alongside DNP protons experience similar changes in chemical shifts as the BIPY
2+
and encircled DNP resonances, which would not be expected if they were not also
participating in π–π stacking interactions.
In addition to these accumulated aromatic ring-current shifts, a number of
through-space correlations between alongside DNP protons and the BIPY
2+ protons
of CBPQT
4+ verify that the folded structure contributes significantly to the average
solution-state secondary structure of these oligorotaxanes. A detailed
co-conformational analysis [114] revealed that the oligorotaxane foldamers are
quite dynamic in solution. The alongside DNP units and DNP & CBPQT
4+
subcomplexes execute rapid 180
rotations within the D–A stack on the
1 H NMR
timescale in a process we call “superrotation,” which leads to signal averaging of
otherwise constitutionally heterotopic protons. The complicated dynamics of these
compounds calls for more specialized analytical techniques and computational
modeling to gain a deeper understanding of the timescales involved and the
alternative co-conformations that are accessed as intermediates.
4 Computational Evaluation of D–A
Oligo-Pseudorotaxanes
As the evolution of molecular nanotechnology carries us closer to the rational
design and synthesis of macromolecules with three-dimensional geometries and
properties that rival the intricacy and functionality of Nature’s proteins and
enzymes, more and more demands will be placed on the predictions of chemical
theory. Collaboration between theorists and experimentalists is therefore
Fig. 11 The changes in chemical shift of DNP and BIPY
2+ protons of the Happy oligorotaxanes
with respect to their parent non-interlocked components, plotted against the number of components in the oligorotaxane. The DNP proton traces are separated into alongside DNP units (a 2 /a 6 ,
a 3 /a 7 , a 4 /a 8 ) and inside DNP units (i 2 /i 6 , i 3 /i 7 ), corresponding to their positions in the molecules
with respect to CBPQT
4+
288
C.J. Bruns and J.F. Stoddart
2+
and encircled DNP resonances, which would not be expected if they were not also
participating in π–π stacking interactions.
In addition to these accumulated aromatic ring-current shifts, a number of
through-space correlations between alongside DNP protons and the BIPY
2+ protons
of CBPQT
4+ verify that the folded structure contributes significantly to the average
solution-state secondary structure of these oligorotaxanes. A detailed
co-conformational analysis [114] revealed that the oligorotaxane foldamers are
quite dynamic in solution. The alongside DNP units and DNP & CBPQT
4+
subcomplexes execute rapid 180
rotations within the D–A stack on the
1 H NMR
timescale in a process we call “superrotation,” which leads to signal averaging of
otherwise constitutionally heterotopic protons. The complicated dynamics of these
compounds calls for more specialized analytical techniques and computational
modeling to gain a deeper understanding of the timescales involved and the
alternative co-conformations that are accessed as intermediates.
4 Computational Evaluation of D–A
Oligo-Pseudorotaxanes
As the evolution of molecular nanotechnology carries us closer to the rational
design and synthesis of macromolecules with three-dimensional geometries and
properties that rival the intricacy and functionality of Nature’s proteins and
enzymes, more and more demands will be placed on the predictions of chemical
theory. Collaboration between theorists and experimentalists is therefore
Fig. 11 The changes in chemical shift of DNP and BIPY
2+ protons of the Happy oligorotaxanes
with respect to their parent non-interlocked components, plotted against the number of components in the oligorotaxane. The DNP proton traces are separated into alongside DNP units (a 2 /a 6 ,
a 3 /a 7 , a 4 /a 8 ) and inside DNP units (i 2 /i 6 , i 3 /i 7 ), corresponding to their positions in the molecules
with respect to CBPQT
4+
288
C.J. Bruns and J.F. Stoddart