5  NMR studies of self-diffusion in liquids

Characterization of Molecular Systems and Monitoring of Chemical Reactions in Ionic Liquids by Nuclear Magnetic Resonance Spectroscopy

“…Routine NMR hardware equipped with a pulsed-field gradient is suitable for studying fast diffusion in organic solvents as well as a slower diffusion in viscous liquids. 256 However, special attention should be paid to minimizing convection effects and to maintaining temperature stabilization. 257,258 A higher quality of diffusion spectral data may be obtained with dedicated hardware.…”

“…273 A mixing time of >50 ms led to an increasing contribution of spin diffusion that resulted in unrealistically short hydrogen-hydrogen distances. 273 Diffusion coefficients were determined using DOSY methodology [255][256][257] by collecting a series of 1 H NMR spectra, measured as a function of gradient amplitude. 61,62 rows in pseudo-2D DOSY spectrum.…”

DOSY NMR applied to analysis of flavonoid glycosides from Bidens sulphurea

“…[1 -9] This technique is based on the molecular diffusion, consisting of the random motion of particles (molecules) in a gas or liquid driven by the thermal energy of the system. [10,11] Moreover, as a characteristic feature of a given substance, the diffusion coefficient, D, depends on the effective molecular weight, size and shape, and can provide information on molecular dynamics, including intermolecular interactions, aggregation and conformational changes, and can also be used to estimate the molecular size in solution. [2,5,11 -20] The pulse sequences used in a DOSY experiment are based on the PGSE NMR [11,15,21 -23] method and Hahn's nuclear spin echo and has five stages: excitation (net magnetization becomes detectable by the application of a 90 • rf pulse), encoding (applying the first gradient pulse to encode the spin initial positions), evolution (diffusion delay time, , allows the spin translational displacement), decoding (applying a gradient pulse identical to the first one to refocus those spins that did not migrate during the time ) and acquisition of the signal.…”

“…[21] The best DOSY sequences have Stejskal-Tanner [24] diffusion delay and use bipolar gradient pulses to facilitate phase coherence [2,7,25] and two additional gradient pulses to eliminate eddy currents that can form around the gradient coil, reducing artifacts. [11,26,27] Thus, with a DOSY experiment, the components of a solution can be distinguished without previous separation. This possibility reduces the degradation risks and accelerates the identification process of these compounds, mainly if the spectra have high resolution in the chemical shift.…”

Stability Evaluation and Degradation Studies of DAC® Hyaluronic-Polylactide Based Hydrogel by DOSY NMR Spectroscopy

“…Moreover, the D value of the resonance of HDO molecule in the mix of fragments reported above shows a variable value of D of HDO, in fact in the mix of 13 kDa and 208 kDa D was measured in 4.45 × 10 −9 m 2 s −1 . On the basis of the literature diffusion of net water as a trace of the protonated water molecule, in practice HDO (1% of H 2 O in D 2 O) a value D = 1.12 × 10 −9 m 2 s −1 is reported also with NMR [ 37 , 38 , 39 ] and with other physical techniques [ 40 , 41 ]. The variability of the diffusion of the HDO molecule is evidently strongly affected by the size and the dispersity of the macromolecules in the solution.…”