1 research outputs found
Using Inclusion Complexes with Cyclodextrins To Explore the Aggregation Behavior of a Ruthenium Metallosurfactant
The
aggregation behavior of a chiral metallosurfactant, bisĀ(2,2ā²-bipyridine)Ā(4,4ā²-ditridecyl-2,2ā²-bipyridine)ĀrutheniumĀ(II)
dichloride (Ru<sub>2</sub><sup>4</sup>C<sub>13</sub>), 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 (Ī²-CD and Ī³-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 Ī²-CD, more stable
than the one formed with the wider Ī³-CD, is capable of resolving
the Ī and Ī enantiomers at high CD/surfactant molar ratios.
The chiral recognition is possible due to the very specific interactions
taking place when the Ī²-CD coversīøvia its secondary rimīøpart
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