NMR study of the influence of pH on phenol sorption in cationic CTAB micellar solutions

Abstract

Interactions between phenol and cationic cetyltrimethylammonium bromide (CTAB) micelles have been investigated by means of nuclear magnetic resonance spectroscopy. The combined use of 1 H and NOESY techniques revealed that phenol has different preferred locations of interaction depending on the pH. At neutral pH (6.70) conditions, phenol molecules are preferentially located in the outer micelle region, at the micelle-water interface, while at more basic pH (9.94), the deprotonated phenol molecules (C 6 H 5 O -) are immersed into the palisade layer of the micelle. In addition, quantitative estimates of the solubilized fraction of phenol were obtained by using PFG-NMR. The results indicate that the phenol-CTAB interactions, although already present in neutral pH conditions, are largely favored in basic conditions as a consequence of the strong electrostatic interaction between the negatively charged phenolate ions and the positive charge of the cationic surfactant head group.(e)

Fluoride binding in water with the use of micellar nanodevices based on salophen complexes

“…The burying of a charged species in CTABr micelles has already been described in the literature. 38,39 It has been reported that phenol, which is located at the micelle surface when protonated, buries itself into CTABr micelles when it is deprotonated, driven by the favourable electrostatic interactions between the negatively charged phenolate ions and the positive charge of the cationic surfactant head group. As far as Receptor 2 is concerned, the PRE experiments show that its location is not markedly affected by complexation with fluor-ide and this can be explained by the fact that its lipophilicity keeps it in the internal core where it was already hosted before the addition of fluoride.…”

In search of an optimal acid-base indicator for examining surfactant micelles: Spectrophotometric studies and molecular dynamics simulations

“…NMR spectroscopy was often used for revealing the location of the indicators within the micellar pseudophases [20,25,26], together with theoretical approaches applied to the same or similar systems [27][28][29][30][31].…”

Solubilization of organics I: 1H NMR chemical shift perturbations, diffusometry, and NOESY indicate biphenyls internalize in micelles formed by cetyltrimethylammonium bromide

“…Aromatic rings are known to introduce differential ring current effects depending upon their proximity and orientation on neighboring protons . The ring current shifts the resonances of the interacting CH 2 ‐chain protons (low‐frequency or high‐frequency) depending upon whether they interact with the center or the edges of the aromatic rings .…”

“…Although solubilization of organics including pollutants and pharmaceuticals in micelles is an intensive area of research, details of the loci of internalization and the intermolecular interactions defining them are seldom elucidated . NMR studies along these lines, however, have been reported on the solubilization of substituted benzenes in CTAB, valsartan in SDS and CTAB, and polyaromatics in nonionic dendritic micelles; however, making direct comparisons with our studies is challenging due to the differences in molecular systems. Kreke et al attempted to assign the resonances of CTAB in presence of dichloro benzoates, but the conclusions were tentative, considering the resonance overlap in this region.…”

“…1 H chemical shift perturbation, diffusion coefficient measurements using pulse field gradients, and nuclear Overhauser effect (NOE) spectroscopy had been applied to probe the solubilization of aromatics in micelles . The systems investigated span a wide range of complexity, but the measurements are relatively unique and powerful due to its ability to follow the spectral changes of the constituents (surfactants and solubilizates) independently …”