2 research outputs found
Size-Selective Permeation of Water-Soluble Polymers through the Bilayer Membrane of Cyclodextrin Vesicles Investigated by PFG-NMR
Cyclodextrin
vesicles (CDVs) consist of a bilayer of amphiphilic
cyclodextrins (CDs). CDVs exhibit CD cavities at their surface that
are able to recognize and bind hydrophobic guest molecules via size-selective
inclusion. In this study, the permeability of α- and β-CDVs
is investigated by pulsed field gradient-stimulated echo (PFG-STE)
nuclear magnetic resonance. Diffusion experiments with water and two
types of water-soluble polymers, polyethylene glycol (PEG) and polypropylene
glycol (PPG), revealed three main factors that influence the exchange
rate and permeability of CDVs. First, the length of the hydrophobic
chain of the CD amphiphile plays a crucial role. Reasonably, vesicles
consisting of amphiphiles with a longer aliphatic chain are less permeable
since both membrane thickness and melting temperature <i>T</i><sub>m</sub> increase. Second, the exchange rate through the bilayer
membrane depends on the molecular weight of the polymer and decreases
with increasing weight of the polymer. Most interestingly, a size-selective
distinction of permeation due to the embedded CDs in the bilayer membrane
was found. The mechanism of permeation is shown to occur through the
CD cavity, such that depending on the size of the cavity, permeation
of polymers with different cross-sectional diameters takes place.
Whereas PPG permeates through the membrane of β-CD vesicles,
it does not permeate α-CD vesicles