DOI: 10.1002/chem.201502056
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Supramolecular Chemistry |Hot Paper|
Efficient Self-Assembly of Di-, Tri-, Tetra-, and Hexavalent Hosts
with Predefined Geometries for the Investigation of Multivalency
[
a]
[a]
[b]
[a]
[b]
Igor Linder, Stefan Leisering, Rakesh Puttreddy, Nadine Rades, Kari Rissanen, and
[a]
Christoph A. Schalley*
Abstract: Coordination-driven self-assembly of differently
shaped di- to hexavalent crown-ether host molecules is de-
scribed. A series of [21]crown-7- and [24]crown-8-substituted
bipyridine and terpyridine ligands was synthetized in a “tool-
box” approach. Subsequent coordination to 3d transition
metal and ruthenium(II) ions provides an easy and fast
access to host assemblies with variable valency and pre-de-
fined orientations of the crown-ether moieties. Preliminary
isothermal calorimetry (ITC) titrations provided promising re-
sults, which indicated the host complexes under study to be
suitable for the future investigation of multivalent and coop-
erative binding. The hosts described herein will also be suit-
able for the construction of various multiply threaded me-
chanically interlocked molecules.
Introduction
and guests with different predefined geometries and sizes is
crucial.
The interest in exploring and understanding multivalency phe-
nomena is steadily growing. This concept describes the molec-
ular-recognition events of two or more binding partners with
multiple binding sites, which often strengthens the binding in
the whole system despite the existence of only weak reversible
(Pseudo)rotaxanes based on the crown-ether/secondary di-
alkyl ammonium recognition motif are one of the widely used
[
4]
host–guest systems in supramolecular chemistry. Because
binding is relatively strong and exhibits pH responsiveness,
this recognition motif has been intensely utilized for the con-
[1]
[5]
interactions in each single binding site. Several studies al-
ready provided the basis for a better understanding of the
multivalency effect, in particular of the cooperativity of two or
struction of stimuli-responsive bistable rotaxanes. Recently,
[
6]
Bruns et al. reviewed rotaxane-based molecular muscles, of
which switchable polyrotaxanes containing tri- and tetravalent
crown ether and secondary ammonium ion platforms were
[2]
more binding events. For a systematic study, ligands and re-
ceptors with a predefined size, shape, and valency are re-
[
7]
presented. After deprotonation of the ammonium binding
sites, the host moieties switch to the second binding sites in-
ducing a contraction or expansion of these artificial muscles.
To enable the construction of such oligovalent assemblies,
a precise control over the size and shape of the molecules is
[
3]
quired. Nevertheless, certain flexibility is often advantageous,
because the binding between rigid counterparts often suffer
from thermodynamic, as well as kinetic constraints. Because
the influence of these parameters on the binding strength of
a multivalent complex is still not fully clear, further studies are
required to understand multivalent binding qualitatively and
quantitatively and to investigate cooperativity between the in-
dividual binding events. Synthetic hosts and guests have the
advantage that they can be systematically varied with respect
to, for example, the number of binding sites, their arrange-
ment in space, or the rigidity of the spacers connecting them.
Therefore, the design and synthesis of various sets of hosts
[
8]
required, because a mismatch may result in strain. Therefore,
designing the orientation of the binding sites of a single bind-
ing partner and in the final architecture is pivotal for assembly
formation.
Covalent synthesis allows an effective access to simple
model compounds, but becomes more challenging with in-
creasing complexity and number of binding sites of the de-
sired architectures. On the other hand, it often provides high-
yielding procedures for the syntheses of polyvalent com-
pounds, such as polymers or dendrimers; however, at the price
that control over the relative positions and orientations of the
binding sites is rather limited.
[
a] I. Linder, S. Leisering, N. Rades, Prof. C. A. Schalley
Institut für Chemie und Biochemie der Freien Universität Berlin
Takustrasse 3, 14195 Berlin (Germany)
In contrast, non-covalent chemistry proved to be a powerful
tool for constructing highly complex architectures with specific
E-mail: c.schalley@fu-berlin.de
[
9]
[
b] Dr. R. Puttreddy, Prof. K. Rissanen
University of Jyvaskyla, Department of Chemistry
Nanoscience Center, P.O. Box. 35
functions from much simpler building blocks. Self-assembly
and self-sorting together with coordination chemistry allow to
efficiently program the structure by virtue of reversibility and,
as a consequence, error correction. Especially, the use of coor-
dination chemistry turned out to be an efficient tool for
4
0014 University of Jyvaskyla (Finland)
Chem. Eur. J. 2015, 21, 13035 – 13044
13035
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim