Pulse field gradient dynamics

We finish this section by comparing our results with NMR and incoherent neutron scattering experiments on water dynamics. Self-diffusion constants on the millisecond time scale have been measured by NMR with the pulsed field gradient spin echo (PFGSE) method. Applying this technique to oriented egg phosphatidylcholine bilayers, Wassail [68] demonstrated that the water motion was highly anisotropic, with diffusion in the plane of the bilayers hundreds of times greater than out of the plane. The anisotropy of... 

Ye, G., Hayden, C. A. and Coward, G. R. 2007. Proton dynamics of nation and Nafion/Si02 composites by solid state NMR and pulse field gradient NMR. Macromolecules 40 1529-1537. 

Related Methods Pulsed Field Gradient NMRand Dynamic Light Scattering... 

Abbreviations MD, molecular dynamics TST, transition state theory EM, energy minimization MSD, mean square displacement PFG-NMR, pulsed field gradient nuclear magnetic resonance VAF, velocity autocorrelation function RDF, radial distribution function MEP, minimum energy path MC, Monte Carlo GC-MC, grand canonical Monte Carlo CB-MC, configurational-bias Monte Carlo MM, molecular mechanics QM, quantum mechanics FLF, Hartree-Fock DFT, density functional theory BSSE, basis set superposition error DME, dimethyl ether MTG, methanol to gasoline. 

Packer and Rees [3] extended the work of Tanner and Stejskal by the development of a theoretical model using a log-normal size distribution function. Measurements made on two water-in-oil emulsions are used to obtain the self-diffusion coefficient, D, of the water in the droplets as well as the parameters a and D0 0. Since then, NMR has been widely used for studying the conformation and dynamics of molecules in a variety of systems, but NMR studies on emulsions are sparse. In first instance pulsed field gradient NMR was used to measure sdf-diffusion coefficients of water in plant cells (e.g. ref. [10]). In 1983 Callaghan... 

Jost S, Bar NK, Fritzsche S, Haberlandt R, and Karger J. Diffusion of a mixture of methane and xenon in silicalite A molecular dynamics study and pulsed field gradient nuclear magnetic resonance experiments. J Phys Chem B 1998 102 6375-6381. 

Mesoporous structures are commonly characterized with diffraction, electron microscopy methods [14], and gas sorption techniques. The ensemble diffusion behavior of small molecules has been examined with pulsed-field gradient NMR spectroscopy [15] and neutron scattering [16]. Here, we are interested in techniques which give a more direct access to the real structure of the mesoporous host and to the dynamics on a single-molecule basis, and thus reveal structural and dynamic features which are not obscured by ensemble or statistical averaging as in conventional techniques. 

This important relation is used to determine coil size from measured diffusion coefficient (for example, by dynamic light scattering—see Section 8.9, or by pulsed-field gradient NMR). The size determined from a measurement of diffusion coefficient is the hydrodynamic radius ------... 

The availability of pulsed field gradient (PEG) techniques has had the most significant impact in terms of making it possible to perform 2D- and 3D-NMR experiments on polymer samples. These methods have taken the place of traditional radiofrequency phase cycling methods for coherence selection. By optimizing the use of the spectrometer s dynamic range, PEG techniques not only save time but also drastically reduce artifact noise. 

R156 W. S. Price, Probing Molecular Dynamics in Biochemical and Chemical Systems Using Pulsed Field Gradient NMR Diffusion Measurements , p. Pl/31... 

To prove the formation of vesicles a number of indirect techniques can be used such as dynamic light scattering, the use of fluorescent probes and pulsed field gradient NMR self-diffusion measurements. Some more direct techniques such as freeze-fracture and negative staining electron microscopy are less biased by the interpretation of the scientist, but also these methods have their limitations. Cryo-electron microscopy, as introduced by Dubochet in the 80s, is the method of choice when it comes to visualization of small colloidal structures. Recent developments in the vitrification of specimens make it now possible to observe vesicles and other aggregated structures artifact free. 

---