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

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) (CnGS, 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 lambda=450-600 nm indicates an anomaly in the growth of CnGS+DNA aggregates with increasing concentration of CnGS, possibly involving changes of structure and size of aggregates. Using dynamic light scattering, changes of the effective diameter of CnGS+DNA (n=12 and 16) aggregates formed in the CnGS concentration range 0.002-0.140 mmol/l were observed. SAX diffractograms show the presence of long-range organization of CnGS+DNA (n=12, 13, 14 and 16) aggregates due to DNA interaction with CnGS above the critical micellar concentration. The CnGS+DNA (n=12, 13 and 14) aggregates at 25 degrees 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 degrees C. The aggregates undergo structural changes induced by temperature in the range 60-95 degrees C, which are accompanied by changes of the diffraction patterns, namely in the region of reciprocal spacing s=0.15-0.30 nm(-1).