Organoplatinum Compounds as Anion-Tuneable Uphill Hydroxide Transporters.

Active transport of ions uphill, creating a concentration gradient across a cell membrane, is essential for life. It remains a significant challenge to develop synthetic systems that allow active uphill transport. Here, a transport process fuelled by organometallic compounds is reported that creates a pH gradient. The hydrolysis reaction of Pt complexes results in the formation of aqua complexes that established rapid transmembrane movement ("flip-flop") of neutral Pt-OH species, leading to protonation of the OH group in the inner leaflet, generating OH ions, and so increasing the pH in the intravesicular solution. The organoplatinum complex effectively transports bound hydroxide ions across the membrane in a neutral complex. The initial net flow of the Pt complex into the vesicles generates a positive electric potential that can further drive uphill transport because the electric potential is opposed to the chemical potential of OH . The OH ions equilibrate with this transmembrane electric potential but cannot remove it due to the relatively low permeability of the charged species. As a result, effective hydroxide transport against its concentration gradient can be achieved, and multiple additions can continuously drive the generation of OH against its concentration gradient up to ΔpH>2. Moreover, the external addition of different anions can control the generation of OH depending on their anion binding affinity. When anions displayed very high binding affinities towards Pt compounds, such as halides, the external anions could dissipate the pH gradient. In contrast, a further pH increase was observed for weak binding anions, such as sulfate, due to the increase of positive electric potential.