FIGURE 1.
Structures of the compounds investigated. CPCs are classified mainly on the basis of their historical discovery and/or intended use or application. The classes comprise (1, 2) amino acid homopolymers, (3) DNA transfection agents, (4) cationic lipids, and (7, 8) CPPs. Individual structures are (1) nona-l-arginine, (2) hexadeca-l-lysine (PLL16), (3) linear polyethylenimine (LPEI), (4) 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP), (5) cell-permeant acridine orange (AOR), (6) cell-impermeant propidium iodide, (7) HIV-1 Tat(47–57), and (8) penetratin. Not shown are monomeric l-arginine and cell-impermeant ethidium bromide (similar to 6). Charges at physiological pH were assigned on the basis of literature values of the pKa. These were 12.5, 10.3, ∼7, and 10.2 for 1, 2, 3, and 5, respectively (19,54).