Thermochemical Determinations of Compounds Using the Extended Kinetic Method

Hey everyone!  My name is Kathy Huynh.  I’m a rising senior and Chemistry major at the College.  I began working in Professor Poutsma’s research lab at the beginning of my junior year and this is my first time participating in summer research at the College.

Professor Poutsma has several projects he is currently working on, but I have been involved with his research involving the gas-phase thermochemistry of protein and non-protein amino acids, in addition to other compounds, and will be continuing to work on this project throughout the summer.  Thermochemistry is the broad topic of the changes involved in species during chemical reactions.  In Prof. Poutsma’s lab, known affectionately as the ionlab, we are looking at two thermochemical properties in particular; the gas-phase basicities (GPB) and proton affinities (PA) of various compounds.

Experimentally, we are using the extended kinetic method to determine the GPBs and PAs of these compounds.  Using this method, proton-bound heterodimers are formed using the amino acid of interest and a set of references.  The instrumentation used in this process is a triple quadrupole mass spectrometer and collision-induced dissociation as the ionization source.

Once ionized, the heterodimer is fragmented by either one of two dissociation channels:

B1—H+—B2  →  B1H+ + B2                 B1—H+—B2  →  B2H+ + B1

Using transition state theory, the ratio between rate constants of the two reactions can be related to the ratios between fragmentation ions.  After compiling the fragmentation data over three separate days for each analyte-reference heterodimer, kinetic method plots are made to determine either the GPB or PA of the analyte.

Additionally, theoretical determinations are made for these amino acids.  This is done using the computer programs, GaussView and Gaussian 98W.  The first program creates an input file of your amino acid structure and the latter program performs the necessary calculations.  These computations are made to increase the validity and confidence of our experimental data.

I am extremely excited to be able to document my summer experience involving this project.

– Kathy