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1.
Nabila M. Guindy Zeinab M. Abou-Gamra Michel F. Abdel-Messih 《Monatshefte für Chemie / Chemical Monthly》2000,131(8):857-866
Summary. The kinetics of the formation of the 1:3 complex of chromium(III) with L-glutamic acid and DL-lysine were studied spectrophotometrically at and 550 nm. The reaction was found to be first order in both reactants. Increasing the hydrogen ion concentration from 3.2×10−5 to 1.0×10−3 molċdm−3 retarded the reaction rate which is of the form . Values of 28.8 and 63.6 kJċmol−1 were obtained for the energy of activation and −184 and −116 Jċ K−1ċmol−1 for the entropy of activation for L-glutamic acid and DL-lysine. The logarithms of the formation constants of the two complexes were found to be 5.9 and 5.1.
Received January 7, 2000. Accepted (revised) March 8, 2000 相似文献
2.
Biljana Šmit Biljana Petrović Sofija Sovilj Dragan Čanović Živadin D. Bugarčić 《Monatshefte für Chemie / Chemical Monthly》2008,139(10):1197-1202
The reactions of cisplatin with nizatidine and ranitidine were studied in D2O at pD 7.4 and 298 K by means of 1H NMR spectroscopy. The second order rate constants, k
2, for the reaction of cisplatin with nizatidine is (2.71 ± 0.11) × 10−4 M
−1 s−1, and for the reaction with ranitidine (6.72 ± 0.17) × 10−4 M
−1 s−1. The reactions of nizatidine and ranitidine were also studied with other Pd(II) and Pt(II) complexes. The set of the complexes
was selected because of their difference in reactivity, steric hindrance, and binding properties.
Correspondence: Prof. Dr. Živadin D. Bugarčić, Faculty of Science, University of Kragujevac, Radoja Domanovića 12, 34000 Kragujevac,
Serbia. 相似文献
3.
Nabila M. Guindy Zeinab M. Abou-Gamra Michel F. Abdel-Messih 《Monatshefte für Chemie / Chemical Monthly》2000,48(2):857-866
The kinetics of the formation of the 1:3 complex of chromium(III) with L-glutamic acid and DL-lysine were studied spectrophotometrically at and 550 nm. The reaction was found to be first order in both reactants. Increasing the hydrogen ion concentration from 3.2×10−5 to 1.0×10−3 molċdm−3 retarded the reaction rate which is of the form . Values of 28.8 and 63.6 kJċmol−1 were obtained for the energy of activation and −184 and −116 Jċ K−1ċmol−1 for the entropy of activation for L-glutamic acid and DL-lysine. The logarithms of the formation constants of the two complexes were found to be 5.9 and 5.1. 相似文献
4.
Jun Yue Bai Liang Wang Hong Jing Wang Peng Fei Huang Yu Qing Zhao Sheng Di Fan 《Mikrochimica acta》2006,156(3-4):321-326
The electrochemical behavior of epinephrine (EP) at a mercaptoacetic acid (MAA) self-assembled monolayer modified gold electrode
was studied. The MAA/Au electrode is demonstrated to promote the electrochemical response of epinephrine by cyclic voltammetry.
The possible reaction mechanism is also discussed. The diffusion coefficient D of EP is 6.85 × 10−6 cm2 s−1. In 0.1 mol L−1 phosphate buffer (pH 7.20), a sensitive oxidation peak was observed at 0.177 V, and the peak current is proportional to the
concentration of EP in the range of 1.0 × 10−5–2.0 × 10−4 mol L−1 and 1.0 × 10−7–1.0 × 10−6 mol L−1. The detection limit is 5 × 10−8 mol L−1. The modified electrode is highly stable and can be applied to the determination of EP in practical injection samples. The
method is simple, quick, sensitive and accurate. 相似文献
5.
Electrochemical investigations of the reaction mechanism and kinetics between riboflavin immobilised on zirconium phosphate
(ZPRib) in carbon paste and NADH showed results yielding reliable information about aspects on the mechanism of the electron
transfer reaction between the flavin and NADH. The formal potential (E°′) of the adsorbed riboflavin was −220 mV versus SCE at pH 7.0. A shift about 250 mV towards a more positive potential compared
with its value in solution was assigned to the interaction between the basic nitrogen of riboflavin and the acid groups of
ZP. The invariance of the E°′ with the pH of the contacting solution and the effect of different buffer constituents were attributed to the protection
effect of ZP over the riboflavin. The electrocatalytic oxidation of NADH at the electrode was investigated using cyclic voltammetry
and rotating disk electrode methodology using a potential of −50 mV versus SCE. The heterogeneous electron transfer rate constant,
k
obs, was 816 M−1 s−1 and the Michaelis-Menten constant, K
M, was 1.8 mM (confirming a charge transfer complex intermediate in the reaction) for an electrode with a riboflavin coverage
of 6.8 × 10−10 mol cm−2. This drastic increase in the reaction rate between NADH and the immobilised riboflavin was assigned to the shift of the
E°′. A surprising effect with addition of calcium or magnesium ion to the solution was also observed. The E°′ was shifted to −150 mV versus SCE and the reaction rate for NADH oxidation increased drastically.
Received: 22 February 1999 / Accepted: 10 March 1999 相似文献
6.
A new chemiluminescence (CL) method combined with flow injection technique is described for the determination of Cr(III) and
total Cr. It is found that a strong CL signal is generated from the reaction of Cr(III), lucigenin and KIO4 in alkaline condition. The determination of total Cr is performed by pre-reduction of Cr(VI) to Cr(III) by using H2SO3. The CL intensity is linearly related to the concentration of Cr in the range 4.0 × 10−10–1.0 × 10−6 g mL−1. The detection limit (3s
b) is 1 × 10−10 g mL−1 Cr and the relative standard deviation is 1.9% (5.0 × 10−8 g mL−1 of Cr(III) solution, n = 11). The method was applied to the determination of Cr(III) and total Cr in water samples and compared satisfactorily with
the official method. 相似文献
7.
M. H. Pournaghi-Azar H. Dastangoo M. Ziaei 《Journal of Solid State Electrochemistry》2007,11(9):1221-1227
The electrocatalytic activity of a Prussian blue (PB) film on the aluminum electrode by taking advantage of the metallic palladium
characteristic as an electron-transfer bridge (PB/Pd–Al) for electrooxidation of 2-methyl-3-hydroxy-4,5-bis (hydroxyl–methyl)
pyridine (pyridoxine) is described. The catalytic activity of PB was explored in terms of FeIII [FeIII (CN)6]/FeIII [FeII (CN)6]1− system. The best mediated oxidation of pyridoxine (PN) on the PB/Pd–Al-modified electrode was achieved in 0.5 M KNO3 + 0.2 M potassium acetate of pH 6 at scan rate of 20 mV s−1. The mechanism and kinetics of the catalytic oxidation reaction of PN were monitored by cyclic voltammetry and chronoamperometry.
The results were explained using the theory of electrocatalytic reactions at chemically modified electrodes. The charge transfer-rate
limiting reaction step is found to be a one-electron abstraction, whereas a two-electron charge transfer reaction is the overall
oxidation reaction of PN by forming pyridoxal. The value of α, k, and D are 0.5, 1.2 × 102 M−1 s−1, and 1.4 × 10−5 cm2 s−1, respectively. Further examination of the modified electrodes shows that the modifying layers (PB) on the Pd–Al substrate
have reproducible behavior and a high level of stability after posing it in the electrolyte or Pyridoxine solutions for a
long time. 相似文献
8.
Francisco Ros Pilar Jiménez María Victoria Roux 《Monatshefte für Chemie / Chemical Monthly》2007,138(10):941-949
Summary. The cohesion potential energy of the crystal of one enantiomer of ethyl 3-cyano-3-(3,4-dimethyloxyphenyl)-2,2,4-trimethylpentanoate,
−47.7 ± 0.1 kJ mol−1 (0–90°C), was found out from the heat of sublimation (123.2 ± 5.1 kJ mol−1, 78.6°C) and the kinetic energies for the gas phase and the crystal. It was found that the entropy function of Debye’s theory of solids mathematically agreed with the vibrational entropy of the gas (variationally obtained), allowing to disclose
the vibrational energy using the Debye energy function (E
vib 835.0 kJ mol−1 (78.6°C), E
0 included). E
kin for the crystal (771.1 kJ mol−1 (78.6°C)) was obtained by Debye’s theory with the experimental heat capacity. The cohesion energy represented a moderate part of the sublimation energy.
The cohesion energy of the racemic crystal, −44.2 kJ mol−1, was obtained by the heat of formation of the crystal in the solid state (3.0 kJ mol−1, 83.3°C) and E
kin for the crystal (by Debye’s theory). The decrease in cohesion on formation of the crystal accounted for the energy of formation. The change in potential
energy on liquefaction of the racemate from the gas state was disclosed obtaining added-up E
vib + rot for the liquid in the way as to E
vib for the gas, the Debye entropy function being increasedly suited for the liquid (E
vib + rot 763.4 kJ mol−1 (115.4°C)). Positive ΔE
pot, 13.0 kJ mol−1, arised from the increase in electronic energy (Δ
l
νmean − 154.3 cm−1, by the dielectric nature of the liquid), added to the cohesion energy. 相似文献
9.
Günter Grampp Stephan Landgraf Tomasz Wesierski Beata Jankowska Ewa Kalisz Dana-Maria Sabou Boryana Mladenova 《Monatshefte für Chemie / Chemical Monthly》2002,133(10):1363-1372
Summary. The kinetics of the CrO(O2)2 formation by H2O2 and Cr2O7
2− in aqueous acidic media was measured at 293 ± 2 K in a pH range between 2.5 and 3.3. Using the stopped-flow method with rapid scan UV-VIS detection, the rate law of the formation
of CrO(O2)2 was determined. For the media HClO4, HNO3 and CH3COOH, the reaction order in the Cr2O7
2− concentration was found to be 0.5. For [H2O2] as well as for [H+], the reaction was first order in all acids used. In HCl and H2SO4 media the reaction was first order in Cr2O7
2−. At T = 293 ± 2 K the rate constant for the formation of Cr(O)(O2)2 was found to be (7.3 ± 1.9) · 102 M−3/2 s−1 in HClO4.
Corresponding author. E-mail: grampp@ptc.tu-graz.ac.at
Received January 30, 2002; accepted (revised) June 5, 2002 相似文献
10.
Ashraf A. Mohamed 《Monatshefte für Chemie / Chemical Monthly》2001,132(8):919-928
Summary. A new selective, sensitive, and simple kinetic method is developed for the determination of trace amounts of iodide. The
method is based on the catalytic effect of iodide on the reaction of triflupromazine (TFP) with H2O2. The reaction is followed spectrophotometrically by tracing the oxidation product at 498 nm within 1 min after addition of
H2O2. The optimum reaction conditions are TFP (0.4 × 10−3
M), H2SO4 (1.0M), H3PO4 (2.0M), and H2O2 (1.6M) at 30°C. Following this procedure, iodide can be determined with a linear calibration graph up to 4.5 ng ċ cm−3 and a detection limit of 0.04 ng ċ cm−3, based on the 3 Sb criterion. The method can also be applied to the determination of iodate and periodate ions. Determination of as little as
0.2, 1.0, 2.0, and 4.0 ng ċ cm−3 of I−, IO3
-, or IO4
- in aqueous solutions gave an average recovery of 98% with relative standard deviations below 1.6% (n = 5). The method was applied to the determination of iodide in Nile river water and ground waters as well as in various food
samples after alkaline ashing treatment. The method is compared with other catalytic spectrophotometric procedures for iodide
determination.
Received January 19, 2001. Accepted (revised) March 12, 2001 相似文献
11.
Functionalized polypyrrole films were prepared by incorporation of Fe(CN)6
3− as doping anion during the electropolymerization of pyrrole at a glassy carbon electrode from aqueous solution. The electrochemical
behavior of the Fe(CN)6
3−/Fe(CN)6
4− redox couple in polypyrrole was studied by cyclic voltammetry. An obvious surface redox reaction was observed and dependence
of this reaction on the solution pH was illustrated. The electrocatalytic ability of polypyrrole film with ferrocyanide incorporated
was demonstrated by oxidation of ascorbic acid at the optimized pH of 4 in a glycine buffer. The catalytic effect for mediated
oxidation of ascorbic acid was 300 mV and the bimolecular rate constant determined for surface coverage of 4.5 × 10−8 M cm−2 using rotating disk electrode voltammetry was 86 M−1 s−1. Furthermore, the catalytic oxidation current was linearly dependent on ascorbic acid concentration in the range 5 × 10−4–1.6 × 10−2 M with a correlation coefficient of 0.996. The plot of i
p versus v
1/2 confirms the diffusion nature of the peak current i
p.
Received: 12 April 1999 / Accepted: 25 May 1999 相似文献
12.
Selective Indicator Reaction for Kinetic Determination of Traces of Manganese(II), Ribavirin and Tiazofurin 总被引:1,自引:0,他引:1
Gordana A. Milovanović Mira M. Čakar Nevenka B. Vučić Milan Jokanović 《Mikrochimica acta》2000,135(3-4):173-178
In this work it was established that, in the presence of ammonium carbonate, traces of manganese(II) catalyse the oxidation
of Nile Blue A by hydrogen peroxide, which enables its kinetic determination in the concentration range from 6.6 to 65.9 ng
cm−3, the detection limit being 8.0 × 10−2 ng cm−3. Antiviral/antitumour substances modify the catalytic activity of manganese(II): 1-β-D-ribofuranosyl-1,2,4-triazole-3-carboxamide,
ribavirin, increases the catalytic effect of manganese(II), while 2-β-D-ribofuranosyl-thiazole-4-carboxamide, tiazofurin,
acts as an inhibitor. On the basis of these effects, a kinetic method for determining ribavirin concentrations from 0.5 × 10−1 to 4.0 × 10−1 μg cm−3 and tiazofurin concentrations from 0.3 to 2.6 μg cm−3 is proposed. The kinetics of the indicator reaction were studied in the presence of the substances examined, the kinetic
equations established, and the constants of the corresponding reaction rates calculated. The effect of temperature on these
reactions was also investigated. The method was applied to the determination of manganese(II) in mineral water and ribavirin
in pharmaceutical preparations.
Received December 16, 1999. Revision June 6, 2000. 相似文献
13.
Vesna Kuntić Dusěan Malesěev Zorica Radović Vladana Vukojević 《Monatshefte für Chemie / Chemical Monthly》2000,131(7):769-777
Summary. In the present work, rutin (3,3′ ,4′ ,5,7-pentahydrohyflavone-3-rhamnoglucoside) was determinated via a complexing reaction with a titanyloxalate anion. K2[TiO(C2O4)2] and rutin react in 50% ethanol forming a 1:2 complex in a pH range from 4.00 to 11.50, in which the TiO(C2O4)2
2− ion is linked to rutin through the 4-carbonyl and 5-hydroxyl group. The thermodynamic stability constant log β2
0 of the complex is determined to 10.80 at pH = 6.50. The change of the standard Gibbs free energy Δ G0 amounts to −61 kJċ mol−1, indicating that the process of complex formation is spontaneous. The optimal conditions for the spectrophotometric determination
of microconcentrations of rutin are at pH=6.40 and λ= 430 nm, where the complex shows an absorption maximum with a molar absorption coefficient a
430=(60±2)ċ103 dm3ċ mol−1ċ cm−1. The method is applied rutin determination from tablets.
Received January 4, 2000. Accepted (revised) February 17, 2000 相似文献
14.
M. López-Sánchez M. J. Ayora-Cañada A. Molina-Díaz M. Siam W. Huber G. Quintás S. Armenta B. Lendl 《Analytical and bioanalytical chemistry》2009,394(8):2137-2144
A mid-infrared enzymatic assay for label-free monitoring of the enzymatic reaction of fructose-1,6-bisphosphatase with fructose
1,6-bisphosphate has been proposed. The whole procedure was done in an automated way operating in the stopped flow mode by
incorporating a temperature-controlled flow cell in a sequential injection manifold. Fourier transform infrared difference
spectra were evaluated for kinetic parameters, like the Michaelis–Menten constant (K
M) of the enzyme and V
max of the reaction. The obtained K
M of the reaction was 14 ± 3 g L−1 (41 μM). Furthermore, inhibition by adenosine 5′-monophosphate (AMP) was evaluated, and the K
MApp value was determined to be 12 ± 2 g L−1 (35 μM) for 7.5 and 15 μM AMP, respectively, with V
max decreasing from 0.1 ± 0.03 to 0.05 ± 0.01 g L−1 min−1. Therefore, AMP exerted a non-competitive inhibition. 相似文献
15.
Summary. It was found that the hypericinate salts of (R)-1-phenylethylamine and (S)-1-(1-naphthyl)-ethylamine display a small chiroptical signal of the same sign only at high concentrations in an apolar solvent.
No further indications of a chiral discrimination between the helical conformers of hypericinate could be found in these cases.
However, upon esterification of the 3-hydroxyl group of hypericin with (1S)-camphanic chloride, the two diastereomers were found in an 1:1 ratio equilibrating rather fast at temperatures above 30°C
with one diastereomer in excess. From the temperature dependence of the equilibrium positions (measured by means of CD and
1H NMR), a ΔG
0 value of 5.8±0.5 kJ·mol−1 was derived. Accordingly, the chiral discrimination of the (M)-configured enantiomer of the helix by the (S)-configured auxiliary occurred at an intermediate level. From the temperature dependence of the equilibration kinetics an
activation energy of E
a = 70±0.5 kJ·mol−1 was derived, which thus defines the upper limit of the helix inversion of hypericin and hypericinate. This value is by about
10 kJ·mol−1 lower than the recently estimated limit.
Corresponding author. E-mail: heinz.falk@jku.at
Received March 22, 2002; accepted April 3, 2002 相似文献
16.
Günter Grampp Stephan Landgraf Tomasz Wesierski Beata Jankowska Ewa Kalisz Dana-Maria Sabou Boryana Mladenova 《Monatshefte für Chemie / Chemical Monthly》2002,212(4):1363-1372
The kinetics of the CrO(O2)2 formation by H2O2 and Cr2O7
2− in aqueous acidic media was measured at 293 ± 2 K in a pH range between 2.5 and 3.3. Using the stopped-flow method with rapid scan UV-VIS detection, the rate law of the formation
of CrO(O2)2 was determined. For the media HClO4, HNO3 and CH3COOH, the reaction order in the Cr2O7
2− concentration was found to be 0.5. For [H2O2] as well as for [H+], the reaction was first order in all acids used. In HCl and H2SO4 media the reaction was first order in Cr2O7
2−. At T = 293 ± 2 K the rate constant for the formation of Cr(O)(O2)2 was found to be (7.3 ± 1.9) · 102 M−3/2 s−1 in HClO4. 相似文献
17.
Peter Klampfer Primož Benkič Maja Ponikvar Ana Rahten Antonija Lesar Adolf Jesih 《Monatshefte für Chemie / Chemical Monthly》2003,134(1):1-9
Summary. Hydrazinium(+2) fluoroarsenate(III) fluoride was prepared by the reaction of hydrazinium(+2) fluoride and liquid arsenic
trifluoride. N2H6AsF4F is stable at 273 K, but decomposes slowly at room temperature. N2H6AsF4F crystallizes in the orthorhombic space group Pnn2 with a = 774.0(2) pm, b = 1629.2(4) pm and c = 436.6(1) pm; V = 0.5506(3) nm3, Z = 4 and d
c
= 2.461 g cm−3. The structure consists of N2H6
2+ cations, AsF4
− anions, and F− anions and is interconnected by a hydrogen bonding network. Distorted trigonal-bipyramidal AsF4
− units are very weakly interconnected and form chains along the b axis. Bands in the Raman spectrum are assigned to the vibrations of N2H6
+2 cations and AsF4
− anions.
Corresponding author. E-mail: adolf.jesih@ijs.si
Received April 18, 2002; accepted July 15, 2002 相似文献
18.
Aqueous solution of water soluble colloidal MnO2 was prepared by Perez-Benito method. Kinetics of l-methionine oxidation by colloidal MnO2 in perchloric acid (0.93 × 10−4 to 3.72 × 10−4 mol dm−3) has been studied spectrophotometrically. The reaction follows first-order kinetics with respect to [H+]. The first-order kinetics with respect to l-methionine at low concentration shifts to zero order at higher concentration. The effects of [Mn(II)] and [F−] on the reaction rate were also determined. Manganese (II) has sigmoidal effect on the rate reaction and act as auto catalyst.
The exact dependence on [Mn(II)] cannot be explained due to its oxidation by colloidal MnO2. Methionine sulfoxide was formed as the oxidation product of l-methionine. Ammonia and carbon dioxide have not been identified as the reaction products. The mechanism with the observed
kinetics has been proposed and discussed. 相似文献
19.
A compact miniaturized continuous flow system for the determination of urea content in milk 总被引:1,自引:0,他引:1
Willian Toito Suarez Osmundo Dantas Pessoa-Neto Vagner Bezerra dos Santos Ana Rita de Araujo Nogueira Ronaldo Censi Faria Orlando Fatibello-Filho Mar Puyol Julián Alonso 《Analytical and bioanalytical chemistry》2010,398(3):1525-1533
A multicommutation-based flow system with photometric detection was developed, employing an analytical microsystem constructed
with low temperature co-fired ceramics (LTCC) technology, a solid-phase reactor containing particles of Canavalia ensiformis DC (urease source) immobilized with glutaraldehyde, and a mini-photometer coupled directly to the microsystem which monolithically
integrates a continuous flow cell. The determination of urea in milk was based on the hydrolysis of urea in the solid-phase
reactor and the ammonium ions produced were monitored using the Berthelot reaction. The analytical curve was linear in the
urea concentration range from 1.0 × 10−4 to 5.0 × 10−3 mol L−1 with a limit of detection of 8.0 × 10−6 mol L−1. The relative standard deviation (RSD) for a 2.0 × 10−3 mol L−1 urea solution was lower than 0.4% (n = 10) and the sample throughput was 13 h−1. To check the reproducibility of the flow system, calibration curves were obtained with freshly prepared solutions on different
days and the RSD obtained was 4.7% (n = 6). Accuracy was assessed by comparing the results of the proposed method with those from the official procedure and the
data are in close agreement, at a 95% confidence level. 相似文献
20.
A rapid flow-injection method with chemiluminescence (CL) detection is described for the determination of glutathione (GSH).
The method is based on the CL reaction of luminol and hydrogen peroxide. GSH can greatly enhance the chemiluminescence intensity
in 0.1 mol/L borax–sodium hydroxide buffer solution (pH = 9.7). The maximum CL intensity was directly proportional to the
concentration of GSH in the range 3.0 × 10−7–2.0 × 10−5 mol/L, and the detection limit was 6.8 × 10−8 mol/L. The relative standard deviation was 3.4% for 5.0 × 10−6 mol/L of GSH (n = 11).
Received October 23, 2001; accepted June 18, 2002 相似文献