Functional subunits in the nucleic acid bases uracil and thymine

Lauer, Günther; Schäfer, Werner; Schweig, Armin

doi:10.1016/s0040-4039(00)91259-0

Cited by 77 publications

(44 citation statements)

References 9 publications

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“…5 is parallelled by the calculations (Table 2), which also predict a small decrease in the splitting.…”

Section: Diketonessupporting

confidence: 63%

“…A number of carbonyls and dicarbonyls have been investigated by ultraviolet photoelectron spectroscopy (UPS) (1,2), although few ydicarbonyls have been studied except for benzoquinone and its substituted derivatives (3)(4)(5)(6). For most dicarbonyl compounds, interest arises in the mechanism of the interaction between the two carbonyl groups, and whether it occurs throughspace or through-bond (2,3,(7)(8)(9).…”

Section: Introductionmentioning

confidence: 99%

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Ultraviolet photoelectron spectra of 2-norbornanone, 2,5-norbornanedione, their alkyl derivatives and thio-analogues. An investigation of transannular interactions by photoelectron spectroscopy

Frost¹,

Westwood²

1980

Can. J. Chem.

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. Can. J. Chem. 58, 1659(1980). He1 photoelectron spectra are reported for a series of methyl-substituted monoketones and diketones based on Znorbornanone. The effect of methyl substitution, and the inductive effect of a second carbonyl group has been studied. The diketones show a small separation between the two ketone moieties due to a through-bond interaction.Replacement with a thiocarbonyl group permits a comparison of the relative C=S and C = O interactions. The relative merits of the semi-empirical HAM13 and CND012 methods for such molecules are assessed.

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“…5 is parallelled by the calculations (Table 2), which also predict a small decrease in the splitting.…”

Section: Diketonessupporting

confidence: 63%

Section: Introductionmentioning

confidence: 99%

Ultraviolet photoelectron spectra of 2-norbornanone, 2,5-norbornanedione, their alkyl derivatives and thio-analogues. An investigation of transannular interactions by photoelectron spectroscopy

Frost¹,

Westwood²

1980

Can. J. Chem.

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“…More highly resolved experimental information about the occupied valence orbitals of biological purines will greatly facilitate an understanding of their ground-state electronic structure. In recent studies of biological pyrimidines it has been found that UV photoelectron spectroscopy can provide this information (11)(12)(13). The present study of adenine, 9-methyladenine, and 6-methylaminopurine is a detailed photoelectron examination of biological purines.…”

mentioning

confidence: 87%

Ultraviolet photoelectron studies of biological purines: the valence electronic structure of adenine.

Peng¹,

Padva²,

Lebreton³

1976

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

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The UV photoelectron spectra of adenine, 9-methyladenine, and 6-methylaminopurine contain highly resolved bands arising from the six highest occupied molecular orbitals. The spectra have been analyzed using UV absorption data, photoelectron data from previous studies of heterocyclic compounds, and results from both semi-empirical and ab initio molecular orbital calculations. The analysis indicates that the first, third, and fifth photoelectron bands in adenine and the two methyl substituted derivatives arise from 7r orbitals. The second, fourth, and sixth bands arise from nitrogen atom lonepair orbitals. Compared to adenine, the six uppermost orbitals of 9-methyladenine and 6-methylaminopurine have lower ionization potentials. This destabilization of the valence electrons is expected to play an important role in causing the increase in base stacking forces observed in methyl substituted adenines.The binding characteristics of biological purines are thought to be strongly influenced by charge transfer interactions (1-3) and polarization forces (3, 4) involving these molecules. Because electrons residing in the highest occupied and lone-pair orbitals of purines are easily removed, such electrons play an important role in determining binding characteristics. The energy levels of valence electrons in biological purines have been extensively investigated in both semi-empirical and ab initio molecular orbital calculations (5-8). To date, UV absorption measurements have provided virtually all of the experimental information available about these molecules (6, 7, 9, 10). It is found, however, that the absorption spectra of purines contain strongly overlapping bands which preclude a simple interpretation. More highly resolved experimental information about the occupied valence orbitals of biological purines will greatly facilitate an understanding of their ground-state electronic structure. In recent studies of biological pyrimidines it has been found that UV photoelectron spectroscopy can provide this information (11-13). The present study of adenine, 9-methyladenine, and 6-methylaminopurine is a detailed photoelectron examination of biological purines. EXPERIMENTAL Photoelectron spectra were measured with a Perkin Elmer PS-18 spectrometer equipped with a heated probe. Adenine and 6-methylaminopurine were obtained from Sigma Chemical Co. 9-Methyladenine was obtained from Fox Chemical Co. All compounds were used without further purification. The spectra were run in the temperature range 126-185o. Ionization potentials were calibrated using the 2P3/2 and 2P1/2 bands of Xe and Ar. For all three molecules, spectra measured from the same sample over a 1-to 2-hr period were identical, indicating that no decomposition occurred. Fig. 1 shows He I photoelectron spectra of the molecules stud- RESULTS AND DISCUSSIONied. An examination of the spectra indicates that adenine exhibits six widely separated bands in the energy region 8.5-13.2 eV and that the ordering of these bands is identical in all three of the molecules inve...

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“…Presumably geometric restrictions prevent optimum interaction of n, and a in the latter 'A recent study (22) has shown that the n,-r and n, f r levels in 2-methyl-2-azabicyclo[3.2.l]octa-3-ene are separated by 2.77 eV. It is difficult to compare this separation with those found here because the substitution of the double-bond differs.…”

Section: I2mentioning

confidence: 54%

Influence of remote substituents on ionization potential. Part II. Enamines

Brown¹

1976

Can. J. Chem.

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Electronic interactions in vinylamines can be divided into ns-T conjugation, and effects arising as a consequence of the electron-withdrawing abilities ( -I ) of both the nitrogen and *-system. Dehydroquinuclidine represents an ideal model which minimizes n,-*conjugation, and exhibits a pe spectrum which indicates that both the nx and *-orbitals are stabilized by about 0.4 eV relative to quinuclidine and bicyclooctene respectively. This stabilization is proposed to be a consequence of -I effects of each group and/or rehybridization of the nitrogen. Similar inductive effects are assumed to operate in enarnines which do not prohibit n~-* interaction. In these cases, strong conjugative effects are operative in addition to the -I effects.R. S. BROWN. Can. J. Chem. 54, 1521Chem. 54, (1976 On peut diviser les interactions Clectroniques des vinylamines en conjugaison n, -T et en effets derivant des propriktts Clectroaffinitaires ( -I ) B la fois de l'azote et du systkme T . La dihydroquinuclidine represente un modkle ideal qui minimise la conjugaison n, -T et qui montre un spectre pe indiquant que les orbitales r et n, sont stabilisees respectivement par environ 0.4 eV par rapport B la quinuclidine et au bicyclooctkne. On propose que cette stabilisation provient des effets -I de chaque groupe et/ou de la rthybridisation de I'azote. On fait l'hypothkse que des effets inductifs semblables sont en operation dans les Cnamines qui n'empCchent pas les interactions n, -r. Dans ces cas, des effets de conjugaison trks puissants sont en operation en plus des effets -I.[Traduit par le journal]Enamines have become progressively important as synthetic intermediates since their utility was first demonstrated by Stork et al. in 1954 (2). Their ability to undergo electrophilic additions at both carbon and nitrogen has been ascribed to resonance forms such as 1 and 2 which formally place high electron density at either end of the three-atom four-electron system (for a compendium of leading references on this feature and its chemical consequences see ref.3).,-.The enamine nitrogen can, in principle, exert two opposing effects on the double bond, an electron-withdrawing inductive effect (-I) and an electron-releasing conjugative interaction (+R). In most enamines both effects operate simultaneously, and the physical properties of the molecule will reflect the summation of the two. In terms of electrophilic addition to the carbon end of the enamine, the conjugative 'For part I, see ref. 1. abilities of the amine will far outweigh the -I effect as illustrated in eq. 1.Recognizing the possible opposing influences of the nitrogen on the *-system, we felt such systems were particularly suited to study by photoelectron spectroscopy (pes). In order to individually assess the contribution of the opposing -I and + R effects to the total character of the molecule, a model compound was chosen in which one of the effects is minimized relative to the other. Since conjugative interactions depend markedly upon coplanarity of orbitals for maximum e...

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Functional subunits in the nucleic acid bases uracil and thymine

Cited by 77 publications

References 9 publications

Ultraviolet photoelectron spectra of 2-norbornanone, 2,5-norbornanedione, their alkyl derivatives and thio-analogues. An investigation of transannular interactions by photoelectron spectroscopy

Ultraviolet photoelectron spectra of 2-norbornanone, 2,5-norbornanedione, their alkyl derivatives and thio-analogues. An investigation of transannular interactions by photoelectron spectroscopy

Ultraviolet photoelectron studies of biological purines: the valence electronic structure of adenine.

Influence of remote substituents on ionization potential. Part II. Enamines

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