Spectroscopic detection of chiral compounds is often hampered by a low sensitivity. For Raman optical activity (ROA), the signal can be dramatically increased in surface-enhanced experiments. So far, however, reproducible surface-enhanced ROA (SEROA) spectra were obtained for a reporter molecule only via induced chirality, and the intensities were just proportional to the Raman scattering. In the present study, we show that the signal can be substantially increased if colloidal silver nanoparticles are prepared already in the presence of a chiral analyte. In this case, both the analyte's and reporter's bands are visible. In addition, some experiments provided bisignate SEROA patterns, thus significantly enhancing information about the molecular structure provided by this spectroscopic method. Increased electronic circular dichroism (ECD) of the capped aggregated colloids suggests that ECD and polarized Raman scattering (ECD-Raman) contribute to the monosignate SEROA intensities, while well-dispersed nonaggregating colloids are important for observation of true (bisignate) molecular vibrational SEROA.

• Keywords
• chiral analyte capped colloid, chirality, electronic circular dichroism, silver nanoparticles, surface-enhanced Raman optical activity,
• Publication type
• Journal Article MeSH

Most currently marketed pharmaceuticals are manufactured in the solid state, where the bioavailability of the active pharmaceutical ingredient (API) can be optimized through different polymorphs, cocrystals, solvates, or salts. Efficient techniques are needed to monitor the structure of pharmaceuticals during production. Here, we explore the potential of linearly and circularly polarized Raman microscopy for distinguishing three polymorphs of sofosbuvir, an antiviral drug used to treat hepatitis C. Raman spectra were recorded on a Raman microscope for a polycrystalline API diluted in a KBr matrix. To understand spectral features including the low-frequency region, we simulated band frequencies and intensities using quantum-chemical computational strategies based on cluster and transfer approaches. Very good agreement was achieved between simulated and experimental intensities. The 20 to 200 cm-1 wavenumber region appeared particularly useful for polymorph discrimination already based on unpolarized measurements. The depolarization ratios obtained from linearly polarized Raman spectra made the distinction even more reliable. Moreover, circularly polarized Raman spectra and normalized degrees of circularity provided useful additional information and revealed several tentative markers of the different polymorphs of sofosbuvir. Although in some spectral regions the differences were less obvious, the results indicate that polarized Raman microscopy is a handy tool for discriminating between polymorphs of APIs and other compounds.

• Publication type
• Journal Article MeSH

The physical stability of peptide-based drugs is of great interest to the pharmaceutical industry. Glucagon-like peptide 1 (GLP-1) is a 31-amino acid peptide hormone, the analogs of which are frequently used in the treatment of type 2 diabetes. We investigated the physical stability of GLP-1 and its C-terminal amide derivative, GLP-1-Am, both of which aggregate into amyloid fibrils. While off-pathway oligomers have been proposed to explain the unusual aggregation kinetics observed previously for GLP-1 under specific conditions, these oligomers have not been studied in any detail. Such states are important as they may represent potential sources of cytotoxicity and immunogenicity. Here, we identified and isolated stable, low-molecular-weight oligomers of GLP-1 and GLP-1-Am, using size-exclusion chromatography. Under the conditions studied, isolated oligomers were shown to be resistant to fibrillation or dissociation. These oligomers contain between two and five polypeptide chains and they have a highly disordered structure as indicated by a variety of spectroscopic techniques. They are highly stable with respect to time, temperature, or agitation despite their noncovalent character, which was established using liquid chromatography-mass spectrometry and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. These results provide evidence of stable, low-molecular-weight oligomers that are formed by an off-pathway mechanism which competes with amyloid fibril formation.

• Keywords
• aggregation, amyloid, glucagon-like peptide 1, oligomers, self-assembly,
• MeSH
• Amyloid chemistry   MeSH
• Amyloid beta-Peptides chemistry   MeSH
• Diabetes Mellitus, Type 2 * MeSH
• Chromatography, Gel MeSH
• Glucagon-Like Peptide 1 * MeSH
• Humans MeSH
• Peptide Fragments chemistry   MeSH
• Peptides MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Amyloid MeSH
• Amyloid beta-Peptides MeSH
• Glucagon-Like Peptide 1 * MeSH
• Peptide Fragments MeSH
• Peptides MeSH