THF is a cyclic ether

Quercetin:

• Very soluble in ether, methanol
• soluble in ethanol, acetone, pyridine, acetic acid
• Soluble in alcohol and glacial acetic acid;
• insoluble in water

I have attached one article and one document about solubility of Quercetin. I hope they would be useful.

https://pubchem.ncbi.nlm.nih.gov/compound/Quercetin#section=Solubility

Calculating the polarity of the keratin by the Fedors method, the polarity is 33.84 MPa ^ 1/2, the polarity of (THF) tetrahydrofuran is 18.15 MPa^1/2. In addition to the above, and taking into account the data presented by Mina Karimi-Avargani, the probability that keratin is soluble in THF is low.

Polarity of THF: Handbook of solubility parameter (Allan F. M. barton) Pg. 136

We do have the experience to dissolve quercetin in various solvent and you could try differently for your application; acetone, methanol, alcohol, DMSO etc...However, it might not really stable if you deal with aqueous-based solution for any further evaluation. Thanks.

Dear Zeinab Farouk Akl just in case that this question is still of interest to you: Even if you have only a limited amount of quercetin available, it would be absolutely safe to do a quick solubility experiment yourself. Just take e.g. 100 mg of your quercetin and add THF until it is completely dissolved. This will show you immediately how soluble it is. You can always recover the material without any loss by evaporating the solvent.

According to the useful link provided by Mina Karimi-Avargani quercetin is very soluble in diethyl ether and methanol, and soluble in ethanol. So THF should also be a good solvent. In this context please have a look at the following potentially useful articles which you can keep for future reference:

On the Solubility of Quercetin

https://core.ac.uk/download/pdf/205809123.pdf

(see attached pdf file)

and

Solubility of Flavonoids in Organic Solvents

Article Solubility of Flavonoids in Organic Solvents

The second article has been posted by the authors a public full text, so that you can freely download it as pdf file.

Good luck with your research and best wishes, Frank Edelmann