Surface Properties of Polydimethylsiloxane-Based Inorganic/Organic Hybrid Films Deposited on Polyimide Sheets by the Sol-Gel Method

Polydimethylsiloxane (PDMS)-based inorganic/organic hybrids films were prepared on polyimide sheets by the sol-gel method using silanol-terminated PDMS and titanium tetraisopropoxide as starting materials. The effect of heat-treatment temperature on the surface property of the hybrid films was examined in terms of contact angle of water and Tapping-Mode Atomic Force Microscopy (AFM). AFM phase images showed the presence of domains, 200–500 nm in size, on the surface of these films after heat-treatment below 300°C. These regions were more hydrophilic than the rest of the area. The domains disappeared at 300°C and the surface became homogeneous surface of the peak to valley value, about 10 nm. It is also uniformly hydrophobic and a maximum contact angle (about 115°C) was obtained.     

Synthetic approaches toward ecteinascidins. Part 2. Preparation of the ABCDE ring system of ecteinascidins having characteristic substituents in both benzene rings

A synthesis of an advanced ABCDE ring system (24c) having characteristic substituents in both benzene rings of ecteinascidin marine natural products is described based on our model studies.     

Solid Acid-Base Control of Inorganic/Organic Hybrids by Inorganic Components for Molecule-Selectivity

Solid acid-base properties of methylsiloxane-based inorganic/organic hybrids were controlled by incorporation of inorganic components other than Si into methylsiloxane networks. The effect of different inorganic components on the solid acid-base properties was estimated by first-principles calculations based on density functional theory (DFT). The deprotonation tends to occur in the order Si < Al < Nb inorganic components, suggesting that the acidity increases in the same order. Methylsiloxane-based hybrids with solid acid-base properties were also synthesized by incorporating inorganic components derived from metal alkoxides. Hammett indicators revealed that the solid acidity increased in the order Si < Al < Nb inorganic components, which was consistent with the results of first-principles calculations. Preliminary experiments revealed that the methylsiloxane-based hybrids also provided a solid basic nature by containing Ca and Y inorganic components derived from metal alkoxides. The acidic hybrids were found to have Brønsted acid sites from the FT-IR experiments of adsorbed pyridine on the hybrids.     

Effect of Inorganic Components on Thermal Stability of Methylsiloxane-Based Inorganic/Orgnaic Hybrids

The thermal decomposition behavior of methylsiloxane-based inorganic/organic hybrids containing an inorganic component derived from metal alkoxides such as Si(OCH₃)₄, Al(O^sC₄H₉)₃, Ti(OⁱC₃H₇)₄ and Nb(OC₂H₅)₅ was investigated by means of thermogravimetric and differential thermal analysis (TG-DTA), Fourier transform infrared (FT-IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. The decomposition temperature of methyl groups in methylsiloxane-based inorganic/organic hybrids containing an inorganic component derived from metal alkoxides was higher than that in the methylsiloxane-based inorganic/organic hybrid prepared from only CH₃Si(OC₂H₅)₃. In particular, when incorporating Nb and Ti inorganic components, methyl groups in methylsiloxane-based inorganic/organic hybrids decomposed at about 100 and 200^∘C higher temperatures, respectively, than those in the methylsiloxane-based inorganic/organic hybrid prepared from only CH₃Si(OC₂H₅)₃. The incorporation of an inorganic component other than siloxane into methylsiloxane-based inorganic/organic hybrids was found to thermally stabilize the methyl groups of methylsiloxane networks.     

Ardisimamillosides G and H,two new triterpenoid saponins from Ardisia mamillata

Two new triterpenoid saponins, ardisimamilloside G (1), 3-O-[alpha-L-rhamnopyranosyl-(1-->2)-beta-D-glucopyranosyl-(1-->4)-[beta-D-glucopyranosyl-(1-->2)]-alpha-L-arabinopyranosyl]-13beta,28-epoxy-16-oxo-oleanan-3beta,30-diol and ardisimamilloside H (2), 3-O-[alpha-L-rhamnopyranosyl-(1-->2)-beta-D-glucopyranosyl-(1-->4)-alpha-L-arabinopyranosyl]-3beta-hydroxy-13beta,28-epoxy-16-oxo-oleanan-30-al, were isolated from the roots of Ardisia mamillata HANCE. Structure assignments were established on the basis of spectral data and chemical evidence.     

Acid-catalyzed reactions of 3-(hydroxymethyl)- and 3-(1-hydroxyethyl)pyrazolo[1,5-a]pyridines

Treatment of 3-(hydroxymethyl)pyrazolo[1,5-a]pyridines with trifluoroacetic acid in refluxing dichloro-methane led to the formation of bis(pyrazolo[1,5-a]pyrid-3-yl)methanes or bis[(pyrazolo[1,5-a]pyrid-3-yl)]-methyl ethers depending upon the concentration of trifluoroacetic acid. In contrast, similar treatment of 3-(1-hydroxyethyl)pyrazolo[1,5-a]pyridines gave a mixture of 3-vinylpyrazolo[1,5-a]pyridines and 1,3-bis(pyrazolo-[1,5-a]pyrid-3-yl)-1-butenes.     

Preparation of Silicates Using HSi(OC2H5)3 and Their NO x -Adsorption Behavior

The preparation and NO-adsorption/desorption behavior of Li, Ca and Ba silicates were investigated aiming at the application to a NO_x-absorbent. Li silicate was prepared by reaction of HSi(OC₂H₅)₃ with aqueous lithium silicate solution (LSS). Ca and Ba silicates were prepared from gels obtained using CH₃Si(OC₂H₅)₃, Si(OC₂H₅)₄, HSi(OC₂H₅)₃ and alkaline-earth alkoxides. The surface of these silicates indicated the solid basicity of H₀ = 9 and adsorbed the acidic gas of NO. FT-IR spectra of the silicates adsorbing NO showed the absorption peaks in the range of 1300–1600 cm^{– 1} corresponding to ionic and covalent nitrate NO₃^–. The complete desorption of adsorbed NO species occurred above 500°C in the Li silicate, above 500°C in the Ca and Ba silicates prepared using CH₃Si(OC₂H₅)₃, and above 700°C in the Ba and Ca silicates prepared using Si(OC₂H₅)₄. Regarding the Ca and Ba silicates, the difference in siloxane structure is thought to cause the difference in adsorption state and desorption behavior of NO.     

Reaction paths of the water-assisted neutral hydrolysis of ethyl acetate

Density functional theory calculations were conducted on the title reactions with explicit inclusion of a variety of water molecules. Concerted reaction paths were examined first in the reaction model, ester(H2O)n --> MeCOOH(H2O)(n-1)EtOH, with n = 1-4. Their Gibbs activation energies are much larger than the experimental value, and the concerted paths are unfavorable. Various stepwise paths were investigated, and the ester(H2O)4 reactant gives a likely stepwise path. The n = 4 based reaction models, n = 4 + 5 and n = 4 + 12, were found to have similar proton-relay shapes with good hydrogen-bond directionality. The distinction of either the concerted or the stepwise path is described by the position of only one proton in the "junction" water molecule.     

Absolute stereochemistries and total synthesis of (+)/(−)-macrosphelides, potent, orally bioavailable inhibitors of cell-cell adhesion

In the current studies, we used the single-crystal X-ray analysis and Kakisawa-Kashman modification of the Mosher NMR method to determine the complete relative and absolute stereochemistries of the (+)-macrosphelides A (+)-1 and B (+)-2. The stereostructure of (+)-2 was determined by chemical comparison with artificial (+)-2 from (+)-1. We also report the convergent total synthesis of (+)-1 and (+)-3, as well as their antipodes, utilizing an asymmetric dihydroxylation for introduction of chirality and Yamaguchi macrocyclization to form the 16-membered trilactone macrolides.     

Topological dependency of the aromatic sextets in polycyclic benzenoid hydrocarbons. Recursive relations of the sextet polynomial

Mathematical meaning of the Clar's “aromatic sextet” is clarified by analysing the topological dependency of the sextet polynomial. Generalised recursive method for obtaining the sextet polynomial of a polyhex graph is presented. It is shown that the concept of the “super sextet” is necessarily introduced, if one-to-one correspondence between the Kekulé and sextet patterns is assumed. Topological dependency of the maximum number of resonant sextets is clarified and discussed in relation to the aromaticity and stability of polycyclic benzenoid hydrocarbons.