Day: December 1, 2014

Evolution of Selected Isoprene Oxidation Products in Dark Aqueous Ammonium Sulfate

MS Defense:  DM Ashraf Ul Habib
Chemistry Department

Lynn Mazzoleni, Advisor
Thursday, December 4  1pm,  Chem Sci 101
Evolution of Selected Isoprene Oxidation Products in Dark Aqueous Ammonium Sulfate

The climate of the world is changing but our understanding of atmospheric processes is limited. Atmospheric aerosol is a trace but very influential medium of the atmosphere. Especially little is known about the organic aerosol components and their aqueous phase chemical evolution. To address this, the aqueous phase processing of glyoxylic acid, py­ruvic acid, oxalic acid and methylglyoxal was studied simulating dark and radical free atmospheric aqueous aerosol. A novel observation of the cleavage of a carbon-carbon bond in pyruvic acid and glyoxylic acid leading to their decarboxylation was made in the presence of ammonium salts but decarboxylation was not observed from oxalic acid. The empirical rate constants for decarboxylation were determined and are competitive with nighttime OH radical reactions. The structure of the acid, ionic environment of the solu­tions and concentration of species were all found to affect the rate of decarboxylation. A tentative set of reaction mechanisms is proposed involving nucleophilic attack by ammo­nia on the carbonyl carbon leading to fragmentation of the carbon-carbon bond between the carbonyl and carboxyl carbons. Under similar conditions in atmospheric aerosol, the aqueous phase processing may markedly impact the physicochemical properties of aerosol.


Synthetic Oligodeoxynucleotide Purification via Catching by Polymerization

Suntara (Boat) Fueangfung

Advisor: Dr. Shiyue Fang

Doctoral candidate, Department of Chemistry

Michigan Technological University

Friday, December 5, 2014, 9:00 am

Admin Building, Room 404

PhD Defense

Synthetic Oligodeoxynucleotide Purification via Catching by Polymerization

Abstract

Large quantities of pure synthetic oligodeoxynucleotides (ODNs) are important for preclinical research, drug development, and biological studies. These ODNs are synthesized on an automated synthesizer. It is inevitable that the crude ODN product contains failure sequences which are not easily removed because they have the same properties as the full length ODNs. Current ODN purification methods such as polyacrylamide gel electrophoresis (PAGE), reversed-phase high performance liquid chromatography (RP HPLC), anion exchange HPLC, and affinity purification can remove those impurities. However, they are not suitable for large scale purification due to the expensive aspects associated with instrumentation, solvent demand, and high labor costs.

To solve these problems, two non-chromatographic ODN purification methods have been developed. In the first method, the full-length ODN was tagged with the phosphoramidite containing a methacrylamide group and a cleavable linker while the failure sequences were not. The full-length ODN was incorporated into a polymer through radical acrylamide polymerization whereas failure sequences and other impurities were removed by washing. Pure full-length ODN was obtained by cleaving it from the polymer. In the second method, the failure sequences were capped by a methacrylated phosphoramidite in each synthetic cycle. During purification, the failure sequences were separated from the full-length ODN by radical acrylamide polymerization. The full-length ODN was obtained via water extraction. For both methods, excellent purification yields were achieved and the purity of ODNs was very satisfactory. Thus, this new technology is expected to be beneficial for large scale ODN purification.