Drug–biomolecule interactions in the excited states*

Drug–biomolecule interactions in the excited state are relevant from a photobiological point of view as they can be correlated with a number of photosensitization disorders such as photocarcinogenicity, photoallergy, phototoxicity, etc. Nonsteroidal antiinflammatory 2-arylpropionic acids and antibacterial fluoroquinolones have been selected as typical examples of photoactive drugs. Protein photosensitization has revealed photoadduct formation; the major amino acids involved are Tyr, Trp, and His. Generation of specific antibodies has allowed us to identify relevant structures of the drug epitopes. Then, drugs have been submitted to systematic steady-state and time-resolved studies on their photophysical properties, alone and in the presence of biomolecules: proteins, DNA, and their simple building blocks. The results are discussed in the framework of the chemical mechanisms underlying photosensitization by drugs and also in connection with the potential of drug excited states as (chiral) reporters for the binding sites of biomolecules.