Release characteristics of the non-toxic insect repellant 2-undecanone from its crystalline inclusion compound with α-cyclodextrin

Abstract

2-Undecanone (methyl nonyl ketone), a natural non-toxic insect repellant compound, was recently isolated from the trichomes of wild tomatoes, and is currently being introduced as a replacement for insect repellants containing N,N-diethyl-meta-toluamide or DEET, which are permitted for use on children older than 2 months. In an effort to improve the delivery of the somewhat volatile 2-undecanone, we have successfully formed the crystalline inclusion compound (IC) between 2-undecanone and α-cyclodextrin (α-CD), using a coprecipitation method. Employing WAXD, DSC, FT-IR, and NMR observations, we have confirmed that 2-undecanone is included as a guest inside the host α-CD cavities, and forms a channel-type crystalline IC. The release characteristics of 2-undecanone insect repellant from its α-CD-IC were studied using TGA either at a heating rate of 20 °C/min in nitrogen, and air atmospheres or at constant temperatures of 25, and 40 °C over a period of 24 h. The release/loss of 2-undecanone insect repellant from its α-CD-IC was ~60% after 24 h at 40 °C. By comparison, ~97% of pure 2-undecanone was volatilized, and lost over 24 h at 40 °C. In addition, insecticidal activity of 2-undecaonone from its α-CD complex against German cockroaches was evaluated. The results show an excellent repellency that 100% of the cockroaches were repelled for the first 2 days after application. These results suggest that the gradual, long-term delivery of the insect repellant 2-undecanone can be significantly improved through employment of its crystalline α-CD-IC.