The Dominant Role of Oxygen in Modulating the Chemical Evolution Pathways of Tyrosine in Peptides: Dityrosine or Melanin.

In diverse biological systems, the oxidation of tyrosine to melanin or dityrosine is crucial for the formation of crosslinked proteins and thus for the realization of their structural, biological, and photoactive functionalities; however, the predominant factor in determining the pathways of this chemical evolution has not been revealed. Herein, we demonstrate for tyrosine-containing amino acid derivatives, peptides, and proteins that the selective oxidation of tyrosine to produce melanin or dityrosine can be readily realized by manipulating the oxygen concentration in the reaction system. This oxygen-dependent pathway selection reflects the selective chemical evolution of tyrosine to dityrosine and melanin in anaerobic and aerobic microorganisms, respectively. The resulting melanin- and dityrosine-containing nanomaterials reproduce key functions of their natural counterparts with respect to their photothermal and photoluminescent characteristics, respectively. This work reveals the plausible role of oxygen in the chemical evolution of tyrosine derivatives and provides a versatile strategy for the rational design of tyrosine-based multifunctional biomaterials.