Spin Relaxation Does Not Preclude Magnetic Field Effects on Lipid Autoxidation.

Spin correlations between radicals underpin key biological processes, and spin relaxation describes their decay due to environmental interactions. Radical pairs involving lipid peroxide radicals in bilayers have been proposed as a source of magnetic field effects (MFEs) in lipid autoxidation, but their viability has been questioned due to rapid relaxation in dynamic membranes. This study investigates whether MFEs can persist in lipid bilayers despite spin relaxation. Using an integrative approach combining all-atom molecular dynamics simulations, density functional theory (DFT) calculations, and spin dynamics modeling using Bloch-Redfield-Wangsness relaxation theory, we investigate a palmitoyl-linoleoyl-phosphatidylcholine (PLPC) model membrane containing 13ze-lipid peroxide radicals. We identify the peroxide group rotation and the lipid backbone dynamics as key drivers of spin relaxation. By computing g-tensors and hyperfine coupling constants via DFT and incorporating their molecular-dynamics-derived fluctuations into spin-dynamics simulations, we assess relaxation from hyperfine interactions, g-tensor fluctuations, and spin-rotational coupling. Our results demonstrate that MFEs persist in lipid bilayers despite thermal motion. Relaxation is dominated by g-fluctuations, which enhance MFEs at high magnetic fields. Surprisingly, our calculations also suggest possible MFEs in weak magnetic fields. These findings broaden the understanding of biological MFEs and highlight potential biomedical implications for ferroptosis, cancer, and oxidative stress-related diseases.