Transmembrane Transport of Inorganic Phosphate by a Strapped Calix[4]pyrrole

Synthetic anion receptors are increasingly being exploredfor thetransport of anions across lipid membranes because of their potentialtherapeutic applications. A considerable amount of research focuseson the transport of chloride, whereas the transmembrane transportof inorganic phosphate has not been reported to date, despite thebiological relevance of this anion. Here we present a calix[4]pyrrolewith a bisurea strap that functions as a receptor and transporterfor H2PO4 (-), relying on theformation of eight hydrogen bonds and efficient encapsulation of theanion. Using a phosphate-sensitive lanthanide probe and P-31 NMR spectroscopy, we demonstrate that this receptor can transportphosphate into vesicles by H2PO4 (-)/Cl- antiport, H2PO4 (-) uniport, and Cs+/H2PO4 (-) symport mechanisms. This first example of inorganicphosphate transport by a neutral receptor opens perspectives for thefuture development of transporters for various biological phosphates.