Selective metal deposition on photoswitchable molecular surfaces

We report here a novel phenomenon: selective metal deposition on photoswitchable diarylethene (DAE) surfaces. Magnesium vapor was deposited by vacuum evaporation on the colored DAE but not on the uncolored surface. The selective deposition originates in the change of the glass transition temperature of the amorphous DAE film resulting from photoisomerization and therefore from changes of surface molecular motion. We clarified that Mg atoms on the uncolored surface actively migrated on the surface and were desorbed from the surface. The possibility of depositing other metals is also discussed. Light-controllable metal-integrated deposition was demonstrated as a new function of the photoswitchable molecular surfaces. This study reveals new features of the photoswitchable molecular surfaces, and their potential suggests bright prospects for future applications in organic electronics.     

Design, synthesis, and properties of 2',4'-BNA(NC): a bridged nucleic acid analogue

The novel bridged nucleic-acid analogue 2',4'-BNA(NC) (2'-O,4'-C-aminomethylene bridged nucleic acid), containing a six-membered bridged structure with an N-O linkage, was designed and synthesized efficiently, demonstrating a one-pot intramolecular NC bond-forming key reaction to construct a perhydro-1,2-oxazine ring (11 and 12). Three monomers of 2',4'-BNA(NC) (2',4'-BNA(NC)[NH], [NMe], and [NBn]) were synthesized and incorporated into oligonucleotides, and their properties were investigated and compared with those of 2',4'-BNA (LNA)-modified oligonucleotides. Compared to 2',4'-BNA (LNA)-modified oligonucleotides, 2',4'-BNA(NC) congeners were found to possess: (i) equal or higher binding affinity against an RNA complement with excellent single-mismatch discriminating power, (ii) much better RNA selective binding, (iii) stronger and more sequence selective triplex-forming characters, and (iv) immensely higher nuclease resistance, even higher than the S(p)-phosphorthioate analogue. 2',4'-BNA(NC)-modified oligonucleotides with these excellent profiles show great promise for applications in antisense and antigene technologies.     

Release and transfer of polystyrene dewetting pattern by hydration force

We studied the release and transfer of polystyrene (PS) microdots on mica. The PS dots were released from the mica in water. The release was affected by the density of K(+) ions on the mica surface, which was controlled by pretreatment with K(2)CO(3) solutions. The release of PS dots became dominant at the concentrations above [K(+)]crit = 1 x 10(-4) M in the K(2)CO(3) solution. In this concentration region, repulsive forces appeared as a result of the hydration of K(+) ions on the mica (J. Colloid Interface Sci. 1981, 83, 531). This result suggests that the repulsive hydration force causes the release of the PS dots. Followed by the release process, we successfully demonstrated the transfer of the array of PS dots from the mica to another substrate.     

Microcapsules with macroholes prepared by the competitive adsorption of surfactants on emulsion droplet surfaces

We demonstrate a simple, unique method for preparing microcapsules with holes in their shells. Cross-linked polymelamine microcapsules are prepared by the phase-separation method. The holey shell of each microcapsule is synthesized on the surface of an oil-in-water (O/W) emulsion droplet where a water-soluble polymeric surfactant and an oil-soluble surfactant are competitively adsorbed. The water-soluble polymeric surfactant provides a reaction site for shell formation. The oil-soluble surfactant molecules seem to self-assemble while the shells are being formed, so holes appear where they assemble. The critical degree of surface coverage of an emulsion droplet by the water-soluble polymeric surfactant needed to form the holey shells is determined to be 0.90 from theoretical calculations in which competitive adsorption is considered. Theoretical consideration suggests that the size and quantity of the holes in the microcapsule shells are controlled by the composition of the surfactants adsorbed on the surface of an emulsion droplet. This theoretical consideration is confirmed by experiments. The prepared microcapsule with controllable macroholes in its shell has the potential to be used for controlled release applications and can be used to fabricate a microcapsule that encapsulates hydrophilic compounds.     

Freezing phenomena of lennard-jones fluid confined in jungle-gym nanospace: a monte carlo study

We performed grand canonical Monte Carlo simulations for a Lennard-Jones fluid confined in a jungle-gym (JG) nanospace of cubic structure modeled on a specific type of metal organic frameworks (MOFs) to investigate freezing phenomena. Our simulations clarified that the JG nanospace with the pore sizes from 5sigma to 11sigma strongly depresses freezing due to a geometrical hindrance effect, resulting in far lower freezing temperature than the bulk freezing point. The fluid-rod interaction is found to give little effect on the freezing temperature in the larger pore sizes. For smaller pores from 2sigma to 3sigma, on the other hand, a dominant factor is a template effect to enhance the localization of molecules into a specific configuration that matches the locations of potential minima, leading to a variety of molecular configurations. In this range of smaller pore sizes, the solidification temperatures are higher than those of the larger pores mainly due to strong influence of the fluid-rod interaction but are still lower than the bulk freezing temperature. In addition, a unique solid-to-solid transition is observed in a specific size of pore of 2.73sigma, which is caused by structural correlation between adjacent cells. On the basis of these results, a phase diagram in the JG nanospace is drawn.     

Self-assembled monolayer compatible with metal surface acoustic wave devices on lithium niobate

The formation of a siloxane self-assembled monolayer (SAM) film on a lithium niobate substrate was investigated for surface acoustic wave (SAW) sensor devices for the detection of hydrogen. The most widely used SAM coupling reagent, octadecyltrichlorosilane, etches aluminum metal features that are integral to sensor devices, due to the formation of high local concentrations of hydrochloric acid. An alternative coupling reagent, octadecyltrimethoxysilane (OTMS), does not show any etching of metal parts. OTMS and related molecules are compatible with conventional SAW device manufacturing techniques and other devices that contain metal features susceptible to etching by acid released in the SAM formation process.     

Electrokinetic effect of the bottom surface of a vessel on pearl-chain formation of silica particles

We have tackled in situ electric conductance measurements under microscopic observations for alignments of silica particles that are induced by ionic polarization of the electrical double layer (EDL) around the particles. Using the in situ conductance measurements, we have presented evidence that electro-osmotic flow at a vessel bottom/water interface would be coupled with the ionic polarization in the EDL of spherical silica particles settling at the bottom (Langmuir 2007, 23, 8797). In this study, we followed this phenomenon further. We altered the zeta potential of a platform of a glass plate on which a pearl chain of silica particles was formed under an ac electric field to control the mobility of electro-osmotic flow at the macroscopic interface of the platform/water. As the magnitude of the zeta potential of the platform increased, the surface distance between neighboring particles in the pearl chains decreased and the in situ conductance totally increased due to the enhancement of the dipole moments induced by the ionic polarizations of the particles. These results could be explained by considering that the electro-osmotic contribution to the surface conduction around the particles would be coupled with that occurring at the platform/water interface.     

Self-motion of a phenanthroline disk on divalent metal ion aqueous solutions coupled with complex formation

The self-motion of a 1,10-phenanthroline disk on divalent metal ion aqueous solutions was investigated as a simple autonomous motor coupled with complex formation. The characteristic features of motion (continuous and oscillatory motion) and their concentration regions differed among metal ions, and the frequency of oscillatory motion depended on the temperature of the aqueous solution. The nature of the characteristic motion is discussed in relation to the stability constant of complex formation between phenanthroline and a metal ion, and the difference in surface tension between phenanthroline and its metal complex as the driving force.