Dong Wang

Amphiphilic short peptide modulated wormlike micelle formation with pH and metal ion dual-responsive properties

Amphiphilic short peptides (ASPs) and surfactants (C14DMAO) were employed to prepare wormlike micelles. Herein, ASPs were used to induce wormlike micelle formation. The formation mechanism was investigated by cryo-TEM, FTIR, CD and a rheometer. C14DMAO could be protonated by a proton which was dissociated from the carboxyl headgroups of ASPs. The mean area of the headgroup would be reduced due to the interaction of protonated cationic surfactants and dissociated anionic ASPs which would lead to wormlike micelle formation. And the length of the wormlike micelles could be modulated by the size of the hydrophobic part of ASPs. The wormlike micelles could also respond to pH and metal ions, respectively. When the pH was regulated from 5.96 to 3.23, the wormlike micelles transformed into a nanofiber network. Nevertheless, when the pH was regulated to over 9, spherical micelles would be formed and the solution would lose its viscoelasticity. When a certain amount of metal salts were added into the wormlike micelle solution with a pH of 5.96, the viscosity of the solution increased significantly. The coordination interaction between metal ions and C14DMAO was considered as the responsive mechanism. Metal ions with high valence have more obvious effects on wormlike micelles.

Structural Features of Micelles of Zwitterionic Dodecyl-phosphocholine (C₁₂PC) Surfactants Studied by Small-Angle Neutron Scattering.

Small-angle neutron scattering (SANS) was used to investigate the size and shape of zwitterionic dodecyl phosphocholine (C12PC) micelles formed at various concentrations above its critical micelle concentration (CMC = 0.91 mM). The predominant spherical shape of micelles is revealed by SANS while the average micellar size was found to be broadly consistent with the hydrodynamic diameters determined by dynamic light scattering (DLS). Cryogenic tunneling electron microscopy (cryo-TEM) shows a uniform distribution of structures, proposing micelle monodispersity ( Supporting Information ). H/D substitution was utilized to selectively label the chain, head, or entire surfactant so that structural distributions within the micellar assembly could be investigated using fully protonated, head-deuterated, and tail-deuterated PC surfactants in D2O and fully deuterated surfactants in H2O. Using the analysis software we have developed, the four C12PC contrasts at a given concentration were simultaneously analyzed using various core-shell models consisting of a hydrophobic core and a shell representing hydrated polar headgroups. Results show that at 10 mM, C12PC micelles can be well represented by a spherical core-shell model with a core radius and shell thicknesses of 16.9 ± 0.5 and 10.2 ± 2.0 Å (total radius 27.1 ± 2.0 Å), respectively, with a surfactant aggregation number of 57 ± 5. As the concentration was increased, the SANS data revealed an increase in core-shell mixing, characterized by the emergence of an intermediate mixing region at the spherical core-shell interface. C12PC micelles at 100 mM were found to have a core radius and shell thicknesses of 19.6 ± 0.5 and 7.8 ± 2.0 Å, with an intermediate mixing region of 3.0 ± 0.5 Å. Further reduction in the shell thickness with concentration was also observed, coupled with an increased mixing of the core and shell regions and a reduction in miceller hydration, suggesting that concentration has a significant influence on surfactant packing and aggregation within micelles.

Near-infrared light-sensitive liposomes for controlled release

A photoresponsive amphiphilic lipid molecule with phosphatidylcholine as the headgroup and a near-infrared (NIR) light-responsive unit on the hydrophobic moiety was synthesized. Liposomes constituting the NIR-responsive lipid, cholesterol and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, were constructed and applied as a photocontrolled release system. The precisely controlled release of the loaded cargo was demonstrated by adjusting the irradiation parameters and content of the photoresponsive species. The low cytotoxicity and good biocompatibility of the photoresponsive lipid was demonstrated by MTT assay. This study provides us with a new choice for developing a photoresponsive drug delivery system.

Fusion and leakage of catanionic surfactant vesicles induced by α-helical peptides: the effect of membrane charge

Leakage and fusion of vesicles have triggered great interest because they are important steps in the transportation of materials in living systems. In this paper, we have shown a process of vesicle leakage and fusion induced by a type of α-helical peptide through the adsorption of peptide molecules on or their absorption in the membrane of vesicles. The fusion process was monitored by dynamic light scattering and cryogenic transmission electron microscopy, and the leakage process was tested with fluorescence dequenching of carboxyfluorescein molecules. The mechanism of leakage and fusion was deduced through circular dichroism and ζ-potential measurements. It was found that the positively charged peptides could only interact with negatively charged vesicles and that the interaction between peptides and negative vesicles depended on the charge density of the membrane. This study could enhance the understanding of the transport of materials in vivo and promote potential applications in drug delivery systems.

Tuning One-Dimensional Nanostructures of Bola-Like Peptide Amphiphiles by Varying the Hydrophilic Amino Acids.

By combining experimental measurements and computer simulations, we here show that for the bola-like peptide amphiphiles XI4 X, where X=K, R, and H, the hydrophilic amino acid substitutions have little effect on the β-sheet hydrogen-bonding between peptide backbones. Whereas all of the peptides self-assemble into one dimensional (1D) nanostructures with completely different morphologies, that is, nanotubes and helical nanoribbons for KI4 K, flat and multilayered nanoribbons for HI4 H, and twisted and bilayered nanoribbons for RI4 R. These different 1D morphologies can be explained by the distinct stacking degrees and modes of the three peptide β-sheets along the x-direction (width) and the z-direction (height), which microscopically originate from the hydrogen-bonding ability of the sheets to solvent molecules and the pairing of hydrophilic amino acid side chains between β-sheet monolayers through stacking interactions and hydrogen bonding. These different 1D nanostructures have distinct surface chemistry and functions, with great potential in various applications exploiting the respective properties of these hydrophilic amino acids.

Peptide Self-Assembled Nanostructures with Distinct Morphologies and Properties Fabricated by Molecular Design

Six surfactant-like peptides with the same amino acid composition but different primary sequences are designed, including G3A3V3I3K3, K3I3V3A3G3, I3V3A3G3K3, K3G3A3V3I3, V3G3I3A3K3, and K3A3I3G3V3. These peptides form antiparallel β-sheets during self-assembly. Because the constituent residues have different side chain size and hydrophobicity, sequence changes adjust group distribution and hydrophobicity on the two sides of a given β-sheet. This consequently tunes the binding energy of the side-to-side pairing conformations and leads to different self-assembled structures. G3A3V3I3K3 and K3I3V3A3G3 form short nanorods with diameters of 8.5 ± 1.0 nm and lengths <150 nm. I3V3A3G3K3 and K3G3A3V3I3 form nanosheets with heights of 4.0 ± 0.5 nm and limited lengths and widths. V3G3I3A3K3 and K3A3I3G3V3 form long fibrils with diameters of 7.0 ± 1.0 nm and lengths of micrometer scale. These nanostructures exhibit different capacity in encapsulating insoluble hydrophobic drug molecules and delivering them into the cells. The nanosheets of I3V3A3G3K3 and K3G3A3V3I3 can encapsulate both nile red and doxorubicin molecules to an extent of up to 17-23% in mole ratio. Moreover, the shape and size of the nanostructures affect the drug delivery into cells greatly, with the nanosheets and short rods exhibiting higher efficiency than the long fibrils. The study provides new insights into programmed peptide self-assembly toward specific functionalities.

Short peptide mediated self-assembly of platinum nanocrystals with selective spreading property

Spherical assemblies with core/shell configurations are prepared through C-terminal amidated short peptide mediated self-association of platinum nanocrystals. The interactions between the peptides might drive the self-assembly of platinum nanocrystals and determine their surface properties. Thus, the nanosize assemblies collapse and spread on a hydrophilic surface, whereas maintaining their spherical shapes on a hydrophobic surface.

Unusual surface and solution behaviour of keratin polypeptides

Keratins are filament proteins, but we report in this work that water-soluble keratin polypeptides hydrolyzed from wool could readily adsorb onto the surface of water and could thus be used as surface active biomaterials. Neutron reflection measurements with the help of deuterium labelling were used to determine the adsorbed amount and distribution of the polypeptide layers formed. It was found that the interfacial layers were comprised of two main regions, a dense top layer of 18–25 A and a loose bottom layer of 25–30 A. Half of the top dense layer was exposed to air with the remainder of the top layer and the diffuse bottom layer immersed in the aqueous solution. Both the volume fraction and the layer thickness increased with keratin solution concentration as did the adsorbed amount which was seen to plateau just above 2 mg m−2 at approximately 0.1 g dm−3 (2.1 μM). Increase in [NaCl] led to reduced surface adsorption, accompanied with the thinning of the top layer. Cryo-TEM imaging revealed that the keratin aggregates had an ellipsoidal structure with radii ranging from 60 A to 220 A. The ellipsoidal shape was well supported by SANS, with the major radius of 140 A and the minor radius of 60 A. With increasing [NaCl], the ellipsoids became thinner but longer, a feature consistent with the observed trend from surface adsorbed layer. This unusual behaviour could be explained by the electrostatic screening effect. As the salt concentration increased, the polypeptide chains became stiffer and more readily aligned, resulting in thinner layers and longer aggregates.

Influence of Conventional Surfactants on the Self-Assembly of a Bola Type Amphiphilic Peptide

Structural and morphological regulation is a distinctly important topic in peptide self-assembly, and is also regarded as the fundamental point in peptide-based biomaterials development. In this paper, we showed that adding anionic surfactant SDS to a bola amphiphilic peptide KI4K could result in the reconstruction of β-sheet secondary structure besides the changes in self-assembly morphologies from nanotubes to helical ribbons, nanofibers, or straight nanotapes according to the negatively stained transmission electron microscopy, atomic force microscopy, circular dichroism spectroscopy, and Fourier transform infrared spectroscopy results. The inducing effect of SDS was observed at both above and below its CMC but with different transformation rates. Through comparison to other surfactants, including CTAB, C12EO4, and AOT, we proposed that the transitions of KI4K self-assemblies induced by anionic surfactants could be mainly attributed to the effect of hydrophobic interaction and electrostatic attraction between surfactants and peptide molecules. Rheological property measurement and dye adsorption experiments were also carried out to evaluate the properties of hydrogels formed by the peptide/surfactant hybrids. The samples formed self-supporting hydrogels at proper SDS or AOT concentrations, and the charges of hydrogel could be regulated by peptide to surfactant ratio.

Dual-Responsive Viscoelastic Lyotropic Liquid Crystal Fluids to Control the Diffusion of Hydrophilic and Hydrophobic Molecules.

A smart lyotropic liquid crystal (LLC) system was prepared to control the diffusion rate of hydrophilic and hydrophobic molecules. The LLC system is composed of a nonionic surfactant (tetraethylene glycol monododecylether; C12 EO4 ) and an anionic azobenzene surfactant (Azo-surfactant). C12 EO4 was the main component of the LLC system. The Azo-surfactant, which can undergo photo-isomerization, played the role of trigger in this system. LLC gels formed in a solution comprised of Azo-surfactant (10 mm) and C12 EO4 (300 mm). The LLC gels became broken when more Azo-surfactant was added (e.g., up to 15 mm) and the viscoelasticity was lost. Surprisingly, when we used UV light to irradiate the 300 mm C12 EO4 /15 mm Azo-surfactant sample, the gel was recovered and high viscoelasticity was observed. However, under visible-light irradiation, the gel became broken again. The gel formation could also be triggered by heating the sample. On heating the 300 mm C12 EO4 /15 mm Azo-surfactant sample, the system thickened to a point at which typical gel behavior was registered. When the sample was cooled, the gel broke again. The LLC could be used for controlled release of hydrophilic and hydrophobic molecules, and could be considered as a versatile vehicle for the delivery of actives in systems of practical importance.