Cary B. Bauer

Metal ion separations in polyethylene glycol-based aqueous biphasic systems : correlation of partitioning behavior with available thermodynamic hydration data

Abstract Solvent extraction, utilizing an oil-water mixture (e.g, chloroform-water) and a suitable complexant, is a proven technology for the selective removal and recovery of metal ions from aqueous solutions. Aqueous biphasic systems (ABS), formed by mixing certain inorganic salts and water-soluble polymers, or by mixing two dissimilar water-soluble polymers, have been studied for more than 40 years for the gentle, non-denaturing separation of fragile biomolecules, yet ABS have been virtually ignored as a possible extraction technology for metal ions. In this report we review our metal ion partitioning work and discuss the three major types of partitioning: (1) those rare instances that the metal ion species present in a given solution partitions to the PEG-rich phase without an extractant; (2) the use of halide salts which produce a metal anion complex that partitions to the PEG-rich phase; and (3) the use of a water-soluble extractant which distributes to the PEG-rich phase. In addition, we correlate the partitioning behavior we observed with available thermodynamic data for metal ions and their complexes.

Metal Ion Separations in Polyethylene Glycol-Based Aqueous Biphasic Systems

Solvent extraction utilizing an oil-water mixture (e.g., chloroform-water) and a suitable complexant, is a proven technology for the selective removal and recovery of metal ions from aqueous solutions. Aqueous biphasic systems (ABS), formed by mixing certain inorganic salts and water-soluble polymers, or by mixing two dissimilar water-soluble polymers, have been studied for more than 40 years for the gentle, non-denaturing separation of fragile biomolecules, yet ABS have been virtually ignored as a possible extraction technology for metal ions. In this report we review our metal ion partitioning work and discuss the three major types of partitioning: (1) those rare instances that the metal ion species present in a given solution partitions to the PEG-rich phase without an extractant; (2) the use of halide salts which produce a metal anion complex that partitions to the PEG-rich phase; and (3) the use of a water-soluble extractant which distributes to the PEG-rich phase. In addition, we correlate the partitioning behavior we observed with available thermodynamic data for metal ions and their complexes.

Partitioning behavior of group 1 and 2 cations in poly(ethylene glycol)-based aqueous biphasic systems

The partitioning behavior of several Group 1 and 2 cations was investigated in poly(ethylene glycol) (PEG)-based aqueous biphasic systems. All of these metal ions prefer the salt-rich phase over the PEG-rich phase with distribution ratios all well below one regardless of the system investigated. The relative salting-out ability of the individual cations can be directly correlated to their Gibbs free energy of hydration (delta G(hyd)). In addition, the relative magnitude of the distribution ratios for these metal ions can also be explained in terms of delta G(hyd).

PARTITIONING BEHAVIOR OF 99Tc AND,129I FROM SIMULATED HANFORD TANK WASTES USING POLYETHYLENE-GLYCOL BASED AQUEOUS BIPHASIC SYSTEMS

ABSTRACT Three simulated Hanford tank wastes, SY-101, NCAW, and SST, were prepared and contacted with aqueous solutions of 20-60% (w/w) polyethylene glycol (PEG)-2000. The combined salting out action of OH-, C03 2’, SO4 2rsquo;, PO4 3\ and possibly other minor constituents in the waste simulants, results in the formation of aqueous biphasic systems (ABS). Investigation of the partitioning behavior of 99Tc (as 99Tc04) and 129I (as 99T) from the waste simulant phase to the upper PEG-rich phase at 25 and 50°C revealed distribution ratios as high as 190 for 99Tc04 and 7.5 for 129I. The partitioning of several of the other major species in these solutions (Na+, P04 3, C03 2’, S04 2\ PEG), as well as the general physical characteristics of the ABS were also investigated. In general, the observed distribution ratios are affected (increased if they prefer the PEG-rich phase, decreased if they prefer the salt-rich phase) by increasing the concentration of PEG-2000 used to form the ABS which increases the differenc...

The effects of choice of anion (X=C1−, SCN−, NO3−) and polyethylene glycol (PEG) chain length on the local and supramolecular structures of LnX3/PEG complexes

We have structurally characterized many LnCl3, Ln(SCN)3 and Ln(NO3)3 complexes of triethylene through heptaethylene glycols. The chain length typically controls the primary coordination sphere and the number of additional inner-sphere ligands (anions, water or solvent molecules) present. Of the three anions studied, the nitrate anion, with its preference for bidentate coordination and its hard oxygen donors, has the greatest effect on the PEG conformations. A third aspect of these complexes which has typically been overlooked is the nature of the supramolecular structures generated by hydrogen bonding of the PEG alcoholic termini and water molecules. In this presentation we review the several different structural series and discuss subtle trends that are apparent from small differences in the observed inner and outer-sphere coordination as a function of anion type, PEG chain length, and metal ionic radius.

The crown ether extraction of group 1 and 2 cations in polyethylene glycol-based aqueous biphasic systems at high alkalinity

The crown ethers 1,4,7,10,13-pentaoxacyclopentadecane (15- crown-5) and 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6) have been utilized to study the partitioning of Group 1 and 2 cations between aqueous layers in an aqueous biphasic system formed by the salting out of PEG-2000 (polyethylene glycol of 2000 average molecular weight) with NaOH. Partitioning to the PEG-rich phase is generally only achieved by the addition of high concentrations of NaNO,. In the presence of NO3-, the metal ion partitioning results correlate with the log K values for 18-crown-6 complexation in H,O. This trend does not hold for 15-crown-5.

X-ray structures of the Dictyostelium discoideum myosin motor domain with six non-nucleotide analogs.

The three-dimensional structures of the truncated myosin head from Dictyostelium discoideum myosin II complexed with dinitrophenylaminoethyl-, dinitrophenylaminopropyl-, o-nitrophenylaminoethyl-,m-nitrophenylaminoethyl-,p-nitrophenylaminoethyl-, ando-nitrophenyl-N-methyl-aminoethyl-diphosphate·beryllium fluoride have been determined to better than 2.3-Å resolution. The structure of the protein and nucleotide binding pocket in these complexes is very similar to that of S1dC·ADP·BeF x (Fisher, A. J., Smith, C. A., Thoden, J., Smith, R., Sutoh, K., Holden, H. M., and Rayment, I. (1995) Biochemistry 34, 8960–8972). The position of the triphosphate-like moiety is essentially identical in all complexes. Furthermore, the alkyl-amino group plays the same role as the ribose by linking the triphosphate to the adenine binding pocket; however, none of the phenyl groups lie in the same position as adenine in S1dC·MgADP·BeF x , even though several of these nucleotide analogs are functionally equivalent to ATP. Rather the former location of adenine is occupied by water in the nanolog complexes, and the phenyl groups are organized in a manner that attempts to optimize their hydrogen bonding interactions with this constellation of solvent molecules. A comparison of the kinetic and structural properties of the nanologs relative to ATP suggests that the ability of a substrate to sustain tension and to generate movement correlates with a well defined interaction with the active site water structure observed in S1dC·MgADP·BeF x .

Aqueous Biphase Systems for Liquid/Liquid Extraction of f-Elements Utilizing Polyethylene Glycols

Abstract Aqueous biphasic systems formed by adding a H2O soluble polymer (polyethylene glycol) to an aqueous salt solution ((NH4)2SO4 or K2CO3) have been investigated for use in extracting aqueous Am3+, Pu4+, UO2 2+, and Th4+ ions into the polymer-rich phase. Extraction occurs only in the presence of complexing dyes which preferentially partition to the polymer-rich phase. Three such dyes, arsenazo III, alizarin complexone, and xylenol orange were investigated. Arsenazo III extracts all four metal ions from SO4 2- media but not from CO3 2- solutions. Alizarin complexone quantitatively extracts Th4+ and Pu4+ from SO4 2- media, while Am3+ is the best extracted ion in CO3 2- solution. Xylenol orange extracts only Am3+ from CO3 2- media. In SO4 2- solutions low concentrations of xylenol orange extract Th4+ and Pu4+, while Am3+ and UO2 2+ are extracted at higher concentrations of xylenol orange. H2SO4 can be used to strip the metal ions, while NH4OH often but not always enhances the extraction.

SELECTIVE AND QUANTITATIVE PARTITIONING OF PERTECHNETATE IN POLYETHYLENE-GLYCOL BASED AQUEOUS BIPHASIC SYSTEMS

ABSTRACT The partitioning behavior of technetium has been investigated in polyethylene glycol (PEG)-based aqueous biphasic systems using K3P04, K2C03, Na3(citrate), (NH4) 3(citrate), (NH4) 2S04, and NaOH as biphase-forming salts, and PEGs with average molecular weights of 1500, 2000, 3400, and 6000. Pertechnetate quantitatively partitions to the PEG-rich phase in these systems. The distribution ratios increase with increasing salt or PEG concentration used to form the aqueous biphasic systems, consistent with the increasing phase incompatibility. At a given concentration of salt and PEG, DTc values in the various systems increase in the order NaOH < (NH4) 2S04 < (NH4)3(citrate) < K2C03 < K3P04 and PEG-1500 < PEG-2000 < PEG-3400 < PEG-6000. The distribution ratios are lower at very high or very low pH values than they are in the 3-9 pH range. Matrix ions may also influence the DTcvalues by affecting the aqueous biphasic system composition. Technetium can be stripped from the loaded PEG-rich phase by contac...

Crown ethers as actinide extractants in acidic aqueous biphasic systems: partitioning behavior in solution and crystallographic analyses of the solid state

Abstract The partitioning behavior of UO 2 2+ , Pu 4+ , Th 4+ , and Am 3+ has been investigated in aqueous biphasic systems formed by the addition of polyethylene glycol of average molecular weight 2000 (PEG-2000) and (NH 4 ) 2 SO 4 . Water-soluble crown ethers 18-crown-6 and 15-crown-5 have been utilized as extractants. A positive correlation has been observed between crown ether concentration and metal ion partitioning with D An decreasing in the order UO 2 2+ > Pu 4+ > Th 4+ > Am 3+ . A distribution ratio above unity, however, has only been observed for UO 2 2+ at very high (1.25 M) concentrations of 18-crown-6. In general the distribution ratios for 15-crown-5 are all lower. Matrix ions introduced as NH 4 NO 3 , H 2 SO 4 , or HNO 3 drastically reduce the observed distribution ratios and level the extractant dependencies.