I am looking for something that can passively diffuse across an artificial lipid bilayer, so analogs that need active transport won't work for me. Thanks.
ATP is not available in an acetomethyl ester form (your would hve to add esterase in the second compartment). You may try mixing ATP with a ionic lipid like Lipofectamin or any other lipid used for plasmid transfection. The process may not be efficient but you can probably use very high concentration.