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1.
抗氧剂亚硫酸钠、亚硫酸氢钠及焦亚硫酸钠氧化反应速率常数的测定 总被引:2,自引:0,他引:2
为评价抗氧剂的抗氧化能力, 测定了抗氧剂亚硫酸钠、亚硫酸氢钠及焦亚硫酸钠在水溶液中与氧反应的速率常数. 在溶液中连续通入足量的氧气, 维持溶解氧浓度恒定. 用碘量法测定亚硫酸钠、亚硫酸氢钠及焦亚硫酸钠在水溶液中不同时刻的浓度, 用氧电极测定溶液中溶解氧的浓度, 作出亚硫酸钠、亚硫酸氢钠及焦亚硫酸钠的降解曲线, 计算亚硫酸钠、亚硫酸氢钠及焦亚硫酸钠氧化反应速率常数. 结果表明, 亚硫酸钠、亚硫酸氢钠及焦亚硫酸钠在水溶液中与氧的反应均为零级反应. 由于在溶液中这三种抗氧剂存在解离平衡, 当溶液的pH值相同时这三种抗氧剂实质上是一样的, 其平均表观反应速率常数在25 ℃温度和pH 6.8, 4.0及9.2条件下分别为(1.34±0.03)×10-3, (1.20±0.02)×10-3和(6.58±0.02)×10-3 mol•L-1•h-1. 相似文献
2.
Photosubstitution of the sulfo group for hydrogen (chlorine in chloranil) is observed under irradiation of sulfonated derivatives
of hydroquinone formed upon dissolving of p-benzoquinone and p-chloranil in aqueous solutions of sodium sulfite. The quantum yield of the photochemical reaction is 0.18 ± 0.02 for p-benzoquinone. The rate constant of the thermal reaction of substitution is 5.5 × 10−4 l mol−1 s−1. The substitution reaction is sensitized by eosin upon irradiation with visible light. During the course of irradiation of
sulfohydroquinones, the formation of a product with an absorption maximum at 235 nm was found. The product decays with a rate
constant of 0.005 s−1. 相似文献
3.
Herein, a sodium montmorillonite-modified carbon paste electrode is described for the electrochemical determination of guanine.
Guanine yields a well-defined and very sensitive oxidation peak at the sodium montmorillonite-modified carbon paste electrode.
Compared with the unmodified carbon paste electrode, the modified electrode facilitates the electron transfer of guanine,
since it notably increases the oxidation peak current and lowers the oxidation overpotential of guanine. Based on this, a
simple sensitive reliable electrochemical method is proposed for the detection of guanine after all the experimental parameters,
such as solution pH value, sodium montmorillonite content in the carbon paste electrode, accumulation potential, and time,
are optimized. Under the optimized conditions, the oxidation peak current of guanine varies linearly with its concentration
in the range 5.0×10−8 to 2.0×10−5 M and the detection limit (signal-to-noise=3) is 2.0×10−8 M after 4-min accumulation. This method is successfully demonstrated with urine samples.
Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 2, pp. 178–182.
The text was submitted by the authors in English. 相似文献
4.
Horacio Corti Rosa Crovetto Roberto Fernández-Prini 《Journal of solution chemistry》1980,9(8):617-625
The conductivities of aqueous solutions of sodium borate at 25°C and lithium borate at various temperatures are reported.
The conductivity of the B(OH)
4
−
ion is 35.3 ±0.2 S-cm2-mole−1 at 25°C. The electrolytes are both associated, the lithium salt being more associated than the sodium salt. The mobilities
and association constants obtained from the conductivity data agree with a model recently proposed for the H2O−B(OH)
4
−
interactions. A discrepancy in the reported thermodynamic behavior of NaB(OH)4 aqueous solutions has been resolved by means of the association constants obtained in the present study. Thus the usefulness
of the conductivity measurements to determine excess chemical potentials of binary electrolytes in dilute solution is again
shown. 相似文献
5.
Maha El-Tohamy Sawsan Razeq Magda El-Maamly Abdalla Shalaby 《Central European Journal of Chemistry》2010,8(4):937-945
The construction and performance characteristics of phenytoin sodium selective electrodes are detailed. Two types of electrodes:
plastic membrane I and coated wire II, were constructed based on the incorporation of phenytoin sodium with tungstosilicic
acid. The influence of membrane composition, kind of plasticizer, pH of the test solution, soaking time and the electrodes’
foreign ions were investigated. The electrodes showed a Nernstian response with a mean calibration graph slope of 30.9±0.1
and 28.9±0.1 mV decade−1 at 25°C for electrode I and II respectively, over a phenytoin sodium concentration range of 5×10−3−5×10−6 M and 1×10−3−1×10−6 M with a detection limit 1.3×10−6 M and 2.5×10−7 M for electrode I and II, respectively. The electrodes gave average selective precision and were usable within the pH range
6–10. Interference studies from common cations, alkaloids, sugars, amino acids and drug excipients are reported. The results
obtained by the proposed electrodes were also applied successfully for the determination of the drug in pharmaceutical preparations
and biological fluids. 相似文献
6.
P. P. Levin P. V. Aboltin T. F. Shevchenko G. R. Kalamkarov 《High Energy Chemistry》2010,44(6):520-523
The kinetics of quenching of the all-trans-retinal triplet state by air oxygen in aqueous solutions of bovine serum albumin and in a cardiolipin liposome suspension
was investigated by nanosecond laser photolysis. It was established that the quenching reaction rate constant in the albumin
solution (1.8 × 108 l mol−1 s−1) was an order of magnitude less than in liposomes (3.1 × 109 l mol−1 s−1). These constants were 5.0 × 109 and 1.1 × 109 l mol−1 s−1 in methanol and aqueous solutions containing 10 vol % methanol, respectively. The effect of hindered oxygen access to the
Lall-trans-retinal attached to albumin is discussed in terms of its influence on the photooxidation processes in the retina. 相似文献
7.
Silver nanoparticles are prepared by reducing Ag+ ions with sodium borohydride in aqueous solutions containing carbonate ions (5 × 10−5−1 × 10−2 mol l−1). It is established that carbonate ions represent an efficient stabilizer that provides nanoparticles with electrostatic
protection via the formation of an electrical double layer. The maximum stability of a silver dispersion is observed at a
carbonate ion concentration of 1 × 10−3 mol l−1. The average size of silver nanoparticles is 10.0 ± 2.5 nm. The formation kinetics of silver nanoparticles is described by
an equation for a first-order reaction with a rate constant of 2.3 × 10−3 s−1 (±20%). 相似文献
8.
Jonathan F. Ojo Jide Ige Grace O. Ogunlusi Olanrewaju Owoyomi Esan S. Olaseni 《Transition Metal Chemistry》2006,31(6):782-785
The kinetics of the reactions between Fe(phen)
3
2+
[phen = tris–(1,10) phenanthroline] and
Co(CN)5X3− (X = Cl, Br or I) have been investigated in aqueous acidic solutions at I = 0.1 mol dm−3 (NaCl/HCl). The reactions were carried out at a fixed acid concentration ([H+] = 0.01 mol dm−3) and the second-order rate constants for the reactions at 25 °C were within the range of (0.151–1.117) dm3 mol−1 s−1. Ion-pair constants K
ip for these reactions, taking into consideration the protonation of the cobalt complexes, were 5.19 × 104, 3.00 × 102 and 4.02 × 104 mol−1 dm−3 for X = Cl, Br and I, respectively. Activation parameters measured for these systems were as follows: ΔH* (kJ K−1 mol−1) = 94.3 ± 0.6, 97.3 ± 1.0 and 109.1 ± 0.4; ΔS* (J K−1) = 69.1 ± 1.9, 74.9 ± 3.2 and 112.3 ± 1.3; ΔG* (kJ) = 73.7 ± 0.6, 75.0 ± 1.0 and 75.7 ± 0.4; E
a
(kJ) = 96.9 ± 0.3, 99.8 ± 0.4, and 122.9 ± 0.3; A (dm3 mol−1 s−1) = (7.079 ± 0.035) × 1016, (1.413 ± 0.011) × 1017, and (9.772 ± 0.027) × 1020 for X = Cl, Br, and I respectively. An outer – sphere mechanism is proposed for all the reactions. 相似文献
9.
The following reaction rate constants of oxygen atoms with iodomethane and chlorine were measured using resonance fluorescence
under jet conditions at 298 K: k
1 = (2.4 ± 0.5) × 10–15 and k
2 = (6.9 ± 0.2) × 10−14 cm3/s, respectively. 相似文献
10.
WANG Weiping TANG Jianghong PENG Xuhong HU Zhide & CHEN Xingguo Department of Chemistry Lanzhou University Lanzhou China 《中国科学B辑(英文版)》2006,49(4):332-337
1 Introduction Studies on the interaction of the complexes formed between proteins and amphiphilic molecules in aque- ous solutions have become a new focus and great pro- gress has been made in recent years[1―5]. An under- standing of these systems is of great importance in many biological processes and clinical use of drugs. The globular anionic protein human serum albumin (HSA) is widely used as a protein model in many studies[1―4,6]. Its principal function is to transport fatty acids an… 相似文献
11.
A. M. Nazarov E. M. Chainikova R. L. Safiullin S. L. Khursan V. D. Komissarov 《Reaction Kinetics and Catalysis Letters》1997,61(1):173-174
The rate constants of benzophenone oxide decay measured at 25°C by flash photolysis (FPh) strongly depend on the nature of
the solvent [2k=(2.6±0.3)×107 L mol−1 s−1 in CH3CN, and (2.0±0.2)×109 L mol−1 s−1 in pentane]. 相似文献
12.
The redox characteristics of the drug domperidone at a glassy-carbon electrode (GCE) in aqueous media were critically investigated
by differential-pulse voltammetry (DPV) and cyclic voltammetry (CV). In Britton–Robinson (BR) buffer of pH 2.6–10.3, an irreversible
and diffusion-controlled oxidation wave was developed. The dependence of the CV response of the developed anodic peak on the
sweep rate (ν) and on depolizer concentration was typical of an electrode-coupled chemical reaction mechanism (EC) in which an irreversible
first-order reaction is interposed between the charges. The values of the electron-transfer coefficient (α) involved in the rate-determining step calculated from the linear plots of E
p,a against ln (ν) in the pH range investigated were in the range 0.64 ± 0.05 confirming the irreversible nature of the oxidation peak. In
BR buffer of pH 7.6–8.4, a well defined oxidation wave was developed and the plot of peak current height of the DPV against
domperidone concentration at this peak potential was linear in the range 5.20 × 10−6 to 2.40 × 10−5 mol L−1 with lower limits of detection (LOD) and quantitation (LOQ) of 6.1 × 10−7 and 9.1 × 10−7 mol L−1, respectively. A relative standard deviation of 2.39% (n = 5) was obtained for 8.5 × 10−6 mol L−1 of the drug. These DPV procedures were successfully used for analysis of domperidone in the pure form (98.2 ± 3.1%), dosage
form (98.35 ± 2.9%), and in tap (97.0 ± 3.6%) and wastewater (95.0 ± 2.9%) samples. The method was validated by comparison
with standard titrimetric and HPLC methods. Acceptable error of less than 3.3 % was also achieved.
Figure In aqueous media at pH 7.6- 8.4, the DPV and cyclic voltammetry of the drug domperidone (I) at GCE showed an irreversible
and diffusion controlled oxidation wave. The values of the electron transfer coefficient (α) involved in the rate determining
step were found in the range 0.64± 0.05 confirming the irreversible nature of the peak. The analysis of the drug in pure form
and in wastewater samples was successfully achieved 相似文献
13.
A 3-amino-5-mercapto-1,2,4-triazole (TA) self-assembled monolayer-modified gold electrode (TA SAM/Au) is characterized by
X-ray photoelectron spectroscopy, A.C. impedance, cyclic voltammetry, chronoamperometry and chronocoulometry. The TA SAM/Au
exhibited good promotion of the electrochemical oxidation of dopamine. Some electrochemical parameters of dopamine such as
electron transfer number, exchange current density, standard heterogeneous rate constant, diffusion coefficient, etc., were
measured by different electrochemical methods. The peak currents of dopamine were linearly dependent on its concentration
in the range of 1.5 × 10−6–1.0 × 10−4 mol L−1, with a detection limit of 5.0 × 10−7 mol L−1. The oxidative peak potentials of dopamine and ascorbic acid were well separated at about 190 ± 10 mV in pH 2.0 BR buffers
at TA SAM/Au, the oxidation peak current increases approximately linearly with increasing concentration of both dopamine and
ascorbic acid in the concentration range of 9.98 × 10−6–4.54 × 10−4 mol L−1. It can be used for simultaneous determination of dopamine and ascorbic acid. 相似文献
14.
ZHU Hongping ZHANG Zhaoxia ZHAO Hongwei WANG Wenfeng & YAO Side . Shanghai Institute of Applied Physics Chinese Academy of Sciences Shanghai China . Graduate University of the Chinese Academy of Sciences Beijing China 《中国科学B辑(英文版)》2006,49(4):308-314
Reactive oxygen species (ROS) are generated dur- ing radiation, respiratory burst, normal metabolic processes and so on. There are enzymatic and non-enzymatic antioxidants such as superoxide dis- mutase (SOD), glutathione peroxidase (GSH-Px), vi- tamin E (VE) and carotenoids that can either inhibit or repair the ROS-induced damage. ROS is essential to maintain physiological homeostasis. However, exces- sive ROS give rise to oxidative damage to proteins, lipids and DNA which related t… 相似文献
15.
S. P. Sovilj V. M. Vasié D. Lj. Stojié 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2008,82(5):709-712
The influence of cationic surfactant hexadecyltrimethylammonium bromide (CTAB) on the kinetics of the spontaneous reduction
of the analytically important compound, sodium hexanitrocobaltate(III), was studied. The spontaneous reduction was monitored
spectrophotometrically at pH 2 and 5 and at concentrations of CTAB from 1 × 10−5 to 5 × 10−4 M. The mechanism of this process was described using two consecutive first-order reactions. A decrease in the rate constant
for reduction at pH 5 in solutions containing CTAB in concentrations of 5.6 × 10−5 M (critical micelle concentration) compared with its rate in an aqueous solution was observed. These effects could be explained
by electrostatic and hydrophobic/hydrophilic interactions between the micellar pseudophase and the hexanitrocobaltate(III)
ion.
The article is published in the original. 相似文献
16.
Won-Sik Han Young-Hoon Lee Soon-Nyeo Lee Tae-Kee Hong 《Journal of Analytical Chemistry》2011,66(9):854-858
Iodide ion selective poly(aniline) solid contact electrode based on quinine-Cu ionophore as a sensing material has been successfully
developed. The electrode exhibits good linear response of 52.0 mV/decade (at 20 ± 0.2°C, r
2 = 0.9998) within the concentration range of 1 × 10−6.4–1 × 10−1.0 M KI. The composition of this electrode was quinine-Cu 2.0: PVC 30.0: bis(2-ethylhexyl)sebacate 68.0 (mass). This plasticizer
provides the best response characteristics. The electrode shows good selectivity for iodide ion in comparison with any other
anions and is suitable for use with aqueous solutions of pH 3.3–9.4. The standard deviations of the measured EMF difference
were ±1.4 and ±1.3 mV for iodide sample solutions of 1.0 × 10−2 M and 1.0 × 10−3 M, respectively. The stabilization time was less than 10 min and response time was less than 15 sec. 相似文献
17.
The electrochemical oxidation of sulfite catalyzed by acetylferrocene (AFc) at a glassy carbon electrode (GCE) in 0.2 M NaClO4 aqueous solution has been studied by cyclic voltammetry. Although sulfite itself showed a sluggish electrochemical response at the GCE, the response could be enhanced greatly by using AFc as a mediator, which enables a sensitive determination of the substrate (sulfite). The reaction rate constant for catalytic oxidation was evaluated as (7.02 ± 0.05) × 104 M ?1 s?1 by chronoamperometry. Experimental conditions that maximize the current efficiency of the electrocatalytic oxidation, such as the pH and both the catalyst (AFc) and substrate (sulfite) concentrations, were also investigated. The electrochemical kinetics of electrocatalytic oxidation of sulfite by AFc has been studied by cyclic voltammetry. In the presence of 5 × 10?4 M AFc, the oxidation current is proportional to the sulfite concentration and the calibration plot was linear over the concentration range 2 × 10?4–2.4 × 10?3 M . This result can be applied in the determination of real samples. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
18.
Wensheng Huang Chunhai Yang Wanyun Qu Shenghui Zhang 《Russian Journal of Electrochemistry》2008,44(8):946-951
In this work, an electrochemical method for the determination of malachite green was developed on the basis of enhancement
effect of an anionic surfactant: sodium dodecyl benzene sulfonate. It is found that the oxidation peak current of malachite
green at carbon paste electrode significantly increases in the presence of low concentration of sodium dodecyl benzene sulfonate
in pH 6.5 phosphate buffer, suggesting that sodium dodecyl benzene sulfonate shows obvious enhancement effect for the determination
of malachite green. The experimental parameters, such as supporting electrolyte, kind of surfactant, concentration of sodium
dodecyl benzene sulfonate and accumulation time, were optimized, and then a sensitive and convenient electrochemical method
was proposed for the determination of malachite green. The oxidation peak current is proportional to the concentration of
malachite green over the range from 8.0 × 10−9 to 5.0 × 10−7 mol l−1, and the detection limit is 4.0 × 10−9 mol l−1 after 5 min of accumulation. Finally, this new method was successfully employed to detect malachite green in fish samples.
Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 8, pp. 1019–1024.
The text was submitted by the authors in English. 相似文献
19.
Joanna Wiśniewska 《Transition Metal Chemistry》2007,32(1):107-111
The kinetics of the oxidation of promazine by trisoxalatocobaltate(III) were studied in the presence of a large excess of
the cobalt(III) in tris buffer solution using u.v.–vis spectroscopy ([CoIII] = (0.6 − 2) × 10−3
M, [ptz] = 6 × 10−5
M, pH = 6.6–7.8, I = 0.1 M (NaCl), T = 288−308 K, l = 1 cm). The reaction proceeds via two consecutive reversible steps. In the first step, the reaction leads to formation of cobalt(II) species and a stable cationic
radical. In the second step, cobalt(III) is reduced to cobalt(II) ion and a promazine radical is oxidized to the promazine
5-oxide. Linear dependences of the pseudo-first-order rate constants (k
1 and k
2) on [CoIII] with a non-zero intercept were established for both redox processes. Rates of reactions decreased with increasing concentration
of the H+ ion indicating that the promazine and its radical exist in equilibrium with their deprotonated forms, which are reactive
reducing species. The activation parameters for reactions studied were as follows: ΔH≠ = 44 ± 1 kJ mol−1, ΔS≠ = −100 ± 4 JK−1 mol−1 for the first step and ΔH≠ = 25 ± 1 kJ mol−1, ΔS≠ = −169 ± 4 J K−1 mol−1 for the second step, respectively. Mechanistic consequences of all the results are discussed. 相似文献
20.
The •OH and the NO2
• radicals generated pulse radiolytically in N2O-saturated aqueous solution at pH 8–8.5 oxidize Mesna to form the corresponding thiyl radicals which on reaction with thiolate
ions form an RSSR•
− type of transient with λmax = 420 nm. The rate constants for the formation of these transients were determined. In the absence of O2 at pH=6, the RS• radicals formed show an absorption maximum at 360 nm and an ε=200±50 dm3 mol−1 cm−1. The rate constant k (•OH+RSH) was 6×109 dm3 mol−1 s−1 as determined from competition kinetics. In the presence of O2 the Mesna thiyl radical was seen to rapidly add oxygen to form an RSOO• type of species with λmax = 535 nm, ε=700±50 dm3 mol−1 cm−1 and k (RS•+O2)=1.3×108 dm3 mol−1 s−1. Both the RS• and the RSOO• radicals formed by the oxidation of Mesna were able to abstract H-atoms from ascorbate ions and k(RS• +AH−)=~k(RSOO•+AH−)=~6−7×108 dm3 mol−1 s−1-. Moderately strong oxidants like CCl3OO• and the (CH3)3CO• radicals, having a reduction potential of +1.4−1.6 V vs NHE were unable to oxidize Mesna. The results thus reflect on the
pro- and anti-oxidant properties of Mesna. 相似文献