Preparative isolation of terpene trilactones from Ginkgo biloba leaves

This study investigated and compared some techniques for the preparative isolation of terpene trilactones, including ginkgolides (GA and GB, etc.) and bilobalide (BB), from Ginkgo biloba leaves. The crude Ginkgo biloba L. extracts (GBE) were prepared using an extractor with solvent refluxing operated under an optimal extraction condition. The extraction yield was 20-23% and the purity of terpene trilactones was about 1.0-1.4 wt%. Before the isolation operations, the extracts were dissolved in de-ionized water. The isolation procedures included the method of liquid-liquid extraction and the method of column chromatography. For the method of liquid-liquid extraction using ethyl acetate as the organic solvent operated under the optimal extraction conditions, the purity, concentration ratio, and yield of terpene trilactones were 13.5-18.0%, 15-16, and >99%. For the method of column chromatography, XAD-7HP, XAD-4, and C-18 adsorbents with different polarities were used as the packing materials. Only for the XAD-7HP column, a part of more polar impurities was efficiently separated with the majority of terpene trilactones by a proper step-gradient elution, which resulted in an efficient isolation: the purity, concentration ratio, and yield of terpene trilactones were approximately 20, approximately 15, and approximately 80%. In comparison, the XAD-7HP column achieved the highest purity, but at the expense of the yield of terpene trilactones; on the contrary, the liquid-liquid extraction method, achieving the highest yield but with a slightly lower purity, was proved to be superior to the method of column chromatography in the current isolation stage.     

Impurity analysis of 1,4-dioxane in nonionic surfactants and cosmetics using headspace solid-phase microextraction coupled with gas chromatography and gas chromatography-mass spectrometry

1,4-Dioxane impurity in nonionic surfactants and cosmetics were analyzed using solid-phase microextraction (SPME) coupled with gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). Experimental results show that there is no significant difference using SPME-GC and SPME-GC-MS for analysis of 1,4-dioxane in three types of nonionic surfactants at the 95% confidence level. The relative standard deviation (R.S.D.) values of each analytical method were smaller than 3%. The amount of 1,4-dioxane was found to vary from 11.6 +/- 0.3 ppm to 73.5 +/- 0.5 ppm in 30% of nonionic surfactants from manufacturers in Taiwan. These methods were linear over the studied range of 3-150 ppm with correlation coefficients higher than 0.995. The recoveries of 1,4-dioxane for these nonionic surfactants following SPME were all higher than 96 +/- 1% (n = 3). The detection limits of 1,4-dioxane for these nonionic surfactants following SPME were from 0.06 ppm to 0.51 ppm. The experimentally determined level of 1,4-dioxane in cosmetics from manufacturers in Taiwan varied from 4.2 +/- 0.1 ppm to 41.1 +/- 0.6 ppm in 22% of daily used cosmetics following SPME coupled with GC and GC-MS. Conventional solvent extraction takes around 1 h for extraction and reconcentration but SPME takes only around 10 min. SPME provides better analyses of 1,4-dioxane in nonionic surfactants and cosmetics than conventional solvent extraction and head space pretreatments in term of simplicity, speed, precision, detection limit, and solvent consumption.     

Spectrophotometric Determination of Titanium in Super Alloys with Diantipyrylmethane and Tiron

Diantipyrylmethane and tiron spectrophotometric determinations of Ti in the super alloys, Inconel 718 and Inconel 600, have been studied thoroughly. Both reagents formed stable yellow complexes with Ti(IV) in acidic medium. The possible interference from Ni, Fe and Cr was examined. Interference from Fe(III) was eliminated by the reduction of Fe(III) to Fe(II). Cr was removed as chromyl chloride which led to a dramatic improvement in the analytical results for Ti by the tiron photometric method. However, the removal of Cr was not necessary when the diantipyrylmethane method was employed. Consequently, lengthy manipulation of super alloys was required for the tiron determination. These two spectrophotometric methods are compared in terms of simplicity, reproducibility and accuracy.     

Solution behavior of ampholytic styrene ionomers

In this article are described the solution properties of ampholytic ionomers obtained by the radical copolymerization of styrene with the ion-pair comonomer 3-methacrylamidopropyltrimethylammonium, 2-acrylamido-2-methylpropanesulfonate. The solution properties were studied in mixed solvents, with a good solvent for the polystyrene backbone and another for the ionic moieties, and in the individual good solvent of benzyl alcohol. The data obtained strongly support extensive intermolecular ionic interactions in solution.     

Metal-induced coordination inversion and carbon-nitrogen bond rearrangement. Structurally characterized phenyl isocyanate inserted into aluminum methyl compounds and O- and N-bound aluminum compounds

[C(4)H(3)N(CH(2)NMe(2))-2]AlMe(2) (1) is prepared in 88% yield by the reaction of substituted pyrrole [C(4)H(4)N(CH(2)NMe(2))-2] with 1 equiv of AlMe(3) in methylene chloride. Reaction of compound 1 with 1 equiv of phenyl isocyanate in toluene generates a seven-membered cycloaluminum compound [C(4)H(3)N[CH(2)NPh(CONMe(2))]-2] AlMe(2) (2). The phenyl isocyanate was inserted into the aluminum and dimethylamino nitrogen bond and induced an unusual rearrangement which results in C-N bond breaking and formation. A control experiment shows that the reaction of substituted pyrrole [C(4)H(4)N(CH(2)NMe(2))-2] with 1 equiv of phenyl isocyanate in diethyl ether yields a pyrrolyl attached urea derivative [C(4)H(3)N(CH(2)NMe(2))-2-[C(=O)NHPh]-1] (3). The demethanation reaction of AlMe(3) with 1 equiv of 3 in methylene chloride at 0 degrees C afforded O-bounded and N-bounded aluminum dimethyl compounds [C(4)H(3)N(CH(2)NMe(2))-2-[C(=O)NPh]-1]AlMe(2) (4a) and [C(4)H(3)N(CH(2)NMe(2))-2-[CO(=NPh)]-1]AlMe(2) (4b) in a total 78% yield after recrystallization. Both 4a and 4b are observed in (1)H NMR spectra; however, the relative ratio of 4a and 4b depends on the solvent used. Two equivalents of AlMe(3) was reacted with 3 in methylene chloride to yield a dinuclear aluminum compound AlMe(3)[C(4)H(3)N(CH(2)NMe(2))-2-[C(=O)NPh]-1] AlMe(2) (5). Reaction of 5 with another equivalent of ligand 3 results in the re-formation of compounds 4a and 4b.     

METHANE OXIDATIVE COUPLING: SYNERGISTIC PROMOTION OF BINARY METAL FLUORIDES TO THORIA BASED CATALYST ThO_2/LaF_3/BaF_2

Introductionlnthcstud}ofmcthaneoxidativccoupIing(0CM),aseriesofcatalystshavebeendevelopedandox}'genspeciesoncatal}'stst"ereinvestigatedextensively.Alotofpapershavebeenpublishedonthisarea.Anongkindsof0CMcatalystsmetalhalidespromotedmctaloxides.cspcciall}'Li /Mg0catal}'stl1~3l.havcbecnmostoftenstudied.Themostpromisingindustrialoncshavebeenthoughttoberarcearthoxidesbasedcatalysts.H.L.Wanelajl#Ihavesuccessfull\'madeuseofmetalfluoridesin0CM,andfoundthebcttcrpron1otingcffectofmctalfluoridcstomc…     

On the structure-function relationship of nitrogenase M-cluster and P-cluster pairs

It A proposed that the M-cluster cage (Kim-Rees model) in active N₂-ase can exert shape-selective molecular-sieve effects in molecular recognition of exogenous substrates, by providing inside multinuclear active-sites the cavity for N₂, C₂H₂, cyclopropene, and N₂O reduction, with [Mo-3Fe]-site available only for N₂ reduction: on the other handn-RC— CH,n-RC— N,n-RN-C , C—N^– and N₃ ^–, are bound outside the cavity at the [2Fe]-site left by the labilizable ligand Y. A terminal carboxylate of the Mo-bound (R)-homocitrate is just in position to protect a H₂-evolution site on the P-cluster pair from CO inhibition, and also to take part in mediating a P-cluster-to-Mo-site H⁺-relay system (involving two hydrogen-bonded H₂O) specifically required for N. reduction. The nonreducibility of CO at the [Mo-3Fe]-site is also explained. Experimental support for molecular-sieve effects of M-cluster cage has been obtained from the observed decrease in ethene-cis-d: selectivity by competitive inhibition of HC—CH reduction in D₂O by N—N.Dedicated to Jiaxi Lu on the occasion of his 80th birthday.     

Synthesis of carbonate-containing high temperature poly(arylene-siloxanylenes)

A method for the first synthesis of high molecular weight carbonate-containing siloxanylene polymers was successfully developed. The procedure covered the preparation and polymerization of pure carbonate-containing bis-silanols which included bis(4-hydroxydimethylsilylphenyl)-carbonate, bis[4-(1-hydroxy-1,1,3,3-tetramethyldisiloxanyl)-phenyl] carbonate, and their meta analogs. Because conventional siloxane polymerization methods, such as the heterocondensation of bis-silanols with diaminosilanes or homocondensation reactions catalyzed by alkali reagents, decomposed carbonate linkages, a new polymerization technique that involved the use of phosgene was used. The procedure was both facile and effective in the polymerization of other arylene bis-silanols.     

Synthesis and properties of high strength high modulus ABA block copolymers

A series of novel ABA block copolymers were synthesized containing a rigid-rod (B) block for reinforcement and a flexible coil (A) block as the matrix. Poly[(benzo[1, 2d: 4, 5d′]bisthiazole-2,6-diyl)-1,4-phenylene] (PBT) was the rigid-rod (B) block utilized in this study and was polymerized in such a way as to provide carboxylic acid end-groups. The carboxy-terminated PBT was copolymerized with the AB monomers, 3,4-diaminobenzoic acid and 4-amino-3-mercaptobenzoic acid, which generates a benzimidazole or benzthiazole (A) block, as well as grafts the blocks together. Composition of the blocks could be varied by the weight of AB monomer used in the copolymerizations. Solution behavior of the copolymers in methanesulfonic acid was determined, and fibers were obtained by wet spinning techniques. The block copolymers exhibited typical tenacities of 200 ksi, 16 Msi modulus, and an elongation to break of 1.4%. Critical concentration values for fabrication increased approximately 3% over mechanical mixtures of the same heterocyclic components.     

A stereocontrolled synthesis of Z and E terminal dienes from pinacol E-1-trimethylsilyl-1-propene-3-boronate

Pinacol $\text{E}$-1-trimethylsilyl-1-propene-3-boronate reacts with aldehydes to form (±)-($\text{R}$*,$\text{S}$*)-3-trimethylsilyl-4-hydroxy-1-alkenes, which can be deoxysilylated stereoselectively to either 98% $\text{Z}$ or 99% $\text{E}$ 1,3-dienes, including the separate components of the red bollworm moth pheromone.