Research Interests of Dr. Travis D. Fridgen
THIS PAGE IS WILDLY OUT OF DATE. Please see my pubs page for more information about our research.
The long term goals of my research program include the ability to spectroscopically characterize and distinguish conformers and isomers of biologically interesting species such as protonated or metal-cation-bound dimers of DNA bases. The wavenumber positions of infrared (IR) modes for neutral species shift upon protonation or complexation with a metal ion, sometimes subtly and sometimes dramatically depending on the vibrational mode. These shifts occur even though the structure of the new species has not changed dramatically. Identifying and quantifying these spectroscopic shifts will greatly improve the potential for analytical applications of IR spectroscopy for these species, such as identifying possible structural anomalies from the normal conformation of the molecule. Similarly, our research will better enable the identification of these ions and molecules in other environments such as interstellar space. Furthermore, the infrared spectroscopic data will provide structural information which will, in turn, help us understand the nature of strong ionic hydrogen bonding and ion-dipole bonding which is prevelent in nature.
IR spectroscopy is sensitive to structural and environmental changes. Observation and interpretation of the spectra of sequentially solvated species will bridge the gap between structural studies conducted in the gas phase and those conducted in the condensed phases. With the instrumentation in my lab it is possible to study the effects of solvation, one solvent molecule at a time and make a considerable contribution to a poorly understood phenomenon. A fundamental thrust of the my research will be the spectroscopic study of the effects of environment on hydrogen bonds. This is experimentally tenable by observing the shifts in the wavenumber position of vibrational modes when complexed with a solvent molecule or when partaking in intramolecular hydrogen bonding. In the figure to the right the IRMPD spectrum of the proton-bound glycine dimer is displayed (black) in the OH/NH stretching region. There are two intramolecular hydrogen bonds which show up as broad features from about 2700 to 3300 cm-1.
These studies are made possible due to CFI Funding and IRIF (province of NL) which was used to purchase a Bruker 7.0 T Fourier Transform Ion Cyclotron Resonance Mass Spectrometer (tutorial) to which we have coupled a Nd/YAG pumped optical parametric oscillator which is capable of producing high-intensity tunable infrared radiation from about 1000 to 6600 cm-1.
A large component of this work also includes computational studies. This work will push forward the development of computational methods for predicting spectra and structures of large molecules and ionic species for which we will provide experimental data on which to build the model. Along with calculations of infrared spectra to compare with and aid in the assignment of experimental spectra current computational studies are focused on proton-bound dimers containing high-dipole moment monomers. These species have a curious structure about the central proton in that the proton is bound more strongly to the monomer with the lower proton affinity. For example, methanol has a lower proton affinity than acetonitrile by about 25 kJ mol-1, yet the proton is predicted to lie significantly closer to the methanol oxygen.
Another example of this coupling of state-of-the-art experimental IRMPD spectroscopy and computational methods are the ongoing studies of hydrated metal ion-bound DNA base complexes. To the immediate right is the experimental IRMPD spectrum of hydraded Li+-bound uracil dimer. The Li+-bound uracil dimer is linear about the O-Li+-O bond but only one water molecule is required to induce hydrogen bonding in a "base-pairing" type structure.
We are also in the early stages of mating our cryogenic matrix isolation apparatus will be coupled to an electrospray ion (ESI-MS) source for generating protonated or metalated species, mass selecting them and depositing the ions in a Ne matrix at 4 K for infrared spectroscopic study. We have a Sciex 150EX Single Quadrupole Mass Spectrometer which will be used in this study. This will be the first time matrix isolation and electrospray ionization mass spectometry will be coupled.
These techniques will provide new and complementary structural information on solvated ionic species.
Funding is gratefully acknowledged from:
Memorial University of Newfoundland
Dean of Science for student travel funds