NMR Investigation of Exchange Dynamics and Binding of Phenol and Phenolate in DODAC Vesicular Dispersions

Abstract

The interaction between phenol molecules, both in their undissociated and dissociated states, and cationic dioctadecyl dimethylammonium chloride (DODAC) vesicles were thoroughly investigated using NMR techniques. In particular, diffusion and relaxation measurements, combined with the two sites Kärger model, were used to evaluate the exchange dynamics and the binding of the aromatic molecules to the vesicles. The results reveal that, besides concentration and vesicle preparation method, pH conditions have the biggest impact on the phenol sorption behavior. Although the dissociated form of phenol formed at high pH is more hydrophilic, the results indicated that phenol-DODAC interactions were largely favored in basic conditions as a consequence of the strong electrostatic interaction between the phenolate anions and the cationic surfactant headgroup.

WITHDRAWN: Ionic liquid mixtures with tunable physicochemical properties

“…The effect of the mole composition on the ion mobility of the pyrrolidinium binary mixtures is more evident in Figure 3 and also reported in can show bi-exponential behavior and, therefore, leading to two different diffusion coefficients [40][41][42]. Otherwise, for the PYR 14 -PYR 18 mixtures, attenuation for the signals 3 and 6 can be better described as mono-exponential ( Figure 5).…”

Size-Selective Permeation of Water-Soluble Polymers through the Bilayer Membrane of Cyclodextrin Vesicles Investigated by PFG-NMR

“…Sets of echo decays obtained with different observation times were analyzed by a least-squares fitting procedure implemented in a MATLAB (The Mathworks, Inc.) program. Details about the procedure and the relevant equations have been described in previous publications. ,, Here, a global set of fixed parameters consisting of the corresponding spin relaxation times ( T 1e , i , T 2e , i ) is employed, where the values for internal and external chains are identical, as shown for PEG chains in polymer capsules previously . Effective relaxation times T e , i of encapsulated and free chains are thus assumed to be identical.…”

“…For this purpose, a two-site exchange model developed by Kärger for exchange in diffusion experiments has to be applied to the diffusion data sets, yielding permeation rates through vesicle walls or, more generally, exchange rates between the sites. This technique has been applied to study the permeation of water-soluble polymers or small molecules through the walls of hollow colloidal particles in various systems, such as block-co-polymer vesicles, − polyelectrolyte multilayer capsules, − or lipid vesicles , (see also a recent review article) . With PFG-NMR, it is possible to determine the hydrodynamic vesicle radius, the equilibrium distribution of encapsulated species, and the permeability of the vesicle wall without labeling the observed molecules.…”

Conformation and Dynamics of the Cyclic Lipopeptide Viscosinamide at the Water-Lipid Interface

“…The line broadening and chemical shifts remained constant over the titrated P:L range. Irrespective of the particular chemical exchange kinetics (either fast or slow) on the NMR frequency time scale, the observation of a single set of VA resonances with chemical shifts independent of the P:L clearly indicates that partitioning of VA in the DPC is already highly pronounced towards the lipid phase at the lowest P:L. This was confirmed using diffusion NMR spectroscopy, a well-established technique to investigate partitioning of molecules in a water/lipid dispersion through the diffusion coefficient of the solute molecules [32,33,34,35]. In the case at hand, difficulties in extracting the DPC diffusion coefficient from overlapping VA and DPC resonances were avoided by taking advantage of the fact that only DPC contributes to the 31 P-NMR spectrum.…”