UV-induced transformations of matrix-isolated 6-azacytosine

Abstract

UV-induced transformations were studied for monomers of 6-azacytosine isolated in low-temperature Ar matrices. In contrast to cytosine, where the amino-hydroxy () tautomer is the lowest-energy form, the amino-oxo () and imino-oxo () isomers of 6-azacytosine were found to be the most stable and most populated. Due to the high relative energy of the tautomer of 6-azacytosine, this form is not populated in low-temperature matrices after their formation and prior to any irradiation. Excitation of 6-azacytosine monomers with UV light from the 328-300 nm range led to structural transformations of and forms. The initially most populated tautomer was observed either to convert, in a phototautomeric reaction, into the product or to undergo photodecarbonylation to yield 4-amino-1,2,3-(2)-triazole. The relative efficiencies of the two processes depend on the wavelength and on the pulsed or continuous-wave character of the UV light used for excitation. For the tautomer of 6-azacytosine, the excitation with UV 328-300 nm light induced the photoconversion of the initially more populated anti isomer into the syn form. This transformation was found to be partially photoreversible.

Conformational Space, IR-Induced, and UV-Induced Chemistry of Carvacrol Isolated in a Low-Temperature Argon Matrix

“…These photoreactions yield a molecule of CO and a complementary cyclic photoproduct with one carbon atom less in the cycle. Such cases of decarbonylation were reported for 2-indolinone, diglycolic anhydride, azacytosine, diketene, dimethyl ester of squaric acid, and isatin, to name a few. In the photochemistry of carvacrol, the decarbonylation could proceed via the initial hydroxy-oxo tautomerism, leading to an alkyl-substituted cyclohexadienone and subsequent formation of alkyl-substituted cyclopentadiene, exemplified as pathway 1 → [ 2 ] → 3b → 7b (see Scheme ).…”

Infrared Spectrum and UV-Induced Photochemistry of Matrix-Isolated Phenyl 1-Hydroxy-2-Naphthoate

“…The spectra of the irradiated matrices reveal the photogeneration of carbon monoxide (CO), which gives rise to the bands at 2138 cm −1 (in the Ar matrix) and at 2139 cm −1 (in the N2 matrix), which were assigned to the well-isolated monomer, and at 2126/2122/2118/2114 cm −1 (Ar) and 2126/2117 cm −1 (N2) due to CO molecules interacting with other species in the matrices (Figure 4) [31][32][33][34][35]. These results doubtlessly indicate the occurrence of photodecarbonylation.…”