Metal-ion mediated photolytic regulation of diphenylalanine stability: Implications for prebiotic chemical evolution

Early Earth's UV-rich environment, together with abundant transition metals, likely shaped the stability of biomolecules. We investigated how cations influence the UV (254 nm) stability of diphenylalanine (FF). Among nine geologically relevant cations examined, Cu(Ⅱ) and Fe(Ⅲ) exhibited significantly different photolytic effects, Fe(Ⅲ) accelerated FF degradation, and Cu(Ⅱ) stabilized FF. Other metal ions had a minimal impact on FF stability. Mechanistic investigations revealed that Cu(Ⅱ) preferentially binds to the amide nitrogen, whereas Fe(Ⅲ) coordinates, primarily through oxygen atoms, significantly perturb the electron distribution of the phenyl and amide groups, thereby enhancing their susceptibility to hydroxyl radical attack. EPR spectroscopy further confirmed that Fe(Ⅲ) produces substantially higher levels of ⋅OH than Cu(Ⅱ), implicating ROS as the key driver of degradation. By uncovering cation-specific mechanisms of photodegradation, this study provides a physicochemical framework for understanding how metal ions may have influenced the selection and accumulation of proto-biomolecules in early chemical evolution.