Transmembrane Transport of Inorganic Phosphate by a Strapped Calix[4]pyrrole
Alessio Cataldo, Karolis Norvaiša, Lau Halgreen, Samantha E. Bodman, Kristin Bartik, Stephen J. Butler, Hennie Valkenier
Abstract
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 H 2 PO 4 –, relying on the formation of eight hydrogen bonds and efficient encapsulation of the anion. Using a phosphate-sensitive lanthanide probe and 31 P NMR spectroscopy, we demonstrate that this receptor can transport phosphate into vesicles by H 2 PO 4 – /Cl – antiport, H 2 PO 4 – uniport, and Cs + /H 2 PO 4 – 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.