Tautomer‐Selective Spectroscopy of Nucleobases, Isolated in the Gas Phase

Vries, Mattanjah S. de

doi:10.1002/9783527658824.ch7

Cited by 6 publications

(8 citation statements)

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“…As mentioned in the Introduction, three tautomeric structures of neutral G have been previously found in the gas phase, GKA(1,9), GKA(1,7), and GEA(9) (Scheme ), , whereas, in aqueous solution, GKA(1,9) and GKA(1,7) or GKA(3,7), GKA(3,9), and GKA(7,9) are suggested to be the stable tautomers, depending on the method used to calculate the hydration effect. , In this regard, we have calculated different structures of the [GAg–H 2 O] + complex considering the GKA(1,9), GKA(1,7), GEA(9), GKA(3,7), GKA(3,9), and GKA(7,9) tautomers of G as well as GEA(7). Several local minima were found, and the four lowest energy structures are displayed in Table , while a complete list of the different isomers studied in this work is presented in Tables SI 1–6 and Figures SI 1–6 (Supporting Information).…”

Section: Resultsmentioning

confidence: 99%

“…In recent years, relentless efforts have been focused on the study of isolated neutral bases in the gas phase so that detailed comparisons between theory and experiment can be made. Readers are referred to refs and for a review of all these works.…”

Section: Introductionmentioning

confidence: 99%

“…In this regard, there have been several studies devoted to characterize the different tautomers of G that coexist in the gas phase, including REMPI (IR-UV hole burning) spectroscopy, − IR laser spectroscopy in He-nanodroplets, and Fourier transform microwave (FTMW) spectroscopy in a molecular beam . Although several discrepancies were found between the different reports, it was finally concluded that, in the gas phase, the most populated isomers of G are the two keto-amino tautomers, GKA(1,9) and GKA(1,7), and two rotamers of the enol-amino tautomer GEA(9), , shown in Scheme together with the calculated relative stabilities in gas and aqueous phase . The numbers in parentheses indicate the N heteroatoms to which the H atoms are bonded.…”

Section: Introductionmentioning

confidence: 99%

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Guanine Tautomerism in Ionic Complexes with Ag⁺ Investigated by IRMPD Spectroscopy and Mass Spectrometry

et al. 2021

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In this paper, we present the IRMPD spectra of three ionic complexes between guanine (G) and silver (Ag + ): [GAg-H 2 O] + , [GAgG] + produced in the electrospray ionization source of the mass spectrometer, and [GAg] + produced by collision induced dissociation of the [GAgG] + complex. On the basis of the comparison of theoretically calculated IR spectra, we show that there are two isomers of each complex containing two different keto-amino (KA) tautomers of G (GKA(1,9) and GKA(1,7)). The observed isomers are the most stable structures in aqueous solution, and their experimentally estimated relative populations are in better agreement with the calculated relative populations in solution than in the gas phase, both at 298 K. We concluded that these observations suggest that GKA(1,9) and GKA(1,7) coexist in solution according to previous theoretical reports (Colominas, C.; et al. J. Am. Chem. Soc. 1996, 118, 6811). We were unable to find any evidence of the presence of the GEA(9), GKA(3,7), GKA(3,9), or GKA(7,9), whose relative stabilities in solution are strongly dependent on the theoretical method used to account for the solvent effect (Hanus, M.; et al.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Guanine Tautomerism in Ionic Complexes with Ag⁺ Investigated by IRMPD Spectroscopy and Mass Spectrometry

et al. 2021

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“…DNA non-canonical nucleobases, like the 7H tautomeric forms of DNA nucleobases adenine and guanine studied in this work (see Figure 1), feature in non-negligible yields in our genetic material and possess markedly different electronic properties, which are known to affect their reactivity [32]. These species are rarely studied in the literature in their singlet form [32], and even less so in the cationic (doublet) manifold, despite being important to describe some of the photo-processes underpinning DNA damage and repair. The study of these species is however fundamental to understand how prebiotic extreme UV-light exposure in DNA nucleobases, and their ability to withstand such radiation, may have played a role in selecting our genetic lexicon [13,14,33].…”

Section: Introductionmentioning

confidence: 93%

Modelling Photoionisations in Tautomeric DNA Nucleobase Derivatives 7H-Adenine and 7H-Guanine: Ultrafast Decay and Photostability

2021

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The study of radiation effects in DNA is a multidisciplinary endeavour, connecting the physical, chemical and biological sciences. Despite being mostly filtered by the ozone layer, sunlight radiation is still expected to (photo)ionise DNA in sizeable yields, triggering an electron removal process and the formation of potentially reactive cationic species. In this manuscript, photoionisation decay channels of important DNA tautomeric derivatives, 7H-adenine and 7H-guanine, are characterised with accurate CASSCF/XMS-CASPT2 theoretical methods. These simulation techniques place the onset of ionisation for 7H-adenine and 7H-guanine on average at 8.98 and 8.43 eV, in line with recorded experimental evidence when available. Cationic excited state decays are analysed next, uncovering effective barrierless deactivation routes for both species that are expected to decay to their (cationic) ground state on ultrafast timescales. Conical intersection topographies reveal that these photoionisation processes are facilitated by sloped single-path crossings, known to foster photostability, and which are predicted to enable the (VUV) photo-protection mechanisms present in these DNA tautomeric species.

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“…An aspect hardly considered thus far is the photoionisation and subsequent relaxation of non-canonical nucleobases, which are molecular species present in non-negligible amounts in DNA. [16,17] Excited state studies on non-canonical nucleobases such as isocytosine, [18][19][20] an isomer of cytosine (see Figure 1), have attracted much less attention compared to their canonical counterparts and their behaviour remains largely unexplored to our knowledge despite its biological relevance.…”

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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Tautomer‐Selective Spectroscopy of Nucleobases, Isolated in the Gas Phase

Cited by 6 publications

References 74 publications

Guanine Tautomerism in Ionic Complexes with Ag⁺ Investigated by IRMPD Spectroscopy and Mass Spectrometry

Guanine Tautomerism in Ionic Complexes with Ag⁺ Investigated by IRMPD Spectroscopy and Mass Spectrometry

Modelling Photoionisations in Tautomeric DNA Nucleobase Derivatives 7H-Adenine and 7H-Guanine: Ultrafast Decay and Photostability

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

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Tautomer‐Selective Spectroscopy of Nucleobases, Isolated in the Gas Phase

Cited by 6 publications

References 74 publications

Guanine Tautomerism in Ionic Complexes with Ag+ Investigated by IRMPD Spectroscopy and Mass Spectrometry

Guanine Tautomerism in Ionic Complexes with Ag+ Investigated by IRMPD Spectroscopy and Mass Spectrometry

Modelling Photoionisations in Tautomeric DNA Nucleobase Derivatives 7H-Adenine and 7H-Guanine: Ultrafast Decay and Photostability

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

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Guanine Tautomerism in Ionic Complexes with Ag⁺ Investigated by IRMPD Spectroscopy and Mass Spectrometry

Guanine Tautomerism in Ionic Complexes with Ag⁺ Investigated by IRMPD Spectroscopy and Mass Spectrometry