For
the 2-mer, two families of conformers are predicted by theory that
have widely different energies and cross-sections (see plot at right).
The lowest-energy structures are folded so that the phenyl groups in the
chain stack on top of each other. The Na+ ion binds to the
two terminal OH groups and two carbonyl oxygen atoms (shown in purple
in the two figures below). The average cross-section of these folded forms
(133 ± 2 Å2) agrees very well with the experimental
value obtained from the ATDs (135 ± 2 Å2) shown
as the red shaded area in the plot. The higher-energy structures, with
an average cross-section of 160 ± 3 Å2, are quasi-linear
with the Na+ ion bound to two carbonyl oxygens near the middle
of the chain.
The
cross-section difference between the folded and linear forms of the 2-mer
is large enough (~20%) that if both species were present they should be
easily separated in the drift cell. However, only one peak is observed
in the 2-mer ATDs at all temperatures (80-550 K) and the cross-section
obtained from the ATD agrees very well with the value predicted for the
folded form. Thus, the higher-energy linear forms are not likely present
in the experiments.
Similar scatter plots and structures were also
predicted for the 2-mer cationized by Li+ and K+.
A
comparison between the experimental cross-sections obtained from the 300
K ATDs and the average cross-section predicted for the folded forms of
Li+PET2, Na+PET2, and K+PET2
are shown in the table (at left).
For
the 2-mer, two families of conformers are predicted by theory that
have widely different energies and cross-sections (see plot at right).
The lowest-energy structures are folded so that the phenyl groups in the
chain stack on top of each other. The Na+ ion binds to the
two terminal OH groups and two carbonyl oxygen atoms (shown in purple
in the two figures below). The average cross-section of these folded forms
(133 ± 2 Å2) agrees very well with the experimental
value obtained from the ATDs (135 ± 2 Å2) shown
as the red shaded area in the plot. The higher-energy structures, with
an average cross-section of 160 ± 3 Å2, are quasi-linear
with the Na+ ion bound to two carbonyl oxygens near the middle
of the chain.
A
comparison between the experimental cross-sections obtained from the 300
K ATDs and the average cross-section predicted for the folded forms of
Li+PET2, Na+PET2, and K+PET2
are shown in the table (at left).