Report No xxxx - Instytut Fizyki JÄ drowej PAN

1 H MAS NMR OF FLAVONOIDS
Katarzyna Paradowska*, Agnieszka Zielińska*, Iwona Wawer*, Wacław Kołodziejski**
*Department of Physical Chemistry , Faculty of Pharmacy, Medical University of Warsaw,
Banacha 1, 02-097 Warsaw, Poland; **Department of Inorganic and Analytical Chemistry,
Faculty of Pharmacy, Medical University of Warsaw, Banacha 1, 02097 Warsaw, Poland
Flavonoids, polyphenol-type compounds with several OH groups are widely
distributed in plants. 1 H and 13 C NMR solution spectra of naturally occurring flavonoids and
flavonoid glycosides are routinely used for their identification in plant material. Since
antioxidant and radical scavenging activity of flavonoids depends on their molecular
structure, it is important to collect data on the preferred conformation and the intramolecular
and intermolecular interactions. There are only few X-ray crystallographic data, because
suitable single crystals of flavonoids are difficult to obtain. Therefore, solid state NMR can be
a complementary source of information. 13 C CPMAS NMR spectra for a series of flavonoids
were studied previously [1], enabling the conclusions as to the orientation of OH groups in the
solids. According to our knowledge there was no 1 H NMR study of solid flawonoids. Large
dipolar coupling for 1 H- 1 H interaction of 20-50 kHz cause that this interaction cannot be
averaged out fully in standard MAS experiment. Usually, the spectra of organic solids
obtained with low rotational speed give broad signals covering whole spectral region [2].
1 H MAS spectra of flavonoids: chrisin, kaempferol, morin and quercetin were recorded on
a Bruker DSX-400 wide bore spectrometer equipped with a BL 2.5 mm probehead enabling
high speed rotation. The samples were spun at 32 kHz in a ZrO 2 rotor.
The spectra recorded with rotational speed of 32 kHz exhibited broad signal with
maximum at ca. 7 ppm, however the resonances of protons involved in an intramolecular
hydrogen bond C5-OH…O=C at ca. 10.5 ppm can be distinguished.
Keywords: flavonoids, 1 H MAS NMR, hydrogen bonds
1. I. Wawer and A. Zielinska, Magn. Reson. Chem., 39 (2001) 374-380
2. A.Temeriusz, M.Rowińska, K.Paradowska, I.Wawer, Carbohydr. Res., 338 (2003) 183-188
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