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.     

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.     

Fragmentation of the metastable molecular ion of methyl lactate: The formation of oxygen-protonated methanol [CH3OH2]+ involving double hydrogen atom transfers

The spontaneous unimolecular dissociation reaction of methyl lactate (1) ionized by electron impact was investigated by a combination of mass-analyzed ion kinetic energy spectrometry and deuterium labeling. The metastable ions 1^+· decompose in a variety of ways: four fragment peaks are observed at m/z 89, 76, 61, and 45, which correspond to the losses of ?H₃, CO, CH₃?O, and ?OOCH₃, respectively. Double hydrogen atom transfer occurs in the third reaction. The source-generated m/z 61 ions decompose into oxygen-protonated methanols at m/z 33 ([CH₃OH ₂ ⁺ ]) by the loss of CO with double hydrogen atom migration. Both hydroxyl and methyne hydrogen atoms in 1 ^+· are present in the resultant protonated methanols.     

Quasi-variational inequalities, generalized Nash equilibria, and multi-leader-follower games

In Pang and Fukushima (Comput Manage Sci 2:21–56, 2005), a sequential penalty approach was presented for a quasi-variational inequality (QVI) with particular application to the generalized Nash game. To test the computational performance of the penalty method, numerical results were reported with an example from a multi-leader-follower game in an electric power market. However, due to an inverted sign in the penalty term in the example and some missing terms in the derivatives of the firms’ Lagrangian functions, the reported numerical results in Pang and Fukushima (Comput Manage Sci 2:21–56, 2005) are incorrect. Since the numerical examples of this kind are scarce in the literature and this particular example may be useful in the future research, we report the corrected results. The online version of the original article can be found under doi:.     

Effect of melt viscosity and surface tension of polymers on the percolation threshold of conductive-particle-filled polymeric composites

The electrical conductivities of carbon-black-filled low-density polyethylene (LDPE), poly(methyl methacrylate) (PMMA), and poly(vinyl chloride)-vinyl acetate (PVC/ VAc) copolymer were measured as functions of carbon content and melt viscosity of the matrix at the temperatures at which the composites were prepared. Sharp breaks in the relationship between the carbon filler content and the conductivity of composites were observed in all specimens at some content of the carbon filler. The conductivity jumps as much as 10 orders of magnitude at the break point. This phenomenon has been known as the “percolation threshold”. The critical carbon content corresponding to the break point