UV-induced hydrogen-atom elimination and migration of 9-methyladenine in low-temperature noble-gas matrices

The UV-induced photoreaction of 9-methyladenine was investigated by low-temperature matrix-isolation infrared (IR) spectroscopy with an aid of the density-functional-theory (DFT) calculation. Shorter-wavelength irradiation, λ > 240 nm, caused the elimination of a hydrogen atom in the amino group, resulting in the production of two kinds of amino radicals: One immediately changed to an imine isomer by migration of the eliminated hydrogen atom to a nitrogen atom in the pyrimidine ring, while the other stayed unreacted in the matrix for a long time. The imine returned to the original reactant, 9-methyladenine, by longer-wavelength irradiation, λ > 270 nm. The conformations of the unreacted radical and the imine were determined by comparison of the observed IR spectra with the spectral patterns obtained by DFT calculations.

► Photoreactions of 9-methyladenine in low-temperature matrices were investigated.
► IR spectra of the photoproducts, an amino radical and an imine, were observed.
► Conformations of the photoproducts were determined with an aid of DFT calculation.
► Amine–imine tautomerism was observed by changing the wavelength of irradiation.