Mass Transport Properties in Supramolecular Systems Studied by Diffusion and Relaxation NMR
Doctoral thesis, 2008
This thesis shows how diffusion and relaxation NMR can be applied in various aspects to study mass transport in supramolecular systems. Information about these systems can be obtained, either by direct measurement of the molecules that are incorporated in a supramolecular structure, or via probe molecules, which indirectly gives information about the system. Through the relation between molecular size and diffusion, probes can be used for the evaluation of sizes of objects in solution. This was demonstrated in Paper III, where vesicles were characterized with respect to size using diffusion measurements.
By measuring diffusion as a series of various observation times, the exchange dynamics of a molecule between two separate environments with different diffusion can be investigated and mean residence times can be extracted. In Paper I it is shown that organosilica nanoparticles, synthesized with and without oil, can take up triethylamine and tributylamine from water solutions. The mean residence times were longer in particles compared to in the bulk, and significantly longer for particles synthesized in the presence of oil.
The diffusion and relaxation of molecules in self-assembled structures, such as microemulsions and L3-phases, can reveal information about the microstructure in the system. Paper IV, shows that up to 16% of a drug compound (δ-aminolevulinic acid) could be added to a propylene glycol/monoolein/water system, without affecting the L3-phase. In Paper II, the lipid composition was varied in a water-in-oil microemulsion. At high concentration of triglycerides of medium chain length a microstructure that slowed down the water diffusion was formed. This was also observed with T2 relaxation as well as by chemical shift changes as seen by routine 1D-1H NMR experiments.
In Paper VI transport of hexamethyldisilane in mucus and mucin showed that surfactants are of high importance in the transport mechanism in mucus. Measuring the diffusion of a probe in a complex network structure may reveal information about the actual environment in which it is diffusing. In Paper V, dendrimers were shown to be suitable for probing polymer hydrogels. The susceptibility effect was also investigated in a magnetic field study in which the 1H Larmor frequency was varied from 400 to 900 MHz.