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Pure Appl. Chem., 2009, Vol. 81, No. 9, pp. 1687-1694

Published online 2009-08-19

Photochemistry of anthocyanins and their biological role in plant tissues

Frank H. Quina1*, Paulo F. Moreira, Jr.1, Carolina Vautier-Giongo2, Daniel Rettori2,3, Rita F. Rodrigues4, Adilson A. Freitas4, Palmira F. Silva4 and António L. Maçanita4

1 Instituto de Química, Universidade de São Paulo, CP 26790, São Paulo 05513-970, Brazil
2 Departamento de Ciências Exatas e da Terra, Universidade Federal de São Paulo, Diadema, SP, Brazil
3 Faculdade de Farmácia, Universidade Bandeirante de São Paulo, São Paulo, Brazil
4 Centro de Química Estrutural, Instituto Superior Técnico, Technical University of Lisbon, Portugal

Abstract: Anthocyanins, the major red, purple, and blue pigments of plants, absorb visible as well as UV radiation and are effective antioxidants and scavengers of active oxygen species. In plant leaves, one of the functional roles proposed for anthocyanins is protection of the photosynthetic apparatus from the effects of excess incident visible or UV-B radiation and photooxidative stress. In essence, a photoprotective role requires that the excited singlet states of both complexed and uncomplexed anthocyanins deactivate back to the ground state so quickly that intersystem crossing, photoreaction, and diffusion-controlled quenching processes cannot compete. Studies of the photochemical properties of synthetic analogs of anthocyanins and of several naturally occurring anthocyanins show that this is indeed the case, uncomplexed anthocyanins decaying back to the ground state via fast (subnanosecond) excited-state proton transfer (ESPT) and anthocyanin-copigment complexes by fast (subpicosecond) charge-transfer-mediated internal conversion.