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Biomedical subjects

David E Bergbreiter

Publications and source records attributed to David E Bergbreiter.

11 recordsLinked to original sources
PubMed2006

Synthesis, characterization, and utility of thermoresponsive natural/unnatural product macroligands for affinity chromatography.

[Structure: see text] The synthesis and characterization of thermoresponsive, water-soluble poly-N-isopropyl acrylamide (PNIPAM) derived macroligands displaying cyclosporin A (CsA) and dexamethasone (Dex) for use as novel affinity resins are described. Characterization of these soluble macroligands, including ligand loading and integrity, was determined by 1H NMR spectroscopy. One of the CsA macroligands was used in a protein affinity experiment to capture known binding proteins of CsA, the cyclophilins, from Jurkat T-cell lysates.

Chromatography, Affinity↗
PubMed2005

Specific ion effects on the water solubility of macromolecules: PNIPAM and the Hofmeister series.

Aqueous processes ranging from protein folding and enzyme turnover to colloidal ordering and macromolecular precipitation are sensitive to the nature and concentration of the ions present in solution. Herein, the effect of a series of sodium salts on the lower critical solution temperature (LCST) of poly(N-isopropylacrylamide), PNIPAM, was investigated with a temperature gradient microfluidic device under a dark-field microscope. While the ability of a particular anion to lower the LCST generally followed the Hofmeister series, analysis of solvent isotope effects and of the changes in LCST with ion concentration and identity showed multiple mechanisms were at work. In solutions containing sufficient concentrations of strongly hydrated anions, the phase transition of PNIPAM was directly correlated with the hydration entropy of the anion. On the other hand, weakly hydrated anions were salted-out through surface tension effects and displayed improved hydration by direct ion binding.

Acrylic Resins↗
PubMed2003

Poly(4-tert-butylstyrene) as a soluble polymer support in homogeneous catalysis.

[reaction: see text] Use of soluble poly(4-tert-butylstyrene) (PtBS) as a support in synthesis is demonstrated. These soluble polymers supported catalysts that were used in a monophasic medium. Subsequent separation of the catalysts after reaction was effected either by cooling- or by water-induced liquid/liquid-phase separation. Specific catalysts studied included both phosphine and DMAP nucleophilic catalysts. Low loadings of an azo dye quantified the efficiency of separation and recovery of these catalysts through multiple reaction cycles.

Journal Article↗
PubMed2003

Phase-selective solubility of poly(N-alkylacrylamide)s.

The extent of the phase-selective solubility of poly(N-alkylacrylamide)s was studied by UV-vis and fluorescence spectroscopy using poly(N-isopropylacrylamide) and poly(N-octadecylacrylamide) as representative polar and nonpolar poly(N-alkylacrylamide)s in a mixture of polar and nonpolar thermomorphic solvents. Phase-selective solubilities of greater than 10000:1 were seen with each labeled polymer in polar and nonpolar solvents such as heptane and DMF or heptane and 90% EtOH-H(2)O. Using a poly(N-acryloxysuccinimide) as a common precursor, a pool-split synthesis was devised to prepare a library of poly(N-alkylacrylamide)s whose members varied only in the size of their N-alkyl substituent. The solubilities of these library members were measured in both the polar and nonpolar phases of a thermomorphic heptane/90% EtOH-H(2)O mixture at 25 degrees C. Such solvent mixtures are miscible hot (70 degrees C) and biphasic cold (25 degrees C). The results show that poly(N-pentylacrylamide) is selectively soluble (>99.5%) in the polar EtOH-rich phase at rest. Poly(N-alkylacrylamide)s with larger N-alkyl groups are predominantly (C(6), 85%; C(7), 95%) or exclusively (>C(8), >99.5%) in the heptane-rich phase at rest.

Journal Article↗
PubMed2003

Using soluble polymers in latent biphasic systems.

A new strategy for carrying out reactions with a soluble polymer-bound reagent or catalyst is described. In this latent biphasic process, a solvent mixture at the cusp of immiscibility is prepared and used to carry out a reaction under homogeneous conditions. Then, after the reaction is complete, this mixture is perturbed by the addition of solvent or some other perturbing agent to produce a biphasic mixture. The product-containing phase is then separated under liquid/liquid conditions from the polymer-containing phase. The generality of this process is demonstrated using both dye-labeled polymers as surrogates for polymer-bound catalysts and with various polymer-bound organic and transition metal catalysts or reagents. In cases where a polymeric catalyst is used, the addition of fresh solvent and substrate reforms the original mixture allowing facile reuse of the catalyst.

Journal Article↗
PubMed2003

Measuring LCSTs by novel temperature gradient methods: evidence for intermolecular interactions in mixed polymer solutions.

Herein we describe studies of molecular interactions in thermoresponsive polymers as they go through phase transitions in aqueous solutions. By using our recently reported linear temperature gradient setup for studying the effects of temperature on chemical processes, we demonstrate the ability to probe lower critical solution temperature (LCST) behavior with excellent precision. This method also provides a simple and convenient way to assay the LCST of solutions containing more than one polymer and follow the clouding kinetics of polymer mixtures in real time.

Journal Article↗
PubMed2002

Soluble polymer-supported catalysts containing azo dyes.

[structure: see text] Azo benzene derivatives were incorporated into soluble polymer-bound catalysts by two different approaches. The first was to attach the dye to the polymer-bound catalysts, using the dye as an innocent spectator to study the phase preference, concentration, and recoverability of a catalyst. The second approach used an azo dye as a ligand to form an effective soluble polymer-bound Pd(II) catalyst for Heck reactions.

Journal Article↗