title: Dimeric and monomeric surfactants derived from sulfur-containing amino acids.
abstract: 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 E(T)(30) (Reichardt's betaine dye), was similar to sodium dodecyl sulphate (SDS) micelles.
authors.affiliation: iMed.UL, Faculty of Pharmacy, University of Lisbon, Av. Prof. Gama Pinto, 1649-003 Lisbon, Portugal. cfaustino@ff.ul.pt
authors.forename: Célia M C
authors.initials: CM
authors.lastname: Faustino
authors.forename: António R T
authors.initials: AR
authors.lastname: Calado
authors.forename: Luís
authors.initials: L
authors.lastname: Garcia-Rio
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D000900:Anti-Bacterial Agents / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D000935:Antifungal Agents / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D002176:Candida albicans; D019281:Dimerization; D004553:Electric Conductivity; D004926:Escherichia coli; D008823:Micelles; D008826:Microbial Sensitivity Tests; D015394:Molecular Structure; D020102:Mycobacterium smegmatis; D011550:Pseudomonas aeruginosa; D013210:Staphylococcus; D013455:Sulfur / Q000737:chemistry*; D013500:Surface Tension; D013501:Surface-Active Agents / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology
chemical_list: D000596:Amino Acids; D000900:Anti-Bacterial Agents; D000935:Antifungal Agents; D008823:Micelles; D013501:Surface-Active Agents; D013455:Sulfur