The structure of sperm chromatin differs significantly from that of chromatin in somatic cells. In somatic cells, the base unit of chromatin is the nucleosome consisting of DNA wrapped around an octamer of histone proteins to form a "bead on a string" structure. In mature sperm cells, the vast majority (>90%) of somatic histones ultimately get replaced during spermatogenesis by cationic peptides known as protamines. These protamines are short (4-8 kDa), highly basic peptides that contain 50-70% arginine residues. The high number of cationic arginine residues enables a strong binding to negatively charged DNA phosphates resulting in a near-crystalline condensation of the DNA in sperm chromatin to a volume roughly 6 times more compact than is achieved by mitotic chromosomes. Sperm chromatin, like viruses, therefore represent some of the tightest packaging of DNA in vivo. Within the sperm nuclei, protamine-DNA forms toroidal structures with DNA helices inside the toroid arranged parallel to one another in a hexagonal array. This unique structure and composition of sperm chromatin is believed to be critical for facilitating both the transport of sperm DNA and protecting its genetic intergrity. During maturation, protamines are initially phosphorylated and subsequently dephosphorylated. It has long been thought that this phosphorylation serves an important function to weaken interactions, enabling the correct binding of protamines to DNA and neighboring protamines during the late phases of spermatogenesis. Improper sperm chromatin remodeling is known to correlate with infertility, DNA fragmentation, and poor reproductive outcomes. Male germ cells, including sperm, are known to produce reactive oxygen species (ROS). While a certain level of ROS is necessary for proper physiological function, an overproduction can negatively affect sperm development. Due to the tight packaging of DNA in sperm chromatin, all DNA repair functions are inactive, making sperm DNA particularly sensitive to oxidative damage. One of the key consequences of exessive oxidative stress in sperm is DNA damage including DNA base oxidation, single and double strand breaks, and DNA fragmentation. Sperm DNA fragmentation has long been considered indicators of male fertility. Recent studies have highlighted the significance of both single and double strand breaks, linking them to reproductive complications such as fertilization failure, increased miscarriage rates, and potentially harmful mutations in offspring. It is believed that DNA damage susceptibility is typically greater in histone-rich regions of the sperm chromatin due to their lower DNA packaging density compared to protamine-rich regions. This has been supported by recent studies on mouse sperm nuclei, which found that histone-rich peripheral and basal regions are particularly prone to oxidation. However, recent findings show that protamines can carry multiple post-translational modifications (PTMs) that would also likely decrease local DNA compaction, potentially resulting in increased DNA damage in these regions. While the common understanding has been that tighter packaging in condensed DNA provides greater protection against ROS damage, the precise relationship between DNA packaging density and susceptibility to oxidative damage in condensed DNA remains unclear and warrants further investigation. Polycations, with a charge equal to or greater than +3, can condense DNA into well-ordered nanoparticles termed polyplexes. These polycation-DNA complexes, including reconstituted protamine-DNA, have also been shown to be organized into a hexagonal array of DNA helices and form toroidal shapes, making them ideal models for studying protamine-mediated DNA packaging in sperm. Previous research has shown that the equilibrium spacing between DNA helices within these polyplexes depends on both the length and composition of the polycation. Polyplexes have potential applications in fields such as nonviral gene delivery and nucleotide-based vaccines. However, their utility is constrained by two factors: their long-term stability in solution, and the extent to which they can protect the encapsulated gene of interest. Improving our understanding of these factors will be crucial for the future exploitation of polyplexes in these fields. In this study, we used reconstituted systems made with DNA and various polycationic peptides to directly examine the influence of DNA packaging on its protection against free radical damage. UV-Vis spectroscopy and dynamic light scattering (DLS) experiments were carried out to assess DNA precipitation capability of the polycations and characterize the colloidal properties of the resultant polyplexes. DNA packaging densities within all polyplexes were quantified using small-angle X-ray scattering (SAXS). To mimic oxidative stress conditions, free radicals were generated from the thermal decomposition of 2,2'-Azobis(2amidinopropane) dihydrochloride (AAPH) that produces peroxyl radicals in the presence of oxygen. The free radicalinduced damage of supercoiled plasmid DNA in the condensed state was then evaluated by gel electrophoresis. Our results indicate that the extent of DNA protection in the condensed state depends on both the packaging density within the polyplex condensate and the length, or equivalently charge, of the polycation. Using hexaarginine peptides as protamine mimics, the effect of a phosphorylated serine residue was also studied. To better understand the potential mechanisms involved, we conducted molecular dynamics (MD) simulations to study the intrinsic dynamic behavior of condensing agents of different lengths within the polyplexes. These simulations revealed that shorter peptides exhibit a higher degree of motion within the polyplexes, which may account for the heightened sensitivity of oligocation polyplexes to free radical damage.