A self-ordered, crystalline glass, mesoporous nanocomposite with high proton conductivity of 2 x 10(-2) S cm-1 at intermediate temperature

We prepared a TiO2-P2O5 self-ordered, crystalline glass, mesoporous nanocomposite (CGMN) with water-holding capacity at an intermediate temperature region (130-200 degrees C). This TiO2-P2O5 CGMN showed the high proton conductivity of 2 x 10-2 S cm-1 at 160 degrees C under fully saturated humidification conditions (100% RH). Additionally, these conductivities were stable at intermediate temperature conditions. The TiO2-P2O5 CGMN may have a potential not only for the fuel cell electrolytes operated at intermediate temperature conditions but also for electrochemical devices, including electrochromic displays, chemical sensors, lithium rechargeable batteries, and others.     

Palladium-catalyzed hydrocarbonation and hydroamination of 3,3-dihexylcyclopropene with pronucleophiles

The reaction of 3,3-dihexylcyclopropene 1 with carbon and amine pronucleophiles 2 in the presence of palladium catalysts proceeded smoothly to give the corresponding hydrocarbonation products 3, allylated nucleophiles, in good to high yields. For example, in the presence of catalytic amounts of Pd(PPh(3))(4) and dppf, the reaction of 3,3-dihexylcyclopropene with ethyl 2-cyanopropionate and ethyl 2-cyanophenylacetate gave ethyl 2-cyano-2-methyl-4-undecenoate and ethyl 2-cyano-2-phenyl-4-undecenoate in 82 and 86% yield, respectively.     

Anionic polymerization of p-diisopropenylbenzene in tetrahydrofuran: Reactivity of pendent double bond

Anionic polymerization of p-diisopropenylbenene was found to be an equilibrium polymerization not only with respect to the monomer but also with respect to the pendent double bond. The polymerization was studied from kinetic as well as from the thermodynamic point of view, especially to ascertain the reactivity of the pendent double bond as compared with the double bond of monomeric analog. It was shown that the crosslinking rate constant of the pendent double bond is lower by about three to four orders than the propagation rate constant of the monomeric analog. The rate of cyclization was also very slow. From the equilibrium, the heat and entropy of polymerization of the monomer were determined as ΔH_ss = ?5.8 kcal/mole and ΔS_ss = ?18.0 cal/deg mole, respectively, and those of the pendent double bond as ΔH_ss = ?6.3 kcal/mole and ΔS_ss = ?27.8 cal/deg mole. When compared with the polymerization of α-methylstyrene, the low thermodynamic polymerizability of the pendent double bond is attributed to the low heat of polymerization, which may arise from the large steric hindrance of neighboring groups. The effect is much smaller for the equilibrium than for the rate of polymerization, however.     

Calorimetric investigation of polymerization reactions. II. Copolymerization of diethyl fumarate with styrene

The bulk copolymerization of diethyl fumarate with styrene initiated by benzoyl peroxide or azobisisobutyronitrile was investigated with a differential scanning calorimeter (DSC) operated isothermally. The heat of copolymerization decreased almost linearly with the increase in diethyl fumarate content in the copolymer. The heat of homopolymerization for diethyl fumarate was equal to 15.5 ± 0.3 kcal/mole. Monomer reactivity ratios at 100°C were also determined. The rate of copolymerization was followed over the whole range of conversion. A gel effect was noticed in copolymerizations at lower but not at higher temperatures. The initial rate of copolymerization exhibited a maximum at an intermediate monomer feed composition, differing from the previously reported tendency. The difference was found to be due to the method used for determining the rate of copolymerization, and the superiority of the DSC method was proved. The mechanism of the radical-radical termination process was discussed. From the viewpoint of chemically controlled termination, the cross-termination factor ? was estimated to be 2.0, which is reasonable considering the steric hindrance; assumption of the predominance of a diffusion-controlled termination reaction was also consistent with the results.     

The asymmetric power of chiral ligands determined by competitive asymmetric autocatalysis

Asymmetric autocatalytic reactions were initiated by using two competing chiral ligands bearing opposite configurations. The absolute configuration of the resulting highly enantioenriched product reflects the different efficiencies of the two catalysts. Thus, our method provides a simple and efficient way to compare the asymmetric power of chiral ligands for enantioselective catalysis both qualitatively and quantitatively.     

Improved synthesis of oligonucleotides containing 2-thiouridine derivatives by use of diluted iodine solution

It is known that the 2-thiocarbonyl group of 2-thiouridine (s²U) derivatives reacts easily with various oxidizing agents used in oligonucleotide synthesis to give a complex mixture. In this letter, we report an improved method for the synthesis of oligonucleotides containing s²U derivatives. It turned out that the 2-thiocarbonyl group of oligonucleotides containing s²U derivatives was stable in a 0.02 M solution of iodine in pyridine-THF-H₂O. These conditions were successfully applied to the synthesis of oligonucleotides containing s²U derivatives on an automated DNA/RNA synthesizer. Moreover, no undesirable side reactions were detected so that these modified oligonucleotides could be obtained in markedly improved yields.     

Studies on the stereochemistry of aplyronine A: Determination of the stereochemistry of the C21---C34 fragment

The absolute stereochemistry of the C21---C34 fragment 2 of aplyronine A (1), a potent antitumor substance of marine origin, was determined by enantioselective synthesis.     

Calorimetric investigation of polymerization reactions. I. Diffusion-controlled polymerization of methyl methacrylate and styrene

The rate of bulk polymerization of methyl methacrylate and styrene was determined directly, continuously and over the whole range of conversion with a differential scanning calorimeter (DSC) operated isothermally. At the later stages of the accelerated polymerization of methyl methacrylate, a previously unknown inflection or peak in the rate of polymerization was observed. The variation of the rate after the onset of the gel effect, including this peculiar inflection, was interpreted on the basis of the diffusion behavior of monomer molecules and polymeric radicals in the polymer–monomer system, their diffusion rates being predicted from the free volume theory. The final conversion at which no further polymerization proceeds was determined for both monomers. It was affirmed quantitatively that the final conversion has a close relation with the transition of the polymer–monomer system from a viscous liquid to a glassy state.     

Design of Dual‐Emission Chemosensors for Ratiometric Detection of ATP Derivatives

Nucleoside pyrophosphate (nucleoside PP) derivatives are widespread in living cells and play pivotal roles in various biological events. We report novel fluorescence chemosensors for nucleoside PPs that make use of coordination chemistry. The chemosensors, which contain two Zn^II–dipicolylamine units, bind strongly to nucleoside PPs (K_app>10⁶ M ^?1) in aqueous solution and sense them by a dual‐emission change. Detailed fluorescence and UV/Vis spectral studies revealed that the emission changes of the chemosensors upon binding to nucleoside PPs can be ascribed to the loss of coordination between Zn^II and the acridine fluorophore. This is a unique sensing system based on the anion‐induced rearrangement of the coordination. Furthermore, we demonstrated the utility of these chemosensors in real‐time monitoring of two important biological processes involving nucleoside PP conversion: the apyrase‐catalyzed hydrolysis of nucleoside PPs and the glycosyl transfer catalyzed by β‐1,4‐galactosyltransferase.     

Effect of polymer as cosolvent on chemical reactions in solution—II. Effects of polyoxyethylene and polystyrene on the reaction of dansyl chloride with primary amino-ended polyoxyethylene in chloroform

The second-order rate constants for the reaction of 5-dimethylamino-1-naphthalenesulphonyl chloride (dansyl chloride) with primary amino-ended polyoxyethylene in chloroform were measured in the presence of polymers such as polyoxyethylene and polystyrene and compared with those in the presence of low molecular weight models, diethoxyethane and toluene respectively. Both polymers exhibit the polymer effect which is characterized by acceleration of the reaction depending on the degree of polymerization of the polymer cosolvent and on the fraction of the cosolvent. The effect by polymer cosolvents on chemical reactions between a low molecular weight species and a polymer is explained generally in terms of the thermodynamics of polymer solutions.