Effects of temperature and concentration of the accelerators ethoxylated alcohols, diethyl suberate and tributyl phosphate on the mobility of [C-14]2,4-dichlorophenoxy butyric acid in plant cuticles

Intrinsic activities of monodisperse ethoxylated dodecanols (MEDs), diethyl suberate (DESU) and tributyl phosphate (TBP) were investigated using Steph anotis floribunda leaf cuticular membranes (CMs) and [C-14]2,4-dichlorophen oxy butyric acid (2,4-DB) as a model solute. When sorbed in c degrees uticu lar membranes, MEDs, DESU and TBP increase solute mobility and are called a ccelerators for this reason. With MEDs, dose-effect curves Clog mobility vs accelerator concentration) were Linear but, with DESU and TBP, curves conv ex to the x axes were obtained that approached a maximum at 90 and 150 g kg (-1), respectively. Accelerators increased the mobility of 2,4-DB in the CM s by 9- to 48-fold, and effects were larger at lower temperatures (range 15 -30 C). Activation energy for diffusion of 2,4-DB was 105 kJ mol(-1) decrea sing with increasing accelerator concentrations to 26 kJ mol(-1) with DESU at 90 g kg(-1) and 64 kJ mol(-1) with TBP at 150 g kg(-1). Thus, the intrin sic activity of DESU was much higher than that of TBP, which implies that, for a given effect, less DESU than TBP would be needed. MEDs were also very effective accelerators, lowering activation energies to 36 kJ mol(-1). Dat a are discussed in relation to increasing rates of foliar penetration of ac tive ingredients at low temperatures. (C) 2001 Society of Chemical Industry .