title: Using inclusion complexes with cyclodextrins to explore the aggregation behavior of a ruthenium metallosurfactant.
abstract: The aggregation behavior of a chiral metallosurfactant, bis(2,2'-bipyridine)(4,4'-ditridecyl-2,2'-bipyridine)ruthenium(II) dichloride (Ru2(4)C13), synthesized as a racemic mixture was characterized by small-angle neutron scattering, light scattering, NMR, and electronic spectroscopies. The analysis of the SANS data indicates that micelles are prolate ellipsoids over the range of concentrations studied, with a relatively low aggregation number, and the micellization takes place gradually with increasing concentration. The presence of cyclodextrins (β-CD and γ-CD) induces the breakup of the micelles and helps to establish that micellization occurs at a very slow exchange rate compared to the NMR time scale. The open structure of this metallosurfactant enables the formation of very stable complexes of 3:1 stoichiometry, in which one CD threads one of the hydrocarbon tails and two CDs the other, in close contact with the polar head. The complex formed with β-CD, more stable than the one formed with the wider γ-CD, is capable of resolving the Δ and Λ enantiomers at high CD/surfactant molar ratios. The chiral recognition is possible due to the very specific interactions taking place when the β-CD covers-via its secondary rim-part of the diimine moiety connected to the hydrophobic tails. A SANS model comprising a binary mixture of hard spheres (complex + micelles) was successfully used to study quantitatively the effect of the CDs on the aggregation of the surfactant.
authors: Departamento de Química Física I, and ‡Departamento de Química Orgánica I, Facultad de Ciencias Químicas, Universidad Complutense de Madrid , Ciudad Universitaria s/n, Madrid 28040, Spain.
authors: Nerea
authors: N
authors: Iza
authors: Andrés
authors: A
authors: Guerrero-Martínez
authors: Gloria
authors: G
authors: Tardajos
authors: María José
authors: MJ
authors: Ortiz
authors: Eduardo
authors: E
authors: Palao
authors: Teresa
authors: T
authors: Montoro
authors: Aurel
authors: A
authors: Radulescu
authors: Cécile A
authors: CA
authors: Dreiss
authors: Gustavo
authors: G
authors: González-Gaitano
mesh_terms: D015082:2,2'-Dipyridyl / Q000031:analogs & derivatives* / Q000737:chemistry; D056831:Coordination Complexes / Q000737:chemistry*; D003505:Cyclodextrins / Q000737:chemistry*; D008823:Micelles; D009942:Organometallic Compounds / Q000737:chemistry*; D012428:Ruthenium / Q000737:chemistry*; D013237:Stereoisomerism; D013501:Surface-Active Agents / Q000737:chemistry*
chemical_list: D056831:Coordination Complexes; D003505:Cyclodextrins; D008823:Micelles; D009942:Organometallic Compounds; D013501:Surface-Active Agents; C000603305:bis(2,2'-bipyridine)(4,4'-ditridecyl-2,2'-bipyridine)ruthenium(II) dichloride; D015082:2,2'-Dipyridyl; D012428:Ruthenium