10.6 Self-Assembly with Anions as Secondary Building Blocks
Taking tetraoxacalix[2]arene[2]triazine as a functionalization platform, we designed
a series of amphiphilic molecules by introducing long alkyl chains on the larger rims
[45]. These amphiphilic molecules self-assembled into stable vesicles in a mixture of
THF and water, with the surface of the vesicles engineered by electron-deficient
cavities. When anions including NO 3
À , F
À
, Cl
À , Br
À
, BF 4
À , SCN
À , and ClO 4
À were
allowed to interact with the vesicles and monitored with DLS, the size of selfassembled vesicles were selectively influenced, giving a selectivity of
F
À
< ClO 4
À
< SCN
À
< BF 4
À
< Br
À
< Cl
À
< NO 3
À
. As the effect of anions on
vesicles is almost in agreement with the order of binding constants at molecular
level, it indicates that anion-π interaction most probably competed over other
possible weak interactions and accounts for this interesting selectivity. Upon the
affinity of vesicular surface to anions, the change of the surface zeta (ζ) potential of
the vesicles might contribute to the enlargement of vesicles. Later we designed
macrocyclic amphiphiles bearing different hydrophilic substituent groups on the
larger rim of the triazine rings, in order to explore the self-assemblies of amphiphilic
molecules and to probe the responses of vesicles toward anions in water [46]. The
nature of substituents showed significant effect on the self-assembly, only substituents with proper hydrophilicity and length could form vesicles. Vesicular surfaceanion study confirmed the function of anion-π interaction and enhanced regulation as
a result of cooperative anion-π and hydrogen bonding. Very recently, we further
modified the macrocyclic amphiphiles by introducing L-prolinol on triazines [47].
The resulting vesicles formed with this amphiphiles are decorated by chiral cavities
on the surface and show selective response to chiral anions including (2S, 3S)-2,3dihydroxysuccinate (D-tartrate), S-mandelate, and S-(+)-camphorsulfonate against
their respective enantiomers. DFT calculations revealed that the enantioselectivity
stemmed from cooperative anion-π interactions and hydrogen bonding between the
chiral electron-deficient cavity and the organic anions.
In 2015, we reported an example of anion-π-controlled self-assembly and disassembly [48]. The idea was established on the interaction between tetraoxacalix[2]
arene[2]triazine as host molecule and anionic surfactants including sodium dodecyl
sulfate (SDS), sodium laurate (SLA), and sodium methyl dodecylphosphonate
(SDP) as the guest species. 1:1 mixture of the host-guest solution was quickly
injected in water to afford an aqueous solution with final concentration being
6 Â 10
À4 M. After vortexing for 1 min, the solution produced an opalescent colloidal
solution, indicating the formation of self-assembled aggregates. Very low critical
aggregation concentrations (CAC) in the range of 5.0–7.5 Â 10
À6 M were obtained.
The vesicular morphology of the aggregates was revealed with SEM, TEM, and
XRD techniques. To get more insights on the formation of vesicles, SEM-EDS
analysis was set up to reveal the building units of the vesicles. Element peaks
corresponding to host and guest were observed, indicating both components contributed to the formation of the vesicles. The anion-π interaction between host and
guest was supported by means of HRMS, single crystal structure, and DFT calculation. In other words, host and anionic surfactant formed supramolecular amphiphilic
10 Application of Anion-π Interaction on Supramolecular Self-Assembly
271
Taking tetraoxacalix[2]arene[2]triazine as a functionalization platform, we designed
a series of amphiphilic molecules by introducing long alkyl chains on the larger rims
[45]. These amphiphilic molecules self-assembled into stable vesicles in a mixture of
THF and water, with the surface of the vesicles engineered by electron-deficient
cavities. When anions including NO 3
À , F
À
, Cl
À , Br
À
, BF 4
À , SCN
À , and ClO 4
À were
allowed to interact with the vesicles and monitored with DLS, the size of selfassembled vesicles were selectively influenced, giving a selectivity of
F
À
< ClO 4
À
< SCN
À
< BF 4
À
< Br
À
< Cl
À
< NO 3
À
. As the effect of anions on
vesicles is almost in agreement with the order of binding constants at molecular
level, it indicates that anion-π interaction most probably competed over other
possible weak interactions and accounts for this interesting selectivity. Upon the
affinity of vesicular surface to anions, the change of the surface zeta (ζ) potential of
the vesicles might contribute to the enlargement of vesicles. Later we designed
macrocyclic amphiphiles bearing different hydrophilic substituent groups on the
larger rim of the triazine rings, in order to explore the self-assemblies of amphiphilic
molecules and to probe the responses of vesicles toward anions in water [46]. The
nature of substituents showed significant effect on the self-assembly, only substituents with proper hydrophilicity and length could form vesicles. Vesicular surfaceanion study confirmed the function of anion-π interaction and enhanced regulation as
a result of cooperative anion-π and hydrogen bonding. Very recently, we further
modified the macrocyclic amphiphiles by introducing L-prolinol on triazines [47].
The resulting vesicles formed with this amphiphiles are decorated by chiral cavities
on the surface and show selective response to chiral anions including (2S, 3S)-2,3dihydroxysuccinate (D-tartrate), S-mandelate, and S-(+)-camphorsulfonate against
their respective enantiomers. DFT calculations revealed that the enantioselectivity
stemmed from cooperative anion-π interactions and hydrogen bonding between the
chiral electron-deficient cavity and the organic anions.
In 2015, we reported an example of anion-π-controlled self-assembly and disassembly [48]. The idea was established on the interaction between tetraoxacalix[2]
arene[2]triazine as host molecule and anionic surfactants including sodium dodecyl
sulfate (SDS), sodium laurate (SLA), and sodium methyl dodecylphosphonate
(SDP) as the guest species. 1:1 mixture of the host-guest solution was quickly
injected in water to afford an aqueous solution with final concentration being
6 Â 10
À4 M. After vortexing for 1 min, the solution produced an opalescent colloidal
solution, indicating the formation of self-assembled aggregates. Very low critical
aggregation concentrations (CAC) in the range of 5.0–7.5 Â 10
À6 M were obtained.
The vesicular morphology of the aggregates was revealed with SEM, TEM, and
XRD techniques. To get more insights on the formation of vesicles, SEM-EDS
analysis was set up to reveal the building units of the vesicles. Element peaks
corresponding to host and guest were observed, indicating both components contributed to the formation of the vesicles. The anion-π interaction between host and
guest was supported by means of HRMS, single crystal structure, and DFT calculation. In other words, host and anionic surfactant formed supramolecular amphiphilic
10 Application of Anion-π Interaction on Supramolecular Self-Assembly
271