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Bridging Structural and Dynamical Models of a Confined Sodium Nitroprusside Complex

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journal contribution
posted on 04.09.2018, 00:00 by Fabien Deligey, Sabine Bouguet-Bonnet, Abdelatif Doudouh, Pierre-Louis Marande, Dominik Schaniel, Axel Gansmüller
Sodium nitroprusside (SNP), an active pharmaceutical ingredient, is encapsulated in biocompatible amorphous silica matrices and characterized by solid-state NMR. Through complementary NMR and pair distribution function (PDF) study, we previously showed that when confined in 1–2 nm sized nanopores of an amorphous silica matrix, the complex displays a “liquid like” isotropic motion (NMR) but still retains an associated anion/cation preferential arrangement (PDF). In this study, we present new insights into the physical state of the confined drug to explain the coexistence of these two seemingly contradictory characteristics. By performing temperature-dependent T1 relaxation experiments on the samples with different hydration levels, we retrieve respective motional activation energies for all three guest species inside the pores (sodium cations, nitroprusside anions, and water). For the hydrated samples, we identify a temperature range where results ascertain isotropic but correlated ionic motion of the SNP ions. In contrast, for the driest samples, we detect NMR interactions that unravel adsorbed guest populations interacting with the pore surface. These descriptions of SNP dynamical properties clarify its unusually high ability to crystallize inside the mesoporous matrices.