Photochemical syn–anti Isomerization Reaction in N4-Hydroxycytosine. An Experimental Matrix Isolation and Theoretical Study

Lapiński, Leszek; Nowak, Maciej J.; Adamowicz, Ludwik

doi:10.1562/0031-8655(2001)074<0253:psairi>2.0.co;2

Cited by 7 publications

(12 citation statements)

References 26 publications

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“…Even after prolonged irradiation it was not possible to convert more than 15% of the initial form into the photoproduct. Evidently, a photostationary state was achieved (similar to that previously observed for N 4 -hydroxycytosines [8,9]). Changing the applied wavelength of the UV irradiation did not result in an increase in the percentage of the converted material.…”

Section: Resultssupporting

confidence: 81%

“…Bands caused by this vibration were previously observed in the spectra of N 4 -hydroxycytosine (9) and 1-methyl-N 4 -hydroxycytosine (8) at similar frequencies, 3650 and 3648 cm 21 , respectively. The positions of these bands did not change much on syn-anti isomerization of the imino-oxo tautomers abundant for the two compounds (8,9). This was also the case for N 2hydroxyisocytosine studied in this article; neither the position nor the shape of this band changed significantly on the observed photoreaction.…”

Section: Resultssupporting

confidence: 57%

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Photochemical syn–anti Isomerization Reactions in N2-Hydroxyisocytosines—An Experimental Matrix Isolation and Theoretical Study¶

Lapiński¹,

Nowak²,

Kwiatkowski³

et al. 2003

Photochem Photobiol

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N2-hydroxyisocytosine and 1-methyl-N2-hydroxyisocytosine were studied using a matrix isolation technique combined with infrared absorption spectroscopy. For N2-hydroxyisocytosine isolated in an Ar matrix (at 10 K), two imino-oxo isomers, one with the hydroxyimino =N-OH group directed toward the N1-H group (the form called further anti) and the second with the =N-OH group directed toward N3-H (syn), were observed in the ratio 1.4:1. The syn isomer is converted totally to the anti form after UV (lambda > 295 nm) irradiation of the matrix. A small amount of the N(3)H-hydroxy-amino tautomer of N2-hydroxyisocytosine was also detected in the matrix. This form did not react photochemically. For 1-methyl-N2-hydroxyisocytosine, only the syn form of the imino-oxo tautomer was observed after deposition of the matrix. UV (lambda > 295 nm) irradiation induced a photoreaction converting this isomer into the anti form. After 15% of the starting material had been converted into the product, a photostationary state was achieved, and no further progress of the reaction was observed. Subsequent UV irradiation (lambda > 335 nm) caused a back reaction, leading to a disappearance of the anti form and to the recovery of the initial syn isomer. All isomers were identified by comparing their experimental IR spectra with the spectra theoretically calculated at the DFT(B3LYP)/6-31G(d,p) level, where DFT is the density functional theory. Good agreement between the observed and predicted patterns of the spectral lines allowed for reliable identification. The experimental IR spectra were interpreted and discussed. The relative energies of the 12 isomers of N2-hydroxyisocytosine were calculated at the MP2/6-31G(d,p) and MP4//MP2/6-31G(d,p) levels. For six isomers of 1-methyl-N2-hydroxyisocytosine, the calculations were carried out at the MP2/6-31G(d,p) level. The anti form of the imino-oxo tautomer of N-hydroxyisocytosine and the syn form of the imino-oxo tautomer of 1-methyl-N2-hydroxyisocytosine were predicted to be the most stable.

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Section: Resultssupporting

confidence: 81%

Section: Resultssupporting

confidence: 57%

Photochemical syn–anti Isomerization Reactions in N2-Hydroxyisocytosines—An Experimental Matrix Isolation and Theoretical Study¶

Lapiński¹,

Nowak²,

Kwiatkowski³

et al. 2003

Photochem Photobiol

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“…The band observed at the highest frequency (3654 cm −1 ) can be assigned to the stretching OH vibration in the C=N–OH group. Bands caused by this vibration were previously observed in the spectra of N 4 ‐hydroxycytosine (9) and 1‐methyl‐N 4 ‐hydroxycytosine (8) at similar frequencies, 3650 and 3648 cm −1 , respectively. The positions of these bands did not change much on syn – anti isomerization of the imino–oxo tautomers abundant for the two compounds (8,9).…”

Section: Resultssupporting

confidence: 58%

“…Recently, we reported the photochemical syn – anti isomerization observed for 1‐methyl‐N 4 ‐hydroxycytosine (8) and N 4 ‐hydroxycytosine (9) isolated in noble gas low‐temperature matrices. Analogous reactions were found by us for a number of N 4 ‐hydroxy (or N 4 ‐methoxy) cytosines substituted with one, two or three methyl groups at different positions in the pyrimidine ring.…”

Section: Introductionmentioning

confidence: 99%

“…Their photochemical behavior, described above, is quite typical of oxime molecules (compare our recent study [10] on the classical cases: benzaldoxime and pyridine‐4‐aldoxime). A theoretical model of the photoreaction in N 4 ‐hydroxycytosines, including the potential energy surfaces in the ground and excited states, is presented in References (8) and (9).…”

Section: Introductionmentioning

confidence: 99%

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Photochemical syn-anti Isomerization Reactions in N2-Hydroxyisocytosines-An Experimental Matrix Isolation and Theoretical Study¶

Lapiński¹,

Nowak²,

Kwiatkowski³

et al. 2007

Photochemistry and Photobiology

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N2‐hydroxyisocytosine and 1‐methyl‐N2‐hydroxyisocytosine were studied using a matrix isolation technique combined with infrared absorption spectroscopy. For N2‐hydroxyisocytosine isolated in an Ar matrix (at 10 K), two imino–oxo isomers, one with the hydroxyimino =N–OH group directed toward the N1–H group (the form called further anti) and the second with the =N–OH group directed toward N3–H (syn), were observed in the ratio 1.4:1. The syn isomer is converted totally to the anti form after UV (λ > 295 nm) irradiation of the matrix. A small amount of the N(3)H‐hydroxy–amino tautomer of N2‐hydroxyisocytosine was also detected in the matrix. This form did not react photochemically. For 1‐methyl‐N2‐hydroxyisocytosine, only the syn form of the imino–oxo tautomer was observed after deposition of the matrix. UV (λ > 295 nm) irradiation induced a photoreaction converting this isomer into the anti form. After 15% of the starting material had been converted into the product, a photostationary state was achieved, and no further progress of the reaction was observed. Subsequent UV irradiation (λ > 335 nm) caused a back reaction, leading to a disappearance of the anti form and to the recovery of the initial syn isomer. All isomers were identified by comparing their experimental IR spectra with the spectra theoretically calculated at the DFT(B3LYP)/6‐31G(d,p) level, where DFT is the density functional theory. Good agreement between the observed and predicted patterns of the spectral lines allowed for reliable identification. The experimental IR spectra were interpreted and discussed. The relative energies of the 12 isomers of N2‐hydroxyisocytosine were calculated at the MP2/6‐31G(d,p) and MP4//MP2/6‐31G(d,p) levels. For six isomers of 1‐methyl‐N2‐hydroxyisocytosine, the calculations were carried out at the MP2/6‐31G(d,p) level. The anti form of the imino–oxo tautomer of N2‐hydroxyisocytosine and the syn form of the imino–oxo tautomer of 1‐methyl‐N2‐hydroxyisocytosine were predicted to be the most stable.

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Photochemical syn–anti isomerization reactions in N4-methoxycytosines

Lapiński¹,

Ramaekers²,

Kierdaszuk³

et al. 2004

Journal of Photochemistry and Photobiology A: Chemistry

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Photochemical syn–anti Isomerization Reaction in N4-Hydroxycytosine. An Experimental Matrix Isolation and Theoretical Study

Cited by 7 publications

References 26 publications

Photochemical syn–anti Isomerization Reactions in N2-Hydroxyisocytosines—An Experimental Matrix Isolation and Theoretical Study¶

Photochemical syn–anti Isomerization Reactions in N2-Hydroxyisocytosines—An Experimental Matrix Isolation and Theoretical Study¶

Photochemical syn-anti Isomerization Reactions in N2-Hydroxyisocytosines-An Experimental Matrix Isolation and Theoretical Study¶

Photochemical syn–anti isomerization reactions in N4-methoxycytosines

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