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.     

Purification of amino acids and small peptides with hollow fibers

Permeation through hollow fibers made of a perfluorinated ionomer membrane of the Nafion type is shown to be a possible way to separate amino acids and small peptides. The fiber has a surface area to volume ratio of 56 cm² cm^?3. Twenty-six different amino acids and small peptides with up to six amino acid units were used for permeation studies. The results show that the bulk pH is the essential parameter acting on the permeation rates and diffusion coefficients through the tubing wall. The cationic forms of the solutes, at a pH lower than their isoelectric points, were highly retained by the cation-exchange membrane. The anionic forms of the solutes, at a pH higher than the isoelectric point, were less retained. The zwitterionic and non-ionic forms had the highest permeation rates, reaching 2.2 × 10^?3 s^?1. The effect of methanol addition was studied. The permeation rates increased, but the selectivity decreased     

Holographic sensors for the determination of ionic strength

Holographic sensors for monitoring ionic strength have been fabricated from charged sulphonate and quaternary ammonium monomers, incorporated into thin, polymeric hydrogel films which were transformed into volume holograms. The diffraction wavelength or reflected colour of the holograms was used to characterise their swelling or de-swelling behaviour as a function of ionic strength in various media. The effects of co-monomer structure, buffer composition, ion composition, pH and temperature were evaluated, whilst the reversibility and reproducibility of the sensor was also assessed. An acrylamide-based hologram containing equal molar amounts of negatively and positively charged monomers was shown to be able to quantify ionic strength independent of the identity of the ionic species present in the test solution. The sensor was fully reversible, free of hysteresis and exhibited little response to pH between 3 and 9 and temperature within the range 20-45 °C. The system was successfully used to quantify the ionic strength of milk solutions, which contain a complex mixture of ions and biological components.     

Evidence for strong heterodimeric interactions of phenylboronic acids with amino acids

Strong heterodimeric interactions of phenylboronic acids with l-proline or betaine are evident in the solid state. The interaction energy is over 23 kcal/mol (at MP2/6-31+G^∗).     

Homogeneous catalytic aminocarbonylation of iodoalkenes and iodobenzene with amino acid esters under conventional conditions and in ionic liquids

Amino acid methyl esters were used as amine nucleophiles in palladium catalysed aminocarbonylation of iodobenzene and iodoalkenes (1-iodo-cyclohexene and 17-iodo-androst-16-ene). 2-Oxo-carboxamide type derivatives can be isolated as a result of double CO insertion by using iodobenzene as a substrate at elevated carbon monoxide pressure. On the contrary, carboxamides of expected structure were obtained exclusively in excellent yields in the whole pressure range by using iodoalkenes. The aminocarbonylation of 17-iodo-androst-16-ene in [bmim][PF₆] or [bmim][BF₄] (where bmim=1-butyl-3-methyl-imidazolium cation) ionic liquids was also carried out and the ionic liquid-catalyst mixtures have been reused several times with only a small loss of activity.     

Influence of ionic liquids as electrolyte additives on chiral separation of dansylated amino acids by using Zn(II) complex mediated chiral ligand exchange CE

In this work, investigation of the comparative influence of diverse ionic liquids (ILs) as electrolyte additives on the chiral separation of dansylated amino acids by using Zn(II)‐L‐arginine complex mediated chiral ligand exchange CE (CLE‐CE) was conducted. It has been found that not only the varied substituted group number, but also the alkyl chain length of the substituted group on imidazole ring in the structure of ILs show different influence on chiral separation of the analytes in the CLE‐CE system, which could be understood by their direct influence on EOF. Meanwhile, the variation of anion in the structure of ILs displayed remarkably changed performance and the ILs with Cl^? showed the most obvious promoting effect on the chiral separation performance. Among the investigated seven ILs, 1‐butyl‐3‐methylimidazolium chloride was validated to be the proper electrolyte additive in the CLE‐CE system. Moreover, it has been observed that 1‐butyl‐3‐methylimidazolium chloride also has obvious promotive effect on the labeling performance. The results have demonstrated that the ILs with different structures have important relation to their performance in CLE‐CE and to their labeling efficiency in dansylation of the analytes.     

Specific ionic effect for simple and rapid colorimetric sensing assays of amino acids using gold nanoparticles modified with task-specific ionic liquid

In this study, a novel task-specific ionic liquid functionalized gold nanoparticle (TSIL-GNP) was successfully prepared and applied in the recognition of amino acids. Particularly, the surface of GNP was modified with the ionic liquid containing carbamido and ester group via thiol, which was characterized by Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). The stability of this material in aqueous solution improves apparently and can remain unchanged for more than three months. The effect of pH was also discussed in this study. Attractive ionic interaction would effectively weaken intensity of the covalent coupling between the metal ion and the functional groups of amino acids. Thus, TSIL-GNP was successfully applied to recognizing serine, aspartic acid, lysine, arginine, and histidine in the presence of Cu²⁺ through distinctive color changes. Suspension would be generated once a spot of cysteine was added into the GNPs solution. Results indicated that it had a good linear relationship between extinction coefficients and concentration of amino acids in a wide range of 10⁻³–10⁻⁶ M. Moreover, the proposed strategy was successfully used to analyze the histidine in urinary samples. In brief, TSIL-GNP is a suitable substrate for discrimination of five amino acids in a rapid and simple way without sophisticated instruments.     

Chromatographic amino acid analysis of protein hydrolysed in polyacrylamide after removal of ammonia

Summary A simple method for the removal of NH₃ from amino acids is presented. The method is based on a cation-exchange resin from which amino acids are eluted with NH₄OH. The eluent is then removed under reduced pressure. The method allows the ninhydrin-based detection of amino acids after hydrolysis of stained protein bands in polyacrylamide gels. This was previously not possible since NH₃ produced by the hydrolysis of polyacrylamide interferes with the ninhydrin-detection of basic amino acids. The method should also be applicable to the detection of amino acids with o-phthalaldehyde.     

Increments to chiral recognition facilitating enantiomer separations of chiral acids, bases, and ampholytes using Cinchona-based zwitterion exchanger chiral stationary phases

The intramolecular distances of anion and cation exchanger sites of zwitterionic chiral stationary phases represent potential tuning sites for enantiomer selectivity. In this contribution, we investigate the influence of alkanesulfonic acid chain length and flexibility on enantiomer separations of chiral acids, bases, and amphoteric molecules for six Cinchona alkaloid-based chiral stationary phases in comparison with structurally related anion and cation exchangers. Employing polar-organic elution conditions, we observed an intramolecular counterion effect for acidic analytes which led to reduced retention times but did not impair enantiomer selectivities. Retention of amphoteric analytes is based on simultaneous double ion pairing of their charged functional groups with the acidic and basic sites of the zwitterionic selectors. A chiral center in the vicinity of the strong cation exchanger site is vital for chiral separations of bases. Sterically demanding side chains are beneficial for separations of free amino acids. Enantioseparations of free (un-derivatized) peptides were particularly successful in stationary phases with straight-chain alkanesulfonic acid sites, pointing to a beneficial influence of more flexible moieties. In addition, we observed pseudo-enantiomeric behavior of quinine and quinidine-derived chiral stationary phases facilitating reversal of elution orders for all analytes.     

High-performance liquid chromatography utilization of ionic liquids as mobile phase additives for separation and determination of the isomers of amino benzoic acids

For the isomers of amino benzoic acid, including o-, m-, p-amino benzoic acid, the beneficial effects of using the ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF₄]), as mobile phase additives on retention behavior and separation were investigated. Chromatographic separation of the o-, m-, p-amino benzoic acid was performed on a reversed-phase C18 column by ultraviolet detection at 245 nm. The effects of several chromatographic parameters, concentrations and pH values of [BMIm][BF₄] solutions, methanol concentration and length of alkyl chain on different ionic liquids, on the separation and determination of the isomers were evaluated. The optimized chromatographic conditions were established using an aqueous 0.5 μmol/L [BMIm][BF₄] solution (pH 3.0)/methanol (40:60, v/v) as mobile phase without need of gradient elution, with separation of three amino benzoic acids achieved within four min. The calibration curve showed good linearity over the tested range of 2 mg/L to 120 mg/L for the three isomers with a correlation coefficients of 0.9999. The recoveries of the three amino benzoic acids of spiked components were between 99.8% and 100%. The method has been successfully applied to the determination of p-amino benzoic acid in the pharmaceutical, Bromine Mitag Procaine Injection.     

Effect of some amino acids and peptides on silicic acid polymerization

The polymerization of silicic acid in aqueous solutions at different pH was followed by the colorimetric molybdosilicate method. The role of four amino acids (serine, lysine, proline and aspartic acid) and the corresponding homopeptides was studied. All four amino acids behave the same way and favor the condensation of silicic acid. Peptides exhibit a stronger catalytic effect than amino acids but they appear to behave in very different ways depending on the nature of side-groups and pH. Poly-lysine and poly-proline for instance lead to the precipitation of solid phases containing both silica and peptides. The role of these biomolecules on the polymerization of silicic acid is discussed in terms of electrostatic interactions, hydrogen bonds and solubility.     

Exchange studies of 5-sulphosalicylic acid in amberlite IRA 401 Cl anion exchange resin

Exchange studies of 5-sulphosalicylic acid in Amberlite IRA 401 Cl anion exchange resin have been carried out at 25°C in a stirred vessel. The exchange rates have been interpreted on the basis of a simple diffusion model.     

Multiparametric analysis of amino acids and organic acids in rat brain tissues using GC/MS

Using design of experiment (DOE) theory coupled with multivariate statistical analysis, we have developed a simple and reliable GC/MS-based analytical assay for simultaneous analysis of amino acids and organic acids in rat brain tissue samples. The process of water extraction (pH 10.0) was extensively evaluated using brain tissue samples and a set of 21 reference standards. Acceptable calibration curves were obtained over a wide concentration range, 0.2-35.0 microg/mL for standards and 15.0-2.4 mL/g (tissue) for brain tissue samples. The precision was mostly better than 10% for both the mixed standards and the brain tissue samples. The brain tissue samples exhibited good stability within 48 h with RSD generally less than 15%. Furthermore, the developed analytical method was successfully applied in distinguishing the subtle variation among different parts of the brain tissues, such as cerebral cortex, hippocampus, and thalamus.     

Effect of ionic strength on the formal potential of the glass electrode in various saline media

We examined the variation with ionic strength (I, adjusted with KCl, KNO₃, KBr, NaCl or NaClO₄) of the formal potential (E_const) for glass electrodes exhibiting a Nernstian response (i.e. E_cell=E_const−s log [H⁺]). For this purpose, we investigated the different factors included in the formal potential, so we obtained reported values for the liquid junction potential as a function of ionic strength and determined the logarithm of the activity coefficient for the proton in various saline media, using Pitzer equations.     

Chemoselective and enantioselective analysis of proteinogenic amino acids utilizing N-derivatization and 1-D enantioselective anion-exchange chromatography in combination with tandem mass spectrometric detection

D-Amino acid analysis in biological samples still poses a challenge to analytical chemists. In higher developed species trace amounts of d-amino acids have to be detected in vast excesses of the corresponding L-enantiomers. This method utilizes an easy-to-carry-out derivatization step on the amino group with an iron ferrocenyl propionate hydroxy succinimide ester followed by one-dimensional enantioselective anion exchange chromatography with cinchona alkaloid based chiral stationary phases (CSPs). MS detection is carried out in the highly sensitive SRM (selected reaction monitoring) mode, which allows a chemoselective differentiation of amino acid derivatives as well as their enantioselective separation in one step. Application of this method allows LOD (limits of detection) in the low μmol L(-1) range and baseline enantioseparation for all proteinogenic amino acids except for Pro, Arg and His. The D-enantiomers of isomeric Leu and Ile were separated chromatographically and pose an example for the complementary selectivities of LC and MS. A successful application of this procedure to unprocessed human urine indicated the eligibility to analyse biological samples.     

A review of quantitative ion exchange,high performance liquid and gas chromatographic analysis of amino acids in physiological fluids

Methodologies for quantitative analysis of amino acids in physiological fluids based on classical ion exchange, high performance liquid chromatography, and gas chromatography are analyzed. As judged by the relative number of reports on these techniques, it appears that classical ion exchange continues to be the main method of choice for amino acid determinations and only limited advantage has been taken of the benefits (e.g. lower capital outlay and running costs and shorter analysis times) offered by other techniques. More importantly, however, there appears to be insufficient quantitative evaluation of the methodologies used. As a result, the validity of many reports based on data from amino acid analysis of physiological samples may be questioned.     

氨基膦酸树脂吸附镨的研究

氨基膦酸树脂 (简称ＡＰＡＲ)是一类性能优良的螯合树脂 ,功能基为 ＣＨ2 ＮＨＣＨ2 Ｐ(Ｏ) (ＯＨ) 2 ,由于功能基上同时含有Ｎ和Ｏ等配位原子 ,它能与多种金属离子形成比较稳定的配合物。近年来有关含磷的螯合树脂吸附金属离子的各种研究比较活跃[1～ 4] 。本文就氨基膦酸树脂在ＨＡｃ ＮａＡｃ体系中对镨 (Ⅲ )的吸附行为进行了研究。获得了诸多基本参数 ,为氨基膦酸树脂在湿法冶金中对镨离子的富集、提取等方面的应用提供了理论依据。1　实验部分1 1　试剂及仪器72 1型分光光度计 ,ＳＨＡ Ｃ水浴恒温振荡器(± 0 .1℃ ) ,ｐＨＳ 3ｃ型…