Influence of the Vesicular Bilayer Structure on the Sorption of Ethylbenzyl Alcohol

Abstract

The influence of the physicochemical properties of the vesicular bilayer on the sorption of poorly water soluble compounds was investigated with pulsed field gradient 1H nuclear magnetic resonance (PFG-NMR) for the case of phosphatidylcholine and dioctadecyldimethylammonium bromide (DODAB), using 4-ethylbenzyl alcohol as a model compound. Hereby, the effect of bilayer thickness at a constant physicochemical state was studied using a range of phosphatidylcholines of varying chain lengths, whereas DODAB was preferred to check the influence of the bilayer physicochemical state since this cationic lipid is characterized by three different states within the studied temperature range. When the phospholipid alkyl chain length was changed, no differences were observed in the sorption which was linked to the surface-mediated sorption. On the other hand, when the chemical composition was preserved but the temperature and thus the physical state of the bilayer were changed, the sorption in dioctadecyldimethylammonium bromide (DODAB) vesicles changed dramatically. From those experiments, a strong relationship between the ordering of the surfactant molecules and the sorption can be assumed.

The Stejskal–Tanner equation generalized for any gradient shape—an overview of most pulse sequences measuring free diffusion

“…If the spins have randomly moved during the echo to other regions where the magnetic field is different due to its inhomogeneity, the refocusing will no longer be complete, resulting in a loss of signal [ Fig. [14], it is clear that the diffusion flux will work against the concentration gradient, thus creating a net transport from the highly concentrated to the less concentrated regions. The main mechanism by which spins move position during the spin-echo experiment is the translational motion of the molecules carrying the spins.…”

“…From Eq. [14], it is clear that the diffusion flux will work against the concentration gradient, thus creating a net transport from the highly concentrated to the less concentrated regions. This effectively makes the concentration distribution time-dependent until a uniform distribution is reached.…”

“…The diffusion coefficient's dependence on size and shape can for example provide insight into the nature and molar mass of the supramolecular complexes formed (1)(2)(3)(4), or indicate whether a protein is globular or unstructured (5). Typical examples are the determination of the critical micellar concentration (CMC) of surfactants (11) or the binding of small molecules with micelles or vesicles (12)(13)(14). As for the chemical shift, slow, intermediate, and fast exchange regimes can be distinguished relative to a diffusion time-scale.…”

“…When the diffusion coefficients of both states are sufficiently different (e.g., pro-teinÀligand interactions), both a qualitative and quantitative assessment of the binding interaction can be obtained (9,10). Typical examples are the determination of the critical micellar concentration (CMC) of surfactants (11) or the binding of small molecules with micelles or vesicles (12)(13)(14). In the situation of slow exchange on the diffusion timescale, but where the resonances of the different states cannot be resolved within the 1D spectrum, the analysis of the resulting multiexponential signal decay can provide the populations of the different exchanging components (15,16).…”

NMR of liquid crystals and micellar solutions

“…The effect of bilayer thickness at a constant physicochemical state was studied using a range of phosphatidylcholines of varying chain lengths, whereas DODAB was preferred to check the influence of the bilayer physicochemical state since this cationic lipid is characterized by three different states within the studied temperature range. 68 The membrane location of two fragments in two different Kþ-channels, the KvAP (from Aeropyrum pernix) and the HsapBK (human) corresponding to the putative ''paddle'' domains, has been investigated by CD, fluorescence and NMR spectroscopy. Both domains interact with q = 0.5 phospholipid bicelles, DHPC micelles and with POPC vesicles.…”