Reversible oxygenation of bis[β-(2-pyridyl)-α-alaninato]Co(II) complex in aqueous solution at room temperature

The reversible oxygenation capability of bis[β-(2-pyridyl)-α-alaninato]Co(II) (Co(PyA)2) in aqueous solution at room temperature was studied. Time-dependent oxygenation and deoxygenation behavior was tested continuously by UV–Vis spectrophotometry under O2 or N2 atmosphere, respectively. Experimental results showed that Co(PyA)2 retained about 40% of its original oxygenation capacity even after 1000 oxygenation–deoxygenation cycles, and retained 10% of the original oxygenation capacity even after more than 3000 cycles during 11 days of continuous reaction. The reversible oxygenation of Co(PyA)2 was characterized by oxygenometry and volumetry. Comparison experiments and theoretical modeling results revealed that comparable coordination structures mean Co(PyA)2 and bis(histidinato)Co(II) (Co(His)2) have similar oxygenation capacities. However, the five-coordinate bonding of Co(PyA)2 causes it to show faster rate of oxygen release than those of Co(His)2.

Graphical abstractThe reversible oxygenation capability of bis[b-(2-pyridyl)-a-alaninato]Co(II) (Co(PyA)2) in aqueous solution at room temperature was studied. Experimental results showed that Co(PyA)2 retained 10% of the original oxygenation capacity after more than 3000 cycles during 11 days of continuous reaction. Theoretical results revealed that the five-coordinate bonding of Co(PyA)2 play a key role to improve its oxygenation ability.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The Co–PyA complex showed more than 3000 reversible cycles of uptaking dioxygen. ► The analogous coordinating structures of Co-His play a key role in uptaking dioxygen reversibly. ► The structures of the Co–PyA was deduced by theoretical calculation.