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1.
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 cm 2/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 (3 σ). The proposed method was successfully applied to determination of metol content in synthetic samples and photographic solutions. 相似文献
2.
In this work, we investigate the electrochemical activity of dopamine (DA) and uric acid (UA) using both a bare and a modified
carbon paste electrode as the working electrode, with a platinum wire as the counter electrode and a silver/silver chloride
(Ag/AgCl) as the reference electrode. The modified carbon paste electrode consists of multi-walled carbon nanotubes (>95%)
treated with α-cyclodextrine, resulting in an electrode that exhibits a significant catalytic effect toward the electro-chemical
oxidation of DA in a 0.2-M Britton–Robinson buffer solution (pH 5.0). The peak current increases linearly with the DA concentration
within the molar concentration ranges of 2.0 × 10 −6 to 5.0 × 10 −5 M and 5.0 × 10 −5 to 1.9 × 10 −4 M. The detection limit (signal to noise >3) for DA was found to be 1.34 × 10 −7 M, respectively. In this work, voltammetric methods such as cyclic voltammetry, chronoamperometry, chronocuolometry, differential
pulse and square wave voltammetry, and linear sweep and hydrodynamic voltammetry were used. Cyclic voltammetry was used to
investigate the redox properties of the modified electrode at various scan rates. The diffusion coefficient ( D, cm 2 s −1 = 3.05 × 10 −5) and the kinetic parameters such as the electron transfer coefficient ( α = 0.51) and the rate constant ( k, cm 3 mol −1 s −1 = 1.8 × 10 3) for DA were determined using electrochemical approaches. By using differential pulse voltammetry for simultaneous measurements,
we obtained two peaks for DA and UA in the same solution, with the peak separation approximately 136 mV. The average recovery
was measured at 102.45% for DA injection. 相似文献
3.
The electrocatalytic oxidation of quinine sulfate (QS) was investigated at a glassy carbon electrode, modified by a gel containing
multiwall carbon nanotubes (MWCNTs) and room-temperature ionic liquid of 1-Butyl-3-methylimidazolium hexafluorophate (BMIMPF 6) in 0.10 M of phosphate buffer solution (PBS, pH 6.8). It was found that an irreversible anodic oxidation peak of QS with
E
pa as 0.99 V appeared at MWCNTs-RTIL/glassy carbon electrode (GCE). The electrode reaction process was a diffusion-controlled
one and the electrochemical oxidation involved two electrons transferring and two protons participation. Furthermore, the
charge-transfer coefficient ( α), diffusion coefficient ( D), and electrode reaction rate constant ( k
f) of QS were found to be 0.87, 7.89 × 10 −3 cm 2⋅s −1 and 3.43 × 10 −2 s −1, respectively. Under optimized conditions, linear calibration curves were obtained over the QS concentration range 3.0 × 10 −6 to 1.0 × 10 −4 M by square wave voltammetry, and the detection limit was found to be 0.44 μM based on the signal-to-noise ratio of 3. In
addition, the novel MWCNTs-RTIL/GCE was characterized by the electrochemical impedance spectroscopy and the proposed method
has been successfully applied in the electrochemical quantitative determination of quinine content in commercial injection
samples and the determination results could meet the requirement. 相似文献
4.
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
5.
A 66-kDa thermostable family 1 Glycosyl Hydrolase (GH1) enzyme with β-glucosidase and β-galactosidase activities was purified
to homogeneity from the seeds of Putranjiva roxburghii belonging to Euphorbiaceae family. N-terminal and partial internal amino acid sequences showed significant resemblance to plant GH1 enzymes. Kinetic
studies showed that enzyme hydrolyzed p-nitrophenyl β- d-glucopyranoside ( pNP-Glc) with higher efficiency ( K
cat/ K
m = 2.27 × 10 4 M −1 s −1) as compared to p-nitrophenyl β- d-galactopyranoside ( pNP-Gal; K
cat/ K
m = 1.15 × 10 4 M −1 s −1). The optimum pH for β-galactosidase activity was 4.8 and 4.4 in citrate phosphate and acetate buffers respectively, while
for β-glucosidase it was 4.6 in both buffers. The activation energy was found to be 10.6 kcal/mol in the temperature range
30–65 °C. The enzyme showed maximum activity at 65 °C with half life of ~40 min and first-order rate constant of 0.0172 min −1. Far-UV CD spectra of enzyme exhibited α, β pattern at room temperature at pH 8.0. This thermostable enzyme with dual specificity
and higher catalytic efficiency can be utilized for different commercial applications. 相似文献
6.
A new high α 1A adrenoreceptor (α 1AAR) expression cell membrane chromatography (CMC) method was developed for characterization of α 1AAR binding interactions. HEK293 α 1A cell line, which expresses stably high levels of α 1AAR, was used to prepare the stationary phase in the CMC model. The HEK293 α 1A/CMC-offline-HPLC system was applied to specifically recognize the ligands which interact with the α 1AAR, and the dissociation equilibrium constants ( K
D) obtained from the model were (1.87 ± 0.13) × 10 −6 M for tamsulosin, (2.86 ± 0.20) × 10 −6 M for 5-methylurapidil, (3.01 ± 0.19) × 10 −6 M for doxazosin, (3.44 ± 0.19) × 10 −6 M for terazosin, (3.50 ± 0.21) × 10 −6 M for alfuzosin, and (7.57 ± 0.31) × 10 −6 M for phentolamine, respectively. The competitive binding study between tamsulosin and terazosin indicated that the two drugs
interacted at the common binding site of α 1AAR. However, that was not the case between tamsulosin and oxymetazoline. The results had a positive correlation with those
from radioligand binding assay and indicated that the CMC method combined modified competitive binding could be a quick and
efficient way for characterizing the drug–receptor interactions. 相似文献
7.
Fast scanning chip calorimetry (FSC) has been used for analysis of the crystallization behavior of a polyamide 11/organo-modified montmorillonite (PA 11/OMMT) nanocomposite. The addition of OMMT leads to a significant increase of the crystallization temperature of the polymer matrix only on cooling faster than about 10 0 K s –1. In case of slow cooling at rates typically used in standard differential scanning calorimetry (DSC), the nucleating effect of OMMT on crystallization of PA 11 is negligible. The critical cooling rate to suppress crystallization of PA 11 and to completely vitrify the relaxed melt increases at least by one order of magnitude due to the addition of OMMT. Furthermore, the enthalpy of crystallization is nearly independent on the cooling conditions in the analyzed cooling rate range from 10 –2 to 2?×?10 3 K s –1 in PA 11/OMMT nanocomposites. Isothermal crystallization experiments confirmed that the nucleating effect of OMMT on the crystallization of PA 11 increases with supercooling, being therefore of particular importance at cooling conditions relevant in polymer processing. The evaluation of the kinetics of crystallization of the PA 11/OMMT nanocomposite by FSC and DSC in a wide range of cooling rates/supercooling has been completed by analysis of the effect of OMMT on the α/δ’ polymorphism of PA 11 and the spherulitic superstructure. 相似文献
8.
The effect of variation the cooling rate in a wide range between 10 ?2 and 10 3 K s ?1 on solidification the relaxed melt of random isotactic copolymers of propylene with low amount of 1-hexene or 1-octene has been studied. Emphasis has been placed on the structure formation at rapid cooling and an evaluation of the conditions required to permit crystallization, mesophase formation, or suppression of any ordering. The presence of low amount of either 1-hexene or 1-octene co-units in the propylene chain decreases drastically the critical cooling rate required for suppression of crystallization from about 150–200 K s ?1 in the homopolymer to about only 10 K s ?1 in the copolymers; increasing the cooling rate beyond these limits allowed mesophase formation or even generation of fully amorphous samples. The study of the kinetics of formation of specific structures is completed by a complementary analysis of the X-ray structure, morphology and superstructure of the ordered phase. The hindrance of non-isothermal crystallization and mesophase formation of random copolymers of propylene with 1-hexene or 1-octene is compared with that in propylene–1-butene copolymers; addition of only 2–3 mol% 1-hexene or 1-octene into the propylene chain leads to even larger hindrance of the ordering process than the addition of more than 10 mol% 1-butene. 相似文献
9.
There is a lack of fundamental knowledge about the scale up of biosurfactant production. In order to develop suitable technology
of commercialization, carrying out tests in shake flasks and bioreactors was essential. A reactor with integrated foam collector
was designed for biosurfactant production using Bacillus subtilis isolated from agricultural soil. The yield of biosurfactant on biomass ( Y
p/x), biosurfactant on sucrose ( Y
p/s), and the volumetric production rate ( Y) for shake flask were obtained about 0.45 g g −1, 0.18 g g −1, and 0.03 g l −1 h −1, respectively. The best condition for bioreactor was 300 rpm and 1.5 vvm, giving Y
x/s, Y
p/x, Y
p/s, and Y of 0.42 g g −1, 0.595 g g −1, 0.25 g g −1, and 0.057 g l −1 h −1, respectively. The biosurfactant maximum production, 2.5 g l −1, was reached in 44 h of growth, which was 28% better than the shake flask. The obtained volumetric oxygen transfer coefficient
( K
L
a) values at optimum conditions in the shake flask and the bioreactor were found to be around 0.01 and 0.0117 s −1, respectively. Comparison of K
L
a values at optimum conditions shows that biosurfactant production scaling up from shake flask to bioreactor can be done with
K
L
a as scale up criterion very accurately. Nearly 8% of original oil in place was recovered using this biosurfactant after water
flooding in the sand pack. 相似文献
10.
Simultaneous determination of catechol (CC) and hydroquinone (HQ) were investigated by voltammetry based on glassy carbon
electrode (GCE) modified by poly (diallyldimethylammonium chloride) (PDDA) functionalized graphene (PDDA-G). The modified
electrode showed excellent sensitivity and selectivity properties for the two dihydroxybenzene isomers. In 0.1 mol/L phosphate
buffer solution (PBS, pH 7.0), the oxidation peak potential difference between CC and HQ was 108 mV, and the peaks on the
PDDA-G/GCE were three times as high as the ones on graphene-modified glass carbon electrode. Under optimized conditions, the
PDDA-G/GCE showed wide linear behaviors in the range of 1 × 10 −6−4 × 10 −4 mol/L for CC and 1 × 10 −6−5 × 10 −4 mol/L for HQ, with the detection limits 2.0 × 10 −7 mol/L for CC and 2.5 × 10 −7 mol/L for HQ ( S/N = 3) in mixture, respectively. Some kinetic parameters, such as the electron transfer number ( n), charge transfer coefficient ( α), and the apparent heterogeneous electron transfer rate constant ( k
s), were calculated. The proposed method was applied to simultaneous determine CC and HQ in real water samples of Yellow River
with satisfactory results. 相似文献
11.
A carbon past electrode modified with [Mn(H 2O)(N 3)(NO 3)(pyterpy)],
( \text pyterpy = 4¢- ( 4 - \text pyridyl ) - 2,2¢:\text6¢,\text2¢¢- \text terpyridine ) \left( {{\text{pyterpy}} = 4\prime - \left( {4 - {\text{pyridyl}}} \right) - 2,2\prime:{\text{6}}\prime,{\text{2}}\prime\prime - {\text{terpyridine}}} \right) complex have been applied to the electrocatalytic oxidation of nitrite which reduced the overpotential by about 120 mV with
obviously increasing the current response. Relative standard deviations for nitrite determination was less than 2.0%, and
nitrite can be determined in the ranges of 5.00 × 10 −6 to 1.55 × 10 −2 mol L −1, with a detection limit of 8 × 10 −7 mol L −1. The treatment of the voltammetric data showed that it is a pure diffusion-controlled reaction, which involves one electron
in the rate-determining step. The rate constant k′, transfer coefficient α for the catalytic reaction, and diffusion coefficient of nitrite in the solution, D, were found to be 1.4 × 10 −2, 0.56× 10 −6, and 7.99 × 10 −6 cm 2 s −1, respectively. The mechanism for the interaction of nitrite with the Mn(II) complex modified carbon past electrode is proposed.
This work provides a simple and easy approach to detection of nitrite ion. The modified electrode indicated reproducible behavior,
anti-fouling properties, and stability during electrochemical experiments, making it particularly suitable for the analytical
purposes. 相似文献
12.
Summary. Hydrazones containing 1-phenyl-1,2,3,4-tetrahydroquinoline units were synthesized starting from diphenylamine. These compounds
were found to constitute novel hole transporting materials and were characterized by the time of flight method. The hole drift
mobility in these compounds exceeds 10 −6 cm 2 V −1 s −1 at an electric field of 10 6 V cm −1. 相似文献
13.
Molecular dynamics simulation was applied to investigating the evolvement rule of cobalt melt microstructure during solidification at different cooling rates. The cooling rate for the formation of amorphous phase is determined by analyzing the radial distribution function, the H–A bond-type index and the mean square displacement. The simulation results showed that the nucleation undercooling increases with the initial temperature, and in the undercooling versus temperature curve, there are two inflection points. Besides, when the initial temperature reaches 2450 K, the undercooling will be stabilized at 1061 K. As the cooling rate is less than 1.0?×?1011.0 K s?1, the FCC and HCP crystal structures will be obtained. Amorphous structure will be obtained if the cooling rate is more than 1.0?×?1013.0 K s?1. If the cooling rate of the Co melt is between 1.0?×?1011.0 and 1.0?×?1013.0 K s?1, the crystal and amorphous structures will be coexistent, which indicates that the critical cooling rate of crystal–amorphous transition is 1.0?×?1011.0 K s?1. 相似文献
14.
The electrochemical behavior of sodium alendronate on copper microparticle- and copper nanoparticle-modified carbon paste
electrodes was investigated. In the voltammograms recorded using microparticles, a single anodic oxidation peak appeared,
while using nanoparticles, two anodic peaks appeared. The anodic currents were related to the electrocatalytic oxidation of
alendronate via the active species of Cu(III). The catalytic rate constant for the electrocatalytic oxidation process and
the diffusion coefficient of alendronate were obtained to be 1.57 × 10 3 cm 3 mol −1 s −1 and 2.44 × 10 −6 cm 2 s −1, respectively. A sensitive and time-saving detection procedure was developed for the analysis of alendronate, and the corresponding
analytical parameters were reported. Alendronate was determined with a limit of detection of 11.26 μmol L −1 with a linear range of 50–6,330 μmol L −1. The proposed amperometric method was applied to the analysis of commercial pharmaceutical tablets, and the results were
in good agreement with the declared values. 相似文献
15.
A p-duroquinone (tetramethyl- p-benzoquinone) modified carbon paste electrode (DMCPE) was employed to study the electrocatalytic reduction of nitrite in
aqueous solutions using cyclic voltammetry (CV), double potential-step chronoamperometry, and differential pulse voltammetry
(DPV). It has found that under an optimum condition (pH 1.00), the reduction of nitrite at the surface of DMCPE occurs at
a potential of about 660 mV less negative than that of an unmodified carbon paste electrode (CPE). The catalytic rate constant,
k′ h, based on Andrieux and Saveant theoretical model was calculated as for scan rate 10 mV s -1. Also, the apparent diffusion coefficient, D
app, was found as 2.5 × 10 –10 and 3.61 × 10 –5 cm 2 s -1
for p-duroquinone in carbon paste matrix and nitrite in aqueous buffered solution, respectively. The values for αn α were estimated to be −0.65 and −0.19 for the reduction of nitrite at the surface of DMCPE and CPE, respectively. The electrocatalytic
reduction peak currents showed a linear dependence on the nitrite concentration, and a linear analytical curve was obtained
in the ranges of 5.0 × 10 –5 M to 8.0 × 10 –3 M and 6.0 × 10 –6 M to 8.0 × 10 –4 M of nitrite concentration with CV and DPV methods, respectively. The detection limits (2σ) were determined as 2.5 × 10 –5 M and 4.3 × 10 –6 M by CV and DPV methods. This method was also applied as a simple, selective and precise method for determination of nitrite
in real samples (the weak liquor from the wood and paper factory of Mazandaran province in Iran) by using a standard addition
method. 相似文献
16.
This paper describes the use of an aluminum electrode covered by metallic palladium and modified by Prussian blue prepared
by a simple and rapid electroless method for the electro-oxidation of morphine. Two different pathways for electro-oxidation
of morphine at various pH ranges were suggested. Also, some thermodynamic and kinetic parameters such as the number of electrons
involved in the rate determining step, n
α
, transfer coefficient α, and the total electrons ( n) involved in morphine oxidation at the time scale of the cyclic voltammetric technique, the catalytic rate constant of the
electrochemical process k, and diffusion coefficient of morphine D were determined. The mean values obtained are 0.5, 0.5, 1, 26.8 M -1 s -1 and 3.1 × 10 −5 cm 2 s −1, respectively. 相似文献
17.
Mesoporous Mn–Ni oxides with the chemical compositions of Mn 1-x
Ni
x
O
δ
( x = 0, 0.2, and 0.4) were prepared by a solid-state reaction route, using manganese sulfate, nickel chloride, and potassium
hydroxide as starting materials. The obtained Mn–Ni oxides, mainly consisting of the phases of α- and γ-MnO 2, presented irregular mesoporous agglomerates built from ultra-fine particles. Specific surface area of Mn 1–x
Ni
x
O
δ
was 42.8, 59.6, and 84.5 m 2 g −1 for x = 0, 0.2, and 0.4, respectively. Electrochemical properties were investigated by cyclic voltammetry and galvanostatic charge/discharge
in 6 mol L −1 KOH electrolyte. Specific capacitances of Mn 1-x
Ni
x
O
δ
were 343, 528, and 411 F g −1 at a scan rate of 2 mV s −1 for x = 0, 0.2, and 0.4, respectively, and decreased to 157, 183, and 130 F g −1 with increasing scan rate to 100 mV s −1, respectively. After 500 cycles at a current density of 1.24 A g −1, the symmetrical Mn 1–x
Ni
x
O
δ
capacitors delivered specific capacitances of 160, 250, and 132 F g −1 for x = 0, 0.2, and 0.4, respectively, retaining about 82%, 89%, and 75% of their respective initial capacitances. The Mn 0.8Ni 0.2O
δ
material showed better supercapacitive performance, which was promising for supercapacitor applications. 相似文献
18.
The diffusion coefficient of water into thin polymer layers of glutar aldehyde cross-linked atelocollagen type I matrix (sample
1, the typical layer thickness was about 0.065 × 10 −3 m) at 23 °C was 1.142 × 10 −10 m 2 s −1. At twice the concentration of the cross-linking agent (sample 2) the diffusion coefficient was 2.795 × 10 −10 m 2 s −1. This increase was attributed to the more ordered morphology and the creation of ordered microvoids in the film. A larger
surface area is then available for the transport of diffusing molecules, allowing a higher penetration rate of the solvent.
Received: 11 January 2000/Accepted: 6 May 2000 相似文献
19.
The preparation and electrochemical characterization of glassy carbon electrodes modified with plumbagin were investigated
by employing cyclic voltammetry, chronoamperometry and rotating disc electrode techniques. The cyclic voltammograms of the
electroreduction of oxygen showed an enhanced current peak at approximately −0.289 V in air-saturated phosphate buffer pH
= 7 and scan rate 10 mV s −1. The thermodynamic and kinetic parameters of the reduction of oxygen at glassy carbon have been evaluated using cyclic voltammetry.
The experimental parameters were optimized and the mechanism of the catalytic process was discussed. The obtained values of
E°′ (V vs. Ag/AgCl), the apparent electron transfer rate constant k s (s −1), heterogeneous rate constant for the reduction of O 2 at the surface of the modified electrode k h (M −1 s −1) and α (charge transfer coefficient of oxygen) were as follows: −0.146, 23.4, 9.9 × 10 3 and 0.57, respectively. In addition, plumbagin exhibited strong catalytic activity toward the reduction of H 2O 2. 相似文献
20.
This paper describes the use of an aluminum electrode plated by metallic palladium and modified by Prussian blue (PB/Pd-Al)
in the electrocatalytic reduction of hydrogen peroxide (H 2O 2). The effect of pH on the electroreduction of H 2O 2 on the modified electrode is investigated and a simple irreversible reduction pathway is suggested. The electroreduction
kinetics including transfer coefficient α, potential-dependent charge transfer rate constants k
f, and diffusion coefficient D are estimated by means of forced hydrodynamic voltammetry using a rotating disk PB/Pd-Al electrode. The mean values obtained
for kinetics are 0.38, 10 −2 cm −1, and 7.6 × 10 −6 cm 2 s −1, respectively. The long-term stability of the modifying layers on the Al substrate was studied. 相似文献
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