Quercetin conjugated to hyaluronic acid: synthesis, UV–Vis and antioxidant activity characterization by reaction on Fe(III)

Quercetin is a bioactive compound with well-documented antioxidative properties responsible for its significant pharmacological potential. However, the employment of quercetin is severely constrained by poor water solubility and limited stability under oxidative conditions. To overcome these limitations, a green synthetic strategy was developed to conjugate quercetin to a hydrophilic natural polysaccharide, such as hyaluronic acid. The final aim was the enhancement of the bio-delivery of this natural flavonoid. Likewise, the important issue of the chemical integrity/ stability of the quercetin was thoroughly assessed, through a deep UV–vis spectroscopic analysis. Furthermore, to demonstrate that quercetin covalently bound to hyaluronic acid retains the reducing activity of its free form, an oxidative assay based on the Fe(III)/ Fe(II) redox couple was developed.