Nanoparticles mediated chiral interactions of pharmaceutical compounds: a combined SERS and DFT study

The investigation of pharmaceutical compounds by means of Raman spectroscopy has attracted much interest in the last years. The method allows getting information about structural properties of different molecules based on... [ view full abstract ]

The investigation of pharmaceutical compounds by means of Raman spectroscopy has attracted much interest in the last years. The method allows getting information about structural properties of different molecules based on their specific vibrational structure. Nowadays Raman spectroscopy is gaining popularity in different areas of the pharmaceutical industry mainly due to its ability to provide information on the fundamental vibrational bands (the fingerprint region), offering a high degree of specificity in analysis1. It also forms an ideal complement for existing methods of analysis such as nuclear magnetic resonance, mass spectrometry and elemental analysis.
On the other hand chiral recognition and differentiation in living organisms represents one of the most intriguing natural phenomena, which assures in the organism a high fidelity transfer of the molecular information. This phenomenon has a significant role in the pharmaceutical industry, since chirality plays a key role in the development of target drug candidates, being a structural variable parameter that needs elucidation. In this context, the subject of chiral purity gained a particular importance in the pharmaceutical industry.
In this paper we will show that by taking advantage of the unique plasmonic properties of noble metal nanoparticles, the chiral separation of propranolol enantiomers was successfully studied and proved by Surface-Enhanced Raman Spectroscopy (SERS)2. The quantum chemistry calculations of native cyclodextrin - propranolol enantiomers complexes have been used as a further proof of the proposed interaction mechanism. It has been observed (experimentally and theoretically) that β-cyclodextrin (compared with the other two classes of native α and γ cyclodextrins) had the best chiral recognition ability for propranolol enantiomers, hence producing the largest difference in the SERS spectra of propranolol enantiomers - native cyclodextrin complexes.