Jong-Hwan Jeon

Synthesis of sulfonic acid-containing POSS and its filler effects for enhancing thermal stabilities and lowering melting temperatures of ionic liquids

To improve the thermal stability and lower the melting temperature of ion salts for using as ionic liquids (ILs), we designed an efficient filler based on octa-substituted polyhedral oligomeric silsesquioxane (POSS). Accordingly, the sulfonic acid-presenting POSS showed superior properties as a filler for improving thermal properties of ILs. In this report, initially the synthetic procedure for the sulfonic acid POSS is illustrated. We found that the POSS filler has good dispersibility in the ion salts, providing the series of homogeneous mixtures with various types of ion salts or ILs. Next, it is indicated that the degradation temperatures of the ion salts were significantly elevated by adding the POSS filler. Moreover, lowering effects on the melting temperatures were observed. In particular, we can demonstrate the transformation of ion salts to ILs by mixing with a small amount of the POSS filler. The data on the thermodynamic parameters during the melting process suggest that the symmetrical structure of the silica cube and the disturbance of the crystalline formation by POSS should contribute to the modulation of thermal properties of the ion salts.

Enhancement of optical properties of dyes for bioprobes by freezing effect of molecular motion using POSS-core dendrimers.

We demonstrate that the POSS-core dendrimer induced various kinds of favourable properties of trisvinyl-pyridinium triphenylamine (TP3PY) as a bioprobe. By using the amphiphilicity of the POSS core, the complexes of TP3PY with G2 POSS-core dendrimer were prepared, and the series of properties were investigated for the application as a bioprobe. Initially, it was shown that the adsorption of TP3PY onto the vessels was highly prohibited by the complex formation with the dendrimers. The solution states of the dendrimer complexes were maintained at least for 7 days. Moreover, it was found that the improvement of quantum yields and the elongation of fluorescent lifetimes were observed by the complexation with the dendrimers. Similar photochemical properties were obtained in a glassy state of 2-methyltetrahydrofuranat -196°C. The molecular rotations occurring at the excited state could be restricted by the complex formation with dendrimers. These characteristics induced by the complexation with the POSS-core dendrimer are of significance to improve the signal to noise ratio and the accuracy on the detection as a bioprobe.

Hypoxic condition-selective upconversion via triplet-triplet annihilation based on POSS-core dendrimer complexes.

The influence on the efficiencies of the triplet-triplet annihilation (TTA)-supported upconversion by oxygen under biomimetic conditions was investigated. From the solution containing the dendrimer complexes based on polyhedral oligomeric silsesquioxane (POSS)-core dendrimer with the Pt complex of octaethylporphyrin (PtOEP) and anthracene in PBS, the fluorescence emission of anthracene depending on the dissolved oxygen (DO) concentrations via the TTA-supported upconversion was obtained with the excitation light at 540 nm. In particular, we observed strong emission only under hypoxic conditions. In addition, it was found that the emission intensity via TTA-supported upconversion can be reversibly regulated by the DO concentrations in the solution.

POSS fillers for modulating the thermal properties of ionic liquids

We report a polyhedral oligomeric silsesquioxane (POSS)-based filler for improving the thermal properties of ionic liquids (ILs). We prepared homogeneous mixtures containing the octa-substituted carboxy-POSS as a filler via a solution process. Initially, it was found that the melting temperatures of the ionic pairs were lowered by adding the POSS filler. Based on this effect, some of ionic salts were transformed into ILs by adding the POSS filler. Reinforcement of thermal stability was also observed from the salts which have an intrinsically low decomposition temperature. According to the thermodynamic parameters in melting, the introduction of the POSS filler significantly reduces both the fusion enthalpy and entropy. Furthermore, from experiments on the substituent effect on POSS, it was found that only octa-carboxy POSS had an effect on the modulation of the thermal properties of ion salts. Considering these results, we summarized that the highly symmetrical rigid structure of the silica cage could be responsible for the improvement of the thermal properties of the ion salt matrices via the strong interaction between the carboxyl groups and the ion salt matrices. Our concept is feasible not only for the conversion of conventional ionic salts into ILs, but also for the development of new series of ILs.

Facile design of organic–inorganic hybrid gels for molecular recognition of nucleoside triphosphates

We report the molecular recognition for nucleoside triphosphates inside the ligand-modified water-soluble organic-inorganic hybrid gels composed of polyhedral oligomeric silsesquioxane (POSS). The series of ligands were designed to make hydrogen bonds with each nucleobase and introduced into the hybrid gels. From the titration experiments, the binding constants between the ligand inside the gels and nucleosides were evaluated. Accordingly, it was found that the ligands inside the gels can form a stable complex only with the target nucleoside triphosphate which has the complementary pattern of the hydrogen bonds (Ka=G-gel/cytidine triphosphate (CTP), 3.5×10(8)M(-1); U-gel/adenosine triphosphate (ATP), 1.6×10(3)M(-1); A-gel/uridine triphosphate (UTP), 1.9×10(7), respectively). With other nucleoside derivatives which have different numbers of phosphate units or different types of nucleobases, the much weaker interaction was detected. These data indicate that the complex formation only with nucleoside triphosphates should occur inside the hybrid gels, and selective recognition of each nucleoside triphosphate can be accomplished.

Development of highly-sensitive detection system in 19F NMR for bioactive compounds based on the assembly of paramagnetic complexes with fluorinated cubic silsesquioxanes

This manuscript reports the detection system with 19F NMR probes for bioactive amine compounds at sub-micro molar concentrations. Water-soluble fluorinated polyhedral oligomeric silsesquioxane (POSS) derivatives were prepared, and the paramagnetic Ni-porphyrin (NiPor) with the fluorinated POSS (F-POSS) was adsorbed in the buffer. By adding the series of amine derivatives to the homogeneous dispersion containing the POSS-NiPor complexes, the changes in the signal intensity were evaluated. It was clearly observed from homogeneous dispersions that the signal intensity of 19F NMR decreased especially in the presence of ethanediamine and hexylamine. From the dynamic light scattering measurements, it was revealed that the assembly of the F-POSS complexes was dramatically induced by the amine compounds when the signal intensity decreased. According to these data, it is proposed that the signal reduction of 19F NMR from the POSS-NiPor complexes could be induced via the strong paramagnetic relaxation enhancement from NiPor in the assembly. Finally, based on the signal reduction by the assembly, we can detect the amine derivatives under 1μM concentration which is similar sensitivity to the conventional fluorescence probes. Our system is valid to monitor the distribution of the bio-active molecules at cellular concentrations.

Adamantane ionic liquids

We report the synthesis and characteristic thermal properties of the adamantane-based ionic salts. The ionic salts with adamantane carboxylates and imidazolium cations were prepared via neutralization. It was found that the assembly of the ion pairs on the adamantane core can improve the thermal stability and lower melting temperatures even though the molecular weight increases. Finally, the thermally-stable room temperature-ionic liquids, which are defined as a salt with the melting temperature below 25 °C, can be obtained based on adamantane. The tetrahedral-like distribution of ion pairs could be responsible for simultaneously improving thermal stability and lowering melting temperatures of ion pairs.