- 1064 Shelby Hall
- (205) 348-8443
- (205) 348-9104
A.B., 1979, Pfeiffer College
Ph.D., 1984, Purdue University
Postdoctoral Associate, 1988-89, Naval Research Laboratory
Mass spectrometry, ion-molecule reactions, dissociation of peptides and proteins ions, FT-ICR and TOF MS/MS analysis
The Cassady group uses mass spectrometry to study the gas-phase properties of biomolecules and to develop new techniques for analyzing these compounds. This work involves three state-of-the-art mass spectrometers: a Bruker BioApex 7e Fourier transform ion cyclotron resonance spectrometer (FT-ICR or FTMS), a Bruker Ultraflex I time-of-flight (TOF) spectrometer, and a Bruker HCTultra PTM Discovery System high capacity quadrupole ion trap (QIT).
Our FT-ICR research deals with multiply-charged peptide and protein ions produced by electropsray ionization (ESI). Because FT-ICR is a trapping form of mass spectrometry, gas-phase biomolecular ions can be allowed to react with neutral molecules. The ions can also be fragmented, which is useful for obtaining structural information. Most of our recent work has centered on the dissociation of deprotonated peptide ions. These ions are often formed in abundance from peptides with acidic residues, including phosphate or sulfate groups. We study how amino acid composition, acidity, and sequence affects dissociation, with the goal being to develop negative ion MS/MS as a tool for sequencing peptides in proteomics research. Our work often involves peptides of known sequence, which are synthesized in-house with our benchtop peptide synthesizer.
Our TOF research involves singly-charged ions produced by matrix-assisted laser desorption ionization (MALDI). The techniques of post-source decay (PSD) and in-source decay (ISD) are used to fragment the ions. The emphasis is on deprotonated peptide ions, as well as metallated ions. The effects of experimental parameters on dissociation are studied. As with our FT-ICR research, we focus on elucidating fragmentation mechanisms and understanding the effects of structural features on dissociation. Molecular dynamics calculations are employed to provide theoretical data that assists in interpreting the experimental results. We are also exploring the use of capped iron oxide nanoparticles as MALDI matrices for organic polymers and biopolymers.
Our QIT research involves electron transfer dissociation (ETD) and collision-induced dissociation (CID) of metallated peptide ions produced by ESI. ETD on metallated ions shows great promise as a method for sequencing peptides that are difficult to sequence by more conventional techniques, such as CID on protonated ions. We are exploring how the identity and properties of metal ions affects fragmentation mechanisms. In addition, we are studying the ability of metal salts to increase protonation of peptides by ESI. This “enhanced protonation” affect could make ETD experiments possible on a variety of peptides and other biomolecules that could not previously be studied by ETD.
“Paramagnetic 19F NMR and Electrospray Ionization Mass Spectrometric Studies of Substituted Pyridine Complexes of Chromium(III): Models for Potential Use of 19F NMR to Probe Cr(III)-nucleotide Interaction,” N.R. Rhodes, K. Belmore, C.J. Cassady, and J. B. Vincent, Polyhedron 64, 136-141 (2013).
“Gas-Phase Deprotonation of the Peptide Backbone for Tripeptides and Their Methyl Esters with Hydrogen and Methyl Side Chains,” S.S. Bokatzian-Johnson, M.L. Stover, D.A. Dixon, and C.J. Cassady, J. Phys. Chem. B. 116, 14844-58 (2012).
“A Comparison of the Effects of Amide and Acid Groups at the C-Terminus on the Collision-Induced Dissociation of Deprotonated Peptides,” S.S. Bokatzian-Johnson, M.L. Stover, D.A. Dixon, and C.J. Cassady, J. Am. Soc. Mass Spectrom. 23, 1544-1557 (2012).
“Fundamental Thermochemical Properties of Amino Acids: Gas-phase and Aqueous Acidities and Gas-phase Heats of Formation,” M.L. Stover, V.E. Jackson, M.H. Matus, C.J. Cassady, and D.A. Dixon, J. Phys. Chem. B 116, 2905-2916 (2012).
“Effects of Transition Metal Ion Coordination on the Collision-induced Dissociation of Polyalanines,” H.M. Watson, J.B. Vincent and C.J. Cassady, J. Mass Spectrom. 46, 1099-1107 (2011).
“Characterizing the Organic Component of Low-molecular-weight Chromium-binding Substance and Its Binding of Chromium,” Y. Chen, H.M. Watson, J. Gao, S.H. Sinha, C.J. Cassady, and J.B. Vincent, J. Nutrition 141, 1225-1232 (2011).
“A Comparison of Positive and Negative Ion Collision-induced Dissociation for Model Heptapeptides with One Basic Residue,” D. Pu, N.L. Clipston, and C.J. Cassady, J. Mass Spectrom. 45, 297-305 (2010).
“Mass Spectrometric and Spectroscopic Studies of the Nutritional Supplement Chromium(III) Nicotinate,” N.R. Rhodes, T. Konovalova, Q. Liang, C.J. Cassady, and J.B. Vincent, Biol. Trace Elem. Res. 130, 114-130 (2009).
“Negative Ion Production from Peptides and Proteins by Matrix-assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry,” J. Gao and C.J. Cassady, Rapid Commun. Mass Spectrom. 22, 4066-4072 (2008).
“The Effects of Chromium(III) Coordination on the Dissociation of Acidic Peptides,” D. Pu, J.B. Vincent, and C.J. Cassady, J. Mass Spectrom. 43, 773-781 (2008).