Photochemical syn–anti isomerization reactions in N4-methoxycytosines

Lapiński, Leszek; Ramaekers, Riet; Kierdaszuk, Borys; Maes, Guido; Nowak, Maciej J.

doi:10.1016/j.jphotochem.2004.02.004

Cited by 8 publications

(3 citation statements)

References 21 publications

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“…Syn → anti and anti → syn phototransformations, similar to those described above, were also observed for matrix-isolated N 4 -methoxycytosines and N 2 -hydroxyisocytosines …”

Section: Concluding Discussionsupporting

confidence: 76%

Photoisomerizations of N⁴-Hydroxycytosines

et al. 2006

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A series of N4-hydroxycytosines, unsubstituted or substituted with methyl groups at N3 or C5 atoms of the heterocyclic ring, was studied using the matrix-isolation method. Depending on the absence or presence of the methyl substituent at N3 or C5 atoms (or at both of them) the syn or anti form of the compounds (or a mixture of both forms) was trapped from the gas phase into a low-temperature matrix. Upon UV (lambda > 295 nm) irradiation of the matrixes the syn --> anti as well as the anti --> syn photoisomerization reactions were observed. The syn and anti isomers of N4-hydroxycytosines were identified by comparing their experimental IR spectra with the theoretical spectra calculated at the DFT(B3LYP)/6-31G(d,p) level. For the majority of the studied compounds, the UV induced reactions led to a photostationary state. The position of the final photostationary state was found to be a sensitive function of weak interactions of a studied N4-hydroxycytosine with the matrix environment: solid argon or solid nitrogen. However, not all of the studied photoisomerizations led to a classical photostationary state. For some of the investigated N4-hydroxycytosines, the position of the photostationary state was shifted very strongly in favor of the photoproduct, whereas for some others the position was shifted so strongly in favor of the starting isomer that no photoisomerization was observed. These experimental findings were elucidated by theoretical investigations of the potential energy surfaces of the ground (S0) and first excited (S1) electronic states of N4-hydroxycytosine. The crucial result of these calculations (carried out at the CASSCF level) was the localization of a conical intersection between S0 and S1 at a structure with perpendicular orientation of the hydroxylimino group with respect to the heterocyclic ring.

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“…Syn → anti and anti → syn phototransformations, similar to those described above, were also observed for matrix-isolated N 4 -methoxycytosines and N 2 -hydroxyisocytosines …”

Section: Concluding Discussionsupporting

confidence: 76%

Photoisomerizations of N⁴-Hydroxycytosines

et al. 2006

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“…UV 328-300 nm excitation of the imino-oxo (IO) form of 6-azacytosine induced bidirectional anti ↔ syn transformation, interconverting the two imino-oxo isomers (IO1 and IO2) into each other. Such phototransformation, converting the isomers by a flip of the H-atom (or a group of atoms) around a double C= =N bond, is a classic photochemical process, observed for a number of matrix-isolated compounds, [40][41][42] including cytosine 15 and 1-methylcytosine. 43 Whereas tautomerism of 6-azacytosine is drastically different from that of cytosine, similarities as well as dissimilarities were found in the photochemical behavior of these two compounds.…”

Section: Concluding Discussionmentioning

confidence: 99%

UV-induced transformations of matrix-isolated 6-azacytosine

Lapiński

Reva

Gerega

et al. 2018

The Journal of Chemical Physics

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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.

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“…Photochemical synanti conversions have also been studied for N 4 -methoxycytosine and 1-methyl-N 4 -methoxycytosine in Ar or N 2 matrices. 411 Irradiation at l 4 295 nm causes, in both cases, isomerism of the syn to the anti forms. This observation indicates that although the synanti conversion of these species requires the rotation of a large methoxy group, interactions with the matrix do not Annu.…”

Section: Base Moleculesmentioning

confidence: 98%

Chemistry in low-temperature matrices

Almond

Goldberg

2007

Annu. Rep. Prog. Chem., Sect. C: Phys. Chem.

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the Progress of Chemistry, Section C. The report is divided into sections: weak adducts and conformational isomers; reactions of atoms; high-temperature molecules; photochemistry; biological molecules; astrochemistry. The last two sections reflect the fact that matrix isolation now extends into areas outside the traditional mainstream disciplines of chemistry. There are a number of areas where substantial progress has been made during the period of this report. First, the routine use of laser-ablation to generate atoms and to initiate atomic reactions in matrices has increased the scope of matrix isolation to synthesise many new molecular species in inorganic chemistry. Laser-ablation allows ground state atoms to be more easily studied than is the case when atoms are produced by thermal methods. Moreover, this procedure allows atoms to be generated from materials where thermal production is difficult. Secondly, the manufacture of more efficient closed-cycle helium refrigerators allows hydrogen matrices to be deposited readily. A significant body of work therefore has focussed upon metal hydrides, dihydrogen complexes and other hydrogen species in matrices. Underpinning all of this experimental work are theoretical calculations, without which the correct identification of most matrix isolation molecules would remain dangerously ambiguous. Infrared spectroscopy remains-as it has for the past 50 years-the workhorse of matrix isolation studies. It does seem that this situation will not change-it is impossible to conceive of another spectroscopic method that combines the necessary sensitivity to study molecules at very low dilution with the structural information required to make a reasonably certain identification.

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Photochemical syn–anti isomerization reactions in N4-methoxycytosines

Cited by 8 publications

References 21 publications

Photoisomerizations of N⁴-Hydroxycytosines

Photoisomerizations of N⁴-Hydroxycytosines

UV-induced transformations of matrix-isolated 6-azacytosine

Chemistry in low-temperature matrices

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Photochemical syn–anti isomerization reactions in N4-methoxycytosines

Cited by 8 publications

References 21 publications

Photoisomerizations of N4-Hydroxycytosines

Photoisomerizations of N4-Hydroxycytosines

UV-induced transformations of matrix-isolated 6-azacytosine

Chemistry in low-temperature matrices

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Photoisomerizations of N⁴-Hydroxycytosines

Photoisomerizations of N⁴-Hydroxycytosines