Kinetic studies for sorption of amino acids using a strong anion-exchange resin. Effect of ionic strength

This work deals with the influence of the ionic strength on the sorption of L-phenylalanine and L-tyrosine by a strong basic anion-exchange resin, converted to the hydroxide form with sodium hydroxide. Equilibrium uptake isotherms were obtained for phenylalanine and tyrosine by carrying out batch experiments at different ionic strength values of the solution. The model used to correlate these results is the modified Langmuir equation which has been applied with success to biological systems. Batch kinetic experiments were performed using a packed bed of differential length inserted in a liquid circulation loop and in which the ionic strength of the solution was varied. Moreover, an experiment at variable pH for tyrosine was also performed. Experimental transient concentration profiles were compared to those predicted by the pore diffusion model and enabled the estimation of the intraparticle diffusivities for phenylalanine and tyrosine.     

Preparation, characterization and thermal studies of some transition metal ternary complexes

Ternary complexes of Co(II), Ni(II), Cu(II) and Zn(II) with nitrilotriacetic acid as a primary ligand and glycine as secondary ligand were prepared in slightly acid medium. Their molecular masses were determined by acid-base titration against standard potassium hydroxide solution. Their molecular structures were found to be [M (HNTA)(glyH)(2H₂O)]. Thermogravimetric analysis confirmed this structure and that the water present is coordinated to the central metal atom. UV-Vis spectra showed that the complexes have octahedral symmetry. IR spectra suggested the presence of intermolecular hydrogen bonding. This phenomenon was supported by mass spectra. The ionization constants of these complexes, as diprotic acids, were determined.     

Preparation,structural characterization and biological studies of some new levofloxacin metal complexes

A new series of metal complexes of Ti(IV), V(IV), Y(III), Zr(IV), Ce(IV) and U(VI) with levofloxacin (Levo) were synthesized and characterized by elemental analysis, molar conductivity, magnetic moment measurements, UV–Vis, FT-IR and ¹H NMR, XRD as well as TG-DTG techniques. The data indicated that levofloxacin reacts as a bidentate ligand chelate to the metal ion through the pyridone oxygen and one carboxylato oxygen. The thermal dehydration and decomposition of the complexes were studied kinetically using Coats–Redfern and Horowitz–Metzger methods, and the thermodynamic data reflected the thermal stability for all complexes. The calculated bond length and the bond stretching force constant, F(U=O), values for UO₂ bond are 1.86 Å and 690.67 N m^?1. The biological activities of the levofloxacin, meta-salts and their metal complexes were assayed against different bacterial and fungal species as well as their effect on degradation of calf thymus DNA.     

Kinetic studies for sorption of some metal ions from aqueous acid solutions onto TDA impregnated resin

Summary Kinetic studies for sorption of uranium, thorium and cobalt ions from hydrochloric acid solutions using tri-dodecyl amine (TDA) loaded on Amberlite XAD4 (polystyrene resin supplied by Rohm and Haas) using the batch technique, have been evaluated and assessed. Analysis of the respective data in accordance with three kinetic models revealed that the particle diffusion mechanism is the rate determining step, and the sorption for each metal ion on the impregnated sorbent follows the first order reversible kinetics. Values of the first order rate constants, rate constants of intraparticle transport, and the particle diffusion coefficients for the studied ions were determined. Sorption isotherms, which have been evaluated from the distribution coefficients for these ions, were found in good fit with the Langmuir and Freundlich isotherms.     

Synthesis,characterization and metal ion sorption studies of graft copolymers of cellulose with glycidyl methacrylate and some comonomers

To develop low-cost and environmentally friendly polymeric materials for enrichment, separation and remediation of metal ions from water, novel reactive graft copolymers based on cellulose extracted from pine needles were synthesized by grafting of poly(glycidyl methacrylate) alone and with comonomers acrylic acid, acrylamide and acrylonitrile by benzoyl peroxide initiation. Structural aspects of graft copolymers have been characterized by elemental analysis, FTIR, and solvent uptake behaviour. An attempt has been made to study sorption of Fe²⁺, Cu²⁺ and Cr⁶⁺ ions on candidate graft copolymers by an equilibration method and to investigate the structural aspects of graft copolymers and establish a relationship between the structural aspects of graft copolymers and metal ion uptake efficiency and selectivity.     

Preparation and characterization of a novel fluorinated acrylate resin

The novel fluorinated acrylate resin was successfully prepared by solution polymerization of 2-(perfluoro-(1,1-bis-isopropyl)-2-propenyl)oxyethyl methacrylate (POMA) with butyl acrylate (BA), methyl methacrylate (MMA) and methacrylic acid (MAA) initiated by AIBN in the co-solvents of ethyl acetate, butyl alcohol and toluene. POMA was synthesized from the intermediate perfluoro nonene and 2-hydroxyethyl methacrylate as the staring reactants. Films of the novel fluorinated acrylate resin were prepared by coating the resin directly on the clean glass sheet and allowed to dry at room temperature. The characteristics of the film such as hydrophobicity, glass transition temperature and thermal stability were characterized with the contact angle, differential scanning calorimetry and thermo-gravimetric analysis respectively. The structure of the novel fluorinated acrylate resin was investigated by Fourier transform infrared (FTIR) spectrometry. The influences of the fluorine content on the performance of the acrylate resin were studied. Results show that the hydrophobicity, chemical resistance, glass transition temperature and thermal stability of the acrylate resin are improved when the fluorinated monomer is introduced to copolymerize with other monomers. However, the hydrophobicity of the fluorinated acrylate resin is improved slightly via annealing.     

Water sorption and diffusion studies in an epoxy resin system

The kinetics of water absorption in epoxide materials was studied by the aid of a diglycidyl ether of bisphenol‐A–triethylenetetramine (DGEBA–TETA) epoxy–resin system containing various amounts of the plasticizer THIOCOL (0–40 phr). The presence of plasticizer permits the formation of products with different crosslinking densities and hydrophilic characters. Dynamic water absorption experiments were carried out at 15, 40, and 70°C. For the fitting of the experimental results, a new model was used, based on a model proposed earlier by Jacobs and Jones. This model considers epoxide product as a two‐phase system consisting of a master phase (where the major part of the water is absorbed), which is homogeneous and nonpolar (phase 1), and of a second phase with different density and/or hydrophilic character (phase 2). By making the assumption that water diffusion can take place independently in the different phases of the material in accordance with Fick's second law, we can calculate the diffusion coefficient D and the water content at saturation M_∞ for each phase separately. Equilibrium water sorption measurements were performed at 40°C, and the data were analyzed and discussed based on the Guggenheim–Anderson–de Boer (GAB) equation, the results being in support of the two‐phase model used in the analysis of absorption kinetics. The linear expansion coefficient and the glass transition temperature of the materials, employed in the discussion of the results, were measured by thermomechanical analysis. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1165–1182, 1999     

Preparation and characterization of a novel pH-sensitive ion exchange resin

Methylacrylic acid/styrene cross-linked with divinylbenzene is a novel pH-sensitive ion exchange resin. Microspheres of this resin were characterized by Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The microspheres showed a pulsatile swelling behavior when the pH of the media changed. The pH-sensitive microspheres were loaded with salbutamol sulfate and the drug-release characteristics were studied under both simulated gastric and intestinal pH conditions. The results obtained showed that the drug release also depended on the pH of the release media.     

聚苯胺/石墨烯涂覆型阴离子交换固定相的制备及表征

该文以聚苯胺/石墨烯复合材料为涂覆材料,制备了一种涂覆型阴离子交换固定相。首先以苯胺和石墨烯为原料制备聚苯胺/石墨烯复合材料,并通过物理吸附涂覆在聚苯乙烯-二乙烯苯微球表面;然后以聚苯胺中的氮原子为反应位点,通过季铵化制备一系列具有不同交换容量的涂覆型阴离子交换固定相。通过扫描电镜(SEM)、傅里叶红外光谱(FT-IR)和元素分析(EA)对该涂覆型阴离子交换固定相进行表征,结果表明聚苯胺/石墨烯成功地涂覆在微球表面且发生了季铵化。通过分离常规阴离子和有机酸,对自制阴离子交换色谱柱的色谱性能进行评价。结果显示,8次季铵化的聚苯胺/石墨烯涂覆聚苯乙烯-二乙烯苯阴离子交换色谱柱对常规阴离子和有机酸呈现良好的分离效果。     

Sorption of protons and metal ions from aqueous solutions by a strong-base anion-exchange resin loaded with sulphonated azo-dyes

Two sulphonated azo-dyes, which bear a nitrogen donor atom in the diazo group and are known to complex many heavy metal ions in aqueous solution, have been found to be sorbed by a strong-base anion-exchange resin (Dowex 1-X8) simply by ion-exchange. The resin containing the dyes behaves like a chelating resin, able to sorb copper(II) and nickel(II) from aqueous solution, if the proper conditions are chosen. The acidity, ionic composition and volume of the aqueous solution, and the amount and nature of the sorbed ligand are the factors which determine the fraction of metal ion sorbed when the batch technique is used. The experimental results are interpreted by using a model of the resin based on the Donnan equilibrium concept, which allows prediction of the sorption conditions on the basis of some independently determined quantities, such as the protonation and complex formation constants in aqueous solution, and the activity of the counter-ion in the resin phase. The exchange of protons between the resin and the aqueous solution can also be explained with this model.     

Preparation and electrochemical characterization of cation- and anion-exchange/polyaniline composite membranes

Composite membranes were prepared by chemical polymerization of a thin layer of polyaniline (PANI) in the presence of a high oxidant concentration on a single face of a sulfonated cation-exchange membrane (CEM) and quaternary aminated anion-exchange membrane (AEM). IR and SEM studies for both types of membranes confirmed PANI loading on the ion-exchange membranes. PANI composite ion-exchange membranes were characterized as a function of the polymerization time by ion-exchange capacity, coating density, and membrane conductance measurements. Membrane potential measurements were performed in various electrolyte solutions in order to observe the selectivity of these membranes for different types of counterions. Membrane potential data in conjunction with membrane conductance data was interpreted on the basis of frictional considerations between membrane matrix and solute. Electrodialysis experiments, using PANI composite ion-exchange membranes with 4 h polymerization time, were performed in single and mixed electrolyte solutions for observing electromigration of solute across PANI composite ion-exchange membranes. Relative dialytic rates of Na(2)SO(4), CaCl(2), and CuCl(2) were estimated with reference to NaCl on the basis of electrodialysis experiments and it was concluded that it is possible to separate different electrolytes using PANI composite ion-exchange membranes.     

Adsorption equilibrium of fructosyltransferase on a weak anion-exchange resin

The adsorption equilibrium of a glycoprotein, fructosyltransferase from Aureobasidium pullulans, on an anion-exchange resin, Sepabeads FP-DA activated with 0.1M NaOH, was investigated. The adsorption isotherms were determined at 20 degrees C in a phosphate-citrate buffer with pH 6.0 using the static method. Sodium chloride was used to adjust the ionic strength in the range from 0.0215 to 0.1215 mol dm(-3) which provided conditions varying from a weak effect of salt concentration on protein binding to its strong suppression. The equilibrium data were very well fitted by means of the steric mass-action model when the ion-exchange capacity of 290 mmol dm(-3) was obtained from independent frontal column experiments. The model fit provided the protein characteristic charge equal to 1.9, equilibrium constant 0.326, and steric factor 1.095 x 10(5).     

Equilibrium,kinetics and thermodynamics studies of Cd sorption onto a dithizone-impregnated Amberchrom CG-300m polymer resin

Amberchrom CG-300m, a styrene acrylic ester polymer resin, was studied for the first time as sorbent for metal ion sorption in a solid-phase extraction system. The polymer sorbent was modified via impregnation with dithizone to improve its efficiency. Efficiency of the modified sorbent improved by more than 47%. The loading capacity of the resin is 3.2 mg dithizone per gram of sorbent. The mechanisms of Cd(II) sorption from aqueous solutions are presented. Capacity of the modified resin for Cd(II) was investigated in batch experiments as a function of pH, initial metal ion concentration, temperature and time. Maximum capacity of 0.551 mg Cd(II) per gram of sorbent was achieved. The dimensionless separation factor, 0 < R_L < 1, associated with the Langmuir isotherm (at T = 294 K) signifies sorption of Cd(II) was favorable, as do negative values of free energy of sorption (ΔG) at temperatures exceeding 293 K. Sorption was endothermic (ΔH > 0) while ΔS > 0 reflects the affinity of the sorbent towards Cd(II). The pseudo-second order model proved to be the best fit model for Cd(II) sorption kinetics data. Particle-diffusion models suggest sorption follows film as well as pore diffusion mechanisms.     

Preparation,characterization, and application of fine metal particles and metal colloids using hydrotriorganoborates

The reduction of transition metal salts and oxides using hydrotriorganoborates in organic media allows the production of X-ray amorphous nanopowders of metals and alloys under mild conditions. For example, the reduction of needle-shaped iron oxides at 80°C in organic solvents leads to acicular iron-magnet pigments suitable for recording magnetic signals. The reduction of TiCl₄ with K[BEt₃H] gives an ether-soluble [Ti(0)·0.5THF]_x which serves as a catalyst for the hydrogenation of titanium or zirconium sponges and related systems and as a powerful activator for heterogeneous hydrogenation catalysts. The use of tetraalkylammonium hydrotriorganoborates as reducing agents leads to colloidal transition metals in organic phases. These colloids may also be obtained using conventional reducing agents after first reacting the metal salts with the stabilizing tetraalkylammonium halide. Colloidal metals prepared in this way serve as sources for heterogeneous metal catalysts.     

Synthesis,characterization and spectroscopic studies of pyrazinamide metal complexes

The present paper deals with the synthesis and characterization of Schiff base complexes of pyrazinamide an antitubercular drug. Metals selected for complexation are copper, silver, gold, zinc, mercury, iron and cobalt. The complexes have been suitably synthesized and isolated in pure powdered form. Analytical data agrees with the compositions M(L), M′(L)₂ and M″(L)₂·2H₂O, respectively where M = Ag, M′ = Cu, Au, Zn and Hg and M″ = Fe and Co, ligand metal ratios were also confirmed by monovariation method and Job’s method of continuous variation. Molar conductance values suggest the non ionic nature of the complexes. The tentative structure assigned to the complexes on the basis of stoichiometry and analytical data were further supported by spectral studies viz; IR, NMR, magnetic susceptibility and electronic spectra. A preliminary attempt has also been made to compare the potencies of metal complexes with parent drug. The Cu and Ag complexes are giving encouraging results. Particle size studies further suggest that the drug molecule undergoes reduction in size on complexation.     

Preparation, characterization, and electrochemical application of metal/metal ion loaded fullerene nanowhiskers

Ce-doped C₆₀ nanowhiskers were prepared by liquid–liquid interfacial precipitation method using C₆₀-saturated benzene and Ce-containing isopropyl alcohol solution. The optical microscopy and scanning electron microcopy images of the Ce-doped nanowhiskers revealed the formation of lengthy nanowhiskers with uniform diameter. The X-ray diffraction pattern of the as-prepared and heat-treated Ce-doped nanowhiskers elucidated the face-centered cubic crystalline nature and the formation of CeO₂ phase at 400 °C. Raman spectroscopic studies on the Ce-doped nanowhiskers revealed the polymerization of the C₆₀ molecules in the nanowhiskers. The diameter of the nanowhiskers was calculated from the transmission electron microscopy (TEM) image, and it varied in the range of 150–300 nm. The scanning TEM mapping analysis was shown to confirm the Ce doping and the location of the Ce ion doping in the nanowhiskers. The electrochemical characterization of the nanowhiskers does not show any sufficient response because of the poor electrical conductivity of the nanowhiskers.     

Transition metal complexes of a Schiff base: synthesis,characterization, and antibacterial studies

Synthesis of a new Schiff base derived from 2-hydroxy-5-methylacetophenone and glycine and its coordination with compounds Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and UO₂(VI) are described. The ligand and complexes have been characterized on the basis of analytical, electrical conductance, infrared, ESR and electronic spectra, magnetic susceptibility measurements, and thermogravimetric analysis. The ligand is a dibasic tridentate (ONO) donor in all the complexes except Zn(II), where it is a monobasic bidentate (OO) donor. The solid state DC electrical conductivity of ligand and its complexes have been measured over 313–398 K, and the complexes were semiconducting. Antibacterial activities of ligand and its metal complexes have been determined by screening the compounds against various Gram (+) and Gram (?) bacterial strains.     

Preparation of organic-inorganic composite anion-exchange membranes via aqueous dispersion polymerization and their characterization

Organic-inorganic composite membranes based on poly(vinyl alcohol)/SiO(2) were prepared via an aqueous dispersion polymerization route and anion-exchange groups were introduced in the membrane matrix by the chemical grafting of 4-vinylpyridine with the desired content. These membranes were extensively characterized for their surface morphology, thermal stability, water content, and surface-charge properties using SEM, TEM, FTIR, TGA, water uptake, and ion-exchange capacity measurements. Counterion transport numbers across these membranes were estimated from membrane potential data. Membrane conductance measurements were also performed and these data were used for the estimation of values of counterion diffusion coefficients in the membrane phase. Physicochemical and electrochemical properties of these membranes and equivalent pore radius (estimated from electroosmotic flux measurements) were found to be highly dependent on the 4-vinylpyridine (4-VP) content in the membrane phase. It was also observed that for better selectivity and membrane conductivity of anion-exchange membranes complete optimization of the loading of 4-VP in the membrane phase is necessary. Furthermore, among these, membrane with 25% loading with 4-VP exhibited very good selectivity, water content, and ion-exchange capacity along with moderate membrane conductivity, which may be used for their application in electro-driven separation at elevated temperatures or for other electrochemical processes.     

Synthesis,characterization, potentiometry,and antimicrobial studies of transition metal complexes of a tridentate ligand

Complexes of Cu(II), Ni(II), Co(II), Mn(II), and Fe(III) with the tridentate Schiff base, 4-hydroxy-3(1-{2-(benzylideneamino)-phenylimino}-ethyl)-6-methyl-2H-pyran-2-one (HL) derived from 3-acetyl-6-methyl-(2H)-pyran-2,4(3H)-dione (dehydroacetic acid or DHA), o-phenylenediamine, and benzaldehyde were characterized by elemental analysis, molar conductivity, magnetic susceptibility, thermal analysis, X-ray diffraction, IR, ¹H-NMR, UV-Vis spectroscopy, and mass spectra. From analytical data, the stiochiometry of the complexes was found to be 1?:?2 (metal?:?ligand) with octahedral geometry. The molar conductance values suggest nonelectrolytes. X-ray diffraction data suggest monoclinic crystal systems. IR spectral data suggest that the ligand is dibasic tridentate with ONN donors. To investigate the relationship between formation constants of metal complexes and antimicrobial activity, the dissociation constants of Schiff base and stability constants of its binary metal complexes have been determined potentiometrically in THF–water (60?:?40) at 30?±?1°C and at 0.1?mol?L^?1 NaClO₄ ionic strength. The potentiometric titrations suggest 1?:?1 and 1?:?2 complexation. Antibacterial and antifungal activities in vitro were performed against Staphylococcus aureus, Escherichia coli, Aspergillus niger, and Trichoderma with determination of minimum inhibitory concentrations of ligand and metal complexes. The structure–activity correlation based on stability constants of metal complexes is discussed. Activity enhances upon complexation and the order of activity is in accord with the stability order of metal ions.