Paul M. Mayer

Gas-Phase Ion Chemistry

Mass Spectrometry

 


 Professor
PhD Chemistry Ottawa 1994
BSc Chemistry Manitoba 1990

118 D'Iorio Hall
ph 613 562 5800 x 6038
fax 613 562 5170
pmmayer@uottawa.ca



My research focuses on the dynamics of the reactions of gas-phase ions. The work involves studying the mechanisms for ion dissociation and reactivity in mass spectrometry and the energetic and entropic factors that influence this reactivity. We pursue this work experimentally with mass spectrometry and theoretically with statistical rate theory and computational chemistry.

The systems we study range from small atmospheric ions and neutrals (N2, CO2, SO2, etc), all the way up to non-covalent polymer/substrate complexes and non-covalent peptide/substrate complexes. In every case we couple the appropriate mass spectrometric technique (electron ionization or electrospray ionization with tandem mass spectrometry on a magnetic sector, triple quadrupole or quadrupole-time-of-flight mass spectrometer) with ab initio molecular orbital calculations (for small systems) or MM/MD simulations for the larger non-covalent complexes. We also compliment this work with information from imaging photoelectron photoion coincidence spectroscopy (iPEPICO done at the Swiss Light Source) and collision-induced emission spectroscopy (in our lab).

Specifically, we are exploring:

 The ion chemistry of small polycyclic aromatic hydrocarbons to help elucidate their role in the chemistry of the interstellar medium. Over the past 25 years of the so-called PAH hypothesis these molecules have been argued to be involved in shielding organic reactions in the interstellar medium (ISM) and playing an active role catalyzing these reactions, especially H2 formation. As part of my collaboration with a group in Toulouse, France, we are determining the energetics, entropics and mechanisms for the photodissociation of these species and modeling experiments on their reactivity with H and H2 with statistical rate theories in an effort to put a solid foundation under these hypotheses, or dispell them completely once and for all.  The work involves tandem mass spectrometry done in my lab, kinetics measurements done with the PIRENEA apparatus in Toulouse and imaging PEPICO (photoelectron photoion coincidence) measurements done at the Swiss Light Source.

The modeling of experimental tandem mass spectrometry data to extract reliable energetics and entropics for the dissociation of non-covalent complexes, be they polymers or peptides. Such complexes are ubiquitous in biology and many researchers employ mass spectrometry to study their properties (conformation, 3-D and 2-D structure). We are focusing on the gas-phase structure and binding in order to shed light on the relationship (positive or negative) between solution-phase and gas-phase structures of such species as polymer/amine complexes, peptide/saccharide complexes, cyclodextrin/drug complexes and more. Specifically we are interested in the intrinsic role molecular conformation plays in the entropy changes that take place during dissociation of a floppy complex, which we can only explore in the gas phase. This work is done with triple-quadrupole and quadrupole-TOF mass spectrometers in our lab and an ion mobility/Q-TOF in the Berezovski lab. 

Chemistry of atomic metal anions.  The chemical concept of metals producing positive ions (cations) and non-metals negative ions (anions), is a fundamental precept taught as early as high school. However, under certain conditions metal anions can be created and as such their electron affinities are well characterized and calculated both experimentally and theoretically.  We have a new, easy method for generating metal anions and are starting to explore their reactions with small neutral molecules.  We are interested in experimentally and computationally characterizing their role in electron transfer, dissociative electron transfer and ion-molecule reactions such as gas-phase oxidative addition-reductive elimination reactions.  Preliminary results on a triple-quadrupole mass spectrometer have demonstrated each of these reactions depending on the metal anion.  We are also starting to explore the potential analytical use of metal anions through their reactions with halogenated contaminants, and as a new method for dissociating proteins and nucleotides by electron transfer dissociation. 

Agilent technologies Canada, Inc. donates ion trap to the Mayer group to pursue the chemstry of metal anionsClick here for details