INFIQC   05475
INSTITUTO DE INVESTIGACIONES EN FISICO- QUIMICA DE CORDOBA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Cambios morfológicos inducidos por Cu 2+ en la agregación de surfactantes gémini
Autor/es:
ERICA M. PACHÓN GÓMEZ; NOELIA D. MACHADO; MARIANA A. FERNANDEZ
Lugar:
Carlos Paz
Reunión:
Conferencia; 13ª Conferencia Latinoamericana de Físico- Química Orgánica; 2015
Institución organizadora:
INFIQC- CONICET- UNC
Resumen:
Amphiphilic compounds have the ability to decrease the surface tension at the interfaces and form various self-organized assemblies, such as micelles or vesicles, in aqueous solution. Gemini surfactants are very interesting systems, consisting of two hydrophobic tails connected by a spacer between polar head groups. Their molecular structures confer them particular physico-chemical properties as lower critical micelle concentration (CMC) and higher efficiency in decreasing the surface tension of water than the corresponding single chain surfactants. Often, they exhibit unusual morphologies in their aggregates, higher solubilizing capacity and interesting properties that can be explored in potential applications.Aggregation shape that is adopted by a particular surfactant is strongly influenced by the surfactant`s molecular geometry (i. e., headgroup area to lipid tail volume ratio) and electrostatic charge. Many amphiphilic systems can coordinate metal ions. In many cases, coordination of a metal can change the surfactant`s geometry and/or electrostatic charge and thus to induce an alteration in the aggregate morphology.In our laboratory, a series of Gemini surfactants (shown in Figure 1) were synthetized from amino acid derivative and fatty acids of different chain length. Syntheses were carried out from cystine (dimer of cysteine) and the corresponding acid chlorides. Gemini surfactants were characterized by different spectroscopic methods as infrared and nuclear magnetic resonance (NMR), and high resolution mass spectrometry.Aggregates formed by each synthesized surfactant were characterized under different conditions of pH and temperature by surface tension, fluorescence quenching and DOSY- NMR. It was found that they form micellar aggregates of small size (diameter ˂10 nm) and low aggregation number (between 12-25 molecules).Solutions of CuSO4 at alkaline medium are instable, however in the presence of Gemini surfactants Cu(II) remains stable in solution at least for 15 days. The interaction between the surfactants and the metallic ion produces self-assembled systems with very different properties than those of the sufactants alone. These new aggregates were studied using dynamic light scattering and microscopic techniques at several pH. We founded interesting differences in the solutions with the pH due probably to the different ligands involved in the interaction when the pH changes. Besides that, the size of the aggregates formed in the presence of the metal increased considerably (diameter >100 nm) compared with the micelles of the gemini, indicating an important morphological change induced by the Cu(II). Additionally the interaction between the gemini surfactant and the metal resulted in an important stabilization of the Cu (II) in aqueous solution. All these results will be discussed in detail in this work.