Takanori Kishida

Binary organogelators which show light and temperature responsiveness.

The gelation ability of 10 alkylammonium (CnH(2n+1)NH3+ where n=4-11, 12 and 16) anthracene-9-carboxylates (1n) has been evaluated. In cyclohexane, 1(4), 1(5), 1(6) and 1(7) only provided precipitates whereas 1(11), 1(12) and 1(16) provided very viscous solutions. In contrast, 1(8) 1(9) and 1(10) resulted in gels. The critical gelation concentration of 1(10) was very low (5.0 x 10(-4) mol dm(-3)). SEM observations showed that in the gel phase the morphology changes from straight fibrils to frizzy fibrils with the increase in n, whereas in the sol phase the formation of the sheet-like, two-dimensional aggregate is recognized. When the cyclohexane 1(10) gel was photoirradiated (lambda > 300 nm), the UV-VIS absorption bands assignable to monomeric anthracene were decreased and the gel was changed into the sol. It was confirmed by dark-field optical microscopy that the fibrillar bundles supporting the gel formation gradually disappear with photoirradiation time. When this sol was warmed at 30 degrees C in the dark, the gel was not regenerated but the precipitation of 1(10) resulted. When this sol was heated once at the bp of cyclohexane and cooled to 15 degrees C, the solution was changed into the gel again. This finding indicates that the fibrillar structure required for the gel formation is not reconstructed at 30 degrees C but obtained only when the hot cyclohexane solution is cooled.

Creation of polynucleotide-assisted molecular assemblies in organic solvents: general strategy toward the creation of artificial DNA-like nanoarchitectures

The influence of added polynucleotide on the gelation ability of nucleobase-appended organogelators was investigated. Uracil-appended cholesterol gelator formed a stable organogel in polar organic solvents such as n-butanol. It was found that the addition of the complementary polyadenylic acid (poly(A)) not only stabilizes the gel but also creates the helical structure in the original gel phase. Thymidine and thymine-appended gelators can form stable gel in apolar solvents, such as benzene, where poly(A)-lipid complex can act as a complementary template for the gelator molecules to create the fibrous composites. Based on these findings, we can conclude that self-assembling modes and gelation properties of nucleobase-appended organogelators are controllable by the addition of their complementary polynucleotide in organic solvents. We believe, therefore, that the present system can open the new paths to accelerate development of well-controlled one-dimensional molecular assembly systems, which would be indispensable for the creation of novel nanomaterials based on organic compounds.