After identifying the best formulation of a single heteromeric oligopeptide chain conjugated OM-pBAE, we set out to decrease the transfection promiscuity through derivatization of pBAE-CRHR with a zwitterionic peptide. To design the zwitterionic peptides, we selected the EK and ER amino acid zwitterion motifs, which display alternating positive and negative charges at physiological pH and have been used as stealth agents in other formulations . We synthesized end-capping peptides with the CRHR moiety followed by 3 or 6 zwitterion motif repeats at the C-terminus (Figure , Figure ). A GG spacer was added between the CHRR and zwitterionic sequences to minimize any alteration to the encapsulating and proton-sponge capacity of the CRHR peptide. The pBAEs modified with the zwitterionic end-capping peptide will be denominated pBAE-CRHR-Zw.