Cationic colloidal systems composed of arginine based surfactants (single or gemini structures) and
membrane additive compounds such as DLPC or cholesterol have been characterized by means of size
distribution and zeta-potential measurements. The single or monocatenary surfactant (LAM) as well as
the gemini with the shortest spacer chain (C6(LA)2) formed micelles, while aqueous solutions of pure
gemini surfactants with longer spacers (C9(LA)2 and C12(LA)2) formed very big aggregates. The addition
of phospholipids or cholesterol changed drastically the aggregation behaviour. In the case of LAM and
C6(LA)2, the incorporation of additives gave rise to the formation of cationic vesicles. For C9(LA)2 and
C12(LA)2, this type of additives promoted the formation of smaller aggregates. All the formulations had
positive zeta-potential values and in general exhibited high colloidal stability. We also evaluated the
hemolysis and the antimicrobial activity of these systems. The capability of disrupting erythrocyte
membranes depends on the hydrophobicity of the molecules and the size of aggregates in the solution.
Gemini surfactants with short spacer chains are more hemolytic than their single chain homologue,
while gemini surfactants with long spacers are much less hemolytic than their single chain counterpart.
Moreover, for the same formulation, the hemolysis depends on the initial concentration of the stock
solution used to set up the hemolysis/concentration curve. Results show that small aggregates interact
easily with these biological membranes. The alkyl spacer chain and the presence of additives also play
an important role in the antimicrobial activity, and, in general, the interaction with bacteria and
erythrocytes is affected by the same parameters. The physico-chemical and biological characterization of
these systems might be important for several biotechnological applications in which cationic vesicular
systems are involved