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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.

Unsymmetrical bolaamphiphiles, ω-[N-β-d-glucopyranosylcarbamoyl]alkanoic acids, with even-numbered oligomethylene chains (12, 14, 16, 18, and 20 carbons) self-assembled in water to form lipid nano- and microtubes. The tubular assemblies were separated by centrifugation and examined by transmission electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy to study the molecular packing within the tubular membranes. The nanotubes encapsulated the staining reagent phosphotungstate, which revealed them to be hollow cylinders up to several hundred micrometers long with 30−43-nm outer diameters and 14−29-nm inner diameters. By comparing the membrane stacking periodicity obtained from powder X-ray diffraction analysis of the dehydrated tubes with the molecular packing within single crystals, we found that the nanotubes consist of an unsymmetrical monolayer lipid membrane (MLM) in which the molecules are packed in a parallel fashion. This suggests that the inner surface of the nanotubes is covered with carboxy headgroups and the outer surface with 1-glucosamide headgroups. The inner diameters of the lipid nanotubes could be controlled in the range 17.7−22.2 nm in steps of ∼1.5 nm/two carbons by varying the oligomethylene spacer length. The microtubes had three types of molecular arrangements. The first type was a symmetrical MLM in which the molecules were packed in an antiparallel fashion. The other two types had unsymmetrical MLM stacking with head-to-head and head-to-tail motifs. Increasing the number of oligomethylene spacers stabilized the unsymmetrical MLM structure in both nano- and microtubes.

New crown-appended cholesterol-based organogelator 1, which has two cholesterol skeletons as a chiral aggregate-forming site, two amino groups as an acidic proton-binding site, and one crown moiety as a cation-binding site, was synthesized, and the gelation ability was evaluated in organic solvents. It can gelate acetic acid, acetonitrile, acetone, ethanol, 1-butanol, 1-hexanol, DMSO, and DMF under 1.0 wt %, indicating that 1 acts as a versatile gelator of various organic solvents. To characterize the aggregation mode in the organogel system, we observed a CD spectrum of the acetic acid gel 1. In the CD spectrum, the lambda(theta)=0 value appears at 353 nm, which is the same as the absorption maximum lambda(max) = 353 nm. The positive sign for the first Cotton effect indicates that the dipole moments of azobenzene chromophores tend to orient in a clockwise direction. Very surprisingly, the TEM images of the 1 + acetic acid gel resulted in the helical ribbon and the tubular structures. Sol-gel polymerization of tetraethoxysilane was carried out using 1 in the gel phase. The silica obtained from the 1 + acetic acid gel showed the helical ribbon with 1700-1800-nm pitches and the tubular structure of the silica with approximately 560-nm outer diameter. As far as can be recognized, all the helicity possesses a right-handed helical motif. Since the exciton-coupling band of the organogel also shows R (right-handed) helicity, we consider that a microscopic helicity is reflected by a macroscopic helicity.

Self‐assembly of glycolipids into open‐ended organic nanotubes (see Figure) is reported here. Depending on the solvent system used and the degree of saturation of the glycolipid, either gels or nanofibers of various morphologies form. Upon standing, the unsaturated glycolipid–based nanofibers transform into nanotubes with inner diameter 10–15 nm and length 10–100 μm.

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Nucleotide-appended bolaamphiphiles 1−7, in which two 3‘-phosphorylated thymidine moieties are connected to both ends of a long oligomethylene spacer, have been first synthesized. Their self-assembling behavior in aqueous solutions was investigated in terms of gelling ability of water molecules. The longer homologues 6 and 7 with the C18 and C20 oligomethylene spacers, respectively, proved to be capable of gelling water very effectively (>25 000 water molecules per molecule) through spontaneous formation of a fibrous network. Gelation behavior of both bolaamphiphiles strongly depended on the pH and temperature of the aqueous solutions used. The gel-to-sol transition temperature (TGS) of 7 was determined to be approximately 85 °C. XRD measurement of a freeze-dried hydrogel from 7 suggested the presence of lamellar organization consisting of monolayer sheets. Hydrogen bonds involving the 5‘-hydroxyl group of the deoxyribose moiety, hydrophobic interaction between the long oligomethylene chains, and π−π stacking of the thymine residues are responsible for the effective hydrogel formation.