Improving the properties of the proton exchange membranes by introducing α-methylstyrene in the pre-irradiation induced graft polymerization

New proton exchange membranes (PEMs) were prepared by pre-irradiation induced grafting of α-methylstyrene (AMS)/styrene (STY)/divinylbenzene (DVB) into the crosslinked polytetrafluoroethylene (RX-PTFE) films and successively sulfonated. The new PEMs showed the improved glass transition temperature and chemical stability as compared with the PEMs prepared by pre-irradiation induced grafting of STY/DVB. The balance of the cost, grafting kinetic, thermal properties and the properties of the resulted proton exchange membrane is the key point of this work.     

Ab initio molecular orbital study of the reactivity of active alkyl groups. V. Nitrosation mechanism of acetone with syn-form of methyl nitrite

The mechanisms of nitrosation of acetone through sodium enolate [CH3CO1CH2]-Na+ (1) or naked enolate [CH3CO1CH2]- (2) with methyl nitrite CH3O3NO2 (3), and the reactivity of the syn-form of 3 (syn-3) during the C-N bond formation process were investigated using ab initio molecular orbital (MO) methods. Our results have demonstrated the predominant formation of E-1-hydroxyimino-2-oxo-propane CH3COCH=NOH (4E) when the complex [CH3CO1CH2NO2(O3CH3)]-Na+ was produced kinetically via a metal-chelated pericyclic transition state (TS(CHELATED)), in which the O3 atom of syn-3 was coordinated to the Na+ atom of 1.     

Isolation and Stereostructures of Dolastatin G and Nordolastatin G, Cytotoxic 35-Membered Cyclodepsipeptides from the Japanese Sea Hare Dolabella auricularia

A bioassay-directed fractionation of the cytotoxic constituents of the Japanese sea hare Dolabella auricularia resulted in the isolation of two 35-membered depsipeptides dolastatin G (1) and nordolastatin G (2), which showed cytotoxicity against HeLa S(3) cells with IC(50) values of 1.0 and 5.3 &mgr;g/mL, respectively. The gross structures of these substances were established by spectroscopic analysis including 2D NMR techniques. The absolute stereostructure of 1 was determined by chiral HPLC analysis of amino acid components obtained from acid hydrolysis of 1 and by the enantioselective syntheses of two degradation products arising from polyketide portions. Nordolastatin G (2) is a congener that has the same absolute stereochemistry as that of 1.     

Spin dynamics in a site diluted finite spin cluster system probed by positive muons

The site diluted finite spin cluster system Rb₂CO _x Mg_1–x F₄ (x=0.15, 0.4, 0.5) has been investigated by the ⁺SR technique. Muon spin relaxation was observed in these diluted magnetic systems in a weak longitudinal field of 100 G. By reducing temperature below 100 K, the experimental data show features of slowing down phenomena of the Co electron moments in the finite spin clusters.     

Threshold electron spectra of semiconductor cluster ions

A simple threshold electron analyzer was constructed and laser photodetachment threshold electron spectra of Si^– and Si ₄ ^– were measured.     

Photoinduced electron-transfer systems consisting of electron-donating pyrenes or anthracenes and benzimidazolines for reductive transformation of carbonyl compounds

Photoinduced electron-transfer reactions of several ketone substrates were studied to evaluate the utilities of 1,6-bis(dimethylamino)pyrene (BDMAP), 1,6-dimethoxypyrene (DMP), 9,10-bis(dimethylamino)anthracene (BDMAA), and 9,10-dimethoxyanthracene (DMA) as electron-donating sensitizers cooperating with 2-aryl-1,3-dimethylbenzimidazolines. BDMAP and DMP generally led higher conversion of ketones and better yield of reduction products compared to BDMAA and DMA.     

Carbazoledioxazines having long alkyl groups. 2. Synthesis of carbazoledioxazines with angular type structure

Carbazoledioxazines with an angular type structure (5,15-dialkyl-7,17-dialkyloxy-9,19-dichloro-5,15-dihydrodiindolo[2,3-c:2′,3′-n]triphenodioxazines) were selectively synthesized by electrochemical oxidative ring closure of precursors (2,5-bis(9-alkyl-2-alkyloxy-3-carbazolylamino)-3,6-dichloro-1,4-benzoquinones). The structure was confirmed by ¹H-nmr and other instrumental analyses. Their thermal properties and solubilities were investigated and were compared with those of carbazoledioxazines with a linear type structure.     

Rapid synthesis of oligosaccharide moieties of globotriaosylceramide using fluorous protective group

The use of the Bfp (bisfluorous chain type propanoyl) group as a fluorous protective group made it possible to rapidly synthesize galabiose and the Gb3 oligosaccharide derivatives by a simple fluorous-organic extraction purification. The fluorous oligosaccharide synthesis using the Bfp group is an excellent strategic alternative to solid phase oligosaccharide synthesis, and removes some of the disadvantages of the solid phase method.