No abstract

A new family of oligopeptide-based bolaamphiphiles, glycylglycine-(1a-h), glycylglycylglycine-(2a-b), sarcosylsarcosine-(3), L-prolyl-L-proline-(4), glycylsarcosylsarcosine-( 5), and glycyl-L-prolyl-L-proline (6)based bolaamphiphiles with a dicarboxylic headgroup at each end, has been synthesized. The oligopeptide fragments were linked via amide bond to a long-chain R,ω-dicarboxylic acid as a hydrocarbon spacer. Self-assembling properties of these bolaamphiphiles in water have been studied by light and cryogenic temperature transmission electron microscopy, infrared spectroscopy, and pH titration. Only sodium or potassium salts (acid soap) of the bolaamphiphiles 1a, 1c, 1e, 2a, and 2b produced well-defined microtubes of 1-3-µm diameter with closed ends. All the tubes encapsulated a number of vesicular assemblies inside the aqueous compartment. The tube formation strongly depends on the connecting alkylene chain length, the alkylene even-odd carbon numbers, and constituent amino acid residues. Vectorial formation of acid-anion dimers and loose interpeptide hydrogen-bond networks are responsible for the microtube self-assembly. The atomic force microscopic observation of the microtube made of 1e revealed a distorted hexagonal arrangement of the headgroups on the surface. A self-assembling model and the tube formation mechanism are also discussed from the viewpoint of proton-triggered self-assembly.

The helical ribbon and double-layered nanotubular structures of the titanium dioxide were created by sol−gel polymerization of Ti(OiPr)4] using 1 as a template in 1-butanol. All TiO2 nanotubes consist of two layers, 8−9 nm of nanospace between layers. In addition, the helicity of the helical ribbon titanium dioxide showed a right-handed motif.

Bolaamphiphiles with a 1-glucosamide-head group at each end, N,N‘-bis(β-d-glucopyranosyl)alkane-1, n-dicarboxamide [Glc-NC( n )CN-Glc, n = 6, 9, 10, 11, 12, 13, and 14], have been synthesized. Self-assembled supramolecular structures in water strongly depend on whether n is even or odd, which respectively give rise to fibrous assemblies or planar platelets as well as amorphous solids. In connection with this even−odd effect of the hydrocarbon links, internal molecular arrangements of the solid fibers were investigated using FT-IR spectroscopy, X-ray diffraction and crystal analyses, and transmission electron microscopy. The oligomethylene groups of the Glc-NC(12)CN-Glc pack in a monoclinic or an orthorhombic mode in the fiber. We propose a possible self-assembled model based on a monolayer sheet, which is stabilized by hydrogen-bond networks via sugar-head and amide groups.

A new sugar-based gelator 1 was synthesized, and its gelation ability was evaluated in organic solvents and water. Very surprisingly, 1 was found to gelate organic solvents as well as water, indicating that 1 can act as an amphiphilic gelator. We characterized on superstructures of an aqueous gel from 1 using SEM, TEM, NMR, IR, and XRD. The aqueous gel 1 formed a three-dimensional network with 20-500 nm diameter puckered fibrils. In addition, the chiral aggregate was found to be largely twisted helical ribbons with ca. 85 nm width, ca. 315 nm pitch, and up to several micrometer length, whose helicity was exclusively left-handed. XRD diagrams indicate that an aqueous gel 1 maintains a bilayered structure with 2.90 nm long-range spacing. This gives the first example of the formation of well ordered bilayer-based aqueous gel. The XRD, FT-NMR, and FT-IR results suggested that the aqueous gel 1 is stabilized by a combination of the hydrogen bonding, π-π interactions, and hydrophobic forces.