Tautomerism of the DNA Base Guanine and Its Methylated Derivatives as Studied by Gas-Phase Infrared and Ultraviolet Spectroscopy

Mons, Michel; Dimicoli, I.; Piuzzi, F.; Tardivel, B.; Elhanine, M.

doi:10.1021/jp0139742

Cited by 197 publications

(286 citation statements)

References 37 publications

(113 reference statements)

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“…All 9-substituted guanines that we have studied as monomers, including four different guanosines, exhibit sharp UV spectra. These all involve the enol tautomer (15)(16)(17). Thus, if the 9-substitution plays a role, it does so only for the keto tautomer, which is required to form the WC structure.…”

Section: Discussionmentioning

confidence: 99%

Photochemical selectivity in guanine–cytosine base-pair structures

Abo-Riziq

Grace

Nir

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

245

284

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Prebiotic chemistry presumably took place before formation of an oxygen-rich atmosphere and thus under conditions of intense short wavelength UV irradiation. Therefore, the UV photochemical stability of the molecular building blocks of life may have been an important selective factor in determining the eventual chemical makeup of critical biomolecules. To investigate the role of UV irradiation in base-pairing we have studied guanine (G) and cytosine (C) base pairs in the absence of the RNA backbone. We distinguished base-pair structures by IR-UV hole-burning spectroscopy as well as by high-level correlated ab initio calculations. The Watson-Crick structure exhibits broad UV absorption, in stark contrast to other GC structures and other base-pair structures. This broad absorption may be explained by a rapid internal conversion that makes this specific base pair arrangement uniquely photochemically stable.ab initio computation ͉ DNA base pairs ͉ IR-UV spectroscopy ͉ jet cooling ͉ photochemistry T he DNA bases involved in reproduction have short S 1 excited state lifetimes, of the order of 1 ps or less (1-7). It has been argued that this phenomenon serves to protect these bases against photochemical damage, because after excitation they do not cross to the reactive triplet state; instead, they rapidly internally convert to the electronic ground state (8). This mechanism may have been particularly significant under the conditions of the early earth, when purines and pyrimidines presumably were assembled into the first macromolecular structures, producing RNA. At that time, the earth was exposed to shorter wavelength UV radiation than it is today. For an analysis of possible prebiotic chemistry, it is necessary not only to consider the individual bases but also to study them as they interact and to do so without the RNA backbone (9). We achieve such an analysis by studying clusters of guanine (G) and cytosine (C) in the gas phase by using double resonant laser spectroscopy techniques. The experimental studies are accompanied by stateof-the-art quantum chemical and molecular dynamics calculations of the pairing of G and C. These two bases can form many different hydrogen-bonded structures, of which at least 20 are within 12 kcal͞mol of the global minimum. Thus, the familiar Watson-Crick (WC) structure may not be unique, based on energies alone. Here, we report a remarkable difference in excited state properties among the WC structure and other structures. The former exhibits broad UV absorption features; this is in contrast with the sharp UV spectra exhibited by non-WC structures. The broad absorption can be explained by recent theoretical results, predicting a pathway for rapid internal conversion (10). If the difference is solely due to lifetime broadening, these results correspond to a lifetime for the WC structures that is at least 2 orders of magnitude shorter than those of observed non-WC structures. Thus, it appears possible that the WC recognition mechanism involves a structure that was significantly more stab...

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Section: Discussionmentioning

confidence: 99%

Photochemical selectivity in guanine–cytosine base-pair structures

Abo-Riziq

Grace

Nir

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

245

284

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“…2,7 The two guanine tautomers that have no free OH stretch frequency in the IR-UV spectra have their origins at 32864 and 33269 cm -1 , respectively. 4 We scanned down to 30000 cm -1 with two color ionization without finding any additional peaks. As the second color, we used both 266 and 193 nm to ensure that we would not miss any excitation due to a high ionization potential.…”

Section: Theoretical Methodsmentioning

confidence: 99%

The Mid-IR Spectra of 9-Ethyl Guanine, Guanosine, and 2-Deoxyguanosine

et al. 2007

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We present the mid-IR (400-1800 cm -1 ) spectra of 9-ethyl guanine, guanosine, and 2-deoxyguanosine measured by IR-UV double-resonance spectroscopy. We compare the recorded mid-IR spectra with the spectra of the most stable structures obtained from RI-MP2 and RI-DFT-D calculations. The results confirm the enol form for all structures and demonstrate the efficacy of a new approach to DFT calculations that includes dispersion interactions.

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“…This journal is © The Royal Society of Chemistry 2012 stable conformers in the gas phase, [52][53][54] 62 although an earlier simulation suggested that the C 6 pucker CI may also be involved. 65 In the solution phase, Gua itself is rarely studied as it has poor solubility, although dGMP -has been studied in a number of experiments with transient absorption 1,16,66 and fluorescence upconversion.…”

Section: Dgmp -mentioning

confidence: 99%

Time-resolved photoelectron imaging of the isolated deprotonated nucleotides

et al. 2014

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Publisher's copyright statement:Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Using time-resolved photoelectron spectroscopy, the excited state dynamics of gas-phase mass-selected nucleotide anions have been monitored following UV excitation at 4.66 eV. The spectra reveal that the dynamics of the 2'-deoxyguanosine 5'-monophosphate anion (dGMP -) are very similar to those of the adenosine nucleotide (dAMP -) and insensitive to a solvation environment. Comparison of our results with other literature suggest s that nucleotides of the two purine bases share a common relaxation pathway, whereby the initially populated 1 ππ* states relax to the ground electronic state without involvement of any other intermediary electronic states. In the analogous pyrimidine nucleotides of thymine and cytosine, dTMP -and dCMP -, no such unified mechanism is observed. Photoexcited dTMP -behaves much like the isolated nucleobase thymine, exhibiting rapid relaxation to the ground electronic state, although with a minor long-lived channel. On the other hand, isolated dCMP -is longer lived than its cytosine nucleobase, and hence it appears that the presence of the sugar and phosphate in the nucleotide arrangement leads to a modification of the available relaxation pathways. Nucleotides are the basic monomer building blocks of DNA and our results present important new benchmark data to develop an understanding of the molecular mechanism by which photodamage can be mediated when DNA is exposed to UV light.

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Tautomerism of the DNA Base Guanine and Its Methylated Derivatives as Studied by Gas-Phase Infrared and Ultraviolet Spectroscopy

Cited by 197 publications

References 37 publications

Photochemical selectivity in guanine–cytosine base-pair structures

Photochemical selectivity in guanine–cytosine base-pair structures

The Mid-IR Spectra of 9-Ethyl Guanine, Guanosine, and 2-Deoxyguanosine

Time-resolved photoelectron imaging of the isolated deprotonated nucleotides

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