| Humic acid (HA), as a crucial component of soil organic matter, significantly influences the environmental behaviors of alkane pollutants, including their transport, transformation, and bioavailability, through its interaction mechanisms with alkanes. Current research on alkane-HA interactions has primarily focused on macroscopic scales, while molecular-scale mechanisms remain unclear. This study integrated quantum chemical calculations, correlation analysis, and the construction of Ridge Regression modeling to investigate the intermolecular interactions between alkanes of varying chain lengths and HA, as well as their influencing factors. The results demonstrate that as the chain length of alkanes increases, their binding energy and interaction strength with HA molecules gradually enhance, driven predominantly by van der Waals (vdW) forces. Medium-chain alkanes (C13–20) exhibited significantly higher binding energy and interaction strength compared to short-chain alkanes (C8–12), attributed to their larger molecular contact area. Furthermore, the electrostatic potential (ESP) distribution of the alkane molecule-HA composite clusters exhibits significant heterogeneity. Correlation analysis revealed that the alkane-HA binding energies (absolute value) and weak interactions showed a highly significant positive correlation (p < 0.05) with the number of atoms, HOMO orbital energy level, total vdW surface area, vdW electronegative surface area, and molecular volume. The Ridge Regression model (R2 ≈ 0.65) identified vdW electronegative surface area as the dominant factor influencing binding energy and weak intermolecular interactions. This study clarifies the critical role of vdW forces in stabilizing the HA-alkane complexes system and provides a theoretical foundation for understanding the interaction mechanisms between environmental organic matter and alkanes. |
