Abstract: This study attempted to demonstrate the molecular association between terpenoid repellents and CO₂, and investigated its influence on their repellency against mosquitoes. Association energy was calculated using computational chemistry software: three-dimensional structures of CO₂, 22 terpenoid repellents and their complexes that are associated with CO₂ were built and optimized using Gaussian View and Gaussian 03W, respectively, and the association energy were obtained in Ampac 8.16. Dependence of repellency on the molecular association was studied by quantitative structure-activity relationship method. Significant activity-affecting parameters were screened from structural descriptors of 22 terpenoid repellents and their complexes, as well as descriptors of characteristic fragments of complexes, which were all calculated by Codessa 2.7.10. The quantitative structure-activity relationship (QSAR) model was obtained to analyze the relationship between the structural descriptors and the logarithm value of the corrected repelling time against Aedes albopictus. Association energies between terpenoid repellents and CO₂ were thus calculated, and the results showed that the molecular association between them was strong enough to form the complexes. A statistical QSAR model with four parameters and with R² of 0.9643 was built, and the most significant activity-affecting parameters were COM-WNSA-3 Weighted PNSA (PNSA3*TMSA/1 000) ［Zefirov’s PC］, f-TerCO₂-Min e-n attraction for a C-O bond, M-Max 1-electron reactivity index for an O atom, M-Min (>0.1) bond order of an H atom, respectively. The results of computational chemistry calculation show that the molecular association between terpenoid repellents and CO2 is present, and the association can affect the repellency greatly.

Key words: Repellent, terpenoid, CO₂, molecular association, quantitative structure-activity relationship (QSAR), quantitative calculation