1
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Gómez S, Cappelli C. When Tautomers Matter: UV-Vis Absorption Spectra of Hypoxanthine in Aqueous Solution from Fully Atomistic Simulations. Chemphyschem 2024; 25:e202400107. [PMID: 38747323 DOI: 10.1002/cphc.202400107] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2024] [Revised: 05/13/2024] [Indexed: 07/03/2024]
Abstract
The UV-Vis spectrum of the solvated purine derivative Hypoxanthine (HYX) is investigated using the Quantum Mechanics/Fluctuating Charges (QM/FQ) multiscale approach combined with a sampling of configurations through atomistic Molecular Dynamics (MD) simulations. Keto 1H7H and 1H9H tautomeric forms of HYX are the most stable in aqueous solution and form different stable complexes with the surrounding water molecules, ultimately affecting the electronic absorption spectra. The final simulated spectrum resulting from the combination of the individual spectra of tautomers agrees very well with most of the characteristics in the measured spectrum. The importance of considering the effect of the solute tautomers and, in parallel, the contribution of the different solvent arrangements around the solute when modeling spectral properties, is highlighted. In addition, the high quality of the computed spectra leads to suggesting an alternative way for acquiring tautomeric populations from combined computational/experimental spectra.
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Affiliation(s)
- Sara Gómez
- Scuola Normale Superiore, Classe di Scienze, Piazza dei Cavalieri 7, 56126, Pisa, Italy
| | - Chiara Cappelli
- Scuola Normale Superiore, Classe di Scienze, Piazza dei Cavalieri 7, 56126, Pisa, Italy
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2
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Romeo-Gella F, Arpa EM, Corral I. A molecular insight into the photophysics of barbituric acid, a candidate for canonical nucleobases' ancestor. Phys Chem Chem Phys 2022; 24:1405-1414. [PMID: 34982082 DOI: 10.1039/d1cp04987a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
This work investigates the photophysics of barbituric acid at different pH conditions using ab initio methods. Our calculations ascribe the most intense bands at ca. 260 nm at neutral pH and 210 nm at acidic pH conditions in the absorption spectra of this chromophore to the lowest lying ππ* transitions. Consistently with the ultrashort excited state lifetimes experimentally registered, the potential energy landscapes of both the neutral and deprotonated forms of barbituric acid combined with the interpretation of their transient absorption spectra suggest the deactivation of these systems along the singlet manifold. Compared to uracil, its closest natural nucleobase, barbituric acid presents a red shifted absorption spectrum, due to the lowering by more than 0.5 eV of the lowest-energy ππ* excited state, and a much more complex topography of the S1 potential energy surface, with several energetically accessible local minima. This fact, however, does not affect the excited state lifetimes, which for barbituric acid were experimentally registered in the sub-ps time scale.
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Affiliation(s)
- Fernando Romeo-Gella
- Departamento de Química, Módulo 13, Universidad Autónoma de Madrid, 28049, Madrid, Spain.
| | - Enrique M Arpa
- Departamento de Química, Módulo 13, Universidad Autónoma de Madrid, 28049, Madrid, Spain.
| | - Inés Corral
- Departamento de Química, Módulo 13, Universidad Autónoma de Madrid, 28049, Madrid, Spain. .,Institute for Advanced Research in Chemistry (IAdChem), Universidad Autónoma de Madrid, 28049, Madrid, Spain
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3
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Jankowska J, Góra RW. Ultrafast nonradiative deactivation of photoexcited 8-oxo-hypoxanthine: a nonadiabatic molecular dynamics study. Phys Chem Chem Phys 2021; 23:1234-1241. [PMID: 33355573 DOI: 10.1039/d0cp05271j] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
In the scientific endeavor to understand the chemical origins of life, the photochemistry of the smallest life building blocks, nucleobases, has been a constant object of focus and intense research. Here, we report the results of the first theoretical study on the photo-properties of an 8-oxo-hypoxanthine molecule, the chromophore of 8-oxo-inosine, which is relevant to the recently proposed, prebiotically plausible synthetic routes to the formation of purine- and pyrimidine-nucleotides. With ab initio and semi-empirical OM2/MRCI quantum-chemistry calculations, we predict a strong photostability of the 8-oxo-hypoxanthine system and see the origin of this effect in ultrafast nonradiative relaxation through puckering of the 6-membered heterocyclic ring.
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Affiliation(s)
- Joanna Jankowska
- Faculty of Chemistry, University of Warsaw, 02-093 Warsaw, Poland.
| | - Robert W Góra
- Department of Physical and Quantum Chemistry, Wroclaw University of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370, Wrocław, Poland.
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4
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Gómez S, Giovannini T, Cappelli C. Absorption spectra of xanthines in aqueous solution: a computational study. Phys Chem Chem Phys 2020; 22:5929-5941. [PMID: 32115599 DOI: 10.1039/c9cp05420k] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
We present a detailed computational analysis of the UV/Vis spectra of caffeine, paraxanthine and theophylline in aqueous solution. A hierarchy of solvation approaches for modeling the aqueous environment have been tested, ranging from the continuum model to the non-polarizable and polarizable quantum mechanical (QM)/molecular mechanics (MM) models, with and without the explicit inclusion of water molecules in the QM portion. The computed results are directly compared with the experimental data, thus highlighting the role of electrostatic, polarization and hydrogen boding solute-solvent interactions.
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Affiliation(s)
- Sara Gómez
- Scuola Normale Superiore, Classe di Scienze, Piazza dei Cavalieri 7, 56126 Pisa, Italy.
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5
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Guo X, Yuan H, Zhu Q, An B, Zhang J. Ab initioinsights on photophysics of 9-methylhypoxanthine. Mol Phys 2016. [DOI: 10.1080/00268976.2016.1164348] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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6
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Guo X, Yuan H, An B, Zhu Q, Zhang J. Ultrafast excited-state deactivation of 9-methylhypoxanthine in aqueous solution: A QM/MM MD study. J Chem Phys 2016; 144:154306. [DOI: 10.1063/1.4946103] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Xugeng Guo
- Institute of Environmental and Analytical Sciences, College of Chemistry and Chemical Engineering, Henan University, Kaifeng 475004, People’s Republic of China
| | - Huijuan Yuan
- Institute of Environmental and Analytical Sciences, College of Chemistry and Chemical Engineering, Henan University, Kaifeng 475004, People’s Republic of China
| | - Beibei An
- Institute of Environmental and Analytical Sciences, College of Chemistry and Chemical Engineering, Henan University, Kaifeng 475004, People’s Republic of China
| | - Qiuling Zhu
- Institute of Environmental and Analytical Sciences, College of Chemistry and Chemical Engineering, Henan University, Kaifeng 475004, People’s Republic of China
| | - Jinglai Zhang
- Institute of Environmental and Analytical Sciences, College of Chemistry and Chemical Engineering, Henan University, Kaifeng 475004, People’s Republic of China
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7
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Zhang L, Zhang Z, Ren T, Tian J, Wang M. New size-expanded RNA nucleobase analogs: a detailed theoretical study. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2015; 140:407-415. [PMID: 25617981 DOI: 10.1016/j.saa.2015.01.006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2014] [Revised: 12/20/2014] [Accepted: 01/05/2015] [Indexed: 06/04/2023]
Abstract
Fluorescent nucleobase analogs have attracted much attention in recent years due to their potential applications in nucleic acids research. In this work, four new size-expanded RNA base analogs were computationally designed and their structural, electronic, and optical properties are investigated by means of DFT calculations. The results indicate that these analogs can form stable Watson-Crick base pairs with natural counterparts and they have smaller ionization potentials and HOMO-LUMO gaps than natural ones. Particularly, the electronic absorption spectra and fluorescent emission spectra are calculated. The calculated excitation maxima are greatly red-shifted compared with their parental and natural bases, allowing them to be selectively excited. In gas phase, the fluorescence from them would be expected to occur around 526, 489, 510, and 462 nm, respectively. The influences of water solution and base pairing on the relevant absorption spectra of these base analogs are also examined.
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Affiliation(s)
- Laibin Zhang
- School of Physics and Engineering, Qufu Normal University, Qufu 273165, PR China.
| | - Zhenwei Zhang
- Linyi Academy of Technology Cooperation and Application, Linyi 276001, PR China
| | - Tingqi Ren
- School of Physics and Engineering, Qufu Normal University, Qufu 273165, PR China
| | - Jianxiang Tian
- School of Physics and Engineering, Qufu Normal University, Qufu 273165, PR China.
| | - Mei Wang
- School of Physics and Engineering, Qufu Normal University, Qufu 273165, PR China
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8
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Voltammetric response of [Co(phen)3]3+ and gold nanoparticles/multi-walled carbon nanotubes to two C-6 substituted purines. J Electroanal Chem (Lausanne) 2015. [DOI: 10.1016/j.jelechem.2015.02.018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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9
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Guo X, Zhao Y, Cao Z. A QM/MM MD insight into photodynamics of hypoxanthine: distinct nonadiabatic decay behaviors between keto-N7H and keto-N9H tautomers in aqueous solution. Phys Chem Chem Phys 2014; 16:15381-8. [DOI: 10.1039/c4cp01928h] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
QM/MM MD simulations reveal different H-bonding networks around DNA base analogues, and the π-electron H-bond in the solvated keto-N7H may facilitate its S1 → S0 nonadiabatic decay.
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Affiliation(s)
- Xugeng Guo
- State Key Laboratory for Physical Chemistry of Solid Surfaces and Fujian Provincial Key Lab of Theoretical and Computational Chemistry
- College of Chemistry and Chemical Engineering
- Xiamen University
- Xiamen 361005, P. R. China
| | - Yuan Zhao
- State Key Laboratory for Physical Chemistry of Solid Surfaces and Fujian Provincial Key Lab of Theoretical and Computational Chemistry
- College of Chemistry and Chemical Engineering
- Xiamen University
- Xiamen 361005, P. R. China
| | - Zexing Cao
- State Key Laboratory for Physical Chemistry of Solid Surfaces and Fujian Provincial Key Lab of Theoretical and Computational Chemistry
- College of Chemistry and Chemical Engineering
- Xiamen University
- Xiamen 361005, P. R. China
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10
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11
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Zhang L, Zhou L, Tian J, Li X. Structural, electronic, and photophysical properties of thieno-expanded tricyclic purine analogs: a theoretical study. Phys Chem Chem Phys 2014; 16:4338-49. [DOI: 10.1039/c3cp54505a] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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12
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Zhang L, Ren T, Tian J, Yang X, Zhou L, Li X. Excited State Properties of Naphtho-Homologated xxDNA Bases and Effect of Methanol Solution, Deoxyribose, and Base Pairing. J Phys Chem B 2013; 117:3983-92. [DOI: 10.1021/jp3123242] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Laibin Zhang
- School of
Physics and Engineering, Qufu Normal University, Qufu, 273165, P. R. China
| | - Tingqi Ren
- School of
Physics and Engineering, Qufu Normal University, Qufu, 273165, P. R. China
| | - Jianxiang Tian
- School of
Physics and Engineering, Qufu Normal University, Qufu, 273165, P. R. China
| | - Xiuqin Yang
- School of
Physics and Engineering, Qufu Normal University, Qufu, 273165, P. R. China
- State Key Laboratory of Crystal Materials, Shandong University, Jinan, 250100, P. R. China
| | - Liuzhu Zhou
- School of
Physics and Engineering, Qufu Normal University, Qufu, 273165, P. R. China
| | - Xiaoming Li
- School of
Physics and Engineering, Qufu Normal University, Qufu, 273165, P. R. China
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13
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Guo X, Lan Z, Cao Z. Ab initio insight into ultrafast nonadiabatic decay of hypoxanthine: keto-N7H and keto-N9H tautomers. Phys Chem Chem Phys 2013; 15:10777-82. [DOI: 10.1039/c3cp44718a] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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14
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Plekan O, Feyer V, Richter R, Moise A, Coreno M, Prince KC, Zaytseva IL, Moskovskaya TE, Soshnikov DY, Trofimov AB. X-ray spectroscopy of heterocyclic biochemicals: xanthine, hypoxanthine, and caffeine. J Phys Chem A 2012; 116:5653-64. [PMID: 22620864 DOI: 10.1021/jp300459p] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The electronic structures of the purine derivatives xanthine, hypoxanthine and caffeine have been investigated in the gas phase using C, N, and O 1s X-ray photoemission (XPS) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The results have been interpreted by means of ab initio calculations using the third-order algebraic-diagrammatic construction (ADC(3)) method for the one-particle Green's function and the second-order ADC method (ADC(2)) for the polarization propagator. The carbon, nitrogen and oxygen K-edge NEXAFS spectra of xanthine and caffeine are very similar, since the molecules differ only by substitution of three hydrogen atoms by methyl groups. For hypoxanthine, the electronic structure and spectra differ considerably from xanthine as the purine ring is more highly conjugated, and there is one less oxo group. Effects due to oxo-hydroxy tautomerism were not observed. However, the two oxo tautomeric forms of hypoxanthine oxo-N(9)-H and oxo-N(7)-H are populated in the gas phase, and the C 1s spectra can be simulated only by taking account of these two tautomers, with appropriate Boltzmann population ratios which we have also calculated. For xanthine and caffeine, single tautomeric forms were observed.
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Affiliation(s)
- Oksana Plekan
- Sincrotrone Trieste, Area Science Park, I-34149 Basovizza (Trieste), Italy
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15
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Villabona-Monsalve JP, Noria R, Matsika S, Peón J. On the Accessibility to Conical Intersections in Purines: Hypoxanthine and its Singly Protonated and Deprotonated Forms. J Am Chem Soc 2012; 134:7820-9. [DOI: 10.1021/ja300546x] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Affiliation(s)
- Juan. P. Villabona-Monsalve
- Instituto de Química, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria,
México, 04510,
D.F., México
| | - Raquel Noria
- Instituto de Química, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria,
México, 04510,
D.F., México
| | - Spiridoula Matsika
- Department
of Chemistry, Temple University, 13th and
Norris Streets, Philadelphia
Pennsylvania 19122, United States
| | - Jorge Peón
- Instituto de Química, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria,
México, 04510,
D.F., México
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16
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Adrover M, Caldés C, Vilanova B, Frau J, Donoso J, Muñoz F. Towards a detailed description of pyridoxamine tautomeric species. NEW J CHEM 2012. [DOI: 10.1039/c2nj40230k] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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17
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Sun X, Lee JK. Stability of DNA Duplexes Containing Hypoxanthine (Inosine): Gas versus Solution Phase and Biological Implications. J Org Chem 2010; 75:1848-54. [DOI: 10.1021/jo9023683] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Affiliation(s)
- Xuejun Sun
- Department of Chemistry and Chemical Biology Rutgers, The State University of New Jersey, New Brunswick, New Jersey 08901
| | - Jeehiun K. Lee
- Department of Chemistry and Chemical Biology Rutgers, The State University of New Jersey, New Brunswick, New Jersey 08901
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18
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Adrover M, Frau J, Caldés C, Vilanova B, Donoso J, Muñoz F. Theoretical and experimental study of the vertical excitation energies in the ionic and tautomeric forms of 4-aminomethylpyridine. J Photochem Photobiol A Chem 2010. [DOI: 10.1016/j.jphotochem.2009.10.003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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19
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Jayanth N, Ramachandran S, Puranik M. Solution Structure of the DNA Damage Lesion 8-Oxoguanosine from Ultraviolet Resonance Raman Spectroscopy. J Phys Chem A 2009; 113:1459-71. [DOI: 10.1021/jp8071519] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Namrata Jayanth
- National Centre for Biological Sciences, TIFR, GKVK Campus, Bellary Road, Bangalore 560065, India
| | - Srinivas Ramachandran
- National Centre for Biological Sciences, TIFR, GKVK Campus, Bellary Road, Bangalore 560065, India
| | - Mrinalini Puranik
- National Centre for Biological Sciences, TIFR, GKVK Campus, Bellary Road, Bangalore 560065, India
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20
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Mburu E, Matsika S. An Ab Initio Study of Substituent Effects on the Excited States of Purine Derivatives. J Phys Chem A 2008; 112:12485-91. [DOI: 10.1021/jp807145c] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Affiliation(s)
- Elizabeth Mburu
- Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122
| | - Spiridoula Matsika
- Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122
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21
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Kulkarni AD, Mennucci B, Tomasi J. Response of Scalar Fields and Hydrogen Bonding to Excited-State Molecular Solvation of Carbonyl Compounds. J Chem Theory Comput 2008; 4:578-85. [DOI: 10.1021/ct7002429] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Anant D. Kulkarni
- Dipartimento di Chimica e Chimica Industriale, Università di Pisa, Via Risorgimento 35, 56126 Pisa, Italy
| | - Benedetta Mennucci
- Dipartimento di Chimica e Chimica Industriale, Università di Pisa, Via Risorgimento 35, 56126 Pisa, Italy
| | - Jacopo Tomasi
- Dipartimento di Chimica e Chimica Industriale, Università di Pisa, Via Risorgimento 35, 56126 Pisa, Italy
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22
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Sun X, Lee JK. Acidity and Proton Affinity of Hypoxanthine in the Gas Phase versus in Solution: Intrinsic Reactivity and Biological Implications. J Org Chem 2007; 72:6548-55. [PMID: 17655363 DOI: 10.1021/jo070996x] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Hypoxanthine is a mutagenic purine base that most commonly arises from the oxidative deamination of adenine. Damaged bases such as hypoxanthine are associated with carcinogenesis and cell death. This inevitable damage is counteracted by glycosylase enzymes, which cleave damaged bases from DNA. Alkyladenine DNA glycosylase (AAG) is the enzyme responsible for excising hypoxanthine from DNA in humans. In an effort to understand the intrinsic properties of hypoxanthine, we examined the gas-phase acidity and proton affinity using quantum mechanical calculations and gas-phase mass spectrometric experimental methods. In this work, we establish that the most acidic site of hypoxanthine has a gas-phase acidity of 332 +/- 2 kcal mol-1, which is more acidic than hydrochloric acid. We also bracket a less acidic site of hypoxanthine at 368 +/- 3 kcal mol-1. We measure the proton affinity of the most basic site of hypoxanthine to be 222 +/- 3 kcal mol-1. DFT calculations of these values are consistent with the experimental data. We also use calculations to compare the acidic and basic properties of hypoxanthine with those of the normal bases adenine and guanine. We find that the N9-H of hypoxanthine is more acidic than that of adenine and guanine, pointing to a way that AAG could discriminate damaged bases from normal bases. We hypothesize that AAG may cleave certain damaged nucleobases as anions and that the active site may take advantage of a nonpolar environment to favor deprotonated hypoxanthine as a leaving group versus deprotonated adenine or guanine. We also show that an alternate mechanism involving preprotonation of hypoxanthine is energetically less attractive, because the proton affinity of hypoxanthine is less than that of adenine and guanine. Last, we compare the acidity in the gas phase versus that in solution and find that a nonpolar environment enhances the differences in acidity among hypoxanthine, adenine, and guanine.
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Affiliation(s)
- Xuejun Sun
- Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854, USA
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23
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Canuel C, Mons M, Piuzzi F, Tardivel B, Dimicoli I, Elhanine M. Excited states dynamics of DNA and RNA bases: characterization of a stepwise deactivation pathway in the gas phase. J Chem Phys 2006; 122:074316. [PMID: 15743241 DOI: 10.1063/1.1850469] [Citation(s) in RCA: 337] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Radiationless deactivation pathways of excited gas phase nucleobases were investigated using mass-selected femtosecond resolved pump-probe resonant ionization. By comparison between nucleobases and methylated species, in which tautomerism cannot occur, we can access intrinsic mechanisms at a time resolution never reported so far (80 fs). At this time resolution, and using appropriate substitution, real nuclear motion corresponding to active vibrational modes along deactivation coordinates can actually be probed. We provide evidence for the existence of a two-step decay mechanism, following a 267 nm excitation of the nucleobases. The time resolution achieved together with a careful zero time-delay calibration between lasers allow us to show that the first step does correspond to intrinsic dynamics rather than to a laser cross correlation. For adenine and 9-methyladenine a first decay component of about 100 fs has been measured. This first step is radically increased to 200 fs when the amino group hydrogen atoms of adenine are substituted by methyl groups. Our results could be rationalized according to the effect of the highly localized nature of the excitation combined to the presence of efficient deactivation pathway along both pyrimidine ring and amino group out-of-plane vibrational modes. These nuclear motions play a key role in the vibronic coupling between the initially excited pipi* and the dark npi* states. This seems to be the common mechanism that opens up the earlier phase of the internal conversion pathway which then, in consideration of the rather fast relaxation times observed, would probably proceed via conical intersection between the npi* relay state and high vibrational levels of the ground state.
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Affiliation(s)
- Clélia Canuel
- Laboratoire Francis Perrin, CNRS URA 2453, DRECAM-SPAM, CEA Saclay, 91191 Gif-sur-Yvette, France
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24
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Zhu X, Gan X, Wang J, Chen T, Li G. A new reduction route of hypoxanthine and its nonenzymatic detection based on silver nanoparticles. ACTA ACUST UNITED AC 2005. [DOI: 10.1016/j.molcata.2005.06.016] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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25
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Shukla MK, Leszczynski J. Multiconfigurational Self-Consistent Field Study of the Excited State Properties of 4-Thiouracil in the Gas Phase. J Phys Chem A 2004. [DOI: 10.1021/jp049358y] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- M. K. Shukla
- Computational Center for Molecular Structure and Interactions, Department of Chemistry, Jackson State University, Jackson, Mississippi 39217
| | - Jerzy Leszczynski
- Computational Center for Molecular Structure and Interactions, Department of Chemistry, Jackson State University, Jackson, Mississippi 39217
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