Makino K, Ohshima H, Kondo T
Faculty of Pharmaceutical Sciences, Science University of Tokyo, Japan.
J Microencapsul. 1986 Jul-Sep;3(3):195-202. doi: 10.3109/02652048609031573.
Excessive proton transfer from bulk solution to the surface of poly(L-lactide) microcapsules was observed. In acidic solutions of pH less than 3.0, the zeta potential of the microcapsules became slightly positive, although poly(L-lactide) has only carbonyl groups and alcoholic hydroxyl groups which can be charged. In an NMR study, the signal of the water protons shifted towards a higher applied field with increasing interaction of water with the poly(L-lactide) microcapsule surface when the microcapsules were dispersed at low concentrations (up to 4 x 10(-3) per cent). In solutions of pH 3.2-7.6, the observed values of the zeta potential were in good accordance with theoretical values calculated assuming that the charged groups distribute uniformly in the microcapsule wall. In this pH range, the average density of charged groups in the wall was estimated to be 0.04 M. The average volume occupied by one polymer unit (one poly(L-lactide) molecule) in the microcapsule membrane was estimated to be (35 A)3, suggesting a rather tight polymer network in the poly(L-lactide) microcapsule membrane.
观察到大量质子从本体溶液转移到聚（L-丙交酯）微胶囊表面。在pH小于3.0的酸性溶液中，尽管聚（L-丙交酯）仅具有可带电的羰基和醇羟基，但微胶囊的zeta电位仍变为略微正值。在一项核磁共振研究中，当微胶囊以低浓度（高达4×10⁻³%）分散时，随着水与聚（L-丙交酯）微胶囊表面相互作用的增加，水质子的信号向更高的外加磁场方向移动。在pH 3.2 - 7.6的溶液中，观察到的zeta电位值与假设带电基团在微胶囊壁中均匀分布计算得到的理论值高度吻合。在此pH范围内，壁中带电基团的平均密度估计为0.04 M。微胶囊膜中一个聚合物单元（一个聚（L-丙交酯）分子）所占的平均体积估计为(35 Å)³，这表明聚（L-丙交酯）微胶囊膜中的聚合物网络相当紧密。
