Synthesis and Characterization of a New Gemini Surfactant Derived from 3α,12α-Dihydroxy-5β-cholan-24-amine (Steroid Residue) and Ethylenediamintetraacetic Acid (Spacer)
journal contributionposted on 17.06.2008, 00:00 by Mercedes Alvarez Alcalde, Aida Jover, Francisco Meijide, Luciano Galantini, Nicolae Viorel Pavel, Alvaro Antelo, José Vázquez Tato
A new gemini steroid surfactant derived from 3α,12α-dihydroxy-5β-cholan-24-amine (steroid residue) and ethylenediamintetraacetic acid (spacer) was synthesized and characterized in aqueous solution by surface tension, fluorescence intensity of pyrene, and light scattering (static and dynamic) measurements. These techniques evidence the existence of a threshold concentration (cac), below which a three layers film is formed at the air−water interface. Above the cac, two types of aggregates―micelles and vesicle-like aggregates―coexist in a metastable state. Filtration of a solution with a starting concentration of 2.6 mM (buffer 150 mM, pH 10) allows isolation of the micelles, which have an average aggregation number of 12, their density being 0.28 g cm−3. Under conditions where only the vesicle-like aggregates are detected by dynamic light scattering, a value of 5.5 × 104 was obtained for their aggregation number at 30 µM, their density being 6.8 × 10−4 g cm−3. At high concentrations, the intensity ratio of the vibronic peaks of pyrene, I1/I3, (= 0.68) is very close to published values for deoxycholate micelles, indicating that the probe is located in a region with a very low polarity and far from water. A hypothesis to explain the observed aggregation behavior (small aggregates are favored with increasing gemini concentration) is outlined.