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Decisive forces for the structure and stability of aggregates composed by synthetic surfactants: ion association selectivity to interfaces and vesicle formation

Grant number: 18/19838-8
Support type:Scholarships in Brazil - Doctorate (Direct)
Effective date (Start): December 01, 2018
Effective date (End): April 30, 2021
Field of knowledge:Physical Sciences and Mathematics - Chemistry
Principal Investigator:Hernan Chaimovich Guralnik
Grantee:Laura Mortara
Home Institution: Instituto de Química (IQ). Universidade de São Paulo (USP). São Paulo , SP, Brazil
Associated research grant:13/08166-5 - Interfacial chemistry: drugs, peptides and ezymes interactions with membrane models, AP.TEM

Abstract

Specific ion effects and hydrophobic effects define properties of complex systems but are far from being understood with molecular detail.Specific ion effect define a variety of phenomena in physical-chemistry and biological systems, from the stability of colloidal suspensions to enzymatic activity and ligand-receptor binding. To establish a rigorous scientific interpretation of this effect have been kept scientist busy for more than a century and nevertheless a complete description of the ion interaction net, water and solute surface is still a challenge. With these studies it is possible to understand about the surface that the ion interact as well as understand about the hydration of the interaction surface and ion hydration and how both hydrations combine. The hydrophobic effect (in the aggregation process) depends, almost exclusively, from the difference of free energy of the exposed areas of the hydro carbonic chains of the surfactant (natural as lipids or synthetic) between solution and aggregate. Despite that, the detail structure of the aggregate, the chain order and the viscosity depends critically on the surfactant detailed molecular structure. An example of this is the difference between membranes constituted of lipids of saturated and unsaturated chains.In this theoretical/experimental project we intend to contribute in order to clarify aspects related to the problems stated above. The thermodynamical micelization of zwitterionic surfactants will be analyzed using calorimetry in the presence of distinct ions, the adsorption of ions to zwiterionic micelles is known but recently we demonstrate that interfacial water is not particularly sensitive to the nature of this ions. This particular and apparent contradiction will be comprehended with the results of this project that include the thermodynamic analysis of the association of ions as well as a complete description of this association using molecular dynamics. Preliminary data show that imidazol derivatives with two hydrocarbon chains form lipossomes if the alkyl tails are C16H33. Vesicles formed by this compound posses a very high transition temperature when compared to a compound with the same carbon numbers in the hydrocarbon tail ans a polar head containing also a quaternary ammonium group and the same counter ion. This difference will be studied based on the properties of the aggregates and characterizations of the before and after phase transition states, using calorimetric techniques and also Electron Paramagnetic Resonance (EPR), that can give, trough labels informations of the packing of the tails. We intend, therefore to study two systems: Zwiterionic micellas and the ion effect of ions with hydrophobic portions in this surface, using molecular dynamics, calorimetry, surface tension. And the aggregation of surfactants with two alkyl tails with different polar heads, that form cationic vesicles in aqueous solution, using calorimetry, EPR, molecular dynamics, to gain insights on the hydrophobic effect on the aggregation and the effect of the polar head on the ion interaction. From the informations that we intent to extract we could further understand the hydrophobic effect and extrapolate the informations to more complexes biological systems. (AU)