origin or comprise thermodynamic phase separation, which typically do not induce
preferred directions. One exception is the intramolecular β-sheet formation of the
side chains in cylindrical brush structures with PLL side chains, which originate
from intramolecular hydrogen bonds. The latter belongs to the class of interactions
that induce a certain orientation. Such directional interactions are the main subject
of this section, where more complex and highly ordered supramolecular structures
are described on the basis of hydrogen bonds and shape-dependent π–π interactions.
Here the investigations are focused on the interplay of both types of interactions
occurring in the same system.
A particularly valuable tool for studying intra- and intermolecular interactions is
solid-state NMR. Advanced solid-state NMR, combined with X-ray scattering and
computer simulation, provides site-selective and noninvasive information of
noncovalent interactions such as hydrogen bonding and π–π interactions. For this
reason, we first briefly introduce the NMR techniques and then describe specific
applications to macromolecular and supramolecular systems, including hybrids of
synthetic polypeptides, hybrids containing synthetic polymers, polymers with
incompatible segments, and systems containing rigid rods or rings.
4.2 Solid-state NMR Techniques for Analyzing Structure
and Dynamics
Signals originating from hydrogen-bonded protons are well separated in
1
H magicangle spinning (MAS) NMR spectra, typically resonating between 8 and 20 ppm
[160]. The
1
H chemical shift includes semiquantitative information about the strength
of the hydrogen bonds. In addition, the
1
H chemical shift is also a sensitive probe with
respect to ring currents associated with aromatic moieties [161]. This is observed as a
low field shift of the chemical shift compared to the corresponding liquid state signal
and may thereby serve as a direct indication of π–π interactions. Likewise, the low
field shift can be simply related to the packing via so-called nucleus independent
chemical shift (NICS) maps [162]. This augments the well-known sensitivity of
13
C
NMR chemical shifts to local conformation [163]. Detailed packing information is
obtained from distance measurements between specific proton sites at adjacent
building blocks via high resolution double quantum (DQ) solid-state NMR under
MAS. Disk-shaped moieties that stack into columnar structures known as discotic
liquid crystals have been studied extensively. In the liquid crystalline (LC) phase, the
disks rotate about the column axis. A particularly simple way of characterizing such
restricted molecular dynamics is provided by the dynamic order parameter S, where
0 S 1. It is defined as the ratio between the motionally averaged and the static
anisotropic NMR interaction, e.g., dipole–dipole coupling, anisotroc chemical shift,
or quadrupole coupling [160]. For the rotation of disks in a perfectly packed column,
166
K. Binder et al.
preferred directions. One exception is the intramolecular β-sheet formation of the
side chains in cylindrical brush structures with PLL side chains, which originate
from intramolecular hydrogen bonds. The latter belongs to the class of interactions
that induce a certain orientation. Such directional interactions are the main subject
of this section, where more complex and highly ordered supramolecular structures
are described on the basis of hydrogen bonds and shape-dependent π–π interactions.
Here the investigations are focused on the interplay of both types of interactions
occurring in the same system.
A particularly valuable tool for studying intra- and intermolecular interactions is
solid-state NMR. Advanced solid-state NMR, combined with X-ray scattering and
computer simulation, provides site-selective and noninvasive information of
noncovalent interactions such as hydrogen bonding and π–π interactions. For this
reason, we first briefly introduce the NMR techniques and then describe specific
applications to macromolecular and supramolecular systems, including hybrids of
synthetic polypeptides, hybrids containing synthetic polymers, polymers with
incompatible segments, and systems containing rigid rods or rings.
4.2 Solid-state NMR Techniques for Analyzing Structure
and Dynamics
Signals originating from hydrogen-bonded protons are well separated in
1
H magicangle spinning (MAS) NMR spectra, typically resonating between 8 and 20 ppm
[160]. The
1
H chemical shift includes semiquantitative information about the strength
of the hydrogen bonds. In addition, the
1
H chemical shift is also a sensitive probe with
respect to ring currents associated with aromatic moieties [161]. This is observed as a
low field shift of the chemical shift compared to the corresponding liquid state signal
and may thereby serve as a direct indication of π–π interactions. Likewise, the low
field shift can be simply related to the packing via so-called nucleus independent
chemical shift (NICS) maps [162]. This augments the well-known sensitivity of
13
C
NMR chemical shifts to local conformation [163]. Detailed packing information is
obtained from distance measurements between specific proton sites at adjacent
building blocks via high resolution double quantum (DQ) solid-state NMR under
MAS. Disk-shaped moieties that stack into columnar structures known as discotic
liquid crystals have been studied extensively. In the liquid crystalline (LC) phase, the
disks rotate about the column axis. A particularly simple way of characterizing such
restricted molecular dynamics is provided by the dynamic order parameter S, where
0 S 1. It is defined as the ratio between the motionally averaged and the static
anisotropic NMR interaction, e.g., dipole–dipole coupling, anisotroc chemical shift,
or quadrupole coupling [160]. For the rotation of disks in a perfectly packed column,
166
K. Binder et al.