Flavonols and flavonoids: UV spectroscopic analysis

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  • Published: Nov 1, 2016
  • Author: David Bradley
  • Channels: UV/Vis Spectroscopy
thumbnail image: Flavonols and flavonoids: UV spectroscopic analysis

Flavoursome spectroscopy

Generic structure of a flavonol showing the A and B rings linked via a heterocyclic C ring and the position of common substituent functional group, R

Various spectroscopic methods, including UV-Vis, infrared, Raman, nuclear magnetic resonance spectroscopy and electrospray ionization mass spectrometry have been used to investigate the relationship between the molecular structure and biological activity of hydroxyflavonol metal complexes. UV-Vis emerges as the most efficient in understanding the interaction of flavonols with DNA.

Flavonoids, of which flavonols are a sub-group, have been investigated for many years because of their purported antioxidant activity, the capacity to scavenge free radicals, their action on digestions, anti-inflammatory properties and even their ability to act against pathogens, whether bacteria, fungi or viruses and even their antimutagenic and anticarcinogenic potential. Polyphenolic flavonols molecules found in a wide variety of foods can have hydroxyl groups at various positions. These compounds can chelate metal ions as well donate hydrogen atoms to free radicals. Moreover, the metal complexes can often be more physiologically and usefully active than the free compounds.

Now, Mariola Samsonowicz and Ewa Regulska Bialystok of the University of Technology, Division of Chemistry, in Bialystok, Poland, have reviewed the spectroscopic analyses of flavonols from fruit and vegetables and other foods derived from plants. The team points out that so far approximately 200 different flavonols from plants are known to science. That number is likely to be much higher given the diversity of plant life, but these perhaps represent the most familiar and the most pertinent to studies of the impact of eating foods rich in flavonols on human health.

Fruit and veg

The most well known sources include the likes of yellow onion, kale, broccoli and scallions and fruits of the Ericaceae (edible examples of which are cranberry and blueberry) and Rutaceae (citrus) families. Flavonols are biosynthesised by light activation and so are present mostly in the skin and leaves, or aerial parts of plants. The flavonols comprise two aromatic rings joined by a three-carbon chain that makes an oxygenated heterocyclic ring and are substituted with various functional groups, commonly hydroxyl groups.

The team's survey of analytical techniques used in investigations of flavonols suggest that there are many practical tools to study the interaction of flavonols and their metal complexes with DNA, including UV–Vis and fluorescence spectroscopy, electrophoresis, voltammetric and viscometric techniques. Additionally, fluorescence spectroscopy and UV–Vis absorption are perhaps the most effective methods because they are particularly sensitive, simple, low cost and efficient.

Efficient UV

A point that is more pertinent for the UV spectroscopist is that in general, if a small molecule interacts with DNA, then the observed hypochromism (changes in absorbance) and red shift (changes in the position of the band) are most likely to be apparent. These changes indicate intercalation of the small molecule into the DNA offering a strong interaction in the molecular stack between the aromatic chromophore and the DNA's base pairs wherein UV–Vis spectroscopy comes into its own.

Related Links

Spectrochim Acta Part A: Mol Biomol Spectrosc 2017, 173, 757-771: "Spectroscopic study of molecular structure, antioxidant activity and biological effects of metal hydroxyflavonol complexes"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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