title: Sodium effect on self-organization of amphiphilic carboxylates: formation of structured micelles and superlattices.
abstract: Not only the self-aggregation of dendritic polycarboxylates into structurally persistent micelles, but also that of the micelles themselves into superlattices is controlled by alkali-metal counterions and shows a pronounced sodium effect. Our combined experimental and computational work has revealed the formation of superlattices for the first time. The behavior of a variety of amphiphilic carboxylates and the different effects of the alkali cations Li(+), Na(+), and K(+) have been investigated by conductivity measurements, cryogenic transmission electron microscopy (cryo-TEM), and molecular-dynamics (MD) simulations. Together, these show that sodium salts of the amphiphiles give the most stable micelles, followed by lithium and potassium. Our results suggest that ion multiplets in bridging positions, rather than contact ion pairs, are responsible for the enhanced stability and the formation of hexagonally ordered superlattices with sodium counterions. Potassium ions do not form such ion multiplets and cannot therefore induce aggregation of the micelles. This sodium effect has far-reaching consequences for a large number of biological and technical systems and sheds new light on the origin of specific-ion effects.
authors.affiliation: Department of Chemistry and Pharmacy, Interdisciplinary Center of Molecular Materials, Friedrich-Alexander-Universität Erlangen-Nürnberg, Henkestrasse 42, 91054 Erlangen, Germany.
authors.forename: Karin
authors.initials: K
authors.lastname: Rosenlehner
authors.forename: Boris
authors.initials: B
authors.lastname: Schade
authors.forename: Christoph
authors.initials: C
authors.lastname: Böttcher
authors.forename: Christof M
authors.initials: CM
authors.lastname: Jäger
authors.forename: Timothy
authors.initials: T
authors.lastname: Clark
authors.forename: Frank W
authors.initials: FW
authors.lastname: Heinemann
authors.forename: Andreas
authors.initials: A
authors.lastname: Hirsch
mesh_terms: D002264:Carboxylic Acids / Q000737:chemistry*; D020285:Cryoelectron Microscopy; D008823:Micelles; D056004:Molecular Dynamics Simulation; D015394:Molecular Structure; D012964:Sodium / Q000737:chemistry*; D013501:Surface-Active Agents / Q000737:chemistry*
chemical_list: D002264:Carboxylic Acids; D008823:Micelles; D013501:Surface-Active Agents; D012964:Sodium