Molecular Defenders: Proteins and Phospholipids Enhancing Natural Rubber's Resilience

Natural rubber (NR), a cis-1,4-polyisoprene biopolymer, exhibits excellent mechanical strength and oxidative stability, partly due to the presence of nonrubber components (NRCs) such as proteins and phospholipids. However, the molecular mechanisms by which NRCs influence NR's performance remain poorly understood. In this study, molecular dynamics (MD) simulations and quantum mechanical (QM) calculations are combined to investigate the role of NRCs in enhancing the thermo-mechanical and oxidative stability of NR. MD simulations show that NRCs form strong hydrogen-bonding (H-bonding) networks, increasing the glass transition temperature (T_g), reducing chain mobility, and introducing physical cross-links that enhance mechanical integrity. QM calculations reveal that specific protein residues (e.g., Pro_H4) have low N-H bond dissociation energies (BDE = 158.61 kJ·mol^-1), allowing efficient hydrogen atom transfer (HAT) to quench free radicals. The combined MD/QM results demonstrate a dual stabilization mechanism: NRC-functionalized model systems exhibit low oxygen permeability (P = 3.0 × 10 ^-9 cm²/s kPa at 298 K), which limits radical formation, while protein-based antioxidants actively scavenge radicals. This synergy between reduced oxygen transport and intrinsic radical quenching provides a molecular basis for the oxidative resistance of NR. These findings clarify the structural role of NRCs in NR and offer a design strategy for developing durable, bioinspired elastomers with built-in oxidative protection.