Biomedical subjects

Scott K Spear

Publications and source records attributed to Scott K Spear.

8 recordsLinked to original sources

PubMed2006

The opposite effect of temperature on polyethylene glycol-based aqueous biphasic systems versus aqueous biphasic extraction chromatographic resins.

Variation in operational temperatures has revealed differences in the partitioning behavior of probe solutes between the phases in aqueous biphasic systems (ABS) and the related aqueous biphasic extraction chromatographic resin (ABEC). This difference has been studied using the hydrophobic anion, 99TcO4-, as a probe and (NH4)2SO4 as the kosmotropic salt. Distribution of the hydrophobic anion 99TcO4- to the PEG-rich phase in a MePEG-5000/(NH4)2SO4 ABS increases with increasing temperature, but decreases are observed in batch uptakes of this anion to ABEC resins from (NH4)2SO4 solutions. Phase diagrams were constructed at five different temperatures from 10 to 50 degreesC using cloud point titration for the ABS and a correlation between the phase divergence, measured in terms of tie line length (TLL), and the temperature of the partitioning system was verified. Thermodynamic parameters (deltaHdegrees,deltaSdegrees, deltaGdegrees, ) as a function of temperature were calculated for the various systems studied and the results imply thermodynamic differences between partitioning in ABS versus ABEC.

Chromatography, Liquid↗

PubMed2006

In search of ionic liquids incorporating azolate anions.

Twenty-eight novel salts with tetramethyl-, tetraethyl-, and tetrabutylammonium and 1-butyl-3-methylimidazolium cations paired with 3,5-dinitro-1,2,4-triazolate, 4-nitro-1,2,3-triazolate, 2,4-dinitroimidazolate, 4,5-dinitroimidazolate, 4,5-dicyanoimidazolate, 4-nitroimidazolate, and tetrazolate anions have been prepared and characterized by using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and single-crystal X-ray crystallography. The effects of cation and anion type and structure on the physicochemical properties of the resulting salts, including several ionic liquids, have been examined and discussed. Ionic liquids (defined as having m.p.<100 degrees C) were obtained with all combinations of the 1-butyl-3-methylimidazolium cation ([C(4)mim](+)) and the heterocyclic azolate anions studied, and with several combinations of tetraethyl or tetrabutylammonium cations and the azolate anions. The [C(4)mim](+) azolates were liquid at room temperature exhibiting large liquid ranges and forming glasses on cooling with glass-transition temperatures in the range of -53 to -82 degrees C (except for the 3,5-dinitro-1,2,4-triazolate salt with m.p. 33 degrees C). Six crystal structures of the corresponding tetraalkylammonium salts were determined and the effects of changes to the cations and anions on the packing of the structure have been investigated.

Journal Article↗

PubMed2005

Identical extraction behavior and coordination of trivalent or hexavalent f-element cations using ionic liquid and molecular solvents.

The extraction of both UO2(2+) and trivalent lanthanide and actinide ions (Am3+, Nd3+, Eu3+) by dialkylphosphoric or dialkylphosphinic acids from aqueous solutions into the ionic liquid, 1-decyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide has been studied and compared to extractions into dodecane. Radiotracer partitioning measurements show comparable patterns of distribution ratios for both the ionic liquid/aqueous and dodecane/aqueous systems, and the limiting slopes at low acidity indicate the partitioning of neutral complexes in both solvent systems. The metal ion coordination environment, elucidated from EXAFS and UV-visible spectroscopy measurements, is equivalent in the ionic liquid and dodecane solutions with coordination of the uranyl cation by two hydrogen-bonded extractant dimers, and of the trivalent cations by three extractant dimers. This is the first definitive report of a system where both the biphasic extraction equilibria and metal coordination environment are the same in an ionic liquid and a molecular organic solvent.

Journal Article↗

PubMed2004

Application of polyethylene glycol-based aqueous biphasic reactive extraction to the catalytic oxidation of cyclic olefins.

Glutaric acid and 1,2,3,4-butanetetracarboxylic acid (BTCA) have been synthesized by sodium tungstate catalyzed oxidation of the cyclic olefins: cyclopentene and 1,2,3,6-tetrahydrophthalic anhydride (THPA), using hydrogen peroxide in a polyethylene glycol (PEG)-2000/NaHSO(4) aqueous biphasic system (PEG-ABS). The production of glutaric acid and BTCA was found to increase from the monophasic to the biphasic regimes, and was found to be greatest at short tie-line lengths (TLLs), close to the system's critical point, yielding glutaric acid and BTCA in 73.1 and 82.5% yield, respectively. The results imply that mutual mixing or contact of the components is important, because the product dicarboxylic acids were found to increase from the monophasic side to the critical point and decrease from the critical point to more divergent regimes. The two reactions were compared with adipic acid synthesis from cyclohexene in terms of the cyclic olefin structure, and the partitioning of the dicarboxylic acid product in the ABS.

Alkenes↗

PubMed2004

Effects of speciation on partitioning of iodine in aqueous biphasic systems and onto ABEC resins.

Polyethylene glycol (PEG)-aqueous biphasic systems (ABS) and PEG-grafted aqueous biphasic extraction chromatographic (ABEC) resins have been shown to remove inorganic species from environmental and nuclear wastes. The partitioning behavior of several iodide species (iodide, iodine, triiodide, iodate, and 4-iodo-2,6-dimethylphenol (I-DMP)) have been studied for PEG (MW 2000)-salt systems and ABEC resins. Iodide partitioning to PEG-rich phases or onto ABEC resins can be enhanced by derivatization with 2,6-dimethylphenol to form 4-iodo-2,6-dimethylphenol or by addition of I(2) to form triiodide. Conversely, iodide partitioning to the PEG-rich phase or onto ABEC resins is reduced by oxidation of iodide to IO(3)(-). Partitioning studies of iodide, iodate, and iodine in a PEG-ABS are compared to results using ABEC resins.

Hydrogen-Ion Concentration↗

PubMed2002

Dissolution of cellulose [correction of cellose] with ionic liquids.

We report here initial results that demonstrate that cellulose can be dissolved without activation or pretreatment in, and regenerated from, 1-butyl-3-methylimidazolium chloride and other hydrophilic ionic liquids. This may enable the application of ionic liquids as alternatives to environmentally undesirable solvents currently used for dissolution of this important bioresource.

Cellulose↗

PubMedDate not supplied

Production of bioactive cellulose films reconstituted from ionic liquids.

A new method for introducing enzymes into cellulosic matrixes which can be formed into membranes, films, or beads has been developed using a cellulose-in-ionic-liquid dissolution and regeneration process. Initial results on the formation of thin cellulose films incorporating dispersed laccase indicate that active enzyme-encapsulated films can be prepared using this methodology and that precoating the enzyme with a second, hydrophobic ionic liquid prior to dispersion in the cellulose/ionic liquid solution can provide an increase in enzyme activity relative to that of untreated films, presumably by providing a stabilizing microenvironment for the enzyme.

Catalysis↗

PubMedDate not supplied

Ionic liquid-reconstituted cellulose composites as solid support matrices for biocatalyst immobilization.

Preparation of cellulose-polyamine composite films and beads, which provide high loading of primary amines on the surface allowing direct one-step bioconjugation of active species, is reported using an ionic liquid (IL) dissolution and regeneration process. Films and bead architectures were prepared and used as immobilization supports for laccase as a model system demonstrating the applicability of this approach. Performance of these materials, compared to commercially available products, has been assessed using millimeter-sized beads of the composites and the lipase-catalyzed transesterification of ethyl butyrate.

Biocompatible Materials↗