The transport by 1 was then monitored at pH 7 (~25% H2PO4 -) 40 and a significantly smaller signal appeared for the intravesicular phosphate, under the same conditions as above. The intensity of the 31 P NMR signals increased over 12 hours, to a value which is about a fourth of the one observed after 12h at pH 5 (Figure ). At pH 8 (~3% H2PO4 -) 40 no internal signal appeared, even after 12h. The amount of transported phosphate correlates with the concentration of H2PO4 -in solution, confirming our hypothesis that phosphate is predominantly transported in the form of H2PO4 -. Control compounds 2 and 3 did not give rise to an internal 31 P signal, even after 12h at pH 5, confirming the results obtained in the [Eu.pBOH2] + assay.