Carotenoids nuclear magnetic resonance

Other spectroscopic methods such as infrared (ir), and nuclear magnetic resonance (nmr), circular dichroism (cd), and mass spectrometry (ms) are invaluable tools for identification and stmcture elucidation. Nmr spectroscopy allows for geometric assignment of the carbon—carbon double bonds, as well as relative stereochemistry of ring substituents. These spectroscopic methods coupled with traditional chemical derivatization techniques provide the framework by which new carotenoids are identified and characterized (16,17). 

Although saponification was found to be unnecessary for the separation and quantification of carotenoids from leafy vegetables by high performance liquid chromatography (HPLC) or open column chromatography (OCC), saponification is usually employed to clean the extract when subsequent purification steps are required such as for nuclear magnetic resonance (NMR) spectroscopy and production of standards from natural sources. 

Because carotenoids are light- and oxygen-sensitive, a closed-loop hyphenated technique such as the on-line coupling of high performance liquid chromatography (HPLC) together with nuclear magnetic resonance (NMR) spectroscopy can be used for the artifact-free structural determination of the different isomers. 

Keywords Carotenoids analysis sample preparation UV/Visible spectroscopy geometrical isomers optical isomers HPLC mass spectrometry nuclear magnetic resonance metabolites. 

In order to unequivocally identify the structure of a specific carotenoid geometrical isomer (e.g. 9-cw-lycopene) to a peak in a chromatogram, nuclear magnetic resonance (NMR) is used (Hengartner et al, 1992). 

The ability to incorporate carotenoids into pigment protein complexes allowed solid-state magic angle spinning (MAS) nuclear magnetic resonance (NMR) experiments to be carried out on isotopicaUy-labeled... 

R165 K. Holtin and K. Albert, The Use of Nuclear Magnetic Resonance Detection of LC in Carotenoid Analysis , in Carotenoids Physical, Chemical, and Biological Functions and Properties, ed. J. T. Landrum, CRC Press, Boca Raton, Fla., 2010, p. 61. 

Carotenoids have also been characterized by nuclear magnetic resonance (NMR), infrared (IR), and Raman spectroscopy as well as by x-ray analysis and mass spectrometry (6). Because of their low volatility and relatively high molecular weight, the C-40 carotenoids have not as yet been separated by gas chromatography. Currently, carotenoids are primarily isolated by liquid chromatography on solid supports. 

---