We therefore hypothesized that PEI modifications through acetylation or succinylation would similarly increase polymer-DNA repulsions and reduce polymer-DNA attractions, leading to less compact DNA packaging. Consistent with our hypothesis, the scattering profiles of acPEI complexes showed a systematic shift in the Bragg reflection peak towards a lower scattering vector Q, indicative of larger DNA-DNA spacings with increasing degrees of acetylation. This shift corresponds to Bragg spacings ranging from 24.7 Å for unmodified PEI to 28.8 Å for acPEI50, reflecting an approximately 58% volume increase within the two polyplexes. Surprisingly, zPEI did not exhibit the same behavior. At lower succinylation levels (≤ 5%), a Bragg peak shift to lower Q was noticeable, with a maximum Bragg spacing of 26.7 Å at 5% succinylation. However, at higher succinylation levels (> 5%), the Bragg reflection in zPEI/DNA shifted to higher Q, indicating smaller DNA-DNA spacings and more compact DNA within these complexes. For instance, zPEI30/DNA had a Bragg spacing of 25.2 Å, closer to the spacing observed in unmodified bPEI. zPEI40 did not condense DNA and no Bragg spacing was observed. The scattering intensity profiles also displayed a scattering peak broadening, possibly indicating the presence of multiple phases within these samples. Circular dichroism (CD) experiments confirmed that the DNA conformation within zPEI and acPEI complexes remained consistent with B-form DNA (Figure ).