge capacity of the optimized cell has found to be ∼175 mAh g−1 of MoO3 for an initial ten charge–discharge cycles. 相似文献
12.
Electrostatic interaction between poly(methyl methacrylate) latex particles with different levels of chitosan modification
and bovine serum albumin (BSA) was investigated. The critical flocculation concentration is in the range 5–15 nmol dm−3 for these latex products toward added BSA. A series of isothermal equilibrium adsorption experiments shows that the adsorption
process is divided into two distinct intervals. Adsorption of BSA on latex particles in intervals I and II is primarily controlled
by charge neutralization and hydrophobic interaction, respectively. Intervals I and II can be reasonably described by an empirical
parabola equation and the Langmuir isotherm model, respectively. The maximum amount of BSA adsorbed per unit weight of polymer
particles was observed at pH ≅ 5. A maximum elution yield of about 80% can be achieved using NaSCN as the elution electrolyte,
and NaSCN is more effective in inducing desorption of BSA from the particle surface than NaCl. The chitosan content has very
little effect on the interaction between latex particles and BSA. By contrast, the influence of the content of 2,2′-azobis(2-amidinopropane)
dihydrochloride, a cationic initiator used in preparing the chitosan-modified latex products, on the BSA adsorption process
is significant.
Received: 26 March 1999 Accepted in revised form: 3 June 1999 相似文献
13.
M. Prabu S. Selvasekarapandian M. V. Reddy B. V. R. Chowdari 《Journal of Solid State Electrochemistry》2012,16(5):1833-1839
Olivine-structured LiCoPO4 is synthesized by a Pechini-type polymer precursor method. The structure and the morphology of the compounds are studied
by the Rietveld-refined X-ray diffraction, scanning electron microscopy, Brunauer, Emmett, and Teller surface area technique,
infrared spectroscopy, and Raman spectroscopy techniques, respectively. The ionic conductivity (σ ionic), dielectric, and electric modulus properties of LiCoPO4 are investigated on sintered pellets by impedance spectroscopy in the temperature range, 27–50 °C. The σ (ionic) values at 27 and 50 °C are 8.8 × 10−8 and 49 × 10−8 S cm−1, respectively with an energy of activation (E
a) = 0.43 eV. The electric modulus studies suggest the presence of non-Debye type of relaxation. Preliminary charge–discharge
cycling data are presented. 相似文献
14.
Ab initio calculations were performed to investigate the structure and bonding of the phenol dimer and its cation, especially
the OH stretching frequencies. Some stable structures of the phenol dimer and its cation were obtained at the Hartree–Fock
level and were found to be in agreement with predictions based on spectroscopic investigations. In these dimers the phenol
moieties are bound by a single OH⋯O hydrogen bond. The hydrogen bond is much stronger in the dimer cation than in the neutral
dimer. The calculated binding energy of the phenol dimer in the most stable structure was 6.5–9.9 kcal/mol at various levels
of calculation, compared with the experimental value of 5 kcal/mol or greater. The binding energy of the phenol dimer cation
is more than 3 times (24.1–30.6 kcal/mol) as large as that of the neutral dimer. For the phenol dimer the OH stretching frequency
of the proton-accepting phenol (PAP) is 3652 cm−1 and that of the proton-donating phenol (PDP) is 3516 cm−1; these are in agreement with observed values of 3654 and 3530 cm−1, respectively. For the phenol dimer cation the OH stretching frequency of the PAP is 3616–3618 cm−1 in comparison with an observed value of 3620 ± 3 cm−1. That of the PDP in the dimer cation is calculated to be 2434–2447 cm−1, which is 1210–1223 cm−1 lower than that of the bare phenol. The large reduction in the OH stretching frequency of the PDP in the phenol dimer cation
is attributed to the formation of a stronger hydrogen bond in the cation than in the neutral dimer.
Received: 24 March 2000 / Accepted: 26 April 2000 / Published online: 11 September 2000 相似文献
15.
Poly(vinyl alcohol) gel was prepared by γ-ray irradiation of an aqueous solution of the polymer and its swelling behavior
in solutions of the alkali-metal and alkaline-earth-metal salts was investigated. The gel deswelled in solutions containing
strongly hydrated anions and swelled in solutions containing strongly hydrated cations. The degree of swelling of the gel
was in the following order: SO4
2−<Cl−<Br− ≅ NO3
−<I− for the anions and K+<Na+<Li+ and Sr2+<Ca2+<Mg2+ for the cations. These results were interpreted in terms of interactions between the polymer and the ions through the hydration
layers.
Received: 6 November 2000 Accepted: 24 May 2001 相似文献
16.
An Cu(II)-imprinted interpenetrating polymer network (IPN) gel of epoxy-diethylenetriamine and methacrylic acid-acrylamide-N,N′-methylene-bis-(acrylamide) was synthesized by the ionic imprint polymer (IIP) technique. The first polymer network is formed by epoxy gelation
with diethylenetriamine. The other is formed by copper methacrylate co- polymerization with acrylamide and cross-linker N,N′-methylene-bis-(acrylamide). The adsorption–desorption characteristics of the IPN gel as a highly selective solid-phase extraction (SPE)
and preconcentration adsorbent for Cu2+ from aqueous solution were investigated. The experimental results show that trace Cu2+ ions can be quantitatively enriched at pH 5 with recovery >95%. The maximum static adsorption capacity of the ion-imprinted
functionalized gel adsorbent was 76 mg g−1. Comparing with non-imprinted IPN gel, the imprinted IPN gel has higher adsorption capacity and selectivity for Cu2+ by the static adsorption–desorption experiment. Simultaneously, the times of adsorption equilibration and complete desorption
were remarkably short. The precision (RSD) for 11 replicate adsorbent extractions of 20 ng mL−1 Cu2+ was 3.4%. The established procedure was applied to two real water samples with satisfactory results. The prepared ion-imprinted
IPN gel adsorbent was shown to be promising for solid-phase extraction coupled with atomic absorption spectrometry (AAS) for
the determination of trace copper in real samples. In addition, the coordination interaction of Cu2+ and functional groups of the IPN gel adsorbent was primarily discussed by FT-IR spectra. 相似文献
17.
The results of large-scale valence ab initio calculations of the potential-energy curves for the ground states and several
excited states of Cd–rare gas (RG) van der Waals molecules are reported. In the calculations, Cd20+ and RG8+ cores are simulated by energy-consistent pseudopotentials, which also account for scalar-relativistic effects and spin-orbit
interaction within the valence shell. The potential energies of the Cd–RG species in the ΛS coupling scheme have been evaluated by means of ab initio complete-active-space multiconfiguration self-consistent-field
(CASSCF)/CAS multireference second-order perturbation theory (CASPT2) calculations with a total 28 valence electrons, but
the spin-orbit matrix has been computed in a reduced configuration interaction space restricted to the CASSCF level. Finally,
the Ω potential curves are obtained by diagonalization of the modified spin-orbit matrix (its diagonal elements before diagonalization
substituted by the corresponding CASPT2 eigenenergies). The calculated potential curves, especially the spectroscopic parameters
derived for the ground states and several excited states of the Cd–RG species are presented and discussed in the context of
available experimental data. The theoretical results exhibit very good agreement with experiment.
Received: 20 April 2000 / Accepted: 1 September 2000 / Published online: 21 December 2000 相似文献
18.
M. C. Bacchus-Montabonel 《Theoretical chemistry accounts》2000,104(3-4):296-301
Ab initio potential-energy curves and coupling matrix elements of the Σ and Π molecular states involved in the collision
of the Si2+, Si3+ and Si4+ multicharged ions on atomic hydrogen and helium have been determined by means of configuration interaction methods. The total
and partial electron capture cross sections have been determined using a semiclassical or a quantal approach in the 0.002–0.1 au
velocity range. A detailed comparison with very recent theoretical and experimental rate coefficient results is made.
Received: 14 September 1999 / Accepted: 3 February 2000 / Published online: 2 May 2000 相似文献
19.
Klaus-Michael Ochsenkühn Theopisti Lyberopoulou G. Koumarianou Maria Ochsenkühn-Petropoulou 《Mikrochimica acta》2008,160(4):485-492
In the time period from June 2005 to May 2006 in 42 sampling campaigns 84 filter samples of airborne particulate matter, coarse
(PM10–2.5) and fine (PM2.5), were collected using a Gent stacked filter unit in the coastal industrial area of Aspropyrgos in Attica, Greece. The average
PM10 (PM10–2.5 + PM2.5) concentration was found to be 66 μg · m−3, exceeding more than 1.6 times the annual limit of 40 μg · m−3. The samples were analysed for Cl−, NO3
−, SO4
2−, Ca2+, Mg2+, Na+, K+ and NH4
+ using ion chromatography. The data were compared with results obtained with other spectrometric methods, such as inductively
coupled plasma-atomic emission spectrometry, atomic absorption spectrometry, energy dispersive X-ray fluorescence and reflectometry.
The determined average ionic content comprised about 44% of the PM10 mass. The ionic composition, as well as the possible matrix compounds in both fractions were evaluated by dividing the sampling
period into summer and winter season. In the PM10–2.5/PM2.5 fraction in summer time the concentrations of Ca2+, Mg2+ and NO3
− were enriched in the coarse fraction. In winter time all species were enriched in the coarse fraction, especially Ca2+, Cl− and NO3
−. NH4
+ was constantly higher in the fine fraction in summer as well as in winter time. Factor analysis was applied to obtain correlations
between cations and anions leading to matrix compounds in both fractions. From the evaluation of the results obtained, some
of the local air pollution sources could be identified.
Correspondence: Klaus-Michael Ochsenkühn, Laboratory for Trace Element Studies, Institute of Physical Chemistry, NCSR “Demokritos”,
Aghia Paraskevi 15310, Athens, Greece 相似文献
20.
Silicone surfactants containing different pendant hydrophilic groups such as diethanol tertiary amine (SHE, nonionic), diethanol
methyl quaternary amine (cationic) and triethyl quaternary amine (cationic) have been synthesized and characterized by 1H and 13C NMR and gel permeation chromatography. The solution behavior of these novel surfactants has also been investigated by surface
tension measurement and a fluorescence method. It has been observed that the surface tension of these surfactants decreases
as a function of time at a very low polymer concentration (1 × 10−4 wt%). At higher concentration (0.1 wt%), the equilibrium surface tensions reached very low values compared to that of typical
polymer surfactants, for example, poly(ethylene oxide–propylene oxide) block copolymer (EPE0.8). In addition, the low I
1/I
3 values of these silicone surfactants indicate the formation of polymer aggregates in aqueous solution, and an extremely low
I
1/I
3 value of SHE (1.06) compared to other polymeric surfactants (EPE0.8) and conventional surfactants [poly(ethylene glycol n-nonyl phenyl ethers), cetyltrimethylammonium bromide, and sodium dodecyl sulfate] indicates its stronger hydrophobicity.
Received: 15 May 2000 Accepted: 18 October 2000 相似文献