Abstract: 【Aim】 Using repellent is one of the most important methods for mosquito control. In our previous study, we found that there is an interaction between repellent molecules and human-secreted attractant molecules during the use of repellents. To understand the true nature of this interaction, in this study the interactions between three repellents and one attractant L-lactic acid were explored through computational quantum chemistry based on the analysis of numerical changes of geometric structure, binding energy, charge population and thermodynamic parameters. This study might reveal the form, strength and law of the interactions between the repellent molecules and the human-secreted attractant molecules in silico. 【Methods】 The structures of three representative mosquito repellents 8-hydroxylcarveol formate (R1), hydroxy citronellal-1,2-propanediol acetal (R2) and N,N-diethyl-3-methyl benzoyl amide (DEET), the attractant L-lactic acid, and their complexes were constructed by using Gaussian 09 software package. Geometry optimizations and vibration frequency calculations of the repellents, the attractant and their complexes were done at the M06-2X-D3/6-311G (d,p) level. The single point energy of the repellents, the attractant and their complexes were calculated at the M06-2X-D3/6-311+G (d,p) level. 【Results】 The association distances and angles between the repellents R1, R2 and DEET and the attractant L-lactic acid were among 2.64-2.74 Å and 170-175°, respectively, and after the association, the bond length of oxygen hydrogen bond in carboxyl of L-lactic acid were stretched to 0.019, 0.029 and 0.022 Å, respectively. The binding energies (ΔE) of the association process were -50.278, -72.385 and -66.977 kJ/mol, the enthalpy change (ΔH) -43.715, -65.559 and -60.465 kJ/mol, the entropy change (ΔS) -0.138, -0.159 and -0.157 kJ/mol·K, the free energy(ΔG) -2.652, -18.090 and -13.784 kJ/mol, and the total net charge of L-lactic acid varied from 0 e to -0.0248, -0.0250 and -0.0168e, respectively. 【Conclusion】 The repellents R1, R2 and DEET and the attractant L-lactic acid are associated by moderately strong hydrogen bond. The hydrogen bond between R2 and L-lactic acid are the strongest, and the complex formed is the most stable.

Key words: Mosquito repellent, L-lactic acid, weak interaction, hydrogen bond, binding energy, charge population, thermodynamic parameter