Structure of Proton-Bound Methionine and Tryptophan Dimers in the Gas Phase Investigated with IRMPD Spectroscopy and Quantum Chemical Calculations.

The structures of three proton-bound dimers (MetH, MetTrpH, and TrpH) are investigated in the gas phase with infrared multiple photon disassociation (IRMPD) spectroscopy in combination with quantum chemical calculations. Their IRMPD spectra in the range of 600-1850 cm are obtained experimentally using an FT-ICR mass spectrometer and the CLIO free electron laser as an IR light source. The most abundant conformers are elucidated by comparing the IRMPD spectra with harmonic frequencies obtained at the B3LYP-GD3BJ/6-311++G** level of theory.

Theoretical studies of infrared signatures of proton-bound amino acid dimers with homochiral and heterochiral moieties.

Proton-bound homochiral and heterochiral dimers, X-H -X, of five amino acids (X = Ser, Ala, Thr, Phe, and Arg) are investigated theoretically using quantum chemical density functional theory (DFT) calculations and molecular dynamics simulations with the aim to unveil diastereomer-specific mid-infrared (mid-IR) absorption bands in the spectral range of 1000 to 1800 cm . The theoretical calculations performed in this work imply that all systems, except Ala H , have distinct mid-IR absorption bands in homochiral and heterochiral configurations, which make them appropriate systems to be studied experimentally with mid-IR spectroscopy. We show that intermolecular interaction with the side chain, in the form of hydrogen bonding or cation-π interaction, is necessary for chiral effects to be present in the mid-IR spectra of proton-bound dimers of amino acids.

Low-Energy Collisions of Protonated Enantiopure Amino Acids with Chiral Target Gases.

Here we report on the gas-phase interactions between protonated enantiopure amino acids (L- and D-enantiomers of Met, Phe, and Trp) and chiral target gases [(R)- and (S)-2-butanol, and (S)-1-phenylethanol] in 0.1-10.0 eV low-energy collisions.

Fragmentation of positively-charged biological ions activated with a beam of high-energy cations.

First results are reported on the fragmentation of multiply protonated polypeptide ions produced in electrospray ionization mass spectrometry (ESI-MS) with a beam of high-energy cations as a source of activation. The ion beam is generated with a microwave plasma gun installed on a benchtop Q Exactive mass spectrometer. Precursor polypeptide ions are activated when trapped inside the collision cell of the instrument (HCD cell), and product species are detected in the Orbitrap analyzer.