Photochemistry of the hemiketal form of anthocyanins and its potential role in plant protection from UV-B radiation

Abstract

There is presently strong evidence that anthocyanins protect plant tissues from excessive solar radiation. In support of this, we have shown that the red flavylium form of anthocyanins (AH+) dissipates more than 99% of the absorbed radiation energy into heat through a series of ultra-fast excited-state processes, among which excited-state proton transfer to water plays the major role. In this work, it is shown for the first time that the less exuberant (colorless) hemiketal form of three common anthocyanins (pelargonin, cyanin, and malvin) is equally efficient at dissipating the absorbed (UV-B) radiation into heat by fast photo-tautomerization, which yields the cis-chalcone form in its ground state in a few picoseconds.