Mixed Cationic Surfactant Vesicles in (Dioctadecyldimethylammonium Bromide)/NaCl and (Dioctadecyldimethylammonium Chloride)/NaBr Aqueous Dispersions

One of the most challenging characteristics not fully understood yet of the cationic surfactant salt dioctadecyldimethylammonium (DODA⁺) halide is concerned with the effects of the counterion (usually Br⁻ and Cl⁻) on the surfactant assembly into vesicle structures in aqueous solution. These counterions play a key role in the self-organization of DODA⁺ into bilayer structures. Differential scanning calorimetry (DSC) and dynamic light scattering (DLS) techniques were used here to investigate systematically the effects of the single salts NaCl and NaBr, respectively, on the thermal behavior and structural organization of the cationic dioctadecyldimethylammonium bromide and chloride (DODAB and DODAC) in water. The results undoubtedly indicate that the added Br⁻ or Cl⁻, respectively, into DODAC and DODAB aqueous dispersions, replaces partially the bound counterions (Cl⁻ and Br⁻) from the vesicles, yielding formation of DODAB/DODAC mixed vesicles. As a conclusion, single salts may be used to tune the thermal and structural characteristics of cationic vesicles.     

Reactivity of Hydroxamate Ions in Cationic Vesicular Media for the Cleavage of Carboxylate Esters

The hydrolysis of carboxylate esters viz. p‐nitrophenyl acetate (PNPA), p‐nitrophenyl butyrate (PNPB) and p‐nitrophenyl octanoate (PNPO) in the presence of cationic vesicles of the surfactant dioctadecyldimethylammonium bromide (DODAC) by different hydroxamate ions i.e. acetohydroxamate (AHA^?), benzohydroxamate (BHA^?) and salicylhydroxamate (SHA^?) were studied. The kinetic data was supported by spectrophotometric measurements. The effects of vesicular size on the reaction have been discussed. The differential reactivity under endo‐ and exovesicular conditions has also been evaluated. Critical vesicle concentrations (CVC) of cationic vesicular surfactants were determined from conductometric and fluorimetric measurements at 300 K. Fluorescence probe pyrene and pyrene‐1‐carboxaldehyde have been used for determination of CVC. Further, thermodynamic parameters viz. Standard Gibb's energy (?G°), enthalpy (?H°), and entropy (?S°) of vesicles has also been evaluated within a temperature range of 303.15–328.15 K.     

季铵盐改性蒙脱石的超结构及其抗菌性能

为研究季铵盐改性对蒙脱石的结构及抗菌性能的影响,分别采用十八烷基三甲基氯化铵（OTAC）和双十八烷基二甲基氯化铵（DODAC）对蒙脱石进行插层改性,并分析了蒙脱石的d001层间距及抗菌性能随季铵盐用量变化的规律.蒙脱石的d001层间距先随季铵盐用量的增加而增大;当OTAC与蒙脱石的质量比超过35%或DODAC与蒙脱石的质量比超过15%时,其d001层间距开始略微下降,同时出现季铵盐以不同倾斜角排列的层间超结构现象.在水分散体系中,改性蒙脱石的抗菌性能先随季铵盐用量的增大而上升;当其出现超结构后,由于蒙脱石及季铵盐与细菌的接触几率受到限制,其抗菌性能开始急剧下降.在干燥条件下超结构对蒙脱石的抗菌性能影响甚微,经不同用量季铵盐改性的蒙脱石都具有极佳的抗霉菌性能.