Richard W. Taylor

USE OF LIGAND-MODIFIED MICELLAR-ENHANCED ULTRAFILTRATION IN THE SELECTIVE REMOVAL OF METAL IONS FROM WATER

Abstract Ligand-modified micellar-enhanced ultrafiltration (LM-MEUF) is a membranebased separation technique which can selectively remove specific ions from an aqueous solution containing several ions of like charge. In LM-MEUF, surfactant and amphiphilic ligand are added to the contaminated water. The surfactant forms aggregates called micelles, and the ligand is selected to complex the ion of interest and to solubilize strongly in the micelles. The result is micelles containing a high fraction of the ligand and the target ion. If the surfactant is chosen to have the same charge as the target ion, other ions in solution with this same charge will not associate with the micelles, making the retention of ions by the micelles very selective. The solution is then passed through an ultrafiltration membrane with pore sizes small enough to block the passage of micelles. In this study, divalent copper is the target ion in a solution also containing divalent calcium. A cationic surfactant is used with N-n-dodecyl...

Factors affecting solute entrapment in phospholipid vesicles prepared by the freeze-thaw extrusion method: a possible general method for improving the efficiency of entrapment

It is often assumed that the internal solute concentrations of phospholipid vesicles are equal to those in the medium in which they were prepared, particularly when freeze-thaw cycles are employed during the procedure. Conditions are reported here which when used to prepare vesicles by the polycarbonate filter extrusion method, produce approximately 12- and approximately 7-fold higher internal concentrations of Ca2+ and sucrose, respectively, than exist in the external medium. Formation of these large gradients is dependent upon the use of freeze-thaw cycles during preparation, on the presence of tetraethylammonium perchlorate in the medium, and is independent of media pH across the region of pH 5-9. Gradient formation is antagonized by high concentrations of an impermeant solute (NaCl). It is proposed that gradients form because solutes are concentrated by exclusion from ice during freezing but that they are normally dissipated by osmotic lysis during thawing. The presence of a permeant solute such as tetraethylammonium perchlorate provides an alternative mechanism to balance osmotic pressure, thereby preserving the gradients of impermeable species.

Selective Removal of Copper from an Aqueous Solution Using Ligand-Modified Micellar-Enhanced Ultrafiltration Using an Alkyl-β-diketone Ligand

Abstract The semiequilibrium dialysis technique has been used to investigate the concentration of Cu2+ using a water-insoluble liquid ion exchanger or ligand with cationic surfactant in a ligand-modified micellar-enhanced ultrafiltration (LM-MEUF) process. In LM-MEUF the surfactant and the ligand are added to an aqueous solution containing ions of like charge, one of which needs to be selectively removed. The ligand forms a complex with the target ion of interest and solubilizes or dissolves inside the organic interior of the micelles. Therefore, it is possible to replace typical solvent extraction solvents such as kerosene by micelles. In this study copper chloride/calcium chloride solutions were treated for the extraction of copper using a commercially available ligand, 1-phenyl-3-isoheptyl-1,3-propane dione in cetyltrimethylammonium bromide (CTAB), a cationic surfactant. The effect of pH and the concentrations of copper, calcium, surfactant, and ligand on the efficiency of copper removal from water are...

Performance analysis of two frozen image based backup/restore methods

Backup and restore are critical tasks performed on every system that holds important data. This paper evaluates the performance of two innovative backup methods based on frozen image technologies. VERITAS netbackup instant recovery option utilizes frozen images created from file system or volume manager utilities and manages these frozen images as backups. Because creating frozen images involve no actual copying of data, such backups are significantly faster. In addition, the frozen images reside on online storages, making restore from them much more efficient as well. In this paper, we conducted backups and restores in a database environment to demonstrate the advantages of using the frozen image based backup/restore with the VERITAS file systems storage checkpoint and VERITAS volume managers volume snapshot. With both methods, taking a full backup of a 26 gigabytes database took less than 4% of the time compared to traditional tape-based backup. The amount of time to restore different database objects from frozen images ranges from 3 to 47% of the time restoring from tapes. While both backup and restore from frozen images are much more efficient than traditional backup methods, they are meant to complement, not to replace the traditional backups. This is because frozen images share common resources with the system they are protecting and are subjected to the same risks that might damage the data. The traditional backup method offers protection against a wider array of risks that can cause data loss and should be kept in as part of an overall data protection strategy

Monensin Improves the Effectiveness of meso-Dimercaptosuccinate when Used to Treat Lead Intoxication in Rats

Among divalent cations, the ionophore monensin shows high activity and selectivity for the transport of lead ions (Pb2+) across phospholipid membranes. When coadministered to rats that were receiving meso-dimercaptosuccinate for treatment of Pb intoxication, monensin significantly increased the amount of Pb removed from femur, brain, and heart. It showed a tendency to increase Pb removal from liver and kidney but had no effect of this type in skeletal muscle. Tissue levels of several physiologic (calcium, cobalt, copper, iron, magnesium, manganese, molybdenum, zinc) and nonphysiologic (arsenic, cadmium, chromium, nickel, strontium) elements were also determined after the application of these compounds. Among the physiologic elements, a number of significant changes were seen, including both rising and falling values. The size of these changes was typically around 20% compared with control values, with the largest examples seen in femur. These changes often tended to reverse those of similar size that had occurred during Pb administration. Among the nonphysiologic elements, which were present in trace amounts, the changes were smaller in number but larger in size. None of these changes appears likely to be significant in terms of toxicity, and there were no signs of overt toxicity under any of the conditions employed. Monensin may act by cotransporting Pb2+ and OH– ions out of cells, in exchange for external sodium ions. The net effect would be to shuttle intracellular Pb2+ to extracellular dimercaptosuccinic acid thereby enhancing its effectiveness. Thus, monensin may be useful for the treatment of Pb intoxication when applied in combination with hydrophilic Pb2+ chelators.

Ionomycin, a Carboxylic Acid Ionophore, Transports Pb2+ with High Selectivity

Studies utilizing phospholipid vesicle loaded with chelator/indicators for polyvalent cations show that ionomycin transports divalent cations with the selectivity sequence Pb2+ > Cd2+ > Zn2+ > Mn2+ > Ca2+ > Cu2+ > Co2+ > Ni2+ > Sr2+. The selectivity of this ionophore for Pb2+ is in contrast to that observed for A23178 and 4-BrA23187, which transport Pb2+ at efficiencies that are intermediate between those of other cations. When the selectivity difference of ionomycin for Pb2+ versus Ca2+ was calculated from relative rates of transport, with either cation present individually and all other conditions held constant, a value of ∼450 was obtained. This rose to ∼3200 when both cations were present and transported simultaneously. 1 μm Pb2+inhibited the transport of 1 mm Ca2+ by ∼50%, whereas the rate of Pb2+ transport approached a maximum at a concentration of 10 μm Pb2+ when 1 mm Ca2+ was also present. Plots of log rateversus log ionomycin or log Pb2+ concentration indicated that the transporting species is of 1:1 stoichiometry, ionophore to Pb2+, but that complexes containing an additional Pb2+ may occur. The species transporting Pb2+ may include H·IPb·OH, wherein ionomycin is ionized once and the presence of OH− maintains charge neutrality. Ionomycin retained a high efficiency for Pb2+ transport in A20 B lymphoma cells loaded with Indo-1. Both Pb2+ entry and efflux were observed. Ionomycin should be considered primarily as an ionophore for Pb2+, rather than Ca2+, of possible value for the investigation and treatment of Pb2+intoxication.

Mechanism and specificity of lanthanide series cation transport by ionophores A23187, 4-BrA23187, and ionomycin

A23187, 4-BrA23187, and ionomycin transport several lanthanide series trivalent cations at efficiencies similar to Ca2+, when compared at cation concentrations of approximately 10(-5) M, ionophore concentrations of approximately 10(-6) M, and a pH of 7.00. Selectivity sequences and the range of relative rates are as follows: A23187, Nd3+ > La3+ > Eu3+ > Gd3+ > Er3+ > Yb3+ > Lu3+ (approximately 34-fold); 4-BrA23187, Nd3+ > Eu3+ > Gd3+ > La3+ > Er3+ > Yb3+ > Lu3+ (approximately 34-fold); ionomycin, La3+ > Yb3+ > Nd3+ > Lu3+ > Er3+ > Eu3+ > Gd3+ (approximately 4-fold). At concentrations between 9 and 250 microM, La3+ is transported by an electroneutral mechanism, predominately through mixed complexes of the type (ionophore)2La-OH (A23187 and 4-BrA23187) or (ionophore)La-OH (ionomycin), when no membrane potential is present. For all three ionophores, an induced potential of approximately 160 mV accelerates transport by approximately 50-100%. However, measured values of H+/La3+ exchange indicate that only 4-BrA23187 displays a significant electrogenic activity under these conditions. At a La3+ concentration of 17 mM, transport by all three ionophores is electroneutral and apparently occurs through complexes of type (ionophore)3La (A23187 and 4-BrA23187) or (ionophore)La-OH (ionomycin). Analysis of these patterns in a context of comproportionation equilibria involving the transporting species and free La3+ indicates that the species containing three ionophore molecules are formed on the membrane when aqueous phase solution conditions would strongly favor a 1:1 complex, based upon previous studies in solution. The implications of this and other findings are discussed.

General features in the stoichiometry and stability of ionophore A23187-cation complexes in homogeneous solution

Existing literature describing the stoichiometry and stability of complexes between A23187 and divalent cations in solution has been extended to include additional transition series cations, the heavy-metal cations Cd2+ and Pb2+, plus seven lanthanide series trivalent cations. Stability constants of 1:1 complexes between the ionophore and the divalent cations vary by 6.2 orders of magnitude between Cu2+ and Ba2+ which are the strongest and weakest complexes, respectively. Considering alkaline-earth and first-series transition cations together, the pattern of stability constants obeys the extended Irving-Williams series as is seen with many nonionophorous liganding agents. Cd2+ and Pb2+ are bound with an affinity similar to those of Mn2+ and Zn2+, whereas the lanthanides are bound with little selectivity and slightly higher stability. Titration of the ionophore in the 10(-5) M concentration range with di- and trivalent cations gives rise first to complexes of stoichiometry MA2 and subsequently to MA as the metal concentration is increased. The second stepwise stability constants for formation of the MA2 species exceeds the first constant by approximately 10-fold. With lanthanides, heavy metals, and transition-metal cations, OH-, at near physiological concentrations, competes significantly with free ionophore for binding to the 1:1 complexes. This competition is not apparent when Ca2+ or Mg2+ are the central cations. Possible implications of the 1:1 complex selectivity pattern, the ionophore-hydroxide competitive binding equilibria, and potential ternary complexes involving 1:1 ionophore:cation complexes and other anions present in biological systems are discussed with respect to the ionophores transport selectivity and biological actions.

Effects of solute concentration on the entrapment of solutes in phospholipid vesicles prepared by freeze-thaw extrusion

Phospholipid vesicles prepared by the freeze-thaw extrusion method contain internal solute concentrations which are much higher than the external values (entrapment ratios much greater than 1). This concentrating effect is a complex function of the total impermeant solute concentration in the medium used to prepare vesicles, the presence or absence of permeant solutes in the medium and the apparent competitive binding interactions between solutes and phospholipid. Increases in water phase solute concentration during freezing are thought to underlie the concentrating phenomenon, while osmotic pressure driven lysis of vesicles during thawing appears to limit its magnitude. By judicious selection of solute concentration and physical properties, further increases in the entrapment ratio should be obtainable, improving the usefulness of these vesicles as drug delivery vesicles and experimental systems.

Transport Properties of the Calcium Ionophore ETH-129

The transport mechanism and specificities of ionophore ETH-29 have been investigated in a highly defined phospholipid vesicle system, with the goal of facilitating the application of this compound to biological problems. ETH-129 transports Ca(2+) via an electrogenic mechanism, in contrast to A23187 and ionomycin, which function in a charge neutral manner. The rate of transport is a function of membrane potential, increasing by 3.9-fold per 59 mV over a broad range of that parameter. Rate is independent of the transmembrane pH gradient and strongly stimulated by the uncoupler carbonyl cyanide m-chlorophenylhydrazone when no external potential has been applied. The effect of uncoupler reflects the collapse of an opposing potential arising during Ca(2+) transport, but also reflects the formation of a mixed complex between the uncoupler, ETH-129, and Ca(2+) that readily permeates the vesicle membrane. Oleate does not substitute for the uncoupler in either regard. ETH-129 transports polyvalent cations according to the selectivity sequence La(3+) > Ca(2+) > Zn(2+) approximately equal to Sr(2+) > Co(2+) approximately equal to Ni(2+) approximately equal to Mn(2+), with the magnitude of the selectivity coefficients reflecting the cation concentration range considered. There is little or no activity for the transport of Na(+), K(+), and Mg(2+). These properties suggest that ETH-129 will be useful for investigating the consequences of a mitochondrial Ca(2+) overload in mammalian cells, which is difficult to pursue through the application of electroneutral ionophores.