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Our group uses mass spectrometry to study the gas-phase properties of biomolecules and to develop new techniques for analyzing these compounds. This work involves two state-of-the-art instruments: a Bruker BioApex 47e Fourier transform mass spectrometer (FT-ICR or FTMS) and a Bruker Reflex III time-of-flight (TOF) mass spectrometer.
Current 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 and sequence affects dissociation, with the goal being to develop negative ion dissociation as a tool for sequencing peptides. Our work generally 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). A technique known as post-source decay (PSD) is used to fragment the ions. The effects of experimental parameters on dissociation are studied. As with our FT-ICR research, we focus on elucidatingfragmentation 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.
"Negative ion production from peptides and proteins by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry." Gao, J.; Cassady, C. J. Rapid Commun. Mass Spectrom. 22, 4066-4072 (2008).
"Negative ion dissociation of peptides containing hydroxyl side chains." Pu, D.; Cassady, C. J. Rapid Commun. Mass Spectrom. 22, 91-100 (2008).
"The effects of chromium(III) coordination on the dissociation of acidic peptides." Pu, D.; Vincent, J. B.; Cassady, C. J. J. Mass. Spectrom. 43, 773-781 (2008).
"Gas-phase acidities of aspartic acid, glutamic acid, and their amino acid amides." Li, Z.; Matus, M. H.; Velazquez, H. A.; Dixon, D. A.; Cassady, C. J. Int. J. Mass Spectrom. 265, 213-223 (2007).
"Low-molecular-weight chromium-binding substance from chicken liver and American alligator liver." Hatfield, M. J.; Gillespie, S.; Chen, Y.; Li, Z.; Cassady, C. J.; Vincent, J. B. Comp. Biochem. Physiol. B: Biochem. Mol. Biol. 144B, 423-431 (2006).
"C-terminal amino acid residue loss for deprotonated peptide ions containing glutamic acid, aspartic acid, or serine residues at the C-terminus." Li, Z.; Yalcin, T.; Cassady, C. J. J. Mass. Spectrom. 41, 939-949 (2006).
"A Comparison of Negative and Positive Ion Time-of-Flight Post-Source Decay Mass Spectrometry for Peptides Containing Basic Residues." Clipston, N. L.; Jai-nhuknan, J.; Cassady, C. J. Int. J. Mass Spectrom., 222 (2003), 363-381.
"Effects of Peptide Chain Length on the Gas-Phase Proton Transfer Properties of Doubly-Protonated Ions from Bradykinin and its N-Terminal Fragment Peptides." Pallante, G. A.; Cassady, C. J. Int. J. Mass Spectrom. 115 (2002), 115-131.
"Gas-phase Basicities for Ions from Bradykinin and Its des-Arginine Analogues." Ewing, N. P.; Pallante, G. A.; Zhang, X.; Cassady, C. J. J. Mass Spectrom. 36 (2001), 875-881.
"Dissociation of Multiply-charged Negative Ions for Hirudin (54-65), Fibrinopeptide B, and Insulin A (Oxidized)." Ewing, N. P.; Cassady, C. J. J. Am. Soc. Mass Spectrom. 12 (2001), 105-116.
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