Structural requirements of synthetic anionophores for inorganic phosphate and phosphate esters

The transmembrane transport of anions is a promising application of synthetic anion receptors. Numerous anionophores have been developed for chloride over the past decades. Despite the biological relevance of phosphate and phosphate esters, very few reports on their transport by synthetic systems exist. Here we report a systematic study on the transport of diphenyl phosphate, phenyl phosphate, and inorganic phosphate by five different anionophores. The transport of these phosphates into liposomes was monitored by fluorescence spectroscopy, 31P NMR spectroscopy, and an ion selective electrode. The results of these experiments showed that diphenyl phosphate is readily transported by most chloride ionophores. The transport of phenyl phosphate is more challenging, but can be enhanced by better shielding of the phosphate group. Inorganic phosphate is the most challenging to transport and was achieved using a macrocyclic anionophore with eight preorganised H-bond donors. These results pave the way for the development of anionophores for inorganic phosphate as well as phosphate esters.