By convenient processing, such as room-temperature preservation and evaporation of solvents, and using organic solvents which are good solvents of nanotube materials, we have succeeded in mass-producing over 1 kg of solid-powdery organic nanotubes with the amounts of solvents lower than 1,000-10,000th of that needed for conventional methods.
Figure 4 illustrates that the synthesized amphiphilic molecules can form nanotube assemblies in only one step, without undergoing multiple steps like nanotubes in water, resulting in the production of a large amount of nanotubes in a very short time. We have confirmed that the white solid powders consist of organic nanotubes of 40-200 nm in inner diameter, 70-500 nm in outer diameter, and several µm in length using transmission and scanning electron microscopes (Figure 5).
In this work, we have produced over 1 kg of nanotubes using organic solvents of approximately 10 L (conventional methods need 20,000 L of water). Furthermore, in preparation of nanotubes enabling encapsulation of functional substances, conventional methods need a vacuum-drying process over several days, but our organic solvent method makes the drying process easy to accomplish in several hours.
The characteristics, sizes, and functions of our organic nanotubes are different from those of carbon nanotubes, and hereafter their applications, research and development, and research for practical use will be accelerated as a work originating from Japan. We have thus named our nanotubes the "Organic Nanotube AIST," and we have recently applied for this to be registered as our trademark.
Cyclic molecules, called "cyclodextrin," which are constituted of 6-8 glucose molecules connected circularly, have been widely used in a variety of fields, such as food, medicine, and house hold goods. Encapsulating various organic low-molecular-weight compounds in their hydrophobic pockets, the molecules have functions in making unstable substances stable, in the slow release of medicines and aroma chemicals, and in making water-insoluble substances soluble.
On the other hand, organic nanotubes formed by self-assembly of glycolipids can be well dispersed in water. Furthermore, the nanotubes can encapsulate 10-50-nm scale substances, e.g. proteins, nucleic acids, viruses, and metal nanoparticles, which cyclodextrin molecules cannot, to disperse them in water. Actually, using organic nanotubes of 30-60 nm in inner diameter, we have succeeded in the encapsulation of metal nanoparticles of 1-20 nm in diameter and spherical proteins of 12 nm in diameter (ferritin) as shown in Figure 6.
Recently products utilizing encapsulation functions of cyclodextrin have been researched and developed, and many of them have already been produced on a commercial basis. However, our nanotubes, enabling mass-production and encapsulation of large molecules, are promising for industrial applications as new materials with encapsulation functions.