Radiochemical separations by ion exchange.
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Ion Exchange↗
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Asymmetric hydrogenation using chiral Rh complexes immobilised with a new ion-exchange strategy.
Rh diphosphine complexes using DuPhos and JosiPhos as chiral ligands have been immobilised by ion exchange into the mesoporous material MCM-41. When used as catalysts for the enantioselective hydrogenation of dimethyl itaconate and methyl-2-acetamidoacrylate, these heterogeneous catalysts give catalytic performance in terms of yield and enantioselection that are comparable to the corresponding homogeneous catalysts. Furthermore, the heterogeneous catalysts can be readily recovered and reused without loss of catalyst performance. A second immobilisation strategy is described in which [Rh(COD)2]+BF4- is initially immobilised by ion exchange and subsequently modified by the chiral diphosphine and this give comparable catalyst performance. This immobilisation strategy opens up the possibility of easy ligand-screening for parallel synthesis and libraries.
Acrylates↗
Engineering surface charges in a subtilisin: the effects on electrophoretic and ion-exchange behaviour.
The introduction or removal of multiple charged amino acid residues in the subtilisin Savinase by genetic engineering allowed us to modify the electrostatic properties of this enzyme in a systematic way. The effects of these charge changes were investigated experimentally using ion-exchange chromatography and electrophoretic mobility in native gels all under identical conditions. The experiments clearly demonstrated that the overall charge of a given protein is not the only factor determining electrophoretic mobility at low or moderate ionic strengths. For a series of variants having identical overall positive charge a linear relation was observed between mobility towards the cathode and the total number of charged residues present. This effect was found to depend on the type of (chloride) salt used: calcium ions give rise to complete screening of all negative charges, whereas only partial screening is found for magnesium and sodium ions. In contrast, in the presence of sodium phosphate the overall charge of the enzyme becomes slightly negative. These data indicate that cations as well as anions may strongly perturb the overall charge of proteins depending on the type of salt and on the number of charged amino acid residues present. The ion-exchange behaviour demonstrated similar results, i.e. showing stronger enzyme adsorption with increasing numbers of surface charges on a cation-exchange column run below the isoelectric point of the proteins. However, the apparent sign reversal noted above for electrophoresis with sodium phosphate did not appear in the ion-exchange experiments. This work provides further insight into the adsorption of proteins to surface and the role played by small ions, particularly when electrostatic forces dominate the adsorption process.
Amino Acid Sequence↗
The effect of valence on the ion-exchange process: theoretical and experimental aspects on compound binding/release.
The effect of valence of mobile counter-ions (extracting electrolytes), mobile co-ions, and drug-like compounds was evaluated on drug binding/release in ion-exchange fibers. The experimental results support the Donnan theory and suggest that incorporation of monovalent salicylic acid (SA) and divalent 5-hydroxyisophthalic acid (di-COOH) into the anion-exchange fibers was attained mainly as a result of electrostatic (ionic) interaction, with additional contribution of non-electrostatic interactions. Increasing the capacity of ion-exchanger increased the molar amount of compound loading. More efficient release of model anions was observed at increasing valence or concentration of the extracting counter-ion. Potency to release the compounds decreased in the order of citrate (-3) > sulfate (-2) > chloride (-1). The valence of co-ions (sodium (+1) vs. calcium (+2)) in the external solution had only a slight effect on the release. Due to dual site binding (two ionized carboxylate groups), the amount of di-COOH bound into the fibers was half of that of monovalent SA. Also the release was significantly reduced, as the electrostatic interaction was stronger in the case of divalent compound. Simulations on the effect of valence on the Donnan potential and theoretical modeling of the release efficiencies by the external ions supported successfully the conclusions above.
Anion Exchange Resins↗
Medical uses of ion-exchange resins.
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Ion Exchange↗
Mathematical modeling of salt-gradient ion-exchange simulated moving bed chromatography for protein separations.
The salt-gradient operation mode used in ion-exchange simulated moving bed chromatography (SMBC) can improve the efficiency of protein separations. A detailed model that takes into account any kind of adsorption/ion-exchange equilibrium, salt gradient, size exclusion, mass transfer resistance, and port periodic switching mechanism, was developed to simulate the complex dynamics. The model predictions were verified by the experimental data on upward and downward gradients for protein separations reported in the literature. All design and operating parameters (number, configuration, length and diameter of columns, particle size, switching period, flow rates of feed, raffinate, desorbent and extract, protein concentrations in feed, different salt concentrations in desorbent and feed) can be chosen correctly by numerical simulation. This model can facilitate the design, operation, optimization, control and scale-up of salt-gradient ion-exchange SMBC for protein separations.
Chromatography, Ion Exchange↗
Charge engineering of a protein domain to allow efficient ion-exchange recovery.
We have created protein domains with extreme surface charge. These mutated domains allow for ion-exchange chromatography under conditions favourable for selective and efficient capture, using Escherichia coli as a host organism. The staphylococcal protein A-derived domain Z (Zwt) was used as a scaffold when constructing two mutants, Zbasic1 and Zbasic2, with high positive surface charge. Far-ultraviolet circular dichroism measurements showed that they have a secondary structure content comparable to the parental molecule Zwt. Although melting temperatures (Tm) of the engineered domains were lower than that of the wild-type Z domain, both mutants could be produced successfully as intracellular full-length products in E. coli and purified to homogeneity by ion-exchange chromatography. Further studies performed on Zbasic1 and Zbasic2 showed that they were able to bind to a cation exchanger even at pH values in the 9 to 11 range. A gene fusion between Zbasic2 and the acidic human serum albumin binding domain (ABD), derived from streptococcal protein G, was also constructed. The gene product Zbasic2-ABD could be purified using cation-exchange chromatography from a whole cell lysate to more than 90% purity.
Bacterial Proteins↗
Adsorption and isotope effects by ion exchange with 1-aza-12-crown-4 bonded Merrifield peptide resin.
Magnesium isotope effects were investigated by chemical ion exchange with synthesized 1-aza-12-crown-4 bonded Merrifield peptide resin using elution chromatography. The capacity of azacrown ion exchanger was 0.89 meq/g dry resin. The heavier isotopes of magnesium were enriched in the resin phase, while the lighter isotopes were enriched in the solution phase. The hydration effect is less than the complexation and isotope mass effects. The single stage separation factor was determined according to the method of Glueckauf from the elution curve and isotopic assays. The separation factors of 24Mg(2+)-25Mg(2+), 24Mg(2+)-26Mg(2+), and 25Mg(2+)-26Mg(2+) were 1.012, 1.023, and 1.011, respectively.
Chromatography, Ion Exchange↗
Use of ion-exchange membranes to measure transfer free energies of charged local anesthetics: correlation to anesthetic potency.
Ion-selective electrodes, sensitive to local anesthetic cations, were prepared with carboxylated poly(vinyl chloride) (PVC) membranes. Three plasticizers with varying degrees of polarity were used to adjust the hydrophobicity of the membrane. The affinity of the drug to the ion-exchange membrane was measured by the electromotive force of the cation-selective electrodes. The difference in the transfer free energies of the anesthetics for the membrane was estimated in reference to dibucaine. The values correlated to their clinical potencies. By comparing drugs with similar structures, the transfer free energy per methylene moiety linked to the hydrophilic domain was found to be -1.7 kJ.mol-1, and that of Cl linked to the hydrophobic domain was -3.1 kJ.mol-1. Interferences from Na+ and K+ were estimated as the selectivity coefficients against dibucaine. The values were 2.6 x 10(-5) for Na+ and 1.2 x 10(-4) for K+. The ion-exchange membrane appears to mimic the surface properties of cell membranes. These cation-selective electrodes have potential applicability in measuring charged local anesthetic concentrations (activities) in biological materials under limited conditions.
Anesthetics↗
Screening for drug abuse: use of NaCl to increase drug recovery from papers coated with ion-exchange resin.
Use of papers loaded with ion-exchange resins to adsorb drugs from urine specimens resulted in large losses during the procedure. The first step, removal of drugs from urine specimens, was 25-85% efficient. The second step, elution of drugs from paper for further processing, was approximately 40-70% complete. The efficiency of the first step was decreased and the efficiency of the second step was increased by addition of NaCl, except in the case of barbiturates. Presence of salt during elution increased the yield of dihydromorphine by 20%, of methadone by 16%, of amphetamine by 34%, and of chlorpromazine by 40%, but did not enhance the yield of pentobarbital. Overall recovery rates were: 51% for the opiates, 57% for methadone, 72% for a phenothiazine tranquillizer, but only 35% for amphetamine and 15% for a barbiturate.
Amphetamine↗
Quantitation of lens protein mixed disulfides by ion-exchange chromatography.
A sensitive and high resolution ion-exchange chromatographic method was employed to analyse lens protein mixed disulfides. The mixed disulfides were analysed and quantified as glutathione sulfonic acid and cysteic acid after the lens proteins were subjected to performic acid oxidation. The oxidized product was applied on a 0.9 X 15 cm column packed with BioRad Aminex A-28 resin (9 microns beads). The column was maintained at 55 degrees C and eluted with 0.3 M sodium acetate buffer, pH 5.1 at 60 ml hr-1 for 40 min before switching to 0.5 M of the same buffer. The glutathione subsequently reacted with ninhydrin and monitored for absorbance at 570 nm. The glutathione sulfonic acid emerged at 69 min, cysteic acid at 35 min, and both were clearly resolved from neighboring peaks and could be detected at less than nmol level. In the lens, both glutathione and cysteine protein mixed disulfides were only found in the TCA-insoluble protein fraction. Normal rat lens contained 0.35 nmol per lens of protein-bound glutathione but 10-fold this amount of protein-bound cysteine. The hyperglycemic condition had little effect on the protein thiol mixed disulfide level except that at a more advanced diabetic condition, equal depletion of cysteine and glutathione mixed disulfides were found. On the other hand, oxidative conditions induced a marked elevation of glutathione mixed disulfide but not of the cysteine mixed disulfide.
Animals↗
[Speciation analysis of arsenic in traditional Chinese medicines by hydride generation-atomic fluorescence spectrometry with ion exchange resin separation].
A method for the determination of arsenic species (arsenide, arsenate) in traditional Chinese medicines using hydride generation atomic fluorescence spectrometry (HG-AFS) with ion exchange resin separation has been studied. The ion exchange resin was used to separate the arsenide and arsenate, and the separation conditions were investigated. The experimental conditions that influence the fluorescence intensity and the reduction of arsenic(V) were investigated and optimized, and the influence of foreign ions and its elimination were studied. The proposed method was applied to the determination of arsenic species in water leachate of traditional Chinese medicines. A detection limit of 89.1 ng x mL(-1) and a recovery range of 91.1%-109.3% were obtained.
Arsenates↗
[Effects of ion exchange and their clinical use].
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Ion Exchange↗
[Ion exchangers; synthesis, properties and applications].
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Ion Exchange↗
Ligand-exchange separation of amino acids. II. Influence of the eluent composition and of the nature of the ion exchanger.
The ligand-exchange separation of amino acids in protein hydrolysates has been studied in ammoniacal media. The various factors influencing the chromatographic behaviour have been investigated. The selectivity of the process and the column efficiency depend appreciably on the resin matrix and the nature of the functional groups. The best results have been obtained with the acrylic-type Bio Rex 70 resin, in the copper(II) form. The zinc(II) form of this support has also been tested; the elution order of glycine, alanine and leucine is the same as with the copper(II) form, but the affinities of these molecules for the zinc(II) resin are weaker. The influence of the concentrations of copper(II) and ammonia on the elution volumes obtained for all the amino acids with the copper(II) Bio Rex 70 resin has been studied. The general variation of retention and selectivity with eluent composition confirms the theoretical expressions established previously. Ligand-exchange chromatography has been compared to the conventional ion-exchange process using acidic or basic species. This study reveals analogies and differences between both techniques, and shows that ligand exchange can provide new opportunities for the separation of amino acids.
Amino Acids↗
Hemoglobin Raleigh as the cause of a falsely increased hemoglobin A1C in an automated ion-exchange HPLC method.
Irreversible glycation of the hemoglobin A0 (HbA0) beta chain leads to the production of HbA1C, which can be used to monitor long-term blood glucose control in patients with diabetes mellitus. HbA1C is less positively charged than nonglycated HbA0, and this decrease in charge is the basis of ion-exchange and electrophoretic methods that measure HbA1C. We recently identified a sample that appeared to contain 46% HbA1C by an automated ion-exchange HPLC method (Bio-Rad Variant) but only 3.8% by an immunoinhibition latex agglutination method. A combination of traditional and mass spectrometric protein analysis and genomic DNA analysis of the Hb beta chain and genes revealed that the patient was heterozygotic for Hb-Raleigh, a variant containing a valine-->alanine substitution at position 1 of the beta chain. The amino-terminal alanine in this variant Hb is posttranslationally modified by acetylation, leading to a charge difference similar to glycation and making the behavior of HbA1C and Hb Raleigh virtually identical in the ion-exchange HPLC method. This observation suggests that it is important to confirm HbA1C values in excess of 15%, especially if they are not consistent with the clinical picture, by an independent HbA1C method such as immunoassay or boronic acid affinity chromatography. However, for this particular variant Hb, even these latter methods might be misleading, because the acetylated N-terminal amino acid of the Hb-Raleigh beta chain cannot be glycated.
Aged↗
Influence of chemical conditioning on the ion exchange capacity and on kinetic of zinc uptake by clinoptilolite.
Aim of this study was to evaluate the feasibility of the use of clinoptilolite as a barrier material to eliminate heavy metals from roof runoff. The effect of chemical conditioning with 1 M NaCl solution upon the ion exchange capacity and on kinetic of zinc uptake by clinoptilolite has been investigated. According to the batch experiments the modified clinoptilolite has up to 100% higher sorption capacity, regarding Zn than the natural material. The pre-treatment of clinoptilolite results in an acceleration of the ion exchange process up to 40% regarding zinc. In order to define the reasons of this behaviour, both materials, modified and natural, were analysed for: (i) chemical composition, (ii) density, (iii) pore size distribution and (iv) zeta potential. The clogging of the pores, the charge of the grain surface, the pH of the initial metal solution and the ion metal concentration are the factors which are mainly affecting the ion exchange capacity and the rate of zinc uptake by clinoptilolite.
Facility Design and Construction↗
Chromatography in presence of high concentrations of salts on columns of celluloses with and without ion exchange groups (hydrogen bond chromatography). Its application to purification of yeast enzymes.
1. All the water-soluble yeast enzymes tested, which were only partially precipitated at best in the presence of high concentration of salts such as ammonium sulfate or sodium formate, were adsorbed on a column of cellulose in the presence of the same concentrations of the salts, and the adsorbed enzymes were chromatographically eluted by decreasing the concentration of the salts. 2. Even in the presence of high concentration of the salts, the adsorbed enzymes were eluted by urea or by "hydroxy-rich" reagents such as sucrose. 3. Under the experimental conditions used, the salt concentrations required for elution of the adsorbed enzymes were lower with cellulose than with DEAE-cellulose, CM-cellulose, or P-cellulose, indicating that ion exchange groups, either cationic or anionic, affected the adsorption, although the ion exchange groups of DEAE-cellulose, CM-cellulose, and P-cellulose were weakly but definitely functional as ion exchangers even in the presence of high concentrations of the salts. 4. The principal attractive force between cellulose and the enzyme was deduced to be due to hydrogen bonding. 5. This hydrogen bond chromatography was applied for the purification of some yeast enzymes.
Alcohol Oxidoreductases↗