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Photoluminescent spherical nanostructures were prepared through the self-assembly of a tyrosine-containing bolaamphiphilic molecule, and their antenna effect was examined. The photoluminescent spherical nanostructures were simply prepared by self-assembly of bolaamphiphile molecules in an aqueous solution in which water-soluble photosensitizers and lanthanide ions were dissolved. The photosensitizers and lanthanide cations were incorporated with the phenol group and the carboxyl end of the tyrosine moiety, respectively. Through fluorescence microscopy and photoluminescence spectroscopy analyses, the various combinations of two lanthanide ions (Eu and Tb) and four photosensitizers were screened for synergetic photoluminescence with bolaamphiphile self-assembly. The bolaamphiphile assembly enhanced the photoluminescence intensity by a factor of around 2 when it was associated with Tb and salicylic acid. This enhancement is driven by the phosphorescence enhancement of the photosensitizer induced by the π-π interactions with the phenol group in tyrosine. These results indicate that the tyrosine-containing bolaamphiphile is a promising molecule that can easily produce a soft nanoscaled host matrix with an antenna effect for photoluminescence.

An artificial photosynthesis system coupled with an enzyme was constructed using the nanospherical self-assembly of tyrosyl bolaamphiphiles, which worked as a host matrix exhibiting an antenna effect that allowed enhanced energy transfer to the ZnDPEG photosensitizer. The excited electrons from the photosensitizer were transferred to NAD+ to produce NADH, which subsequently initiated the conversion of an aldehyde to ethanol by alcohol dehydrogenase. Production of NADH and ethanol was enhanced by increasing the concentration of tyrosyl bolaamphiphiles. Spectroscopic investigations proved that the photosensitizer closely associated with the surface of the bolaamphiphile assembly through hydrogen bonds that allowed energy transfer between the host matrix and the photosensitizer. This study demonstrates that the self-assembly of bolaamphiphiles could be applicable to the construction of biomimetic energy systems exploiting biochemical activity.

Bolaamphiphilic molecules with tyrosyl end groups formed interior-filled spherical self-assemblies, which are distinct from the vesicular or tubular structures of other similar peptidic bolaamphiphile assemblies reported in the literature. In this study, the self-assembly mechanism of these tyrosyl bolaamphiphiles was investigated taking into consideration the solvent effects on the molecular interaction forces using molecular modeling. The dissipative particle dynamics simulation of an aqueous tyrosyl bolaamphiphile solution suggested that the interior-filled assemblies were produced by a solvent-regulated assembly of small aggregates of bolaamphiphiles. These small aggregates were generated by hydrophobic interactions at an early stage, and then further assembled to form large spherical assemblies through intermolecular forces, including hydrogen bonds between the intermediate aggregates. Additional experiments and density functional theory calculations based on solvent variations proved that smaller assembled structures could be obtained by disrupting the hydrogen bonds between the intermediates. The assembly mechanism of these peptidic bolaamphiphiles afforded a facile way to create condensed supramolecular structures with controlled sizes.