Trapped Ion Dynamics Group
Current research projects in the Trapped Ion Dynamics Group are designed to study the
structural dynamics of nanoscale gas-phase species including small metal clusters and biomolecules.
Diffraction Measurements of Metal Cluster Symmetry
The study of small metal clusters has made extensive contributions to understanding
the size-dependent, many-body character of nanoscale physics and chemistry. Important examples
which have increased our appreciation of the different forms in which size dependence is manifest
include measurements and calculations of metal cluster melting, the transition of planar to
three-dimensional structures and the reactivity of gold cluster nanocatalysts. Measurements conducted
in our laboratory investigate the development of cluster structures with size range to develop an
understanding of how these structures evolve through intermediate sizes to achieve “magic number”
structures composed of closed electronic or atomic shells. The structural symmetries of cluster ions stored
within a quadrupole ion trap are probed by electron diffraction as a function of cluster size and
temperature. The experimental configuration enables the accumulation of size selected clusters, collisional
relaxation of the vibrational energy and adequate exposure time to collect electron diffraction data from
~104 clusters. It is precisely the ability to isolate a single cluster size having a well
defined temperature which provides for a controlled investigation of quantum size effects.
Biomolecule Dynamics and Interactions Probed by Fluorescence
The three-dimensional structures and dynamics of proteins and other biomolecules
play a central role in determining their unique functions in living organisms and their specific
interactions with other molecules. One major challenge of life science is to grasp how a given sequence
of amino acid residues gives rise to the native structure and function. We have developed a probe of
the conformational dynamics of unsolvated proteins and peptides that is based on modulation of the
fluorescence of a covalently attached dye through intramolecular quenching by tryptophan (Trp)
or other residues. These gas-phase measurements are used in combination with solution measurements
and theoretical calculations to advance our understanding of how the solvent environment affects the
behavior of biomolecules and non-covalent complexes.
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