Here, the x-axis shows the nitrogen-to-phosphate (N/P) charge ratio between polycation amines (N) and DNA phosphates (P) and the y-axis shows the fraction of soluble DNA remaining after centrifugation determined by UV-Vis absorbance at 260 nm. All data shown are reported as mean ± standard deviation (n = 3). precipitation curves plotted as the normalized absorbance at 260 nm as a function of increasing N/P charge ratio, or the ratio of cationic amine (N) groups from the polycations to negatively charged nucleic acid phosphate (P) groups. For all polycations studied except R3, noticeable DNA condensation is observed with increasing polycation concentrations from N/P 0.25 to full condensation. All cationic systems studied fully condensed DNA at N/P charge ratios between 1-2. The shortest peptide studied, R3, required the highest N/P charge ratio (N/P ~ 2) to fully precipitate DNA. The longest polycations (PolyR, polyK and protamine) are observed to fully condense DNA at N/P ~ 1.0 -1.2 while the intermediate length hexaarginine peptides (R6 and R3pSR3) fully condense DNA at N/P ~1.5. The extent of precipitation also varied depending on the polycation length and charge. The three longest polycations condensed in a linear fashion maintaining an ~1:1 ratio. For example, at N/P 0.5, where sufficient polycation has been added to compensate for half of the negatively charged DNA phosphates, we observe ~50% of the DNA is precipitated. This trend continues until complete DNA complexation is observed at N/P ~1. The precipitation of DNA by the trivalent cation proceeds in a very different manner. As shown in Figure , R3 did not show appreciable DNA precipitation until N/P ~1.2. However, at higher N/P ratios, DNA precipitation of DNA by R3 proceeds in a cationdependent manner with full precipitation observed at N/P ~2. The hexaarginine peptides (R6 and R3pSR3) show intermediate behavior with full condensation observed only at N/P ≥ 1.5. Although DNA precipitation is continuous at all N/P ratios < 1.5, less DNA is precipitated by these two peptides when compared to salmon protamine, polyR, or polyK. At N/P 1, for example, only ~60% of the total DNA is precipiated with both hexaarginine peptides. X-ray diffraction experiments were used to determine the DNA packaging densities within the fully condensed polyplexes. All polycations studied were able to spontaneously condense DNA resulting in a hexagonal packaging of DNA helices within the polyplexes as depicted in were condensed at an N/P charge ratio of 3 to ensure complete DNA condensation as observed in Figure . All polyplexes studied resulted in the formation of tightlypacked, colloidal nanoparticles with hydrodynamic radii ranging from ~70-200 nm. All DLS results were performed in triplicate, and hydrodynamic radius results are reported as mean ± standard deviation.