Surface-enhanced Raman spectroscopy (SERS) has been widely
applied
in the identification and characterization of DNA structures with
high efficiency. Especially, the SERS signals of the adenine group
have exhibited high detection sensitivity in several biomolecular
systems. However, there is still no unanimous conclusion regarding
the interpretation of some special kinds of SERS signals of adenine
and its derivatives on silver colloids and electrodes. This Letter
presents a new photochemical azo coupling reaction for adenyl residues,
in which the adenine is selectively oxidized to (E)-1,2-di(7H-purin-6-yl) diazene (azopurine) in the
presence of silver ions, silver colloids, and electrodes of nanostructures
under visible light irradiation. The product, azopurine, is first
found to be responsible for the SERS signals. This photoelectrochemical
oxidative coupling reaction of adenine and its derivatives is promoted
by plasmon-mediated hot holes and is regulated by positive potentials
and pH of solutions, which opens up new avenues for studying azo coupling
in the photoelectrochemistry of adenine-containing biomolecules on
electrode surfaces of plasmonic metal nanostructures.