The unusual increase in jCO2 correlates well with the decrease in ∆A from 298-323 K, and the steady decrease from 323-423 K is consistent with the increasing free energy barrier for translocation (Figure ). The translocation trends for pore-16 follow the temperature dependence of free energy (Figure ). O2 is a larger molecule than CO2. Given that CO2 translocation follows an energy barrier, one expects O2 to experience an even more significant barrier. This is indeed observed from PMF calculation (Figure ). This translates into a slower translocation rate for O2 than CO2, leading to highly selective CO2 transport.