Hydrosoluble Cyclodextrin/Poloxamer Polypseudorotaxanes at the Air/Water Interface, in Bulk Solution, and in the Gel State

Abstract

The interactions between poloxamer 407 (Pluronic F127, PF127) and two hydrophilic derivatives of beta-cyclodextrin, i.e., hydroxypropyl-beta-cyclodextrin (HPbetaCD; molar substitution (MS) 0.65) and methylated-beta-cyclodextrin (MbetaCD; MS 0.57), were characterized by means of surface tension measurements, pi-A isotherms, isoperibol microcalorimetry, 1H NMR, and rheometry. An effective complexation of poloxamer with the two CDs was evidenced as a change in the surface pressure of the pi-A isotherm of PF127 on a subphase of CD solution, with a positive excess being observed at the expanded region and a negative excess at the collapsed region. Such changes indicated that when the CD lies with the main axis perpendicular to the interface at low pressure no complexation occurs, but as the pressure increases and the CDs eventually change their arrangement to be with the main axis parallel to the interface, the amphiphilic copolymer can form polypseudorotaxanes. Addition of CDs to PF127 micellar solutions led to the exothermic rupture of micelles, a shift in the cmc toward higher values, changes in the chemical shifts of H3, H4, and H5 of MbetaCD and of the methyl groups of PF127, and an increase in the gel temperature. The interaction was stronger between poloxamer and MbetaCD, compared to HPbetaCD, with the stoichiometry of the polypseudorotaxanes being preferably ca. 1:20 in both cases. SEM images revealed formation of nanorods of stacked polypseudorotaxanes. Complexation with a high affinity constant between unimers and CDs in bulk solution was also evidenced by competitive displacement of methyl orange. Feasible structural models of the PF127:CD polypseudorotaxanes at both the air-water interface and in the bulk solution are proposed.

Cyclodextrin Inclusion Complex to Improve Physicochemical Properties of Herbicide Bentazon: Exploring Better Formulations

“…However, the surface tension of water decreased to 65.3±0.2 mN/m in presence of HPCD. This value is in agreement to those reported by Leclercq [37] and Nogueiras-Nieto [38], which pointed out that some modified CDs provoke a decrease in surface tension in a different way compared from typical surfactants. We have found that although there was no change in surface tension of Btz or βCD solutions, the inclusion complex showed a lower value.…”

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

“…MO is a dye with a strong absorbance in the visible region of the spectrum, sensitive to the nature of the microenvironment in which it is present, 29 such as micelles and cyclodextrins. 11,29 The absorbance spectra of MO in water, DIMEB, and F127 ( Figure 1A, (1À3)) reveals a strong solvatochromism. In each case, the spectral contour of the main band can be fitted to a sum of two Gaussians (Supporting Information Figure SI 2).…”

“…In fact, we do not rule out that, under specific conditions (concentration, CD/ polymer ratio, etc), inclusion complexes are indeed formed once easier access to the polymer chains has been established by unimer formation, in agreement with other studies. 11,12,36 However, IC formation cannot be the cause of micellar breakup due to the extremely fast kinetics of the process revealed by these TR-SANS experiments. Slow time evolution of the structures has also been recently reported 36 and obtained by quenching of the samples below the CMT.…”

Temperature-Sensitive Gels for Intratumoral Delivery ofβ-Lapachone: Effect of Cyclodextrins and Ethanol

“…This fact can be explained by the formation of supramolecular assemblies named polypseudorotaxanes in which the PPO blocks are inserted in the cyclodextrin cavities [22]. As a consequence, the copolymer unimers involved in the supramolecular structure find that it is difficult to form micelles.…”