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1.
Three platinum(II) complexes were synthesized and studied to characterize their ability as an anion carrier in a PVC membrane electrode. The polymeric membrane electrodes (PME) and also coated glassy carbon electrodes (CGCE) prepared with one of these complexes showed excellent response characteristics to perchlorate ions. The electrodes exhibited Nernstian responses to ClO4 ions over a wide concentration range from 1.5 × 10−6 to 2.7 × 10−1M for PME and 5.0 × 10−7 to 1.9 × 10−1M for CGCE with low detection limits (9.0 × 10−7M for PME and 4.0 × 10−7M for CGCE). The electrodes possess fast response time, satisfactory reproducibility, appropriate lifetime and, most importantly, good selectivity toward ClO4 relative to a variety of other common anions. The potentiometric response of the electrodes is independent of the pH of the test solution in the pH range 2.0–9.0. The proposed sensors were used in potentiometric determination of perchlorate ions in mineral water and urine samples. Correspondence: Ahmad Soleymanpour, Department of Chemistry, Damghan Basic Science University, Damghan, Iran.  相似文献   

2.
The oxidation process of the cyclic acetal sorbitylfurfural (SF) has been thoroughly examined from the kinetic, spectroscopic and theoretical point of view. Oxidation has been initiated by the radiolitically produced OH radical in the presence of variable oxygen amounts. Two competing reaction pathways are evidenced which lead to quite different products, although they do not affect the acetal ring integrity. The peroxidation of the hydroxylated furanic ring (k 4=(6.1±0.9)×108 M−1 s−1) maintains the ring structurevia HO2 elimination (k 6=(1.9±0.4)×105 s−1). Unlike that, the peroxidation of the pseudo-allylic radical (k 5=(1.9±0.9)×109 M−1 s−1), formedvia β-cleavage, fixes the destructured intermediate, leading to a tetroxide, which slowly decomposes through a Russell mechanism (k 8=(2.3±0.6)×102 s−1). It is confirmed that the steady state concentration of the tetroxide is very low, which suggests a molar absorption coefficient for it around 1.2×104 M−1 cm−1 at 265 nm. The end products of the latter pathway have been characterized as carboxylic and butenald-sorbitol derivatives. The kinetic and spectral data of every step of the process have been fitted by the above outlined mechanism. The energetics of the mechanism has been detailed byab initio computations as well, carrying further substantiation to it. Semi-empirical calculations were also employed to describe the spectral properties of each intermediate.  相似文献   

3.
The role of serum fatty acid binding proteins (FABPs) in arachidonic acid (AA) uptake by murine peritoneal macrophages has been studied. The kinetics of [3H]arachidonic acid uptake by the cells was investigated over a wide range of AA concentration (10−10–10−5 M). It was shown that these putative fatty acid transporters dramatically change the uptake processes. In the presence of FABPs, the time-course curves of AA uptake exhibited two distinct periods: one with a rapid AA uptake during the first hour with an equilibrium in 1–2.5 h and another with an equilibrium reached in 20 h, whereas in the absence of FABPs the uptake curves were smooth without kinks and with the equilibrium reached in 10 h. In addition, it was shown that the amount of incorporated AA was linearly dependent on the concentration of AA over the range of 10−10–10−6 M in the presence of serum FABPs and 10−10–10−7 M in their absence. We assume that the changes in the character of AA uptake by macrophages in the presence of FABP soccur due to the interaction of FABPs with the cell plasma membrane.  相似文献   

4.
Excited-state proton transfer (ESPT) of pyranine (8-hydroxypyrene-1,3,6-trisulphonate, HPTS) to acetate in methanol has been studied by steady-state and time-resolved fluorescence spectroscopy. The rate constant of direct proton transfer from pyranine to acetate (k 1) is calculated to be ∼1 × 109 M−1 s−1. This is slower by about two orders of magnitude than that in bulk water (8 × 1010 M−1 s−1) at 4 M acetate.  相似文献   

5.
The paper is concerned with the determination of traces of thallium, as T1(I), in the presence of very large amounts of lead, by d.c. anodic stripping voltammetry, by adding both a complexing agent and anionic surfactant. The supporting complexing agent was 0.1M solution of EDTA (pH 4.4). The influence of the several surfactants on the signals of lead and thallium was investigated.In 0.1M EDTA at pH 4.4 at the absence of a surfactant, lead does not interfere at concentrations below 10–4 M. When the electrolyte contains also an anionic surfactant, lead can be tolerated at concentrations up to 2 × 10–3–6 × 10–3 M (depending on the type of the surfactant), and the height of the thallium peak remains unaffected. This makes the determination of 10–8 M T1(I) possible when the molar excess of lead is 2–6 × 105 fold. The method has been tested by determining the thallium content of soil extracts.  相似文献   

6.
Electrospray Ionization Mass Spectrometry (ESI/MS) has been used to determine the association constants (KAs) and binding stoichiometries for parent para-Sulphonato-calix[n]arenes and their derivatives with bovine serum albumin (BSA). KA values were determined by titration experiments using a constant concentration of protein. KA measurements were carried out in a methanol–formic acid solution. 5,11,17,23–tetra-Sulphonato-calix[4]arene (1a) and 25-mono-(2-aminoethoxy)-5,11,17,23-tetra-Sulphonato-calix[4]arene (1d) interact strongly with BSA showing 3 non-equivalent binding sites with KA1 = 7.69 × 105 M−1, KA2 = 3.85 × 105 M−1, KA3 = 0.33 × 105 M−1 and KA1 = 1.69 × 105 M−1, KA2 = 2.94 × 105 M−1, KA3 = 0.60 × 105 M−1, respectively. The strength of the interactions between the calixarene and BSA is inversely proportional to the size of macrocyclic ring: n = 4 > n=6>>n=8.  相似文献   

7.
Dimethylgermylene and its Ge=Ge doubly bonded dimer, tetramethyldigermene, have been characterized directly in solution by 308-nm laser flash photolysis in n-hexane solution, as well as 254-nm photolysis in hydrocarbon glasses at t = 77 K. An absorption band maximum of λ max ≈ 430 nm and molar absorption coefficient of ε ≈ 2,700 M−1 cm−1 have been shown to be attributable to low-temperature glasses, while the absorption band maximum of λ max ≈ 480 nm and molar absorption coefficient of ε ≈ 2,400 M−1 cm−1 have been shown to be related to dimethylgermylene in n-hexane solution. The molar absorption coefficient of tetramethyldigermene (λ max ≈ 380 nm) was determined to be ε ≈ 84,000 M−1 cm−1. The germylene is formed via (formal) cheletropic photocycloreversion of 7,7′-dimethylgerma-1,4,5,6-tetraphenyl-2,3-benzo-norbornadiene. Tetramethyldigermene and 1,2,3,4-tetraphenylnaphthalene in the triplet state were formed, together with dimethylgermylene. We attempted to explain the various contradictory interpretations of experimental data existing in the literature on this reaction.  相似文献   

8.
The antioxidant activity of heterocyclic thioamides based on imidazole, triazole, tetrazole, thiazole, thiazoline, and thiadiazole is estimated by spectrophotometry using the rate constant of reaction with the chromogenic radical 2,2′-diphenyl-1-picrylhydrazyl. The rate constant of direct transfer of a hydrogen atom to the radical in carbon tetrachloride is maximal for 1-methylimidazoline-2-thione. The protective antioxidant effect of the preparations in ethanol falls down abruptly from 4-phenylthiazoline-2-thione (k = 1.06 × 104 M−1min−1) to the thioamides based on triazole and thiazoline (k ∼ 20 M−1min−1). In acetonitrile, thiazole derivatives show the most substantial antioxidant activity, k = n ×104 M−1min−1, which goes down to zero if the aromaticity of the heterocycle is broken. As established, for the pseudo first order reaction between thioamides and the chromogenic radical, the reaction rate linearly depends on the concentration of thioamides. A spectrophotometry kinetic method for the quantification of heteroaromatic thioamides is elaborated.  相似文献   

9.
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   

10.
The structural and thermodynamic properties of oligomeric anions [M n X3n+ 1] (M = Al, Ga, In; X = F, Cl, Br, I; n = 2, 3, 4) have been obtained by the density functional theory B3LYP method with the LAN2DZ(d) and LAN2DZ(d)+ basis sets. A wide diversity of structural isomers was found for trimeric fluoride anions M3F10. Among the trimers, except In3F10, the most stable is a linear isomer composed of two MX3 molecules coordinated to the MX4 anion. The formation of tetrameric anions M4X13 was demonstrated to be thermodynamically allowed at low temperatures at MX3: X > 4: 1. The existence of higher oligomers is less probable. The affinity of oligomer halides (MX3) n for halide ions increases with an increase in n. The propensity to form oligomeric anions decreases in the series F > Cl ≥ Br > I. The fluoride systems show a tendency to form structures with CN = 5 and 6, these structures for In being the most stable. Original Russian Text ? A.Yu. Timoshkin, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 1, pp. 87–100.  相似文献   

11.
Radioactivation analysis is the only method which allows the determination of individual rare earth element impurities in rare earth elements of high purity. The determination of dysprosium, europium, samarium and gadolinium in yttrium oxide is complicated by the short half-life of165Dy (138 min.) and by the difficulty of separating traces of these elements from the matrix. A chromatographic method has been developed, for the separation of traces of Dy, Eu, Sm and Gd from ytrium, on a column packed with anion exchangerAV-17, by means of elution with 0.1N and 0.3M solutions of EDTA-sodium salt, followed by the separation of the mixture of the rare earth impurities on a microcolumn of cation exchangerKU-2, using a 0.17M solution of ammonium α-hydroxyisobutyrate as the eluent. The sensitivity of the determination of Dy, in the case of irradiating 10 mg of Y2O3 with a flux of 1.2·1013 n·cm−2·sec−1 for 5 min. was 1·10−7%; the corresponding values for Sm, Eu and Gd, when irradiating a 100 mg sample of Y2O3 for 20 hours with the same flux, were 2·10−7%, 1·10−8% and 5·10−6%, respectively.  相似文献   

12.
Preliminary treatment of TlN3(A) with light (λ = 365 nm, I > 1 × 1014 quantum cm−2 s−1) in a vacuum (1 × 10−5 Pa) at 293 K led to the formation of a new long-wave region of spectral sensitivity. The products of photolysis of TlN3(A) thallium and nitrogen formed in the stoichiometric ratio on the sample surface. The topography and kinetics of thallium accumulation were determined, and the effective rate constants for photolysis evaluated. Measurements of the contact voltage, current-voltage characteristics, and photocurrent showed that the photolysis of thallium azide resulted in the formation of TlN3(A)-Tl (photolysis product) microheterogeneous systems. A model of photolysis of TlN3(A) was suggested. According to this model, photolysis included the generation, recombination, and redistribution of nonequilibrium charge carriers in the contact field and the formation of the end products of photolysis. The limiting stage of photolysis of TlN3(A) was the diffusion of interstitial thallium cations toward the neutral (T n Tl m )0 center. Original Russian Text ? E.P. Surovoi, L.I. Shurygina, L.N. Bugerko, N.V. Borisova, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 4, pp. 784–790.  相似文献   

13.
 Berberine hydrochloride is an alkaloid with little or no fluorescence in water. In sodium dodecylsulfate solutions, the fluorescence intensity of this compound is enhanced several folds by ion-pairing with the anion of the surfactant. The enhanced fluorescence intensity reaches a maximum at a surfactant concentration of 4·10−3M and then decreases to a constant value at the critical micelle concentration and beyond. At concentrations near the maximum, a calibration sensitivity of 3.23·106/M was obtained. In addition, a good linear dynamic range and a low limit of detection (4·10−5 and 1.5·10−7M, respectively) were determined. This observation indicates that this surfactant medium could be effectively used in fluorometric trace analysis of berberine hydrochloride. It was also observed in this work that solvents of low dielectric constant tend to stabilize this compound and thereby enhance its fluorescence.  相似文献   

14.
The electrochemical and spectroelectrochemical properties of the sensitizer dye Z907 (cis-RuLL'(SCN)2 with L=4,4-dicarboxylic acid-2,2-bipyridine and L'=4,4-dinonyl-2,2-bipyridine) adsorbed on fluorine-doped tin oxide (FTO) and TiO2 surfaces have been investigated. Langmuirian binding constants for FTO and TiO2 are estimated to be 3 × 106 M−1 and 4 × 104 M−1, respectively. The Ru(III/II) redox process is monitored by voltammetry and by spectroelectrochemistry. For Z907 adsorbed onto FTO, a slow EC-type electrochemical reaction is observed with a chemical rate constant of ca. k = 10−2 s−1 leading to Z907 dye degradation of a fraction of the FTO-adsorbed dye. The Z907 adsorption conditions affect the degradation process. No significant degradation was observed for TiO2-adsorbed dye. Degradation of the Z907 dye affects the electron hopping conduction at the FTO–TiO2 interface.  相似文献   

15.
The nature of adsorption behavior of Au(III) on polyurethane (PUR) foam was studied in 0.2M HCl aqueous solution. The effect of shaking time and amount of adsorbent were optimized for 3.16·10−5M solution of Au(III) in 0.2M HCl. The classical Freundlich and Langmuir adsorption isotherms have been employed successfully. The Freundlich parameters 1/n and adsorption capacityK are 0.488±0.016 and (1.40±0.22)·10−2 mol·g−1, respectively. The Langmuir constants of saturation capacityM and binding energyb are (1.66±0.08)·10−4mol·g−1 and 40294±2947 l·g−1, respectively, indicating the monolayer chemical sorption. The mean free energy (E) of adsorption of Au(III) on PUR foam has been evaluated using D-R isotherm and found to be 11.5±0.16 kJ·mol−1 reflecting the ion exchange type of chemical adsorption. The effect of temperature on the adsorption has also been studied. the isosteric heat of adsorption was found to be 44.03±1.66 kJ·mol−1. The thermodynamic parameters of ΔG, ΔH, ΔS and equilibrium constantK c have been calculated. The negative values of ΔG, ΔH and ΔS support that the adsorption of Au(III) on PUR foam is spontaneous, exothermic and of ion exchange chemisorption. The nature of the Au(III) species sorbed on PUR foam have been discussed.  相似文献   

16.
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) × 10−4M −1 s−1, and for the reaction with ranitidine (6.72 ± 0.17) × 10−4M −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   

17.
The kinetics of the reaction between [ReN(H2O)-(CN)4]2− with different κ2 N,O-donor ligands (quin and 2,3-dipic, respectively) have been studied in the pH 4–12 range in aqueous solution. Two consecutive reaction steps with the formation of the [ReN(η1-quin)(CN)4]3− and [ReN(μ2-quin) (CN)3]2− complexes, respectively, were spectrophotometrically observed and kinetically investigated. The same reaction mechanism is proposed for these two ligands. The first fast reaction (for quin) is attributed to the aqua substitution of [ReN(H2O)(CN)4]2− with forward and reverse rate constants of 1.96(5) × 10−1 M−1 s−1 and 5.6(3) × 10−2 s−1, while a rate of 2.64(3) M−1 s−1 was observed for the reaction between the conjugate base [ReN(OH)(CN)4]3− and quin at 40.2 °C. Due to small absorbance changes, it was difficult to obtain any good quality data for the fast reactions for 2,3-dipic. The second, slower reaction is attributed to cyano substitution with rate constants (k 3 K 1) of 4.17(4) × 10−3 for quin and 4.68(7) × 10−3 M−1 s−1 for 2,3-dipic, at 80.02 °C, respectively. The acid dissociation constant for the aqua complex was spectrophotometrically determined as 11.58(3) and 11.54(2) and kinetically as 11.51(8) and 11.41(1), at 80.4 °C, respectively. Negative values of −83.5(2) and −144.1(2) J K−1 mol−1 as well as the of 71.4(3) and 47.3(3) kJ mol−1, for the slow quin and 2,3-dipic reactions, respectively, point to an ordered transition state where bond formation is responsible for the major driving force of the reaction. The and for the fast forward reaction of quin is indicative of expected associative activation in the transition state. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

18.
Candida guilliermondii FTI 20037 was cultured in sugarcane bagasse hydrolysate supplemented with 2.0 g/L of (NH4)2SO4, 0.1 g/L of CaCl2·2H2O, and 20.0 g/L of rice bran at 35°C; pH 4.0; agitation of 300 rpm; and aeration of 0.4, 0.6, or 0.8 vvm. The high xylitol production (20.0 g/L) and xylose reductase (XR) activity (658.8 U/mg of protein) occurred at an aeration of 0.4 vvm. Under this condition, the xylitol dehydrogenase (XD) activity was low. The apparent K M for XR and XD against substrates and cofactors were as follows: for XR, 6.4×10−2 M (xylose) and 9.5×10−3 mM (NADPH); for XD, 1.6×10−1 M (xylitol) and 9.9×10−2 mM (NAD+). Because XR requires about 10-fold less xylose and cofactor than XD for the condition in which the reaction rate is half of the V max, some interference on the overall xylitol production by the yeast could be expected.  相似文献   

19.
 The construction and electrochemical response characteristics of poly(vinyl) chloride matrix membrane sensors for menadione (vitamin K3) are described. Membranes incorporating the ion association complexes of menadione anion with bathophenanthroline nickel(II) and iron(II) as electroactive materials show linear response for menadione over the range 10−1–10−5M with anionic slopes of 58.2–51.4 mV per concentration decade. Both sensors exhibit fast response time (20–30 s), low detection limit (2 × 10−5M), good stability (4–6 weeks) and selectivity coefficient (10−1–10−3). Direct potentiometric determination of menadione under static and hydrodynamic mode of operations shows average accuracies of 98.8 and 98.5% with relative standard deviations of 0.6% and 1.3%, respectively. Application of the method for the determination of menadione in human plasma gives favourable results compared with those obtained by the standard spectrophotometric method. Received February 26, 2001. Revision October 1, 2001.  相似文献   

20.
Quartz crystal microbalance (QCM) was used to study the self-assembly of per-6-thio-β-cyclodextrin (t7-βCD) on gold surfaces, and the subsequent inclusion interactions of immobilized βCD with adamantane-poly(ethylene glycol) (5,000 MW, AD-PEG), 1-adamantanecarboxylic acid (AD-C) and 1-adamantylamine (AD-A). From a 50 μM solution of t7-βCD in 60:40 DMSO:H2O, a t7-βCD layer was formed on gold with surface density of 71.7 ± 2.7 pmol/cm2, corresponding to 80 ± 3% of close-packed monolayer coverage. Gold sensors with immobilized t7-βCD were then exposed alternately to six different concentrations of AD-PEG, 500 μM AD-C or 500 μM AD-A aqueous solutions for association, and water for dissociation. Association of AD-PEG conformed to a Langmuir isotherm, with a best fit equilibrium constant K = 125,000 ± 18,000 M−1. For AD-C and AD-A, association (k a ) and dissociation (k d ) rate constants were extracted from kinetic profiles by fitting to the Langmuir model, and equilibrium constants were calculated. The parameters for AD-C were found to be: k a = 100 ± 5 M−1 s−1, k d = 110 (±18) × 10−4 s−1, and K = 9,400 ± 1,700 M−1. For AD-A, k a = 58 ± 6 M−1 s−1, k d = 154 (±7) × 10−4 s−1, and K = 3,800 ± 400 M−1. The results demonstrate the utility of QCM as a tool for studying small molecule surface adsorption and guest–host interactions on surfaces. More specifically, the kinetic and thermodynamic data of AD-C, AD-A, and AD-PEG inclusion with immobilized t7-βCD form a basis for further surface association studies of AD-X conjugates to advance surface sensory and coupling applications.  相似文献   

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