Cinchona alkaloids are well-known antimalarial compounds also used in asymmetric synthesis in organic chemistry. In this work, vibrational spectra of quinine, quinidine, cinchonine, and cinchonidine were acquired and interpreted on the basis of theoretical calculations. Normal Raman spectra of the alkaloids in solution exhibit similar patterns and cannot be used for differentiation between the derivatives (e.g. quinine and cinchonidine) and corresponding pseudoenantiomers (e.g. quinine and quinidine). Thus, Raman Optical Activity (ROA) method was applied to show distinct differences related to the configuration of chiral atoms. ROA allowed unequivocal identification of the pseudoenantiomers based on the sign of the characteristic bands from a single measurement. The experiments were supported by the theoretical approach including conformational study followed by wavenumber calculations and Potential Energy Distribution (PED) analysis. For quinine, vibrational spectroscopy was additionally used to show its structural changes in aqueous solutions at various pH and its distribution in a pharmaceutical product. Spatial distribution of quinine in a drug was observed by the FT-Raman mapping technique.
The composition of the lung tissue of mice was investigated using Raman confocal microscopy at 532 nm excitation wavelength and was supported with various staining techniques as well as DFT calculations. This combination of experimental and theoretical techniques allows for the study of the distribution of lung lipofibroblasts (LIFs), rich in vitamin A, as well as the chemical structure of vitamin A. The comparison of the Raman spectra derived from LIFs with the experimental and theoretical spectra of standard retinoids showed the ability of LIFs to store all-trans retinol, which is partially oxidized to all-trans retinal and retinoic acid. Moreover, we were able to visualize the distribution of other lung tissue components including the surfactant and selected enzymes (lipoxygenase/glucose oxidase).
In this paper, a novel approach to analyze in situ (−)-bornyl acetate (BA) in pichtae essential oil (Siberian fir needle oil, Abies sibirica oil) by means of Raman optical activity (ROA) is reported. As part of this approach, a conformational study in the gas phase of (+)-and (−)-BA has been carried out, predicting the presence of three conformers for each enantiomer at 298.15 K. The structures of these conformers were optimized with density functional theory with the Becke 3LYP functional and 6-311++g * * basis set. Subsequently, the Raman and ROA spectra were simulated in order to compare them with the experimentally measured spectra of the neat enantiomers of BA. Finally, the combination of Raman and ROA spectroscopy as well as DFT calculations was successfully applied not only for the detection of BA but also for the determination of the specific enantiomer of BA present in the investigated pichtae essential oil samples. Thus, the ROA technique described here has the potential to be used as a fast and easy commercial method to control the quality of essential oils.
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