dodecyl-4,4
0 -bipyridinium (G27) bearing hydrophilic head groups and a hydrophobic tail is pronouncedly weakened by the mutual electrostatic repulsion between
dicationic bipyridinium units [38]. UV-vis spectroscopy shows that the transmittance
of free G27 at 450 nm hardly changes versus their concentration from 0.01
to 0.15 mM and no critical aggregation concentration is observed, indicating that
G27 cannot aggregate into assembly at low concentration individually. Recently,
“supramolecular amphiphiles,” which are facilitated by noncovalent interaction,
have emerged as a smart strategy to construct supramolecular nanoarchitectures.
Benefiting from the intrinsic advantages of supramolecules, when equivalent molar
of G27 is associated with H5, the external surroundings were changed to adjust
to amphiphilic assembly (Fig. 21). At a concentration of 0.1 mM, the transmittance
of G27 & H5 dramaticly change at 450 nm, indicating amphiphilic aggregation is
formed. The aspect of aggregation of G27 & H5 is also as observed from its TEM
and SEM experiments. As expected, nanorods with the width of about 180 nm are
observed in TEM images. Moreover, the supramolecular amphiphilic aggregation of
G27 & H5 is switchable by introducing extra host to bind with G27 & H5. It is well
known that α-cyclodextrin (α-CD) can bind long alkyl chain and 4,4
0 -azodibenzoic
acid (AZA) with associate constants of 10
3 and 10
4 M
À1 , respectively. By adding
one equivalent complex of AZA & α-CD to the solution of G27 & H5, nearly no
amphiphilic change is observed to the four-component system because α-CD prefers
to bind more with AZA to form a more stable complex rather than the alkyl chain of
G27 . Upon irradiation of the four-component solution with 365 nm, most of AZA
guests were transformed to the cis-AZA, and free α-CD is associated with the alkyl
chain of G27 & H5 to form a [3]pseudorotaxane of G27 & H5Áα-CD. The newly
formed G27 & H5Áα-CD is absolutely hydrophilic, and the amphiphilic aggregates
disassemble to free G27 & H5Áα-CD. After subsequent irradiation of the fourcomponent solution with 450 nm light, the system recovered to G27 & H5 and
trans-AZA & α-CD, and amphiphilic aggregation phenomenon is reappeared and
confirmed by UV-vis spectroscopy and TEM imaging. Benefiting from the inherent
photoisomerization of AZA guest, the four components can be reversed between [3]
pseudorotaxane and [2]pseudorotaxane by photoinduced interconversion to conduct
the amphiphilic aggregates.
Nanosupramolecular assemblies with controlled topological features have important applications in functional materials. Liu and co-workers present a novel way to
obtain supramolecular nanosutructures via host-induced supramolecular aggregation
of bipyridinium-modified diphenylalanine peptide (G25) through host-guest interactions with water-soluble macrocycles; benefiting from that, bipyridinium guests
can form inclusion complexes with a variety of common water-soluble macrocycles
[28]. Different macrocycles binding on the bipyridinium unit of G25 can provide
diverse hydrophobic external surrounding to induce G25 complex to implement the
specific nanosupramolecular assembly. Four water-soluble macrocycles contain H5,
cucurbit[7]uril (CB[7]), cucurbit[8]uril (CB[8]), and water-soluble pillar[5]arene
(WP5A) were selected in this system. Spectroscopy titrations determine the
association constants to be 7.9 Â 10
6 , 5.3 Â 10
4 , 8.1 Â 10
4 , and 8.2 Â 10
4 M
À1 ,
respectively. Although all the four water-soluble macrocycles have strong interaction
22
L. Chen and Y. Liu
0 -bipyridinium (G27) bearing hydrophilic head groups and a hydrophobic tail is pronouncedly weakened by the mutual electrostatic repulsion between
dicationic bipyridinium units [38]. UV-vis spectroscopy shows that the transmittance
of free G27 at 450 nm hardly changes versus their concentration from 0.01
to 0.15 mM and no critical aggregation concentration is observed, indicating that
G27 cannot aggregate into assembly at low concentration individually. Recently,
“supramolecular amphiphiles,” which are facilitated by noncovalent interaction,
have emerged as a smart strategy to construct supramolecular nanoarchitectures.
Benefiting from the intrinsic advantages of supramolecules, when equivalent molar
of G27 is associated with H5, the external surroundings were changed to adjust
to amphiphilic assembly (Fig. 21). At a concentration of 0.1 mM, the transmittance
of G27 & H5 dramaticly change at 450 nm, indicating amphiphilic aggregation is
formed. The aspect of aggregation of G27 & H5 is also as observed from its TEM
and SEM experiments. As expected, nanorods with the width of about 180 nm are
observed in TEM images. Moreover, the supramolecular amphiphilic aggregation of
G27 & H5 is switchable by introducing extra host to bind with G27 & H5. It is well
known that α-cyclodextrin (α-CD) can bind long alkyl chain and 4,4
0 -azodibenzoic
acid (AZA) with associate constants of 10
3 and 10
4 M
À1 , respectively. By adding
one equivalent complex of AZA & α-CD to the solution of G27 & H5, nearly no
amphiphilic change is observed to the four-component system because α-CD prefers
to bind more with AZA to form a more stable complex rather than the alkyl chain of
G27 . Upon irradiation of the four-component solution with 365 nm, most of AZA
guests were transformed to the cis-AZA, and free α-CD is associated with the alkyl
chain of G27 & H5 to form a [3]pseudorotaxane of G27 & H5Áα-CD. The newly
formed G27 & H5Áα-CD is absolutely hydrophilic, and the amphiphilic aggregates
disassemble to free G27 & H5Áα-CD. After subsequent irradiation of the fourcomponent solution with 450 nm light, the system recovered to G27 & H5 and
trans-AZA & α-CD, and amphiphilic aggregation phenomenon is reappeared and
confirmed by UV-vis spectroscopy and TEM imaging. Benefiting from the inherent
photoisomerization of AZA guest, the four components can be reversed between [3]
pseudorotaxane and [2]pseudorotaxane by photoinduced interconversion to conduct
the amphiphilic aggregates.
Nanosupramolecular assemblies with controlled topological features have important applications in functional materials. Liu and co-workers present a novel way to
obtain supramolecular nanosutructures via host-induced supramolecular aggregation
of bipyridinium-modified diphenylalanine peptide (G25) through host-guest interactions with water-soluble macrocycles; benefiting from that, bipyridinium guests
can form inclusion complexes with a variety of common water-soluble macrocycles
[28]. Different macrocycles binding on the bipyridinium unit of G25 can provide
diverse hydrophobic external surrounding to induce G25 complex to implement the
specific nanosupramolecular assembly. Four water-soluble macrocycles contain H5,
cucurbit[7]uril (CB[7]), cucurbit[8]uril (CB[8]), and water-soluble pillar[5]arene
(WP5A) were selected in this system. Spectroscopy titrations determine the
association constants to be 7.9 Â 10
6 , 5.3 Â 10
4 , 8.1 Â 10
4 , and 8.2 Â 10
4 M
À1 ,
respectively. Although all the four water-soluble macrocycles have strong interaction
22
L. Chen and Y. Liu