Lactoferrin denaturation induced by anionic surfactants : the role of the ferric ion in the protein stabilization.

Here, investigation was made of the interaction between lactoferrin (Lf) and the anionic surfactants sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (SDBS), and sodium decyl sulfate (DSS), using isothermal titration calorimetry, Nano differential scanning calorimetry (NanoDSC), and fluorescence spectroscopy. The Lf-surfactant interaction was enthalpically favorable (the integral enthalpy change ranged from ?5.99?kJ?mol?1, for SDS at pH?3.0, to ?0.61?kJ?mol?1, for DSS at pH?12.0) and promoted denaturation of the protein. The Lf denaturation efficiency followed the order DSS?<?SDS?<?SDBS. The adsorption capacity of the protein with respect to surfactant strongly depended on pH and the surfactant structure, reaching a maximum value of 505 SDBS molecules per gram of Lf at pH?3.0. The different efficiencies of the surfactants in denaturing Lf were attributed to the balance of hydrophobic and electrostatic interactions, which also depended on pH and the surfactant structure, highlighting the SDBS-tryptophan residue specific interaction, where SDBS acted as a quencher of fluorescence. Interestingly, the NanoDSC and fluorescence measurements showed that the ferric ion bound to Lf increased its stability against denaturation induced by the surfactants. The results have important implications for understanding the influence of surfactants on structural changes in metalloproteins

Solvophobic effect of 1-alkyl-3-methylimidazolium chloride on the thermodynamic of complexation between ?-cyclodextrin and dodecylpyridinium cation.

Preferential solvation participate in various supramolecular self-assembly processes, whose thermodynamic properties can be modulated by the addition of ionic liquids (ILs). However, the effects of these liquids on the thermodynamics of the host-guest complexation process remain unexplored. In this study, the thermodynamic properties of the complexation between 1-dodecylpyridinium cations (C12Py+) and ?-cyclodextrin (?CD) species in aqueous solutions with different concentrations of 1-alkyl-3-methylimidazolium halides (CnmimX) were investigated by isothermal titration calorimetry. In water, C12Py+ and ?CD form a 1:1 inclusion complex, which is enthalpically ( ?9.2 ? 0.1?kJ mol?1) and entropically ( 16.1 ? 0.2?kJ mol?1) favorable. However, in IL aqueous solutions, all the ?CD?C12Py+ thermodynamic parameters of the complexation change and this IL effect is dependent on the carbon chain length of Cnmim+ cations. ILs with shorter alkyl chains (Cnmim+, n ? 4) decreases the system entropy, while ILs with longer alkyl chains (Cnmim+, n ? 6) reduce the enthalpy values. These effects are attributed to i) preferential solvation of surfactant tails by ILs; ii) ability of the ILs to modify the 3D water structure and iii) inclusion of IL molecules into the inner cavities of ?CD

Aggregation of sodium dodecylbenzene sulfonate : weak molecular interactions modulated by imidazolium cation of short alkyl chain length.

Ionic liquids (ILs) can modify cooperative process in aqueous solutions to a large extent, including anionic surfactant aggregation. Here, the micellization of sodium dodecylbenzene sulfonate (SDBS) was evaluated in low concentrations of 1-alkyl-3-methylimidazolium chloride (CnmimCl, n = 0, 2, and 4) aqueous solutions through fluorescence spectroscopy, isothermal titration calorimetry, dynamic light scattering, and conductometry. The thermodynamic stability of SDBS aggregates strongly depended on the IL structure and concentration, following the order C4mim+ > C0mim+ ? C2mim+. At 1.0 mmol L?1 of the ILs, the increase of the hydrophobicity of the imidazolium cation decreased the enthalpic favorableness, changing from ?3.75 ? 0.07 kJ mol?1, for C0mim+, to ?2.69 ? 0.01 kJ mol?1, for C4mim+. On the other hand, the entropic feasibility showed an opposite trend, i.e., the higher hydrophobicity of C4mim+ overcame the kosmotropic effect of IL cations in the bulks. We suggested that the imidazolium cations interact with the SDBS monomers on the micellar surface, mainly through hydrophobic, ?-?, and electrostatic interactions for C4mim+ and C2mim+, and through electrostatic interactions and hydrogen bonds for C0mim+