摘要:

The cleavage of fed' -butyI hydrspersxlde by ferrous ions at pH 4 8 yrerdea two distinctive radlcals, alkoxyl and methyl radicals, detected by the electron spin resonance (ESW) technieue with the sF;n trap 5 5-dimethyl-? pyrrslsne-N-oxide (DMPOO) Free radicail formation was found to be dependent span the ferrous ran concentration Usrng drfferent BMPB concentrations, it was proved that aBkoxy l radtcais were formed intinally polysaccharzdes (PS), such a s giucomannan, lscust bean gum, xanthan, and carrageenan, retarded free radical formation, but no similar effect was obsermd far chztosan It is csnciuded that the suppressing effect is caused by the tron blndlng abrlnty of each PS.

ISSN:0193-2691    

DOI:10.1080/01932699908943815

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The zeta-potentials of silica, copper, platinum and gold particles have been measured as a function of pH. The isoelectric points were found to be at pH 3.0, 5.8, 3.0 and 3.5, respectively. In the pH range 3.0 to 5.8 copper and silica particles are oppositely charged and accordingly the coating of silica with copper particles could be demonstrated. In the case of gold and platinum the sign of the charge is such that direct adhesion to silica particles cannot be expected and this was also demonstrated in the case of platinum.

ISSN:0193-2691    

DOI:10.1080/01932699908943816

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The gelation of polyvinylalcohol with glutaraldehyde confined in a water/ oil (= 3/1 in volume ratio) saturated sandstone (Bentheimer) was characterized by H NMR spin-lattice relaxation rate (1/ T)measurements and Pulse Field Gradient (PFG) NMR diffusion measurements. The gelation rate was found to be (12.8 ± 1.3) 10−15−1at 340 K, which is approximately an order of magnitude faster than in bulk solution. In comparison, the gelation rate within the same porous material containing no oil phase was even faster, by a factor of 2.

ISSN:0193-2691    

DOI:10.1080/01932699908943817

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The experimental evidence concerning the transverse shear viscoelastic modulus of amphiphile films is reviewed. A large body of evidence suggests that this modulus reflects dynamic chain melting of the hydrocarbon moieties of the surfactant molecules. However, various aspects of the observed phenomena cannot be incorporated within such a model, indicating that the search for a full molecular understanding is still incomplete.

ISSN:0193-2691    

DOI:10.1080/01932699908943818

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Enzymes in microemulsions, liposomes, aqueous monomer surfactant solutions or pure water have been entrapped in gelatin-based gels. These gels have been used as minireactors for stereoselective resolution of racemic 2-octanol in esterifications with alkanoic acids or in transesterifications with vinyl butyrate. The microstructures were stabilized by the anionic surfactant sodium 1,4-bis(2-ethylhexyl) sulfosuccinate (AOT) or the zwitterionic surfactant soybean lecithin. The enzymes used were commercial lipases from Chromobacterium viscosum or Candida antarctica (SP 525). The incubation temperature was 298.2 K. The enantiomeric excess (e.e.) values were high in all systems studied, but the reaction rates depended on the gel used. In AOT-stabilized and in ethanol-free lecithin-stabilized gels the conversion was close to 0.45. However, in the ethanol-containing lecithin gels, the conversion was lower and decreased with increased ethanol content, due to competing reactions. In the hydrogels, the conversion and e.e. values were high, but the reaction rates were low.

ISSN:0193-2691    

DOI:10.1080/01932699908943819

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Unsaturated C18fatty acids are the largest constituents of the vegetable oils that are used in the pharmaceutical and cosmetic industries. To investigate effects of various vegetable oils on the stability of multiple emulsions, configuration of oleic, linoleic and linolenic acids at the liquid paraffin-water interface was studied by measuring the interfacial tensions and calculating the interfacial excess and molecular cross-sectional areas of the acids at 0.1 to 10% w/ w concentrations as well as of the pure acids. Linolenic acid produced the lowest interfacial tension followed by oleic and linoleic acids. The results have been explained in terms of preferential interfacial adsorption and hydrophobic hydration. Linolenic acid has the highest interfacial excess value of 2.24 × 10−10moles/ cm2followed by oleic acid, 1.49 × 10−1moles/ cm2and linoleic acid,1.33 x 1010−10moles/ cm2The findings suggest that hydrophobic hydration of the fatty acids depends strongly on the number of the double bonds present. The study contributes to explaining stability problems involved in the vegetable oil based multiple emulsion systems.

ISSN:0193-2691    

DOI:10.1080/01932699908943820

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

ISSN:0193-2691    

DOI:10.1080/01932699908943821

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor