Published: November 15, 2011 r2011 American Chemical Society 676 dx.doi.org/10.1021/la203748q | Langmuir 2012, 28, 676–688 ARTICLE pubs.acs.org/Langmuir Interactions of a Hydrophobically Modified Polycation with Zwitterionic Lipid Membranes Mariusz Kepczynski,* ,† Dorota Jamr oz,* ,† Magdalena Wytrwal, † Jan Bednar, ‡,§ Ewa Rzad, † and Maria Nowakowska † † Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Krak ow, Poland ‡ Charles University in Prague, First Faculty of Medicine, Institute of Cellular Biology and Pathology, Albertov 4, 128 01 Prague 2, Czech Republic § University of Grenoble 1/CNRS, LIPhy UMR 5588, 140 Av. de la Physique, Grenoble, F-38041, France b S Supporting Information ’ INTRODUCTION The interactions between polycations and lipid or cell mem- branes play an important role in many biophysical applications. The most important of them include (i) delivery of genetic materials to cells in a targeted and safe manner, 1À3 (ii) usage as biocidal agents, 4À6 and (iii) obtaining stabilized vesicles by covering the liposomes surface with multilayer films. 7,8 Because of these issues, the impact of both natural and synthetic polycations on phospholipid bilayer has been extensively studied using various experimental techniques. 9 The success of gene therapy largely depends on the availabil- ity of suitable delivery vehicles. Polycations, especially poly- (ethylenimine) (PEI), are frequently studied as nonviral syn- thetic transfectants, which are characterized by excellent gene complexing ability (formation of polyplexes) and eminent trans- fectant properties. 3 Unfortunately, they show in vitro cytotoxi- city, which constitutes the major challenge for their clinical applications. 3,10 Transport of molecules to and from the cell nucleus, mediated by polycations, is likely to be the result of nonspecific interactions between the polyplexes and the nuclear membrane. 2 To date, research has focused rather on the efficiency of transfecting the cell membranes. The molecular mechanisms of both the transfection and the polycation-induced cytotoxicity are yet unknown. Much empirical evidence suggests though that the important role in these processes is the ability of polycations to disrupt the nuclear membrane and to increase the membrane permeability. It is known that the transfection process occurs when small pores open in the nuclear membrane to admit genetic materials. 2 It is well-known that most antimicrobial peptides disrupt the bacterial membrane via transmembrane pore formation and/or membrane destabilization. 11,12 The majority of these peptides are cationic or amphipathic. Recently, polymers containing quaternary ammonium or alkyl pyridinium moieties have been commonly used as biocides. 5 The quaternary amino groups in antimicrobial polymer are believed to be responsible for causing cell death by disrupting the cell membrane, thus allowing release of the intracellular contents. Received: September 24, 2011 Revised: November 8, 2011 ABSTRACT: The interactions between synthetic polycations and phospho- lipid bilayers play an important role in some biophysical applications such as gene delivery or antibacterial usage. Despite extensive investigation into the nature of these interactions, their physical and molecular bases remain poorly understood. In this Article, we present the results of our studies on the impact of a hydrophobically modified strong polycation on the properties of a zwitter- ionic bilayer used as a model of the mammalian cellular membrane. The study was carried out using a set of complementary experimental methods and molecular dynamic (MD) simulations. A new polycation, poly(allyl-N,N- dimethyl-N-hexylammonium chloride) (polymer 3), was synthesized, and its interactions with liposomes composed of 2-oleoyl-1-palmitoyl-sn-glycero-3- phosphocholine (POPC) were examined using dynamic light scattering (DLS), zeta potential measurements, and cryo-transmission electron microscopy (cryo-TEM). Our results have shown that polymer 3 can efficiently associate with and insert into the POPC membrane. However, it does not change its lamellar structure, as was demonstrated by cryo-TEM. The influence of polymer 3 on the membrane functionality was studied by leakage experiments applying a fluorescence dye (calcein) encapsulated in the phospholipid vesicles. The MD simulations of model systems reveal that polymer 3 promotes formation of hydrophilic pores in the membrane, thus increasing considerably its permeability.