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.

Structural and Spectroscopic Characterization of TPGS Micelles: Disruptive Role of Cyclodextrins and Kinetic Pathways

“…This behavior can be explained in terms of the two simultaneous equilibria that are taking place: (Figure 7). A similar behavior has been observed in gemini cationic surfactants with different spacer groups 55 , and most recently in a ruthenium metallosurfactant 56 .…”

Antibiotic-in-Cyclodextrin-in-Liposomes: Formulation Development and Interactions with Model Bacterial Membranes

“…PPA148 and DIMEB solutions were mixed in volume fractions ranging from 0 to 1 mL with an increment of 0. The stoichiometry of the complex was obtained by normalizing the variations of the chemical shifts of the host by its mole fraction (XCD) and plotting them against cyclodextrin mole fraction (XCD) (32). The shift of the DIMEB hydrogen resonance depends on the mole fraction of pure drug, pure DIMEB and drug/DIMEB complexes.…”

Amphiphilic hybrids containing inorganic constituent: More than soap

“…A Ru(II) polypyridyl porphyrin conjugate amphiphile, combines photo induced charge separation and enhanced cellular uptake properties into a single amphiphilic system as an effective photodynamic therapeutic anticancer agent [36 • ]. Another interesting study was published by Iza et al in 2015. Superior control over the aggre gation behavior of a Ru(II) metallosurfactant could be achieved by further influence of cyclodextrins sliding off and on the hydrophobic chain [37].…”

“…Another interesting study was published by Iza et al in 2015. Superior control over the aggre gation behavior of a Ru(II) metallosurfactant could be achieved by further influence of cyclodextrins sliding off and on the hydrophobic chain [37]. A novel idea was presented in a paper by Schubert et al, who have linked two parts with different solvent compatibilities to each other via Ru(II) resulting in a unique hybrid block copolymer compound [38].…”