Use of the self-assembly of tyrosine-containing bolaamphiphile molecules as a reactive template for metal deposition

Self-Assembling Peptidic Bolaamphiphiles for Biomimetic Applications

Bolaamphiphile, which is a class of amphiphilic molecules, has a unique structure of two hydrophilic head groups at the ends of the hydrophobic center. Peptidic bolaamphiphiles that employ peptides or amino acids as their hydrophilic groups exhibit unique biochemical activities when they self-organize into supramolecular structures, which are not observed in a single molecule. The self-assembled peptidic bolaamphiphiles hold considerable promise for imitating proteins with biochemical activities, such as specific affinity toward heterogeneous substances, a catalytic activity similar to a metalloenzyme, physicochemical activity from harmonized amino acid segments, and the capability to encapsulate genes like a viral vector. These diverse activities give rise to large research interest in biomaterials engineering, along with the synthesis and characterization of the assembled structures. This review aims to address the recent progress in the applications of peptidic bolaamphiphile assemblies whose densely packed peptide motifs on their surface and their stacked hydrophobic centers exhibit unique protein-like activity and designer functionality, respectively.

Low molecular weight self-assembling peptide-based materials for cell culture, antimicrobial, anti-inflammatory, wound healing, anticancer, drug delivery, bioimaging and 3D bioprinting applications

In this review, we have focused on the design and development of low molecular weight self-assembling peptide-based materials for various applications including cell proliferation, tissue engineering, antibacterial, antifungal, anti-inflammatory, anticancer, wound healing, drug delivery, bioimaging and 3D bioprinting. The first part of the review describes about stimuli and various noncovalent interactions, which are the key components of various self-assembly processes for the construction of organized structures. Subsequently, the chemical functionalization of the peptides has been discussed, which is required for the designing of self-assembling peptide-based soft materials. Various low molecular weight self-assembling peptides have been discussed to explain the important structural features for the construction of defined functional nanostructures. Finally, we have discussed various examples of low molecular weight self-assembling peptide-based materials for cell culture, antimicrobial, anti-inflammatory, anticancer, wound healing, drug delivery, bioimaging and 3D bioprinting applications.

Tailoring a Tyrosine-Rich Peptide into Size- and Thickness-Controllable Nanofilms

Self-assembled nanostructures of tyrosine-rich peptides have a number of potential applications such as biocatalysts, organic conducting films, and ion-selective membranes. In modulating a self-assembly process of peptides, the interfacial force is an important factor for kinetic control. Here, we present the formation of large-sized and thickness-controllable nanofilms from the YYACAYY peptide sequence (Tyr-C7mer peptide) using Langmuir-Blodgett and Langmuir-Schaefer deposition methods. The Tyr-C7mer peptide showed typical surfactant-like properties, which were demonstrated via the isotherm test (surface pressure-area) by spreading the Tyr-C7mer peptide solution onto an air/water interface. Uniform and flat peptide nanofilms were successfully fabricated and characterized. The redox activity of densely packed tyrosine moieties on the peptide nanofilm was also evaluated by assembling silver nanoparticles on the nanofilm without requiring any additives.

Interior-filled self-assemblies of tyrosyl bolaamphiphiles regulated by hydrogen bonds

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.

An enzyme-coupled artificial photosynthesis system prepared from antenna protein-mimetic tyrosyl bolaamphiphile self-assembly

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.

Biomimetic Catalytic and Sensing Cascades Built with Two Designer Bolaamphiphilic Self-Assemblies

A system performing both a catalytic hydrolysis reaction and the direct optical monitoring of the product was created by the combination of two bolaamphiphile self-assemblies. Two bolaamphiphilic self-assemblies were applied as a biomimetic catalyst of p-nitrophenyl acetate (p-NPA) hydrolysis and an optical sensor probe that detects p-NPA hydrolysis through photoluminescence quenching by p-nitrophenol (p-NP), the product of p-NPA hydrolysis. One bolaamphiphilic self-assembly with a histidine moiety catalytically hydrolyzed the p-NPA substrate, and the other self-assembly of tyrosyl bolaamphiphile monitored the product of p-NP by photoluminescence quenching. The progression of the reaction and quenching degree were adjusted by controlling the quantity of histidyl and tyrosyl self-assemblies, respectively. The reaction and subsequent sensing cascade could be interrupted by a reducing agent. The addition of NaBH4 induced the chemical conversion of p-NP to p-aminophenol, which retarded photoluminescence quenching. Thus, it was demonstrated that hydrolysis of an organic substrate and subsequent monitoring of the hydrolysis reaction could be achieved through a combination of independent bolaamphiphilic self-assemblies. This study demonstrated the construction of a catalytic reaction and detection system incorporating designer biomimetic self-assemblies whose functionalities were devised to realize deliberate functions.

Carbonic anhydrase-mimetic bolaamphiphile self-assembly for CO2 hydration and sequestration

A biomimetic catalyst was prepared through the self-assembly of a bolaamphiphilic molecule with histidine moieties for the sequestration of carbon dioxide. The histidyl bolaamphiphilic molecule bis(N-α-amidohistidine)-1,7-heptane dicarboxylate has been synthesized and self-assembled to produce analogues of the active sites of carbonic anhydrase (CA) after association with Zn(2+) ions. Spectroscopic analysis demonstrated the coordination of the Zn(2+) ions with histidine imidazole moieties, which is the core conformation of CA active sites. The Zn-associated self-assembly worked as a CA-mimetic catalyst that shows catalytic activity for CO2 hydration. Evaluation of the kinetics of using para-nitrophenylacetate revealed that the kinetic parameters of the CA-mimetic catalyst were maximized at the optimal Zn concentration and that excess Zn ions resulted in deteriorated catalytic activity. The performance of the CA-mimetic catalyst was enhanced by changing the pH value and temperature of the reaction, which implies that the hydrolysis of the substrate is the rate-determining step. The catalyst-assisted sequestration of CO2 was demonstrated by CaCO3 precipitation upon the addition of Ca(2+) ions. This study offers an easy way to prepare enzyme analogues for CO2 sequestration through the self-assembly of bolaamphiphile molecules with designer biochemical moieties.

Use of tyrosyl bolaamphiphile self-assembly as a biochemically reactive support for the creation of palladium catalysts

The self-assembly of tyrosine-containing bolaamphiphile was applied as a catalyst support on which palladium (Pd) catalysts were loaded to exploit the biochemical activity of tyrosine. The bolaamphiphile self-assembled to form spherical structures exposing tyrosine moieties on the surface. The phenyl group of tyrosine was then used to create the Pd catalyst on the spherical self-assembly. Silver (Ag) clusters were decorated on the surface, exploiting the reducing function of the phenyl group. These Ag clusters were further applied to create Pd catalysts through the galvanic replacement reaction in the next step. The produced Pd catalyst showed reliable catalytic activity in decomposing dichromate with a pseudo-first-order reaction rate. The reaction rate constant increased proportionally to the Pd loading on the self-assembly support. In addition, as a solid support, the bolaamphiphile self-assembly made catalyst recovery easy, and the recovered Pd catalysts showed consistent activity after several cycles. The experimental results demonstrated that the bolaamphiphile self-assembly is a promising organic support with biochemical activity for the facile creation of metallic catalysts.

pH-sensitive transformation of the peptidic bolaamphiphile self-assembly: exploitation for the pH-triggered chemical reaction

Control of the macroscopic self-assembled structure of the amphiphilic molecule has been a challenging issue in micro/nanotechnologies. In this study, the microtubular self-assembly of a novel peptidic bolaamphiphile, bis(N-α-amido-glycylglycine)-1,10-decene dicarboxylate, which undergoes reversible structural transformation between microtubes and precipitates as a function of pH, was exploited for pH-triggered chemical release. At neutral and basic conditions above a pH of 6, the peptidic bolaamphiphilic molecule self-assembled to form tubular structures several hundreds of micrometers in length. When the solution became acidic below a pH of 4, the tubular assembly disintegrated to form aggregated precipitates. The reversible transformation of precipitate to microtube was achieved by raising the pH above 6. From the Raman spectroscopy results, it was revealed that the hydrogen bonds of the amide group and carboxylate were enhanced under the acidic conditions. These variation of the hydrogen bonds resulted in precipitation of peptidic bolaamphiphilic molecules while rupturing the microtubular structure. The pH-sensitive microscopic structural transformation was exploited for release of a chemical in which the pH-triggered release of a model chemical, a fluorescence dye of ANS, was demonstrated. The ANS dye was released gradually with decreasing pH, which suggests gradual disintegration of the microtubular self-assembly. Furthermore, this pH-triggered release of a chemical was exploited for the chemical reaction of gold ion reduction to produce solid clusters. This study demonstrated the reversible transformation of peptidic bolaamphiphile and its application as a pH-sensitive host matrix.

Enhanced photoluminescence by tyrosine-containing bolaamphiphile self-assembly

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.