The effect of surface adsorption on the structure and stability of proteins is a matter of increasing interest in biotechnology. Therefore, we have examined the effect of adsorption to silica on the thermal stability of 7 proteins employing differential scanning calorimetry (DSC) and front surface fluorescence (FSF) spectroscopy. In general, it was found that surface adsorption decreased the thermal stability of the bound protein. Using lysozyme for further studies, DSC, FSF, and FTIR spectroscopies, as well as enzymatic activity measurements, were used to explore the effect of decreasing surface apolarity on stability. It was observed that increasing surface apolarity produced decreasing stability and increasing structural alteration of the adsorbed protein.
High-resolution
solid-state analysis of multicomponent molecular
systems, e.g., pharmaceutical formulations, is a great challenge.
Solid-state nuclear magnetic resonance (ssNMR) spectroscopy plays
a critical role in the characterization of solid dosage forms due
to its capabilities of chemical identification, quantification, and
structural elucidation at a molecular level. However, the low NMR
sensitivity as well as the high spectral complexity and low drug loading
of multicomponent products hinder an in-depth investigation of the
active pharmaceutical ingredient (API) at the natural isotopic abundance.
Herein, we developed two new three-dimensional (3D) ssNMR methods,
including 1H–19F–1H
and 19F–19F–1H correlations
and successfully applied them to characterize a fluorinated drug molecule,
aprepitant, and its commercial nanoparticulate formulation EMEND (Merck
& Co, Inc., Kenilworth, NJ, USA). These 1H-detection
methods utilize the significantly enhanced sensitivity and resolution
of 1H and 19F afforded by 60 kHz ultrafast magic
angle spinning (MAS) and enable the analysis of milligram samples.
The 3D techniques simultaneously provide homonuclear 1H–1H and 19F–19F, and heteronuclear 1H–19F correlations of the crystalline aprepitant
without interferences from other pharmaceutical components in the
drug product. Moreover, our results demonstrate that 19F is a highly sensitive spin for probing molecular details of fluorinated
drug substances in solid formulations, due to its high isotopic abundance,
large gyromagnetic ratio, and absence of signal interference from
pharmaceutical excipients, as well as for characterizing structural
properties of a broad range of fluorine-containing materials.
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