Accelerators increase permeability of cuticles for the lipophilic solutes metribuzin and iprovalicarb but not for hydrophilic methyl glucose

作者：Shi T; Schonherr J; Schreiber L^*

来源：Journal of Agricultural and Food Chemistry, 2005, 53(7): 2609-2615.

DOI：10.1021/jf048242w

• adjuvant
• cuticular permeability
• foliar uptake
• pesticide efficacy
• partition coefficient

Effects of diethylsuberate (DESU), tributyl phosphate (TBP), and monodisperse ethoxylated alcohols (EAs) on rate constants of penetration (k) of model solutes across astomatous cuticular membranes isolated from Madagascar ivy (Stephanotis floribunda) and pear (Pyrus communis) leaves were studied. Model solutes (selected on the basis of their octanol/water partition coefficients, K-ow) were iprovalicarb (log K-ow = 3.18), metribuzin (log K-ow = 1.60), and methyl glucose (MG) (log K-ow = -3.0). K-ow varied by more than 6 orders of magnitude. Accelerators had wax/water partition coefficients (log K-ww) ranging from 1.75 (DESU) to 4.32 (C12E2), and their equilibrium concentrations in Stephanotis wax varied from 0 to about 160 g kg(-1). Accelerators increase solute mobility in cuticles by increasing fluidity of cutin and waxes. This effect was quantified by plotting log k versus the accelerator concentration in wax. With the lipophilic solutes metribuzin and iprovalicarb, these plots were linear. Slopes of these plots characterize the intrinsic activities of the accelerators, and they decreased in the order DESU (0.029) > TBP (0.015) > EAs (0.01). Using these intrinsic activities, the effects of accelerators on rate constants of penetration can be calculated for any accelerator concentration in wax. For instance, at 50 g kg(-1), rate constants for lipophilic solutes increased by factors of 28 (DESU), 5.6 (TBP), and 3.2 (C12En), respectively. Permeability of cuticles for the hydrophilic MG was not increased by DESU, TBP, C12E2, and C12E4, while C12E6 and C12E8 increased it. Small hydrophilic solutes such as MG can access aqueous pores in cuticles, and this pathway is not affected by changes in fluidity of amorphous waxes. After rate constants of penetration of ionic CaCl2 were compared with those for nonionic MG, it was concluded that 60% of the MG diffused across aqueous pores, while 40% used an alternative pathway. Because the solubility of MG in wax is extremely low, it is unlikely that MG diffused along the lipophilic pathway used by metribuzin and iprovalicarb. This agrees with the observation that DESU and TBP had no effect on rate constants for MG. An alternative pathway of unknown properties is suggested. It is speculated that C12E6 and C12E8 sorbed in cuticles might have generated a polar pathway for MG.

• 出版日期2005-4-6