Photochemistry of Naphthoquinones

Abstract

Quinones are widely distributed in living organisms, are present in medicines and used as reagents by chemists. In nature, certain benzoquinones are so commonly found that they are called ubiquinones (ubiquitous); others, the plastoquinones, participate in the process of photosynthesis, without being directly excited by light. These processes will not be seen here. The participation of excited quinones in the generation of singlet oxygen and other reactive oxygen species (ROS) will be addressed. The photochemistry of quinones, which are colored compounds, has been studied since the mid-XIX century, with Klinger; in Part 1, after the Introduction, we will present a summary of the most relevant results, so far, mainly for naphthoquinones, starting with fundamental concepts of organic photochemistry of ketones. We will see, for example, how biological quinones can, when excited by light, deactivate without generating harmful reactive species. In Part 2 some of the spectroscopic techniques with lasers, used in contemporary photochemistry will be reviewed. And, finally, these techniques will be applied to the study of naphthoquinones related to natural products and the results will be discussed.