Can Mesoporous Silica Speed Up Degradation of Benzodiazepines? Hints from Quantum Mechanical Investigations

This work reports for the first time a quantum mechanical study of the interactions of a model benzodiazepine drug, i.e., nitrazepam, with various models of amorphous silica surfaces, differing in structural and interface properties. The interest in these systems is related to the use of mesoporous silica as carrier in drug delivery. The adopted computational procedure has been chosen to investigate whether silica-drug interactions favor the drug degradation mechanism or not, hindering the beneficial pharmaceutical effect. Computed structural, energetics, and vibrational properties represent a relevant comparison for future experiments. Our simulations demonstrate that adsorption of nitrazepam on amorphous silica is a strongly exothermic process in which a partial proton transfer from the surface to the drug is observed, highlighting a possible catalytic role of silica in the degradation reaction of benzodiazepines.

High Resolution Magic Angle Spinning (HRMAS) Pulse Field Gradient (PFG) NMR Diffusometry Studies of Swollen Polymers

In this chapter, the combination of high resolution magic angle spinning (HRMAS) NMR spectroscopy and pulse field gradient (PFG) NMR diffusometry techniques to study solvent transport in swollen polymers is presented. The MAS suppression of magnetic susceptibility differences that exist for liquids absorbed in heterogenous polymer materials is shown to provide significant improvements in the NMR spectral resolution, thereby allowing the use of PFG NMR diffusion experiments to probe multiple chemical environments simultaneously. Recent examples of using 1H HRMAS PFG NMR experiments to measure solvent diffusion in 3D-printed siloxane polymer composites are detailed, along with an example of characterizing diffusion in methanol fuel cell anion exchange polymer membranes. These results demonstrate the power of HRMAS PFG NMR diffusometry to obtain information for complex chemical mixtures absorbed in polymers.

Supramolecular Organization in Confined Nanospaces

Empty spaces are abhorred by nature, which immediately rushes in to fill the void. Humans have learnt pretty well how to make ordered empty nanocontainers, and to get useful products out of them. When such an order is imparted to molecules, new properties may appear, often yielding advanced applications. This review illustrates how the organized void space inherently present in various materials: zeolites, clathrates, mesoporous silica/organosilica, and metal organic frameworks (MOF), for example, can be exploited to create confined, organized, and self-assembled supramolecular structures of low dimensionality. Features of the confining matrices relevant to organization are presented with special focus on molecular-level aspects. Selected examples of confined supramolecular assemblies - from small molecules to quantum dots or luminescent species - are aimed to show the complexity and potential of this approach. Natural confinement (minerals) and hyperconfinement (high pressure) provide further opportunities to understand and master the atomistic-level interactions governing supramolecular organization under nanospace restrictions.

Negative and Positive Confinement Effects in Chiral Separation Chromatography Monitored with Molecular-Scale Precision by In-Situ Electron Paramagnetic Resonance Techniques

Separation of compounds using liquid chromatography is a process of enormous technological importance. This is true in particular for chiral substances, when one enantiomer has the desired set of properties and the other one may be harmful. The degree of development in liquid chromatography is extremely high, but still there is a lack in understanding based on experimental data how selectivity works on a molecular level directly at the surfaces of a porous host material. We have prepared amino-acid containing organosilica as such host materials. Watching the rotational dynamics of chiral spin probes using electron paramagnetic resonance spectroscopy allows us to differentiate between surface adsorbed and free guest species. Diastereotopic selectivity factors were determined, and the influence of chiral surface group density, chemical character of the surface groups, pore-size, and temperature was investigated. We found higher selectivity values in macroporous solids with a rather rigid organosilica network and at lower temperature, indicating the significant effect of confinement effects. In mesoporous materials features are opposed with regards to the T-dependent behavior. From EPR imaging techniques and the resulting (macroscopic) diffusion coefficients, we could confirm that the correlations found on the microscopic level transform also to the macroscopic behavior. Thus, our study is of value for the development of future chromatography materials by design.

Multiple scale investigation of molecular diffusion inside functionalized porous hosts using a combination of magnetic resonance methods

Diffusion in organo-functionalized porous hosts could be tracked by evaluation of spin exchange processes using EPR spectroscopy.

Influence of the structural and textural properties of ordered mesoporous materials and hierarchical zeolitic supports on the controlled release of methylprednisolone hemisuccinate

To alleviate the chronic inflammation, nasal obstruction, and loss of sense of smell that produces the rhinosinusitis disease, ordered mesoporous materials and hierarchical zeolites could be used for slow and sustained corticoid (methylprednisolone hemisuccinate conjugate) release. The correlations between the delivery performance of methylprednisolone hemisuccinate and the physicochemical properties of carriers' release systems, including pore mesostructure, texture and size, and surface chemistry, have been well established. Different two-dimensional (2-D) and three-dimensional (3-D) mesostructured materials (MCM-41, SBA-15, expanded SBA-15, FDU-12, and SBA-16) were employed. In addition, for the first time to the best of our knowledge, materials based on hierarchical zeolites with additional mesoporosity (h-ZSM-5 and h-BETA zeolites) were also tested. In particular, two materials (3-D cubic mesoporous silica SBA-16 and hierarchical Beta zeolite) have been probed to be potential candidates, exhibiting high drug adsorption capacities and slow drug release rates, which is the most favourable way of drug release in the particular rhinosinusitis application. Solid-state ¹H-²⁹Si HETCOR NMR analyses confirm the strong interactions of the drug with the surface of h-BETA and 3-D SBA-16 materials, via hydrogen bonding of carboxylic, ketone, and aliphatic moieties of the methylprednisolone hemisuccinate at surface silanol sites. Because of the remarkable release performance, it is expected that 3-D mesoporous silica SBA-16 and hierarchical Beta zeolite can be attractive candidates for current applications in nasal inflammation treatments. The drug release rate can be further retarded by decreasing the pH to around 4.6; at this point more attraction forces were detected as proved by zeta-potential measurements. Therefore, a slower delivery trend of methylprednisolone hemisuccinate has been observed for all the materials, which is more pronounced in the case of SBA-15 and SBA-16.