Micellization thermodynamics as a function of the temperature of a cationic zwitterionic dodecyl phosphocholine and anionic sodium dodecyl sulfate mixed micelles with fluorometry

Abstract

Abstract As fluorescence parameters such as lifetime, quantum yield, anisotropy and polarisation quantum are extremely sensitive to fluorophores’ microenvironmental changes, changes in the properties of the fluorescence probe have been widely used to study hydrophobic interactions in protein and membrane biology. The current study determines the critical micelle concentration (CMC) of mixed micelles of sodium dodecyl sulfate (SDS) and cationic surfactant N-dodecyl phosphocholine (DPC) based on fluorescence intensity measurements. biomolecular structure analysis and dynamics revealed through the measure of changes in the nanosecond time range. As the temperature rises, the onset of micellization tends to occur at higher concentrations. It was measured versus micelle concentration over a temperature range of (288–338) K. The obtained results were used to estimate the micellization thermodynamic parameters. Surfactant CMC drops to a minimum ( T = 308 K) and then rises with temperature forming a parabolic curve as a function of temperature, according to experimental data. The CMCs are first correlated by a polynomial equation to determine the enthalpy of micellization. Both $$\Delta {H}_{\mathrm{mic}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>Δ</mml:mi> <mml:msub> <mml:mi>H</mml:mi> <mml:mi>mic</mml:mi> </mml:msub> </mml:mrow> </mml:math> and $$\Delta {S}_{\mathrm{mic}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>Δ</mml:mi> <mml:msub> <mml:mi>S</mml:mi> <mml:mi>mic</mml:mi> </mml:msub> </mml:mrow> </mml:math> appear to decrease monotonically as temperature rises. ΔG mic is negative, indicating that the micellization process is exothermic and favorable. The compensation temperature (Tc) ranged from (313–318) K by linear regression over the whole temperature range and for DPC, SDS, and mixed micelles together.