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 cyclobutane β-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 dodecyltrimethylammonium 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 β-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.