Biological Physics Group, School of Physics and Astronomy , University of Manchester , Oxford Road , Manchester M13 9PL , U.K.
STFC ISIS Facility, Rutherford Appleton Laboratory , Didcot OX11 0QX , U.K.
Langmuir. 2018 Mar 20;34(11):3395-3404. doi: 10.1021/acs.langmuir.8b00143. Epub 2018 Mar 5.
The interaction of nonionic surfactant hexaethylene glycol monododecyl ether (CE) with a reconstituted cuticular wheat wax film has been investigated by spectroscopic ellipsometry and neutron reflection (NR) to help understand the role of the leaf wax barrier during pesticide uptake, focusing on the mimicry of the actions adjuvants impose on the physical integrity and transport of the cuticular wax films against surfactant concentration. As the CE concentration was increased up to the critical micelle concentration (CMC = 0.067 mM), an increasing amount of surfactant mass was deposited onto the wax film. Alongside surface adsorption, CE was also observed to penetrate the wax film, which is evident from the NR measurements using fully protonated and chain-deuterated surfactants. Furthermore, surfactant action upon the model wax film was found to be physically reversible below the CMC, as water rinsing could readily remove the adsorbed surfactant, leaving the wax film in its original state. Above the CMC, the detergency action of the surfactant became dominant, and a significant proportion of the wax film was removed, causing structural damage. The results thus reveal that both water and CE could easily penetrate the wax film throughout the concentration range measured, indicating a clear pathway for the transport of active ingredients while the removal of the wax components above the CMC must have enhanced the transport process. As the partial removal of the wax film could also expose the underlying cutaneous substrate to the environment and undermine the plant's health, this study has a broad implication to the roles of surfactants in crop care.
已通过椭圆偏光和中子反射（NR）研究了非离子表面活性剂己二醇单十二醚（CE）与重组角质小麦蜡膜的相互作用，以帮助了解在农药吸收过程中叶片蜡质屏障的作用，重点是模拟助剂对蜡质膜物理完整性和运输的影响角质层蜡膜对抗表面活性剂浓度。随着 CE 浓度增加到临界胶束浓度（CMC = 0.067 mM），越来越多的表面活性剂质量沉积在蜡膜上。除了表面吸附外，还观察到 CE 穿透蜡膜，这从使用全质子化和链氘化表面活性剂的 NR 测量中可以明显看出。此外，在 CMC 以下，发现模型蜡膜上的表面活性剂作用是物理可逆的，因为水冲洗可以轻易去除吸附的表面活性剂，使蜡膜保持原始状态。在 CMC 以上，表面活性剂的去污作用占主导地位，大量蜡膜被去除，造成结构损坏。因此，结果表明，在测量的浓度范围内，水和 CE 都可以很容易地穿透蜡膜，这表明活性成分的传输有明显的途径，而 CMC 以上蜡质成分的去除必须增强了运输过程。由于蜡膜的部分去除也可能使下面的皮肤基质暴露于环境中并破坏植物的健康，因此本研究对表面活性剂在作物保护中的作用具有广泛的意义。
