Flavone conjugates

Chrysoeriol-7-0-(2"-0-apiosyl)glucoside Figure 1.6 Flavone conjugates occurring in celery. 

Klejdus, B., D. Vitamvasova-Sterbova, and V. Kubafl. 2001. Identification of iso-flavone conjugates in red clover (Trifolium pratense) by liquid chromatography-mass spectrometry after two-dimensional solid-phase extraction. Anal. Chim. Acta 450(l-2) 81-97. 

Figure 7.22 The colour of red, yellow and orange bell peppers is due to the respective accumulation of lutein, zeathanthin and capsanthin. Flavonol and flavone conjugates also occur.

The UV spectra of all flavonoidal alkaloids is related entirely to the flavonoid part of the molecule. Table I lists the data reported for each alkaloid. Flavones exhibit maxima in the region of 270-325 nm whereas the flavanones show maxima at about 250-320 nm. The flavan vochysine shows an absorbtion only at 275 nm since there is no conjugation system in ring C. 

There are few studies on vacuolar importation of flavonoids other than anthocyanins and PAs. Klein et al. reported uptake of flavone glycosides by isolated H. vulgare primary leaf vacuoles via a vacuolar H -ATPase linked mechanism,and by vacuoles from Secale cereale (rye) mesophyll via a possible ABC transporter mechanism. Li et al. "" found medicarpin conjugated to glutathione was also sequestered by an ABC transporter mechanism. 

Klein, M. et al., A membrane-potential dependant ABC-like transporter mediates the vacuolar uptake of rye flavone glucuronides regulation of glucuronide uptake by glutathione and its conjugates. Plant J., 21, 289, 2000. 

Electron impact mass spectral data for conjugated, reduced and higher flavonoids have been summarized (B-75MI22201) and a review of electron impact, chemical ionization and field desorption mass spectra of flavones, flavonols, isoflavones and flavanones has been published (B-80MI22201). 

Flavones show antioxidant activity in different models. They neutralize free radicals, complex iron ions, and can prevent lipid oxidation (Pietta, 2000). This antioxidant activity is related to the phenolic hydroxyls present on the flavone nucleus, and the presence of ortho-dihydroxyl grouping (catechol groups) is known to be particularly effective for antioxidant activity. Conjugations with sugars always decrease the antioxidant activity, but can have positive effects on the solubility of the flavonoids in aqueous systems. 

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