MNDO and IR spectroscopic studies of tautomerism of isocytosine

Stepanian, S. G.; Radchenko, E. D.; Sheina, G. G.; Blagoı̆, Yu. P.

doi:10.1016/0022-2860(90)80318-e

Cited by 28 publications

(23 citation statements)

References 19 publications

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“…[20,21] However the analysis of the IR spectra of UV irradiated isocytosine in an argon matrix has given evidence for more tautomeric form. [21][22][23][24] Those are the amino oxo and amino hydroxy forms of the compound. No information for the presence of the imino tautomers has been reported.…”

Section: Introductionmentioning

confidence: 99%

Photo-induced Dissociation of the N1–H Bond in the Imino Tautomers of Isocytosine in Water Medium

Dimitrov

Delchev

2020

Croat. Chem. Acta

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The imino tautomers of isocytosine were objects of investigation at the TD-DFT level of theory-TD BLYP/6-311++G(d,p). We studied the mechanisms of the H1-N detachment in these tautomers through excited-state reaction paths. It was proposed that these transformations occur through the 1 πσ* excited-state reaction paths of the imino tautomers. The mechanisms involve dissociations of the N1-H bonds in the tautomers and lead to crossings between the reaction paths of 1 πσ* and S0 electronic states. One can suppose that such processes would facilitate the tautomerizations of the imino tautomers if further mechanisms have been found.

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Section: Introductionmentioning

confidence: 99%

Photo-induced Dissociation of the N1–H Bond in the Imino Tautomers of Isocytosine in Water Medium

Dimitrov

Delchev

2020

Croat. Chem. Acta

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“…[15] When the rotational isomerism of the exo-OH and exo-NH groups is taken into account, 21 planar tautomers/ rotamers are possible. A number of experimental [16][17][18][19][20] and theoretical [21][22][23][24][25] works dedicated to the tautomerism of isocytosine have been published. These studies have revealed that isocytosine isolated in the gas phase, or in inert gas matrices, exists predominantly in the hydroxy-amino form 2,4-I with a smaller proportion existing in the keto-amino form 2,3-I.…”

Section: Introductionmentioning

confidence: 99%

Tautomerism and the Protonation/Deprotonation of Isocytosine in Liquid‐ and Solid‐States Studied by NMR Spectroscopy and Theoretical Calculations

et al. 2011

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Isocytosine crystallizes as a 1:1 ratio of two tautomers in a manner similar to that of the guanine and cytosine pairs in DNA. The solid‐state NMR chemical shifts of crystalline neutral isocytosine, the sodium salt of isocytosine, and those of isocytosine hydrochloride were measured and related to the NMR parameters in aqueous and organic solutions. The experimental chemical shifts were compared with those calculated by three different methods: (1) calculations on isolated molecules, (2) calculations on isocytosine clusters of various sizes, and (3) infinite crystal calculations, that is, the gauge‐including projector‐augmented wave (GIPAW) method. The data obtained with the GIPAW method were in best agreement with the experimental data.

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“…This is the first system for which we have made this comparison directly, both forms having been reported in the literature to be stable in the gas phase. [28] Isocytosine is one of the many different non‐canonical instances that may feature in DNA and continues our work to assess theoretically the photoionisation of our genomic material. [ 29 , 30 ] We start by considering the lowest‐lying ionisation potentials of keto‐ and enol‐isocytosine, which feature a range of accessible

and

states at energies similar to those previously reported for cytosine.…”

Section: Introductionmentioning

confidence: 99%

Modelling Photoionisation in Isocytosine: Potential Formation of Longer‐Lived Excited State Cations in its Keto Form

Segarra‐Martí

Bearpark

2021

ChemPhysChem

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Studying the effects of UV and VUV radiation on non-canonical DNA/RNA nucleobases allows us to compare how they release excess energy following absorption with respect to their canonical counterparts. This has attracted much research attention in recent years because of its likely influence on the origin of our genetic lexicon in prebiotic times. Here we present a CASSCF and XMS-CASPT2 theoretical study of the photoionisation of non-canonical pyrimidine nucleobase isocytosine in both its keto and enol tautomeric forms. We analyse their lowest energy cationic excited states including 2 p þ , 2 n þ O and 2 n þ N and compare these to the corresponding electronic states in cytosine. Investigating lower-energy decay pathways we find -unexpect-edly -that keto-isocytosine + presents a sizeable energy barrier potentially inhibiting decay to its cationic ground state, whereas enol-isocytosine + features a barrierless and consequently ultrafast pathway analogous to the one previously found for the canonical (keto) form of cytosine + . Dynamic electron correlation reduces the energy barrier in the keto form substantially (by ~1 eV) but it is nevertheless still present. We additionally compute the UV/Vis absorption signals of the structures encountered along these decay channels to provide spectroscopic fingerprints to assist future experiments in monitoring these intricate photo-processes.

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MNDO and IR spectroscopic studies of tautomerism of isocytosine

Cited by 28 publications

References 19 publications

Photo-induced Dissociation of the N1–H Bond in the Imino Tautomers of Isocytosine in Water Medium

Photo-induced Dissociation of the N1–H Bond in the Imino Tautomers of Isocytosine in Water Medium

Tautomerism and the Protonation/Deprotonation of Isocytosine in Liquid‐ and Solid‐States Studied by NMR Spectroscopy and Theoretical Calculations

Modelling Photoionisation in Isocytosine: Potential Formation of Longer‐Lived Excited State Cations in its Keto Form

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