Chromium (III) removal by microporous ion exchanger Amberlite.120 (Na+): kinetic, equilibrium and thermodynamic studies

Cr (III) sorption on microporous strong cation exchanger Amberlite.120 (Na⁺) is studied as a function of time and temperature. The pH changes show the co-sorption of H⁺ ions along with the chromium. The rate constant values for Cr (III) sorption are calculated for both film and particle diffusion processes. However, the particle diffusion is found to be more dominant than the film diffusion. The temperature is found to have a positive effect on both the diffusional processes. The low values of energy of activation also confirm the diffusional nature of the process. Equilibrium data are explained with the help of Langmuir equation. Various thermodynamic parameters (??H, ??S and ??G) for Cr (III) exchange on the resin are calculated. The ??G values are found to be negative, while both the ??H and ??S values obtained are positive.     

Sorption of thallium(III) ions from aqueous solutions using titanium dioxide nanoparticles

Titanium dioxide nanoparticles (NPs) were employed for the sorption of Tl(III) ions from aqueous solution. The process was studied in detail by varying the sorption time, pH, Tl(III) concentration, temperature, and amount of sorbent. The sorption was found to be fast and to reach equilibrium within 2 min, to be less efficient at low pH values, and to increase with pH and temperature. The sorption fits the Langmuir equation and follows a pseudo second order model. The mean energy of the sorption is approximately 15 kJ mol^?1 as calculated from the Dubinin–Radushkevich isotherm. The thermodynamic parameters for the sorption were also determined, and the ΔH ⁰ and ΔG ⁰ values indicate endothermic behavior.     

Preparation,characterization and applications of polyurethane foam functionalized with resorcinol for quantitative separation and determination of silver(I) and mercury(II) from tap and wastewater

A stable chelating resin matrix was prepared by covalently linking resorcinol with polyurethane foam matrix through a –N=N– group. Preconcentration and determination of trace Ag⁺ and Hg²⁺ ions from samples of different origin, using Res-PUF, were studied. Various conditions influencing the sorption of these metal ions onto Res-PUF were optimized. The kinetics of sorption of the Ag⁺ and Hg²⁺ by Res-PUF were found to be fast, reached equilibrium in few minutes (5–10?min) and followed a first-order rate equation with an overall rate constant k in 0.102 and 0.267/min, respectively. Study of the variation of the sorption of the tested metal ions with temperature yielded average values for ΔG, ΔH and ΔS of ?3.94, ?22.02 and ?58.37, respectively. The mean free sorption energy (E) computed from the Dubinin–Radushkevich (D–R) isotherm was found to be equal to 8.91 kJ/mol, which reflects the chelation sorption process. The capacities of the foam material were 0.15 and 0.07?mmol/g for Ag⁺ and Hg²⁺, respectively. Preconcentration factors of?>?50 were achieved (RSD?≈?5.99). The proposed preconcentration procedure was applied successfully to the determination of trace metal ions in natural and wastewater samples.     

Diethylenetriamine-functionalized chitosan magnetic nano-based particles for the sorption of rare earth metal ions [Nd(III), Dy(III) and Yb(III)]

The recovery of three rare earth (RE) metals ions [Yb(III), Dy(III) and Nd(III), belonging to heavy, mild and light REs, respectively] was investigated using hybrid chitosan-magnetic nano-based particles functionalized by diethylenetriamine (DETA). The effect of pH on sorption performance was analyzed: the optimum initial pH value was found close to 5 (equilibrium pH value close to 6.5). The nanometric size of sorbent particles (30–50 nm) minimized the contribution of resistance to intraparticle diffusion on the control of uptake kinetics, which is efficiently modeled using the pseudo-second order rate equation: under selected experimental conditions the contact time required for reaching equilibrium was less than 1 h. Sorption isotherms were efficiently modeled using the Langmuir equation: maximum sorption capacities reached about 50 mg metal g^?1, regardless of the RE. The temperature had a very limited effect on sorption capacity (in the range 300–320 K). The thermodynamic parameters were determined: the sorption was endothermic (positive values of ΔH°), spontaneous (negative values of ΔG°) and contributed to increasing the disorder of the system (positive values of ΔS°). The three REs have similar sorption properties on DETA-functionalized chitosan magnetic nano-based particles: the selective separation of these elements seems to be difficult. The sorbed metal ions can be removed from loaded sorbents using thiourea, and the sorbent can be recycled for at least five sorption/desorption cycles with a limited loss in sorption performance (by less than 6 %). The saturation magnetization was close to 20 emu g^?1; this means that nano-based superparamagnetic particles can be readily recovered by an external magnetic field, making the processing of these materials easy.     

Thermodynamic activation parameters for viscous flow of aqueous solutions of butylamines

The thermodynamic activation parameters, enthalpies, ΔH?^≠, free energies, ΔG ^≠, and entropies, ΔS?^≠, for viscous flow of the systems, water (W)?+?n-butylamine (NBA), W?+?sec-butylamine (SBA) and W?+?tert-butylamine (TBA), have been determined by using the density and the viscosity data. These properties and their excess values have been represented graphically against their composition. With respect to the composition, ΔG ^≠ show a typical behaviour for all the systems – a fast rise in the water-rich region with a maximum followed by the values that decline up to the pure state of amines. The ΔH?^≠ and ΔS?^≠ versus composition curves follow the similar trend. For all systems the excess properties, ΔG ^≠E, ΔH ^?≠E and ΔS?^≠E are characterized by sharp maxima in the water-rich region, which are thought to be mainly due to the hydrophobic hydration and the hydrophilic effect.     

Spectroscopic investigations of hematoxylin–Eu(III) complex interacting with Herring-sperm DNA

The interaction of HE–Eu(III) complex (HE?=?hematoxylin) with Herring-sperm DNA (hsDNA) has been studied by absorption spectra, fluorescence, and viscosity measurements in physiological buffer (pH?=?7.40). The binding constant of HE–Eu(III) complex to hsDNA was obtained by double reciprocal method at 298 and 310?K and the corresponding thermodynamic parameters (Δ_r Hm??=?8.55?×?10⁴?J?mol^?1, Δ_r Gm??=??3.01?×?10⁴?J?mol^?1, Δ_r Sm??=?387.95?J?mol^?1?K^?1) were calculated, showing that the interaction between HE–Eu(III) complex and hsDNA was driven mainly by entropy. The value of K indicated that the binding mode of HE–Eu(III) complex with DNA was not classical intercalation. These results were further supported by viscosity method and competitive binding experiment. Scatchard analysis suggests that the interaction mode was a mixed binding, which contains partial intercalation and groove binding.     

Anticancer activity of lanthanum (III) and europium (III) 5-fluorouracil complexes on Caco-2 cell line

Lanthanide complexes are of increasing importance in cancer diagnosis and therapy. In the present study 1:1 and 1:3 solid complexes of La (III)–5-FU (5-fluorouracil) were prepared and characterized. In solution, the formation of 1:1 La (III) and Eu (III) complexes enabled the enhancement of 5-FU's effectiveness. Binding constants of the 1:1 complexes of both metals were estimated using spectrophotometry and HPLC with fluorescence detection methods. The thermodynamic parameters ΔG ^° , ΔH ^° and ΔS ^° were calculated using differential scanning calorimetry. Evaluation of the cytotoxic activity of the 1:1 La (III)- and Eu (III)–5-FU complexes was performed through two methodologies, trypan blue for cell viability where La (III)- and Eu (III)–5-FU complexes were found to have 52,000 and 80,000 dead cells, respectively, and via flow cytometric analysis to measure the apoptotic values, which were found to be 59.87 and 86.86% respectively.     

Thermolysis of 3-methyl-3-(o-aryl)-1,2-dioxetanes: Activation parameters and chemiexcitation yields

3-Methyl-3-(o-tolyl)-1,2-dioxetane 1 and 3-methyl-4-(o-bromophenyl)-1,2-dioxetane 2 were synthesized in low yield by the β-bromo hydroperoxide method. The activation parameters were determined by the chemilumin-escence method (for 1 ΔG^? = 24.7 ± 0.3 kcal/mol, ΔH^? = 25.4, ΔS^? = + 1.9 e.u., k₆₀ = 3.4 × 10^?4s^?1; for 2 ΔG^? = 24.7 ± 0.4 kcal/mol, ΔH^? = 24.7, ΔS^? = 0.0 e.u., k₆₀ = 4.1 × 10^?4s^?1). Thermolysis of 1–2 directly produced high yields of excited triplets as expected for this type of dioxetane [triplet chemiexcitation yields (?⁷) for 1 0.03; for 2 0.02; the ?^T/?^S ratios were estimated to be approximately 200 for both compounds]. The effect of ortho-aryl substituents was inconsistent with electronic effects. The ortho substitution in 1–2 resulted in a marked increase in stability of the dioxetanes. The results are discussed in relation to a diradical-like mechanism.     

Thermodynamic activation parameters for viscous flow of dilute aqueous solutions of ethylenediamine,trimethylenediamine and N,N-dimethyltrimethylenediamine

The density and the viscosity data have been used to determine the thermodynamic activation parameters, free energies (ΔG ^?), enthalpies (ΔH ^?) and entropies (ΔS ^?), for viscous flow of the systems; water (W) + ethylenediamine (ED), W + trimethylenediamine (TMD) and W + N,N-dimethyltrimethylenediamine (DMTMD) in the temperature range of 303.15–323.15 K over the composition range of 0 ≤ X ₂ ≤ 0.45, where X ₂ is the mole fraction of diamines. On addition of diamines to water, ΔG ^?, ΔH ^? and ΔS ^? values increase sharply, pass through a maximum and then decline. The heights of maximum in the ΔG ^? versus X ₂ curve vary as, W + DMTMD > W + TMD > W + ED. For all systems, the excess properties, ΔG ^{? E} , ΔH ^{? E} and ΔS ^{? E} are positive. The observed increase in thermodynamic values may be due to combined effect of hydrophobic hydration of diamines and water–diamine interaction as a result of hydrophilic effect.     

A kinetic study of the oxidation of L-ascorbic acid by chromium(VI)

The reaction between chromium(VI) and L-ascorbic acid has been studied by spectrophotometry in the presence of aqueous citrate buffers in the pH range 5.69–7.21. The reaction is slowed down by an increase of the ionic strength. At constant ionic strength, manganese(II) ion does not exert any appreciable inhibition effect on the reaction rate. The rate law found is where K_p is the equilibrium constant for protonation of chromate ion and k_r is the rate constant for the redox reaction between the active forms of the oxidant (hydrogenchromate ion) and the reductant (L-hydrogenascorbate ion). The activation parameters associated with rate constant k_r are E_a = 20.4 ± 0.9 kJ mol^?1, ΔH^≠ = 17.9 ± 0.9 kJ mol^?1, and ΔS^≠=?152 ± 3 J K^?1 mol^?1. The reaction thermodynamic magnitudes associated with equilibrium constant K_p are ΔH⁰ = 16.5 ± 1.1 kJ mol^?1 and ΔS⁰ = 167 ± 4 J K^?1 mol^?1. A mechanism in accordance with the experimental data is proposed for the reaction. © 1993 John Wiley & Sons, Inc.     

Demetallation of α, β, γ, δ-tetra(p-sulfophenyl)porphineiron(III) in sulfuric acid-ethanol-water media

The rate of demetallation of α, β, γ,δ-tetra(p-sulfophenyl)porphineiron (III), Fe(TPPS)^3-, was determined in sulfuric acid-ethanol-water media for 8.5-10.65M sulfuric acid at different temperatures. The overall reaction was the conversion of the complex Fe(TPPS)^3- into the diacid species H₄TPPS^2- without other spectrophotometrically important species being formed to an appreciable extent, as shown by three isosbestic points at 418, 462, and 563 nm. The rate was first order in the Fe(TPPS)^3- concentration. The pseudo-first-order rate constants k were exponentially dependent on the sulfuric acid concentration, and log k was linearly dependent on the Hammett acidity function –H₀. The average ΔH? and ΔS? values for five reaction media were 18.4 ± 1.4 kcal/mol and 19 ± 3 cal/°K · mol, respectively. The linear relationship between log k and (-H₀) and the approximately constant values of ΔH? ΔS? over the acid range investigated indicated that the same mechanism of demetallation was operative over this acid range. Because of the dependence of the pseudo-first-order rate constants on the acidity of the medium, the mechanism probably involves the addition of protons to pyrrole N atoms to assist in the breaking of iron (III)-nitrogen bonds.     

Norfloxacin La(III)-based complex: synthesis,characterization, and DNA-binding studies

A La(III) complex, [La^IIICl₂(NOR)₂]Cl (2), containing norfloxacin (NOR) (1), a synthetic fluoroquinolone antibacterial agent, has been synthesized and characterized by elemental analysis, IR, UV–vis spectra and ¹H NMR spectroscopy, and molar conductance measurements. The interaction between 2 and CT-DNA was investigated by steady-state absorption and fluorescence techniques in different pH media, and showed that 2 could bind to CT-DNA presumably via non-intercalative mode and the La(III) complex showed moderate ability to bind CT-DNA compared to other La(III) complexes. The binding site number n, and apparent binding constant K_A, corresponding thermodynamic parameters ΔG^#, ΔH^#, ΔS^# at different temperatures were calculated. The binding constant (K_A) values are 0.23 ± 0.05, 0.56 ± 0.05, and 0.18 ± 0.08 × 10⁵ L mol^?1 for pH 4, 7, and 11, respectively. It was also found that the fluorescence quenching mechanism of CT-DNA by La(III) complex was a static quenching process.     

Separation of Y from Sr by zirconium vanadate gel ion-exchanger sorbent: kinetics and thermodynamic study

A new zirconium vanadate (Zr–V) ion-exchanger was synthesized and characterized for fast and selective separation procedure of ⁹⁰Y from ⁸⁹Sr. The method was based on ⁹⁰Y(III) sorption from aqueous HCl solution containing ⁸⁹Sr(II) onto Zr–V gel exchanger. The kinetics of Y(III) sorption from HCl solution by Zr–V exchanger was subjected to Weber–Morris, Lagergren, Bhattacharya and Venkobachar, and Bt models. Initially, the uptake of Y(III) onto the exchanger was fast followed by kinetically first-order sorption with an overall rate constant, K _Lager = (3.55 ± 0.03) × 10^?4 min^?1. Film and intraparticle transport are the two steps that might influence Y(III) sorption. The negative values of ΔG of ⁹⁰Y retention dictate that, the process is a spontaneous. The negative values of ΔH and ΔS reflect the exothermic nature of ⁹⁰Y(IIsorption and the random uptake of ⁹⁰Y(III) onto Zr–V sorbent. Zr–V exchanger offers unique advantages of ⁹⁰Y(III) retention over conventional solid sorbents in rapid and effective separation of traces of ⁹⁰Y(III) from Sr. The exchanger was successfully packed in column for an effective separation of ⁹⁰Y.     

Uptake properties of Eu(III) on Na-attapulgite as a function of pH, ionic strength and temperature

Herein, the sorption properties of Eu(III) on Na-attapulgite were performed by using batch sorption experiments under different experimental conditions, such as contact time, pH, ionic strength, humic acid and temperatures. The results indicated that the sorption of Eu(III) on Na-attapulgite was strongly dependent on pH and temperature. At low pH values, the sorption of Eu(III) was influenced by ionic strength, whereas the sorption was not affected by ionic strength at high pH values. The sorption of Eu(III) was mainly dominated by ion exchange or outer-sphere surface complexation at low pH values, and by inner-sphere surface complexation or surface precipitation at high pH values. The sorption of Eu(III) onto Na-attapulgite increased with increasing temperature. The Langmuir and Freundlich models were applied to simulate the sorption isotherms, and the results indicated that the Langmuir model simulated the sorption isotherms better than the Freundlich model. The thermodynamic parameters (∆G ^o, ∆S ^o, ∆H ^o) were calculated from the temperature dependent sorption isotherms at 293, 313 and 333 K, respectively, and the results indicated that the uptake of Eu(III) on Na-attapulgite was an endothermic and spontaneous process. The results of high Eu(III) sorption capacity on Na-attapulgite suggest that the attapulgite is a suitable material for the preconcentration and immobilization of Eu(III) ions from large volumes of aqueous solutions.     

Kinetic modeling analysis for the removal of cesium ions from aqueous solutions using polyaniline titanotungstate

Polyaniline titanotungstate has been synthesized by incorporation of organic polymer polyaniline into the inorganic precipitate of titanotungstate. This material was characterized using X-ray, IR and TGA studies. The influences of initial concentration of metal ions, particle size and temperature have been reported. The comparison of composite and inorganic materials was studied and indicating that the composite material is better than the inorganic in selectivity of Cs⁺ ions. Thermodynamic parameters, such as changes in Gibbs free energy (ΔG), enthalpy (ΔH), and entropy (ΔS) have been calculated. The numerical values of ΔG decrease with an increase in temperature, indicating that the sorption reaction of adsorbent was spontaneous and more favorable at higher temperature. The positive values of ΔH correspond to the endothermic nature of sorption processes and suggested that chemisorptions were the predominant mechanism. A comparison of kinetic models applied to the sorption rate data of Cs⁺ ions was evaluated for the pseudo first-order, the pseudo second-order, intraparticle diffusion and homogeneous particle diffusion kinetic models. The results showed that both the pseudo second-order and the homogeneous particle diffusion models were found to best correlate the experimental rate data. Self diffusion coefficient (D_i), Activation energy (Ea) and entropy (ΔS^*) of activation were also computed from the linearized form of Arrhenius equation.     

Thermodynamic denaturation of β-lactoglobulin in the presence of cetylpyridinium chloride

In this work, we determined the stability parameters of bovine β-lactoglobulin, variant A, (BLG-A), in relation to their transition curves induced by cetylpyridinium chloride (CPC) as a cationic surfactant. The experiments took place over the temperature range of 298 K to 358 K. For each transition curve at any specific temperature, the conventional method of analysis, which assumes a linear concentration dependence of the pre- and post-transition base lines, gave the most realistic values for ΔG_D(H₂O). Results show that the minimum value of ΔG_D(H₂O) occurs at T = 328 K. Using the Gibbs–Helmholtz equation, the values of enthalpy, ΔH_D, and entropy, ΔS_D, of denaturation have been calculated considering temperature dependence of ΔG_D at any specified concentration of CPC. The values of 12.05 kJ · mol⁻¹, 18.54 kJ · mol⁻¹, and 18.32 J · mol⁻¹ · K⁻¹, were obtained for ΔG_D(H₂O), ΔH_D(H₂O), and ΔS_D(H₂O), respectively. The results show that the enthalpy term dominates the entropy term.     

Kinetics of substitution of aqua ligands from cis‐diaqua (ethylenediamine)platinum(II) perchlorate by L‐asparagine in aqueous medium

The kinetics of the interaction of L ‐asparagine with [Pt(ethylenediamine)(H₂O)₂]²⁺ have been studied spectrophotometrically as a function of [Pt(ethylenediamine)(H₂O)₂²⁺], [L ‐asparagine], and temperature at pH 4.0, where the substrate complex exists predominantly as the diaqua species and L ‐asparagine as the zwitterion. The substitution reaction shows two consecutive steps: the first step is the ligand‐assisted anation and the second one is the chelation step. Activation parameters for both the steps have been calculated using Eyring equation. The low ΔH₁^≠ (43.59 ± 0.96 kJ mol^?1) and large negative values of ΔS₁^≠ (?116.98 ± 2.9 J K^?1 mol^?1) as well as ΔH₂^≠ (33.78 ± 0.51 kJ mol^?1) and ΔS₂^≠ (?221.43 ± 1.57 J K^?1 mol^?1) indicate an associative mode of activation for both the aqua ligand substitution processes. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 252–259, 2003     

Influence des effets de substituants sur la protonation de la pyridine

Standard thermodynamic values of proton ionisation of 3 substituted (Cl?, Br?, I?, C₂H₅? and CH₂CN?) pyridine derivatives are determined at 25°C, in an aqueous medium of ionic strength 0.5 M KNO₃.Free energies are deduced from equilibrium constants log K potentiometrically calculated. Enthalpies are obtained from calorimetric measurements.ΔG^o, ΔH^o and ΔS^o values are discussed in the context of the results of our earlier studies on this subject.The Hammett plot corresponding to the thirteen systems examined gives the proton ionisation constant of a substituted pyridine from the equation log K = 5,48 – 5,94Σσ.Besides, a linear relationship is found between ΔG^o and ΔH^o, which confirms the observation made previously in other series of pyridine derivatives.     

Thermodynamic studies of hydrogen iodide in dioxane-water mixtures from electromotive force measurements

The standard potentials of the silver-silver iodide electrode were measured in 10,20,30 and 40% (w/w) dioxane-water mixtures at 15,25,35 and 45°C. These values have been used to determine the thermodynamic quantities ΔG_t°, ΔS_t°, ΔH_t° for the transfer of H⁺I^? from water to various dioxane-water mixtures. The ionic ΔG_t° values for H⁺, Cl^?, Br^? and I^? are determined using Feakins method. The chemical and electrical contributions of ΔG_t° are also calculated using the method proposed by Roy and co-workers. The significance of these thermodynamic functions is discussed in relation to the acid—base character of the solvents.