Study of the Interaction between a Nonyl Phenyl Ether and β-Cyclodextrin:  Declouding Nonionic Surfactant Solutions by Complexation

Abstract

Absorption and fluorescence measurements for aqueous solutions at 298 K containing pentaoxyethylene nonyl phenyl ether (NPE5), in the absence and presence of beta-cyclodextrin (beta-CD), were analyzed to determine the effect of the complexation on the aggregation of the surfactant. For the binary system, the appearance of a new emission band and the presence of an isoemissive point in the emission spectra at the time and frequency domains indicate the formation of an excimer within the micellar core. The addition of beta-CD induces the formation of an inclusion complex strong enough to break the aggregates and avoid the excimer formation. For the ternary system, the increase in fluorescence has been used to assess the binding constants of 1:1 + 2:1 stoichiometries. Static light scattering, 1H NMR diffusion-ordered spectroscopy (DOSY), and two-dimensional rotating-frame Overhauser enhancement spectroscopy (ROESY) experiments were used to characterize the cloud point of NPE5 at 298 K, and to ascertain the effects of complexation on the clouding process. In the presence of beta-CD, the analysis of the 1H NMR spectra and the self-diffusion coefficients reveal the existence of interactions between the beta-CD and the aggregates that increase the cloud-point concentration more than expected. Under conditions of excess of beta-CD, ROE enhancements point to a complex of dominant 2:1 stoichiometry (beta-CD:NPE5) in which the hydrophobic moiety of the surfactant threads two beta-CDs.

The diffusion NMR studies of crown ethers–cyclodextrin complexation process

“…The values of the diffusion coefficients of free cyclodextrins and crown ethers (10 m M solutions in D 2 O) are presented in Table 1. The results for cyclodextrins stay in accordance with literature values: 2.92 versus 2.29–3.00 for α‐cyclodextrin,17–20 2.81 versus 2.16–3.29 for β‐cyclodextrin9, 10, 12, 17, 18, 20–26 and 2.48 versus 2.10–3.20 for γ‐CD,7, 10, 17, 20, 27 (all values × 10 10 m 2 /s; in D 2 O, buffered or not; at 298–300 K). The origin of such significant dispersion of the literature values is not clear—the influence of concentration, sequence used by authors, or buffering agents' presence does not explain this.…”

Polyrotaxane‐Mediated Self‐Assembly of Gold Nanospheres into Fully Reversible Supercrystals

“…The supramolecules were prepared in water by a-CD complexation of a new thiolfunctionalized Igepal surfactant IgeSH (Scheme 1; see Supporting Information for synthesis and characterization) which stabilizes the surface of the nanocrystals. The choice of the Igepal as capping agent is dictated by its high tendency to form CD polyrotaxanes, [11] the luminescent properties of such amphiphiles and their CD complexes, [11b] and the versatility that commercially available Igepal surfactants have shown as stabilizers of metal nanoparticles. [12] An inclusion complex was formed between a-CD and IgeSH by mixing both compounds in water (Figure 1 a, and see the Supporting Information).…”

Polyrotaxane‐Mediated Self‐Assembly of Gold Nanospheres into Fully Reversible Supercrystals

“…The concentration of capping molecules around a nanocrystal has been estimated at approximately 5×10 3 molecules (see Supporting Information). The emission spectra exhibit a wide emission band centered at λ =300 nm11b that is not quenched by the metal core (Figure 2 b). Although no significant changes of the IgeS‐AuNPs LSPR band have been detected upon macrocycle addition (inset in Figure 2 a), an enhancement of the fluorescence intensity of IgeS‐AuNPs has been detected (Figure 2 b).…”

“…The supramolecules were prepared in water by α‐CD complexation of a new thiol‐functionalized Igepal surfactant IgeSH (Scheme ; see Supporting Information for synthesis and characterization) which stabilizes the surface of the nanocrystals. The choice of the Igepal as capping agent is dictated by its high tendency to form CD polyrotaxanes,11 the luminescent properties of such amphiphiles and their CD complexes,11b and the versatility that commercially available Igepal surfactants have shown as stabilizers of metal nanoparticles 12…”