Novel C2-symmetric chiral 18-crown-6 derivatives with two aromatic sidearms as chiral NMR discriminating agents

Novel C₂-symmetric chiral 18-crown-6 derivatives with two aromatic sidearms 2-4 were prepared, and their enantiomeric recognition abilities as chiral NMR discriminating agents towards primary ammonium salts were examined. Among these chiral crown ethers, the most effective enantiomeric discrimination of racemic ammonium salts in the ¹H NMR spectra was attained by the derivative with two pyrenylmethyl sidearms.     

Synthesis of polyacetals with various main‐chain structures by the self‐polyaddition of vinyl ethers with a hydroxyl function

To establish the optimum conditions for obtaining high molecular weight polyacetals by the self‐polyaddition of vinyl ethers with a hydroxyl group, we performed the polymerization of 4‐hydroxybutyl vinyl ether (CH₂?CH? O? CH₂CH₂CH₂CH₂? OH) with various acidic catalysts [p‐toluene sulfonic acid monohydrate, p‐toluene sulfonic anhydride (TSAA), pyridinium p‐toluene sulfonate, HCl, and BF₃OEt₂] in different solvents (tetrahydrofuran and toluene) at 0 °C. All the polymerizations proceeded exclusively via the polyaddition mechanism to give polyacetals of the structure [? CH(CH₃)? O? CH₂CH₂CH₂CH₂? O? ]_n quantitatively. The reaction with TSAA in tetrahydrofuran led to the highest molecular weight polymers (number‐average molecular weight = 110,000, weight‐average molecular weight/number‐average molecular weight = 1.59). 2‐Hydroxyethyl vinyl ether, diethylene glycol monovinyl ether, cyclohexane dimethanol monovinyl ether, and tricyclodecane dimethanol monovinyl ether were also employed as monomers, and polyacetals with various main‐chain structures were obtained. This structural variety of the main chain changed the glass‐transition temperature of the polyacetals from approximately ?70 °C to room temperature. These polyacetals were thermally stable but exhibited smooth degradation with a treatment of aqueous acid to give the corresponding diol compounds in quantitative yields. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4053–4064, 2002     

Structure of methanol confined in MCM-41 investigated by large-angle X-ray scattering technique

Large-angle X-ray scattering (LAXS) measurements over a temperature range from 223 to 298 K have been made on methanol confined in mesoporous silica MCM-41 with two different pore diameters, 28 A (C14) and 21 A (C10), under both monolayer and capillary-condensed adsorption conditions. To compare the structure of methanol in the MCM-41 pores with that of bulk methanol, X-ray scattering intensities for bulk methanol in the same temperature range have also been measured. The radial distribution functions (RDFs) for the monolayer methanol samples showed that methanol molecules are strongly hydrogen bonded to the silanol groups on the MCM-41 surface, resulting in no significant change in the structure of adsorbed methanol with respect to the pore size and temperature. On the other hand, the RDFs for the capillary-condensed methanol samples showed that hydrogen-bonded chains of methanol molecules are formed in both pores. However, the distance and number of hydrogen bonds estimated from the RDFs suggested that hydrogen bonds between methanol molecules in the pores are significantly distorted or partly disrupted. It has been found that the hydrogen bonds are more distorted in the smaller pores of MCM-41. With decreasing temperature, however, the hydrogen-bonded chains of methanol in the pores were gradually ordered. A comparison of the present results on methanol in MCM-41 pores with those on water in the same pores revealed that the structural change with temperature is less significant for confined methanol than for confined water.     

Stereoregularity of poly(methyl α-chloroacrylate)

Triad and tetrad tacticities of poly(methyl α-chloroacrylate) and poly(methyl α-chloroacrylate-β-d₁) were determined by nuclear magnetic resonance (NMR) spectroscopy. Methyl α-chloroacrylate-β-d₁ and its polymer were first synthesized. Isotactic poly(methyl α-chloroacrylate) was prepared with ethylmagnesium chloride-benzal-acetophenone in combination as catalyst. The syndiotacticity of radically polymerized polymers increased with decreasing polymerization temperature. For radical polymerization, enthalpy and entropy differences between isotactic and syndiotactic additions were calculated to give ΔH ? ΔH = 850 cal/mole and ΔS ? ΔS = 0.93 eu. The stereoregularity of the polymer prepared with phenylmagnesium bromide catalyst was analyzed in fairly good agreement with first-order Markov statistics, while polymerization with fluorenyllithium seems predominantly to proceed by a mechanism similar to free-radical mechanism. Stereoregularity-controlling power for individual substituents is briefly discussed.     

Graft copolymerization of anhydro sugar derivatives from macromolecular halides

Cationic graft copolymerizations of bicyclic acetals, 1,6-anhydro-2,3,4-tri-O-benzyl-β-D -glucopyranose (LGTBE) and 1,6-anhydro-2,3,4-tri-O-methyl-β-D -glucopyranose (LGTME), were investigated with macromolecular carbenium ions formed from polymers that contain reactive halogens. Macromolecular complex catalysts formed from chlorosulfonated polyethylene or poly(isoprene-co-chloromethylstyrene) by the action of phosphorus pentafluoride yielded graft copolymers with low proportions (0.6–16%) of poly(LGTBE) or poly(LGTBE-co-epichlorohydrin) branchings. It was found that macromolecular complex catalysts formed from poly(styrene-co-fluoromethylstyrene) or poly(methyl methacrylate-co-fluoromethylstyrene) by the action of boron trifluoride etherate give graft copolymers with high proportions (up to 80%) of poly(LGTBE) or poly(LGTME) branchings. In addition, the model reactions for the graft copolymerization of LGTBE were examined with organic halide-PF₅, organic halide-AgPF₆, and organic fluoride-BF₃·OEt₂ catalytic systems, of which the last two indicate that the polymerization is effected by a carbenium ion mechanism.     

A monoterpene glucoside and three megastigmane glycosides from Juniperus communis var. depressa

A new monoterpene glucoside (1) and three new natural megastigmane glycosides (2-4) were isolated along with a known megastigmane glucoside (5) from twigs with leaves of Juniperus communis var. depressa (Cupressaceae) collected in Oregon, U.S.A., and their structures were determined on the basis of spectral and chemical evidence. In addition, the antibacterial activities of the isolated components against Helicobacter pylori were also investigated.     

Reactive oxygen species scavenging ability of a new compound derived from weathered coal

The scavenging activity of three fulvic acids (named XWCS-1, XWCS-4, and XWCS-8 according to time taken for ozonolysis) obtained by ozonolysis of humic acid extracted from Xinjiang (China) weathered coal and a fulvic acid (named XWCFA) extracted from the same coal towards reactive oxygen species such as superoxide radical (O(2)(.)(-)) and hydroxyl radical ((.)OH) was investigated with an electron spin resonance (ESR)-spin trapping method using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a spin trap. O(2)(.)(-) was generated with a hypoxanthine-xanthine oxidase system. (.)OH was generated by three different methods; (i) FeSO(4)-hydrogen peroxide (H(2)O(2)) system, (ii) Cu(en)(2)-H(2)O(2) system, and (iii) UVB photolysis of H(2)O(2). At physiological pH, XWCS-1 had the greatest O(2)(.)(-) scavenging activity, followed by XWCS-4, XWCS-8 and XWCFA. XWCFA had the greatest ?OH scavenging activity among the four fulvic acids, whereas XWCS-1 and XWCS-4 enhanced the production of (.)OH from a metal-catalyzed hydroxyl radical generating system, suggesting that these molecules act as prooxidants in the presence of metal ion.     

An efficient vanadium-catalyzed bromination reaction

An efficient catalytic oxidative bromination of arenes, alkenes, and alkynes in aqueous media was achieved under relatively mild conditions by using NH₄VO₃ catalyst combined with H₂O₂, HBr, and KBr. Dodecyltrimethylammonium bromide was found to serve as an efficient surfactant to facilitate the NH₄VO₃-catalyzed bromination in aqueous media.     

Ion flotation—spectrophotometric determination of traces of chromium(VI)

Ion flotation is used to concentrate chromium(VI) in the range 3–70μg l^-1 from 14 samples. The chromium(III)—diphenylcarbazone complex formed by reaction with diphenylcarbazide is floated efficiently with sodium lauryl sulfate, and the subsided foam is measured spectrophotometrically after simple dilution. Continuous flotation methods at solution flow rates of 2, 3 and 4 l h^-1 are discussed.     

Supramolecular ferroelectric liquid crystals. Hydrogen-bonded complexes between benzoic acids and chiral stilbazoles

Supramolecular ferroelectric liquid crystalline complexes have been obtained from 4-alkoxybenzoic acids and optically active trans-4-substituted-4'-stilbazoles. Chiral smectic C phases are induced by the formation of supramolecular mesogenic structure through the selective intermolecular hydrogen bond between the achiral benzoic acids and the chiral non-mesogenic stilbazoles.