Fixed-site heteropolysiloxane membranes containing polytopic grafted macrocyclic receptors were synthesized and used in separations of organic acids of biological importance (aspartic acid, succinic acid, tartaric acid). They presented promising transport fluxes and selectivities of the aspartic acid from a mixture of the three cited above acids, as function of operating conditions. The cooperative transport was based on new multiple molecular recognition principles and dependent on a membrane potential generated by the co-transport of protons. Thus these membranes simulated biological organic compound transport in cell membranes.