Another topic of great physiological relevance is the ability of artificial transporters to facilitate Cl -/HCO3 -exchange -a process that is crucial for vital biological functions, such as respiration and digestion. To investigate this, we measured chloride transport by 2 in sodium bicarbonate solution, using the lucigenin method. As shown in Fig. , the chloride influx under these conditions is slower than in sodium nitrate, with a specific initial rate [I] = 9.2 s -1 , i.e. almost 10 times lower than for chloride/nitrate exchange. This is likely due to the soft nature of 2 and hence reduced affinity to hard anions, such as HCO3 -.