Our research uses a combination of mass spectrometry and optical laser spectroscopy to investigate the properties of isolated biological ions in the highly-controllable gas-phase environment. Using this approach, we can examine the intrinsic properties of biomolecular ions, including their geometric structure, relative stability and dynamics. Experiments are also performed on the biological ion of interest complexed with small numbers of water molecules or counter-ions to investigate the details of how a biological molecule interacts with its immediate environment.
Previous work includes studies of the deprotonated Adenosine 5'-triphosphate and Adenosine 5'-diphosphate ions, while current work is strongly focused on investigating negatively-charged glycosoaminoglycan saccharides.
Gas-phase studies of inorganic compounds can provide important information on fundamental properties including metal-ligand binding energies, ligand-exchange reactions, electron affinities and electronic structure. A wide range of solution-phase inorganic species can be transferred directly into the gas-phase using electrospray ionisation, where they are investigatied using mass spectrometry and laser spectroscopy. For example, transition metal complex anions including PtBr4 2– and IrCl6 2– have been studied allowing us to compare ligand binding energies and the ground-state potential energy surfaces. Ion-pairing interactions have also been investigated in mixed charge systems such as K+·Pt(CN)6 2–· and K+·Cr2O7 2–. Current work is focused on investigating how such systems interact with small numbers of solvent molecules to investigate the microsolvation environment.
We have constructed a custom-built laser interfaced mass spectrometer for conducting laser spectroscopy of gas-phase biological ions. Ions are introduced into the gas-phase using electrospray ionization (ESI) prior to entering a tandem mass spectrometer. Mass-selected ions are then isolated in an octopole ion-trap, and cryogenically cooled prior to laser excitation. The instrument allows the application of a broad range of laser spectroscopies, including two-colour IR and UV-VIS. We have free access to a wide range of laser light sources (IR, UV/VIS and femtosecond) within the York Centre for Laser Spectroscopy).
In addition to the custom-built ESI laser mass spectrometer, we are converting commercial mass spectrometers (Finnegan LCQ and Brucker Esquire) for performing laser spectroscopy within a quadrupole ion trap. These instruments are also available for performing mass spectrometry experiments including collision-induced dissociation measurements.
Computational chemistry is a key component of our research, allowing us to interpret experimental results. Ab initio and density functional theory methods are applied to determine geometric structures and provide details of potential energy surfaces. Calculations are also of crucial importance for interpreting the results of our laser spectroscopy experiments.
Recent work includes the development of a new methodology for identifying the low-energy structures of conformationally and tautomerically flexible systems. The method uses molecular dynamics to generate initial structures, followed by a classification process that groups conformers into “families” to ensure that a representative sample of structures is retained for further analysis. Hierarchical ab initio calculations of typical conformers of the families are then performed to identify the lowest-energy structures. This procedure should provide a useful methodology for conducting higher-level ab initio calculations of medium-sized gas-phase biological molecules for interpreting contemporary laser spectroscopy measurements.