共查询到20条相似文献,搜索用时 31 毫秒
1.
A. M. Radalla 《Journal of solution chemistry》2010,39(9):1394-1407
The binary and ternary complexes of Cu2+, Ni2+, Co2+ and Zn2+ metal ions with resorcinol (R) as primary ligand and some biologically important aliphatic dicarboxylic acids (adipic, succinic,
malic, malonic, maleic, tartaric and oxalic acids) as secondary ligands were studied in aqueous solution at 25 °C and I=0.1 mol⋅dm−3 NaNO3 using the potentiometric technique. The formation of different 1:1 and 1:2 binary complexes and 1:1:1 ternary complexes is
inferred from the corresponding potentiometric pH-titration curves. The ternary complex formation was found to take place
in a stepwise manner. The protonation constants of the ligands were determined and used for determining the stability constants
of the different complexes formed in aqueous solutions. The lower stability of the 1:2 binary complexes compared to the corresponding
1:1 systems of all ligands studied were in accordance with statistical considerations. The order of stability of the complexes
formed in solution was investigated in terms of the nature of the resorcinol, carboxylic acid, and metal ion used. The values
of Δlog 10
K, percentage of relative stabilization (% R.S.), and log 10
X for mixed-ligand complexes studied have been evaluated and discussed. The concentration distribution of the various species
formed in solution was evaluated. The mode of chelation of the ternary complexes was ascertained by conductivity measurements. 相似文献
2.
Xingchao Wang Yudai Huang Dianzeng Jia Zaiping Guo Duo Ni Ming Miao 《Journal of Solid State Electrochemistry》2012,16(1):17-24
Olivine LiFePO4/C nanocomposite cathode materials with small-sized particles and a unique electrochemical performance were successfully prepared
by a simple solid-state reaction using oxalic acid and citric acid as the chelating reagent and carbon source. The structure
and electrochemical properties of the samples were investigated. The results show that LiFePO4/C nanocomposite with oxalic acid (oxalic acid: Fe2+= 0.75:1) and a small quantity of citric acid are single phase and deliver initial discharge capacity of 122.1 mAh/g at 1
C with little capacity loss up to 500 cycles at room temperature. The rate capability and cyclability are also outstanding
at elevated temperature. When charged/discharged at 60 °C, this materials present excellent initial discharge capacity of
148.8 mAh/g at 1 C, 128.6 mAh/g at 5 C, and 115.0 mAh/g at 10 C, respectively. The extraordinarily high performance of LiFePO4/C cathode materials can be exploited suitably for practical lithium-ion batteries. 相似文献
3.
4.
de Cássia Silva Luz R Damos FS Gandra PG de Macedo DV Tanaka AA Kubota LT 《Analytical and bioanalytical chemistry》2007,387(5):1891-1897
The determination of reduced glutathione (GSH) in human erythrocytes using a simple, fast and sensitive method employing a
glassy carbon electrode modified with cobalt tetrasulfonated phthalocyanine (CoTSPc) immobilized in poly(l-lysine) (PLL) film was investigated. This modified electrode showed very efficient electrocatalytic activity for anodic oxidation
of GSH, decreasing substantially the anodic overpotentials for 0.2 V versus Ag/AgCl. The modified electrode presented better
performance in 0.1 mol l−1 piperazine-N,N′-bis(2-ethanesulfonic acid) buffer at pH 7.4. The other experimental parameters, such as the concentration of CoTSPc and
PLL in the membrane preparation, pH, type of buffer solution and applied potential, were optimized. Under optimized operational
conditions, a linear response from 50 to 2,160 nmol l−1 was obtained with a high sensitivity of 1.5 nA l nmol−1 cm−2. The detection limit for GSH determination was 15 nmol l−1. The proposed sensor presented good repeatability, evaluated in terms of the relative standard deviation (1.5%) for n = 10. The modified electrode was applied for determination of GSH in erythrocyte samples and the results were in agreement
with those obtained by a comparative method described in the literature The average recovery for these fortified samples was
100 ± 1)%. Applying a paired Student’s-t test to compare these methods, we could observe that, at the 95% confidence level, there was no statistical difference between
the reference and the proposed methods. 相似文献
5.
Isolation of Phosphate-Solubilizing Fungi from Phosphate Mines and Their Effect on Wheat Seedling Growth 总被引:1,自引:0,他引:1
Chunqiao Xiao Ruan Chi Huan He Guanzhou Qiu Dianzuo Wang Wenxue Zhang 《Applied biochemistry and biotechnology》2009,159(2):330-342
Three phosphate-solubilizing fungi, identified as Penicillium expansum, Mucor ramosissimus, and Candida krissii, were isolated from phosphate mines (Hubei, People’s Republic of China) and characterized. All the isolates demonstrated
diverse levels of phosphate-solubilizing capability in National Botanical Research Institute’s phosphate growth medium containing
rock phosphate as sole phosphate source. Acidification of culture medium seemed to be the main mechanism for rock phosphate
solubilization. Indeed, citric acid, oxalic acid, and gluconic acid were shown to be present in the culture medium inoculated
with these isolates. Moreover, the isolates produced acid and alkaline phosphatases in culture medium, which may also be helpful
for RP solubilization. A strong negative correlation between content of soluble phosphorus and pH (r = – 0.89; p < 0.01) in culture medium was observed in this study. All the isolates promoted growth, soil available phosphorus, phosphorus,
and nitrogen uptake of wheat seedling in field soil containing rock phosphate under pot culture conditions, thus demonstrating
the capability of these isolates to convert insoluble form of phosphorus into plant available form from rock phosphate, and
therefore hold great potential for development as biofertilizers to enhance soil fertility and promote plant growth. 相似文献
6.
Sandra Dimitrovska-Lazova Valentin Mir?eski Daniela Kovacheva Slobotka Aleksovska 《Journal of Solid State Electrochemistry》2012,16(1):219-225
In this paper, the synthesis of YCoO3 by solution combustion method and investigation of its catalytic activity using cyclic voltammetry is presented. The perovskite
phase was obtained by thermal initializing of the solutions of the metal nitrates and the fuel (urea). The obtained solid
precursor was further heated yielding the perovskite phase. The obtained perovskite compound has orthorhombic unit cell, within
the space group Pnma, with unit cell parameters a = 5.4223 ?, b = 7.3657 ?, and c = 5.1385 ?. The catalytic activity of the prepared perovskite was investigated by cyclic voltammetry using YCoO3-modified paraffin impregnated graphite electrode, in several electrolytes. It was found that the YCoO3 perovskite has a distinct catalytic activity towards the oxidation of chloride anions in which Co3+ ions being the active centers. Also, this material enhances the oxidation of methanol in KOH. 相似文献
7.
Eduardo Marafon Lauro T. Kubota Yoshitaka Gushikem 《Journal of Solid State Electrochemistry》2009,13(3):377-383
SiO2/ZrO2/C carbon ceramic material with composition (in wt%) SiO2 = 50, ZrO2 = 20, and C = 30 was prepared by the sol–gel-processing method. A high-resolution transmission electron microscopy image
showed that ZrO2 and the graphite particles are well dispersed inside the matrix. The electrical conductivity obtained for the pressed disks
of the material was 18 S cm−1, indicating that C particles are also well interconnected inside the solid. An electrode modified with flavin adenine dinucleotide
(FAD) prepared by immersing the solid SiO2/ZrO2/C, molded as a pressed disk, inside a FAD solution (1.0 × 10−3 mol L−1) was used to investigate the electrocatalytic reduction of bromate and iodate. The reduction of both ions occurred at a peak
potential of −0.41 V vs. the saturated calomel reference electrode. The linear response range (lrr) and detection limit (dl)
were: BrO3
−, lrr = 4.98 × 10−5–1.23 × 10−3 mol L−1 and dl = 2.33 μmol L−1; IO3
−, lrr = 4.98 × 10−5 up to 2.42 × 10−3 and dl = 1.46 μmol L−1 for iodate. 相似文献
8.
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
9.
A sensitive catalytic method is developed for the spectrophotometric determination of oxalic acid. It is based on the catalytic
action of oxalic acid on a new indicator reaction – the oxidation of Bromophenol Blue by dichromate in dilute sulfuric acid
medium. The reaction rate is monitored spectrophotometrically by measuring the absorbance at 600 nm after quenching the reaction
with sodium hydroxide. A calibration graph from 0.1 to 8.0 μg mL−1 of oxalic acid and a detection limit of 0.04 μg mL−1 was obtained. The applicability of this method was demonstrated by the determination of oxalic acid in water extracts from
vegetables such as spinach, mushrooms and fresh kidney beans.
Received October 18, 1999. Revision June 14, 2000. 相似文献
10.
An optical chemical sensor based on 2-mercaptopyrimidine (2-MP) in plasticized poly(vinyl chloride) (PVC) membrane incorporating
(N,N-diethyl-5-(octadecanoylimino)-5H benzo[a]phenoxazine-9-amine (ETH 5294) and sodium tetraphenyl borate (NaTPB) for batch and
flow-through determination of mercury ion is described. The response of the sensor is based on selective complexation of Hg2+ with 2-MP in the membrane phase, resulting in an ion exchange process between H+ in the membrane and Hg2+ in the sample solution. The influences of several experimental parameters, such as membrane composition, pH, and type and
concentration of the regenerating reagent, were investigated. The sensor has a response range of 2.0 × 10−9 to 2.0 × 10−5 mol L−1 Hg2+ with a detection limit of 4.0 × 10−10 mol L−1 and a response time of ≤45 s at optimum pH of 6.5 with high measurement repeatability and sensor-to-sensor reproducibility.
It shows high selectivity for Hg2+ over several transition metal ions, including Ag+, Cd2+, Co2+, Cr3+, Cu2+, Fe3+, Mn2+, Ni2+, and common alkali and alkaline earth ions such as Na+, K+, Mg2+, Ca2+, and Pb2+. The sensor membrane can be easily regenerated with dilute acid solutions. The sensor has been used for the determination
of mercury ion concentration in water samples. 相似文献
11.
The electrochemical behaviors of metol on an ionic liquid N-butylpyridinium hexafluorophosphate modified carbon paste electrode (IL-CPE) were studied in this paper. The results indicated
that a pair of well-defined quasi-reversible redox peaks of metol appeared with the decrease of overpotential and the increase
of redox peak current, which was the characteristics of electrocatalytic oxidation. The electrocatalytic mechanism was discussed
and the electrochemical parameters were calculated with results of the charge-transfer coefficient (α) as 0.45, the electrode reaction rate constant (k
s) as 4.02 × 10−3 s−1, and the diffusion coefficient (D) as 6.35 × 10−5 cm2/s. Under the optimal conditions, the anodic peak current was linear with the metol concentration in the range of 5.0 × 10−6 ∼ 1.0 × 10−3 mol/L (n = 11, γ = 0.994) and the detection limit was estimated as 2.33 × 10−6 mol/L (3σ). The proposed method was successfully applied to determination of metol content in synthetic samples and photographic solutions. 相似文献
12.
Mylonaki S Kiassos E Makris DP Kefalas P 《Analytical and bioanalytical chemistry》2008,392(5):977-985
An experimental setup based on a 23 full-factorial, central-composite design was implemented with the aim of optimising the recovery of polyphenols from olive
leaves by employing reusable and nontoxic solutions composed of water/ethanol/citric acid as extracting media. The factors
considered were (i) the pH of the medium, (ii) the extraction time and (iii) the ethanol concentration. The model obtained
produced a satisfactory fit to the data with regard to total polyphenol extraction (R
2 = 0.91, p = 0.0139), but not for the antiradical activity of the extracts (R
2 = 0.67, p = 0.3734). The second-order polynomial equation obtained after analysing the experimental data indicated that ethanol concentration
and time mostly affected the extraction yield, but that increased pH values were unfavourable in this regard. The maximum
theoretical yield was calculated to be 250.2 ± 76.8 mg gallic acid equivalent per g of dry, chlorophyll-free tissue under
optimal conditions (60% EtOH, pH 2 and 5 h). Liquid chromatography–electrospray ionisation mass spectrometry of the optimally
obtained extract revealed that the principal phytochemicals recovered were luteolin 7-O-glucoside, apigenin 7-O-rutinoside and oleuropein, accompanied by smaller amounts of luteolin 3′,7-O-diglucoside, quercetin 3-O-rutinoside (rutin), luteolin 7-O-rutinoside and luteolin 3′-O-glucoside. Simple linear regression analysis between the total polyphenol and antiradical activity values gave a low and
statistically insignificant correlation (R
2 = 0.273, p > 0.05), suggesting that it is not the sheer amount of polyphenols that provides high antioxidant potency; instead, this
potency is probably achieved through interactions among the various phenolic constituents. 相似文献
13.
The reaction products of Co(II)-2,3- and -2,5-dichlorobenzoate with imidazole (1, 2; CoL 2⋯2imdċ2H2O, L=C7H3Cl2O, imd=imidazole) were characterized by their spectroscopic and thermochemical properties. The compounds crystallize in the monoclonic system with space group = P21/c, a=13.848(3), b=12.841(3) ?, c= 7.064(2) ?, β=98.12 °, V=1243.5(4) ?3, Z=2 for 1 and space group =P21/n, a=13.293(3), b= 6.964(2), c=13.800(3) ?, β=108.92(3) °, V=1208.6(4) ?3, Z=2 for 2. The complexes lose their crystal water in one step at 333 K and subsequently decompose to CoO with intermediate formation of Co3O4. 相似文献
14.
Hisayoshi Matsushima Adriana Ispas Andreas Bund Waldfried Plieth Yasuhiro Fukunaka 《Journal of Solid State Electrochemistry》2007,11(6):737-743
The electrodeposition process of Co films in a sulfuric acid solution was examined in a magnetic field (0–5 T). The surface
morphology of Co films electrodeposited without a magnetic field was drastically modified with the variation of hydrogen gas
evolution rate. Crystalline α-Co was formed in the range of pH = 1.5–6.0, while β-Co was not observed. When the magnetic field
was superimposed perpendicular to the electric field in the acidic solution (pH = 1.5), the hydrogen evolution rate was promoted
by MHD convection, which enhanced the ionic mass transfer (H+ and Co2+) near the electrode surface. Moreover, crystalline β-Co was formed simultaneously with the appearance of the elongated ridge-shape
precipitates under a higher magnetic field (≥3 T).
Contribution to special issue “Magnetic field effects in Electrochemistry” 相似文献
15.
Wiesława Wołodkiewicz Tadeusz Głowiak 《Monatshefte für Chemie / Chemical Monthly》2000,131(7):711-719
Summary. The reaction products of Co(II)-2,3- and -2,5-dichlorobenzoate with imidazole (1, 2; CoL
2⋯2imdċ2H2O, L=C7H3Cl2O, imd=imidazole) were characterized by their spectroscopic and thermochemical properties. The compounds crystallize in the monoclonic
system with space group = P21/c, a=13.848(3), b=12.841(3) ?, c= 7.064(2) ?, β=98.12 °, V=1243.5(4) ?3, Z=2 for 1 and space group =P21/n, a=13.293(3), b= 6.964(2), c=13.800(3) ?, β=108.92(3) °, V=1208.6(4) ?3, Z=2 for 2. The complexes lose their crystal water in one step at 333 K and subsequently decompose to CoO with intermediate formation
of Co3O4.
Received August 9, 1999. Accepted (revised) February 11, 2000 相似文献
16.
Zanaty Rady Komy 《Mikrochimica acta》2000,135(1-2):35-43
A highly sensitive, selective, and rapid differential pulse anodic stripping voltammetric method at HMDE is described for
the determination of trace concentrations of Mn2+. The determination of Mn2+ in non-buffered chloride solution is seriously disturbed by the presence of Ni2+, Co2+, Cr3+, Zn2+ and Cu2+ due to intermetallic compound formation. The procedure is based on the addition of low amounts of cyanide as a masking agent.
The interference of < 20 μgL−1 of Ni2+, Co2+ and Cr3+ and < 75 μgL−1 of Cu2+ and Zn2+ can thus be avoided, as the formed cyanide complexes prevent intermetallic compound formation during the short accumulation
period. Thus, the addition of cyanide greatly improves the DPASV determination of manganese in non-buffered medium. A comparison
between the determination of Mn2+ in the presence of a mixed cyanide/non-buffered chloride and in the ammoniacal buffer solution shows that the peak current
of manganese in the presence of cyanide is four times higher with the same peak potential. The proposed method is shown to
be applicable for the Mn2+ determination in both ground and tap water. A good agreement is obtained between the results by DPASV and AAS.
Received May 14, 1999. Revision May 25, 2000. 相似文献
17.
M. Houshmand A. Jabbari H. Heli M. Hajjizadeh A. A. Moosavi-Movahedi 《Journal of Solid State Electrochemistry》2008,12(9):1117-1128
The electrocatalytic oxidation of aspirin and acetaminophen on nanoparticles of cobalt hydroxide electrodeposited on the surface
of a glassy carbon electrode in alkaline solution was investigated. The process of oxidation and the kinetics have been investigated
using cyclic voltammetry, chronoamperometry, and steady-state polarization measurements. Voltammetric studies have indicated
that in the presence of drugs, the anodic peak current of low valence cobalt species increases, followed by a decrease in
the corresponding cathodic current. This indicates that drugs are oxidized on the redox mediator which is immobilized on the
electrode surface via an electrocatalytic mechanism. With the use of Laviron’s equation, the values of anodic and cathodic
electron-transfer coefficients and charge-transfer rate constant for the immobilized redox species were determined as α
s,a = 0.72, α
s,c = 0.30, and k
s = 0.22 s−1. The rate constant, the electron transfer coefficient, and the diffusion coefficient involved in the electrocatalytic oxidation
of drugs were reported. It was shown that by using the modified electrode, aspirin and acetaminophen can be determined by
amperometric technique with detection limits of 1.88 × 10−6 and 1.83 × 10−6 M, respectively. By analyzing the content of acetaminophen and aspirin in bulk forms using chronoamperometric and amperometric
techniques, the analytical utility of the modified electrode was achieved. The method was also proven to be valid for analyzing
these drugs in urine samples. 相似文献
18.
Paula V. Messina Juan Manuel Ruso Gerardo Prieto Marcos D. Fernández-Leyes Pablo C. Schulz Félix Sarmiento 《Colloid and polymer science》2010,288(4):449-459
The aim of this article is the evaluation of Ca2+ and Mg2+ subphases presence effect on mixed monolayers composed by dehydrocholic acid (HDHC) and didodecyldimethylammonium bromide
(DDAB). The monolayer stability was analyzed by the evaluation of thermodynamic parameters, ΔG
mixE and α. At all calcium ion-tested concentration, the mixed systems X
HDHC = 0.6 and 0.8 at π = 30 mJ m−2 were always the most favored proportions. The X
HDHC = 0.6 system was also stable in magnesium presence, and the X
HDHC = 0.2-mixed monolayer went through a stable to an unstable state as the content of Ca2+ or Mg2+ augment. Finally, the X
HDHC = 0.4 monolayer showed a particular behavior, i.e., remained stable at low cation concentration, unstable at intermediate
concentration and stable again at high concentration. The effect was similar at Mg2+ presence. 相似文献
19.
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
20.
Srabanti Ghosh S. C. Bhattacharya Abhijit Saha 《Analytical and bioanalytical chemistry》2010,397(4):1573-1582
The gamma irradiation method has provided a route for synthesis of highly water-soluble, good-quality luminescent CdS/dendrimer
nanocomposites with amino- or carboxyl-terminated PAMAM dendrimer. An attempt has been made to probe ascorbic acid with the
as-synthesized CdS/dendrimer nanocomposites (DNC). Ascorbic acid (AA) is an important biological antioxidant and marker for
different diseases in clinical chemistry as well as in quality control in the food industry. Micromolar concentrations of
AA significantly quenched the photoluminescence (PL) of both amino (–NH2) and carboxylic (–COOH) functionalized semiconductor nanocomposites. The quenching followed a linear Stern–Volmer equation
and time-resolved photoluminescence spectroscopy confirmed its static nature. A strong size dependence of the quenching pattern
was observed. The binding constants, and the corresponding thermodynamic parameters ΔG
θ, ΔH
θ, ΔS
θ at different temperatures were calculated. CdS DNC showed selectivity towards ascorbic acid even in the presence of possible
interfering molecules, such as uric acid, tartaric acid and citric acid. Nanocomposites-based assay techniques could override
the complications involved in multitudes of assay procedures, providing a simple and fast new strategy for the quantification
of Ascorbic acid in the range of 16.6 to 100 μM (R = 0.998, n = 9). The proposed method was applied to the detection of ascorbic acid in Vitamin C tablets with satisfactory results. 相似文献