Dynamic Molecular Invasion into a Multiply Interlocked Catenane

Article abstract of DOI:10.1002/anie.201708248

A multiply interlocked catenane with a novel molecular topology was synthesized; a phthalocyanine bearing four peripheral crown ethers was quadruply interlocked with a cofacial porphyrin dimer bridged with four alkylammonium chains. The supramolecular conjugate has two nanospaces surrounded by a porphyrin, a phthalocyanine, and four alkyl chains to accommodate guest molecules. Because the phthalocyanine can move along the alkyl chains, it acts as an adjustable wall, thus permitting the invasion of large molecules into the nanospaces without spoiling the affinity of the association. The dynamic molecular invasion allowed the intercalation of dianionic porphyrins into both nanospaces with high affinity. A photometric titration experiment revealed the two-step inclusion phenomenon. The multiply interlocked catenane complexed with three Cu²⁺ ions, and the spin–spin interaction was switched off by the intercalation of dianionic porphyrins.

Full text of DOI:10.1002/anie.201708248

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Accepted Article
Title: Dynamic Molecular Invasion into Multiply Interlocked Catenane
Authors: Yasuyuki Yamada, Ryohei Ito, Sayaka Ogino, Tatsuhisa Kato,
and Kentaro Tanaka
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201708248
Angew. Chem. 10.1002/ange.201708248
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10.1002/anie.201708248
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Dynamic Molecular Invasion into Multiply Interlocked Catenane
Yasuyuki Yamada[a], [b], Ryohei Itoh[a], Sayaka Ogino[a], Tatsuhisa Kato[c], and Kentaro Tanaka[a],*
Abstract: A multiply interlocked catenane with a novel molecular
topology was synthesized; a phthalocyanine bearing four peripheral
crown ethers was quadruply interlocked with a cofacial porphyrin
dimer bridged with four alkylammonium chains. The supramolecular
conjugate has two nanospaces surrounded by a porphyrin, a
phthalocyanine, and four alkyl chains to accommodate guest
molecules. Because the phthalocyanine is movable along the alkyl
chains, it acts as an adjustable wall, permitting the invasion of large
molecules to the nanospaces without spoiling the affinity of the
association. The dynamic molecular invasion allowed the
intercalation of dianionic porphyrins into both the nanospaces with a
high affinity. A photometric titration experiment revealed the two-step
inclusion phenomenon. The multiply interlocked catenane
complexed with three Cu2+ ions, and the spin–spin interaction was
switched off by the intercalation of dianionic porphyrins.
are attracted to one of the recognition sites, the planar core with
the rings still has the ability to move along the threads. This is
because the affinity between the ring and recognition point does
not help to anchor the ring at this position, but only increases the
probability of the position. This flexibility of the interlock linkage
satisfies the requirement of the dynamic invasion of a guest
molecule. The molecular system permits the invasion of a large
guest molecule by expanding the access and stabilizing the
host–guest interaction by induced fit based on the interactions
between the ring and recognition point (Figure 1).
Induced fit is an important concept for protein–ligand
interactions; this lowers the final-state energy by a dynamic
conformational change of the host to fit the guest molecules,
maximizing their affinity through enthalpy increase.[1] On the
other hand, if the host has a narrow access for incorporating the
guest, the transition process during the complexation requires a
higher activation energy. Although the access to the host can be
expanded to lower the activation energy, such as flexibility would
generally decrease the affinity between the host and guest,
because the flexibility causes a larger entropy loss during the
complexation. Hence, to improve the accessibility of the guest to
the host without losing the affinity, it would be advantageous to
introduce another concept to couple with induced fit.
Figure 1. Schematic representation of the dynamic invasion of large guest
molecules into a mechanically interlocked host.
Recently, we reported a four-fold rotaxane composed of a
porphyrin with four alkylammonium chains and a phthalocyanine
with four peripheral crown ethers.[10] Two porphyrinoids faced
each other and formed a nanospace with four alkyl pillars in the
supramolecular conjugate. In this paper, we report the structural
expansion of the conjugate to a D4h symmetrical mechanically
interlocked molecule [H61·4H]4+ with a novel molecular topology
(Figures 2a and 2b) and the dynamic invasion phenomenon of
the multiply interlocked catenane. A phthalocyanine bearing four
peripheral crown ethers was quadruply interlocked with a
porphyrin dimer bridged with four alkylammonium chains in the
catenane. Consequently, three -planar components were
cofacially assembled through the flexible linkages, producing
two nanospaces separated by the phthalocyanine that acted as
an adjustable wall along the four threads. It was envisioned that
the nanospaces would accommodate planer guest molecules
using – interactions through dynamic molecular inclusion.[11]
A
molecular elevator[2,3] is
a
molecular machine[4–9]
composed of two planar molecular components joined with more
than two interlock linkages. The component with macrocyclic
rings fused with
a planar core can move between two
competitive recognition sites through the linear threads attached
on the other planar component. Strength of the interactions
between the recognition sites is modulated by external stimuli
such as pH switching, changing the relative position of the two
planar components. However, although the macrocyclic rings
[a]
Dr. Y. Yamada, Mr. R. Itoh, Ms. S. Ogino, Prof. Dr. K. Tanaka
Department of Chemistry, Faculty of Science
Nagoya University
Furo-cho, Chikusa-ku, Naogya, 464-8602 (Japan)
E-mail: kentaro@chem.nagoya-u.ac.jp
Dr. Y. Yamada
Research Center for Materials Science
Nagoya University
[b]
[c]
Furo-cho, Chikusa-ku, Naogya, 464-8602 (Japan)
Prof. Dr. T. Kato
Department of Interdisciplinary Environment, Graduate School of
Human and Environmental Studies
Kyoto University
Yoshidanihonmatsu-cho, Sakyo-ku, Kyoto, 606-8501 (Japan)
Supporting information for this article is given via a link at the end of
the document.
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The multiply interlocked catenane [H61·4H]4+·4Cl– was
synthesized as summarized in Figure 2c by utilizing the four-fold
rotaxane formation method reported previously.[10,12] A porphyrin
template bearing four alkylammonium sidechains with terminal
benzaldehyde moieties [H23·4H]4+·4BARF– was complexed with
1 equiv of a phthalocyanine bearing four peripheral 24-crown-8
units 2, affording a four-fold pseudorotaxane. Condensation of
the four terminal benzaldehyde units of the pseudorotaxane with
4 equiv of pyrrole in the presence of BF3·OEt2, followed by
oxidation with chloranil, successfully furnished the second
porphyrin ring, simultaneously forming six macrocycles
consisting of four alkyl chains and two porphyrins as the four-
way nodes. Each alkyl chain went through the peripheral crown
ethers on the phthalocyanine. Consequently, the phthalocyanine
was entrapped in the four-pillared conjugate by multiple
catenane linkages, affording [H61·4H]4+·4Cl–. The compound
showed ion peaks corresponding to the multiply interlocked
molecule in the electrospray ionization time-of-flight (ESI-TOF)
mass spectrum (Figure S10). Surprisingly, the 1H-NMR
spectrum indicated the highly symmetrical D4h structure of
[H61·4H]4+·4Cl–, and the spectrum was assignable as one-eighth
part of the entire structure of [H61·4H]4+ despite the intricate
structure (Figures 3, S11 and S12). The simple symmetry
suggests that all the alkylammonium chains of the cage were
mechanically interlocked inside each crown ring on the
phthalocyanine. Notably, the signals of the pyrrolic NH protons
of both the porphyrin and phthalocyanine (Ha and H in Figure 3,
respectively) showed significant high-field shifts from those of
each component themselves, indicating a close cofacial stacking
of the porphyrins form both sides of the phthalocyanine,
because the chemical shifts of the signals have similar tendency
as those of the pyrrolic NH protons of closely stacked
phthalocyanines in a conjugate composed of stacked porphyrins
and phthalocyanines reported previously.[10a,12] Because the
length of the C10 alkyl chains connecting the porphyrins with the
central phthalocyanine (13 Å) is much longer than the stacking
Figure 2. (a) Chemical structure of a multiply interlocked catenane [H61·4H]4+
(b) Generic topology of [H61·4H]4+. (c) Synthetic procedure of [H61·4H]4+·4Cl–.
.
Figure 3. (a) 1H-NMR spectrum (400 MHz) of the multiply interlocked catenane [H61·4H]4+·4Cl– was obtained in CD2Cl2 at 293 K. The signals labeled with a–
q can be assigned to the resonance of the porphyrin dimer quadruply connected through the alkylammonium chains (shown in pink), and the signals labeled
with – can be assigned to the resonances of the phthalocyanine unit (shown in orange).
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Figure 4. (a) Schematic representation of the deprotonation of the ammonium ions of the trinuclear Cu(II) complex [Cu31·4H]4+. (b) Spectral change during the addition of
0–10 equiv of phosphazene P1-tBu base. [Cu31·4H]4+·4Cl– was dissolved in CH2Cl2 at a concentration of 2 M at 293 K. Inset: Titration curve monitored by the absorption
change at 693 nm.
distance between a porphyrin and phthalocyanine (3–4 Å), the
alkyl chains should be bent or twisted along the stacking axis in
CH2Cl2. The D4h symmetrical 1H-NMR spectrum in CD2Cl2
indicates that each component moves faster compared to the
NMR timescale at room temperature. It is probable that the
flexible interlocked linkages in [H61·4H]4+·4Cl– also enhance the
dynamic conformational change in the solution.
the ammonium ion to the lone pairs of the oxygen atoms.[13,14]
Therefore, deprotonation of the ammonium ions would result in a
relational change of the porphyrins and phthalocyanine in the
conjugate. The addition of a phosphazene base (P1-tBu) caused
significant spectral changes in the UV–visible absorption spectra
of the trinuclear Cu2+ complex ([Cu31·4H]4+·4Cl–) in CH2Cl2
(Figure 4). As the concentration of P1-tBu against
[Cu31·4H]4+·4Cl– was increased, the intensity of the Q-bands of
the phthalocyanine and the Soret bands of the porphyrins
gradually increased with hypsochromic and bathochromic shifts,
respectively. These changes can also be attributed to the
changes in the stacking structure in [Cu31·4H]4+ caused by the
deprotonation of the ammonium protons, affording the fully
deprotonated species Cu31. Apparent isosbestic points on the
spectra and sigmoidal shape of the titration curve indicate that
the deprotonation of the ammonium ions of [Cu31·4H]4+ occurred
in a concerted fashion. The CW-EPR spectrum of Cu31 was
reproducible in a simulation as the S = 1/2 pattern in the ground
state resulted from the alternation of one of the three spins to
antiferromagnetic (Figures 5b and S16). The deprotonation led
to only a small change in the distance between the metal
centers within the boundary, where significant dipole interactions
were observed between the electron spins (at the zero-field
splitting parameter D = 25 mT), but the orbital overlapping of the
three Cu(II) complexes dynamically changed between
ferromagnetic and antiferromagnetic interactions. Hence, it can
be concluded that the deprotonation induced the rotation or
slipping in the stacking of the complexes, thus increasing the
orbital overlapping between the radicals (Figure 5c).
Because of the stacking interactions between the
phthalocyanine and porphyrins, the UV–visible spectrum of
[H61·4H]4+·4Cl– in CH2Cl2 showed a significant bathochromic
shift and broadening of the Q-bands of the phthalocyanine unit
and a hypsochromic shift of the Soret band of the porphyrin units
as shown in Figure S13. Similar spectral features were observed
in the UV–visible spectrum of [Cu31·4H]4+·4Cl– in CH2Cl2 (red
line in Figure S14), and a close stacking between the Cu-
phthalocyanine and Cu-porphyrins in [Cu31·4H]4+·4Cl– is
expected. In fact, a distinct spin–spin interaction was observed
between the three Cu2+ spins in [Cu31·4H]4+·4Cl– in the
continuous-wave electron paramagnetic resonance (CW-EPR)
spectrum of [Cu31·4H]4+ in a frozen CH2Cl2 solution measured at
4 K (Figure 5a). The quartet state (S = 3/2) in the ground state
was evidenced by the temperature dependence of the signals
from 4 K to 40 K and explains the ferromagnetic interaction
among the three radicals on the Cu centers (Figure S15). The
interactions between the ammonium ions and the crown ethers
in the catenane were stabilized by the electrostatic interactions
between the positive charge on the ammonium ion and the
slightly negative core of the crown ether derived from the dense
ether oxygens as well as by the hydrogen bonding arising from
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Figure 5. (a) Experimental (red curve) and simulated (black curve) ESR spectra of the trinuclear Cu(II) complex [Cu31·4H]4+·4Cl– in the absence of
phosphazene base (P1-tBu) in CH2Cl2 at 4 K ([[Cu31·4H]4+·4Cl–] = 500 M). (b) Experimental (blue curve) and simulated (black curve) ESR spectra of
[Cu31·4H]4+·4Cl– in the presence of 8 equiv of phosphazene base (P1-tBu) in CH2Cl2 at 4 K ([[Cu31·4H]4+·4Cl–] = 500 M). (c) Schematic representation of
the spin–spin interaction of the dx2y2 orbitals inside the multiply interlocked catenane before and after the deprotonation of ammonium ions.
In the multiple catenane, although the phthalocyanine is
closely stacked with the porphyrins, the caged structure has a
high potential to be a molecular host for functionalized molecular
assemblies. The multiple catenane has the structural features of
a host for anionic porphyrins, because it has four ammonium
moieties and a couple of cages surrounded by a porphyrin, a
phthalocyanine, and four alkyl pillars. Planer anionic porphyrins
could be captured into the cages by a combination of –
stacking and electrostatic interactions. Moreover, the most
salient feature of the cages is the frontages that are flexibly
extensible by the molecular-elevator motion of the
phthalocyanine on the alkylammonium rails. Figure 6 shows the
photometric titration of the multiple catenane [Cu31·4H]4+·4Cl–
with 5,15-bis(4-sulfonatophenyl)-10,20-diphenylporphyrin (trans-
TPPdiS2–) with a large -planer structure and two anions. Trans-
TPPdiS2– is slightly larger for sliding into the cage through the
window, because the peripheral phenyl rings are orthogonal to
the porphyrin plane. However, the addition of an increasing
was able to slip into the cage and quantitatively complexed with
[Cu31·4H]4+ in a stepwise manner to form a stable 1:2 complex
even in this highly diluted condition, which indicates two binding
events were not cooperative, but the first guest affected the
second binding. It is reasonable to consider that the frontages of
the cages extended flexibly to adapt the penetration of the
guests. Although the guest inclusion process does not need
deprotonation from ammonium moieties, the first hyperchromic
shifts remind the spectral change in Figure 4(b). It is probably
because geometrical correlation of the guest and phthalocyanine
is similar with the porphyrin-phthalocyanine interaction in [Cu31].
The second hypochromic shifts can be attributed to the tight
stacking of the trans-TPPdiS2– to the phthalocyanine. These
spectral changes provide
a description of the stacking
interactions affecting the phthalocyanine.
To clarify the intercalation phenomenon of trans-TPPdiS2–,
the EPR spectrum of the complex was obtained in frozen
dichloromethane at 4 K (Figure S17). In sharp contrast to the
spectrum in the absence of trans-TPPdiS2–, the spectrum of
[Cu31·4H]4+:trans-TPPdiS2– = 1:2 complex showed a typical
doublet (S = 1/2) pattern corresponding to the isolated spins of
the Cu2+ ions, indicating negligible spin–spin interactions
between the three Cu2+ spins owing to the accommodation of
two trans-TPPdiS2– in the two different nanospaces of
[Cu31·4H]4+. Thus, we demonstrated the discrete quintuple
arraying of porphyrinoids through dynamic molecular
incorporation into the flexible and adaptable cages in the
amount of trans-TPPdiS2– from
[Cu31·4H]4+·4Cl– (2 M) caused
0
to
1
equiv against
a
spectral change with
hyperchromic shifts in the Q-bands of the phthalocyanine unit
and the spectra through isosbestic points. Furthermore,
subsequent addition of 1 to 2 equiv of trans-TPPdiS2– resulted in
a different course of spectral change with hypochromic shifts of
the Q-bands and the spectra through other isosbestic points.
Linear titration curves were obtained in each step as shown in
the inset of Figure 6. These results indicate that trans-TPPdiS2–
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Figure 6. (a) Schematic representation of the complexation of [Cu31·4H]4+·4Cl– with two dianionic porphyrins. (b) UV–visible spectral change of the trinuclear
Cu(II) complex [Cu31·4H]4+·4Cl– (2 M) during the addition of 0–1 equiv of a dianionic porphyrin trans-TPPdiS2–. (c) UV–visible spectral change of the
trinuclear Cu(II) complex [Cu31·4H]4+·4Cl– (2 M) during the addition of 1–2 equiv of a dianionic porphyrin trans-TPPdiS2– in CH2Cl2 at 293 K. (d) Titration
curve monitored by the absorption change at 710 nm.
multiple interlocked catenane and strong interactions among the
porphyrinoid components as evidenced from the UV–visible
spectra.
Nagoya University for elemental analysis. This work was
financially supported by a JSPS KAKENHI Grant-in-Aid for
Scientific Research (A) (Number 15H02167) to KT, JSPS
KAKENHI Grant-in-Aid for challenging Exploratory Research
(Number 16K13961) and the Tokuyama Science Foundation to
YY.
In conclusion, we constructed a new molecular topology
consisting of multiply interlocked catenanes [H61·4H]4+ and
[Cu31·4H]4+, where a phthalocyanine bearing four peripheral
crown ethers was entrapped in a quadruply interlocked structure
in a pillared conjugate consisting of two porphyrins joined with
four alkylammonium chains, affording two symmetrical cages.
The linkages composed of crown ethers and alkylammonium
chains provide important mechanisms for both the dynamic
conformational transition triggered by external stimuli and
dynamic molecular invasion using the movable phthalocyanine
as an adjustable wall. The former dynamic function resulted in
the switching of the spin–spin interaction of the trinuclear Cu(II)
complex by inducing rotation in the tacking of the
supramolecular conjugate. The latter dynamic invasion
phenomenon is based on the electrostatic and – interactions
via keeping the window open compensated by the positional
flexibility of the crown ethers on the alkylammonium chains.
Commonly, in molecular inclusion phenomena or molecular
recognition processes, flexibility on the molecular size or shape
of a host molecule is incompatible with a high affinity of
association and accuracy of selectivity. However, the interlock
system accommodates the size of a guest molecule without
affecting the affinity of the association. This approach could
expand the design of molecular host–guest systems.
Keywords: Catenane, Rotaxane, Molecular Cage, Molecular
Inclusion
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Acknowledgements
We thank Dr. Kin-ichi Oyama of the Chemical
Instrumentation Facility, Research Center for Materials Science,
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Table of Contents
COMMUNICATION
A
multiply interlocked catenane
Dr. Yasuyuki Yamada, Ryohei Itoh,
Sayaka Ogino, Prof. Dr. Tatsuhisa
Kato, and Prof. Dr. Kentaro Tanaka*
having novel molecular topology
was synthesized. The catenane
has movable phthalocyanine along
the threads and showed dynamic
invasion phenomena by adaptation
to the size of a guest molecule
without affecting the affinity of the
association.
Page No. – Page No.
Dynamic Molecular Invasion into
Multiply Interlocked Catenane
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