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1.
The hydrogen peroxide-oxidation of o-phenylenediamine (OPD) catalyzed by horseradish peroxidase (HRP) at 37 °C in 50 mM phosphate buffer (pH 7.0) was studied by calorimetry. The apparent molar reaction enthalpy with respect to OPD and hydrogen peroxide were −447 ± 8 kJ mol−1 and −298 ± 9 kJ mol−1, respectively. Oxidation of OPD by H2O2 catalyzed by HRP (1.25 nM) at pH 7.0 and 37 °C follows a ping-pong mechanism. The maximum rate Vmax (0.91 ± 0.05 μM s−1), Michaelis constant for OPD Km,S (51 ± 3 μM), Michaelis constant for hydrogen peroxide Km,H2O2 (136 ± 8 μM), the catalytic constant kcat (364 ± 18 s−1) and the second-order rate constants k+1 = (2.7 ± 0.3) × 106 M−1 s−1 and k+5 = (7.1 ± 0.8) × 106 M−1 s−1 were obtained by the initial rate method. 相似文献
2.
Claudio Baggiani Patrizia Baravalle Laura Anfossi Cinzia Tozzi 《Analytica chimica acta》2005,542(1):125-134
A pyrimethanil-imprinted polymer (P1) was prepared by iniferter-mediated photografting a mixture of methacrylic acid and ethylene dimethacrylate onto homemade near-monodispersed chloromethylated polydivinylbenzene beads. The chromatographic behaviour of a column packed with these imprinted beads was compared with another column packed with irregular particles obtained by grinding a bulk pyrimethanil-imprinted polymer (P2). The comparison was made using the kinetic model of non-linear chromatography, studying the elution of the template and of two related substances, cyprodinil and mepanipyrim. Extension of the region of linearity, capacity factors for the template and the related substances, column selectivity, binding site heterogeneity, apparent affinity constant (K) and lumped kinetic association (ka) and dissociation rate constant (kd) were studied during a large interval of solute concentration, ranging between 1 and 2000 μg/ml. From the experimental results obtained, in the linearity region of solute concentration column selectivity and binding site heterogeneity remained essentially the same for the two columns, while column capacity (at 20 μg/ml, P1 = 23.1, P2 = 11.5), K (at 20 μg/ml, P1 = 8.3 × 106 M−1, P2 = 2.5 × 106 M−1) and ka (at 20 μg/ml, P1 = 3.5 μM−1 s−1, P2 = 0.47 μM−1 s−1) significantly increased and kd (at 20 μg/ml, P1 = 0.42 s−1, P2 = 0.67 s−1) decreased for the column packed with the imprinted beads. These results are consistent with an influence of the polymerisation method on the morphology of the resulting polymer and not on the molecular recognition properties due to the molecular imprinting process. 相似文献
3.
Reaction of trans-[PtClMe(SMe2)2] with the mono anionic ligands azide, bromide, cyanide, iodide and thiocyanate result in substitution of the chloro ligand as the first step. In contrast the neutral ligands pyridine, 4-Me-pyridine and thiourea substitute a SMe2 ligand in the first step as confirmed by 1H NMR spectroscopy and the kinetic data. Detailed kinetic studies were performed in methanol as solvent by use of conventional stopped-flow spectrophotometry. All processes follow the usual two-term rate law for square-planar substitutions, kobs = k1 + k2[Y] (where k1 = kMeOH[MeOH]), with k1 = 0.088 ± 0.004 s−1 and k2 = 1.18 ± 0.13, 3.8 ± 0.3, 17.8 ± 1.3, 34.9 ± 1.4, 75.3 ± 1.1 mol−1 dm3 s−1 for Y− = N3, Br, CN, I and SCN respectively at 298 K. The reactions with the neutral ligands proceed without an appreciable intercept with k2 = 5.1 ± 0.3, 15.3 ± 1.8 and 195 ± 3 mol−1 dm3 s−1 for Y = pyridine, 4-Me-pyridine and thiourea, respectively, at 298 K. Activation parameters for MeOH, , Br−, CN−, I−, SCN−, and Tu are ΔH≠ = 47.1 ± 1.6, 49.8 ± 0.6, 39 ± 3, 32 ± 8, 39 ± 5, 34 ± 4 and 31 ± 3 kJ mol−1 and ΔS≠ = −107 ± 5, −77 ± 2, −104 ± 9,−113 ± 28, −85 ± 18, −94 ± 14 and −97 ± 10 J K−1 mol−1, respectively. Recalculation of k1 to second-order units gives the following sequence of nucleophilicity: (1:13:42:57:170:200:390:840:2170) at 298 K. Variation of the leaving group in the reaction between trans-[PtXMe(SMe2)2] and SCN− follows the same rate law as stated above with k2 = 75.3 ± 1.1, 236 ± 4 and 442 ± 5 mol−1 dm3 s−1 for X− = Cl, I and N3, respectively, at 298 K. The corresponding activation parameters were determined as ΔH≠ = 34 ± 4, 32 ± 2 and 39.3 ± 1.7 kJ mol−1 and ΔS≠ = −94 ± 14, −86 ± 8 and −68 ± 6 J K−1 mol−1. All the kinetic measurements indicate the usual associate mode of activation for square planar substitution reactions as supported by large negative entropies of activation, a significant dependence of the reaction rate on different entering nucleophiles and a linear free energy relationship. 相似文献
4.
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
5.
W. Rucks Winkeljohn 《Tetrahedron letters》2004,45(45):8295-8297
The oxidation of a series of substituted pyridines by dimethyldioxirane (1) produced the expected N-oxides in quantitative yields. The second order rate constants (k2) for the oxidation of a series of substituted pyridines (2a-g) by dimethyldioxirane were determined in dried acetone at 23 °C. An excellent correlation with Hammett sigma values was found (ρ = −2.91, r = 0.995). Kinetic studies for the oxidation of 4-trifluoromethylpyridine by 1 were carried out in the following dried solvent systems: acetone (k2 = 0.017 M−1 s−1), carbon tetrachloride/acetone (7:3; k2 = 0.014 M−1 s−1), acetonitrile/acetone (7:3; k2 = 0.047 M−1 s−1), and methanol/acetone (7:3; k2 = 0.68 M−1 s−1). Kinetic studies of the oxidation of pyridine by 1 versus mole fraction of water in acetone [k2 = 0.78 M−1 s−1 (χ = 0) to k2 = 11.1 M−1 s−1 (χ = 0.52)] were carried out. The results showed the reaction to be very sensitive to protic, polar solvents. 相似文献
6.
Kazuaki Tokuhashi Liang Chen Shuzo Kutsuna Tadafumi Uchimaru Masaaki Sugie Akira Sekiya 《Journal of fluorine chemistry》2004,125(11):1801-1807
The rate constants for the reactions of OH radicals with CF3OCHFCF3, and CF3CHFCF3 have been measured over the temperature range 250-430 K. Kinetic measurements have been carried out using the flash photolysis, and laser photolysis methods combined, respectively, with the laser induced fluorescence technique. The influence of impurities in the samples has been investigated by using gas chromatography. No sizable effect of impurities was found on the measured rate constants of these fluorinated compounds, if the purified samples were used in the measurements. The following Arrhenius expressions were determined: k(CF3OCHFCF3) = (4.39 ± 1.38) × 10−13 exp[−(1780 ± 100)/T] cm3 molecule−1 s−1, and k(CF3CHFCF3) = (6.19 ± 2.07) × 10−13 exp[−(1830 ± 100)/T] cm3 molecule−1 s−1. 相似文献
7.
Inger-Mari Krokeide 《Thermochimica Acta》2007,454(2):144-146
Isothermal titration calorimetry (ITC) has been used to observe the chitinase-catalyzed hydrolysis of tetra-N-acetylchitotetraose. Enzymatic hydrolysis of tetra-N-acetylchitotetraose by chitinase B from Serratia marcescens produces exclusively two molecules of di-N-acetylchitobiose allowing for the determination of a single glycosidic bond hydrolysis heat that was used to monitor the rate of the enzymatic reaction. The change in heat rate with respect to time (dQ/dt) was translated to the reaction rate, and the total heat produced was related to substrate concentration throughout the reaction. Reaction rates versus substrates concentration were fit to Michaelis-Menten plots, yielding a kcat of 40.9 ± 0.5 s−1 and a Km of 54 ± 2 μM. 相似文献
8.
The kinetics of the radical reactions of CH3 with HCl or DCl and CD3 with HCl or DCl have been investigated in a temperature controlled tubular reactor coupled to a photoionization mass spectrometer. The CH3 (or CD3) radical, R, was produced homogeneously in the reactor by a pulsed 193 nm exciplex laser photolysis of CH3COCH3 (or CD3COCD3). The decay of CH3/CD3 was monitored as a function of HCl/DCl concentration under pseudo-first-order conditions to determine the rate constants as a function of temperature, typically from 188 to 500 K. The rate constants of the CH3 and CD3 reactions with HCl had strong non-Arrhenius behavior at low temperatures. The rate constants were fitted to a modified Arrhenius expression k = QA exp (−Ea/RT) (error limits stated are 1σ + Students t values, units in cm3 molecule−1 s−1): k(CH3 + HCl) = [1.004 + 85.64 exp (−0.02438 × T/K)] × (3.3 ± 1.3) × 10−13 exp [−(4.8 ± 0.6) kJ mol−1/RT] and k(CD3 + HCl) = [1.002 + 73.31 exp (−0.02505 × T/K)] × (2.7 ± 1.2) × 10−13 exp [−(3.5 ± 0.5) kJ mol−1/RT]. The radical reactions with DCl were studied separately over a wide ranges of temperatures and in these temperature ranges the rate constants determined were fitted to a conventional Arrhenius expression k = A exp (−Ea/RT) (error limits stated are 1σ + Students t values, units in cm3 molecule−1 s−1): k(CH3 + DCl) = (2.4 ± 1.6) × 10−13 exp [−(7.8 ± 1.4) kJ mol−1/RT] and k(CD3 + DCl) = (1.2 ± 0.4) × 10−13 exp [−(5.2 ± 0.2) kJ mol−1/RT] cm3 molecule−1 s−1. 相似文献
9.
A simple procedure was developed to prepare a glassy carbon electrode modified with single-wall carbon nanotubes (SWCNTs) and Os(III)-complex. The glassy carbon (GC) electrode modified with CNTs was immersed into Os(III)-complex solution (direct deposition) for a short period of time (60 s). 1,4,8,12-Tetraazacyclotetradecane osmium(III) chloride, (Os(III)LCl2)·ClO4, irreversibly and strongly adsorbed on SWCNTs immobilized on the surface of GC electrode. Cyclic voltammograms of the Os(III)-complex-incorporated-SWCNTs indicate a pair of well defined and nearly reversible redox couple with surface confined characteristic at wide pH range (1-8). The surface coverage (Γ) and charge transfer rate constant (ks) of the immobilized Os-complex on SWCNTs were 3.07 × 10−9 mol cm−2, 5.5 (±0.2) s−1, 2.94 × 10−9 mol cm−2, 7.3 (±0.3) s−1 at buffer solution with pH 2 and 7, respectively, indicate high loading ability of SWCNTs for Os(III) complex and great facilitation of the electron transfer between electroactive redox center and carbon nanotubes immobilized on the electrode surface. Modified electrodes showed higher electrocatalytic activity toward reduction of BrO3−, IO3− and IO4− in acidic solutions. The catalytic rate constants for catalytic reduction bromate, periodate and iodate were 3.79 (±0.2) × 103, 7.32 (±0.2) × 103 and 1.75 (±0.2) × 103 M−1 s −1, respectively. The hydrodynamic amperometry of rotating modified electrode at constant potential (0.3 V) was used for nanomolar detection of selected analytes. Excellent electrochemical reversibility of the redox couple, good reproducibility, high stability, low detection limit, long life time, fast amperometric response time, wide linear concentration range, technical simplicity and possibility of rapid preparation are great advantage of this sensor. 相似文献
10.
The kinetics of oxidative addition of CH3I to [Rh(FcCOCHCOCF3)(CO)(PPh3)], where Fc = ferrocenyl and (FcCOCHCOCF3)− = fctfa = ferrocenoylacetonato, have been studied utilizing UV/Vis, IR, 1H and 31P NMR techniques. Three definite sets of reactions involving isomers of at least two distinctly different classes of RhIII-alkyl and two different classes of RhIII-acyl species were observed. Rate constants for this reaction in CHCl3 at 25 °C, applicable to the reaction sequence below, were determined as k1 = 0.00611(1) dm3 mol−1 s−1, k−1 = 0.0005(1) s−1, k3 = 0.00017(2) s−1 and k4 = 0.0000044(1) s−1 while k−3 ? k3 and k−4 ? k4 but both ≠0. The indeterminable equilibrium K2 was fast enough to be maintained during RhI depletion in the first set of reactions and during the RhIIIalkyl2 formation in the second set of reactions. From a 1H and 31P NMR study in CDCl3, Kc1 was found to be 0.68, Kc2 = 2.57, Kc3 = 1.00, Kc4 = 4.56 and Kc5 = 1.65. 相似文献
11.
Abelson tyrosine-protein kinase 1 (ABL1) catalysed phosphorylation involves the addition of a phosphate group from ATP to the tyrosine residue on the substrate abltide. The phosphorylation reactions were carried out by incubating ABL1, ATP and the substrate abltide. Adsorption at the glassy carbon electrode surface in either reaction mixtures or control solutions, followed by differential pulse voltammetry in buffer allowed detection of the variation of abltide tyrosine residue oxidation peak reflecting the occurrence of the phosphorylation reaction. The effect of abltide, ATP and ABL1 concentrations as well as the time course of the phosphorylation reaction were studied. The influence of co-adsorption of ABL1, ATP and phosphorylated abltide was evaluated and the conditions for the electrochemical detection of ABL1-catalysed phosphorylation optimised. The Michaelis–Menten constant for abltide binding KM ∼ 4.5 μM, turnover number kcat ∼ 11 s−1 and enzyme efficiency kcat/KM ∼ 2.3 s−1 μM−1 were calculated. The inhibition of ABL1 by imatinib mesylate and danusertib was also electrochemically investigated and IC50 values of 0.53 and 0.08 μM determined. 相似文献
12.
A graphene (GR) and multi-walled carbon nanotubes (MWCNT) hybrid was prepared and modified on a 1-hexylpyridinium hexafluorophosphate based carbon ionic liquid electrode (CILE). Hemoglobin (Hb) was immobilized on GR-MWCNT/CILE surface with Nafion as the film forming material and the modified electrode was denoted as Nafion/Hb-GR-MWCNT/CILE. Spectroscopic results revealed that Hb molecules retained its native structure in the GR-MWCNT hybird. Electrochemical behaviors of Hb were carefully investigated by cyclic voltammetry with a pair of well-defined redox peaks obtained, which indicated that direct electron transfer of Hb was realized in the hybrid modified electrode. The result could be attributed to the synergistic effects of GR-MWCNT hybrid with enlarged surface area and improved conductivity through the formation of a three-dimensional network. Electrochemical parameters of the immobilized Hb on the electrode surface were further calculated with the results of the electron transfer number (n) as 1.03, the charge transfer coefficient (a) as 0.58 and the electron-transfer rate constant (ks) as 0.97 s−1. The Hb modified electrode showed good electrocatalytic ability toward the reduction of different substrates such as trichloroacetic acid in the concentration range from 0.05 to 38.0 mmol L−1 with a detection limit of 0.0153 mmol L−1 (3σ), H2O2 in the concentration range from 0.1 to 516.0 mmol L−1 with a detection limit of 34.9 nmol/L (3σ) and NaNO2 in the concentration range from 0.5 to 650.0 mmol L−1 with a detection limit of 0.282 μmol L−1 (3σ). So the proposed electrode had the potential application in the third-generation electrochemical biosensors without mediator. 相似文献
13.
Isothermal depolymerization of the two polymers of C60, i.e. of 1D orthorhombic phase (O) and of “dimer state” (DS) have been studied by means of Infra-red spectroscopy in the temperature ranges 383-423 and 453-503 K, respectively. Differential Scanning Calorimetry (DSC) has been used to obtained depolymerization polytherms for O-phase and DS. Standard set of reaction models have been applied to describe depolymerization behavior of O-phase and DS. The choice of the reaction models was based primarily on the isotherms. Several models however demonstrated almost equal goodness of fit and were statistically indistinguishable. In this case we looked for simpler/more realistic mechanistic model of the reaction. For DS the first-order expression (Mampel equation) with the activation energy Ea = 134 ± 7 kJ mol−1 and preexponential factor ln(A/s−1) = 30.6 ± 2.1, fitted the isothermal data. This activation energy was nearly the same as the activation energy of the solid-state reaction of dimerization of C60 reported in the literature. This made the enthalpy of depolymerization close to zero in accord with the DSC data on depolymerization of DS. Mampel equation gave the best fit to the polythermal data with Ea = 153 kJ mol−1 and preexponential factor ln(A/s−1) = 35.8. For O-phase two reasonable reaction models, i.e. Mampel equation and “contracting spheres” model equally fitted to the isothermal data with Ea = 196 ± 2 and 194 ± 8 kJ mol−1, respectively and ln(A/s−1) = 39.1 ± 0.5 and 37.4 ± 0.2, respectively and to polythermal data with Ea = 163 and 170 kJ mol−1, respectively and ln(A/s−1) = 32.5 and 29.5, respectively. 相似文献
14.
Javid T Safarov 《The Journal of chemical thermodynamics》2003,35(12):1929-1937
The (p,ρ,T) and (ps,ρs,Ts) properties of {(1−x)CH3OH + xLiBr} over a wide range of state parameters are reported for the first time. The experiments were carried out in a constant volume piezometer over a temperature range from 298.15 K to 398.15 K, at 0.08421, 0.13617, 0.19692, 0.23133 and 0.26891 mole fractions and from atmospheric pressure up to 60 MPa. The experimental uncertainties are ΔT=±3 mK for temperature, Δp=±5·10−2 MPa for high pressure and Δp=±5·10−4 MPa for atmospheric pressure, Δρ=±3·10−2 kg · m−3 for density. An equation of state was derived for correlation of the experimental data of the solutions. 相似文献
15.
The complex [(IMesH2)(PPh2Cy)Cl2RuCHPh] was synthesised and shown to be an active catalyst in ring-closing metathesis of a diallylmalonate. Its phosphine exchange was investigated in C6D6 using magnetisation transfer 31P NMR spectroscopy and it was found to operate via a dissociative mechanism with k353 = 4.1 ± 0.9 s−1, ΔH‡ = 84 ± 10 kJ mol−1 and ΔS‡ = 4 ± 28 J mol−1 K−1. 相似文献
16.
Absolute rate constants for the reaction of t-butylperoxy radicals with hexaphenylditin and hexaphenyldilead have been found to fit the equations log (kp/M−1·s−1) = (5.5±0.15) − (3800±150)/Θ and log (kp/M−1·s−1) (9.5±0.3) − (6000±250)/Θ, where Θ = 2.303 RT cal mol−1, respectively. 相似文献
17.
Measurement of methyl mercury (I) and mercury (II) in fish tissues and sediments by HPLC-ICPMS and HPLC-HGAAS 总被引:1,自引:0,他引:1
A procedure for the extraction and determination of methyl mercury and mercury (II) in fish muscle tissues and sediment samples is presented. The procedure involves extraction with 5% (v/v) 2-mercaptoethanol, separation and determination of mercury species by HPLC-ICPMS using a Perkin-Elmer 3 μm C8 (33 mm × 3 mm) column and a mobile phase 3 containing 0.5% (v/v) 2-mercaptoethanol and 5% (v/v) CH3OH (pH 5.5) at a flow rate 1.5 ml min−1 and a temperature of 25 °C. Calibration curves for methyl mercury (I) and mercury (II) standards were linear in the range of 0-100 μg l−1 (r2 = 0.9990 and r2 = 0.9995 respectively). The lowest measurable mercury was 0.4 μg l−1 which corresponds to 0.01 μg g−1 in fish tissues and sediments. Methyl mercury concentrations measured in biological certified reference materials, NRCC DORM - 2 Dogfish muscle (4.4 ± 0.8 μg g−1), NRCC Dolt - 3 Dogfish liver (1.55 ± 0.09 μg g−1), NIST RM 50 Albacore Tuna (0.89 ± 0.08 μg g−1) and IRMM IMEP-20 Tuna fish (3.6 ± 0.6 μg g−1) were in agreement with the certified value (4.47 ± 0.32 μg g−1, 1.59 ± 0.12 μg g−1, 0.87 ± 0.03 μg g−1, 4.24 ± 0.27 μg g−1 respectively). For the sediment reference material ERM CC 580, a methyl mercury concentration of 0.070 ± 0.002 μg g−1 was measured which corresponds to an extraction efficiency of 92 ± 3% of certified values (0.076 ± 0.04 μg g−1) but within the range of published values (0.040-0.084 μg g−1; mean ± s.d.: 0.073 ± 0.05 μg g−1, n = 40) for this material. The extraction procedure for the fish tissues was also compared against an enzymatic extraction using Protease type XIV that has been previously published and similar results were obtained. The use of HPLC-HGAAS with a Phenomenox 5 μm Luna C18 (250 mm × 4.6 mm) column and a mobile phase containing 0.06 mol l−1 ammonium acetate (Merck Pty Limited, Australia) in 5% (v/v) methanol and 0.1% (w/v) l-cysteine at 25 °C was evaluated as a complementary alternative to HPLC-ICPMS for the measurement of mercury species in fish tissues. The lowest measurable mercury concentration was 2 μg l−1 and this corresponds to 0.1 μg g−1 in fish tissues. Analysis of enzymatic extracts analysed by HPLC-HGAAS and HPLC-ICPMS gave equivalent results. 相似文献
18.
The complexation of europium ion (Eu(III)) with a soil fulvic acid (FA) has been studied at pH 5 in 0.01 M NaClO4 by different experimental methods, i.e. synchronous fluorescence spectroscopy (SyFS) and time resolved laser-induced fluorescence spectroscopy (TRLFS). A series of SyFS quenching spectra was obtained by increasing the Eu(III) concentration and keeping the FA concentration constant. The emission spectra and fluorescence lifetimes of the Eu(III) bound to the FA were also measured by a TRLFS system using the same solution used in the SyFS spectral measurement. From the analysis of the fluorescence data obtained by the SyFS and the TRLFS using a non-linear least-squares method, the concentration of the binding sites (CL) of the FA accessible for the Eu(III) and the corresponding conditional stability constants (log K) were estimated. The two different methods gave rise to constants being comparable with one another. The log K and CL values (mean ± standard deviation of three determinations) determined by the SyFS were 6.4 ± 0.2 (6.7 ± 0.1 μmol L−1: by the TRLFS) and 10 ± 1 μmol L−1 (7 ± 1 μmol L−1: by the TRLFS), respectively. The applicability of the FA fluorescence quenching techniques for estimating the europium binding parameters was proved by the direct monitoring of the Eu(III) bound to the FA using the TRLFS system. 相似文献
19.
A natural smectite clay sample from Serra de Maicuru, Pará State, Brazil, had aluminum and zirconium polyoxycations inserted within the interlayer space. The precursor and pillarized smectites were organofunctionalized with the silyating agent 3-mercaptopropyltrimethoxysilane. The basal spacing of 1.47 nm for natural clay increased to 2.58 and 2.63 nm, for pillared aluminum, SAl/SH, and zirconium, SZr/SH, and increases in the surface area from 44 to 583 and 585 m2 g−1, respectively. These chemically immobilized clay samples adsorb divalent copper and cobalt cations from aqueous solutions of pH 5.0 at 298±1 K. The Langmuir, Redlich-Peterson and Toth adsorption isotherm models have been applied to fit the experimental data with a nonlinear approach. From the cation/basic center interactions for each smectite at the solid-liquid interface, by using van’t Hoff methodology, the equilibrium constant and exothermic thermal effects were calculated. By considering the net interactive number of moles for each cation and the equilibrium constant, the enthalpy, ΔintH0 (−9.2±0.2 to −10.2±0.2 kJ mol−1) and negative Gibbs free energy, ΔintG0 (−23.9±0.1 to −28.7±0.1 kJ mol−1) were calculated. These values enabled the positive entropy, ΔintS0 (51.3±0.3 to 55.0±0.3 JK−1 mol−1) determination. The cation-sulfur interactive process is spontaneous in nature, reflecting the favorable enthalpic and entropic results. The kinetics of adsorption demonstrated that the fit is in agreement with a second-order model reaction with rate constant k2, varying from 4.8×10−2 to 15.0×10−2 and 3.9×10−2 to 12.2×10−2 mmol−1 min−1 for copper and cobalt, respectively. 相似文献
20.
The influence of different parameters on the sorption profiles of trace and ultra traces of gold (I) species from the aqueous cyanide media onto the solid sorbents ion exchange polyurethane foams (IEPUFs) and commercial unloaded polyurethane foams (PUFs) based polyether type has been investigated. The retention of gold (I) species onto the investigated solid sorbents followed a first-order rate equation with an overall rate constant k in the range 2.2-2.8 ± 0.2 s−1. The sorption data of gold (I) followed Freundlich and Langmuir isotherm models. Thus, the a dual-mode of sorption mechanism involving absorption related to “weak base anion exchanger” and an added component for “surface adsorption” seems the most likely proposed dual mechanism for retention profile of gold (I) by the IEPUFs and PUFs solid sorbents. The capacity of the IEPUFs and PUFs towards gold (I) sorption calculated from the sorption isotherms was found to be 11.21 ± 1.8 and 5.29 ± 0.9 mg g−1, respectively. The chromatographic separation of the spiked inorganic gold (I) from de ionized water at concentrations 5-15 μg mL−1 onto the developed IEPUFs and PUFs packed columns at 10 mL min−1 flow rate was successfully achieved. The retained gold (I) species were then recovered quantitatively from the IEPUFs (98.4 ± 2.4%, n = 5) and PUFs (95.4 ± 3.4%, n = 5) packed columns using perchloric acid (60 mL, 1.0 mol L−1) as a proper eluating agent. Thiourea (1.0 mol L−1)-H2SO4 (0.1 mol L−1) system was also used as eluating agent for the recovery of gold (I) from IEPUFS (95.4 ± 5.4%, n = 3) and also PUFs (93.4 ± 4.4%, n = 3) packed columns. The performance of the IEPUFs and PUFs packed columns in terms of the height equivalent to the theoretical plates (HETP), number of plates (N), and critical and breakthrough capacities towards gold (I) species were evaluated. The developed IEPUFs packed column was applied successfully for complete retention and recovery (98.5 ± 2.7) of gold (III) species spiked onto tap- and industrial wastewater samples at <10 μg Au mL−1 after reduction to gold (I). The IEPUFs packed column was applied satisfactorily for complete retention and recovery (98.5 ± 2.7) of total inorganic gold (I) and/or gold (III) species spiked to tap- and industrial wastewater samples at <10 μg mL−1 gold. Chromatographic separation of gold (I) from silver (I) and base metal ions (Fe, Ni, Cu and Zn) using IEPUFS packed columns was satisfactorily achieved. The proposed method was applied successfully for the pre-concentration and separation from anodic slime and subsequent FAAS determination of analyte with satisfactory results (recoveries >95%, relative standard deviations <4.0%). 相似文献