The formation of colourless gadolinium complexes (x,y,z), between x gadolinium ions, y ligands and z protons, of some organic acids, has been studied in aqueous solution. In this work we present the results of investi...The formation of colourless gadolinium complexes (x,y,z), between x gadolinium ions, y ligands and z protons, of some organic acids, has been studied in aqueous solution. In this work we present the results of investigations on the interaction of the gadolinium ion (Gd3+) with malic acid (C4H6O5, a-hydroxyl dicarboxylic acid), in dilute aqueous solution for pH values between 5.5 and 7.5. Colourless gadolinium complexes of malate ions have no absorption band UV-visible, the indirect photometric detection (IPD) technique was used and studies have identified a major tri-nuclear complex of malate ion (﹣OOC-CH2-CHOH-COO﹣). The formation of this new colourless complex is derived from three Gd(III) ions that react with two malate ions and two hydronium ions (H3O+), giving for this colourless complex, a (3,2,2) composition and apparent stability constant depends on the acidity of the medium, with logK'322 = 18.88 ± 0.05 at pH = 6.30. To complement previous results and to propose a probable structure for this new complex detected in solution, studies of IR spectroscopy have been conducted to identify the chelation sites for both ligands. The results were analysed and show that this organometallic gadolinium complex, contains two different sites, respectively, two lateral tetradentate mono-nuclear sites and a single central bidentate mono-nuclear site. From these results, the reaction of formation, the stability constant and the probable structure of this new colourless organometallic gadolinium complex are proposed.展开更多
The technique of supported liquid membranes was used to achieve the facilitated transport of Cr(III) ions, using tow amphiphilic carriers, the methyl cholate and resorcinarene. For prepared SLMs, toluene as organic ph...The technique of supported liquid membranes was used to achieve the facilitated transport of Cr(III) ions, using tow amphiphilic carriers, the methyl cholate and resorcinarene. For prepared SLMs, toluene as organic phase and film of polyvinylidene difluoride, as hydrophobic polymer support with 100 μm in thickness and 0.45 μm as the diameter of the pores. The macroscopic parameters (P and J0) on the transport of these ions were determined for different medium temperatures. For these different environments, the prepared SLMs were highly permeable and a clear evolution of these parameters was observed. The parameter J0 depended on the temperature according to the Arrhenius equation. The activation parameters, Ea, ΔH≠ and ΔS≠, for the transition state on the reaction of complex formation (ST) , were determined. To explain these results for this phenomenon, and achieve a better extraction of the substrate, a model based on the substrate complexation by the carrier and the diffusion of the formed complex (ST) was developed. The experimental results verify this model and determine the microscopic parameters (Kass and D*). These studies show that these parameters Kass and D* are specific to facilitated transport of Cr(III) ions by each of the carriers and they are changing significantly with temperature.展开更多
To control the stability of the lysine acetylsalicylate compound (LAS) in aqueous solution, some studies of the hydronium ion-catalyzed, hydroxide ion-catalyzed, and spontaneous reactions of this active ingredient in ...To control the stability of the lysine acetylsalicylate compound (LAS) in aqueous solution, some studies of the hydronium ion-catalyzed, hydroxide ion-catalyzed, and spontaneous reactions of this active ingredient in water solutions have been carried out. The pH-rate profile (log kobs = f(pH)), shows that the hydrolysis reaction of the LAS, is conducted by a catalysis acid-base mechanism, with multiple reaction pathways. The rate constants, kH, kOH and k0 to the reaction pathways catalyzed by H3O+, HO– ions and to the spontaneous reaction, for the hydrolysis reaction of the reagent LAS, were determined. The results show that the studied compound LAS is unstable in basic medium and the hydrolysis reaction catalyzed by HO– ions is predominant.For a known acidity (pH ≈ 10), studies conducted for different temperatures of the medium, clearly indicate, that the experimental rate constant kobs,depends on the temperature according to the Arrhenius equation. The activation parameters: activation energy (Ea), enthalpy (ΔH≠) and entropy (ΔS≠), for the transition state were determined, The very negative value obtained for the activation parameter ΔS*, first indicates that in the transition state there is gain in order, then this late state, resembles the products and that probably for the mechanism of the LAS hydrolysis reaction catalyzed by HO– ions, the rate-determining step is a bimolecular reaction. Finally from all these results, the mechanism for the reaction pathway catalyzed by HO– ions has been elucidated.展开更多
文摘The formation of colourless gadolinium complexes (x,y,z), between x gadolinium ions, y ligands and z protons, of some organic acids, has been studied in aqueous solution. In this work we present the results of investigations on the interaction of the gadolinium ion (Gd3+) with malic acid (C4H6O5, a-hydroxyl dicarboxylic acid), in dilute aqueous solution for pH values between 5.5 and 7.5. Colourless gadolinium complexes of malate ions have no absorption band UV-visible, the indirect photometric detection (IPD) technique was used and studies have identified a major tri-nuclear complex of malate ion (﹣OOC-CH2-CHOH-COO﹣). The formation of this new colourless complex is derived from three Gd(III) ions that react with two malate ions and two hydronium ions (H3O+), giving for this colourless complex, a (3,2,2) composition and apparent stability constant depends on the acidity of the medium, with logK'322 = 18.88 ± 0.05 at pH = 6.30. To complement previous results and to propose a probable structure for this new complex detected in solution, studies of IR spectroscopy have been conducted to identify the chelation sites for both ligands. The results were analysed and show that this organometallic gadolinium complex, contains two different sites, respectively, two lateral tetradentate mono-nuclear sites and a single central bidentate mono-nuclear site. From these results, the reaction of formation, the stability constant and the probable structure of this new colourless organometallic gadolinium complex are proposed.
基金All authors thank the Agence Universitaire de la Fran-cophonie(AUF)for financial support(PCSI 59113PS 014)Professor Jean-François Verchère from the University of Rouen(France)for his advice,fruitful dis-cussions,strong encouragement and exemplary coopera-tion.
文摘The technique of supported liquid membranes was used to achieve the facilitated transport of Cr(III) ions, using tow amphiphilic carriers, the methyl cholate and resorcinarene. For prepared SLMs, toluene as organic phase and film of polyvinylidene difluoride, as hydrophobic polymer support with 100 μm in thickness and 0.45 μm as the diameter of the pores. The macroscopic parameters (P and J0) on the transport of these ions were determined for different medium temperatures. For these different environments, the prepared SLMs were highly permeable and a clear evolution of these parameters was observed. The parameter J0 depended on the temperature according to the Arrhenius equation. The activation parameters, Ea, ΔH≠ and ΔS≠, for the transition state on the reaction of complex formation (ST) , were determined. To explain these results for this phenomenon, and achieve a better extraction of the substrate, a model based on the substrate complexation by the carrier and the diffusion of the formed complex (ST) was developed. The experimental results verify this model and determine the microscopic parameters (Kass and D*). These studies show that these parameters Kass and D* are specific to facilitated transport of Cr(III) ions by each of the carriers and they are changing significantly with temperature.
文摘To control the stability of the lysine acetylsalicylate compound (LAS) in aqueous solution, some studies of the hydronium ion-catalyzed, hydroxide ion-catalyzed, and spontaneous reactions of this active ingredient in water solutions have been carried out. The pH-rate profile (log kobs = f(pH)), shows that the hydrolysis reaction of the LAS, is conducted by a catalysis acid-base mechanism, with multiple reaction pathways. The rate constants, kH, kOH and k0 to the reaction pathways catalyzed by H3O+, HO– ions and to the spontaneous reaction, for the hydrolysis reaction of the reagent LAS, were determined. The results show that the studied compound LAS is unstable in basic medium and the hydrolysis reaction catalyzed by HO– ions is predominant.For a known acidity (pH ≈ 10), studies conducted for different temperatures of the medium, clearly indicate, that the experimental rate constant kobs,depends on the temperature according to the Arrhenius equation. The activation parameters: activation energy (Ea), enthalpy (ΔH≠) and entropy (ΔS≠), for the transition state were determined, The very negative value obtained for the activation parameter ΔS*, first indicates that in the transition state there is gain in order, then this late state, resembles the products and that probably for the mechanism of the LAS hydrolysis reaction catalyzed by HO– ions, the rate-determining step is a bimolecular reaction. Finally from all these results, the mechanism for the reaction pathway catalyzed by HO– ions has been elucidated.
