Interaction of gemini surfactants butane-1,4-diyl-bis(alkyldimethylammonium bromide) with DNA

Abstract

The size and structure of aggregates formed by interaction of DNA with homologous series of cationic gemini surfactants butane-1,4-diyl-bis(alkyldimethylammonium bromide) (C nGS, n = 10–16 is the number of alkyl carbons) were investigated using UV–vis turbidity, dynamic light scattering and small-angle synchrotron X-ray (SAX) diffraction. The detailed analysis of turbidity in the range of λ = 450–600 nm indicates an anomaly in the growth of C nGS + DNA aggregates with increasing concentration of C nGS, possibly involving changes of structure and size of aggregates. Using dynamic light scattering, changes of the effective diameter of C nGS + DNA ( n = 12 and 16) aggregates formed in the C nGS concentration range 0.002–0.140 mmol/l were observed. SAX diffractograms show the presence of long-range organization of C nGS + DNA ( n = 12, 13, 14 and 16) aggregates due to DNA interaction with C nGS above the critical micellar concentration. The C nGS + DNA ( n = 12, 13 and 14) aggregates at 25 °C are packed in a lattice of two-dimensional hexagonal symmetry. With increasing C14GS:DNA molar ratio the changes of the lattice parameter in the range of 4.80–5.27 nm are observed at 25 °C. The aggregates undergo structural changes induced by temperature in the range 60–95 °C, which are accompanied by changes of the diffraction patterns, namely in the region of reciprocal spacing s = 0.15–0.30 nm −1.