Effect of thermal degradation on rheological properties for poly(3-hydroxybutyrate)

Thermal degradation at processing temperature and the effect on the rheological properties for poly(3-hydroxybutyrate) have been studied by means of oscillatory shear modulus and capillary extrusion properties, with the aid of molecular weight measurements. Thermal history at processing temperature depresses the viscosity because of random chain scission. As a result, gross melt fracture hardly takes place with increasing the residence time in a capillary rheometer. Moreover, it was also found that the molecular weight distribution is independent of the residence time, whereas the inverse of the average molecular weight is proportional to the residence time. Prediction of average molecular weight with a constant molecular weight distribution makes it possible to calculate the flow curve following generalized Newtonian fluid equation proposed by Carreau as a function of temperature as well as the residence time.     

Synthetic study of gymnocin-A: synthesis of the ABC ring fragment

The synthesis of the ABC ring fragment of gymnocin-A is described. The key feature of this approach was the convergent BC ring formation using an oxiranyl anion coupling, which was followed by intramolecular Williamson ether synthesis and the reductive etherification of an α-acetoxy acetal. The five-membered A ring was then constructed on the seven-membered B ring by radical cyclization of a β-alkoxy acrylate derivative.     

Multi-way PLS modeling of structure–activity data by incorporating electrostatic and lipophilic potentials on molecular surface

We devised and elaborated a surface-based three-dimensional-quantitative structure–activity relationship (3D-QSAR) method, which had been proposed in the previous study. This approach can be applied to more general case where both the electrostatic and lipophilic potentials on molecular surface simultaneously change. The 3D coordinates of all sampling points on molecular surface are projected into a 2D map by Kohonen neural network (KNN). Each node in the map is coded by the associated molecular electrostatic potential (MEP) or molecular lipophilic potential (MLP) values. The electrostatic and lipophilic KNN maps are generated for each compound and the four-way array is constructed by collecting two KNN maps of all samples. The correlation between four-way array and biological activity is examined by four-way partial least-squares (PLS). For validation, the structure–activity data of estrogen receptor antagonists was investigated. The four-way PLS model gave the high statistics at calibration and validation stages. The coefficients of the four-way PLS model back-projected on molecular surface had a reasonable 3D distribution and it was nicely consistent with active site of the estrogen receptor which was recently made clear by X-ray crystallography.     

Cyclic tetramers composed of rhodium(III), iridium(III), or ruthenium(II) half-sandwich and 6-purinethiones

Six new cyclic tetranuclear complexes [[M(Cp*)(L)](4)](4+) and [[Ru(II)(L)(cymene)](4)](4+) [Cp* = eta(5)-C(5)Me(5), cymene = eta(6)-p-MeC(6)H(4)Pr(i); M = Rh(III) and Ir(III); HL = 6-purinethione (H(2)put) and 2-amino-6-purinethione (H(2)aput)] were prepared in a self-assembly manner and characterized by NMR spectroscopy, electrospray ionization mass spectrometry, and X-ray crystal structure analysis. The two crystal structures of [[Rh(Cp*)(H(0.5)put)](4)](CF(3)SO(3))(2) and [[Ir(Cp*)(Haput)](4)](CF(3)SO(3))(4) revealed that they have similar S(4) structures with an alternate chirality array of CACA, and all ligands adopt a mu-1kappaN(9):2kappa(2)S(6),N(7) coordination mode. The orientations of the four bridging ligands are alternately up and down, and they form a central square cavity. Interestingly, the cationic tetramers of the former are stacked up along the c axis, resulting in an infinite channel-like cavity. The driving force of this stacking is due to intermolecular double hydrogen bonds [N(1)-H...N(21) = 2.752(4) A] at both sides of the cavity. In the two Rh(III)- and Ru(II)-H(2)aput systems, it turned out that the dimeric species are dominantly formed in the reaction solutions but finally convert into the tetrameric species.     

Detection of two variant Vero toxin genes in Escherichia coli by capillary electrophoresis

Three methods [capillary electrophoresis (CE)-allele-specific PCR, CE-single-strand conformation polymorphism (SSCP) and CE-cleavase fragment length polymorphism (CFLP)] were developed in order to effect rapid and specific analysis of the vero toxin (VT)1 and VT2 genes of O157. The allele-specific polymerase chain reaction (PCR) method, which utilized specific duplex PCR with specific primers for VT1 and VT2, showed that VT1 and VT2 consisted of 174 and 128 bp, respectively. Subsequent CE analysis was carried out. Separation time was 4 min. SSCP, which utilized one primer set which reacted with both VT1 and VT2 in the PCR method, was followed by CE analysis of secondary structure of single-strand DNA. Two genes could be analyzed in approximately 18 min. CFLP, like SSCP, is a method for detecting mutation-induced changes in secondary structure of single-stranded DNA. The endonuclease cleavase I recognizes and cleaves the 5' side of hairpin loops in self-annealed single-strand DNA of PCR product 169 bp obtained from VT1 and VT2. The produced DNA fragments are analyzed by CE and the electrophelogram reveals a sequence-specific CFLP. Separation time was 6 min. These techniques are suitable for the detection and the identification of O157.     

Multi-way PLS modeling of structure-activity data by incorporating electrostatic and lipophilic potentials on molecular surface

We devised and elaborated a surface-based three-dimensional-quantitative structure-activity relationship (3D-QSAR) method, which had been proposed in the previous study. This approach can be applied to more general case where both the electrostatic and lipophilic potentials on molecular surface simultaneously change. The 3D coordinates of all sampling points on molecular surface are projected into a 2D map by Kohonen neural network (KNN). Each node in the map is coded by the associated molecular electrostatic potential (MEP) or molecular lipophilic potential (MLP) values. The electrostatic and lipophilic KNN maps are generated for each compound and the four-way array is constructed by collecting two KNN maps of all samples. The correlation between four-way array and biological activity is examined by four-way partial least-squares (PLS). For validation, the structure-activity data of estrogen receptor antagonists was investigated. The four-way PLS model gave the high statistics at calibration and validation stages. The coefficients of the four-way PLS model back-projected on molecular surface had a reasonable 3D distribution and it was nicely consistent with active site of the estrogen receptor which was recently made clear by X-ray crystallography.     

Synthesis of perfluorochemicals for use as blood substitutes,part II: electrochemical fluorination of partly fluorinated compounds

Electrochemical fluorination of 2-methoxy-1,1,1-trifluoro-2-(F-methyl) octane gave the corresponding perfluorinated ether in 27% yield, along with cyclic by-products in 9%. A mixture of partly fluorinated tertiary amines, consisting of 1-dipropylamino-F-1-propene and 1-dipropylamino-2-hydryl-F-propane, did not afford a superior yield of tri(F-propyl)amine compared to the unfluorinated tripropylamine. 1-Diethylamino-2-(F-methyl)-F-1-pentene was fluorinated to give the corresponding F-tertiary amine in fairly good yields, together with 1-di(F-ethyl)amino-2-hydryl-2-(F-methyl)-F-pentane and their fragmented products. The study indicates that blocking of the α-carbon atom of an ether with F-methyl groups seems to reduce fragmentation, resulting in good yields of an unrearranged product. However, partial fluorination of a tertiary amine prior to electrochemical fluorination rather allows high yields of undesired by-products, as far as our experiments were concerned.     

ESR and endor of the free radicals originated from γ-irradiated adamantane

The free radicals produced in γ-irradiated adamantane are investigated by means of ENDOR as well as ESR and early products and their temperature modifications are discussed.