David Rethwisch

Research interests:
membrane separations
polymer science
biochemical engineering 

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Membrane Science
My current studies emphasize the use of photoresponsive polymers as membranes, the use of NMR to study structure-function relationships in polymeric membranes, and the use of enzyme-containing liquid membranes for the separation of racemic mixtures into the optical isomers.

Photoresponsive membranes give us the potential to selectively control the permeation of desired products through a membrane. Photoresponsive membranes also are model systems that relate changes in the per-meability, diffusivity, and solubility of membranes to changes in the polymer conformation.

The diffusion and solubility of solutes in polymeric materials also can be studied by NMR techniques. We are combining experimental measurements of this sort with traditional membrane studies to better understand solution diffusion behavior in polymeric membranes.
We are studying membranes containing enzymes for the large-scale purification of biologically active compounds, which include peptides and optical isomers of carboxylic acids.

Enzymes are used to catalyze regio- and stereoselective esterifications. The resulting esters are transported through the organic liquid membrane and undergo enzyme catalyzed hydrolysis to the parent material in a product stream. We have demonstrated that we can increase the flux of phenylpropionic acid by a factor of more than 1,000 using this technique.

Chemoenzymatic Polymer Synthesis
My group has developed sucrose-containing, biodegradable polymers and hydrogels for potential use as water adsorbents, drug-delivery systems, and biocompatible materials. Specifically, we use the regio-selectivity of enzymes to modify sugar molecules only at selected sites. This allows the copolymerization of sucrose with adipic acid to form a linear polymer.

More recently my group has developed chemoenzymatic syntheses. The inherent selectivity of enzymatic synthesis is used to prepare sugar-based monomers such as sucrose-1'-(meth)acrylate. The resulting monomer is polymerized using standard free-radical polymerization techniques. These polymers are water-soluble in all proportions. Copolymerization with a cross-linker produces hydrogels that can absorb up to 1,000 times their weight in water.

Catalysis
Also under investigation are solid catalyzed, gas-solid reaction systems. We are studying the copper catalyzed reaction of methyl chloride with silicon to produce dimethyldichlorosilane (the precursor to silicone oils and rubbers). Although this reaction has been used commercially for more than 40 years, it still is not well understood.

A particular focus is determination of the reaction mechanism and how it is affected by promoters. In recent studies we have also demonstrated the use of these hydrogels for the controlled release of protein drugs.

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Selected Publications

Doghieri, F., Ghedinni, M. Quinzi, M. Rethwisch, R.G., and Sarti, G.C., "Gas Solubility in Glassy Polymers: Predictions from Non-Equilibrium EOS," Desalination, 144, 73-78 (2002)

Capila, I., Yi, W., Rethwisch, D.G., Matte, A. Cygler, M., and Linhardt, R.J., "Role of Arginine 292 in the Catalytic Activity of Chondroitin AC Lyase from Flavobacterium heparinum," Biochimica et Biophysica Acta - Protein Structure and Molecular Enzymology. 1597, 260-270 (2002).

Li, Y. and Rethwisch, R.G., "Quantitative Production of alpha-Methyl Glucoside Acrylate using Candida Antarctica lipase in Acetone," Biotechnology and Bioegineering, 79, 15-22 (2002)

Kaufmann, K.J. and Rethwisch, D.G., "Introducing Engineering Design in Materials Science," J. Mat. Education, 19, 29-38 (1999).

Kodzwa, M.G., Staben, M.E., and Rethwisch, D.G., "Rhotoresponsive Control of Ion-Exchange in Leucohydroxide Containing Hydrogel Membranes," J. Membrane Sci., 158, 85-92 (1999).

Patil, N.S., Dordick, J.S., and Rethwisch, D.G., "Macroporous Poly(SucroseAcrylate) Hydrogel for Controlled Release of Macromolecules," Biomaterials, 17, 2343-2350 (1996).

Schoenwald, R.D., Deshpande, G., Rethwisch, D.G., and Barfknecht, C.F.,"Penetration into the Anterior Chamber via the Conjuctival/Scleral Pathway," Journal of Ocular Pharmacology and Therapeutics 13, 41-59 (1997).

Patil, N.S., Rethwisch, D.G., and Dordick, J.S., "Sucrose Diacrylate: Unique Chemically and Biologically Degradable Crosslinker for Polymeric Hydrogels," J.Polym. Sci.:Part A Polym. Chem., 35, 2221-2229 (1997).

Wessel, T.J. and Rethwisch, D.G., "Deactivation of CuSi and CuZnSnSi Contact Masses due to Coke Formation during the Direct Synthesis of Methylchlorosilanes," Journal of Catalysis, 161, 861-866 (1996).