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 eva… Show more
“…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.…”
We are grateful to Matthew Conley and Christophe Coperet from ETH Zurich for providing the mesoporous silica materials. We are grateful to Prof. P. Tordo, Dr. O. Ouari, and Dr. G. Casano (Aix-Marseille Universite, France) for providing the biradicals used in the DNP NMR experiments.International audienceWe show how dynamic nuclear polarization (DNP) NMR can be used in combination with models for polarization dynamics to determine the domain sizes in complex materials. By selectively doping a source component with radicals and leaving the target undoped, we Can measure experimental polarization buildup curves which can be compared with simulations based on heterogeneous distributions of polarization-within the sample. The variation of the integrated DNP enhancement as a function of the polarization time is found to be characteristic of the geometry. We demonstrate the method experimentally on four different systems where we successfully determine domain sizes between 200 and 20 000 nm, specifically in powdered histidine hydrochloride monohydrate) pore lengths of mesoporous silica materials, and two domain sizes in two component polymer film coatings. Additionally, we find that even in the apparently homogeneous frozen solutions used as polarization sources in most DNP experiments, polarization is relayed from protons near the radicals to the bulk of the solution by spin diffusion, which explains the experimentally observed buildup times in these samples
“…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.…”
We are grateful to Matthew Conley and Christophe Coperet from ETH Zurich for providing the mesoporous silica materials. We are grateful to Prof. P. Tordo, Dr. O. Ouari, and Dr. G. Casano (Aix-Marseille Universite, France) for providing the biradicals used in the DNP NMR experiments.International audienceWe show how dynamic nuclear polarization (DNP) NMR can be used in combination with models for polarization dynamics to determine the domain sizes in complex materials. By selectively doping a source component with radicals and leaving the target undoped, we Can measure experimental polarization buildup curves which can be compared with simulations based on heterogeneous distributions of polarization-within the sample. The variation of the integrated DNP enhancement as a function of the polarization time is found to be characteristic of the geometry. We demonstrate the method experimentally on four different systems where we successfully determine domain sizes between 200 and 20 000 nm, specifically in powdered histidine hydrochloride monohydrate) pore lengths of mesoporous silica materials, and two domain sizes in two component polymer film coatings. Additionally, we find that even in the apparently homogeneous frozen solutions used as polarization sources in most DNP experiments, polarization is relayed from protons near the radicals to the bulk of the solution by spin diffusion, which explains the experimentally observed buildup times in these samples
“…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.…”
Section: ■ Results and Discussionmentioning
confidence: 99%
“…(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.…”
Dynamic nuclear polarization (DNP) solid-state NMR has been applied to powdered microcrystalline solids to obtain sensitivity enhancements on the order of 100. Glucose, sulfathiazole, and paracetamol were impregnated with bis-nitroxide biradical (bis-cyclohexyl-TEMPO-bisketal, bCTbK) solutions of organic solvents. The organic solvents were carefully chosen to be nonsolvents for the compounds, so that DNP-enhanced solid-state NMR spectra of the unaltered solids could be acquired. A theoretical model is presented that illustrates that for externally doped organic solids characterized by long spin-lattice relaxation times (T(1)((1)H) > 200 s), (1)H-(1)H spin diffusion can relay enhanced polarization over micrometer length scales yielding substantial DNP enhancements (ε). ε on the order of 60 are obtained for microcrystalline glucose and sulfathiazole at 9.4 T and with temperatures of ca. 105 K. The large gain in sensitivity enables the rapid acquisition of (13)C-(13)C correlation spectra at natural isotopic abundance. It is anticipated that this will be a general method for enhancing the sensitivity of solid-state NMR experiments of organic solids.
“… 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.…”
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confidence: 99%
“…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.…”
Particle and domain sizes strongly
influence the properties of
materials. Here we present an NMR approach based on paramagnetic relaxation
enhancement (PRE) relayed by spin diffusion (SD), which allows us
to determine lengths in the nm−μm range. We demonstrate
the method on multicomponent organic polymer mixtures by selectively
doping one component with a paramagnetic center in order to measure
the domain size in a second component. Using this approach we determine
domain sizes in ethyl cellulose/hydroxypropyl cellulose film coatings
in pharmaceutical controlled release formulations. Here we measure
particle sizes ranging from around 50 to 200 nm.
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