Bioanalytical Mass Spectrometry/Peptide and Protein Sequencing/ Ion-Surface Collisions for Surface Characterization of Organic Thin Films

Research in the Wysocki group is separated into three broad areas: (1) determination of peptide dissociation mechanisms as a means for improving programs used for automated sequencing of peptides and proteins, (2) surface characterization of organic thin films, and (3) implementation of surface-induced dissociation onto commercial time-of-flight instruments. The research involves collisions of selected reactive and non-reactive ions with well-ordered surfaces (e.g., self-assembled monolayer films of alkanethiols on gold;Langmuir-Blodgett films). The nature of the surface, the type of projectile ion, and the collision energy are the major experimental variables that are explored.

Research in progress on biomolecules is addressing several different questions involving singly and multiply protonated peptides. All of the related projects are designed to increase the current understanding of the hydrogen bonding interactions and fragmentation patterns of activated protonated peptides. The long range goals of this work are to provide additional "rules" that can be used to enhance automated primary sequencing of peptides and proteins by tandem mass spectrometry and, ultimately, to relate information on gas-phase fragmentation patterns and energetics of dissociation to peptide and protein conformation.

Major aims of our surface characterization research are to determine whether the ion/surface chemistry that is detected when low-energy (eV), gas-phase polyatomic ions collide with a well-ordered surface can be used to quantitate the composition of mixed-composition films and to characterize electron transfer through organic thin films in the absence of solvent. Model compounds ("probe ions") are used to define the reactivity of projectile ions with various functional groups at the surface. Projectile ions used include small, odd-spin species such as distonic radical cations and their conventional counterparts; small aromatic compounds with electron-donating and electron-withdrawing groups; large, refractory molecules such as buckminsterfullerene (C60). These different categories of reagents provide distinct types of information on the mechanisms of electron and atom transfer from surfaces to probe ions and on the analytical utility of ion/surface reactions for surface characterization.

A third area of research is the development of improved mass spectrometers for structural characterization of large molecules. Instruments that allow low-energy ion-surface collisions are not available commercially. Commercial MALDI-TOF(matrix-assisted laser desorption time-of- flight) instruments do not have an efficient means of fragmenting the ions. We have recently shown that surface-induced dissociation can be accomplished with good resolution in a sector/time-of-flight instrument and will extend this work to a commercial MALDI system.

A. R. Dongré, Á. Somogyi, V. H. Wysocki, "Surface-Induced Dissociation: An Effective Tool to Probe Structure, Energetics and Fragmentation Mechanism of Protonated Peptides," J. Mass Spectrom. 1996, 31, 339-350.

A. R. Dongré, J. L. Jones, Á. Somogyi, V. H. Wysocki, "Influence of Peptide Composition, Gas-Phase Basicity and Chemical Modification on Fragmentation Efficiency: Evidence for the Mobile Proton Model," J. Am. Chem. Soc., 1996, 118, 8365-8374.

C. Gu. and V. H. Wysocki "Ion-Surface Reactions Involving Isotopically Labeled Langmuir-Blodgett Films," J. Am. Chem. Soc., 1997, 119, 12010-12011.

H. Nair and V.H. Wysocki "Are Peptides Without Basic Residues Protonated Primarily at the Amino Terminus?," Int. J. Mass Spectrom. Ion Processes, 1998, 174, 95-100.

G. Tsaprailis, H. Nair, A. Somogyi, V.H. Wysocki, W. Zhong, J.H. Futrell, S.G. Summerfield, S.J. Gaskell "Influence of Secondary Structure on the Fragmentation of Protonated Peptides" J. Am. Chem. Soc., 1999, 121, 5142-5154.

C. Gu, V.H. Wysocki "Dissociative and Reactive Hyperthermal Ion-Surface Collisions with Langmuir-Blodgett Films Terminated by CF₃(CH₂)_n, n-Perfluoroalkyl, or n-Alkyl Groups" J. Am. Chem. Soc., in press.