An NMR and UV–visible spectroscopic study of the principal colored component of Stil de grain lake

Water extract from rhamnus berries (Rhamnus catharticus) is the base of Stil de grain lake (also called Buckthorn lake), an ancient dye used in textiles and in paintings. In this work, the main colored component of the lake was separated and its chemical structure determined by advanced NMR techniques. The results show that quercitrin, a glucoside derivative of quercetine (3,5,7,3′,4′-pentahydroxy-flavone) is the principal colored form. This result does not agree with previous literature assignments. In this work a characterization of quercitrin in methanol and in water as a function of pH was carried out by absorption and emission UV–visible spectroscopy.