Morphological manipulation of bolaamphiphilic polydiacetylene assemblies by controlled lipid doping

Nanofiber Formation and Polymerization of Bolalipids with Diacetylene-Modified Single Alkyl Chains

The nanofiber formation in aqueous suspension of two classes of symmetric single-chain bolaamphiphiles with different polar headgroups and a diacetylene-modified alkyl chain with a length of 32, 34, and 36 C atoms was investigated by differential scanning calorimetry, transmission electron microscopy, and small-angle neutron scattering. As observed before for other bolalipids with phosphocholine (PC) and dimethyl-phosphoethanolamine (Me₂PE) headgroups, the molecules form fibers when suspended in water at low temperatures but disassemble into micellar-like aggregates upon heating. The introduction of a diacetylene group in the middle of the long chain leads to a perturbation of chain packing so that this fiber-micelle transition occurs at lower temperature compared to the other bolalipids having unmodified alkyl chains. The aim of our project was the introduction of diacetylene groups into alkyl chains to be able to polymerize the fibers at low temperature. This should enhance the fiber stability and prevent the disassembly into micellar aggregates at higher temperature. Polymerization of aggregates containing diacetylene-modified bolaamphiphiles can be easily traced by UV/vis spectroscopy as colored products are formed. We found that polymerization of bolaamphiphiles with PC headgroups leads to a breakdown of most fibers into micellelike aggregates, and only some longer fibers segments are still detectable. In contrast, the use of Me₂PE headgroups improves polymerizability and length of the polymerized fibers. The compound with 36 C atoms in the chain could be polymerized at low temperatures, and the fibers remained stable at least up to a temperature of 60 °C. This shows that the perturbation of the chain packing due to the diacetylene groups in the chains can be overcome by elongation of the chains, so that thermostable fibers with a diameter of the length of the bolalipid molecule can be successfully formed.

Amphiphilic peptides as novel nanomaterials: design, self-assembly and application

Designer self-assembling peptides are a category of emerging nanobiomaterials which have been widely investigated in the past decades. In this field, amphiphilic peptides have received special attention for their simplicity in design and versatility in application. This review focuses on recent progress in designer amphiphilic peptides, trying to give a comprehensive overview about this special type of self-assembling peptides. By exploring published studies on several typical types of amphiphilic peptides in recent years, herein we discuss in detail the basic design, self-assembling behaviors and the mechanism of amphiphilic peptides, as well as how their nanostructures are affected by the peptide characteristics or environmental parameters. The applications of these peptides as potential nanomaterials for nanomedicine and nanotechnology are also summarized.

Molecular Design and Applications of Self-Assembling Surfactant-Like Peptides

Self-assembling surfactant-like peptides have been explored as emerging nanobiomaterials in recent years. These peptides are usually amphiphilic, typically possessing a hydrophobic moiety and a hydrophilic moiety. The structural characteristics can promote many peptide molecules to self-assemble into various nanostructures. Furthermore, properties of peptide molecules such as charge distribution and geometrical shape could also alter the formation of the self-assembling nanostructures. Based on their diverse self-assembling behaviours and nanostructures, self-assembling surfactant-like peptides exhibit great potentials in many fields, including membrane protein stabilization, drug delivery, and tissue engineering. This review mainly focuses on recent advances in studying self-assembling surfactant-like peptides, introducing their designs and the potential applications in nanobiotechnology.

Diacetylene-containing ligand as a new capping agent for the preparation of water-soluble colloidal nanoparticles of remarkable stability

A new type of strategically designed functional ligands was used to cap gold nanocrystals and form robust colloidal nanoparticles, resistant to pH changes, temperature, and ionic strength variations as well as ligand-exchange reactions. The nanoparticles are coated with ligands that polymerize upon UV-irradiation, consequently embedding the particles in a stable organic shell. The ligand consists of an anchoring thiol group, which binds directly to the nanocrystal surface and two units, one hydrophobic and one hydrophilic. The hydrophobic alkyl unit contains a diacetylene group, which undergoes a 1,4-topochemical polymerization leading to a poly(enyne) structure during UV-irradiation. The hydrophilic unit contains an oligo-ethylene glycol chain, which ensures water solubility, and a terminal carboxylic group. Derived particles were characterized by transmission electron microscopy, surface enhanced Raman spectroscopy, and visible spectroscopy. Their stability was investigated and compared to particles capped with nonpolymerized ligands.

De novo design of a bolaamphiphilic peptide with only natural amino acids

A new self-assembling bolaamphiphilic peptide has been designed and synthesized using only natural amino acids. This simple peptide is composed of two lysines connected by 4-8 alanines to maintain the characteristics of the traditional bolaamphiphiles. Based on an irregular secondary structure, it can self-assemble into nanospheres, nanorods, or nanofibers with lengths up to micrometers. The long nanofibers can be broken into smaller fragments by sonication, however, they could reassemble into nanofibers after incubation. Furthermore, the nanostructures were shown to have considerable thermostability. This new bolaamphiphilic peptide differs from any other self-assembling peptides or bolaamphiphiles, and possibly provides a new approach to fabricate nanomaterials.

Nanotubes from a Vitamin C-Based Bolaamphiphile

A bolaform surfactant, 1,12-diascorbyl dodecanedioate (BOLA12), with ascorbic acid units as the polar headgroups was synthesized for the first time. Once dispersed in water above 0.5% w/w, BOLA12 forms hollow nanotubes as revealed by cryo-TEM experiments. These nanostructures transform into clear micellar solutions on heating. X-ray diffraction and SAXS experiments were performed both on the pure solid and on its aqueous dispersions. The critical aggregation concentration and the phase behavior were determined by conductivity and DSC experiments. The latter technique provided also the amount of strongly bound, solvating water molecules that surround the polar headgroups. BOLA12 shows the same reducing properties of ascorbic acid, as indicated by the antioxidant activity evaluated with the DPPH method. This feature was used for the reduction of Pd(II) ions on the surface of the nanoassemblies, which lead to the formation of large bundles homogeneously coated with palladium as observed in SEM micrographs.

Effect of amphiphilic molecules upon chromatic transitions of polydiacetylene vesicles in aqueous solutions

Effect of amphiphilic molecules upon the chromatic transitions of polymerized 10,12-pentacosadiynoic acid (PCDA) vesicles in aqueous solutions was reported. The colorimetric response of polymerized PCDA vesicles for 1-pentanol is higher than that for ethanol due to more hydrophobic property of 1-pentanol. The colorimetric response of polymerized PCDA vesicles for sodium dodecyl sulfate (SDS) and Triton X-100 is lower than that for cetyltrimethylammonium bromide (CTAB). The strong ability of CTAB to induce chromatic transition of the vesicles is related to the positively charged headgroups of CTAB, which favors approach of CTAB to the negatively charged carboxylate groups at the vesicle surface. The insertion of alkyl chain of CTAB into the hydrophobic domain perturbs the conformation of the conjugated polymer backbone and induces color change of polydiacetylene vesicles. For a series of alkylamine hydrochloric salts, the longer the alkyl chain, the stronger the ability of alkylamine to induce chromatic transition of polydiacetylene vesicles.

Functional Self-Assembling Bolaamphiphilic Polydiacetylenes as Colorimetric Sensor Scaffolds

Conjugated polymers capable of responding to external stimuli by changes in optical, electrical, or electrochemical properties can be used for the construction of direct sensing devices. Polydiacetylene-based systems are attractive for sensing applications due to their colorimetric response to changes in the local environment. Here we present the design, preparation, and characterization of self-assembling functional bolaamphiphilic polydiacetylenes (BPDAs) inspired by nature's strategy for membrane stabilization. We show that by placing polar headgroups on both ends of the diacetylene lipids in a transmembranic fashion and by altering the chemical nature of the polar surface residues, the conjugated polymers can be engineered to display a range of radiation-, thermal-, and pH-induced colorimetric responses. We observed dramatic nanoscopic morphological transformations accompanying charge-induced chromatic transitions, suggesting that both side-chain disordering and main-chain rearrangement play important roles in altering the effective conjugation lengths of the poly(ene-yne). These results establish the foundation for further development of BPDA-based colorimetric sensors.