Research

Research Overview

Our research seeks to answer the following questions:

• What is the relationship between condensed- and gas-phase structure (& other properties)?
• How can biological molecules be made to adopt condensed-phase properties in the gas phase?

We are combining trapping mass spectrometry with laser spectroscopy in order to characterize the structure, stability and dynamics of biomolecules and biomolecular complexes in a controlled gas-phase environment. Native biological systems are highly complex, and their state depends on the interplay of numerous factors. Analyzing these systems in the minimalist environments (gas phase) allows us to separate effects of non-covalent interactions involved in hydration, metal-chelation and drug-binding.

High Resolution Mass Spectrometry

An ion cyclotron resonance mass spectrometer (Apex Qe, 7 Tesla FT-ICR MS) allows for ultra-high mass resolution mass spectrometry. In addition to traditional dissociation methods such as collision-induced dissocation (CID) and electron capture dissociation (ECD), the instrument has been outfitted to perform gas-phase hydrogen/deuterium exchange (HDX).

Examples:

Straus, R. N.; Jockusch, R. A. Hydrogen-Deuterium Exchange and Electron Capture Dissociation to Interrogate the Conformation of Gaseous Melittin Ions. J. Am. Soc. Mass Spectrom. 2019. ASAP

Pan, J.; Heath, B. L.; Jockusch, R. A.; Konermann, L. Structural Interrogation of Electrosprayed Peptide Ions by Gas-Phase H/D Exchange and Electron Capture Dissociation Mass Spectrometry. Anal. Chem. 2012, 84 (1), 373–378.

Intrinsic Photophysics

How do molecules respond to light in the absence of solvent interactions? What does the photophysical response tell us about structure? By probing the fluorescence emitted or dissociation of gaseous ions trapped in a quadrupole ion trap (Esquire 3000+), we glimpse into the intrinsic properties of chromophores.

Fluorescence is detected using an electron-multiplying CCD camera (EM-CCD) coupled to a spectrograph for steady-state measurements, or a single-photon avalanche photo-diode (SPAD) by time-correlated single-photon counting (TCSPC) for time-resolved fluorescence decays.

Examples:

Kusinski, M.; Nagesh, J.; Gladkikh, M.; Izmaylov, A.; Jockusch, R. A. Deuterium Isotope Effect in Fluorescence of Gaseous Oxazine Dyes. Phys. Chem. Chem. Phys. 2019, 21 (10), 5759-5770.

Wellman, S. M. J.; Jockusch, R. A. Moving in on the Action: An Experimental Comparison of Fluorescence Excitation and Photodissociation Action Spectroscopy. J. Phys. Chem. A 2015, 119 (24), 6333–6338.

Nagy, A. M.; Talbot, F. O.; Czar, M. F.; Jockusch, R. A. Fluorescence Lifetimes of Rhodamine Dyes in Vacuo. Journal of Photochemistry and Photobiology A: Chemistry 2012, 244, 47–53.

Bian, Q.; W. Forbes, M.; O. Talbot, F.; A. Jockusch, R. Gas-Phase Fluorescence Excitation and Emission Spectroscopy of Mass-Selected Trapped Molecular Ions. Phys. Chem. Chem. Phys. 2010, 12 (11), 2590–2598.

Forbes, M. W.; Jockusch, R. A. Deactivation Pathways of an Isolated Green Fluorescent Protein Model Chromophore Studied by Electronic Action Spectroscopy. J. Am. Chem. Soc. 2009, 131 (47), 17038–17039.

Gas-phase FRET

Forster Resonance Energy Transfer (FRET) is a common analytical technique used in solution-phase studies. Colloquially known as a "molecular ruler", the technique takes advantage of the distance-dependent radiationless energy transfer between a donor chromophore to an acceptor chromophore. We have been working towards exploiting this phenomenon in the gas-phase for studying conformations of biologically-relevant systems.

Examples:

Czar, M. F.; Zosel, F.; König, I.; Nettels, D.; Wunderlich, B.; Schuler, B.; Zarrine-Afsar, A.; Jockusch, R. A. Gas-Phase FRET Efficiency Measurements To Probe the Conformation of Mass-Selected Proteins. Anal. Chem. 2015, 87 (15), 7559–7565.

Talbot, F. O.; Rullo, A.; Yao, H.; Jockusch, R. A. Fluorescence Resonance Energy Transfer in Gaseous, Mass-Selected Polyproline Peptides. J. Am. Chem. Soc. 2010, 132 (45), 16156–16164.

Instrumentation

Mass Spectrometers (MS)

• Esquire 3000+ Quadrupole Ion Trap MS (Bruker Daltonics)
• APEX Qe 7 Tesla Fourier-Transform Ion Cyclotron MS (Bruker Daltonics)
• nano-ESI or macro-ESI

Optical Spectroscopy

• Nd:YVO₄ cw pump laser
• Ti:Sapphire femtosecond laser
• EM-CCD and Spectrograph
• 532 nm cw laser
• 213 nm UV laser
• Time-correlated Single Photon Counting (TCSPC)

General Lab Equipment

• Capillary Puller
• Centrifuge
• Thermomixer