The study of the interaction of amphiphilic ionic liquids with model membranes: a structural and spectroscopic approach

Author(s)

Natália Fernandes de Oliveira

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Física (IF/SBI)
• Defense date: 2021-03-11

Examining board members

Leandro Ramos Souza Barbosa; Luciana Magalhães Rebelo Alencar; Thereza Amélia Soares da Silva

• Advisor: Leandro Ramos Souza Barbosa

Abstract

Ionic Liquids (ILs) are an interesting class of organic molecules that have been the subject of many different studies over the last few years. Typically, they are composed of an organic cation and an organic or inorganic anion and can be found in liquid in the liquid state at temperatures below 100°C. Due to their peculiar geometry, these compounds have a vast array of potential applications in different areas of knowledge such as green chemistry, pharmacology, biomedicine, and bionanotechnology. Despite that, previous research shows that the toxicity of ILs is higher than previously believed, particularly with systems of biological relevance. Therefore, several physicochemical studies of its interactions with biomimetic membrane systems were carried out in order to identify the molecular mechanisms behind its toxicity. The main goal of this project is to get more information about the interaction of the ionic liquid 1-tetradecyl-3-methylimidazolium chloride ([C14mim]Cl) on biomimetic membrane systems to identify the molecular factors mechanisms behind its toxicity. To do this, we used the lipids POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine), sphingomyelin, and cholesterol in order to simulate erythrocytes plasmatic membrane behavior and analyze the influence of different concentrations of ILs on their structural properties. The interactions between these lipid systems and the IL in question were studied using different biophysical techniques: small-angle X-ray scattering (SAXS), fluorescence quenching, dynamic light scattering (DLS), potential zeta, transmission electron microscopy (TEM), and cryo-electron microscopy (Cryo-EM). According to the results, LI interacted with the bilayer. The hydrodynamic diameter of the vesicles increased from (133.3 ± 0.3)nm to (138 ± 1)nm as the LI was added, and in the micrographs, it was possible to see a dark region around the vesicles, which did not exist in the systems without ionic liquid. The zeta potential of the membranes went from (-1.4 ± 1.6)mV to (61.5 ± 1.4)mV for the systems with 30% of IL, making it clear that the ionic liquid changed the surface charge of the vesicles and their stability. With the SAXS measurements, it was seen that the ionic liquid molecules are concentrated on the outer membrane. The parameter fLI related to the position of the IL was always greater than the parameter fpol related to the position of the lipids polar head, indicating that the IL is in the outer region around the bilayer. The ionic liquid also altered some properties of the membrane, such as the area by lipid A, which increased as the IL was added, and the position of the cholesterol molecule fchol, which got closer and closer to the membrane surface. However, even at higher concentrations, IL was not able to penetrate the membrane, a fact confirmed by fluorescence quenching measures, in which no effect was evident, at least for IL:Lipid ratios less than 3:10. The intensities of the emission spectrum remained always close, and the leakage percentages with values less than 20%. (AU)

• FAPESP's process: 18/04796-8 - The study of the interaction of amphiphilic ionic liquids with model membranes: a structural and spectroscopic approach
• Grantee: Natália Fernandes de Oliveira
• Support Opportunities: Scholarships in Brazil - Master