Beyond Conventional Density Functional Theory: Advanced Quantum Dynamical Methods for Understanding Degradation of Per- and Polyfluoroalkyl Substances

Abstract

Computational chemistry methods, such as density functional theory (DFT), have now become more common in environmental research, particularly for simulating the degradation of per-and polyfluoroalkyl substances (PFAS). However, the vast majority of PFAS computational studies have focused on conventional DFT approaches that only probe static, time-independent properties of PFAS near stationary points on the potential energy surface. To demonstrate the rich mechanistic information that can be obtained from time-dependent quantum dynamics calculations, we highlight recent studies using these advanced techniques for probing PFAS systems. We briefly discuss recent applications ranging from ab initio molecular dynamics to DFT-based metadynamics and real-time time-dependent DFT for probing PFAS degradation in various reactive environments. These quantum dynamical approaches provide critical mechanistic information that cannot be gleaned from conventional DFT calculations. We conclude with a perspective of promising research directions and recommend that these advanced quantum dynamics simulations be more widely used by the environmental research community to directly probe PFAS degradation dynamics and other environmental processes.

Linear perfluoroalkyl carboxylate reduction dynamics with solvated electrons from ferrocyanide and sulfite

“…As such, a good deal of theoretical work has been dedicated to disentangling these fast initial reactions. 12,47–51 RCF 2 COO − + e aq − → RCF 2 (COO − ) − RCF 2 COO − + e aq − → RC˙FCOO − + F − RCF 2 COO − + e aq − → [R(CF 2 ) − COO − ][R(CF 2 ) − COO − ] → RC˙FCOO − + F − …”

The role of helicity in PFAS resistance to degradation: DFT simulation of electron capture and defluorination

“…42 Their subsequent dynamic work on expanded systems further confirmed the behaviours and femto- to picosecond timescale. 43 Taken together these studies suggest that the mechanism linking chain length and degradation rate occurs after electron capture. Furthermore, these theoretical studies are consistent in their treatment of bond strength as the decisive factor in the determination of whether and where defluorination will occur and understate the contribution of how those bonds are arranged within the molecular structure.…”

Influence of Steric and Dispersion Interactions on the Thermochemistry of Crowded (Fluoro)alkyl Compounds

“…On the other hand, per- and polyfluoroalkyl substances (PFAS) have garnered unprecedented attention in recent years, becoming a focal point of scientific inquiry, regulatory concern, and public discourse. − These synthetic compounds, characterized by their remarkable stability and hydrophobic nature, open new perspectives in industrial and commercial applications. , However, their persistent presence in the environment, coupled with potential adverse health effects, has propelled PFAS to the forefront of global environmental and health agendas. Thus, it seems clear that a detailed theoretical understanding of fluorinated organic drugs and PFAS, in particular their thermodynamic properties and kinetic stability, is of high general interest. − …”