Aggregation behavior of tetracarboxylic surfactants derived from cholic and deoxycholic acids and ethylenediaminetetraacetic acid.
The reaction of 3beta-aminoderivatives of cholic and deoxycholic acids (steroid residues) with dimethyl ester of ethylenediaminetetraacetic acid (bridge) leads to the formation of dimers carrying four carboxylic organic functions, two of them located on the side chain of each steroid residue and the other two on the bridge. As tetrasodium salts, these new compounds behave as surfactants and have been characterized by surface tension, fluorescence intensity of pyrene (as a probe), and static and dynamic light scattering measurements. Thermodynamic parameters for micellization were obtained from the dependence of the critical micelle concentration (cmc) with temperature. For both surfactants, the fraction of bound counterions is close to 0.5. The aggregation behavior is similar to one of their bile salt residues [i.e., sodium cholate (NaC) and sodium deoxycholate (NaDC)] and can be summarized as follows: (i) molecular areas at the interface for the new surfactants are fairly close to twice the value for a single molecule in a monolayer of natural bile salts; (ii) the environment where pyrene is solubilized is very apolar, as in natural bile salt aggregates; (iii) Gibbs free energies (per steroid residue) for micellization are not far from published values for NaC and NaDC, and the differences can be understood on the basis of less hydrophobicity of the new surfactants due to the charges in the bridge; and (iv) as for NaC and NaDC, aggregates have rather low aggregation numbers (which depend on the amount of added inert salt, NaCl). A structure based on the disklike model accepted for small bile salt aggregates is proposed.
Alvarez Alcalde
Mercedes
M
Departamento de Química Física, Facultad de Ciencias, Universidad de Santiago de Compostela, Avda. Alfonso X El Sabio s/n, 27002 Lugo, Spain.
Jover
Aida
A
Meijide
Francisco
F
Galantini
Luciano
L
Viorel Pavel
Nicolae
N
Antelo
Alvaro
A
Vázquez Tato
José
J
D003840:Deoxycholic Acid / Q000737:chemistry*; D004492:Edetic Acid / Q000737:chemistry*; D008956:Models, Chemical; D008968:Molecular Conformation; D015394:Molecular Structure; D011721:Pyrenes / Q000737:chemistry; D013501:Surface-Active Agents / Q000737:chemistry*; D013816:Thermodynamics
D011721:Pyrenes; D013501:Surface-Active Agents; D003840:Deoxycholic Acid; D004492:Edetic Acid