Issue 39, 2009
From the journal:

Physical Chemistry Chemical Physics

Gas phase fragmentation of protonated betaine and its clusters†

Jean Ann Wyer,a   Linda Feketeová,bcd   Steen Brøndsted Nielsen*a  and  Richard A. J. O’Hair*bcd  

* Corresponding authors

a Department of Physics and Astronomy, Aarhus University, Ny Munkegade, DK-8000 Aarhus C, Denmark
E-mail: sbn@phys.au.dk
Fax: +45 8612 0740
Tel: +45 8942 4879

b School of Chemistry, University of Melbourne, Victoria 3010, Australia
E-mail: rohair@unimelb.edu.au
Fax: +61 3 9347 5180
Tel: +61 3 8344 2452

c Bio21 Institute of Molecular Science and Biotechnology, The University of Melbourne, Victoria 3010, Australia

d ARC Centre of Excellence for Free Radical Chemistry and Biotechnology, The University of Melbourne, Victoria 3010, Australia

Abstract

Betaine [(CH3)3N+CH2COO−] is a methylated version of glycine and is a zwitterion in its neutral form. In this work, we have subjected protonated betaine, +(CH3)3NCH2COOH, to a range of fragmentation experiments which involve vibrational excitation, electronic excitation and electron capture. Low-energy (eV) collisions in combination with deuterium labelling reveal that the lowest energy dissociation pathway is the formation of N(CH3)3+˙ and ˙CH2COOH. The dominant channel after 50 keV collisions with molecular oxygen is the same as that after low-energy collisions; however, more fragmentation is seen which is most likely due to electronic excitation of the ions in the collision processes. Subsequent dissociation of the radical N(CH3)3+˙ was observed in agreement with the electron ionisation spectrum of N(CH3)3. Electron-induced dissociation by 22 eV electrons produced similar fragments to those formed after high-energy collision-induced dissociation. With caesium atoms as the target gas, protonated betaine captured electrons to give neutrals. These were reionised to cations a microsecond later in collisions with O2. The dominant dissociation channel of the betaine radical, [(CH3)3NCH2COOH]˙, involves formation of N(CH3)3 and ˙CH2COOH, as revealed from the presence of N(CH3)3+˙ radical cations. This channel is associated with a kinetic energy release of 0.1–0.2 eV. The ˙CH2COOH radical is unstable to dissociation into ˙CH3 and CO2 but in charge reversal experiments (two Cs collisions), CH2[double bond, length as m-dash]C(OH)O− anions were formed due to the short time between the collisions (nanoseconds). Density functional theory calculations support the spectral interpretations. Collision-induced dissociation of protonated betaine clusters resulted dominantly in loss of neutral betaines.

Graphical abstract: Gas phase fragmentation of protonated betaine and its clusters

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Article information

DOI
https://doi.org/10.1039/B909653A
Article type
Paper
Submitted
15 May 2009
Accepted
29 Jun 2009
First published
27 Jul 2009

Phys. Chem. Chem. Phys., 2009,11, 8752-8758

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Gas phase fragmentation of protonated betaine and its clusters

J. A. Wyer, L. Feketeová, S. Brøndsted Nielsen and R. A. J. O’Hair, Phys. Chem. Chem. Phys., 2009, 11, 8752 DOI: 10.1039/B909653A

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