Anthocyanins

Anthocyanins are water-soluble vacuolar pigments, which are red, purple or blue colored dependent on their pH. Their aglycon forms are called anthocyanidins. Anthocyanins belong to a group of molecules which are called flavonoids. Flavonoids are secondary plant metabolites, synthesized from the phenylpropanoid pathway. They can be found in all higher plants and divide into nine subgroups: flavanole, flavanonole, chalcone, flavonole, aurone, flavone, flavanone, isoflavone and anthocyanins.

Figure1: backbones of the different flavonoide subtypes

These substances have different functions e.g. in plants, they act as signaling molecules in plant-microbe interactions, provide pigmentation to attract pollinators and play a major key role in UV protection.  In addition, anthocyanins act as powerful antioxidants and can be found in many fruits like cherries, cranberries, blueberries, grapes and other violet fruits. The highest anthocyanin concentration was found in the seed of black soybean, which contains 2g per 100g. The American Cancer Society investigates phytochemicals like anthocyanins or the better known carotenoids, ascorbic acid, folic acid and vitamin E, because they are assumed to prevent or to treat cancer. However, there is a wide field of applications in daily products. For example they are used as food additives or for food coloring in bakery products.  

Figure 2: This plant produces anthocyanins!

A special application is in dye-sensitised solar cells (DSCs). They are necessary to build a modern DSC, also known as the Grätzel cell. The Grätzel cell was invented in 1988 by Brian O'Regan and Michael Grätzel.