Analysis of nuclear relaxation in granular systems

Abstract

The longitudinal nuclear magnetic relaxation time, T 1 , of powdered samples was analyzed following the theory proposed by Browstein and Tarr to explain the T 1 reduction of water confined in biological cells and the proposed by Rabbani and Edmonds where the molecular diffusion in liquids is substituted by spin diffusion to interpret the T 1 behavior in solid particles. We have shown that the multiexponential character of magnetization decay in solid particles with a narrow band size distribution allows to evaluate the spin diffusion coefficient of this material. On the other hand if the diffusion coefficient of a material is given and the average size of a sample of this material is known the relaxation decay curve can be used to determine the surface relaxivity as well as the relative size of particles present in the other samples of same material. However, this analysis is unable to provide the absolut measurement of the grain sizes. Furthermore, it is shown that the grain geometry does not influence the relaxation decay curve.

Measuring Nano- to Microstructures from Relayed Dynamic Nuclear Polarization NMR

“…It is this effect that we exploit here. This basic principle of spin diffusion relayed relaxation has been introduced and used widely in the past in both solids and solutions. − ,,− One of the particularities here is that we introduce differential relaxation into a normally diamagnetic sample by selective doping of one domain, and that we can then determine geometries by comparing polarization dynamics in experiments that are otherwise identical except for the initial conditions of the value of T 1 in the dopant (which corresponds to relayed-PRE) or, here, by changing the equilibrium polarization of the dopant with DNP.…”

Dynamic Nuclear Polarization NMR Spectroscopy of Microcrystalline Solids

“…Stretched exponential functions are typically used to model the build up of magnetization in organic solids heterogeneously doped with paramagnets. 79,80,86 The signal build-up time constant has been denoted T 1 * to differentiate it from T 1 ( 1 H). T 1 ( 1 H) is not measured here since the signal build-up is driven by the diffusion of polarization from fast relaxing/highly polarized surface nuclei in addition to longitudinal relaxation.…”

“…(Although we note that this may not always be possible since some polymorphs are sensitive to even gentle grinding. In rare cases, extreme grinding may also introduce defects into the crystal or at the surface that enhance longitudinal relaxation rates; 80,86,94 which might reduce the DNP enhancement that could be obtained.) DNP-Enhanced Solid-State NMR Spectra of Microcrystalline Sulfathiazole.…”

Nanostructure of Materials Determined by Relayed Paramagnetic Relaxation Enhancement

“… 21 Changes in T 1 in pharmaceutical materials have been observed, induced by crystal defects and production of amorphous material during formulation. 22 The relative determination of the amorphous particle sizes based on this reduction of relaxation time is described in ref ( 23 ). The authors however note that the method is unable to provide an absolute measurement of grain sizes due to too many unknowns.…”

“…This is the measured solvent T 1 , which depends on radical concentration. We note that being able to measure the relaxation rate at the surface of the domain is a big advantage over previously published 23 methods to determine particle sizes using local T 1 differences. The experiment can thus be repeated for a given sample using solutions with different radical concentrations with the only changing parameter in the spin diffusion model being (the measurable) T 1,surface , leading to more accurate fitting results.…”