Reversible oxygenation of α -amino acid-cobalt(II) complexes

We systematically investigated the reversibility, time lapse, and oxygenation-deoxygenation properties of 15 natural α -amino acid-Co(II) complexes through UV-vis spectrophotometer, polarographic oxygen electrode, and DFT calculations, respectively, to explore the relationship between the coordinating structure and reversible oxygenation of α -amino acid-Co(II) complexes. Results revealed that the α -amino acid structure plays a key role in the reversible oxygenation properties of these complexes. The specific configuration of the α -amino acid group affects the e_g ¹ electron of Co(II) transfer to the π∗ orbit of O₂; this phenomenon also favors the reversible formation and dissociation of Co-O₂ bond when O₂ coordinates with Co(II) complexes. Therefore, the co-coordination of amino and carboxyl groups is a determinant of Co complexes to absorb O₂ reversibly. The group adjacent to the α -amino acid unit evidently influences the dioxygen affinity and antioxidation ability of the complexes. The presence of amino (or imino) and hydroxy groups adjacent to the α -amino acid group increases the oxygenation-deoxygenation rate and the number of reversible cycles. Our findings demonstrate a new mechanism to develop reversible oxygenation complexes and to reveal the oxygenation of oxygen carriers.