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

Synthetic anion receptors are increasingly being explored
for the
transport of anions across lipid membranes because of their potential
therapeutic applications. A considerable amount of research focuses
on the transport of chloride, whereas the transmembrane transport
of inorganic phosphate has not been reported to date, despite the
biological relevance of this anion. Here we present a calix[4]pyrrole
with a bisurea strap that functions as a receptor and transporter
for H2PO4–, relying on the
formation of eight hydrogen bonds and efficient encapsulation of the
anion. Using a phosphate-sensitive lanthanide probe and 31P NMR spectroscopy, we demonstrate that this receptor can transport
phosphate into vesicles by H2PO4–/Cl– antiport, H2PO4– uniport, and Cs+/H2PO4– symport mechanisms. This first example of inorganic
phosphate transport by a neutral receptor opens perspectives for the
future development of transporters for various biological phosphates.