Evaluation of the influence of ionization states and spacers in the thermotropic phase behaviour of amino acid-based cationic lipids and the transfection efficiency of their assemblies

Abstract

The influence of both the ionization states and the hydrocarbon chain spacer of a series of amino acid-based cationic lipids was evaluated in terms of gene delivery efficiency and cytotoxicity to the COS-7 cell line and compared with that of Lipofectamine™ 2000. We synthesized a series of amino acid-based cationic lipids with different ionization states (i.e., –NH 2, –NH 3 +Cl − or –NH 3 +TFA −) in the lysine head group and different hydrocarbon chain spacers (i.e., 0, 3, 5 or 7 carbon atoms) between the hydrophilic head group and hydrophobic moieties. In the 3-carbon series, the cationic assemblies formed a micellar structure in the presence of –NH 3 +Cl − and a vesicular structure both in the presence of –NH 2 and –NH 3 +TFA −. Differential scanning calorimetry (DSC) data revealed a significantly lower (8.1 °C) gel-to-liquid crystalline phase transition temperature for cationic assemblies bearing –NH 3 +TFA − when compared to their –NH 2 counterparts. Furthermore, the zeta potential of cationic assemblies having –NH 3 +TFA − in the hydrophilic head group was maximum followed by –NH 3 +Cl − and –NH 2 irrespective of their hydrocarbon chain spacer length. The gene delivery efficiency in relation to the ionization states of the hydrophilic head group was as follows: –NH 3 +TFA − > –NH 3 +Cl − > –NH 2.