Ph.D. Chemical Engineering – University of California, Berkeley, 1984
M.S., Chemical Engineering – University of California, Berkeley, 1980
B.S. Chemical Engineering – Stanford University, 1978
Our primary research interest involves investigations of separation processes for biological macromolecules. One main area of work has involved studies of chromatography, which is widely used in the biotechnology industry for both analytical and process-scale separations. Our research in this area has the general goal of examining the thermodynamic, transport, and biophysical principles which underlie chromatographic separations. Knowledge gained from these investigations can be used to exploit underutilized separation methods for biomolecules as well as to devise entirely new ones.
Chromatofocusing. One area of work has involved investigations of the technique of chromatofocusing. Our main goal is to overcome current limitations in both analytical and preparative applications of this technique. In one particular project, computer-aided design and optimization methods are being developed to optimize the column presaturation and elution conditions so that stable gradients can be formed using simple buffer mixtures and readily available strong-base ion exchangers, rather than the polyampholyte buffers and proprietary weak base column packings normally used for chromatofocusing. Such systems are likely to greatly expand the range of applications possible for the technique, including to peptide separations, to high-speed, high-resolution, and high-sensitivity analytical separations performed using capillary columns, and to various process-scale systems. In a related project we are developing a novel hybrid chromatography method, which we have termed "displacerless" displacement chromatography that incorporates aspects of both chromatofocusing and displacement chromatography.
Development and Characterization of Novel Chromatographic Column Packings. Our work in this area involves both the characterization of novel types of column packings and the development of new characterization methods based on theories of chromatography. One specific project involves studies of adsorbents which have, in addition to a network of smaller pores, a network of very large pores that are either entirely filled with the liquid phase, in which case intraparticle convection may occur, or which contain a small volume fraction of a functionalized hydrophilic polymer. These types of adsorbents possess enhanced mass transfer properties and have advantages over conventional porous particles when used in chromatography. In another project, which is being conducted in collaboration with Grace Vydac, we are investigating a variety of novel silica-based column packings. Another project involves the investigation of slurry packing methods for conventional, microbore, and capillary HPLC columns with the goal of increasing the performance of these columns.
Methods for Proteome Analysis. Novel versions of chromatography are being interfaced to a mass spectrometer to develop improved liquid chromatography - mass spectrometer (LC-MS) methods for proteome analysis. In one project, high-resolution chromatofocusing performed using a micropellicular (nonporous particle) column packing, and employed as a component of a two-dimensional chromatography method, is being interfaced to either ESI-MS or MALDI-TOF-MS to produce a technique that has potential as a replacement for standard two-dimensional polyacrylamide gel electrophoresis (2DE) for the routine characterization of protein molecular weight and isoelectric point. In a related project we are investigating other uses of high-throughput, multidimensional chromatography for proteome analysis. We are also investigating the use of chromatofocusing as a sample prefractionation method for increasing the dynamic range of narrow-pI-range 2DE gels.
Use of Green Fluorescent Protein (GFP) for Protein Purification Process Development. Applications are being developed for the use of the fluorescent protein GFP for purification process development. In one application GFP or GFP fusion proteins are focused onto a retained stepwise pH transition and used for the visualization of viscous fingering and related flow irregularities inside a chromatographic column.
Biomedical Applications of Chromatography. Various applications of analytical chromatography in biomedical science are being investigated. In one study, improved methods are being developed for the high-resolution detection of glycosylated variants of hemoglobin for use in diabetes detection and treatment monitoring.
H. Shen, D. D. Frey, "Serial Displacement Chromatofocusing and its Applications in Multidimensional Chromatography and Gel Electrophoresis: Part I. Theory and General Considerations," J. Chromatogr. A, 1216, 967-976, 2009.
H. Shen, X. Li, C. J. Bieberich, D. D. Frey, "Serial Displacement Chromatofocusing and its Applications in Multidimensional Chromatography and Gel Electrophoresis: Part II. Experimental Results," J. Chromatogr. A, 1216, 977-986, 2009.
K. Brorson, H. Shen, S. Lute, J. Soto Prez, D. D. Frey, "Characterization and Purification of Bacteriophages Using Chromatofocusing," J. Chromatogr. A, 1207, 110-121, 2008.
H. Shen, X. Li, C. J. Bieberich, D. D. Frey, "Reducing Sample Complexity in Proteomics by Chromatofocusing with Simple Buffer Mixtures," Methods Mol. Biol., 424, 187-203, 2007.
X. Ge, M. Hanson, H. Shen, Y. Kostov, K.A. Brorson, D. D. Frey, A. R. Moreria, G. Rao, "Validation of an Optical Sensor-Based High-Throughput Bioreactor System for Mammalian Cell Culture," J. Biotechnol., 122, 293-306, 2006.
D. D. Frey, X. Kang, "New Concepts in the Chromatography of Peptides and Proteins," Curr. Opin. Biotechnol., 16, 552-560, 2005.
J. Soto Pérez, D. D. Frey, "Behavior of the Inadvertent pH Transient Formed by a Salt Gradient in the Ion-Exchange Chromatography of Proteins," Biotechnol. Progr., 21, 902-910, 2005.
H. Shen, D. D. Frey, "Effect of Charge Regulation on Steric Mass-Action Equilibrium for the Ion-Exchange Adsorption of Proteins," J. Chromatogr. A, 1079, 92-104, 2005.
X. Kang, D. D. Frey, "Chromatofocusing of Peptides and Proteins Using Linear pH Gradients Formed on Strong Ion-Exchange Adsorbents," Biotechnol. Bioeng., 87, 376-387, 2004.
H. Shen, D. D. Frey, "Charge Regulation in Protein Ion-Exchange Chromatography: Development and Experimental Evaluation of a Theory Based on Hydrogen Ion Donnan Equilibrium," J. Chromatogr. A, 1034, 55-68, 2004.
X. Kang, D. D. Frey, "High-Performance Cation-Exchange Chromatofocusing of Proteins," J. Chromatogr. A, 991, 117-128, 2003.
X. Kang, D. D. Frey, "Chromatofocusing Using Micropellicular Column Packings with Computer-Aided Design of the Elution Buffer Composition," Anal. Chem., 74, 1038-1045, 2002.
D. D. Frey, C. R. Narahari, C. D. Butler, "General Local-Equilibrium Chromatographic Theory for Eluents Containing Adsorbing Buffers," AIChE J., 48, 561-571, 2002.
D. Farnan, D. D. Frey, Cs. Horváth, "Surface and Pore Diffusion in Macroporous and Gel-Filled Gigaporous Stationary Phases for Protein Chromatography," J. Chromatogr. A, 959, 65-73, 2002.
Illustration of fingering phenomena in a concentrated band of protein focused on a retained pH transition.