Energetic and binding properties of DNA upon interaction with dodecyl trimethylammonium bromide

The interaction of dodecyl trimethylammonium bromide (DTAB), a cationic sur factant, with calf thymus DNA has been studied by various methods, includin g potentiometric technique using DTAB-selective plastic membrane electrode at 27 and 37 degrees C, isothermal titration microcalorimetry and UV spectr ophotometry at 27 degrees C using 0.05 M Tris buffer and 0.01 M NaCl at pH 7.4. The free energy is calculated from binding isotherms on the basis of W yman binding potential theory and the enthalpy of binding according to van' t Hoff relation. The enthalpy of unfolding has been determined by subtracti on of the enthalpy of binding from the microcalorimetric enthalpy, The resu lts show that, after the interaction of first DTAB molecule to DNA (base mo larity) through the electrostatic interaction, the second DTAB molecule als o binds to DNA through electrostatic interaction, At this stage, the predom inant DNA conformational change occurs. Afterwards up to 20 DTAB molecules, below the critical micelle concentration of DTAB, bind through hydrophobic interactions.