Efficient DNA Condensation Induced by Chiral β-Amino Acid-Based Cationic Surfactants

Four cationic chiral amino acid-based surfactants, cis- and trans-1 and cis- and trans-2, have been studied as DNA-condensing agents with enhanced properties and the absence of cell toxicity. The polar head of the surfactant is made of a cydobutane beta-amino acid in which the amino group is a hydrochloride salt and the carboxyl group is involved in an amide bond, allowing the link with hydrophobic C-12 (surfactant 1) or C-16 (surfactant 2) chains. The ability of these surfactants to condense DNA was investigated using a dye exclusion assay, gel electrophoresis, and circular dichroism and compared with the well-studied dodecyltrimethy-lammonium bromide (DTAB) and cetyltrimethylammonium bromide (CTAB). The surfactant with the longest chain length and the trans stereochemistry (trans-2) was found to be the most efficient in condensing the DNA, including CTAB. Surfactant cis-2 was found to be less efficient, probably due to its poorer solubility. The beta-amino acid surfactants with the shorter chain length behaved similarly, such that the cis/trans stereochemistry does not seem to play a role in this case. Interestingly, these were also found to induce DNA condensation for the same concentration as trans-2 and CTAB but showed a lower binding cooperativity. Therefore, a longer alkyl chain only slightly improved the effectiveness of these surfactants. Further, atomic force microscopy revealed that they compact DNA into small complexes of about 55-110 nm in diameter.