Counterion Specificity of Surfactants Based on Dicarboxylic Amino Scids
Journal article, 2009

The behavior in solution of a series of amino acid-based surfactants having two carboxyl groups separated by a spacer of one, two, or three carbon atoms has been investigated. All three surfactants precipitated on addition of acid, but the aspartate surfactant (with a two-carbon spacer) was considerably more resistant to precipitation than the aminomalonate surfactant (one-carbon spacer) and the glutamate surfactant (three-carbon spacer). The interactions with the monovalent counterions lithium, sodium, and potassium were investigated by conductivity. It was found that lithium ions bound the strongest and potassium ions the weakest to the surfactant micelles. These results were interpreted using the hard and soft acid-base theory. Comparing the three surfactants with respect to binding of one specific counterion, sodium, showed that the aminomalonate surfactant, which has the shortest spacer, bound sodium ions the strongest and the glutamate surfactant, which has the longest spacer, had the lowest affinity for the counterion. Also that could be explained by the hard and soft acid-base concept. The glutamate surfactant was found to be considerably more resistant to calcium ions than the two other surfactants. This was attributed to this surfactant forming an intermolecular complex with the calcium ion at the air-water interface while the aminomalonate and the aspartate surfactants, with shorter distance between the carboxylate groups could form six- and seven-membered intramolecular calcium complexes.

Aspartate

Surfactant

Hard-soft

Conductivity

Aminomalonate

Amino acid

Glutamate

Author

Romain Bordes

SuMo Biomaterials

Chalmers, Chemical and Biological Engineering, Applied Surface Chemistry

J. Tropsch

Basf Se

Krister Holmberg

Chalmers, Chemical and Biological Engineering, Applied Surface Chemistry

Journal of Colloid and Interface Science

0021-9797 (ISSN)

Vol. 338 2 529-536

Subject Categories

Chemical Engineering

Other Chemistry Topics

Chemical Sciences

DOI

10.1016/j.jcis.2009.06.032

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7/2/2018 1