Allosteric binding of anionic guests to a bicyclic host which imitates the action of a 'turnstile'

A bicyclic host 1, which has a diethynyl tetrafluorophenyl axis and is expected to behave as an anion-binding 'turnstile', has been designed.     

Sol-gel reaction of porphyrin-based superstructures in the organogel phase: creation of mechanically reinforced porphyrin hybrids

We have demonstrated that a one-dimensional molecular assembly created by an H-aggregated porphyrin.Cu(II) stack can be immobilized, without a morphological change, by sol-gel polycondensation of the peripheral triethoxysilyl groups. The resultant gel prepared according to this flowchart has gained a very high thermal stability as well as a unique mechanical strength.     

Oligosilane-nanofibers can be prepared through fabrication of permethyldecasilane within a helical superstructure of schizophyllan

[chemical structure: see text]. Schizophyllan can interact with permethyldecasilane to produce the corresponding decasilane-nanofiber, in which the decasilane adopts helical conformations in a tubular hollow created by the helical superstructure of schizophyllan.     

Allosteric silver(I) ion binding with peripheral pi clefts of a Ce(IV) double decker porphyrin

[reaction: see text] A cerium(IV) double decker porphyrin (1) bearing four 4-methoxyphenyl groups was synthesized. Compound 1 shows a positive, homotoropic allosteric effect in metal recognition of Ag(+) ion, and the peripheral pi clefts of 1 act as effective binding sites for Ag(+) ion.     

Controlling interparticle spacing among metal nanoparticles through metal-catalyzed decomposition of surrounding polymer matrix

Systematic and reproducible control over average interparticle spacing of Pt, Ni, and Cu nanoparticles embedded in polyimide thin layers was achieved. The metal-catalyzed decomposition of polyimide matrixes surrounding metal nanoparticles causes a decrease in the composite layer thickness, while maintaining the size of nanoparticles. This ability provides an effective methodology for the preparation of metal/polymer nanocomposites with tailored microstructures and holds great promise toward the fundamental understanding of the physical interactions among metal nanoparticles.     

The concept of molecular machinery is useful for design of stimuli-responsive gene delivery systems in the mammalian cell

Since the first generation of molecular machines including photoresponsive crown ethers and its analogues was reported by Shinkai et al., a huge number of molecular machines exhibiting dynamic chemical and physical functions have been designed and developed. On the other hand, non-viral vectors are desired to possess conflicting properties to associate with DNA until reaching the nucleus as their final destination and dissociate from DNA there. In other words, non-viral vectors should work as a sort of molecular machinery. To overcome this dilemma, recently, much attention is focused on the development of the intelligent vectors, also called as ‘stimuli responsive vectors’ working as molecular machines. In this review, stimulus responsive gene delivery systems in which some structural factors and/or physiological properties are regulated in response to extracellular signals such as redox, pH, ultrasound, light, temperature, etc. are introduced as a new generation of non-viral vectors. These extracellular signals such as ultrasound, light, and temperature can be potent stimuli capable of site-, timing-, and duration-specific gene expression. This is a paper selected for “HGCS Japan Award of Excellence 2006”.     

A new synthesis of p-nitrocalix[6]arene

p-Nitrocalix[6]arene which possibly serves as a potential intermediate to derive functionalized calixarenes was synthesized for the first time.     

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.