The structure of DNA-DLPC-cationic gemini surfactant aggregates:: a small angle synchrotron X-ray diffraction study

The structure of aggregates formed by interaction of DNA with unilamellar dilauroylphosphatidylcholine (DLPC) vesicles (DNA:DLPC = 1: 1 base/mol) in the presence of gernini surfactant butane-1,4-diyl-bis(dodecyldimethylammonium bromide) (C12GS) was investigated using synchrotron small angle X-ray diffraction. In the concentration range C12GS(+):DLPC less than or equal to 1 mol/mol, a condensed lamellar L-alpha(c) phase was found with a repeat period of lipid bilayer stacking in the range d similar to 5.70-6.53 nm and the DNA interhelical distance d(DNA)similar to 3.52 - 3.99 nm, depending on the concentration of C12GS. At molar ratio C12GS(+):DLPC greater than or equal to 0.35:1,the diffractograms have shown the presence of a second lamellar phase with the repeat period d similar to 5.31 nm which slightly decreases with increasing concentration of C12GS(+). The increasing fraction of this phase in the aggregates with increasing concentration of C12GS supports the association of this phase with microscopic domains enriched by surfactant molecules. The temperature behaviour of aggregates was investigated in the range 25-60 degreesC and the transversal thermal expansivities of the observed phases were determined. (C) 2004 Elsevier B.V. All rights reserved.