Department of Applied Chemistry, College of Science, China Agricultural University, Beijing 100193, China.
Key Laboratory of Bioorganic Phosphorus Chemistry & Chemical Biology, Ministry of Education, Department of Chemistry, Tsinghua University, Beijing 100084, China.
J Colloid Interface Sci. 2019 Apr 1;541:93-100. doi: 10.1016/j.jcis.2019.01.088. Epub 2019 Jan 22.
Even though amphiphilic natural products have been widely employed in cosmetics, food, and pesticide formulations, the development of a compound with stimuli-responsiveness is still highly significant. Inspired by the low cost, biocompatibility, pH resistance and amphiphilicity of natural glycyrrhizic acid (Gly), we designed and synthesized an amphiphilic homopolymer, namely, poly(glycyrrhizic acid) (PGly), via reversible addition-fragmentation chain transfer (RAFT) polymerization. The two carboxylic groups on the side chain of PGly promoted it as a multiple pH-responsive polymeric surfactant. As the pH was decreased from 5.0 to 2.0, the PGly transformed from the extension to the coil state and further aggregated into nano/micro particles. During this process, the surface charge, surfactivity and diffusion rate of PGly decreased along with the decreasing pH. Moreover, with ultrasonic treatment (UT), the aggregates that formed at lower pH values decreased (pH 3.0 and 2.0) or almost disappeared (pH 4.0), indicating that these insoluble aggregates at lower pH were broken by UT and were then reassembled into the compacted PGly nanoparticles. Based on the above results, the emulsion (20 wt% xylene) stabilized by 0.1 wt% PGly was fabricated using ultrasonic emulsification for which the diameter distribution and the dispersion state can be reversibly regulated by pH (2.0-5.0). This natural polymeric surfactant exhibited a favorable surfactivity and multiple pH responsiveness in the preparation of emulsions, showing its potential for application in the controlled release of pesticide formulations and in the recovery of organic pollution.
尽管两亲性天然产物已广泛应用于化妆品、食品和农药制剂，但开发具有刺激响应性的化合物仍然具有重要意义。受天然甘草酸（Gly）成本低、生物相容性、耐 pH 值和两亲性的启发，我们通过可逆加成-断裂链转移（RAFT）聚合设计并合成了一种两亲性均聚物，即聚甘草酸（PGly）。PGly 侧链上的两个羧酸基团使其成为一种多 pH 响应性聚合物表面活性剂。当 pH 值从 5.0 降低到 2.0 时，PGly 从伸展状态转变为卷曲状态，并进一步聚集形成纳米/微米颗粒。在此过程中，PGly 的表面电荷、表面活性和扩散速率随 pH 值的降低而降低。此外，通过超声处理（UT），在较低 pH 值下形成的聚集体减少（pH 值为 3.0 和 2.0）或几乎消失（pH 值为 4.0），表明较低 pH 值下的这些不溶性聚集体被 UT 破坏，然后重新组装成紧密的 PGly 纳米颗粒。基于上述结果，使用超声乳化制备了由 0.1wt%PGly 稳定的乳液（20wt%二甲苯），其粒径分布和分散状态可以通过 pH 值（2.0-5.0）可逆调节。这种天然聚合物表面活性剂在乳液的制备中表现出良好的表面活性和多重 pH 响应性，显示出在农药制剂的控制释放和有机污染回收方面的应用潜力。
