Self-Assembly of a Pyridine-Based Amphiphile Complexed with Regioisomeric Dihydroxy Naphthalenes into Supramolecular Nanotubes with Different Inner Diameters.

A pyridine-based amphiphile complexed with 1,5-, 1,6-, 2,6-, or 2,7-dihydroxy naphthalene self-assembled in water to form nanotubes with inner diameters of 46, 38, 24, 18, and 11 nm in which the naphthalene molecules formed J-type aggregates. In contrast, the amphiphile complexed with 1,2-, 1,3-, 1,4-, 1,7-, 1,8-, or 2,3-dihydroxy naphthalene formed nanofibers in which the naphthalene molecules formed H-type aggregates. The inner diameter of the nanotubes strongly depended on the regioisomeric dihydroxy naphthalene. UV-vis, fluorescence, infrared spectroscopy, X-ray diffraction analysis, and differential scanning calorimetry showed that nanotubes with smaller inner diameters had weaker intermolecular hydrogen bonds between the tilted amphiphiles complexed with the naphthalene molecules within the membrane walls and showed larger Stokes shifts in the excimer fluorescence of the naphthalene moiety. These findings should be useful not only for fine-tuning the inner diameters of supramolecular nanotubes but also for controlling the aggregation states of functional aromatic molecules to generate nanostructures with useful optical and electronic properties in water.

Moisture-responsive supramolecular nanotubes.

Living organisms have evolved functional structures for seeds dispersal in response to humidity changes. In this study, we construct moisture-responsive nanotubes by the supramolecular coordination of a peptide lipid with metal ions for potential applications in material delivery systems. These hydrophilic nanotubes can uptake atmospheric moisture and the water molecules are associated with unsaturated metal centers of the bis(lipid)-metal(ii) complex, thereby changing the molecular packing and inducing morphological transformation from nanotubes to sheets. The moisture responsivity of nanotubes depends on the hydration behavior of the metal ions. Co(ii)-coordinated nanotube shows higher moisture responsivity than that of the Zn(ii)-coordinated one since Co(ii) ion has stronger association with water molecules. These two nanotubes are self-assembled by the same molecular packings; however, they show different mechanisms in morphological changes. The Co(ii)-coordinated nanotube transforms into a sheet accompanied with the destruction of the complex and reverse molecular packing, whereas Zn(ii)-coordinated nanotube transforms into a sheet with a change in the complex geometry. Further, the Co(ii)-coordinated nanotubes exhibit reversible morphological changes between nanotubes and sheets, while Zn(ii)-coordinated nanotubes exhibit a one-way morphological change. These nanotubes also show potential applications in the release of fragrance oil under high humidity environments.

Preparation and Formation Process of Zn(II)-Coordinated Nanovesicles.

Mixing a glycylglycine lipid and zinc acetate has been reported to form novel supramolecular Zn(II)-coordinated nanovesicles in ethanol. In this study, we investigate in detail the formation of nanovesicles by using three lipids at different temperatures and discuss their formation process. The original lipids show extremely low solubilities and appear as plate structures in ethanol. Within a small window of lipid solubility, the formation of lipid-Zn(II) complexes occurs mainly on the solid surfaces of plate structures. Controlling of the lipid solubility by temperature affects the kinetics of complex formation and the subsequent transformation of the complexes into nanovesicles and nanotubes. An improved method of two-step control of temperature is developed for preparing all the three kinds of nanovesicles. We provide new insights into the formation process of nanovesicles based on several control experiments. A tetrahedral lipid-cobalt(II) complex similarly produces nanovesicles, whereas an octahedral complex gives sheet structures. Mixing of zinc acetate with a ß-alanyl-ß-alanine lipid can only give sheet structures, which lack a polyglycine II hydrogen-bond network and induce no morphological changes. We conclude that the formation of the lipid-Zn(II) complexes on solid plate structures, tetrahedral geometry, and polyglycine II hydrogen-bond network in the complexes shall work cooperatively for the formation of Zn(II)-coordinated nanovesicles.

Zn-Coordinated Lipid Nanocapsules with High Physical Stability and Water-Responsive Morphological Change.

A novel lipid nanocapsule with high physical stability and the ability to undergo a water-responsive morphological change was prepared using a facile method from inexpensive and simple materials such as a glycylglycine-containing lipid and zinc acetate. The zinc-coordinated nanocapsule is comprised of solid bilayer membranes, which are stabilized by polyglycine-II type hydrogen-bond network and Zn-lipid coordination resulting in a high thermal stability in the dry state. The nanocapsules can easily encapsulate guest molecules such as methylene blue in the hollow space by dissolving the molecules in ethanol during preparation. When placed in an aqueous environment, the nanocapsules showed distinctive morphological changes and subsequent release of the methylene blue.

A hydro/organo/hybrid gelator: a peptide lipid with turning aspartame head groups.

This work presents a novel bola-type peptide lipid which can gelate water, organic solvents, and water/organic-solvent mixtures. In its molecular structure, an amphiphilic dipeptide aspartame (L-α-aspartyl-L-phenylalanine methyl ester) is connected at both ends of an alkylene linker. The different morphologies in the hydrogel (helical nanotapes) and the organogel (tape-like nanostructures) were visualized by energy-filtering transmission electron microscopy (EF-TEM) and energy-filtering scanning electron microscopy (FE-SEM), and the molecular arrangement was examined using X-ray diffraction (XRD), infrared (IR) spectroscopy, and circular dichroism (CD) spectroscopy. Possessing a hydrophilic aspartic acid group and a (relatively) hydrophobic phenylalanine methyl ester group, the dipeptide head group can turn about in response to solvent polarity. As a consequence, the solvent condition changed the molecular packing of the gelator and affected the overall supramolecular structure of the gel. It is noted that the peptide lipid gelated mixed solvents of water and organic solvents such as dichloromethane, liquid-paraffin, olive-oil, silicone-oils, and so on. The present hybrid gel can simultaneously hold hydrophilic and hydrophobic functional materials.

Higher lung accumulation of intravenously injected organic nanotubes.

The size and shape of intravenously injected particles can affect their biodistribution and is of importance for the development of particulated drug carrier systems. In this study, organic nanotubes (ONTs) with a carboxyl group at the surface, a length of approximately 2 µm and outer diameter of 70-90 nm, were injected intravenously into tumor-bearing mice. To use ONTs as drug carriers, the biodistribution in selected organs of ONTs postinjection was examined using irinotecan, as an entrapped water-soluble marker inside ONTs, and gadolinium-chelated ONT, as an ONT marker, and compared with that of a 3 µm fluorescently labeled spherical microparticle which was similar size to the length of ONTs. It was found that for irinotecan, its active metabolite and gadolinium-chelated ONTs were highly accumulated in the lung, but to a lower level in the liver and spleen. On the other hand, microparticles deposited less in the lung and more highly in the liver. Moreover, histologic examination showed ONTs distributed more in lung tissues in part, whereas microparticles were present in blood vessels postinjection. These preliminary results support the notion of using negatively charged ONTs as intravascular carriers to maximize accumulation in the lung whilst reducing sequestration by the liver and spleen. This finding suggested that ONTs are potential carriers for lung-targeting drug delivery.

Organic nanotubes for drug loading and cellular delivery.

Organic nanotubes made of synthetic amphiphilic molecules are novel materials that form by self-assembly. In this study, organic nanotubes with a carboxyl group (ONTs) at the surface were used as a carrier for the anticancer drug doxorubicin, which has a weak amine group. The IC(50) values of ONT for cells were higher than that of conventional liposomes, suggesting that ONTs are safe. The results showed that the drug loading of ONTs was susceptible to the effect of ionic strength and H(+) concentration in the medium, and drug release from ONTs was promoted at lower pH, which is favorable for the release of drugs in the endosome after cellular uptake. ONTs loaded with the drug were internalized, and the drug was released quickly in the cells, as demonstrated on transmission electron microscopy images of ONTs and the detection of a 0.05% dose of ONT chelating gadolinium in the cells. Moreover, ONT could be modified chemically with folate by simply mixing with a folate-conjugate lipid. Therefore, these novel, biodegradable organic nanotubes have the potential to be used as drug carriers for controlled and targeting drug delivery.

Necklace-like chains of hybrid nanospheres consisting of Pd nanocystals and peptidic lipids.

In this Communication, we report one-pot, high yield formation of unprecedented 1-D necklace-like chains consisting of hybrid Pd nanocrystals (NCs) embedded in spheres of a peptidic lipid. We employed the synthetic peptidic lipid, 2-(2-tetradecanamidoacetamido)acetic acid (1). We found that in the presence of palladium acetate [Pd(OAc)(2)] 1 can self-assemble into structured spheres which connect each other one by one to form the necklace chains in ethanol solutions by coordination of negatively charged carboxylic (COO(-)) groups with Pd(II). Upon reduction of ethanol, the coordinated Pd(II) are reduced into Pd atoms, which subsequently initiate the generation of Pd nuclei, and finally grow into Pd NCs embedded in the sphere chain of 1.

Metal-complexed nanofiber formation in water from dicarboxylic valylvaline bolaamphiphiles.

Nanofiber formation of dipeptide-based bolaamphiphiles, bis (N-alpha-amide--valyl--valine) 1,n-alkane dicarboxylate (n=6, 8, 10, and 12) in water was analyzed by TEM, SEM, IR, and XRD. The bolaamphiphiles proved to be coordinated to divalent transition-metal cations, such as Co2+, Ni2+, Cu2+, and Zn2+, giving precipitates, colloidal dispersions (loose hydrogels), and hydrogels upon self-assembly at 23 or 70 degrees C. Longer oligomethylene chains and strong interaction between the metal cations and the carboxylate anions are responsible for the hydrogel formation. Energy-filtering transmission electron microscopy (EF-TEM) and field-emission scanning electron microscopy (EF-SEM) images revealed that the colloidal dispersions and the hydrogels consist of a large number of nanofibers with widths of 15-20 nm and lengths of several micrometers. FT-IR and powder XRD measurement supported the existence of a beta-sheet structure-based nanofibers complexing with metal cations.

Amyloid formation of native folded protein induced by peptide-based graft copolymer.

We report here that a native folded holo-myoglobin, when incubated with a synthetic amyloidogenic peptide in aqueous solutions, forms fibrils. These fibrils took a cross-beta form (inter-strand spacing: 4.65 A and inter-sheet spacing: 10.65 A) and bound the amyloidophilic dye Congo red as did the authentic amyloid fibrils. In contrast such fibril formation of myoglobin did not occur in the absence of the peptide. These results suggest the possibility that inter-molecular interaction of native protein with the amyloidogenic peptide trigger the amyloid formation even for the non-pathogenic native protein like myoglobin, which itself exists as a globular form, under certain conditions.

Cross-Section Molecular Imaging of Supramolecular Microtubes with Contact Atomic Force Microscopy.

Bent molecules, distorted layers, columnar domains, and tube membranes (shown schematically in the picture): These hierarchical layers were directly visualized by contact atomic force microscopy along the long axes of the molecules aligned within microtubes made up of bolaamphiphile 1 by self-assembly.