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.