The partitioning of disparlure between hydrophobic organic solvents and water Sierra Rayne a,* , Kaya Forest b a Chemologica Research, 318 Rose Street, PO Box 74, Mortlach, Saskatchewan, Canada, S0H 3E0 b Department of Environmental Engineering, Saskatchewan Institute of Applied Science and Technology, Palliser Campus, 600-6th Avenue NW, PO Box 1420, Moose Jaw, Saskatchewan, Canada, S6H 4R4 Abstract The partitioning behavior of disparlure ((7R,8S)-cis -7,8-epoxy-2-methyloctadecane) - a sex pheromone of the gypsy moth, Lymantria dispar - between aqueous solutions and the organic solvents chloroform and n-heptane has been re-evaluated. Prior estimates from the literature of the aqueous-organic solvent partitioning coefficients (log P) for disparlure in these two solvent systems appear to have been underestimated by about 5-6 orders of magnitude. In the current work, we provide corrected log P(chloroform/water) and log P(heptane/water) values for disparlure of 9.87 and 9.15, respectively. Keywords: disparlure, (7R,8S)-cis -7,8-epoxy-2-methyloctadecane, sex pheromone, gypsy moth, partitioning behavior Introduction The partitioning behavior of disparlure ((7R,8S)-cis - 7,8-epoxy-2-methyloctadecane) - a sex pheromone of the gypsy moth, Lymantria dispar - at hydrophobic/aqueous interfaces is of interest to better understand the interaction of this compound with pheromone-binding proteins in vivo [1]. In their article, Reimer et al. [1] report the following experimental (expt.) and computationally (calc.) derived chloroform/water and n-heptane/water partitioning coef- ficients (log P) for disparlure: log P(chloroform/water): 3.4+/-0.3 (expt.), 3.1 (calc.); log P(heptane/water): 3.8+/- 0.2 (expt.), 3.9 (calc.). Figure 1: Structure of disparlure. The SPARC software program (http://archemcalc.com/ sparc/; October 2011 release w4.6.1691-s4.6.1687) has been validated for accurately estimating the log P values for a wide range of organic compounds [2–4]. This program es- timates log P(n-octanol/water), log P(chloroform/water), and log P(heptane/water) for disparlure of 8.24, 9.87, and 9.15, respectively, at 298.15 K. Previous works have also reported estimated log P(n-octanol/water) of about 8 for disparlure using other software [5, 6]. Disparlure is a long chain hydrocarbon with an epoxide moiety near the center of the alkyl chain. A substantial ∗ Corresponding author. Tel.: +1 306 690 0573. E-mail address: sierra.rayne@live.co.uk (S. Rayne). body of work has established that the difference in par- titioning behavior for ether linkages is minimal between aqueous-organic partitioning systems where the organic phase is capable of hydrogen bonding (e.g., n-octanol) and where the organic phase is non-polar (e.g., chloroform, n- heptane, cyclohexane) [7, 8]. Similar results are obtained where the functional group in question is a carbonyl moi- ety. Consequently, relatively little difference is expected in the log P(n-octanol/water), log P(chloroform/water), and log P(heptane/water) values for disparlure. To confirm that SPARC is estimating accurate log P values for disparlure, the program was tested with other model compounds relevant to the study in question. For 1,2-epoxybutane, the experimental log P(n-octanol/water) is 0.68 [9], which compares very favorably to the SPARC estimated log P(n-octanol/water) of 0.94, and the SPARC estimated log P(chloroform/water) and log P(heptane/wat- er) values of 1.31 and 0.88, respectively. Similarly, epichl- orohydrin has an experimental log P(n-octanol/water) of 0.26 [10], which is in excellent agreement with the SPARC estimated log P(n-octanol/water) of 0.63, and the SPARC estimated log P(chloroform/water) and log P(heptane/wa- ter) values of 1.1 and 0.41, respectively. As well, the environmental contaminant heptachlor epox- ide has an experimental log P(n-octanol/water) of 5.40 [11], also in excellent agreement with the SPARC esti- mated log P(n-octanol/water) of 5.74, and the SPARC es- timated log P (chloroform/water) and log P(heptane/water) values of 7.17 and 5.65, respectively. Thus, SPARC ap- pears capable of accurately predicting log P(n-octanol/ water) values for a range of epoxides, and consistent with our state-of-the-art knowledge regarding aqueous-organic partitioning behavior between various organic solvents, SP- Preprint submitted to viXra January 11, 2013