Photoswitchable rotaxanes on gold nanoparticles

Article abstract of DOI:10.1039/c1ob05128h

We studied rotaxanes that consisted of a molecular axle, with a photoactive 9-Aryl-9-methoxy-acridane moiety at one end, and a tetracationic ring of cyclobis(paraquat-p-phenylene) (CBQT⁴⁺). The aim of the study was to deposit the axle ends onto

Full text of DOI:10.1039/c1ob05128h

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PAPER
Photoswitchable rotaxanes on gold nanoparticles†
Yingxin Duo, Sabine Jacob and Werner Abraham*
Received 24th January 2011, Accepted 28th February 2011
DOI: 10.1039/c1ob05128h
We studied rotaxanes that consisted of a molecular axle, with a photoactive 9-Aryl-9-methoxy-acridane
moiety at one end, and a tetracationic ring of cyclobis(paraquat-p-phenylene) (CBQT4+). The aim of
the study was to deposit the axle ends onto gold nanoparticles (AuNPs). First, we introduced thioctic
acid into the axle molecules. Then, rotaxanes were deposited on AuNPs by two methods: 1)
Pseudorotaxanes were deposited on the gold surface by forming rotaxanes with the AuNP as a
terminator to prevent unthreading of the ring structure; and 2) a chain containing the thioctic ester was
introduced into a complete rotaxane, and then it was deposited on the AuNP with the aid of an
exchange process. The photoheterolysis of the acridane unit resulted in formation of the corresponding
acridinium methoxide; this, in turn, could thermally react to return to the acridane moiety. Due to the
creation of a positive charge, the ring moved from the acridane station to a second, evasive station
within the axle. This switching cycle could also take place when deposited on the gold surface. However,
on the gold surface, the ring movement associated with the switching process was unidirectional.
phenylene) (CBQT4+). Their behaviours in solution have been
1. Introduction
studied previously.7 The switching principle consists of the pho-
toheterolysis of the acridanes that form the 9-arylacridinium
methoxides. The thermal attack of the methoxide ion on the
acridinium ion rebuilds the acridane, thus completing the switch-
ing cycle. 9-Arylacridanes are photoresponsive molecular switches
that change their geometry, redox potential, and colour upon for-
mation of the corresponding acridinium moiety. The acridinium
compounds are metastable and can exist only as long as light is
provided. The lifetime of the rotaxanes in their “acridinium state”
depends strongly on the composition of the solvent.7 However,
to realise the full potential of these rotaxanes, a triggered motion
is required at the transducing surfaces that makes them behave
coherently relative to the surface.
Herein, we describe the photochemical behaviour of rotaxanes
deposited on gold nanoparticles (AuNPs). Metal NPs have stim-
ulated increasing interest in the past decade.8 Several switchable
molecules deposited on NPs have previously been studied with UV-
Vis-spectroscopy and electrochemical methods.9 However, to the
best of our knowledge, photoswitchable, interlocked molecules,
like rotaxanes, deposited on AuNPs have not been previously
described.
Rotaxanes are supramolecules composed of a threadlike molecule
(axle) that incorporates recognition stations and a ring; these two
components are mechanically interlocked. Bistable rotaxanes have
at least two recognition stations; they are molecular shuttles in
which the ring position may be altered. Energy for the shuttling
process stems from Brownian motion.1 Provided that the two
stations have sufficiently different interaction strengths with the
ring, the ring will reside preferably on one of the two recognition
stations. When an outer stimulus weakens the strong interaction
of the station on which the ring resides, the ring will move to the
station with the originally weaker interaction. Thus, a complete
rearrangement of the mechanically bonded components will occur,
i.e., a co-conformation,2 and the shuttle process is referred to as a
switch.1
Solvent,3 chemicals,4 electrons,5 or light can all serve as stimuli
for the switching process. The advantage of light driven systems
is that no chemical fuels are necessary and no waste products are
formed. The reset can be accomplished either photochemically or
thermally.6
Control over the relative position and motion of components
in interpenetrated molecules, like rotaxane supramolecules, may
impart machine-like properties. We have previously reported that
photoswitchable rotaxanes have a switching unit of 9-methoxy-
9-aryl-acridane and a ring component of cyclobis(paraquat-p-
2. Results and Discussion
The immobilisation of photoswitchable rotaxanes on AuNPs is
associated with at least two problems: (1) A functional group
containing sulfur has to be introduced into the rotaxane in order
to use the thiophilicity of gold for attachment; moreover, the
functional group should not interfere with the shuttle movement
of the rotaxanes. (2) Because the gold surface is able to quench
Institute of Chemistry, Humboldt-Universita¨t zu Berlin, Brook-Taylor-Str.
2, D-12489, Berlin, Germany. E-mail: abraham@chemie.hu-berlin.de
† Electronic supplementary information (ESI) available: Additional ex-
perimental information, UV-vis and NMR spectra of selected com-
pounds and transients; assignment of protons of rotaxanes. See DOI:
10.1039/c1ob05128h
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photoexcited states,8,10 the photoreactivity of the photoswitch
bound to the gold has to be protected in order to produce a reaction
similar to that of the same molecules in solution. A spacer unit
between the gold surface and the photoswitch of the rotaxane
would be advantageous.
2.1 Syntheses
The molecular threads 2 and 4, both containing a thioctic
ester unit, were synthesised, starting from the previously reported
threads 1 and 37 (Scheme 1). The acridinium compounds 2 and 4
were easily transformed into the photoactive acridane compounds
5 and 6, which can form pseudorotaxanes with the tetracationic
ring, CBQT4+.
A rotaxane with a thioctic acid as an anchor group was
synthesised, starting with the protected N-alkyl acridinone 7
(Scheme 2). The pseudorotaxane formed with molecular thread
10 and CBQT4+ was reacted with adamantoyl chloride to give
rotaxane 11 after purification (Scheme 3). Again, the photoactive
rotaxane was available by reaction of the acridinium rotaxane with
methanol.
Despite the exclusion of air with an argon atmosphere during the
preparation, the disulfide bridge was partly oxidised. Nevertheless,
the anchor group was able to function (see below).
2.2 Co-conformation of rotaxanes 12 and 13
Apart from the substituent at the N-atom of the acridinium and
acridane moieties, rotaxanes 12 and 13, respectively, were identical
to the rotaxanes that bore a methyl group at the same position,
which were previously characterised.7
The chemically-induced shifts of specific proton signals, both
1
on the ring and on the axle, that were manifest in the H-NMR
spectra indicated the strength of the interactions between specific
regions of the axle with the ring compound. The NMR data
of 12 were fully consistent with a rotaxane co-conformation, in
which the ring surrounded station B. The proton resonances of
the acridinium unit were not shifted with respect to those of the
axle in compound 9. In contrast, the interactions between the ring
and station B were accompanied by significant upfield shifts of
the aromatic proton resonances and the adjacent protons of the
polyether chain; this was caused by strong diamagnetic shielding
due to the p-stacking of the bipyridinium ring and station B
aromatic systems (Scheme 3 and S3, ESI†).
In contrast to rotaxane 12, the proton signals in the 1H NMR
spectra of CBQT4+ and of the aryl protons of stations A and B on
rotaxane 13 were broad or even merged with the baseline at room
temperature (Fig. S1 and S2†). However, the proton signals of the
propoxy chain of station B were quite sharp, and therefore, they
could be assigned. These proton resonances were low-field shifted
compared to those of rotaxane 12, and they were identical to the
proton resonances of compound 10.
Scheme 1 Synthesis of axles containing thioctic ester.
On the other hand, the protons of the acridane subunit and
the methoxy group were low-field shifted due to their location
at the edge of the ring. Both findings, taken together, clearly
and could be assigned by C–H-, H–H-COSY, and ROESY spectra.
The protons of station A were upfield shifted by 2.5 and 3.9 ppm
(Fig. S2b†). Due to the asymmetry of the axle, the bipyridinium
protons appeared as four broad singlets, and the protons of the
methylene groups of CBQT4+ were split into two doublets of the
AB-system (Scheme S4†).
1
demonstrated the occupancy of station A by the ring. H NMR
spectra recorded at lower temperatures revealed that the tetra-
cationic cyclophane encircled station A. At 233◦K, signals were
much sharper; the aryl protons of the two stations were apparent
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Scheme 2 Synthesis of protected axles.
2.3 Synthesis of capped AuNPs
with >300 nm light in dichloromethane (DCM)/methanol (8 : 2)
solution. The UV-Vis absorption spectrum corresponded to that
of the free compounds recorded in the same solvent mixture
(Fig. 1). The smoothly increasing baseline was caused by the
absorption of the AuNPs (surface plasmon resonance). The
photoreaction was easy to follow with UV-Vis spectroscopy,
because only the corresponding acridinium compounds formed by
photoheterolysis were able to absorb light above 350 nm (Fig. 1).
Isosbestic points revealed that the photoreactions of the acridanes
on AuNPs were the same as those of the free compound in solution.
The efficiencies of the photoreactions of 5 and 6 deposited on
AuNPs were comparable to that of the photoreactions of the free
compounds. Clearly, the photoexcited state of the acridanes was
not quenched by the gold surface. When comparable concentra-
tions of free 5 and 5 bound to AuNP were irradiated for 5 s
with > 300 nm light, we observed comparable initial increases of
absorbance at 360 nm (acridinium compound; Fig. 2). However,
the irreversible formation of acridinium compounds was much
higher when 5 was deposited on AuNPs than when 5 was in
solution. This was shown by the decay of the transient absorbance
after irradiation at 360 nm; the residual absorbance of 5 on AuNP
The AuNPs coated with 2, 4–6, 12, and 13 were synthesised by
ligand-exchange reactions.11 To maintain stable dispersion of the
AuNPs, we employed dodecane thiol as a stabilising agent.12
Solutions of thiol-capped AuNPs in dichloromethane were
mixed with acetonitrile solutions of compounds 2, and 4–6,
without and with CBQT4+ and 13, respectively. After stirring for
3 days under an argon atmosphere, the solvents were evaporated.
To remove unbound compounds, the residue was washed with
acetonitrile until no UV/Vis-absorption of the wash solutions
could be detected. The average sizes of the AuNPs were between
2.8 and 3.4 nm (Fig. S3–S6†). According to the average diameter
and the elemental analysis, AuNPs were decorated with four thiol
molecules (ESI†). Only one molecule of rotaxane 13 was deposited
on the AuNPs.
2.4 Photochemistry of immobilised molecular threads
To explore the photoheterolysis of acridanes on gold surfaces,
compounds 5 and 6 were deposited on AuNPs and irradiated
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Fig. 1 a) Spectra of AuNP/5 recorded after irradiation (5, 10, 15, 20,
25 s) with light of wavelengths > 300 nm in DCM/MeOH (8 : 2) solution.
Black curve: addition of HClO4; b) Spectra of 5 in DCM/MeOH recorded
after irradiation (0, 5, 10, 15, 20 s). Black curve: addition of HClO4.
Scheme 3 Synthesis of rotaxanes containing thioctic ester within the axle.
was higher than that of free 5 in solution (compare the curves
in Fig. 2). This indicated that the methoxide ions released upon
photolysis of the acridane compound did not completely react
with acridinium ions at the AuNP surface.
The transient UV-Vis absorption spectra was visualised by
subtraction of the spectra recorded before from the spectra
recorded after the irradiation. This clearly showed the formation
of the acridinium methoxides (e.g., compound 6 in Fig. 3).
The lifetime of the transient acridinium methoxide formed on
AuNPs upon irradiation was considerably shorter than that of the
acridinium methoxide formed in solution (compare Fig. 3b and
3c). Consequently, these results showed that the photoheterolysis
of acridanes could take place on gold surfaces, but with
Fig. 2 Decay curves of the absorbance at 360 nm recorded after a 5 s
irradiation in DCM/MeOH (4 : 1). Continuous line: 5 on AuNP; dotted
line: free 5 in solution.
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Fig. 3 Transient absorption spectra recorded after irradiation. (a) Transient absorption after 5 s irradiation at >300 nm of compound 6 deposited on
AuNP in DCM/MeOH/MeCN (1 : 10 : 10) solution; (b) decay curve of the transient absorbance of 6 on AuNP at 360 nm; (c) decay curve of the transient
absorbance of 6 in DCM/MeOH/MeCN (1 : 10 : 10) solution.
diminished recovery of the acridane compared to photoheterolysis
of free acridanes in solution (Scheme 4).
and 6. These findings indicated that the ring CBQT4+ resided on
the acridane station A. Surprisingly, the proton signals of CBQT4+
were not shifted by complexation with the axle on the gold surface.
2.5 Rotaxanes on AuNP
2.5.1.2 Photoreaction of pseudorotaxanes on AuNPs. The ro-
taxanes formed between CBQT4+ and 5 and 6 on the AuNP
surface were photoactive. Upon irradiation with >300 nm light,
the acridane station A was converted to the acridinium moiety. The
transient UV-Vis absorption of the photoproduct clearly showed
the formation of the acridinium rotaxane (Fig. 4 and S7, ESI†).
Accordingly, the ring moved from the newly-formed acridinium
station towards station B. The thermal reaction between the
methoxide and the acridinium ion restored the starting co-
conformation.
In comparing Fig. 2 and 4, it is clear that the efficiency of
the photoreaction was strongly diminished in the latter. A much
smaller increase of the transient absorption was observed with
comparable excitation conditions, including the absorbance at
the irradiation wavelength and the light intensity (Fig. S7†). The
reaction with the pseudorotaxane 6/CBQT4+ on AuNP showed
lower efficiency than with 5/CBQT4+. The lower efficiencies of
the pseudorotaxanes on AuNP compared to free 5 and 6 could be
attributed to the charge-transfer interaction between the acridane
station A and CBQT4+ and the filter effect of the UV-absorption
2.5.1 Pseudorotaxanes on AuNP.
2.5.1.1 Interactions with CBQT4+. We expected that, when the
exchange of dodecanethiol by threads 5 and 6 was carried out in the
presence of CBQT4+, it would induce the formation of rotaxanes
on the AuNP surface; in this reaction, the AuNP would act as one
of the two necessary terminators that could prevent dethreading
of the ring (Scheme 5).
In fact, NMR spectra of the capped AuNPs in CDCl3/CD3CN
solution exhibited both the proton signals of threads 5 or 6 and
those of CBQT4+ in a 1 : 1 ratio (Scheme S1, ESI†).
As expected, the acridinium compounds were not able to bind
CBQT4+ on the AuNPs.
1
Typical of acridane rotaxanes, in the H NMR spectra, the
proton signals of CBQT4+ and the aryl protons of rotaxanes were
broad or even merged with the baseline at room temperature.7
However, the proton signals of the propoxy chain of the aryl
station B (Scheme 5) were relatively sharp, and therefore, they
could be assigned (Schemes S1 and S2). These proton resonances
were identical with those of the same protons in compounds 5
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Scheme 4 Switching cycle on AuNP.
of the ring. The same finding was observed in solution with
comparable rotaxanes.7
This switch cycle could be repeated at least ten times. However,
about 2% of the acridinium rotaxane was irreversibly formed in
each cycle (Fig. S11†).
2.5.2 Rotaxanes 12 and 13.
2.5.2.3 Photoheterolysis of 13 on AuNP. The UV-Vis spectra
of AuNPs coated with rotaxane 13 exhibited both the absorbance
of the AuNPs and the typical absorption spectrum of the acridane
rotaxane. The latter comprised a superposition of the acridane
chromophore (320 and 280 nm) and the ring, CBQT4+ (260 nm).
Upon addition of diluted acid, the absorption spectrum of the
acridinium rotaxane 12 appeared (Fig. 6).
2.5.2.1 Ring movements. In accordance with the results ob-
tained for rotaxanes in solution, CBQT4+ resided on station B of
rotaxane 12. In contrast, the acridane station A was predominantly
occupied in rotaxane 13. The strong upfield shifts of proton signals
of station B in 12 and of station A in 13 revealed the position of
the ring on the axle (Scheme S5 and S6; Fig. S8, S9†).
The rotaxane 13 deposited on AuNPs was irradiated in a
solvent mixture of DCM/MeCN/MeOH (1 : 10 : 10) with light of
wavelengths > 300 nm. Transient UV-Vis spectra clearly indicated
the formation of the corresponding acridinium rotaxane (Fig. 7).
The absorbance at 260, 360, and 430 nm was attributed to the
acridinium chromophore of rotaxane 12. The negative absorbance
at 283 nm corresponded to the disappearance of the acridane
chromophore of 13. Absorption bands at 410 and 620 nm were
attributed to the radical trication, CBQT∑3+. The appearance of
the radical trication spectrum indicated that electron transfer from
the acridane moiety to CBQT4+ also played a role in depositing
rotaxane 13, as it was observed in solution. However, the fraction
of radical trications was significantly higher with AuNPs than in
solution (compare Fig. 5a and 7).
The productive electron transfer from the acridane moiety to the
tetracationic ring could again transform the acridane unit into the
acridinium unit. Accordingly, after the dark reaction, the initial
absorbance of rotaxane 13 was restored. The cycle of photore-
action – thermal back reaction could be repeated several times
without significant fading of the acridane absorbance.
Because the acridinium moiety was formed by the photolysis
of the acridane station, the ring moved from station A to station
B. The attack of the methoxide ion on the acridinium unit recon-
verted the acridane station, thus starting a new ring movement.7
2.5.2.2 Photoheterolysis of 13 in solution. The transient UV-
Vis-absorption spectra observed upon irradiation of rotaxane 13 in
solution (DCM/MeOH/MeCN 1 : 10 : 10 and ethanol) indicated
the presence of two species. The disappearance of the acridane
chromophore (negative absorption at 285 nm) was accompanied
by increased absorbances at 260, 360, and 430 nm, which
was the characteristic absorption spectrum of the acridinium
chromophore. However, the absorption peaks at 410 and 620 nm
were attributed to the radical trication, CBQT∑3+, generated by
photoinduced electron transfer from the acridane moiety to the
tetracationic ring.12,13 Accordingly, the radical trication of CBQT4+
was not formed upon irradiation of 12.
The radical cation of the acridane moiety decomposed to the
acridinium ion and the methoxy radical. The latter took up an
electron from CBQT∑3+; this resulted in the same products as those
formed by a direct photolysis of the acridane moiety.12
It is noteworthy that the electron transfer was more effective
in ethanol solution (compare Fig. 5a and 5b). The lifetime of
the absorbance at 360 nm, which was assigned to the acridinium
methoxide, was 1400 s in the solvent mixture and 840 s in ethanol.
In contrast, the decay of CBQT∑3+ monitored at 620 nm was faster
(lifetime 200 s in ethanol solution; Fig. S10, ESI†).
The decay of the absorbance at 360 nm corresponded to the
lifetime of the acridinium rotaxane with methoxide as counterion
(Fig. S12, ESI†). This 60 s decay was considerably shorter than
that measured in solution (60 vs. 1400 s, see above).
Converting the acridane rotaxane into the acridinium rotaxane
was accompanied by the movement of the ring CBQT4+ from the
acridane station to the evasive station B (Scheme 6). Accordingly,
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Fig. 4 a) Formation of the acridinium rotaxane. Transient absorption
spectrum recorded after irradiation (<300 n m) of pseudorotaxane
5/CBQT4+ immobilised on AuNP in DCM/MeOH/MeCN (1 : 10 : 10
solution); b) decay curve of the transient absorbance at 360 nm.
Acridinium methoxides were formed from the corresponding
acridane molecules, both by direct photoheterolysis and by
photoinduced electron transfer from the acridane moiety to the
CBQT4+. Switch cycles could be repeated several times without
precipitation of the dispersed nanoparticles. In the switch cycle,
the ring CBQT4+ moved between the acridane station near the
surface and the evasive station more distant from the surface.
Related to the AuNP surface, the movement was unidirectional.
Scheme 5 Deposition of a pseudorotaxane on AuNP.
in the acridinium state, the ring was more distant from the surface.
With respect to the surface of the AuNP, the movement was
unidirectional.
4. Experimental
General methods
Commercially available chemicals and solvents (UVASOL,
Merck) were used as received, unless otherwise noted; solvents
were dried according to standard procedures. Column chromatog-
raphy (CC) was carried out on 200 mesh silica gel (Merck). Melting
points were determined with a Boetius heating microscope.
Electrospray ionisation mass spectroscopy was carried out on a
LTQ-FT (Finnigan MAT, Bremen, Germany), equipped with an
electrospray ion source (Thermo Electron).
3. Conclusions
We have shown that thiol-protected gold nanoparticles could
successfully be functionalised with 1) photoactive molecular
threads that contained both the acridane unit and an evasive
station, 2) pseudorotaxanes formed between these threads and
the CBQT4+ wheel, and 3) bistable [2]rotaxane molecules that con-
tained both the acridane unit and the evasive station. Both of these
molecular threads, the pseudorotaxane and the rotaxane retained
photoreactivity and switching properties at the nanoparticle-
solvent interface.
NMR spectra were recorded on a Bruker DPX 300 (300 MHz)
and a Bruker Advance 400 (400 MHz). The proton signals
were attributed to the different subunits with the aid of
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Fig. 5 Transient absorption spectrum monitored after irradiation of 13 (5 s HBO 500; >300 nm). a) in a solvent of DCM/MeCN/MeOH (1 : 10 : 10);
b) in a solvent of ethanol.
Fig. 7 Transient absorption spectra recorded after irradiation of 13 (5 s)
Fig.
6
UV-Vis spectrum of rotaxane 13 on AuNP in
deposited on AuNP in DCM/MeCN/MeOH (1 : 10 : 10). (1) recorded
immediately after irradiation; (2) recorded after a 3 min delay; (3) recorded
after a 10 min delay.
DCM/MeCN/MeOH (1 : 10 : 10) solution. Continuous line: UV-Vis
spectrum of rotaxane 13 on AuNP in solution; Dotted line: UV-Vis
spectrum of rotaxane 12 generated from 13 by the addition of HClO4.
use by a 60 s plasma treatment at 8 W in a BAL-TEC MED 020
device (Leica Microsystems, Wetzlar, Germany). Supernatant fluid
was removed after 30 s incubation by blotting with a filter paper
until an ultrathin layer of the sample was obtained. The air-dried
specimens were transferred into the microscope for imaging.
two-dimensional NMR spectroscopy, including C-H-COSY, H-
H-COSY, and ROESY.
UV/Vis measurements were performed with a Shimadzu UV
2101 PC spectrometer.
Irradiations of the rotaxane solutions were carried out with a
conventional mercury arc (HBO 500 or HBO 200) combined with
a cut-off filter of 300 nm. Transient absorption spectra between
240 and 500 nm were recorded with the UV 2101 PC spectrometer,
using the fastest scan mode. Turnover of acridinium ions generated
by photolysis was determined by comparing the absorbance at
360 nm with the absorbance obtained upon addition of HClO4.
Transmission electron microscopy (TEM) experiments were
performed using a Tecnai F20 (FEI Company, Oregon, USA)
microscope equipped with a field emission gun operating at an
accelerating voltage of 160 kV. Images were recorded using an
EAGLE 2k-CCD device (FEI Company, Oregon, USA) at full
2048 by 2048 pixel size and a primary magnification of 240k.
Specimen preparation for TEM: TEM samples were prepared by
depositing a droplet of the suspension (5 ml) onto a carbon covered
copper grids (400 mesh) which had been hydrophilized prior to
Syntheses
Assignments of NMR-signals of new compounds are given in the
ESI.†
9-(4-(2-(2-(2-(4-(3-(5-(1,2-Dthiolan-3-yl) pentanoyloxyl) propyl)
phenoxy) ethoxy)ethoxy)ethoxy)phenyl)-10-methylacridinium hex-
afluorophosphate (2). 17a (0.71 g, 1.25 mmol), thioctic acid
(0.31 g, 1.5 mmol), N,N¢-dicylohexyl-carbodiimide (0.31 g, 1.5
mmol) and 4-dimethylamino-pyridine (0.04 g, 0.25 mmol) were
dissolved in dichloromethane (25 mL) and stirred for 3 days
under argon. After filtration and removal of solvents, the crude
product was purified by column chromatography (silica gel,
isopropanol/water/acetic acid = 5 : 2 : 1). The product was dis-
solved in dichloromethane (10 mL) and mixed with a solution
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Scheme 6 Switching cycle of rotaxane 13 on AuNP.
of ammonium hexafluorophosphate (0.2 g, 1.25 mmol) in wa-
ter (50 mL). The aqueous phase was separated and extracted
with dichloromethane. The combined extracts were washed with
water. The combined organic layers were dried over MgSO4.
After filtration and removal of solvents, the residue was dried
in vacuo to give the product as red solid (0.76 g, 81%), m.p. 195–
198 ◦C. C43H50F6NO6PS2 (885.27): calcd. (%): C 54.32, H 5.36, N
1.86, S 8.53; found (%): C 54.29, H 5.38, N 1.84, S 8.45.
with dichloromethane (3 ¥ 10 mL). The combined extracts were
washed with water. The organic layer was dried over MgSO4.
After filtration and removal of solvents, the residue was dried
in vacuo to give the product as dark violate solid (1.22 g, 91%),
m.p. 175-178 ◦C. C44H53F6N2O5PS2 (899.00): calcd. (%): C 58.78,
H 5.94, N 3.12, S 7.13; found (%): C 58.65, H 5.99, N 3.30, S
-
7.33; HRMS (ESI): m/z: found 753.3380; calcd for [M-PF6 ]
[C44H53N2O5S2]+ 753.3390.
-
HRMS (ESI): m/z: found 740.3997; calcd for [M-PF6 ]
[C43H50NO6S2]+ 740.3980.
3-(4-(2-(2-(2-(4-Methoxy-10-methyl-4a,9,9a,10-tetrahydro-
acdrin-9-yl)phenoxy)ethoxy)ethoxy)ethoxy)phenyl)propyl-5-(1,2-
dithiolan-3-yl)pentanoate (5). 2 (100 mg, 0.11 mmol) dissolved
in MeCN/MeOH (10 mL/2 mL) and K2CO3 (150 mg) were
vigorously stirred for 4 h. After filtration and removal of solvents,
the crude product was treated with dry chloroform (3 ¥ 5 mL).
After filtration the solution was evaporated in vacuo to afford the
product as colorless oil (0.76 g, 89%). C44H53NO7S2 (772.03): calcd.
(%): C 68.45, H 6.92, N 1.81, S 8.31; found (%): C 68.32, H 6.66,
N 1.84, S 8.28.
9-(4-(2-(2-(2-(4-(3-(5-(1,2-Dithiolan-3-yl)pentaoyloxy)propyl)-
phenoxy)
ethoxy)ethoxy)ethyl)methylamino)phenyl)-10-methyl-
acridinium hexafluorophosphate (4). 37b (1.04 g, 1.46 mmol),
thioctic acid (0.31 g, 1.5 mmol), N,N¢-dicylohexyl-carbodiimide
(0.31 g, 1.5 mmol) and 4-dimethylamino-pyridine (0.04 g,
0.25 mmol) were dissolved in dichloromethane (25 mL) and stirred
for 3 days under argon. After filtration and removal of solvents,
the crude product was purified by column chromatography
(silica gel, isopropanol/water/acetic acid 5 : 2 : 1). The product
was dissolved in dichloromethane (10 mL) and mixed with a
solution of ammonium hexafluorophosphate (0.2 g, 1.25mmo) in
water (50 mL). The aqueous phase was separated and extracted
3-(4-(2-(2-(2-(4-Methoxy-10-methyl-9,10-dihydroacdrin-9-yl)-
phenyl) methylamino)ethoxy)ethoxy)ethoxy)phenyl)propyl-5-(1,2-
dithiolan-3-yl)pentanoate (6). 4 (300 mg, 0.382 mmol) dissolved
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in MeCN/MeOH (10 mL/2 mL) and K2CO3 (150 mg) were
vigorously stirred for 4 h. After filtration and removal of solvents,
the crude product was dissolved in dry chloroform (20 mL). After
filtration the solvent was evaporated in vacuo to afford the product
as dark oil (235 mg, 78%). C45H56N2O6S2 (785.07): calcd. (%): C
68.85, H 7.19, N 3.57, S 8.17; found (%): C 68.62, H 7.34, N 3.36,
S 8.36; HRMS (ESI): m/z: found 823.3220; calcd for [M+K]+
[C45H56KN2O6S2]+ 823.3211.
argon for 1 h at room temperature. A solution 1-adamantoyl
chloride (0.124 g, 0.62 mmol) in acetonitrile (2 mL) was added
dropwise within 45 min. The reaction mixture was stirred under
argon for 5 days. After filtration and removal of solvents the
residue was washed with dichloromethane until the solution was
colorless. The precipitate was washed with 2 mL of a mixture
of MeCN (400 mL), NH4PF6 (7 g), ethyl acetate (200 mL) and
cyclohexane (100 mL). After filtration the filtrate were purified
by the help of column chromatograohy (silica gel, acetonitrile
(400 mL), NH4PF6 (7 g), ethyl acetate (200 mL), cyclohexane
(100 mL). The collected yellow fractions were evaporated. The
residue was treated with water (20 mL) and dried in vacuo to
give◦the product as yellow powder (0.341 g, 27%), m.p. 218–
222 C. C84H88F30N5O7P5 (2003.49): calcd. (%): C 50.33, H 4.33,
N 3.49; found (%): C 50.12, H 4.53, N 3.26.
10-(3-(tetrahydro-2H-pyran-2yloxy)propyl)acridin-9(10H)-one
(7). Acridin-9(10H)-one (0.98 g, 5 mmol) was suspended in
anhydrous DMF (20 mL). NaH (0.223 g, 5.6 mmol, 60% in
oil) was added and the the mixture was stirred for 6 h under
argon at room temperature. 2-(3-bromopropoxy)tetrahydro-2H-
pyran (2.24g,10 mmol) was added and the reaction mixture was
stirred for 20 h at 60 ◦C under argon. After cooling down to room
temperature, the reaction mixture was poured into water (20 ml).
The aqueous layer was extracted with diethyl ether (3 ¥ 100 mL).
The combined organic phases were washed with water (100 mL),
Brine (50 mL) and water (50 mL). The organic layers were dried
over MgSO4. The solvent was removed, the residue was extracted
with petroleum (25 ml) for 1h. After filtration, the precipitate was
dried in vacuo to give the product as light yellow powder (1.08 g,
64%), m.p. 138–142 ◦C.; C21H23NO3 (337.41): calcd. (%): C 74.75,
H 6.87, N 4.15; found (%): C 74.55, H 6.95, N 4.04; HRMS (ESI):
m/z: found 339.1729; calcd for [M+H+]+ [C21H24NO3]+ 338.1751.
Acridinium Rotaxane 12. 11 (0.150 g, 0.075 mmol) was
dissolved in MeCN (1 mL) and mixed with a dichloromethane
(12 mL) solution of thioctic acid (0.017 g, 0.082 mmol),
N,N¢- dicylohexyl-carbodiimide (0.017 g,0.082 mmol) and 4-
dimethylaminopyridine (0.001 mg, 0.0.82 mmol). The reaction
mixture was stirred under argon for 3 days. After removal of
solvents, the residue was purified by column chromatography
(silica gel, eluent: acetonitrile (400 mL), NH4PF6 (7 g), ethyl
acetate (200 mL), cyclohexane (100 mL)). The crude product was
washed with water and the residue was dried in vacuo to give the
product as dark yellow powder (0.144 g, 88%), m.p. 193–195 ◦C.;
C92H100F30N5O8P5S2 (2191.76), calcd (%): C 50.39, H 4.60, N 3.19,
S 2.92; found (%): C 50.28, H 4.34, N 3.05, S 2.89;
9-(4-(2-(2-(2-(4-(3-Hydroxypropyl))phenoxy)ethoxy)ethoxy)-
ethoxy)phenl)-10-(3-(tetrahydro-2H-pyran-2-yloxy)propyl)acri-
dinium hexafluorophosphate (9). 87a (1.69 g, 3.85 mmol) was
dissolved in dry THF (55 mL) and cooled down to -78 ◦C. BuLi
(4.8 mL, 5.92 mmol (1.6 M in hexane) was added dropwise
within 30 min to this solution at -78 ◦C under argon. 7 (1.3 g,
3.85 mmol) in dry THF (25 mL) was added dropwise to the
reaction mixture within 90 min at -78 ◦C under argon. The
reaction mixture was warmed up to room temperature and stirred
over night. Water (2 mL) was poured into the reaction mixture.
After filtration and removal of solvents, the residue was purified
by column chromatography (silica gel, acetonitrile: 5% aqueous
solution of NH4PF6 40 : 1). The yellow fractions were collected.
The solvents were removed in vacuo. The residue was extracted
with dichloromethane (50 mL). The filtrate was washed with water
(2 ¥ 10 mL). The organic phase was dried (MgSO4). The solvent
was evaporated to give the product as yellow, viscous oil (1.21 g,
38%). C42H50F6NO7P (825.81): calcd. (%): C 61.09, H 6.10, N
1.70; found (%): C 60.80, H 6.45, N 1.56; HRMS (ESI): m/z:
HRMS (ESI) m/z: found 585.5427; calcd for [M-3PF6 ]3+
-
[C92H100F12N5O8P2S2]3+ 585.5429; found 402.9158; calcd for
[M-4PF6 ]4+ [C92H100F6N5O8PS2]4+ 402.9164; found 293.3397;
-
-
calcd for [M-5PF6 ]5+ [C92H100N5O8S2]5+ 293.3401.
Acridane Rotaxane 13.
A suspension of 12 (0.100 g,
0.046 mmol) and NaHCO3 (0.150 g) in MeCN (5 mL) and
MeOH (0.5 mL) was vigorously stirred for 6 h. After fil-
tration and removal of solvents, the residue was dried in
vacuo to give the product as colorless oil (0.088 g, 92%).
HRMS (ESI) m/z: found 901.8196; calcd for [M-2PF6 ]2+
-
[C93H103F12N5O10P2S2]2+ 901.8210; found 552.8914; calcd for
[M-3PF6 ]3+ [C93H103F6N5O10PS2]3+ 552.8924; found 378.4272;
-
calcd for [M-4PF6 ]4+ [C93H103N5O10S2]4+ 378.4281.
-
Acknowledgements
found 680.3648; calcd for [M-PF6 ]+ [C42H50NO7]+ 680.3582.
We thank the Deutsche Forschungsgemeinschaft for financial
support. We express our sincere thanks to Dr Christian Bo¨ttcher
(Free University Berlin, Research Centre of Electron Microscopy)
for his help in the TEM measurements
-
3-(4-(2-(2-(2-(4-(9-Methoxy-10-(3-(tetrahydro-2H -pyran-
2yloxy)propyl)-9,10-dihydroacridin-9-yl)phenoxy)ethoxy)ethoxy)-
ethoxy)phenyl)propan-1-ol (10). 9 (0.60 g, 0.73 mmol) dissolved
in MeCN/MeOH (25 mL/10 mL) and K2CO3 (0.5 g) were
vigorously stirred for 24 h. After filtration and removal of solvents,
the crude product was uptaken with dry chloroform (30 mL). The
suspension was filtered and the filtrate was evaporated in vacuo to
give the product as oil (0.458 g, 88%). HRMS (ESI): m/z: found
750.3409; calcd for [M+K]+ [C43H53KNO8]+ 750.3403.
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The Royal Society of Chemistry 2011
Org. Biomol. Chem., 2011, 9, 3549–3559 | 3559
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