Polydisperse ethoxylated fatty alcohol surfactants as accelerators of cuticular penetration. 1. Effects of ethoxy chain length and the size of the penetrants

Abstract

: The e †ects of polydisperse ethoxylated fatty alcohol (EFA) surfactants on the penetration of six organic compounds varying in size (molar volumes, 107È282 cm3 mol~1) and lipophilicity (log 0É8È6É5) were investigated using K ow astomatous isolated cuticular membranes (CM) of Citrus and pear leaves. Mobilities of model compounds in CM were measured by unilateral desorption from the outer surface (UDOS). Rate constants (k*) obtained in these experiments are directly proportional to di †usion coefficients and, in the absence of EFA, k* values decreased by a factor of 52 when molar volumes increased only 2É64-fold. Under UDOS conditions using micellar surfactant solutions as desorption media, surfactants are sorbed in the CM and the volume fractions sorbed were found to decrease from approximately 0É062 to 0É018 when the average number of ethoxy groups (nE) increased from 5 to 17. In the presence of the EFA surfactants in the CM, solute mobilities increased markedly though this e †ect diminished with increasing nE. Surfactants with nE \ 17 a †ected solute mobilities only marginally. Surfactant e †ects on solute mobility increased with the size of the solutes leading to almost identical mobilities of the model compounds. With the current range of our model compounds, lipophilicity increased with increasing molar volumes, though evidence is presented showing that the mobilities of solutes depend on their molar volumes while lipophilicity has no e †ect. E †ects of micellar aqueous solutions of polydisperse surfactants on solute mobilities followed the pattern observed with monodisperse ones.Experiments simulating foliar uptake (SOFU), by applying 5-kl droplets of solute and increasing amounts of surfactant (1È20 g litre~1) to the outer surface of the CM and then monitoring the rates of appearance at the inner surfaces of the CM, were carried out with 1-(3-Ñuoromethylphenyl)-5-phenoxy-5H-1,2,3,4-tetrazole (WL110547 ; log and cyanazine (log and the sur-K ow \ 3É6) K ow \ 2É1) factants "GenapolÏ C-050 (GP C-050, nE 5) and "GenapolÏ C-200 (GP C-200, nE 17). In the applied range, uptake increased with increase in amount of both surfactants and both surfactants were more e †ective than polyethylene glycol (PEG 400). The smaller, more lipophilic GP C-050 was able to increase the rates of uptake of both compounds greatly, while GP C-200 had a less, though observable, e †ect, similar to the pattern observed in the UDOS experiments. The results indicated that GP C-050 penetrated the cuticle rapidly while sorption of GP C-200 was slower, though better from a concentrated residue in SOFU experi-* To whom correspondence should be addressed. Contract grant sponsor : Shell Forschung AG. 132Peter Baur, B. T erence Grayson, Jo rg Scho nherr ments than from aqueous solution in UDOS experiments. This induced some acceleration e †ects by GP C-200 in SOFU experiments, but these could be countered by reductions in concentrations, and hence driving forces, for penetration at higher levels of application.

Mechanistic Aspects and Effects of Selected Tank-Mix Partners on Herbicidal Activity of a Novel Fatty Acid Ester

“…No superior spreading probably took place in the presence of the high already PA-MPEG concentration, which is also a wetting agent on its own [ 23 , 27 ]. The lack of any significant influence on PA-MPEG efficacy by strong penetration enhancer, Genapol C 050, was at first surprising [ 41 , 42 ]. However, in the presence of 7.5% PA-MPEG in the spray, and assuming a cuticle/water partition coefficient of Genapol C 050 close to 1, the explanation of these results was that Genapol C 050 probably did not simply enter through leaf cuticles [ 43 , 44 ].…”

Effect of humectants on the uptake and efficacy of glufosinate in wild oat (Avena fatua) plants and isolated cuticles under dry conditions

“…Surfactants containing aliphatic moieties and PEG chains of 10 to 15 ethylene oxide (EO) units in length have been shown to enhance the uptake of water soluble compounds (Baur et al 1997;Coret and Chamel 1994), and it has been suggested that they have significant hygroscopic properties Bukovac 1987a, 1987b). However, it was decided to add humectants to the existing formulation as opposed to formulating the herbicide with a high EO content surfactant for two reasons.…”

Water Sorption Isotherms of Surfactants: A Tool To Evaluate Humectancy

“…Surfactants are widely used in agrochemical applications . Non-ionic polyethoxylated surfactants are postulated to have the ability to sorb and retain water, , helping to keep the active ingredient in the spray deposit in a physical state, which favors its uptake into the leaf. , Therefore, the present work studied the humectant properties of selected non-ionic surfactants in a systematic approach. Comprehensive experimental data on the water sorption ability of commonly used non-ionic polydisperse surfactants at the full range of RHs up to 95% are presented.…”

“…A very prominent organic humectant is glycerol, which is commonly used in pharmaceutical, cosmetic, and food products to give them the desired flexibility, softness, and shelf life . In the context of plant protection agents, humectancy of non-ionic polyethoxylated surfactants is believed to be related to a high ethylene oxide (EO) content, because surfactants with a higher EO content enhance cuticular uptake of water-soluble active ingredients. − In most ethoxylated surfactants, the hydrophilic moiety is composed of polyoxyethylene chains. Ethoxylated surfactants are thought to improve the uptake of hydrophilic and lipophilic herbicides by different modes of action .…”