共查询到20条相似文献,搜索用时 15 毫秒
1.
Shaeel Ahmed AL-Thabaiti F. M. Al-Nowaiser A. Y. Obaid A. O. Al-Youbi Zaheer Khan 《Colloid and polymer science》2007,285(13):1479-1485
Stabilization and characterisation of water soluble colloidal MnO2 during the oxidation of sulphur-containing organic reductants “thiourea, thioactamide and methionine” by permanganate in
aqueous neutral media are reported for the first time. Upon addition of permanganate to a solution of methionine, a transient
species appears within the time of mixing, which is stable for several weeks. On the other hand, the transient species is
unstable in the presence of thiourea and thioacetamide, respectively. The nature of manganese (IV) species present in the
solution was characterized by spectrophotometric and coagulation measurements. On addition of HClO4, there is a decrease in the absorbance of the reaction mixture. Under pseudo first-order conditions ([reductants] > []), the reduction rate was very fast up to the formation of water soluble colloidal MnO2. The effect of various parameters, such as hydrogen ion concentration, amount of and concentration of reductants were investigated. Mechanisms consistent with the observed results have been proposed and
discussed. 相似文献
2.
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
3.
Kinetic data for the oxidation of glutathione (reduced, GSH), cysteine, glycine and glutamic acid by colloidal manganese dioxide,
(MnO2)
n
are reported. Colloidal MnO2, oxidized glutathione to disulphide (glutathione, oxidized), was reduced to manganese (II). Glycine and glutamic acid (structural
units of glutathione) are not oxidized by colloidal MnO2, but the other structural unit, cysteine, is also oxidized by the same oxidant under similar experimental conditions. This
is interpreted in terms of the rate-determining colloidal MnO2-S bonded intermediate. The reactivity of GSH towards colloidal MnO2 is very much higher than cysteine. Kinetics of oxidation of GSH and cysteine by colloidal MnO2 were performed spectrophotometrically as a function of [GSH], [cysteine], colloidal [(MnO2)
n
], [HClO4], temperature and trapping agents sodium fluoride and manganese (II) (reduction product of colloidal MnO2). The purpose of this work was to study the role of –NH2, –COOH, –SH groups present in the carbon chain of the above amino acids. It was found that the reactivity of –SH group is
higher than –NH2 and –COOH groups. The mechanisms, involving a colloidal MnO2 complex with GSH and cysteine, are proposed. The complexes decompose in a rate-determining step, leading to the formation
of free radical and manganese (III), which is also an intermediate. The dimerization of radicals takes place in a subsequent
fast step to yield the products. 相似文献
4.
The kinetics of the formation and decomposition of water-soluble colloidal MnO2 in the paracetamol– redox system have been investigated spectrophotometrically in aqueous-neutral media at 30 °C. Upon mixing aqueous solutions of permanganate and paracetamol, a readily distinguishable brown color appears and then disappears slowly. Experiments have been done to confirm the nature of intermediate (Mn(IV)) formed during the reduction of permanganate by paracetamol. The stoichiometry was found to be 1:1. Formation and decomposition of water-soluble colloidal MnO2 depend upon the experimental conditions, i.e., [paracetamol] and [H+]. The effect of total [paracetamol], and [H+] on the rate of the reaction was determined. On the basis of various observations, two mechanisms are proposed: one for MnO2 formation and the other for decomposition. 相似文献
5.
Water-soluble colloidal manganese dioxide has been used to oxidize l-tyrosine in aqueous-acidic medium. The kinetics of the reaction was studied in the absence and presence of non-ionic surfactant (TX-100) using a spectrophotometric technique. As the reaction was fast under pseudo-first-order conditions ([l-tyrosine] [MnO2]), the rate constants as a function of [l-tyrosine], [MnO2], [HClO4] and temperature were obtained under second-order conditions. The rate of the reaction increased and decreased with the increase in [l-tyrosine] and [MnO2], respectively. Perchloric acid, sodium pyrophosphate and sodium fluoride showed catalytic effect. The effect of externally added manganese(II) sulphate is complex. It is not possible to predict the exact dependence of the rate constants on manganese(II) concentration, which has a series of reactions with other reactants. The reaction is inhibited by the non-ionic surfactant TX-100. Activation parameters have been evaluated using Arrhenius and Eyring equations. Based on observed kinetic results, a probable mechanism for the reaction has been proposed which corresponds to fast adsorption of the reductant and hydrogen ion on the surface of colloidal MnO2 followed by one-step two-electron transfer rate limiting process. 相似文献
6.
In a non-aqueous medium, oxidation kinetics of thioglycolic, thiolactic and thiomalic acids by benzimidazolium dichromate have been studied. In the temperature range of 20°C–50°C, oxidation kinetics were examined by spectrophotometry. In terms of oxidant, the reaction is dependent on the unitary order. In the case of thioacids, we find the Michaelis-Menten type kinetics. Hydrogen-ions act as catalyst in this process. The reaction rate slows down as the Mn2+ ion concentration increases. The reaction does not cause acrylonitrile to polymerize. The formation of a thioester into the pre-equilibrium followed by its progressive degradation was postulated as a mechanism. 相似文献
7.
8.
The potential-pH response of an electrolytic manganese dioxide is investigated by means of a cavity microelectrode (CME). The potential-pH curves show a complex evolution that could be explained by the disporportionation of MnOOH species, leading to the formation of Mn2+ ions on the MnO2 surface. Such a behaviour is not suited for pH sensor application. However when the tip of the electrode is coated by a Nafion membrane, the potential-pH evolution shows a unique slope close to −60 mV pH−1. In addition, the sensor exhibits short time responses to pH variations, a good selectivity, and it can be easily renewed compared to classical sensors. 相似文献
9.
Oxidative transformation of ciprofloxacin by alkaline permanganate – A kinetic and mechanistic study
Kiran A. Thabaj Suresh D. KulkarniShivamurti A. Chimatadar Sharanappa T. Nandibewoor 《Polyhedron》2007
This spectroscopic study presents the kinetics and degradation pathways of oxidation of ciprofloxacin by permanganate in alkaline medium at constant ionic strength of 0.04 mol−3. Orders with respect to substrate, oxidant and alkali concentrations were determined. Effect of ionic strength and solvent polarity of the medium on the rate of the reaction was studied. The oxidation products were identified by LC-ESI-MS technique. Product characterization of ciprofloxacin reaction mixtures indicates the formation of three major products corresponding to m/z 263, 306, and 348 (corresponding to full or partial dealkylation of the piperazine ring). The piperazine moiety of ciprofloxacin is the predominant oxidative site to KMnO4. Product analyses showed that oxidation by permanganate results in dealkylation at the piperazine moiety of ciprofloxacin, with the quinolone ring essentially intact. The reaction kinetics and product characterization point to a reaction mechanism that likely begins with formation of a complex between ciprofloxacin and the KMnO4, followed by oxidation at the aromatic N1 atom of piperazine moiety to generate an anilinyl radical intermediate. The radical intermediates subsequently undergo N-dealkylation. Investigations of the reaction at different temperatures allowed the determination of the activation parameters with respect to the slow step of proposed mechanism. The proposed mechanism and the derived rate laws are consistent with the observed kinetics. 相似文献
10.
This article presents a theoretical study on the oxidation reaction of thiourea by hydrogen peroxide in water or alkaline solutions using density functional and ab initio theories. This work also focuses on the analysis of the thermodynamic and kinetic properties of the predicted oxidation mechanism of thiourea using density functional and ab initio theories. The calculated results show that the activation energies, activation enthalpies, and activation Gibbs free energies of the reaction decreased and the releasable reaction energies, enthalpies and Gibbs free energies increased with the cooperation of water or hydroxyl anion. We conclude that the oxidation reaction of thiourea by hydrogen peroxide in water or alkaline solutions was easier and more completed than that in the gas state. The calculated results are consistent with the experiments. 相似文献
11.
以医用纱布(medical gauze,MG)同时作为模板和还原剂,通过原位氧化还原反应,简便地制备了MG负载的MnO2纳米颗粒(MnO2 NPs/MG),并对其形貌、成分进行表征。结果表明,MnO2 NPs均匀地分散于MG纤维表面。结合MnO2纳米材料的吸附性能和MG复合材料的操作便捷性,将MnO2 NPs/MG进一步应用于亚甲蓝染料的去除。结果表明,在中性条件下,通过简单的浸泡搅拌,MnO2 NPs/MG对亚甲蓝的去除率可达85.09%,并且可以通过增大吸附材料用量与染料初始浓度的比例提高去除率。等温吸附和动力学研究证明,MnO2 NPs/MG对亚甲蓝的吸附符合Langmuir吸附等温模型和拟二级动力学模型。 相似文献
12.
以医用纱布(medical gauze,MG)同时作为模板和还原剂,通过原位氧化还原反应,简便地制备了MG负载的MnO2纳米颗粒(MnO2 NPs/MG),并对其形貌、成分进行表征。结果表明,MnO2 NPs均匀地分散于MG纤维表面。结合MnO2纳米材料的吸附性能和MG复合材料的操作便捷性,将MnO2 NPs/MG进一步应用于亚甲蓝染料的去除。结果表明,在中性条件下,通过简单的浸泡搅拌,MnO2 NPs/MG对亚甲蓝的去除率可达85.09%,并且可以通过增大吸附材料用量与染料初始浓度的比例提高去除率。等温吸附和动力学研究证明,MnO2 NPs/MG对亚甲蓝的吸附符合Langmuir吸附等温模型和拟二级动力学模型。 相似文献
13.
N. Xaba 《Journal of organometallic chemistry》2007,692(19):4052-4058
Hydroboration reactions of 1-octene and 1-hexyne with H2BBr·SMe2 in CH2Cl2 were studied as a function of concentration and temperature, using 11B NMR spectroscopy. The reactions exhibited saturation kinetics. The rate of dissociation of dimethyl sulfide from boron at 25 °C was found to be (7.36 ± 0.59 and 7.32 ± 0.90) × 10−3 s−1 for 1-octene and 1-hexyne, respectively. The second order rate constants, k2, for hydroboration worked out to be 7.00 ± 0.81 M s−1 and 7.03 ± 0.70 M s−1, while the overall composite second order rate constants, k K, were (3.30 ± 0.43 and 3.10 ± 0.37) × 10−2 M s−1, respectively at 25 °C. The entropy and enthalpy values were found to be large and positive for k1, whilst for k2 these were large and negative, with small values for enthalpies. This is indicative of a limiting dissociative (D) for the dissociation of Me2S and associative mechanism (A) for the hydroboration process. The overall activation parameters, ΔH≠ and ΔS≠, were found to be 98 ± 2 kJ mol−1 and +56 ± 7 J K−1 mol−1 for 1-octene whilst, in the case of 1-hexyne these were found out to be 117 ± 7 kJ mol−1 and +119 ± 24 J K−1 mol−1, respectively. When comparing the kinetic data between H2BBr·SMe2 and HBBr2·SMe2, the results showed that the rate of dissociation of Me2S from H2BBr·SMe2 is on average 34 times faster than it is in the case of HBBr2·SMe2. Similarly, the rate of hydroboration with H2BBr·SMe2 was found to be on average 11 times faster than it is with HBBr2·SMe2. It is also clear that by replacing a hydrogen substituent with a bromine atom in the case of H2BBr·SMe2 the mechanism for the overall process changes from limiting dissociative (D) to interchange associative (Ia). 相似文献
14.
Kinetics of the redox reaction between colloidal MnO2 and glycolic acid have been studied spectrophotometrically by monitoring the decay in the absorbance of colloidal MnO2 in absence and presence of surfactants. Anionic sodium dodecyl sulfate has no effect, non-ionic Triton X-100 catalyzed the reaction and experiments were not possible in presence of cationic cetyltrimethylammonium bromide due to the precipitation of MnO2.The reaction followed the same type of kinetic behavior, i.e., fractional-, first- and fractional-order dependencies, respectively, in [glycolic acid], [MnO2] and [H+ ] in both the media. Effects of gum arabic and manganese(II) have also been studied and discussed. Mechanisms in accordance with the experimental data are proposed for the reaction. 相似文献
15.
Kinetics of oxidation of DL-malic acid by water soluble colloidal MnO2 (prepared from potassium permanganate and sodium thiosulfate solutions) have been studied spectrophotometrically in the absence and presence of nonionic Triton X-100 surfactant. The reaction is autocatalytic and manganese(II) (reduction product of the colloidal MnO2) may be the autocatalyst. The order of the reaction is first in colloidal [MnO2] as well as in [malic acid] both in the absence and presence of the surfactant. The reaction has acid-dependent and acid-independent paths and, in the former case, the order is fractional in [H+]. The effect of externally added manganese(II) is complex. The results show that the rate constant increases as the manganese(II) concentration is increased. It is not possible to predict the exact dependence of the rate constants on manganese(II) concentration, which has a series of reactions with other reactants. In the presence of TX-100, the observed effect on k is catalytic up to a certain [TX-100]; thereafter, an inhibitory effect follows. The catalytic effect is explained in terms of the mathematical model proposed by Tuncay et al. (in Colloids Surf A Physicochem Eng Aspects 149:279 3). Activation parameters associated with the observed rate constants (kobs/k) have also been evaluated and discussed. 相似文献
16.
Summary Oxidations of hexan-1-ol, hexan-2-ol, hexan-3-ol, heptan-1-ol, heptan-2-ol, octan-1-ol, and octan-2-ol with tetra-1-butylammonium permanganate, dissolved in the same alcohols, proceed partly autocatalytically. The rate constants of both catalytic and non-catalytic reactions have been evaluated. Colloidal manganese dioxide, one of the reaction products, has been identified as the catalyst.
Oxidation höherer Alkanole mit Tetra-1-butylammoniumpermanganat
Zusammenfassung Die Oxidation von 1-Hexanol, 2-Hexanol, 3-Hexanol, 1-Heptanol, 2-Heptanol, 1-Octanol und 2-Octanol durch Tetra-1-butylammoniumpermanganat, gelöst in diesen Alkoholen, verläuft teilweise autokatalytisch. Die Geschwindigkeitskonstanten von katalytischen und nichtkatalytischen Teilreaktionen wurden bestimmt. Das kolloidale Mangandioxid, eines der Reaktionsprodukte, konnte als Katalysator identifiziert werden.相似文献
17.
Meng-Che Tu Han-Yi Chen Yuxi Wang Shabbir M. Moochhala Palaniappan Alagappan Bo Liedberg 《Analytica chimica acta》2015
This article reports on carbon nanotube/manganese dioxide (CNT–MnO2) composites as electrochemical tags for non-enzymatic signal amplification in immunosensing. The synthesized CNT–MnO2 composites showed good electrochemical activity, electrical conductivity and stability. The electrochemical signal of CNT–MnO2 composites coated glassy carbon electrode (GCE) increased by nearly two orders of magnitude compared to bare GCE in hydrogen peroxide (H2O2) environment. CNT–MnO2 composite was subsequently validated as electrochemical tags for sensitive detection of α-fetoprotein (AFP), a tumor marker for diagnosing hepatocellular carcinoma. The electrochemical immunosensor demonstrated a linear response on a log-scale for AFP concentrations ranging from 0.2 to 100 ng mL−1. The limit of detection (LOD) was estimated to be 40 pg mL−1 (S/N = 3) in PBS buffer. Further measurements using AFP spiked plasma samples revealed the applicability of fabricated CNT–MnO2 composites for clinical and diagnostic applications. 相似文献
18.
A. Kathiravan R. Renganathan 《Colloids and surfaces. A, Physicochemical and engineering aspects》2008,324(1-3):176-180
The interaction between colloidal TiO2 and bovine serum albumin (BSA) was studied by using absorption and fluorescence spectroscopic methods. The quenching of the intrinsic protein fluorescence in the presence of different concentrations of colloidal TiO2 was analyzed and number of binding sites (n) and apparent binding constant (K) were measured. The quenching mechanism of albumin by colloidal TiO2 is discussed. The energy transfer efficiency (E) and critical transfer distance (R0) were determined. 相似文献
19.
Kabir-ud-Din Neelam Hazoor Zaidi Mohd Akram Zaheer Khan 《Colloid and polymer science》2006,284(12):1387-1393
Aqueous colloidal manganese dioxide (MnO2) was prepared via titration by using potassium permanganate and sodium thiosulphate in aqueous neutral medium. The kinetics of oxidation of d-glucose onto the surface of colloidal MnO2 have been studied spectrophotometrically. The results show that the rate of initial stage (nonautocatalytic path) increases with increasing the [d-glucose], [H+], and temperature and also upon addition of nonionic surfactant Triton X-100 (TX-100), which indicates that the surfactant enhances the concentration of d-glucose at the surface of the colloidal MnO2. Hydrogen bonding interaction seemingly arises between –OH groups of d-glucose and oxygen of the ether linkages of polyoxyethylene chain of TX-100. A possible mechanism of the oxidative degradation of d-glucose is discussed in terms of d-glucose/TX-100 and colloidal MnO2 interaction. 相似文献
20.
Kabir-ud-Din Mohammad Altaf Mohd. Akram 《Journal of Dispersion Science and Technology》2013,34(6):809-816
The kinetics of the oxidation of L-tryptophan by water-soluble colloidal MnO2 (prepared from potassium permanganate and sodium thiosulfate solutions) has been carried out in aqueous perchloric acid medium at different temperatures. Monitoring the disappearance of the MnO2 spectrophotometrically at 390 nm was used to follow the kinetics. The first-order kinetics with respect to [L-tryptophan] at low concentrations shifted to zero-order at higher concentrations. The reaction followed first-order with respect to [MnO2] but fractional-order with respect to [HClO4]. Adding trapping agents enhanced the rate of the reaction. The Arrhenius and Eyring equations were found valid for the reaction between 35°C and 55°C and different activation parameters (Ea, ΔH#, ΔS#) have been evaluated. On the basis of various observations and product characterization a plausible mechanism has been envisaged for the reaction taking place at the colloid surface. The results suggest formation of an adsorption complex between L-tryptophan and MnO2. The complex decomposes in a rate-determining step, leading to the formation of free radical, which again reacts with the colloidal MnO2 in a subsequent fast step to yield products. Freundlich isotherm is used to explain the adsorption of L-tryptophan on the colloidal MnO2. 相似文献