Mid-IR Spectroscopy of Gas-Phase Biomolecules: Experiment, Theory, and Instrument Development
Examensarbete för masterexamen
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|Type: ||Examensarbete för masterexamen|
|Title: ||Mid-IR Spectroscopy of Gas-Phase Biomolecules: Experiment, Theory, and Instrument Development|
|Authors: ||Andersson, Åke|
|Abstract: ||Experiment With the purpose of understanding weak interactions between amino
acids, two infrared (IR) spectroscopy experiments are performed in the range of
550 − 1850 cm−1 (5.4 − 18 μm) on gas-phase proton-bound amino acid dimers. In both,
electrospray ionization (ESI) is used to deliver the dimers to the gas phase as ions, where
they are trapped in an ion cyclotron resonance (ICR) mass spectrometer. In the first,
the spectra of Met2H+, MetTrpH+, and Trp2H+are obtained with IR multiple photon
disassociation (IRMPD) using the CLIO free electron laser as an IR light source. In the
second, homo- and heterochiral Asn2H+ are similarly studied with IRMPD, this time
using FELIX as the IR light source. The resulting spectra contain enough information
to infer the location of the surplus proton.
Theory For each of the molecules, a conformational search is performed using molecular
dynamics (MD) simulations with varied initial conditions. The conformers are then
optimized and their IR spectra are determined with the density functional theory (DFT)
B3LYP functional. Energy calculations are done with a Gaussian-4 (G4MP2) method
when computationally feasible, and with a complete basis set (CBS-4M) method otherwise.
The room temperature predicted IR spectra are obtained by summing up the IR
spectra of individual conformers multiplied by their Boltzmann factors. Agreement between
experimental and predicted spectra is good with the exception of the region near
1500 cm−1. These frequencies correspond to vibrational bending modes of the protonated
amino group, suggesting that the intermolecular hydrogen bond cannot be approximated
as harmonic. Finally, the intermolecular interactions are classified with the noncovalent
interaction (NCI) method.
Instrument Development Development of a high-resolution mass spectrometer
meant for use in infrared-ultraviolet (IR-UV) ion-dip spectroscopy of gas-phase
biomolecules began in 2018 at the Department of Physics, University of Gothenburg.
At the outset of this work, design of the instrument and its enclosing vacuum chamber
were partially finished, and all major parts were acquired. Designs of interior components
such as sample holder, airlock, nozzle mount, and skimmer flange have been made.
The main chamber and its supporting structure have been assembled. Today, the main
chamber reaches an ultimate pressure of 2.5 × 10−7 mbar, which is well sufficient for
|Issue Date: ||2020|
|Publisher: ||Chalmers tekniska högskola / Institutionen för fysik|
|Collection:||Examensarbeten för masterexamen // Master Theses|
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