Molecular-Level Insights Into Solvent-Dependent Interactions Governing the Solubility of Polyhydroxyalkanoates

Abstract

Polyhydroxyalkanoates (PHA) are biodegradable alternatives to conventional plastics, as they can decompose without generating harmful residues, thereby addressing global plastic pollution. In this work, a molecular-level understanding of solvent-polymer interactions is achieved using Density Functional Theory (DFT). The molecules were optimized at the M06-2X/cc-pVDZ level, and the binding energies (−8.45 to −18.89 kcal/mol) confirm the thermodynamic stability of the complexes and are consistent with experimental solubility patterns. Non-Covalent Interaction (NCI) and Reduced Density Gradient (RDG) analyses demonstrate that the van der Waals interactions dominate with minor contributions from hydrogen bonding. Natural Bond Orbital (NBO) analysis highlights the donor-acceptor interactions with stabilization energies up to ∼17 kcal/mol, while Quantum Theory of Atoms in Molecules (QTAIM) suggests their predominantly closed-shell interactions. Frontier Molecular Orbital (FMO) and Molecular Electrostatic Potential (MESP) analyses further explain the charge transfer and key interaction sites. Thus, this study provides a molecular-level understanding of solvent-PHA interactions for the rational design of sustainable PHA-based materials.