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1.
A doubly hydrophilic triblock copolymer poly(acrylic acid)-b-poly(ethylene glycol)-b-poly(acrylic acid) (PAA-b-PEO-b-PAA) with M
w/M
n = 1.15 was synthesized by atom transfer radical polymerization of t-butyl acrylate (tBA), followed by acidolysis of the PtBA blocks. The pH-sensitive micellization of PAA-b-PEO-b-PAA in acidic solution was investigated by potentiometric titration, fluorescence spectrum, dynamic light scattering and
zeta potential. The pK
a was 6.6 and 6.0 in deionized water and in 0.1 mol/L NaCl solution, respectively. The copolymer formed micelles composed of
a weakly hydrophobic core of complexed PAA and PEO and a hydrophilic PEO shell in 1 mg/mL solution at pH < 5.5 due to hydrogen
bonding. The critical micelle concentration was 0.168 mg/mL at pH 2.0. At pH < 4.5, steady and narrow distributed micelles
were formed. Increasing pH to 5.0, unsteady and broad distributed micelles were observed. At pH > 5.5, the micelle was destroyed
owing to the ionization of the PAA blocks. 相似文献
2.
The microstructure of the micelles formed in aqueous solution by gemini surfactants with aromatic spacers, [Br(CH3)2N+(C
m
H2
m
+1)-(Ph)-(C
m
H2
m
+1)N+(CH3)2Br, m=8 and Ph = o-, m- or p-phenylenedimethylene] has been examined by small-angle neutron scattering. Aggregation of the gemini surfactants with an
o-phenylenedimethylene spacer brings about formation of premicelles and small micelles at concentrations below the second critical
micelle concentration, while above this concentration marked micellar growth and variation in shape occurs. It is suggested
that the minimum aggregate formed at this critical micelle concentration may be the trimer or tetramer and that this result
supports the mechanism of “gemini → submicelle → assembly” for micellar growth.
Received: 8 September 1998 Accepted in revised form: 27 November 1998 相似文献
3.
Xian-Liang Zhou Zhi-Guo Ye Xiao-Zhen Hua Ai-Hua Zou Ying-Hu Dong 《Journal of Solid State Electrochemistry》2010,14(7):1213-1219
Ti/IrO2(x) + MnO2(1-x) anodes have been fabricated by thermal decomposition of a mixed H2IrCl6 and Mn(NO3)2 hydrosolvent. Cyclic voltammetry (CV) and polarization curve have been utilized to investigate the electrochemical behavior
and electrocatalytic activity of Ti/IrO2(x) + MnO2(1-x) anodes in 0.5 M NaCl solution (pH = 2). Ti/IrO2+MnO2 anode with 70 mol% IrO2 content has the maximum value of q*, indicating that Ti/IrO2(0.7) + MnO2(0.3) anode has the most excellent electrocatalytic activity for the synchronal evolution of Cl2 and O2 in dilute NaCl solution. Tafel lines displayed two distinct linear regions with one of the slope close to 62 mV dec−1 in the low potential region and the other close to 295 mV dec−1 in the high potential region. Electrochemical impedance spectroscopic is employed to investigate the impedance behavior of
Ti/IrO2(x) + MnO2(1-x) anodes in 0.5 M NaCl solution. It is observed that as the R
ct, R
s and R
f values for Ti/IrO2(0.7) + MnO2(0.3) anode become smaller, electrocatalytic activity of Ti/IrO2(0.7) + MnO2(0.3) anode becomes better than that of other Ti/IrO2 + MnO2 anodes with different compositions. Ti/IrO2(0.7) + MnO2(0.3) anode fabricated at 400 °C has been observed to possess the highest service life of 225 h, whereas the accelerated life
test is carried out under the anodic current of 2 A cm−2 at the temperature of 50 °C in 0.5 M NaCl solution (pH = 2). 相似文献
4.
Effect of pH and ionic strength on the interaction of humic acid with aluminium oxide 总被引:4,自引:0,他引:4
E. Tombácz Á. Dobos M. Szekeres H. D. Narres E. Klumpp I. Dékány 《Colloid and polymer science》2000,278(4):337-345
The effect of pH and neutral electrolyte on the interaction between humic acid/humate and γ-AlOOH (boehmite) was investigated.
The quantitative characterization of surface charging for both partners was performed by means of potentiometric acid–base
titration. The intrinsic equilibrium constants for surface charge formation were logK
a,1
int=6.7±0.2 and logK
a,2
int = 10.6±0.2 and the point of zero charge was 8.7±0.1 for aluminium oxide. The pH-dependent solubility and the speciation of
dissolved aluminium was calculated (MINTEQA2). The fitted (FITEQL) pK values for dissociation of acidic groups of humic acid were pK
1 = 3.7±0.1 and pK
2 = 6.6±0.1 and the total acidity was 4.56 mmol g−1. The pH range for the adsorption study was limited to between pH 5 and 10, where the amount of the aluminium species in the
aqueous phase is negligible (less than 10−5 mol dm−3) and the complicating side equilibria can be neglected. Adsorption isotherms were determined at pH ∼ 5.5, ∼8.5 and ∼9.5,
where the surface of adsorbent is positive, neutral and negative, respectively, and at 0.001, 0.1, 0.25 and 0.50 mol dm−3 NaNO3. The isotherms are of the Langmuir type, except that measured at pH ∼ 5.5 in the presence of 0.25 and 0.5 mol dm−3 salt. The interaction between humic acid/humate and aluminium oxide is mainly a ligand-exchange reaction with humic macroions
with changing conformation under the influence of the charged interface. With increasing ionic strength the surface complexation
takes place with more and more compressed humic macroions. The contribution of Coulombic interaction of oppositely charged
partners is significant at acidic pH. We suppose heterocoagulation of humic acid and aluminium oxide particles at pH ∼ 5.5
and higher salt content to explain the unusual increase in the apparent amount of humic acid adsorbed.
Received: 20 July 1999 /Accepted in revised form: 20 October 1999 相似文献
5.
Measurements of the electrophoretic mobility (u
E) of particles of colloidal α-alumina were made as a function of pH, electrolyte concentration and electrolyte type (NaCl,
NaNO3 and KCl) using two similar instrumental techniques. Significant differences (50% or less) in the values of u
E of particles in NaCl were obtained from the two instruments; however, the isoelectric points (IEPs) (the pH at which u
E=0), estimated from the two sets of measurements, occurred at 7.5 ± 0.3 and 7.8 ± 0.05 and were not significantly different.
The latter estimate corresponds with those for particles in KCl and NaNO3 of 8.05 ± 0.11 and 7.95 ± 0.18, respectively, made using the same instrument and indicate that the IEP was a weak function
of electrolyte type. When cations acted as counterions (pH > IEP), the absolute magnitudes and the ranges of u
E with electrolyte concentration were found to be significantly less than when anions acted as counterions (IEP > pH). Estimates
of the zeta potential (ζ), made using various procedures, showed variations of up to 25% at low ratios of electrical-double-layer
thickness (κ
−1) to particle radius (a) (κa∼10) and were of a similar scale to differences in u
E, but no significant variations (95% confidence) in ζ were obtained at high values (κa∼200).
Received: 12 July 2000 Accepted: 17 October 2000 相似文献
6.
E. Makrlík P. Toman P. Vaňura V. Kašička R. Rathore 《Journal of solution chemistry》2011,40(8):1418-1426
From extraction experiments and γ-activity measurements, the exchange extraction constant corresponding to the equilibrium Ag+(aq) + 1⋅Cs+(nb) ⇆ 1⋅Ag+(nb) + Cs+(aq) taking part in the two-phase water–nitrobenzene system (where 1 = hexaarylbenzene-based receptor; aq = aqueous phase, nb = nitrobenzene phase) was evaluated to be log 10
K
ex(Ag+, 1⋅Cs+) = −1.0±0.1. Further, the stability constant of the hexaarylbenzene-based receptor⋅Ag+ complex (abbreviation 1⋅Ag+) in nitrobenzene saturated with water, was calculated at a temperature of 25 °C: log 10
β
nb(1⋅Ag+) = 5.5±0.2. By using quantum mechanical DFT calculations, the most probable structure of the 1⋅Ag+ complex species was solved. In this complex having C3 symmetry, the cation Ag+ synergistically interacts with the polar ethereal oxygen fence and with the central hydrophobic benzene ring via cation–π interaction. 相似文献
7.
Rabindra N. Roy Lakshmi N. Roy Shahaf Ashkenazi Joshua T. Wollen Craig D. Dunseth Michael S. Fuge Jared L. Durden Chandra N. Roy Hannah M. Hughes Brett T. Morris Kevin L. Cline 《Journal of solution chemistry》2009,38(4):449-458
The values of the second dissociation constant, pK
2, of N-(2-hydroxyethyl) piperazine-N′-2-ethanesulfonic acid (HEPES) have been reported at twelve temperatures over the temperature range 5 to 55 °C, including
37 °C. This paper reports the results for the pa
H of eight isotonic saline buffer solutions with an I=0.16 mol⋅kg−1 including compositions: (a) HEPES (0.01 mol⋅kg−1) + NaHEPES (0.01 mol⋅kg−1) + NaCl (0.15 mol⋅kg−1); (b) HEPES (0.02 mol⋅kg−1) + NaHEPES (0.02 mol⋅kg−1) + NaCl (0.14 mol⋅kg−1); (c) HEPES (0.03 mol⋅kg−1) + NaHEPES (0.03 mol⋅kg−1) + NaCl (0.13 mol⋅kg−1); (d) HEPES (0.04 mol⋅kg−1) + NaHEPES (0.04 mol⋅kg−1) + NaCl (0.12 mol⋅kg−1); (e) HEPES (0.05 mol⋅kg−1) + NaHEPES (0.05 mol⋅kg−1) + NaCl (0.11 mol⋅kg−1); (f) HEPES (0.06 mol⋅kg−1) + NaHEPES (0.06 mol⋅kg−1) + NaCl (0.10 mol⋅kg−1); (g) HEPES (0.07 mol⋅kg−1) + NaHEPES (0.07 mol⋅kg−1) + NaCl (0.09 mol⋅kg−1); and (h) HEPES (0.08 mol⋅kg−1) + NaHEPES (0.08 mol⋅kg−1) + NaCl (0.08 mol⋅kg−1). Conventional pa
H values, for all eight buffer solutions from 5 to 55 °C, have been calculated. The operational pH values with liquid junction
corrections, at 25 and 37 °C have been determined based on the NBS/NIST standard between the physiological phosphate standard
and four buffer solutions. These are recommended as pH standards for physiological fluids in the range of pH = 7.3 to 7.5
at I=0.16 mol⋅kg−1. 相似文献
8.
Prenesti E Ferrara E Berto S Fisicaro P Daniele PG 《Analytical and bioanalytical chemistry》2007,388(8):1877-1883
A method that uses a Harned cell to perform potentiometric pH measurements has been optimized and applied to an aqueous solution
of simulated seawater that contains sodium perchlorate, sodium sulfate, sodium hydrogen carbonate and boric acid and has an
ionic strength I of 0.57 mol kg−1. The standard metrological approach developed for the measurement of pH in low ionic strength aqueous solutions was maintained,
but a few modifications were necessary, and measurement procedures and calculations were modified ad hoc from those adopted
in conventional protocols. When determining the standard potential of the cell, E°, NaClO4 salt was added to a 0.01 mol/kg HCl solution to attain the same ionic strength as the test solution and to investigate possible
specific effects related to the high levels and the nature of the background electrolyte. An appropriate value of γ
±HCl (0.737) was then selected from the literature, based on a realistic value for I. Finally, in order to convert the acidity function at zero chloride molality into pH, a suitable value of γ
Cl (0.929) was calculated. As a result, we obtained pH = 8.18 (T = 25 °C) with an associated expanded uncertainty U = 0.01 (coverage factor k = 2). The aim was to establish a sound basis for the pH measurement of seawater by identifying the critical points of the
experimental and theoretical procedure, and to discuss further possible developments that would be useful for achieving a
reference solution. 相似文献
9.
A phosphite dehydrogenase gene (ptdhK) consisting of 1,011-bp nucleotides which encoding a peptide of 336 amino acid residues was cloned from Pseudomonas sp. K. gene ptdhK was expressed in Escherichia coli BL21 (DE3) and the corresponding recombinant enzyme was purified by metal affinity chromatography. The recombinant protein
is a homodimer with a monomeric molecular mass of 37.2 kDa. The specific activity of PTDH-K was 3.49 U mg−1 at 25 °C. The recombinant PTDH-K exhibited maximum activity at pH 3.0 and at 40 °C and displayed high stability within a
wide range of pHs (5.0 to 10.5). PTDH-K had a high affinity to its natural substrates, with K
m values for sodium phosphite and NAD of 0.475 ± 0.073 and 0.022 ± 0.007 mM, respectively. The activity of PTDH-K was enhanced
by Na+, NH4+, Mg2+, Fe2+, Fe3+, Co2+, and EDTA, and PTDH-K exhibited different tolerance to various organic solvents. 相似文献
10.
Andre Ricardo de Lima Damásio Tony Márcio da Silva Alexandre Maller Jo?o Atílio Jorge Hector Francisco Terenzi Maria de Lourdes Teixeira de Moraes Polizeli 《Applied biochemistry and biotechnology》2010,160(5):1496-1507
An extracellular polygalacturonase (PG) produced from Paecilomyces variotii was purified to homogeneity through two chromatography steps using DEAE-Fractogel and Sephadex G-100. The molecular weight
of P. variotii PG was 77,300 Da by gel filtration and SDS-PAGE. PG had isoelectric point of 4.37 and optimum pH 4.0. PG was very stable
from pH 3.0 to 6.0. The extent of hydrolysis of different pectins by the purified enzyme was decreased with an increase in
the degree of esterification. PG had no activity toward non-pectic polysaccharides. The apparent K
m and V
max values for hydrolyzing sodium polypectate were 1.84 mg/mL and 432 μmol/min/mg, respectively. PG was found to have temperature
optimum at 65 °C and was totally stable at 45 °C for 90 min. Half-life at 55 °C was 50.6 min. Almost all the examined metal
cations showed partial inhibitory effects under enzymatic activity, except for Na+1, K+1, and Co+2 (1 mM) and Cu+2 (1 and 10 mM). 相似文献
11.
First results on Fe solid-phase extraction from coastal seawater using anatase TiO2 nano-particles 总被引:1,自引:0,他引:1
Christophe R. Quétel Emilia Vassileva Ivan Petrov Kristina Chakarova Konstantin I. Hadjiivanov 《Analytical and bioanalytical chemistry》2010,396(6):2349-2361
This paper describes the application of TiO2 nano-particles (anatase form) for the solid-phase extraction of iron from coastal seawater samples. We investigated the adsorption
processes by infra-red spectroscopy. We compared in batch and on-(mini)column extraction approaches (0.1 and 0.05 g TiO2 per sample, respectively), combined to external calibration and detection by inductively coupled plasma mass spectrometry
at medium mass resolution. Globally, this titania phase was slightly more efficient with seawater than with ultra-pure water,
although between pH 2 and pH 7, the Fe retention efficiency progressed more in ultra-pure water than in seawater (6.9 versus
4.8 times improvement). Different reaction schemes are proposed between Fe(III) species and the two main categories of titania
sites at pH 2 (adsorption of [FeL
x
](3 − x)+ via possibly the mediation of chlorides) and at pH 7 (adsorption of [Fe(OH)2]+ and precipitation of [Fe(OH)3]0). Under optimised conditions, the inlet system was pre-cleaned by pumping 6% HCl for ∼2 h, and the column was conditioned
by aspirating ultra-pure water (1.7 g min−1) and 0.05% ammonia (0.6 g min−1) for 1 min. Then 3 g seawater sample was loaded at the same flow rate while being mixed on-line with 0.05% ammonia at 0.6 g
min−1 to adjust the pH to 7. The iron retained on the oxide powder was then eluted with 3 g 6% HCl (<0.002% residual salinity in
the separated samples). The overall procedural blank was 220 ± 46 (2 s, n = 16) ng Fe kg−1 (the titania was renewed in the column every 20 samples, with 2-min rinsing in between samples with 6% HCl at 1.5 g min−1). The recovery estimated from the Canadian certified reference material CASS-2 was 69.5 ± 7.6% (2 s, n = 4). Typically, the relative combined uncertainty (k = 2) estimated for the measurement of ∼1 μg Fe kg−1 (0.45 μm filtered and acidified to pH 1.5) of seawater was ∼12%. We applied our method to a similar sample, from the coastal
region of the North Sea. The agreement well within stated uncertainties of our result with the value obtained independently
by isotope dilution mass spectrometry further validated our method. 相似文献
12.
The electrochemical solid phase micro-extraction of salicylic acid (SA) at graphite-epoxy-composed solid electrode surface
was studied by cyclic voltammetry. SA was oxidized electrochemically in pH 12.0 aqueous solution at 0.70 V (vs. saturated
calomel electrode) for 7 s. The oxidized product shows two surface-controlled reversible redox couples with two proton transferred
in the pH range of 1.0∼6.0 and one proton transferred in the pH range of 10.0∼13.0 and is extracted on the electrode surface
with a kinetic Boltzman function of i
p = 3.473–4.499/[1 + e(t − 7.332)/6.123] (χ
2 = 0.00285 μA). The anodic peak current of the extracted specie in differential pulse voltammograms is proportional to the
concentration of SA with regression equation of i
p = −5.913 + 0.4843 c (R = 0.995, SD = 1.6 μA) in the range of 5.00∼200 μM. The detection limit is 5.00 μM with RSD of 1.59% at 60 μM. The method
is sensitive and convenient and was applied to the detection of SA in mouse blood samples with satisfactory results. 相似文献
13.
1H NMR chemical shifts of solutions of the following cationic surfactants in D2O were determined as a function of their concentrations: cetyltrimethylammonium chloride, CTACl, a 1 : 1 molar mixture of
CTACl and toluene, cetylpyridinium chloride, CPyCl, cetyldimethylphenylam-monium chloride, CDPhACl, cetyldimethylbenzylammonium
chloride, CDBzACl, cetyldimethyl-2-phenylethylammonium chloride, CDPhEtACl, and cetyldimethyl-3-phenylpropylammonium chloride,
CDPhPrACl. Plots of observed chemical shifts versus [surfactant] are sigmoidal, and were fitted to a model based on the mass-action
law. Satisfactory fitting was obtained for the discrete protons of all surfactants. From these fits, we calculated the equilibrium
constant for micelle formation, K, the critical micelle concentration, CMC and the chemical shifts of the monomer, δmon and the micelle δmic. 1H NMR-based CMC values are in excellent agreement with those which we determined by surface tension measurements of surfactant
solutions in H2O, allowing for the difference in structure between D2O and H2O. Values of K increase as a function of increasing the size of the hydrophilic group, but the free energy of transfer per CH2 group of the phenylalkyl moiety from bulk water to the micellar interface is approximately constant, 1.9±0.1 kJ mol-1. Values of (δmic–δmon) for the surfactant groups at the interface, e.g., CH3–(CH2)15–N+(CH3)2 and within the micellar core, e.g., CH3–(CH2)15–N+ were used to probe the (average) conformation of the phenyl group in the interfacial region. The picture that emerges is
that the aromatic ring is perpendicular to the interface in CDPhACl and is more or less parallel to it in CDBzACl, CDPhEtACl,
and CDPhPrACl.
Received: 23 February 1996 Accepted: 29 August 1996 相似文献
14.
M. H. Soorgi G. H. Rounaghi M. S. Kazemi 《Russian Journal of General Chemistry》2008,78(10):1866-1871
The complex formation between Na+, K+, Cs+, Rb+ and Tl+ metal cations with macrocyclic ligand, dicyclohexyl-18-crown-6 (DCH18C6) was studied in acetonitrile-water (AN-H2O) binary systems at different temperatures using conductometric method. DCH18C6 forms 1:1 complexes with these metal cations.
The stability constants of the complexes were obtained from fitting of molar conductivity curves using a computer program
Genplot. The results show that the selectivity order of DCH18C6 for the metal cations in acetonitrile-water mixtures (AN =
25.3 and 50.4 mol %) is: Tl+ > K+ > Rb+ > Cs+ > Na+. A non-linear behaviour was observed between the log K
f of the complexes versus the composition of the mixed solvent which it related to changes of acidity, basicity, polarity and
also polarizability of AN-H2O mixtures with the composition of this binary solution. The values of standard enthalpy changes (ΔH
s0) for complexation reactions were obtained from the slope of the van’t Hoff plots and the changes in the standard entropy
(ΔS
s0) were calculated from the relationship: ΔG
s,298.150 = ΔH
s0 − 298.15ΔS
s0. The obtained results show that in most cases, the complexes are enthalpy stabilized but entropy destabilized.
Original Russian Text ? M.H. Soorgi, G.H. Rounaghi, M.S. Kazemi, 2008, published in Zhurnal Obshchei Khimii, 2008, vol. 78,
No. 10, pp. 1627–1632. 相似文献
15.
From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium M+(aq)+NaL+(nb)⇔ML+(nb)+Na+(aq) taking place in the two-phase water-nitrobenzene system (M+ = H+, NH4+, Ag+, Tl+; L = tetramethyl p-tert-butylcalix[4]arene tetraketone; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Moreover, the stability constants
of the ML+ complexes in water saturated nitrobenzene were calculated; they were found to increase in the order Tl+<NH4+<Ag+ <H+ <Na+. 相似文献
16.
Phenylalanine dehydrogenase (l-PheDH) from Sporosarcina ureae was immobilized on DEAE-cellulose, modified initially with 2-amino-4,6-dichloro-s-triazine followed by hexamethylenediamine
and glutaraldehyde. The highest activity of immobilized PheDH was determined as 95.75 U/g support with 56% retained activity.
The optimum pH value of immobilized l-PheDH was shifted from pH 10.4 to 11.0. The immobilized l-PheDH showed activity variations close to the maximum value in a wider temperature range of 45–55 °C, whereas it was 40 °C
for the native enzyme. The pH and the thermal stability of the immobilized l-PheDH were also better than the native enzyme. At pH 10.4 and 25 °C, K
m values of the native and the immobilized l-PheDH were determined as K
m Phe = 0.118, 0.063 mM and K
m NAD+ = 0.234, 0.128 mM, respectively. Formed NADH at the exit of packed bed reactor column was detected by the flow-injection
analysis system. The conversion efficiency of the reactor was found to be 100% in the range of 5–600 μM Phe at 9 mM NAD+ with a total flow rate of 0.1 mL/min. The reactor was used for the analyses of 30 samples each for 3 h per day. The half-life
period of the reactor was 15 days. 相似文献
17.
Lokendra Kumar Balvinder Singh Dilip Kumar Adhikari Joydeep Mukherjee Debashish Ghosh 《Applied biochemistry and biotechnology》2012,166(7):1723-1735
Purification and characterization of halotolerant, thermostable alkaline l-glutaminase from a Bacillus sp. LKG-01 (MTCC 10401), isolated from Gangotri region of Uttarakhand Himalaya, is being reported in this paper. Enzyme has
been purified 49-fold from cell-free extract with 25% recovery (specific activity 584.2 U/mg protein) by (NH4)2SO4 precipitation followed by anion exchange chromatography and gel filtration. Enzyme has a molecular weight of 66 kDa. l-Glutaminase is most active at pH 11.0 and stable in the pH range 8.0–11.0. Temperature optimum is 70 °C and is completely
stable after 3 h pre-incubation at 50 °C. Enzyme reflects more enhanced activity with 1–20% (w/v) NaCl, which is further reduced to 80% when NaCl concentration was increased up to 25%. l-Glutaminase is almost active with K+, Zn2+, and Ni2+ ions and K
m and V
max values of 240 μM and 277.77 ± 1.1 U/mg proteins, respectively. Higher specific activity, purification fold, better halo-tolerance,
and thermostability would make this enzyme more attractive for food fermentation with respect to other soil microbe derived
l-glutaminase reported so far. 相似文献
18.
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
19.
Jong Il Lee Yun Jae Kim Heejin Bae Sung Suk Cho Jung-Hyun Lee Suk-Tae Kwon 《Applied biochemistry and biotechnology》2010,160(6):1585-1599
The Thermococcus peptonophilus (Tpe) DNA polymerase gene was expressed under the control of the T7lac promoter on pET-22b(+) in Escherichia coli BL21-CodonPlus(DE3)-RIL in order to fully elucidate its biochemical properties and evaluate its feasibility in polymerase
chain reaction (PCR) application. The expressed enzyme was then purified by heat treatment followed by two steps of column
chromatography after which optimum pH and temperature of the enzyme were evaluated to be 7.0 and 75 °C, respectively. The
optimal buffer for PCR with Tpe DNA polymerase consisted of 50 mM Tris–HCl (pH 8.0), 2 mM MgCl2, 80 mM KCl, and 0.02% Triton X-100. Tpe DNA polymerase revealed a 3.6-fold higher fidelity (3.37 × 10−6) than Taq DNA polymerase (12.13 × 10−6) and performed significantly more efficiently in PCR amplification than both Taq and Pfu DNA polymerases. Ratios of 31:1 of Taq to Tpe DNA polymerases allowed PCR amplification of targets up to 15 kb in length with a 2.2-fold higher fidelity than Taq DNA polymerase. The results of the PCR experiments indicate that Tpe DNA polymerase may provide a higher fidelity DNA amplification in a shorter reaction time. 相似文献
20.
M. A. Deyab 《Journal of Solid State Electrochemistry》2009,13(11):1737-1742
Cyclic voltammetric, potentiodynamic anodic polarization and current–time transient studies were carried out on mild steel
in circulating cooling water containing Cl− and SO4−2 ions under the effect of different variables such as coolant flow, the availability of oxygen, cooling system temperature,
and cooling system pH. The anodic excursion span of mild steel in cooling corrosive solution was characterized by the occurrence
of a well-defined anodic peak (A1), while the reverse sweep was characterized by the appearance of two cathodic peaks (C1
and C2). The presence of Cl− and SO4−2 ions in cooling water enhance the active dissolution of mild steel and tend to breakdown the passive film and induce pitting
attack. The data reveal that increasing flow rate and temperature of cooling solution enhances the anodic peak current density
(j
A1) and shifts the pitting potential (E
pit) towards more active values. It is seen that the peak current density of the anodic peak A1 increases and the pitting potential
(E
pit) displaced in the noble direction in the aerated solution compared that in de-aerated solution. The pitting corrosion of
mild steel by Cl− and SO4−2 ions initiates more readily in acidic medium (pH 2.0). It was found that the incubation time (t
i) increase and in turn the pitting corrosion decrease in the order: pH 10 > pH 6.8 > pH 2.0. 相似文献