https://doi.org/10.1140/epjd/e2002-00169-0
Analytical laser induced liquid beam desorption mass spectrometry of protonated amino acids and their non-covalently bound aggregates
1
MPI für Biophysikalische Chemie, Am Faßberg 11, 37077 Göttingen, Germany
2
MPI für Strömungsforschung, Bunsenstraße 10, 37073 Göttingen, Germany
Corresponding author: a babel@gwdg.de
Received:
28
June
2002
Published online:
13
September
2002
We have used analytical laser induced liquid beam desorption in combination with high
resolution mass spectrometry (
) for the study of protonated amino acids (ornithine,
citrulline, lysine, arginine) and their non-covalently bound complexes in the gas phase desorbed
from water solutions. We report studies in which the desorption mechanism has been
investigated. The results imply that biomolecule desorption at
our conditions is a single step
process involving laser heating of the solvent above its supercritical temperature, a rapid
expansion, ion recombination and finally isolation and desorption of only a small fraction of
preformed ions and charged aggregates. In addition, we report an investigation of the aqueous
solution concentration and pH-dependence of the laser induced desorption of protonated species
(monomers and dimers). The experimental findings suggest that the desorption process depends
critically upon the proton affinity of the molecules, the concentration of other ions,
and of the pH
value of the solution. Therefore the ion concentrations measured in the gas phase very likely
reflect solution properties (equilibrium concentrations). Arginine self-assembles large
non-covalent singly protonated multimers (n=1...8) when sampled by IR laser induced water beam
desorption mass spectrometry. The structures of these aggregates may resemble those of the
solid state and may be preformed in solution prior to desorption. A desorption of mixtures of
amino acids in water solution enabled us to study (mixed) protonated dimers, one of the various
applications of the present technique. Reasons for preferred dimerization – leading to simple
cases of molecular recognition – as well as less preferred binding is discussed in terms of the
number of specific H-bonds that can be established in the clusters.
PACS: 82.80.Rt – Time of flight mass spectrometry / 87.15.-v – Biomolecules: structure and physical properties / 87.15.Nn – Properties of solutions; aggregation and crystallization of macromolecules
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2002
