The 31 P NMR experiments were first performed at pH 5, where H2PO4 -is the predominant phosphate species (~97%). Compound 1 was pre-incorporated (1 mol%) in the lipid bilayer of LUVs (50 mM POPC, ~200 nm) prepared in 400 mM NaCl buffered using 5 mM MES. When a phosphate pulse (100 mM) was added to the exterior of the LUVs, a large signal was observed in the 31 P NMR spectrum at 1.05 ppm. Addition of MnSO4 (2 mM) to the LUV suspension resulted in the full relaxation of the extravesicular phosphate signal. After 1 h of transport followed by 1 h of data acquisition, a clear 31 P NMR signal was visible at 1.2 ppm (Figure ), providing further evidence of the ability of 1 to transport H2PO4 -.