Polymer-Supported Bases. 10. Synthesis of Phosphatidylcholines Using Polymer-Supported or Free Acylimidazoles

Dipalmitoylphosphatidylcholine was synthesized in a good yield by the reaction of L-α-glycerophosphorylcholine with 1-palmitoylimidazole in the presence of DBU. Polymer-supported 1-palmitoylimidazole moiety also could be used as the acylating reagent, though the yield of the choline was moderate.     

Visco-elastic properties of reentrant nematic liquid crystalline mixtures

The visco-elastic properties for binary mixtures of 4-n -hexyloxy-4′-cyanobiphenyl (6OCB) and 4-n-octyloxy-4′-cyanobiphenyl (8OCB) are investigated in detail by a light scattering technique. The mixtures exhibit a reentrant nematic (RN) phase between the smectic A (SmA) and crystal phases in the range 22.0–29.5 wt % of 6OCB. The viscosity and the elastic constant increase with cooling in both the nematic and reentrant nematic phases. It is also found that the mixtures exhibit anomalously large values of viscosity and elastic constant near the phase transition, i.e. a pretransitional phenomenon can be observed. The activation energy for viscosity is smaller in the RN phase than in the ordinary nematic phase appearing at higher temperatures, while the normalized elastic constant (defined as the ratio of the elastic constant to the square of the dielectric anisotropy) is larger. Moreover, the visco-elastic behaviour depends on the specific time during which the sample has been kept in the SmA phase. These results confirm that the SmA phase has a strong influence on the formation of molecular aggregates, which plays an important role in the reentrant phenomenon of these systems.     

Enhancement of Solar Hydrogen Evolution from Water by Surface Modification with CdS and TiO2 on Porous CuInS2 Photocathodes Prepared by an Electrodeposition–Sulfurization Method

Porous films of p‐type CuInS₂, prepared by sulfurization of electrodeposited metals, are surface‐modified with thin layers of CdS and TiO₂. This specific porous electrode evolved H₂ from photoelectrochemical water reduction under simulated sunlight. Modification with thin n‐type CdS and TiO₂ layers significantly increased the cathodic photocurrent and onset potential through the formation of a p–n junction on the surface. The modified photocathodes showed a relatively high efficiency and stable H₂ production under the present reaction conditions.     

New analytical method for the study of the metabolism of gentiopicroside in rats after oral administration by LC–TOF‐MS following picolinoyl derivatization

The metabolism of gentiopicroside (GPS) in vivo was studied for the first time by LC–MS following picolinoyl derivatization. Incubation of erythrocentaurin, one of the main in vitro metabolites of GPS by intestinal bacteria, with liver microsome indicated that GPS might be metabolized to a final metabolite 3,4‐dihydro‐5‐(hydroxymethyl)isochroman‐1‐one (HMIO) in vivo. After hydrolysis with sulfatase, HMIO was successfully detected in rat plasma after oral administration of GPS by LC–MS following picolinoyl derivatization. 4‐Methoxyphenyl methanol was used as an internal standard to quantify HMIO in rat plasma. A metabolic pathway of GPS in rats is proposed. The monoterpene compound GPS was found to be metabolized to dihydroisocoumarin, which may be responsible for the pharmacological effect of GPS.     

Synthesis of an Alternated Heterobimetallic Supramolecular Polymer Based on Ru(II) and Fe(II)

A heterobimetallic supramolecular polymer (polyRuFe) with alternately complexed Ru(II) and Fe(II) is prepared following a stepwise synthetic route through harnessing first the strongly binding metal ion Ru(II) and then the weakly binding metal ion Fe(II). A high yield of product is achieved in each step. The heterometal ions are incorporated into the polymer chain in identical coordination environments formed by two 2,2′:6′,2″-terpyridine moieties. Characterization is accomplished by NMR spectroscopy, MALDI–TOF mass spectrometry, UV–Vis spectroscopy, and cyclic voltammetry. PolyRuFe shows a wide optical window (λ = 311–577 nm) and a broad distinct reversible redox nature of two types, originated from the coupling of the two heterometallic segments into the polymer chain. Such characteristics of polyRuFe suggest its potential for various electrochemical and electro-optical applications.     

Study of the thermal degradability of poly(α-methylstyrene) with modified end groups

To induce degradabilities in polymers in response to environmental conditions, endm odification reactions of poly(α-methylstyrene) (PMS) derivatives were carried out. 2-Phenylallyl halide derivatives such as 2-phenylallyl bromide, 2-(p-tolyl)allyl bromide, and α-trifluoromethylstyrene were found to be suitable end-modification agents. For example, the ω-2-phenylallyl-PMS derivative was prepared with almost quantitative functionality by the reaction of the living PMS derivative with 2-phenylallyl bromide. In a similar way, ω-3,3-difluoro-2-phenylallyl- and ω-2-(4-toly)allyl-PMS derivatives were synthesized. Based on thermogravimetric analysis, the onset of the degradation temperature of the endmodified PMS derivatives decreased in the following order: ω-hydrogen- > ω-3,3-difluoro-2-phenylallyl- > ω-2-phenylallyl- > ω-2-(p-tolyl)allyl-PMS. Actually, the onset temperature of ω-2-(p-tolyl)allyl-PMS derivatives was 50°C lower than that of ω-H-PMS derivatives. These results indicate that the active species is produced effectively at the endunsaturated bond, which initiates depolymerization of the polymer at rather low temperatures. Therefore, it is concluded that a 2-phenylallyl substituent at the end of the PMS chain induces effective degradation through a radical mechanism.     

Analysis of charge transfer distance between Ru(bpy)32+ complexes incorporated into a nafion film as studied by spectrocyclic voltammogram

An ITO electrode was coated by a Nafion film incorporating Ru(bpy)₃²⁺ complex as redox centers either by mixture casting method, adsorption method, or swelling method and the electrochemical reactivity of the modified electrode was determined by the in-situ spectrocyclic voltammogram (SCV) in a sodium perchlorate aqueous solution at pH 1.2. A modified Poisson statistics equation was used to estimate the charge transfer distance (Ro) between the Ru(bpy)₃²⁺ complexes. The estimated charge transfer distances for the electrodes prepared by swelling method (Ro = 1.63 nm for the electrode modified in M/W 1:10, and 1.69 nm in M/W 1:2) and adsorption method (Ro = 1.61 nm) were longer than that for mixture casting method (Ro = 1.5 nm). Based on the different procedure of Ru(bpy)₃²⁺ complex incorporation in the Nafion film, the reasons that affect the apparent charge transfer distance were discussed.     

A hydrogel with rubber elasticity transition

Reaction between dimethyldivinylsilane and 3,6-diazaoctane in the presence of 3-lithio-3,6-diazaoctane yields a new telechelic oligomer, poly(silamine), which consists of alternating 3,3-dimethyl-3-silapentane and N,N′-diethylethylenediamine units in the main chain. Poly(silamine) shows unique phase transition properties in response to the degree of protonation of amino groups in the polymer. Poly(silamine) also shows a strong interaction with several anions. Due to the interaction between poly(silamine) and anions along with the protonation of amino groups in the poly(silamine), the rubber elasticity of poly(silamine) is drastically changed. A discrete volume change can be observed when the environmental pH of the poly(silamine) gels is varied. This can be explained not only by a change in ionic osmotic pressure but also by a change in the rubber elasticity of the networks in the gel.     

Synthesis and reactions of optically pure cyclohexyl(o-methoxyphenyl)phosphine-borane and t-butyl-(o-methoxyphenyl)phosphine-borane

Cyclohexyl(o-methoxyphenyl)menthyloxyphosphineborane and t-butyl(o-methoxyphenyl)menthyloxyphosphine-borane were prepared from dichlorocyclohexylphosphine and t-butyldichlorophosphine by successive treatments with (−)-menthol, o-methoxyphenylmagnesium bromide, and borane-THF complex. The separated pure diastereomers of each of the compounds underwent reaction with lithium naphthalenide to afford optically pure cyclohexyl(o-methoxyphenyl)phosphine-borane and t-butyl(o-methoxyphenyl)phosphine-borane, respectively. These secondary phosphine-boranes reacted readily with various electrophiles in the presence of bases with virtually net retention of configuration. A new chiral phosphine ligand, (S,S)-1,2-bis[cyclohexyl(o-methoxyphenyl)phosphino]ethane was synthesized via the optically pure phosphine-boranes.