Conductometric and fluorometric studies of sodium dodecyl sulphate in aqueous solution and in the presence of amino acids |
| |
Authors: | Anwar Ali Nisar Ahmad Malik Sahar Uzair Maroof Ali |
| |
Institution: | 1. Department of Chemistry, Jamia Millia Islamia (Central University), New Delhi, Indiaanwarali.chem@gmail.com aali2@jmi.ac.in;2. Department of Chemistry, Jamia Millia Islamia (Central University), New Delhi, India |
| |
Abstract: | The critical micelle concentration (CMC) of sodium dodecyl sulphate (SDS) in pure water and in the presence of amino acids (0.01, 0.02 and 0.03 mol kg?1), L-valine (Val) and L-leucine (Leu) was determined from conductometric and fluorometric methods using pyrene as luminescence probe. Depression in the CMC at low concentration of amino acids is attributed to the increased hydrophobic–hydrophobic interaction between the non-polar groups of the surfactant, while, at high concentration, amino acids bind strongly with the anion, DS?, head groups of SDS, thereby, delaying the micelle formation, resulting in increased CMC. A pronounced decrease in the CMC, while a marked increase in λ0+, with decrease in the solvated radius (rather than crystal radius) of the counterions is observed. Negative values of ΔG0m and ΔH0m indicate that micellisation of SDS in the presence of amino acids is thermodynamically spontaneous and exothermic. Highest negative value of ΔH0m in 0.01 m Val, with lowest CMC value, shows that 0.01 m aqueous Val is the most suitable medium favouring the micellisation of SDS. Decrease in I1/I3 from Val to Leu confirms the relative hydrophobicity of two amino acids. The observed values of the packing parameter, P, of SDS in water and in aqueous amino acids suggest that micelles formed are spherical in nature. |
| |
Keywords: | sodium dodecyl sulphate–amino acid interaction thermodynamics of micellisation conductivity fluorescence |
|
|