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David M. Hercules

Title and Contact Information

Centennial Professor of Chemistry Emeritus, Research Professor
Office: 7865 SC
Phone: (615) 343-5230
Email

Education

Ph.D., Massachusetts Institute of Technology, 1957

Specialties

Mass spectrometry
Bioanalytical Chemistry
Analytical Chemistry

In the News

Arts and Science-A&S Faculty Honored with Emeriti Status

Hercules

Research

Mass Spectrometry
Research in the Hercules group deals with the development of new instrumental analytical techniques. The major focus has been on application of novel method of mass spectrometry to the study of synthetic polymers and to biomedical, environmental and analytical chemistry.

The Hercules group is active in the characterization of polymers using mass spectrometry. The focus is both on surface analysis and bulk analysis. Surface analysis of polymers involves studying the surface segregation of one component of a block copolymer. For example, in a styrene-siloxane diblock copolymer, the surface layer will be entirely the siloxane component even though the bulk composition is 10% or less siloxane. The extent of surface segregation is measured by secondary-ion mass spectrometry (SIMS).

Matrix Assisted Laser Desorption/Ionization (MALDI)
MALDI mass spectrometry is being used for bulk analysis of copolymers. Of particular interest is determining the molecular weight distribution of a component of a block copolymer as it exists in the polymer chain. Polyurethanes are specific examples studied recently. Polyurethane properties are determined by the molecular weight of the soft block in the polymer chain. Combination of selective chemical reactions with MALDI permit measurement of the soft block (or hard block) molecular weight distributions in polyurethanes.

Single Molecular Weight (SMW) Oligomers
Synthesis of single molecular weight (SMW) oligomers of reasonable size (molecular weight >5000) is being pursued for a variety of reasons. SMW oligomers are important as calibration standards for polymer chromatography, as models to study fragmentation of polymers in mass spectrometry, and as model compounds for the behavior of intractable polymers in mass spectrometry. They are also valuable for comparing ionization processes in the different types of mass spectrometry.

Electrospray ionization (ESI)
ESI mass spectrometry is a particularly versatile method because one can inject solutions directly into the mass spectrometer. This allows one to determine the species of a given element in solution and to observe changes in speciation as solution conditions are changed. This is particularly attractive for environmental chemistry because the chemical behavior (toxicity) of an element varies significantly with its specific molecular form. Because ESI is a soft ionization method, non-covalent complexes can be observed and these can be used to measure the chirality of molecules, something almost impossible with other forms of mass spectrometry.

MALDI is very useful as a rapid screening, quantitative method which makes it ideal for use with combinatorial studies. Rapid screening in clinical and forensic chemistry is very important, and MALDI, coupled with solid-phase extraction, can be used to screen individual or multiple analytes. It is possible to screen for members of a given drug type (benzodiazepines) or a given clinical component (bile acids). Current research is focused on improved ways to use MALDI to accomplish rapid screening, coupled with chemically-selective solid-phase extraction methods for separation of trace analytes from complex matrices.

Selected Publications

Gies AP, Ellison ST, Stow SM, Hercules DM. Matrix-assisted laser desorption/ionization-time-of-flight/time-of-flight collision-induced dissociation study of poly(p-phenylenediamine terephthalamide) fragmentation reactions. Analytica Chimica Acta. 2014, 808: 124-43.

Gies AP, Hercules DM. Collision induced dissociation study of ester-based polyurethane fragmentation reactions. Analytica Chimica Acta. 2014, 808: 199-219.

Gies AP, Ellison ST, Chakraborty AK, Kwiecien NW, Hercules DM. MALDI-TOF/TOF CID study of poly(butylene adipate) fragmentation reactions. RSC Advances. 2012, 2 (10): 4135-4151.

Gies AP, Ellison ST, Geibel JF, Hercules DM. MALDI-TOF/TOF CID Study of Poly(phenylsulfidesulfone) Fragmentation Reactions. Macromolecules. 2011, 44 (13): 5093-5104.

Gies AP, Schotman A, Hercules DM. MALDI-TOF MS stability study of model poly(p-phenylene terephthalamide)s. Analytical and Bioanalytical Chemistry. 2010, 396 (4): 1481-1490.

Gies AP, Geibel JF, Hercules DM. MALDI-TOF/TOF CID Study of Poly(p-phenylene sulfide) Fragmentation Reactions. Macromolecules. 2010, 43 (2): 952-967.

Gies AP, Geibel JF, Hercules DM. MALDI-TOF MS Study of Poly(p-phenylene sulfide). Macromolecules. 2010, 43 (2): 943-951.

Ellison ST, Gies AP, Hercules DM, Morgan SL. Py-GC/MS and MALDI-TOF/TOF CID Study of Poly(phenyl sulfone) Fragmentation Reactions. Macromolecules. 2009, 42 (15): 5526-5533.

Gibson HW, Farcas A, Jones JW, Ge ZX, Huang FH, Vergne M, Hercules DM. Supramacromolecular Self-Assembly: Chain Extension, Star and Block Polymers via Pseudorotaxane Formation from Well-Defined End-Functionalized Polymers. Journal of Polymer Science Part A-Polymer Chemistry. 2009, 47 (14): 3518-3543.

Lee M, Schoonover DV, Gies AP, Hercules DM, Gibson HW. Synthesis of Complementary Host- and Guest-Functionalized Polymeric Building Blocks and Their Self-Assembling Behavior. Macromolecules. 2009, 42 (17): 6483-6494.

Tata PNV, Subbotina N, Burckart GJ, Muddiman DC, Gusev AI. Species-dependent hepatic metabolism of immunosuppressive agent tacrolimus (FK-506). Xenobiotica. 2009, 39 (10): 757-765.

Ellison ST, Gies AP, Hercules DM, Morgan SL,. Py-GC/MS and MALDI-TOF/TOF CID Study of Polysulfone Fragmentation Reactions. Macromolecules. 2009, 42 (8): 3005-3013.

Gies AP, Ellison ST, Vergne MJ, Orndorff RL, Hercules DM. MALDI-TOF/TOF CID study of poly(alpha-methylstyrene) fragmentation reactions. Analytical and Bioanalytical Chemistry. 2008, 392 (4): 627-642.

Gies AP, Vergne MJ, Orndorff RL, Hercules DM. MALDI-TOF/TOF CID study of 4-alkyl-substituted polystyrene fragmentation reactions. Analytical and Bioanalytical Chemistry. 2008, 392 (4): 609-626.

Gies AP, Kliman M, McLean J, Hercules DM. Characterization of Branching in Aramid Polymers Studied by MALDI-Ion Mobility/Mass Spectrometry. Macromolecules. 2008, 41 (22): 8299-8301.

Hercules DM. Polymer MS-MS by MALDI: some advances and some challenges. Analytical and Bioanalytical Chemistry. 2008, 392 (4): 571-573.

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