Evidence of Strong Guest–Host Interactions in Simvastatin Loaded in Mesoporous Silica MCM-41

Funding Information: This research was funded by the Associate Laboratory for Green Chemistry LAQV, which is financed by national funds from FCT/MEC (UID/QUI/50006/2019) and co-financed by the ERDF under the PT2020 Partnership Agreement (POCI-01-0145-FEDER—007265). This research was funded by the Interreg 2 Seas program 2014–2020, and co-funded by the European Regional Development Fund (FEDER) under subsidy contract 2S01-059_IMODE and 2S07-033_ Site Drug. This research was funded by the Program PHC PESSOA 2018 project nbr 4340/40868R. This research was funded by National Funds through FCT—Portuguese Foundation for Science and Technology, reference UIDB/00100/2020, UIDP/00100/2020, LA/P/0056/2020, UIDB/50025/2020-2023, and PTNMR (ROTEIRO/0031/2013; PINFRA/22161/2016), co-financed by ERDF through COMPETE 2020, Portugal, POCI and PORL and FCT through PIDDAC (POCI-01-0145-FEDER-007688). M.C.C. acknowledges PTNMR&i3N for the researcher contract. T. Cordeiro acknowledges Fundação para a Ciência e a Tecnologia (FCT) for the scholarship SFRH/BD/114653/2016. I. Matos acknowledges FCT for the Investigator FCT contract IF/01242/2014/CP1224/CT0008. Publisher Copyright: © 2023 by the authors.A rational design of drug delivery systems requires in-depth knowledge not only of the drug itself, in terms of physical state and molecular mobility, but also of how it is distributed among a carrier and its interactions with the host matrix. In this context, this work reports the behavior of simvastatin (SIM) loaded in mesoporous silica MCM-41 matrix (average pore diameter ~3.5 nm) accessed by a set of experimental techniques, evidencing that it exists in an amorphous state (X-ray diffraction, ssNMR, ATR-FTIR, and DSC). The most significant fraction of SIM molecules corresponds to a high thermal resistant population, as shown by thermogravimetry, and which interacts strongly with the MCM silanol groups, as revealed by ATR-FTIR analysis. These findings are supported by Molecular Dynamics (MD) simulations predicting that SIM molecules anchor to the inner pore wall through multiple hydrogen bonds. This anchored molecular fraction lacks a calorimetric and dielectric signature corresponding to a dynamically rigid population. Furthermore, differential scanning calorimetry showed a weak glass transition that is shifted to lower temperatures compared to bulk amorphous SIM. This accelerated molecular population is coherent with an in-pore fraction of molecules distinct from bulklike SIM, as highlighted by MD simulations. MCM-41 loading proved to be a suitable strategy for a long-term stabilization (at least three years) of simvastatin in the amorphous form, whose unanchored population releases at a much higher rate compared to the crystalline drug dissolution. Oppositely, the surface-attached molecules are kept entrapped inside pores even after long-term release assays.publishersversionpublishe

Nature of the structural and dynamical disorder in organic cocrystals with a true nanometric size channel-like architecture

The nature of the structural and dynamical disorder of the nanoporous organic cocrystal carbamazepine-tartaric acid designed by liquid assisted grinding is investigated through complementary solid-state NMR, X-ray diffraction and broadband dielectric spectroscopy experiments combined with molecular dynamics simulations. In this article, we especially highlight that the tartaric acid molecules present in the channel-like cocrystalline architecture show both translational and rotational dynamical disorder. Such a disorder seems only partial since tartaric acid molecules are strongly hydrogen-bonded to the carbamazepine molecules which form the channels and they thus share with them some order. Tartaric acid species are organized as one-dimension interrupted single files of molecules weakly hydrogen bonded between them. Translational dynamics occurs by small hops of about 6 to 7 Å consistent with the distance between first neighbors. At short times, it can be described as a single-file diffusion process while at longer times the classical diffusion (Fickian) is recovered. Random motions are explained by the presence of several short single files of molecules in the channel instead of just one single file. Rotational dynamics is interpreted as rotational jumps between preferred orientations. It gives rise to a change of the molecular dipole moments orientations, which are detected by dielectric relaxation spectroscopy. Freezing out of the rotational molecular mobility is detected in the temperature range [173-193] K concomitantly with the presence of a kink in the temperature evolution of the crystalline cell volume which is usually associated with the glass transition phenomenon. It reveals a remarkable link between the molecular mobility of the tartaric acid molecules and the overall crystal anharmonicity. The present findings aim to demonstrate the interest of disordered channel-like cocrystals for investigation of dynamics in nanoconfinement environments