Flavones hydrophobicity

As previously mentioned, certain flavonoids can penetrate into the hydrophobic core of membranes, a feature that mainly relies on their hydrophobic character, which is dictated by flavanoid chemical structure and spatial conformation. When flavonoid hydrophobicity was assessed from the partition coefficient between ra-octanol and an aqueous solution, the following order of hydrophobicity was observed flavone, genistein > eriodictyol, myricetin, quercetin, kaempferol, hesperetin, daidzein > > galangin, morin, flavanone, naringenin, taxifolin (Table 4.1). 

Additionally, it was noticed that flavones were slightly more hydrophobic than flavanones possessing the same number of hydroxyl groups [103]. Flavonols turned out to be the least hydrophobic from all the compounds studied. The degree of DPH fluorescence quenching in PC liposomes by flavonoids was used as a measure of the relative membrane affinity of these... 

Recently performed studies on structure-activity relationships for inhibition of BCRP by flavonoids showed that the presence of the 2,3-double bond in ring C, ring B attached at position 2, an OH group at position 5, lack of hydroxylation at position 3, and hydrophobic groups substituted at positions 6, 7, 8, or 4 are favorable for BCRP modulation [239]. The studies were carried out with five flavonoid subclasses flavones, isoflavones, flavanones, flavonols, and chalcones (Figs. 2 and 6). For several compounds the 50% in-... 

Two-phase solvent systems composed of chloroform-methanol-water at various volume ratios are frequently used for the separation of moderately hydrophobic compounds, including flavone aglycones, phenylpropanoids, iridoid glycosides, and so forth [6]. 

Flavones consist chiefly of glycosides of luteolin, chrysin, and apigenin. They are less common in fruits [8]. Polymethoxylated flavones, the most hydrophobic flavonoids, present in citrus fruits (mainly in the peel, the nonedible part of the fruit) are tangeretin and nobiletin. Apigenin and chrysin possess anti-inflammatory and free-radical scavenging properties in several cancer cell lines and inhibit tumor cell invasion, metastasis, and mitogen-activated protein kinases (MAPK) and their downstream oncogenes [26]. 

However, some substances whose presence is not welcomed remain at least in part through all these stages with the main bulk of the protein, owing to their ability to complex with it by hydrogenbonding or by hydrophobic-hydrophobic interaction. These include nucleic acids, polyphenols and phenolic acids, iso-flavones and, possibly, saponins. It must be added that, though there is evidence that some interference with protein utilisation may still occur, these probably do not represent dangerous toxic hazards. 

---