title: Effects of temperature and concentration of the accelerators ethoxylated alcohols, diethyl suberate and tributyl phosphate on the mobility of [14C]2,4-dichlorophenoxy butyric acid in plant cuticles.
abstract: Intrinsic activities of monodisperse ethoxylated dodecanols (MEDs), diethyl suberate (DESU) and tributyl phosphate (TBP) were investigated using Stephanotis floribunda leaf cuticular membranes (CMs) and [14C]2,4-dichlorophenoxy butyric acid (2,4-DB) as a model solute. When sorbed in cuticular membranes, MEDs, DESU and TBP increase solute mobility and are called accelerators for this reason. With MEDs, dose-effect curves (log mobility vs accelerator concentration) were linear but, with DESU and TBP, curves convex 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 CMs by 9- to 48-fold, and effects were larger at lower temperatures (range 15-30 degrees C). Activation energy for diffusion of 2,4-DB was 105 kJ mol-1, decreasing 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 intrinsic 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. Data are discussed in relation to increasing rates of foliar penetration of active ingredients at low temperatures.
authors.affiliation: Institute of Vegetable and Fruit Science, University of Hannover, Am Steinberg 3, 31157 Sarstedt, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Schönherr
authors.forename: L
authors.initials: L
authors.lastname: Schreiber
authors.forename: A
authors.initials: A
authors.lastname: Buchholz
mesh_terms: D015084:2,4-Dichlorophenoxyacetic Acid / Q000031:analogs & derivatives / Q000493:pharmacokinetics*; D000438:Alcohols / Q000008:administration & dosage / Q000494:pharmacology*; D003998:Dicarboxylic Acids / Q000494:pharmacology*; D004058:Diffusion / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D006540:Herbicides / Q000493:pharmacokinetics*; D006358:Hot Temperature; D007553:Isotope Labeling; D008566:Membranes / Q000187:drug effects / Q000378:metabolism; D010755:Organophosphates / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000494:pharmacology*; D010539:Permeability / Q000187:drug effects; D010574:Pesticide Synergists / Q000493:pharmacokinetics / Q000494:pharmacology*; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism*; D010944:Plants / Q000187:drug effects / Q000378:metabolism*; D010968:Plasticizers / Q000494:pharmacology; D013501:Surface-Active Agents / Q000008:administration & dosage / Q000494:pharmacology
chemical_list: D000438:Alcohols; D003998:Dicarboxylic Acids; D006540:Herbicides; D010755:Organophosphates; D010574:Pesticide Synergists; D010968:Plasticizers; D013501:Surface-Active Agents; C432906:diethyl suberate; D015084:2,4-Dichlorophenoxyacetic Acid; C009524:tributyl phosphate; C004764:4-(2,4-dichlorophenoxy)butyric acid