Dynamical properties of nimodipine molecules confined in SBA-15 matrix

NMR relaxometry in an investigation of the kinetics of the recrystallization of a three-phase system

The method of ¹H Nuclear Magnetic Resonance (NMR) relaxometry is applied to investigate the kinetics of the recrystallization of an active pharmaceutical ingredient (felodipine) from the amorphous phase of its physical mixture with a polymer (polyvinylpyrrolidone, PVP). Comparison of the recrystallization results obtained for amorphous felodipine and its mixtures with PVP shows that the recrystallization process of API is faster in the mixtures and depends on the content of water in the system. The free induction decay (FID) for protons that were detected are composed of three components, and the loss of water from PVP strongly influences the part characterized by the longest spin-spin lattice relaxation time. Analysis of the FID of the physical mixture indicates that the content of water does not change during the recrystalization process. The study shows that the T₁¹H NMR relaxometry method is very useful for analysing the composition of a three-phase mixture and the recrystallization process.

Exploring molecular reorientations in amorphous and recrystallized felodipine at the microscopic level

Molecular reorientations were studied in amorphous, partially and fully recrystallized felodipine (calcium channel blocker, a drug from the family of 1',4-dihydropyridine) using a set of experimental methods: high-resolution solid-state nuclear magnetic resonance (NMR), relaxometry NMR and quasielastic neutron scattering (QENS). The results were compared with molecular dynamics in crystalline felodipine previously investigated [A. Pajzderska, K. Drużbicki, M. A. Gonzalez, J. Jenczyk, J. Mielcarek, J. Wąsicki, Diversity of Methyl Group Dynamics in Felodipine: a DFT Supported NMR and Neutron Scattering Study, CrystEngComm, 2018, 20, 7371-7385]. The kinetics of the recrystallization was also studied. The most stable sample was the sample stored in a closed ampoule (at room temperature, in 0% RH) and its complete recrystallization lasted 105 days. In the fully recrystallized sample, the same molecular reorientation identified in the crystalline form was detected, so reorientations of all methyl groups and the ethyl ester fragment. In the partially recrystallized sample, static disorder caused by the two positions of both side chains was revealed. In the amorphous sample the reorientation of all methyl groups was analyzed and the distribution of correlation times and energy barriers connected with the loss of long-range ordering and disorder of side chains were analyzed. Additionally, inhibition of reorientation in the ethyl ester fragment was observed.

Characterization and evaluation of different mesoporous silica kinds as carriers for the development of effective oral dosage forms of glibenclamide

This work evaluated the suitability of various mesoporous silicas as carriers for developing an oral formulation endowed with improved dissolution properties of glibenclamide, hypoglycemic agent poorly water-soluble. The different silicas were examined for solid-state, morphology, and technological and physical-chemical properties (granulometry, specific surface area, wettability, water content, water activity, apparent density, flowability, compactability). A pairwise comparison allowed a ranking, by importance order, of the parameters examined and, for each parameter, a score was assigned to each silica type. Data statistical treatment (JMP software) indicated Neusilin®US2 and Syloid®XDP3150 as the best materials. Different loading methods were tested: physical mixing; addition of drug dissolved in a volatile solvent, subsequently evaporated; addition of drug dissolved in a solvent. Methods involving drug dissolution enabled drug amorphization and intimate dispersion within the silica porous structure. Dissolution tests indicated Syloid®XDP3150 as the most effective silica in enhancing drug dissolution properties, providing a release rate clearly faster than from commercial tablets. Drug amorphization, improved wettability, increased surface area of the drug, finely dispersed into the highly porous silica, were the main factors responsible for this finding. Moreover, the obtained results suggested that drug dissolution rate can be properly tuned, based on the suited choice of the silica type.

Enhancing the dissolution of phenylbutazone using Syloid® based mesoporous silicas for oral equine applications

Three mesoporous silica excipients (Syloid® silicas AL-1 FP, XDP 3050 and XDP 3150) were formulated with a model drug known for its poor aqueous solubility, namely phenylbutazone, in an attempt to enhance the extent and rate of drug dissolution. Although other forms of mesoporous silica have been investigated in previous studies, the effect of inclusion with these specific Syloid® silica based excipients and more interestingly, with phenylbutazone, is unknown. This work reports a significant enhancement for both the extent and rate of drug release for all three forms of Syloid® silica at a 1:1 drug:silica ratio over a period of 30 min. An explanation for this increase was determined to be conversion to the amorphous form and an enhanced drug loading ability within the pores. Differences between the release profiles of the three silicas were concluded to be a consequence of the physicochemical differences between the three forms. Overall, this study confirms that Syloid® silica based excipients can be used to enhance dissolution, and potentially therefore bioavailability, for compounds with poor aqueous solubility such as phenylbutazone. In addition, it has been confirmed that drug release can be carefully tailored based on the choice of Syloid® silica and desired release profile.

Understanding Surface and Interfacial Chemistry in Functional Nanomaterials via Solid-State NMR

Surface and interfacial chemistry is of fundamental importance in functional nanomaterials applied in catalysis, energy storage and conversion, medicine, and other nanotechnologies. It has been a perpetual challenge for the scientific community to get an accurate and comprehensive picture of the structures, dynamics, and interactions at interfaces. Here, some recent examples in the major disciplines of nanomaterials are selected (e.g., nanoporous materials, battery materials, nanocrystals and quantum dots, supramolecular assemblies, drug-delivery systems, ionomers, and graphite oxides) and it is shown how interfacial chemistry can be addressed through the perspective of solid-state NMR characterization techniques.

Influence of Surface Chemistry on Ibuprofen Adsorption and Confinement in Mesoporous Silicon Microparticles

The effect of adsorption and confinement on ibuprofen was studied by immersion loading the molecules into porous silicon (PSi) microparticles. The PSi microparticles were modified into thermally oxidized PSi (TOPSi) and thermally hydrocarbonized PSi (THCPSi) to evaluate the effects of the loading solvent and the surface chemistry on the obtainable drug payloads. The payloads, location, and the molecular state of the adsorbed drug were evaluated using thermal analysis. The results showed that after the adsorption of ∼800 mg/cm³ (w_drug/v_pores) of drug into the mesopores, depending on the solvent used in the immersion, the drug began to rapidly recrystallize on the external surface of the particles. Moderate concentrations, however, enabled payloads of 800-850 mg/cm³ without excessive surface crystallization, and thus, there was no need for rinsing the samples to remove the externally crystallized portion. The results showed that the confined ibuprofen forms nanocrystals inside of the mesopores after approximately 200 mg/cm³ payloads were obtained, accounting for half of the adsorbed drug amount. The presence of both crystalline and noncrystalline phases was further characterized using variable temperature solid-state nuclear magnetic resonance (NMR) measurements. The interactions between the drug molecules and the pore walls of TOPSi and THCPSi were observed using Fourier transform infrared and ¹H NMR spectroscopies, and the hydrogen bonding between the silanol groups of TOPSi and the adsorbed ibuprofen was confirmed, but having only limited effect on the overall state of the confined drug. In vitro drug permeation studies in Caco-2 and Caco-2/HT29 cocultures showed that the adsorption onto hydrophilic or hydrophobic PSi microparticles had no significant effects on the ibuprofen permeation, whether the drug was partially nanocrystalline or completely in a liquidlike state.