鼠李糖脂的合成及pH值对其表面活性和微乳微结构的影响

从铜绿假单胞菌发酵液中提取纯化鼠李糖脂生物表面活性剂. 用高效液相色谱-电喷雾质谱法(HPLC-ESI-MS)对鼠李糖脂提取物的组成进行了测定. 用临界胶束浓度(CMC)分析了pH值对其表面活性的影响, 用微乳液滴粒径和灼电位考察了pH值对鼠李糖脂/正庚烷/硼砂缓冲液微乳体系微结构的影响. 结果表明, 在弱碱性条件下(pH7.5-9.5), pH的变化对鼠李糖脂的表面活性和微乳微结构均有显著影响. pH小于9.0时, CMC随着pH的升高而降低, 在pH 9.0处达到最低. pH大于9.0时, CMC随着pH值的升高而逐渐升高. 这是氢键和极性头基间的静电排斥力共同作用的结果. 微乳液滴的粒径及灼电位绝对值都随pH值的升高呈增大趋势, 只在pH 9.0处例外. 少量十二烷基硫酸钠(SDS)或正丁醇的加入都使微乳粒径明显增大.

Synthesis of Rhamnolipid and the Effect of pH Value on Its Surface Activity and Microemulsion Microstructures

Rhamnolipid biosurfactants were extracted and purified from the fermentation broth of Pseudomonas aeruginosa. The composition of rhamnolipid extract was analyzed by high-performance liquid chromatography-electrospray ionization-mass spectrometry (HPLC-ESI-MS). The effect of pHvalue on its surface activity was studied by determining its critical micellization concentration (CMC). The effect of pH value on the microstructure of the rhamnolipid/n-heptane/borate microemulsion system was evaluated by considering particle sizes and zeta potential of microdroplets. Results showed that under weak alkaline conditions (pH 7.5-9.0), pH had significant effect on both the surface activity of rhamnolipid and the microemulision microstructures. At a pH lower than 9.0, the CMC decreased as pH increased and reached a minimum at pH 9.0. At a pH higher than 9.0, the CMC increased gradually as pH increased. This was as a result of a joint effect of hydrogen bonding and electrostatic repulsion between polar head groups. Both size and absolute value of zeta potential of microdroplets tended to increase as pH increased except at pH 9.0. By adding a small quantity of sodium dodecyl sulfate (SDS) or n-butanol to the microemulsion system, the particle size increased significantly.