Professor (b. 1955). B.S. 1973, University of Illinois at Urbana-Champaign, M.S. 1980, Colorado State University, Ph.D. (Chem. Eng.) 1981, Iowa State University. Optically based spectroscopies (Raman, infrared, uv-visible absorption, and emission) for separation process analysis; Crystallization from solution; Sensors for process control.
Separation and purification processes are of central importance to the economics of the food, pharmaceutical, and chemical industries. One of the most poorly understood, yet indispensible, purification and separation processes is crystallization from solution. Our research program is based on the use of optically based spectroscopies to obtain fundamental understanding of the mechanisms of crystallization which can be subsequently used for sensor development.
Raman spectroscopy is being employed to study the formation of hydrates, solvates, and crystalline ploymorphs from solution. The occurrence of these various crystalline species has profound effects on pharmaceutical products by introduction of variation in solubility and bioavailability. The focus of the work is in situ characterization of various crystalline forms in order to determine which environmental factors, such as temperature, supersaturation, solvent, and imputrities, cause formation and transformation in solution. Raman spectroscopy is uniquely suited for studies of this type since the same instrument can collect Raman spectra of solutions and solids under identical conditions.
A second major research interest is the use of uv-visible absorption and emission spectroscpies to probe solvation behavior. In these studies a probe molecule exhibiting solvatochromism is introduced into a solution. When solution conditions are changed to induce crystallization, the solvatochromic molecule's optical behavior is drastically changed. In this manner supersaturation can be monitored in a very precise manner and a supersaturation measuring device is under development. In a variation of this approach molecules are utilized which crystallize as an impurity in a given crystal. This technique allows fundamental study of the desolvation process that accompanies crystallization by measuring the change of the solvatochromic molecule as it enters the crystal lattice as well as basic studies of crystal-impurity interactions.
Protein crystallization is under study using fluoresence anisotropy which allows the rotational motion of a protein to be probed. We have found that the rotational motion of a protein is significantly slowed even at times preceding crystallization by as much as a week. Fluorescent molecules are introduced into the crystallizing solutions and bind to the surface of the protein allowing emission properties to be tuned. Current research attempts to develop this technique for screening conditions which promote protein crystallization.
Rounding out the techniques employed is attenuated total reflection- Fourier transform infrared (ATR- FTIR) spectroscopy. By exploiting the unique optical properties of the ATR configuration, we are able to simultaneously measure supersaturation and composition of solution. Research on this topic is aimed at development of analytical systems for process control.
Representative Publications:
This page last updated November 12, 1997.