Research

Research Interest

(1) IRMPD and DFT Spectroscopic Studies

Infrared multiphoton dissociation (IRMPD) spectroscopy is employed to characterize of gas-phase molecular ion structure trapped ion in Fourier Transform Ion Cyclotron Resonance (FT-ICR) mass spectrometry and irradiated with infrared photon. Then, the molecular ion will further undergo various low energy reaction dynamics pathway due to photo absorption. In general, the recorded IRMPD spectrum with respect to dissociation channels contain key information on the molecular ion structure for the particular reaction channel. We investigate the reaction dynamics of chemical interest by using a combination of experimental and theoretical method to answer sophisticated reaction dynamics. Often, we conduct density functional theory based molecular dynamics calculations to equilibrate our molecular ions at certain thermal energy based on integration of Newtonian equation, where F and m is the force and mass of atom.

The theoretical IR spectrum is then calculated by taking the Fourier transform dipole moment autocorrelation function.

Eventually, theoretical spectrum shall provide information about the major population of molecular ion in the reaction chamber as shown above. Sometimes, transient intermediates can be characterized via formation of intra-molecular interaction which induces red shift or blue shift in certain vibrational modes.

(2) Ion-molecule reaction

Ion-molecule reaction is binary collision between ions (cation or anion) with neutral molecules and further result in chemical reaction if there is any. Theoretically, chemical bond dissociation and formation can be observed during the collision due to substantial change in internal energy of the ion complex and further activate various reaction channels. Ion-molecule reaction study is common in atmospheric chemistry, radiation chemistry, etc.

Recently, we found that ion-molecule reaction is efficient to study radical isomerization in molecular peptide ion [M]^●+ especially in tyrosyl-containing molecular peptide. We setup a customized triple quadrupole linear ion trap mass spectrometer for ion molecule reaction between tyrosyl containing molecular peptide ion with an odd electron neutral molecule NO₂ as shown below.

Interestingly, we found the collision is effective to probe the radical isomerization in tyrosyl-containing molecular peptide via radical recombination. We performed density functional theory calculation to characterize the various reaction mechanisms by using Transition State Theory (TST) and further explain the competitive reaction channels that responsible for the product ions that observed in mass spectrometer. Both experimental and theoretical studies concluded that the tyrosine-containing peptide radical cation undergoes radical isomerization upon formation of the π-canonical radical tautomer to produce phenoxy radical tautomer. Unexpectedly, the ion molecule reaction of phenoxy radical with NO₂ result in formation of 3-nitrosyl peptide which is an important bio-molecule in biological system.