Ionic Liquids Containing Silsesquioxane and Cyclic Siloxane Frameworks.

This paper describes the author's recent work on the preparation and properties of thermally stable ionic liquids (ILs) containing siloxane frameworks. Quaternary ammonium and imidazolium salt-type ILs containing random oligosilsesquioxane frameworks were successfully prepared via the hydrolytic condensation of the corresponding organotrialkoxysilanes by using an aqueous superacid bis(trifluoromethanesulfonyl)imide (HNTf2 ) solution as a catalyst and solvent. Imidazolium salt-type ILs containing polyhedral oligomeric silsesquioxane (POSS) frameworks were also prepared through a reaction similar to that described above by using a water/methanol mixed solution of HNTf2 . In addition, amorphous POSSs with two types of ionic groups randomly distributed in the side chain were prepared. These POSSs were ILs exhibiting fluidity at relatively low temperatures. Furthermore, imidazolium and ammonium salt-type ILs containing cyclic oligosiloxane frameworks were prepared through a reaction similar to that of the corresponding organodialkoxysilanes. The thermal decomposition temperatures of the above ILs containing siloxane frameworks were higher than those of general ILs.

Control of Crystalline-Amorphous Structures of Polyhedral Oligomeric Silsesquioxanes Containing Two Types of Ammonium Side-Chain Groups and Their Properties as Protic Ionic Liquids.

Polyhedral oligomeric silsesquioxanes (POSSs), Am-POSS(x,y), prepared by hydrolytic condensation, contains two types of ammonium side-chain groups, where the numbering of x and y represents the type of ammonium ions in the POSS structure, corresponding to primary (1), secondary (2), tertiary (3), and quaternary (4) ammonium ions. Mixtures of the two starting materials selected from organotrialkoxysilanes containing primary, secondary, and tertiary amines and a quaternary ammonium salt [(RO)3Si(CH2)3R', R = CH3 or CH2CH3, R' = NH2, NHCH3, N(CH3)2, and N(CH3)3Cl] were dissolved in dimethyl sulfoxide (DMSO). The hydrolytic condensation was performed in the presence of bis(trifluoromethansulfonyl)imide (HNTf2) and water. All Am-POSS(x,y) structures consisted of a cage-type octamer (T8-POSS), as confirmed by 29Si NMR spectrometry and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analyses indicated that Am-POSS(1,3), Am-POSS(1,4), and Am-POSS(2,4) had amorphous structures. These POSSs have two or three differences in the number of methyl groups between the two types of ammonium side-chains. Conversely, Am-POSS(1,2), Am-POSS(2,3), and Am-POSS(3,4) had crystalline structures. The difference in the number of methyl groups between the two types of ammonium side-chains in these POSSs is only one. Therefore, the crystalline-amorphous structure of Am-POSS(x,y) is controlled by the side-chain group combinations. Furthermore, Am-POSS(1,3), Am-POSS(1,4), and Am-POSS(2,4) are protic ionic liquids with relatively low flow temperatures.

Preparation of Ammonium-Functionalized Polyhedral Oligomeric Silsesquioxanes with High Proportions of Cagelike Decamer and Their Facile Separation.

In this study, we found that ammonium-functionalized polyhedral oligomeric silsesquioxanes (POSSs; 2Am-POSS and Am-POSS) with high proportions of cagelike decamer (T10-POSS; 54% and 45%, estimated from 29Si NMR spectra) could be successfully prepared by the hydrolytic condensation of 3-(2-aminoethylamino)propyltrimethoxysilane and 3-amimopropyltrimethoxysilane, respectively, using trifluoromethanesulfonic acid as a catalyst in hydrophobic alcohols such as 1-hexanol. In addition, on the one hand, it was also found that 2Am-POSS, a mixture of cagelike octamer (T8-POSS), T10-POSS, and cagelike dodecamer (T12-POSS), could be separated into T8-POSS and a mixture of T10- and T12-POSSs by exploiting their different solubilities in 1-butanol. On the other hand, in the case of Am-POSS, T8-POSS and a mixture of T10- and T12-POSSs could be isolated by treatment with ethanol-methanol mixed solvent and 1-propanol. The XRD patterns of cast films of T8-POSS showed many sharp diffraction peaks, indicating crystalline structures, whereas those of T10- and T12-POSSs showed no diffraction peaks, indicating amorphous structures, for both the case of 2Am-POSS and Am-POSS. These results suggest that the difference in crystallinities between the ammonium-functionalized T8-POSS and T10- and T12-POSSs causes their different solubilities in alcohol solvents.

Selective Synthesis of cis-trans-cis Cyclic Tetrasiloxanes and the Formation of Their Two-Dimensional Layered Aggregates.

In this study, a single cyclic tetrasiloxane containing propylammonium trifluoromethanesulfonate and methyl side-chain groups (Am-CyTS) was selectively prepared by the hydrolytic condensation of 3-aminopropyldiethoxymethylsilane using aqueous superacid trifluoromethanesulfonic acid. The (1)H NMR spectrum of Am-CyTS in D2O exhibited a single signal assigned to a methyl group, and the (29)Si NMR spectrum of Am-CyTS in DMSO-d6 also exhibited only one signal. In the matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS) and the electrospray ionization mass spectrometry (ESI MS) analyses, the peaks corresponding to the masses of the cyclic tetrasiloxane were observed. These results indicate that Am-CyTS is a single cyclic tetrasiloxane without isomers. In addition, the result of a single-crystal X-ray structural analysis of its tert-butoxycarbonyl (Boc)-protected compound (Boc-CyTS) indicated the formation of a cis-trans-cis cyclic tetrasiloxane forming two-dimensional layered aggregates. Moreover, it was found that two-dimensional layered aggregates could be formed by drop-casting an aqueous solution of Am-CyTS and chloroform solution of Boc-CyTS onto glass substrates, as shown by powder X-ray diffraction measurements.

Preparation of a sulfo-group-containing rod-like polysilsesquioxane with a hexagonally stacked structure and its proton conductivity.

A sulfo-group-containing rod-like polysilsesquioxane with a hexagonally stacked structure (PSQ-SO3H) was successfully prepared by oxidation and hydrolytic polycondensation of 3-mercaptopropyltrimethoxysilane (MPTMS) in a mixed aqueous solution of NaOH and H2O2. The X-ray diffraction pattern of the PSQ-SO3H film exhibited three diffraction peaks with a d-value ratio of 1:1/√3:1/2, indicating the formation of a hexagonally stacked structure. In addition, the transmission electron microscopy image of PSQ-SO3H exhibited a striped pattern, indicating that the rod-like PSQs were stacked in a parallel fashion. The presence of ionic side-chains composed of the sulfonate anions and sodium cations during the hydrolytic polycondensation of MPTMS was found to be essential for the formation of this regularly structured PSQ. Finally, the proton conductivity of the PSQ-SO3H film, determined by using complex impedance spectroscopy, was relatively high (>10(-2) S cm(-1)) at 80 °C and 30-90 % relative humidity.

Stereoselective synthesis of different cyclic tetrasiloxane isomers depending on the superacid catalyst employed.

In this study, we investigated the hydrolytic condensation of 3-aminopropyldiethoxymethylsilane over different superacid catalysts. We found that cyclic tetrasiloxanes with different stereostructures (Am-CyTS-NNf2 and Am-CyTS-NHf2) could be selectively prepared in high yields (>95%) depending on the superacid catalyst employed (bis(nonafluorobutanesulfonyl)imide or cyclohexafluoropropane-1,3-bis(sulfonyl)imide). The single-crystal X-ray structural analyses of compounds in which amino groups of Am-CyTS-NNf2 and Am-CyTS-NHf2 were protected by the tert-butoxycarbonyl group revealed the formation of all-cis and cis-trans-cis cyclic tetrasiloxanes, respectively.

Preparation of Antifog Hard Coatings Based on Carboxy-Functionalized Polyhedral Oligomeric Silsesquioxane Cross-Linked with Oligo(ethylene glycol)s.

In this study, we prepared antifog hard coatings by heating a mixture of carboxy-functionalized polyhedral oligomeric silsesquioxane (POSS-C) and oligo(ethylene glycol)s (OEGs, HO(CH2CH2O) n H, n = 1-6) in N,N-dimethylformamide, applying the mixture onto a glass substrate, and subsequently removing the solvent via heating. In addition, we evaluated the water resistance, hardness, and antifogging performance of the coatings. In particular, the coating produced at a 2:1 functional group ratio of POSS-C to tetraethylene glycol (OEG, n = 4) coating exhibited high surface hardness (6H), as determined using pencil scratch testing. The coating remained clear after exposure to the vapor of warm water at 40 °C at a height of 2 cm for 10 s, demonstrating its antifogging property. Furthermore, no dissolution or cracking was observed when the POSS-C/OEG coating (n = 4, COOH/OH = 2:1) was immersed in water at room temperature for 1 h, confirming its water resistance. The Fourier transform infrared/attenuated total reflectance results showed the formation of ester bonds, indicating the construction of a network structure that enhanced the water resistance and hardness of the coating.

Swelling and gel/sol formation of perchlorate-type layered double hydroxides in concentrated aqueous solutions of amino acid-related zwitterionic compounds.

ClO(4)(-)MgAl-LDH3, a MgAl (Mg/Al = 3) layered double hydroxide (LDH) containing perchlorate, swells and forms colloidal suspensions (sols) via the gel state in concentrated aqueous solutions of zwitterionic compounds related to amino acids. In total, 36 zwitterionic compounds with different molecular structures and additional functional groups were examined at various concentrations, and the sol-formation ability was judged by the transmittance (at λ = 589 nm) of the resulting suspensions. At low concentration, the obtained suspensions were turbid, with transmittances of ~0%. However, above the threshold concentration (0.3-1.0 M), osmotic swelling occurred and the transmittances of the suspensions increased sharply with increases in concentration to reach maximum values of 70-95%. The threshold concentration and maximum transmittance value depended on the structure and the location of the functional groups. The enhancement of the permittivity of water by the zwitterions and the formation of H-bond networks were assumed to be the reasons for the swelling phenomenon. Similar gel/sol formation was observed for ClO(4)(-)LDHs with Mg/Al = 2, Ni/Al = 2, 3, and Co/Al = 2 and some NO(3)(-)LDHs. Large ClO(4)(-)LDH films could be prepared by filtration of the colloidal suspensions followed by washing and drying processes.

Behavior of chiral induction from polysilsesquioxanes bearing chiral and ammonium groups to anionic pyrene derivatives.

The behavior of chiral induction from ladder-like polysilsesquioxanes (R60- and S60-PSQs) bearing chiral and ammonium side-chain groups (compositional ratio = ca. 60:40) to the anionic pyrene derivative, 1,3,6,8-pyrenetetrasulfonic acid tetrasodium salt (PTSNa4), was investigated. The circular dichroism (CD) spectra of PTSNa4/(R60- and S60-PSQs) mixtures in methanol exhibited reverse peaks at 230-250, 280-290, and 310-370 nm, which were assigned to PTSNa4 and indicated that the achiral PTSNa4 molecule had chirality induced from the chiral PSQs. In addition, it was found that an eximer of PTSNa4 was formed by hybridization with the chiral PSQs, i.e., the emission peaks not only due to a monomer state at 385 and 408 nm but also due to an eximer at 460-520 nm were observed in the fluorescence spectrum excited at 377 nm. This result suggests that the negatively charged PTSNa4 formed an eximer along the positively charged side-chain ammonium groups of PSQs. To investigate the influence of the structures of the pyrene derivatives on chiral induction behavior, the CD measurements of the mixtures of R60- and S60-PSQs in methanol with different pyrene derivative, 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (pyranine), were also performed. It was found that the intensities of the absorptions for the pyanine solutions were lower than those for PTSNa4 solutions. These results suggest that the point-symmetry of the pyrene derivatives influences the level of chiral induction. Therefore, the point-symmetry of pyrene derivatives is an important factor for determining the behavior of chiral induction from chiral PSQs to these compounds.

Preparation of highly water-dispersible titanium-silicon binary oxide materials by sol-gel method.

The preparation of highly water-dispersible titanium-silicon binary oxide materials was performed by the following two-stage sol-gel reactions. First, the mixture of titanium tetraisopropoxide and 3-aminopropyltrimethoxysilane was stirred in a mixed solvent of isopropyl alcohol and 0.5 mol/L methanolic hydrochloric acid at room temperature, followed by heating in an open system until the solvent was evaporated. Then, the aqueous solution obtained by adding water to the resulting product was heated in the open system until the water was completely reevaporated. The resulting product was dispersed well in water, and its aqueous dispersion was highly transparent and cut off UV light, confirmed by UV-Vis measurements. The solid product obtained by lyophilization of its aqueous dispersion was redispersed in water. The average particle size of the product was assessed to be < 10 nm by dynamic light scattering (DLS) in water and transmission electron microscopy (TEM) measurements, indicating that the product was a water-dispersible spherical nanoparticle. It was assumed that the water-dispersible property of the product probably originated from the TiO2/SiO1.5(CH2)3NH3 x Cl core/shell structure. In addition, highly transparent films can be prepared from the aqueous dispersion of the product, and these films also cut off the UV light, evaluated by UV-Vis measurements.

Preparation of Soluble POSS-Linking Polyamide and Its Application in Antifogging Films.

In this study, we prepared a polyhedral oligomeric silsesquioxane (POSS)-linking polyamide (POSS polyamide) by a polycondensation of ammonium-functionalized POSS (POSS-A) and carboxyl-functionalized POSS (POSS-C) in dehydrated dimethyl sulfoxide (DMSO) using 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) as condensing agents. The obtained POSS polyamide was soluble in various highly polar solvents, and it could form a self-standing film. FT-IR, 1H NMR, and 29Si NMR analyses showed that POSS polyamide is a polymer in which POSS-A and POSS-C are linked almost linearly by amide bonds. Furthermore, the cast film obtained by heat-treating the polymer at 150 °C for 30 min exhibited excellent transparency and hard-coating (pencil scratch test: 5H) and antifogging properties (evaluation by water vapor exposure).

Superacid-Catalyzed Preparation of Highly Dispersible Zirconium Oxide and Titanium Oxide Nanoparticles Without Hydrocarbon Units.

Highly dispersible, hydrocarbon-free zirconium oxide and titanium oxide nanoparticles (ZrO2-NTf2- NP and TiO2-NTf2-NP) were successfully prepared via the simple sol-gel reactions of zirconium tetra-n-butoxide and titanium tetra-n-butoxide, respectively, using a water/methanol mixed solution of the bis(trifluoromethanesulfonyl)imide superacid. ZrO2-NTf2-NP could be dispersed in acetone, ethanol, methanol, N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and water, whereas TiO2-NTf2-NP could be dispersed in acetone, DMF, DMSO, and water. The number-average particle sizes of ZrO2-NTf2-NP and TiO2-NTf2-NP were determined to be 3.6±0.6 nm and 5.8±1.1 nm; these values were obtained by dynamic light-scattering measurements of the acetone dispersions (1.0 w/v%). Highly dispersible ZrO2 nanoparticles could be prepared using other acid catalysts containing trifluoromethyl groups, such as trifluoromethanesulfonic acid and trifluoroacetic acid. In contrast, dispersible TiO2 nanoparticles could not be prepared using these acid catalysts.

Nitric oxide release in human aortic endothelial cells mediated by delivery of amphiphilic polysiloxane nanoparticles to caveolae.

Microdomains such as lipid raft and caveolae are organized as functional compartments in plasma membrane of cells. In this study, we note the functional platform of caveolae with dual functions, internalization of external substances and cell signalings leading to nitric oxide release, and hypothesize that the switching of enzyme activity of endothelial nitric oxide synthase can be achieved by targeting caveolae with nanoparticles. We prepared polysiloxane nanoparticles and studied cellular uptake of the nanoparticles and its concomitant influence on the nitric oxide release in human aortic endothelial cells. We found that polysiloxane nanoparticles were endocytosed via caveolae in human aortic endothelial cells and that enhanced nitric oxide release was followed by the cellular uptake of the nanoparticles. Furthermore, we confirmed that endothelial nitric oxide synthase was activated during cellular uptake of the nanoparticles. These findings support our idea that delivery of the polymeric nanoparticles to endothelial cells can lead to the induction of nitric oxide release.

A facile preparation of gel materials from a solution of cellulose in ionic liquid.

This paper reports a facile preparation of a flexible gel material from a solution of cellulose (15% w/w) in an ionic liquid of 1-butyl-3-methylimidazolium chloride by keeping it at room temperature for 7 days. Elemental analysis data indicated that the obtained gel material was composed of cellulose, the ionic liquid, and water. Both XRD and TGA results suggested that crystalline structure of cellulose was largely disrupted in the material. However, the existence of non-crystalline aggregates was assumed by the XRD data of the material. The gel material was probably obtained by the formation of cellulose aggregates in the solution, attributed to the gradual absorption of water. When the material was heated at 120 degrees C, it became soft, and converted into a fluid at 150 degrees C. By keeping the soft material at room temperature for 2 days, a gel material was regenerated, which was more transparent compared with the original material.

Enzymatic alpha-glucosaminylation of maltooligosaccharides catalyzed by phosphorylase.

This paper describes phosphorylase-catalyzed enzymatic alpha-glucosaminylation for the direct incorporation of a 2-amino-2-deoxy-alpha-D-glucopyranose unit into maltooligosaccharides. When the reaction of 2-amino-2-deoxy-alpha-D-glucopyranosyl 1-phosphate as the glycosyl donor with maltotetraose as a glycosyl acceptor was performed in the presence of phosphorylase, glucosaminylated oligosaccharides were produced, which were characterized by MALDI-TOF MS measurement after N-acetylation of the crude products. The N-acetylated derivative of the main product in this system was isolated by using HPLC, and its structure was confirmed by MS and (1)H NMR spectra. Furthermore, glucoamylase-catalyzed reaction of the isolated compound provided support that the alpha-glucosamine unit is positioned at the non-reducing end of the oligosaccharide.

Chemoenzymatic syntheses of amylose-grafted chitin and chitosan.

Amylose-grafted chitin and chitosan were synthesized by chemoenzymatic methods according to the following reaction manners. First, maltoheptaose was introduced to chitosan by a reductive amination using sodium cyanotrihydroborate in a mixed solvent of 1.0 mol/L aqueous acetic acid and methanol at room temperature to produce a maltoheptaose-grafted chitosan (1). The functionality of maltoheptaose to chitosan in 1 depended on reaction time. The phosphorylase-catalyzed enzymatic polymerization of R-D-glucose 1-phosphate was then performed from 1 to obtain amylose-grafted chitosan (2). Maltoheptaose-grafted chitin (3) was synthesized by N-acetylation of 1 using acetic anhydride in a mixed solvent of aqueous acetic acid and methanol. Then, synthesis of amylose-grafted chitin (4) was performed by the phosphorylase-catalyzed enzymatic polymerization under conditions the same as those for 2. The average DPs of amylose graft chains in 2 and 4 depended on the feed ratios of R-D-glucose 1-phosphate to maltoheptaose primers in 1 and 3.

Amphiphilic poly(N-propargylamide) with galactose and lauryloyl groups: synthesis and properties.

An amphiphilic poly(N-propargylamide) with galactose and lauryloyl groups was synthesized by copolymerization of the corresponding N-propargylamide monomers using a Rh catalyst. The obtained copolymer formed a one-handed helical conformation and molecular aggregates in water. The observations by fluorescence microscopy in a cell culture experiment in the presence of dye-labeled copolymer indicated that the copolymer was incorporated into the cells.

Non-bifurcating cervical carotid artery.

Three cases of an extremely rare anomaly of the carotid artery are described herein. In these patients, the common carotid arteries, without bifurcation in the cervical portion, supplied multiple arterial branches, which are more commonly branches of the external carotid artery. The non-bifurcating carotid artery continued into the cranium as a normal internal carotid artery. This anomaly can be attributed to a maldevelopment of the vascular network during embryogenesis.

Effect of layer charge density on orientation and aggregation of a cationic laser dye incorporated in the interlayer space of montmorillonites.

Effect of layer charge density of clay on the orientation and aggregation state of a laser dye, oxazine 4, in dye/clay complexes was investigated using a series of layer-charge-controlled montmorillonites as host materials. By the combination of polarized UV-vis spectroscopy and powder X-ray diffraction methods, it was revealed that the higher layer charge caused the formation of higher-order H-aggregates with the molecular axis nearly perpendicular to the silicate layer, and that the basal spacing was mostly governed by the degree of dye aggregation.

Amylose's recognition of chirality in polylactides on formation of inclusion complexes in vine-twining polymerization.

Amylose selectively includes poly(L-lactide) (PLLA) among the poly(lactide)s (PLAs) to produce an inclusion complex when the phosphorylase-catalyzed polymerization of α-D-glucose 1-phosphate is performed in the presence of PLLA, poly(D-lactide) (PDLA), or poly(DL-lactide) (PDLLA) (vine-twining polymerization). This result indicates that amylose recognizes the chirality in PLAs on the formation of an inclusion complex in vine-twining polymerization. Modeling calculations support the amylose's chiral recognition in favor of PLLA and the atomistic details of the inclusion complex which involved the preferred orientation of the constituent molecular chains with respect to their fiber axis is proposed.