Dimeric and monomeric surfactants derived from sulfur-containing amino acids

Anionic urea-based dimeric (gemini) surfactants derived from the amino acids l-cystine, d-cystine and dl-cystine, as well as monomeric surfactants derived from l-cysteine, l-methionine and l-cysteic acid were synthesized and their solution properties characterized by electrical conductivity, equilibrium surface tension, and steady-state fluorescence spectroscopy techniques. The geminis studied showed the lowest critical micelle concentration (cmc) values, however the monomeric cysteine counterpart exhibited superior efficiency in lowering surface tension, an unusual finding that can be attributed to the free sulfhydryl group. Chirality seems to play a role in the surface active properties of the gemini surfactants, but not on micelle formation. All the surfactants studied showed a higher preference for adsorption at the air/water interface rather than to form micelles, a fact that may be related to the urea moiety. The polarity of the interfacial region, measured with the solvatochromic probe ET(30) (Reichardt’s betaine dye), was similar to sodium dodecyl sulphate (SDS) micelles.

Dimeric (1) and monomeric (2a–c) urea surfactants derived from sulfur-containing amino acids form micelles in aqueous solution where the micellar parameters are dependent on the chemical structure of the surfactant.Figure optionsDownload high-quality image (78 K)Download as PowerPoint slideResearch highlights
► A new class of amino acid-based surfactants, N-carbamoylamino acids, has been synthesized.
► The new amphiphiles, with dimeric and monomeric structures, form micelles in aqueous solution and show great efficiency in surface tension reduction.
► The stereochemistry of the gemini surfactants seems to influence their surface active properties, but not micelle formation.