[en] Full text: Under proper conditions, surfactants can be used for building nanostructured materials thanks to their ability to self-assemble. Particularly, lamellar phases composed by bilayers regularly spaced has been widely applied as hosts for colloidal particles and biomolecules. Related studies to this subject have opened a large investigation area for material science and biomedicine from the assembly manipulation of particles at nanoscale. In this context, synthetic vectors for gene therapy based on complexes prepared originally with cationic lipids and DNA have been proposed as an alternative to viral vectors. More recently, showed a DNA polymorphism in neutral fluid lipid phases experimentally obtained by varying the bending rigidity of bilayers (through changes in membrane composition) or their separation (through changes in hydration). The lipid neutral system has the main advantage to be less toxic and, therefore, corresponds to a potential substitute for its cationic lipid-based predecessors. However, it is necessary to understand the mechanism responsible for the formation of the complex and their physical properties. The first step to achieve this comprehension consists on the structural characterization of lipid-DNA complexes, which is commonly done by a combination between small-angle x-ray scattering (SAXS) and (optic and electron) microscopy. Nowadays, most of the SAXS information for this kind of systems comes only from peaks indexation. In this sense, the goal of the present work is to continue the study initiated in by proposing a novel SAXS model to fit the available experimental data shown in that investigation. This model could be used to analyze several other “lipoplex” systems in the literature and the obtained valuable structural information could be included in sophisticated thermodynamic models. (author)