Abstract: 【Aim】 The research of repellent mechanism is still unsatisfactory. This study intends to investigate the trimolecular association between single terpenoid repellent and two different attractants, and the relationship between the trimolecular association and mosquito repellency through the theoretical calculation. The goal is to develop a new direction for the repellent mechanism research.【Methods】 Gaussian View 4.1 and Gaussian 03W softwares were used to build and optimize the structure of terpenoid repellent monomers and trimolecular complexes which comprise L-lactic acid, ammonia and repellents. The optimized structure and association energy were obtained after optimization. Ampac 8.16 was applied to import all the above structures into the Codessa 2.7.10 software. Various kinds of structural descriptors were calculated, and a series of quantitative models which imply the relationship between structural descriptor of the association and repellent activity were generated by the heuristic method encoded in Codessa 2.7.10. The best quantitative model was picked out through breaking point rule and model validation. 【Results】 The energy of trimolecular association is basically in the range of 20 to 50 kJ/mol, and the R² of the best threeparameter quantitative model is 0.9098. Three structural descriptors contained in the model were the maximum nucleophilic reactivity index for a C atom, topographic electronic index (all bonds) ［Zefirov’s PC］ and exchange energy + e-e repulsion for a H-O bond.【Conclusion】 A terpenoid repellent molecule can associate with two different attractant molecules at the same time, and this trimolecular association matches the basic characteristics of hydrogen bonds. The maximum nucleophilic reactivity index for a C atom, topographic electronic index (all bonds) ［Zefirov’s PC］ and exchange energy + e-e repulsion for a H-O bond, which are three descriptors generated from trimolecular complexes, tightly correlate to the repellency. This research preliminarily illustrates the existence of trimolecular association between terpenoid repellents and attractants, and its influence on the repellency. The result provides a new theoretical basis for the future repellent mechanism research.

Key words: Terpenoid repellent, attractant, trimolecular association, association energy, quantitative structureactivity relationship (QSAR), structural descriptor