Direct joining of a heterogeneous pair of supramolecular nanotubes and reaction control of a guest compound by transportation in the nanochannels

Article abstract of DOI:10.1246/bcsj.20190046

Four novel amino-acid lipids were synthesized and then self-assembled in water to produce four different types of supramolecular nanotubes. The nanotubes consisted of a single monolayer of amino-acid lipids packed in parallel and had similar inner diameters and membrane wall thicknesses but dissimilarly charged surfaces. Mixing of nanotubes that had cationic exterior surfaces with nanotubes that had anionic exterior surfaces resulted in aggregation of the nanotubes. In contrast, mixing of nanotubes with cationic interior surfaces and nanotubes with anionic interior surfaces resulted in end-to-end joining of the two types of nanotubes via electrostatic attractions at the open ends to form heterogeneous nanotubes. Time-lapse fluorescence microscopy confirmed that a fluorophore could be transported through the heterogeneous nanotubes, which had alternating acidic and basic nanochannel segments. In addition, acidbase reactions of the fluorophore could be precisely controlled during transport. This nanotube-joining technique should be useful not only for the construction of multifunctional hybrid nanotubes but also for the production of nanoreactors for chemical/biological reactions and nano-devices for analysis and separation.

Full text of DOI:10.1246/bcsj.20190046

Document type: Article
BCSJ Award Article
Direct Joining of a Heterogeneous Pair of Supramolecular Nanotubes
and Reaction Control of a Guest Compound by Transportation
in the Nanochannels
Naohiro Kameta* and Wuxiao Ding
Nanomaterials Research Institute, Department of Materials and Chemistry, National Institute of Advanced Industrial
Science and Technology (AIST), Tsukuba Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan
E-mail: n-kameta@aist.go.jp
Received: February 26, 2019; Accepted: March 13, 2019; Web Released: April 18, 2019
Naohiro Kameta
Naohiro Kameta received his PhD (2002) in Analytical Chemistry from Ibaraki University and then did
postdoctoral research at Utsunomiya University and Japan Science and Technology Agency (JST, CREST-
SORST). Since 2008, he has worked at AIST, where he is currently a senior researcher developing
interfacial nanomaterials based on supramolecular and colloidal chemistry. He has received an Award for
Encouragement of Research in Polymer Science from the Society of Polymer Science, Japan, and an Award
for Encouragement of Research in Analytical Chemistry from the Japan Society for Analytical Chemistry.
Abstract
morphological and structural features: (i) a perfect one-
dimensional morphology, (ii) distinct, functionalizable inner
and outer surfaces, and (iii) nanochannels with tunable diam-
eters. The one-dimensional morphology is advantageous for
electronic and optical applications, when component molecules
are integrated with dye moieties, because the dye moieties
packed in a highly ordered manner within the membrane walls
of the nanotubes exhibit high-speed charge transport, long-
lasting charge separation, efficient energy transfer, and light
harvesting.2-7 The functionalizable surfaces permit selective
chemical and biological modifications and complexation of
metals on the surfaces, and functionalized nanotubes can serve
as sensing platforms,8,9 reusable and recyclable solid catalysts
with large specific surface areas,10-12 and self-propelled micro-
machines acting as scavengers for viruses and bacteria.13 The
tunability of the nanochannel diameter is important for bio-
logical (e.g., pharmaceutical and medical) and materials sci-
ence applications. For example, the nanochannels can be util-
ized as templates not only to produce conformationally con-
trolled polymers14-17 but also to fabricate nanoparticles, nano-
rods, nanocoils, and nanotubes from metals or other inorganic
materials.10,18-21 Nanochannels are also useful for separating
peptides,22 stabilizing enzymes,23,24 accelerating DNA duplex
formation, and refolding denatured proteins.25-27 Furthermore,
the nanochannels can store and release drugs in response to
external stimuli, including environmental changes.28,29
Four novel amino-acid lipids were synthesized and then self-
assembled in water to produce four different types of supra-
molecular nanotubes. The nanotubes consisted of a single
monolayer of amino-acid lipids packed in parallel and had
similar inner diameters and membrane wall thicknesses but
dissimilarly charged surfaces. Mixing of nanotubes that had
cationic exterior surfaces with nanotubes that had anionic
exterior surfaces resulted in aggregation of the nanotubes. In
contrast, mixing of nanotubes with cationic interior surfaces
and nanotubes with anionic interior surfaces resulted in end-
to-end joining of the two types of nanotubes via electrostatic
attractions at the open ends to form heterogeneous nanotubes.
Time-lapse fluorescence microscopy confirmed that a fluoro-
phore could be transported through the heterogeneous nano-
tubes, which had alternating acidic and basic nanochannel
segments. In addition, acid-base reactions of the fluorophore
could be precisely controlled during transport. This nanotube-
joining technique should be useful not only for the construction
of multifunctional hybrid nanotubes but also for the production
of nanoreactors for chemical/biological reactions and nano-
devices for analysis and separation.
Keywords: Supramolecular nanotube
j
Self-assembly
j
Amino-acid lipids
1. Introduction
The recent development of methods for stepwise self-
assembly and living supramolecular polymerization30 of two
components has permitted the construction of hybrid nanotubes
in which two different nanotube segments are joined end-to-
Supramolecular nanotubes,1 which can be formed by self-
assembly of rationally-designed synthetic lipids and amphi-
philic molecules in the liquid phase, have the following unique
Bull. Chem. Soc. Jpn. 2019, 92, 1053–1059 | doi:10.1246/bcsj.20190046
© 2019 The Chemical Society of Japan | 1053

end.31-33 For example, Fukushima and Aida et al. have suc-
ceeded in fabricating a heterojunction between two semicon-
ducting nanotube segments by self-assembly of one graphene-
like molecule to form a seed nanotube that facilitates self-
assembly of another graphene-like molecule.31 The dissimilar
nanotube segments can communicate electrically and ener-
getically with each other over the heterojunction interface.
However, direct joining of heterogeneous nanotube segments
formed in advance by self-assembly of their respective com-
ponents has been reported to a limited degree,34,35 although
uniaxial stacking of toroidal- and barrel-like nanostructures
acting as homogeneous nanotube segments has been observed
during the formation and elongation of natural and artificial
bionanotubes36-40 and supramolecular nanotubes.41-44
Herein we describe direct joining of supramolecular nano-
tubes that have similar diameters but dissimilarly charged sur-
faces and that are formed by self-assembly of novel amino-acid
lipids. Specifically, nanotubes with cationic interior surfaces
were joined to nanotubes with anionic interior surfaces by
means of an electrostatic attraction between the open ends of
the nanotubes. Time-lapse fluorescence microscopy revealed
that acid-base reactions of a fluorophore could be controlled
during transport of the fluorophore through the resulting hetero-
geneous nanotubes, which had alternating acidic and basic
nanochannel segments.
HN-CH2-CH3), 2.93 (dd, J = 5.0, 13 Hz, 1H; -CH-CH2-C6H5),
2.72 (dd, J = 9.5, 13 Hz, 1H; -CH-CH2-C6H5), 2.01 (t, J = 7.5
Hz, 2H; CH2-CH2-C=O), 1.49 (m, 2H; -CH2-), 1.34 (m, 2H;
-CH2-), 1.24 (m, 14H; -CH2-), 0.96 (t, J = 7.0 Hz, 3H; HN-
CH2-CH3). ESI-MS (cationic mode) m/z: 504.4 [M + H]+.
Anal. calculated for C27H45N5O4: C 64.38, H 9.01, N 13.90;
found: C 64.01, H 9.19, N 13.81.
Phe-C11-Gly-COOH:
1H NMR (500 MHz, DMSO-d6,
25 °C): δ = 12.4 (s, 1H; -COOH), 8.09 (t, J = 6.0 Hz, 1H; NH),
8.04 (t, J = 6.0 Hz, 1H; NH), 7.96 (d, J = 9.0 Hz, 1H; NH),
7.89 (t, J = 6.0 Hz, 1H; NH), 7.25-7.15 (m, 5H; -CH-CH2-
C6H5), 4.44 (m, 1H; -CH-CH2-C6H5), 3.74 (d, J = 6.0 Hz, 2H;
HN-CH2-C=O), 3.70 (d, J = 6.0 Hz, 2H; HN-CH2-C=O),
3.17-2.89 (overlap, 3H; HN-CH2-CH2, -CH-CH2-C6H5), 2.73
(dd, J = 9.5, 13 Hz, 1H; -CH-CH2-C6H5), 2.11 (t, J = 7.5 Hz,
2H; CH2-CH2-C=O), 2.03 (q, J = 7.5 Hz, 2H; CH3-CH2-
C=O), 1.48 (m, 2H; -CH2-), 1.32 (m, 2H; -CH2-), 1.24 (m,
14H; -CH2-), 0.87 (t, J = 7.5 Hz, 3H; CH3-CH2-C=O). ESI-
¹
MS (anionic mode) m/z: 531.2 [M - H] . Anal. calculated for
C28H44N4O6: C 63.13, H 8.33, N 10.52; found: C 63.18, H
8.39, N 10.51.
2.2 Observation of Nanotube Morphology.
Aqueous
dispersions of nanotubes were dropped onto a carbon grid,
negatively stained with 0.2 wt % phosphotungstate in 90:10
(v/v) water/CH3OH (adjusted to pH 7 with NaOH), and
observed with a transmission electron microscope (H-7000,
Hitachi) at 75 kV. The nanotube xerogel was observed with a
scanning electron microscope (S-4800, Hitachi) at 15 kV.
2.3 Analysis of Nanotube Structure. The pH of the aque-
ous dispersions of (¹)-out-nanotube and (¹)-in-nanotube was
adjusted to 4.2, which led to the protonation of the carboxyl
groups on the outer or inner surfaces of both nanotubes, to
clearly observe the amide-I and -II bands related to the
intermolecular hydrogen bond interaction. All nanotubes were
lyophilized and analyzed with a Fourier transform infrared
2. Experimental
2.1 Synthesis and Characterization of Amino-Acid
Lipids. The syntheses of the amino-acid lipids are shown
schematically in Supporting Information.
NH2-Phe-C11-Gly: 1H NMR (500 MHz, DMSO-d6, 25 °C):
δ = 7.97 (t, J = 5.5 Hz, 1H; NH), 7.78 (br, 1H; NH), 7.75 (t,
J = 5.5 Hz, 1H; NH), 7.26 (t, J = 7.0 Hz, 3H; -CH-CH2-C6H5),
7.18 (d, J = 7.0 Hz, 2H; -CH-CH2-C6H5), 3.61 (d, J = 6.0 Hz,
2H; HN-CH2-C=O), 3.09-2.97 (overlap, 5H; HN-CH2-CH2,
HN-CH2-CH3, -CH-CH2-C6H5), 2.87 (dd, J = 5.5, 13 Hz, 1H;
-CH-CH2-C6H5), 2.60 (dd, J = 7.5, 13 Hz, 1H; -CH-CH2-
C6H5), 2.11 (t, J = 7.5 Hz, 2H; CH2-CH2-C=O), 1.48 (m, 2H;
-CH2-), 1.32 (m, 2H; -CH2-), 1.24 (m, 14H; -CH2-), 0.99 (t, J =
7.0 Hz, 3H; HN-CH2-CH3). ESI-MS (cationic mode) m/z:
447.3 [M + H]+. Anal. calculated for C25H42N4O3: C 62.16, H
8.97, N 11.60; found: C 62.08, H 8.99, N 11.61.
¹1
spectrometer (FT-620, JASCO) operated at 4 cm resolution
and equipped with an unpolarized beam, an attenuated total
reflection accessory system (Diamond MIRacle, horizontal
attenuated total reflection accessory with a diamond crystal
prism, PIKE Technologies), and a mercury-cadmium telluride
detector. The zeta potentials of the surfaces of the nanotubes
dispersed in water were measured with a Malvern Zetasizer
Nano ZS system.
Gly-C11-Phe-COOH:
1H NMR (500 MHz, DMSO-d6,
25 °C): δ = 7.91 (t, J = 8.5 Hz, 1H; NH), 7.81 (br, 1H; NH),
7.62 (t, J = 6.0 Hz, 1H; NH), 7.22 (m, 5H; -CH-CH2-C6H5),
4.44 (m, 1H; -CH-CH2-C6H5), 3.62 (d, J = 6.0 Hz, 2H; HN-
CH2-C=O), 3.13-3.00 (overlap, 3H; HN-CH2-CH2, -CH-CH2-
C6H5), 2.84 (dd, J = 9.5, 13 Hz, 1H; -CH-CH2-C6H5), 2.16 (m,
2H; CH3-CH2-C=O), 2.03 (t, J = 7.5 Hz, 2H; CH2-CH2-C=O),
1.49 (m, 2H; -CH2-), 1.39 (m, 2H; -CH2-), 1.24 (m, 14H; -CH2-),
0.99 (t, J = 7.5 Hz, 3H; CH3-CH2-C=O). ESI-MS (anionic
2.4 Dynamic Observation of a Fluorophore in the
Nanochannels. The transport of the fluorophore CypHer5
(GE Healthcare) in the nanochannels of the heterogeneous
nanotubes was monitored with an inverted microscope (IX71;
Olympus) equipped with
a CCD camera (ORCA-ER;
Hamamatsu). The excitation optical source consisted of a high-
pressure mercury lamp (100 W, BH2-REL-T3; Olympus). Fluo-
rescence detection was optimized by means of an appropriate
mirror unit (U-DM-CY5; Olympus). Time-lapse fluorescence
microscopic images were recorded on a PC with the Aqua-
cosmos system (Hamamatsu). The measurement interval was
set to 10 ms.
¹
mode) m/z: 474.3 [M - H] . Anal. calculated for C26H41N3O5:
C 65.66, H 8.69, N 8.83; found: C 65.68, H 8.59, N 8.81.
NH2-Gly-C11-Phe: 1H NMR (500 MHz, DMSO-d6, 25 °C):
δ = 7.97 (d, J = 8.5 Hz, 1H; NH), 7.91 (t, J = 5.5 Hz, 1H;
NH), 7.81 (t, J = 5.5 Hz, 1H; NH), 7.76 (t, J = 5.5 Hz, 1H;
NH), 7.25-7.15 (m, 5H; -CH-CH2-C6H5), 4.44 (m, 1H; -CH-
CH2-C6H5), 3.68 (d, J = 6.0 Hz, 2H; HN-CH2-C=O), 3.11 (s,
1H; H2N-CH2-C=O), 3.09-3.01 (overlap, 4H; HN-CH2-CH2,
3. Results and Discussion
3.1 Construction of Nanotubes with Dissimilarly Charg-
ed Surfaces and Similar Diameters. As previously reported
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© 2019 The Chemical Society of Japan

Figure 1. Chemical structures of amino-acid lipids, schematic representation of nanotubes consisting of a single monolayer formed
by self-assembly of the amino-acid lipids, and photographs showing the results of mixing clear aqueous dispersions of pairs of
nanotube types.
by our group, synthetic glycolipids composed of an oligo-
methylene spacer capped on one end with a large glucose
headgroup and on the other with a small amino or carboxyl
headgroup self-assemble in water to form nanotubes.29 The
nanotubes consist of monolayer membranes in which the
glycolipids pack in parallel. The nanotubes have different exte-
rior and interior surfaces; specifically, the exterior is covered
with the nonionic glucose headgroups and the interior with the
cationic amino headgroups or anionic carboxyl headgroups.
However, we have found it difficult to prepare and combine
nanotubes with dissimilarly charged surfaces and similar diam-
eters (both outer and inner). Especially, we have never suc-
ceeded in control of outer diameters, i.e., monolayer membrane
wall thicknesses, which strongly depend on not only the stack-
ing number of the monolayer membrane but also the molecular
length of the used glycolipids and the tilting angle of the
glycolipids within the single monolayer membrane.
similar diameters (both outer and inner), we designed and syn-
thesized four new amino-acid lipids (Scheme S1-S4). These
lipids, designated NH2-Phe-C11-Gly, Gly-C11-Phe-COOH,
NH2-Gly-C11-Phe, and Phe-C11-Gly-COOH, have an L-
phenylalanine derivative as a large headgroup, a glycine
derivative as a small headgroup, and a 12-aminododecanoic
acid linker connecting the two headgroups (Figure 1).
The nanotubes were generated as follows. Each amino-acid
lipid (10 mg) was dispersed in deionized water (10 mL) by
refluxing for 5 min and was then rapidly cooled in an ice bath.
Transmission electron microscopy revealed that all the amino-
acid lipids formed only nanotubes (Figure 2a-d). The four
types of nanotubes had similar outer diameters (22 nm), inner
diameters (16 nm), and membrane wall thicknesses (3 nm). The
fact that the membrane wall thicknesses were comparable to
the extended molecular lengths (3.2-3.6 nm) of the amino-acid
lipids indicates that the nanotubes consisted of single mono-
layer membranes composed of the lipids.29 Infrared spectros-
copy confirmed that the molecular packing of the lipids within
In this study, with the goal of preparing four types of nano-
tubes with cationic or anionic exterior or interior surfaces and
Bull. Chem. Soc. Jpn. 2019, 92, 1053–1059 | doi:10.1246/bcsj.20190046
© 2019 The Chemical Society of Japan | 1055

the monolayer membranes was similar for the four types of
nanotubes. Specifically, the absence of obvious differences in
the amide-I and -II bands reflected the strength of intermolec-
ular hydrogen bonding (Figure S1). The spectra showed two
peaks, at 1420 and 1026 cm¹1, that were assignable to the CH
deformation and skeletal vibration bands of the glycine moi-
eties of the lipids, suggesting that the lipids in the nanotubes
formed a pseudo-polyglycine-II-type hydrogen bond network
(Figure S1).45-48 The γ(CH2) rocking vibration produced a
single sharp peak at 719 cm¹1, which indicates that the sub-
cellular structure (lateral chain packing) of the oligomethylene
spacers of the lipids in the nanotubes was triclinic parallel
(T// ).49 The specific intermolecular hydrogen bonding and the
subcell structure ensured the parallel molecular packing of the
lipids within the monolayer membrane.
The above-described results indicated that for all the nano-
tubes, the L-phenylalanine-derived headgroups were on the
exterior surfaces, and the glycine-derived headgroups were on
the interior surfaces (Figure 1). The zeta potential of the nano-
tubes formed from NH2-Phe-C11-Gly (designated as (+)-out-
nanotubes) in a water dispersion was approximately 55 mV
(Figure S2), which is consistent with the amino groups of the
L-phenylalanine headgroups being on the exterior surface of the
nanotubes. In contrast, the nanotubes formed from Gly-C11-
Phe-COOH ((¹)-out-nanotubes) had a negative zeta potential
(¹78 mV) derived from the carboxyl groups of the L-phenyl-
alanine headgroups on the outer surfaces. The zeta potentials of
the nanotubes formed from NH2-Gly-C11-Phe and Phe-C11-
Gly-COOH ((+)-in-nanotubes and (¹)-in-nanotubes, respec-
tively) were much smaller than those of the above-mentioned
nanotubes (Figure S2). The smaller zeta potentials are ascrib-
able to the fact that the amino and carboxyl groups of the
glycine headgroups on the interior surfaces of the (+)-in-
nanotubes and (¹)-in-nanotubes had less contact with the bulk
solution (Figure 1).
3.2 Joining of a Heterogeneous Pair of Nanotubes via
Electrostatic Attraction. Mixing of clear aqueous disper-
sions of (+)-out-nanotubes and (¹)-out-nanotubes led to the
formation of a cloudy dispersion (Figure 1, top photograph),
whereas mixing of aqueous dispersions of (+)-out-nanotubes
and (¹)-in-nanotubes or (¹)-out-nanotubes and (+)-in-nano-
tubes resulted in clear dispersions (Figure 1, left and right
photographs, respectively). The formation of the cloudy dis-
persion in the former case suggests that electrostatic attraction
between the cationic exterior surfaces of the (+)-out-nanotubes
and the anionic exterior surfaces of the (¹)-out-nanotubes led
to aggregation. In contrast, in the other two pairings, there were
no attractive interactions between the nanotubes. Transmission
electron microscopy confirmed that mixing the pairs of nano-
tubes did not affect their morphology, diameter, or length.
In contrast, mixing clear aqueous dispersions of (+)-in-
nanotubes and (¹)-in-nanotubes resulted in hydrogel formation
(Figure 1, bottom photograph). Scanning electron microscopy
of the lyophilized hydrogel (xerogel) revealed a network of
entangled nanotubes (Figure 2e). These nanotubes were several
micrometers long, which is much longer than the original nano-
tubes prior to mixing (³300 nm, Figure 2c,d and Figure S3).
Because this elongation was not observed for any of the other
pairs of nanotubes, we attributed it to end-to-end joining of the
Figure 2. (a-d) Transmission electron micrographs of the
four types of nanotubes. The nanotube channels were nega-
tively stained with 2 wt% phosphotungstate. (e) Scanning
electron micrograph of the xerogel obtained by joining the
(+)-in-nanotubes and (¹)-in-nanotubes and subsequent
lyophilization.
(+)-in-nanotubes and (¹)-in-nanotubes to form long heteroge-
neous nanotubes.
To elucidate the joining of the nanotubes, we mixed (¹)-in-
nanotubes containing cis-diamine-Pt(II) complexed to the inte-
rior carboxyl groups50 with vacant (+)-in-nanotubes. Trans-
mission electron microscopy clearly showed a single nanotube
with nanochannel segments encapsulating the dark-colored
Pt(II) complexes alternating with vacant nanochannel segments
(Figure 3). At the interfaces between the open ends of the
nanotubes, local electrostatic attractions between the cationic
inner surfaces of the (+)-in-nanotubes and the anionic inner
1056 | Bull. Chem. Soc. Jpn. 2019, 92, 1053–1059 | doi:10.1246/bcsj.20190046
© 2019 The Chemical Society of Japan

Figure 3. Transmission electron micrograph and schematic representation of heterogeneous nanotubes composed of Pt(II)-complex-
containing (¹)-in-nanotube segments joined end-to-end with vacant (+)-in-nanotube segments.
surfaces of the (¹)-in-nanotubes induced joining of these two
types of nanotubes.
a single heterogeneous nanotube, suggesting that the hetero-
junction between the (+)-in-nanotubes and (¹)-in-nanotubes
was stable enough for smooth transport of the fluorophore. The
encapsulated CypHer5 fluoresced during transport through the
acidic nanochannels of the (¹)-in-nanotubes, whereas no fluo-
rescence was observed during transport through the basic
nanochannels of the (+)-in-nanotubes (Figures 4a¤-f¤). Alter-
nating protonation and deprotonation reactions of CypHer5
could be precisely controlled during transport of the fluoro-
phore through the heterogeneous nanotubes.
3.3 Control of the Reactions of a Fluorophore during
Transport through the Nanochannels. We speculated that
the heterogeneous nanotubes formed by joining the (+)-in-
nanotubes and (¹)-in-nanotubes could be used to control acid-
base reactions of compounds encapsulated in the alternating
acidic and basic nanochannel segments. For the guest com-
pound, we chose the pH-responsive fluorophore CypHer5,51
which fluoresces strongly at pH values lower than its pKa (6.1)
but emits no fluorescence under neutral or basic conditions.
Time-lapse fluorescence microscopy enabled us to visualize
the encapsulation and transport of the CypHer5 in the hetero-
geneous nanotubes. To introduce an aqueous solution of the
fluorophore into the nanochannels by capillary action,52 we first
vacuum-dried the nanotubes to remove water from the nano-
channels. Then we prepared an aqueous solution of CypHer5
containing 0.1 M NaCl to interrupt the electrostatic attraction
between the fluorophore and the charged interior surfaces of
the nanotubes. Upon addition of the nonfluorescent solution of
CypHer5 at pH 7.4 to the vacuum-dried nanotubes on a glass
plate, a bright fluorescent line appeared in the first segment of
the nanotubes (segment 1 in Figure 4a), and as time passed,
the line elongated in one direction (Figure 4b). A new bright
fluorescent line appeared in segment 3, which is remote from
segment 1 (Figure 4c,d). That is, at 40 s after addition of the
CypHer5 to the nanotubes, there was a nonfluorescent segment
(segment 2) between segments 1 and 3. As time passed, fluo-
rescence developed in segment 5, whereas there was no fluores-
cence in segment 4 (Figure 4e,f). This unidirectional move-
ment of the CypHer5 fluorescence corresponded to an event in
4. Conclusion
We succeeded in directly joining two different types of nano-
tubes that had similar diameters but different surface charges.
Electrostatic attraction between the open ends of the two types
of nanotubes, which had cationic interior surfaces and anionic
interior surfaces, respectively, led to end-to-end joining of the
nanotubes. We also found that acid-base reactions of a fluoro-
phore could be controlled during transport through the hetero-
geneous nanotubes, which had alternating acidic and basic
nanochannel segments. This joining technique can be expected
to be useful not only for the construction of multifunctional
hybrid nanotubes but also for the production of nanoreactors
and analytical nanodevices.
This work was supported by JSPS KAKENHI grant
no. JP17H02726.
Supporting Information
Synthesis of amino-acid lipids, molecular packing analysis
of nanotubes, zeta-potential and length-distribution measure-
Bull. Chem. Soc. Jpn. 2019, 92, 1053–1059 | doi:10.1246/bcsj.20190046
© 2019 The Chemical Society of Japan | 1057

(a) 10 ms
(a’)
(b’)
(c’)
Basic nanochannels
Acidic nanochannels
1
1
1 µm
(b) 20 ms
1
1
Emission by protonation
(c) 30 ms
1
2
2
1
Quenching by deprotonation
(d) 40 ms (d’)
3
1
3
2
2
1
Emission by protonation
(e) 50 ms (e’)
3
3
2
5
4
4
5
2
Quenching by deprotonation
(f) 60 ms (f’)
5
4
4
5
Emission by protonation
Figure 4. (a-f) Time-lapse fluorescence micrographs and (a¤-f¤) schematic representation of CypHer5 transport through a hetero-
geneous nanotube 10-60 ms after addition of an aqueous solution of the fluorophore to vacuum-dried nanotubes on a glass plate.
4
S. Sengupta, D. Ebeling, S. Patwardhan, X. Zhang, H.
ments of nanotubes. This material is available on https://doi.
von Berlepsch, C. Böttcher, V. Stepanenko, S. Uemura, C.
Hentschel, H. Fuchs, F. C. Grozema, L. D. A. Siebbeles, A. R.
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