Facilitated Diffusion of Proline across Membranes of Liposomes and Living Cells by a Calix[4]pyrrole Cavitand

The transport of anions and cations through liposomal membranes facilitated by synthetic carriers has been widely described. In contrast, analogous studies describing the facilitated transport of amino acids (aa) are scarce. We describe the use of calix[4]pyrrole receptors as synthetic carriers for the facilitated diffusion of aa across membranes of liposomes and living cells. We demonstrate that a calix[4]pyrrole cavitand is highly effective and selective for the facilitated diffusion of L-proline (L-Pro). We propose a mobile carrier diffusion mechanism to explain the observed aa facilitated diffusion process. The transport process involves the formation of a 1:1 complex between the carrier and the aa (e.g., L-Pro⊂ 1). We also describe the unprecedented application of a synthetic carrier to contribute to the uptake of L-Pro in human cells in addition to that mediated by the natural transporters. The reported results augur well for the potential use of aa synthetic carriers in therapeutic applications.