Rupture of Pluronic Micelles by Di-Methylated β-Cyclodextrin Is Not Due to Polypseudorotaxane Formation

Abstract

Spectroscopic measurements (uv/vis absorbance and fluorescence) and time-resolved small-angle neutron scattering experiments (TR-SANS) were used to follow the breakdown of Pluronic micelles by heptakis(2,6-di-O-methyl)-β-cyclodextrin (DIMEB) over time in order to elucidate the mechanism of micellar rupture, generally attributed to polypseudotorotaxane (PR) formation between the cyclodextrin and the central hydrophobic PPO block. The spectroscopic measurements with two different probes (methyl orange and nile red) suggest that very rapid changes (on the order of seconds) take place when mixing DIMEB with F127 Pluronic and that no displacement of the probe from the cyclodextrin cavity occurs, which is in disagreement with PR formation. TR-SANS measurements demonstrate for the first time that the micelles are broken down in less than 100 ms, which categorically rules out PR formation as the mechanism of rupture. In addition, the same mechanism is demonstrated with other Pluronics, P85 and P123. In the latter case, after micellar rupture, lamellar structures are seen to form over a longer period of time, thus suggesting that after the instantaneous micellar disruption, further, longer-scale rearrangements are not excluded.

Threading Different Rings on X-Shaped Block Copolymers: Hybrid Pseudopolyrotaxanes of Cyclodextrins and Tetronics

“…Both the magnitude of this drop and the speed at which it takes place increases with increasing DIMEB concentration and it is particularly drastic at 3% DIMEB, irrespectively of the molar mass of the block copolymer (SI, Figure S3). This effect of methylated CDs on shifting the unimer-micelle equilibrium has been reported for linear block copolymers 51,52 and other surfactants, like TPGS. 44 For example, using TR-SANS, it has been observed that Pluronic P85, P123 and F127 undergo fast micellar rupture with DIMEB, which has been ascribed to the existence of weak interactions between the PPO methyl groups and those of the primary and secondary rims of the macrocycle, leading to increased solubility.…”

Pseudo-Polyrotaxanes of Cyclodextrins with Direct and Reverse X-Shaped Block Copolymers: A Kinetic and Structural Study

“…32,33 The substitution of the hydroxyl groups on the rims of the CD strongly modifies the aggregation behavior of the Pluronic micelles, depending on the specific nature of the substituents, [34][35][36] and the kinetics and mechanisms of the formation of the PPRs have been studied. [37][38][39] Specifically, the PRs formed with 2-hydroxypropyl β-CD and Pluronic have shown promise in the biomedical field for the treatment of Niemann-Pick disease. [40][41][42] Another type of block-copolymers of interest as guests for cyclodextrins is poloxamines, also known by their commercial name of Tetronic® (BASF).…”

Small molecule self‐assembly in polymer matrices

“…A similar template method was used by Bleta et al for synthesizing mesoporous alumina with controlled pore size, by taking advantage of the micellar co‐assembly of a triblock copolymer and methylated cyclodextrin. Valero et al concluded that methylated β‐cyclodextrins do not form pseudorotaxanes with PEO–PPO–PEO. However, Bleta et al found that the copolymer PEO 20 PPO 70 PEO 20 (Pluronic P123, M w = 5800 g/mol) and a randomly methylated β‐cyclodextrin (denoted by RAMEB) co‐assembled in aqueous solutions.…”