Beiträge zur
            <sup>15</sup>
            N‐NMR‐Spektroskopie Protonierung und Tautomerie in Purinen: Purin und 7‐ und 9‐Methylpurin

Schumacher, M.; Günther, Harald

doi:10.1002/cber.19831160526

Cited by 37 publications

(6 citation statements)

References 24 publications

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“…A detailed NMR study based on longrange 13 C-1 H coupling constants 33 came to the conclusion that in neutral aqueous solutions the N-7(H) : N-9(H) tautomer ratio is 1 : 1 (48 : 52), whereas in DMSO the N-9(H) tautomer is favoured by a factor of 2 (30 : 70). A similar result, with an N-7(H) : N-9(H) tautomer ratio of 35 : 65 in DMSO, was reported from a 15 N NMR study, 34 where the (experimentally not available) chemical shifts of the two tautomers, which contribute to the coalescing signals, were estimated from appropriate model compounds (7-and 9-methylpurine).…”

Section: Tautomerism Of Purinementioning

confidence: 55%

NMR spectra of nitrogen-containing compounds. Correlations between experimental and GIAO calculated data

et al. 1999

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Section: Tautomerism Of Purinementioning

confidence: 55%

NMR spectra of nitrogen-containing compounds. Correlations between experimental and GIAO calculated data

et al. 1999

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“…They recognized that the three-bond coupling constant in the HCNC fragment is greatly reduced by replacing the N− mediator unit with −NH−. Since then, analysis of 3 J H−C has been used several times to determine the structures of individual tautomers in purine derivatives and analogues. , Further, it has been demonstrated that the two-bond coupling of a proton to the pyrrole-type nitrogen ( 1 H−C− 15 NR−) is reduced relative to that involving the pyrimidine-type nitrogen ( 1 H−C 15 N−) . However, the contributions to the coupling pathways that derive from the electron distribution within the heterocyclic system remained unclear.…”

Section: Introductionmentioning

confidence: 99%

Interpretation of Indirect Nuclear Spin−Spin Couplings in Isomers of Adenine: Novel Approach to Analyze Coupling Electron Deformation Density Using Localized Molecular Orbitals

et al. 2010

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Adenine, an essential building block of nucleic acids present in all living systems, can occur in several tautomeric forms. The phenomenon of tautomerism can be investigated by several experimental methods, including nuclear magnetic resonance. In this study, long-range (1)H-(13)C and (1)H-(15)N coupling constants for N-alkyl derivatives related to four tautomers of adenine are investigated in DMSO and DMF solutions. To investigate the structural dependence of the coupling constants and to understand how polarization propagates in the system, Fermi contact (FC) terms were calculated for the individual isomers and analyzed by using density functional theory (DFT), and the coupling pathways were visualized using real-space functions. The coupling electron deformation densities (CDD) of several (1)H-X (X = (13)C, (15)N) pairs are evaluated and compared. In order to analyze the CDD in more detail, a new approach to break down the CDD into contributions from Boys or Pipek-Mezey localized molecular orbitals (LMOs) has been developed. A similar approach has been applied to split the value of the FC contribution to the J coupling into the LMO contributions. On the basis of chemical concepts, the contributions of sigma-bonds, pi-electrons, and lone pairs of electrons are discussed. The lone pair of electrons at the nitrogen atom contributes significantly to the (1)H-C horizontal line(15)N coupling, whereas the (1)H-C=N-(13)C coupling is affected in a somewhat different way. Surprisingly, the contribution of the intervening C horizontal lineN bond to the FC term for (1)H-C=(15)N coupling originates exclusively in sigma-electrons, with a vanishingly small contribution calculated for the pi-electrons of this fragment. This behavior is rationalized by introducing the concept of "hard and soft J elements" derived from the polarizability of the individual components.

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“…The N(7)H tautomer is dominant in the solid state . In aqueous solution purine exists as an approximately equal mixture of the N(7)H and N(9)H forms. − Recent experimental resonance Raman studies suggest that the N(7)H form is predominant in water while theory seems to indicate a small predominance of the N(9)H form (52%) . In DMSO the N(9)H form is preferred (70%) 11,13 and in gas phase the N(9)H tautomer − is dominant.…”

Section: Introductionmentioning

confidence: 99%

A Theoretical Study of the Electronic Spectra of N₉ and N₇ Purine Tautomers

Borin

Serrano‐Andrés

Fülscher³

et al. 1999

J. Phys. Chem. A

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The complete active space (CAS) SCF method and multiconfigurational second-order perturbation theory (CASPT2) have been used to study electronic spectra of the N(9)H and N(7)H tautomers of purine. The calculations include vertical excitation energies, oscillator strengths, dipole moments, and transition moment directions in gas phase. In accord with experiment in nonpolar solvents, the two lowest π → π* excited singlet valence states are predicted to be located at 4.7 and 5.1 eV. The latter is expected to shift to the red in aqueous solutions. A satisfactory interpretation of the electronic spectra above 5.5 eV is obtained if the experimental data are assumed to consist of the superposition of the spectra of the N(9)H and N(7)H tautomers. Two bands reported at 6.2 and 6.6 eV in nonpolar solvents match the corresponding 1Bb and 1Ba states of the N(9)H purine, respectively. The absence of the 6.2 eV-band in water can be explained by the predominance in aqueous solution of the N(7)H form, which has a weak 1Bb transition at 6.4 eV overlapped by a strong 1Ba transition at 6.6 eV.

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Beiträge zur ¹⁵ N‐NMR‐Spektroskopie Protonierung und Tautomerie in Purinen: Purin und 7‐ und 9‐Methylpurin

Cited by 37 publications

References 24 publications

NMR spectra of nitrogen-containing compounds. Correlations between experimental and GIAO calculated data

NMR spectra of nitrogen-containing compounds. Correlations between experimental and GIAO calculated data

Interpretation of Indirect Nuclear Spin−Spin Couplings in Isomers of Adenine: Novel Approach to Analyze Coupling Electron Deformation Density Using Localized Molecular Orbitals

A Theoretical Study of the Electronic Spectra of N₉ and N₇ Purine Tautomers

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Beiträge zur 15 N‐NMR‐Spektroskopie Protonierung und Tautomerie in Purinen: Purin und 7‐ und 9‐Methylpurin

Cited by 37 publications

References 24 publications

NMR spectra of nitrogen-containing compounds. Correlations between experimental and GIAO calculated data

NMR spectra of nitrogen-containing compounds. Correlations between experimental and GIAO calculated data

Interpretation of Indirect Nuclear Spin−Spin Couplings in Isomers of Adenine: Novel Approach to Analyze Coupling Electron Deformation Density Using Localized Molecular Orbitals

A Theoretical Study of the Electronic Spectra of N9 and N7 Purine Tautomers

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Beiträge zur ¹⁵ N‐NMR‐Spektroskopie Protonierung und Tautomerie in Purinen: Purin und 7‐ und 9‐Methylpurin

A Theoretical Study of the Electronic Spectra of N₉ and N₇ Purine Tautomers