​​C-a16​​ is an ionizable lipid engineered through Mannich reaction chemistry, designed to revolutionize mRNA delivery by synergizing high efficiency with minimized immune activation. Synthesized by reacting a phenolic tail derivative, formaldehyde, and a branched tertiary amine core under optimized ethanol conditions, this lipid integrates antioxidant phenol groups directly into its structure. These phenol moieties serve as intrinsic radical scavengers, effectively neutralizing intracellular reactive oxygen species that typically degrade mRNA and trigger inflammation.In lipid nanoparticle formulations, C-a16 constitutes the functional backbone, enabling superior mRNA encapsulation efficiency while maintaining a stable nanoparticle size of approximately 80–100 nm. Critically, it outperforms conventional lipids like DLin-MC3-DMA by achieving significantly higher target-protein expression in vivo alongside markedly reduced pro-inflammatory cytokine secretion. The antioxidant capability is not incidental but fundamental—quenching the phenol groups drastically diminishes both ROS suppression and delivery efficacy, confirming the design's mechanistic elegance.C-a16 represents a paradigm shift: its biomimetic antioxidant architecture addresses the chronic trade-off between delivery potency and immunogenicity, unlocking safer therapeutic applications for vaccines and gene therapies.