Self-propelled oil droplets consuming "fuel" surfactant.

A micrometer-sized oil droplet of 4-octylaniline containing 5 mol % of an amphiphilic catalyst exhibited a self-propelled motion, producing tiny oil droplets, in an aqueous dispersion of an amphiphilic precursor of 4-octylaniline. The tiny droplets on the surface of the self-propelled droplet were conveyed to the posterior surface and released to the aqueous solution. Thus the persistent movement becomes possible in this chemical system, because the processing of chemical energy to mechanical movement proceeds by consuming exogenous fuel, not consuming the oil droplet itself. The mechanism of the unidirectional motion is hypothesized in terms of an asymmetric interfacial tension around the surface of the oil droplet.

Population study of sizes and components of self-reproducing giant multilamellar vesicles.

Population analysis of a system of self-reproducing giant multilamellar vesicles (GMVs) was carried out by means of flow cytometry. The multidimensional distribution of forward light scattering (FS), side light scattering (SS), and fluorescence (FL) intensities originating from each GMV provided information about changes in a population composed of 104 vesicles. FS-FL dot plots indicated that, after the addition of the membrane precursor, the size distribution of the newly generated vesicles was nearly the same as that of the original, but the catalyst content was reduced. This result can be interpreted as evidence for the occurrence of the self-reproduction of GMVs. Moreover, the new GMVs recovered the amount of catalyst to the initial value, keeping their size distribution constant, when a solution of the catalyst was added to the new GMVs. These results are the first experimental evidence for a novel phenomenon on GMV size distribution during their self-reproducing cycle.

Assembling liposomes by means of an oligonucleotide tagged with a lipophilic unit.

We synthesized DNA-cholesterol conjugate molecules and introduced them into 1-palmitoyl-2-oleoyl-sn-3-phosphocholine (POPC) liposomes to create DNA-tagged liposomes. These liposomes aggregated selectively depending on the sequence of DNA tag and the resultant pattern of the aggregation was a wide-spreading network structure, which was observed under a phase contrast microscope. The structure was minutely analyzed by transmission electron microscopy (TEM) and confocal laser-scanning microscopy. As a result, a hierarchical structure of the amphiphilic molecules was constructed from the liposome to the network via clustered structures.