Effect of herbicides on phase transitions of dipalmitoyl phosphatidylcholine vesicles

The gel to liquid-crystalline phase transition of dipalmitoyl phosphatidylcholine (DPPC) vesicles was monitored with a lightscattering technique in the presence and absence of herbicides. The phase transition temperature for pure DPPC was determined as 41.6°C. 2-Methoxy-3,6-dichlorobenzoic acid (dicamba), 2-methoxy-3,6-dichlorophenylacetic acid (methoxy fenac), 2,4,5-T, (2,4,5-trichlorophenoxy) acetic acid (2,4,5-T), (2,4-dichlorophenoxy) acetic acid (2,4-D), 2-(2,4,5-trichlorophenoxy) propionic acid (silvex), and 4(2,4-dichlorophenoxy) butyric acid (2,4-DB) caused a depression in the phase transition temperature (-AT), whose values increased in the following order: 0.6, 3.0, 3.8, 4.6, 7.6 and 9.6°C, respectively. A linear relation was observed between the -AT values and log K (partition coefficient) values for the tested herbicides. This suggested that the perturbation induced in the membrane bilayers by the herbicides was related to the lipid solubilities of the herbicides.