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UNTERRICHT
Gunther Brunklaus and Hans-Wolfgang Spiess
1. INTRODUCTION
Dr. Gunther Brunklaus
MPI für Polymerforschung
Ackermannweg 10, D-55128 Mainz, Germany
Phone: +49 6131 379 240
FAX: +49 6131 379 100
E-Mail: brunklaus@mpip-mainz.mpg.de
62
SOLID STATE NMR OF
SUPRAMOLECULAR SYSTEMS
In the fi eld of materials science, the precise knowledge of structure
and dynamics of macromolecules and supramolecular
systems in principle allows for a rational design of well-defi ned
architectures with tailored properties, such as effi cient proton
exchange membranes 1 (that are used in fuel cells), photonic
sensors and devices 2 or gene delivery systems. 3 The physical
properties of (mainly organic) polymers and supramolecular
aggregates, for instance, can be substantially improved by controlling
their microstructure and processing conditions. Indeed,
the local arrangement of the respective building blocks within
the material relative to each other and their mobility on different
length- and time scales critically determine their specifi c
functions. 4 In fact, in supramolecular chemistry, 5 the same key
elements of organization 6 are used as in nature, namely, hydrogen
bonds, p-stacking, shape control, and surface effects
(cf. Fig. 1). At present, manifold complementary characterization
techniques such as scattering of light, 7 X-rays 8 and neutrons
9 , various forms of microscopy 10 as well as mechanical 11
and dielectric 12 relaxation are available.
Figure 1: Key elements of supramolecular assembly. 6
In addition, Nuclear Magnetic Resonance (NMR) spectroscopy
is a remarkably versatile and powerful tool that has found widespread
applications in materials science. 13 Since NMR allows
for element-specifi c observation of different nuclei, it provides
an outstanding selectivity for local environments. 14 Moreover,
Prof. Dr. Hans-Wolfgang Spiess
MPI für Polymerforschung
Ackermannweg 10, D-55128 Mainz, Germany
Phone: +49 6131 379 120
FAX: +49 6131 379 320
E-Mail: spiess@mpip-mainz.mpg.de
BUNSEN-MAGAZIN · 11. JAHRGANG · 2/2009
dynamic features can be studied over many decades of characteristic
times, ranging from picoseconds to minutes, 15 and
length scales from interatomic distances in the 100 pm range
up to a meter or so in NMR imaging. 16 This wealth of information
accessible by modern NMR spectroscopy is based on the
fact that a large variety of interactions of nuclear spins with
their local surroundings can be selectively exploited. 17 For a basic
description of the NMR experiment and a comprehensive
introduction to the interactions that possibly govern NMR spectra,
we refer to text books 15,17,18 and a previous article within
this series. 19 Indeed, the rich information content of solid-state
NMR spectra renders them rather diffi cult to handle, in particular
if several sources of line-broadening like dipole-dipole
couplings and quadrupolar interactions 20 have to be taken into
account. Recent developments in NMR methodology, however,
provide possibilities to selectively suppress and/or (re-)introduce
nuclear spin interactions where the different sources of
information can be separated and correlated using multidimensional
NMR techniques (see below).
Some advanced NMR techniques are introduced in Section
2, while Section 3 describes selected applications of studying
structure and dynamics of supramolecular structures based
on the key elements presented in Fig. 1, mostly taken from our
own laboratory.
2. NMR METHODOLOGY
In the following section, we describe selected versatile techniques
available in modern high-resolution solid-state NMR
spectroscopy. Most of them are based on either homo- or heteronuclear
dipolar couplings and facilitate studies of self-organisation
in the solid-state.
2.1. ANISOTROPIC SPIN INTERACTIONS
Information that can be extracted from (high-resolution) solidstate
NMR spectra is encoded via spin interactions such as
the chemical shift, the quadrupolar interaction, homo- and heteronuclear
dipolar interactions, as well as J-couplings. In principle,
the relevant spin interactions are anisotropic and can